BIOLOGY GRADE 9

UNIT 1
BIOLOGY AND TECHNOLOGY
Biology is the scientific study of life or living things.
Technology:- the application of scientific knowledge to the practical aims of human life or, as it is sometimes phrased, to the
change and manipulation of the human environment.
Science is a systematic study of natural and physical world through observations and experiments. Science
shapes the way we understand the universe, our planet, ourselves, and other living things. The scope of biology is
also broad and therefore contains many branches and sub branches. The three main branches of Biology are
1. Botany - the study of plants
2. Zoology - the study of animals
3. Microbiology- the study of microorganisms
Some other sub branches of biology are: JOIN ON Telegram @QesemAcademy
Mycology – study about fungi
Protozoology - study about protozoa
Phycology - study about algae and etc.
The scientific method is an organized way of solving problem or answering questions
Before publication of an idea/Research, several other scientists in the same field read and check or evaluate it, the
process is known as peer review
Scientist publish their works on special magazine known as scientific journal
1.1. Renowned Ethiopian biologist
1. Dr. Aklilu Lema - is pioneer Ethiopian biologist
Discovered a remedy for a disease called bilharzia/schistosomiasis that is caused by flat worm, which
spend part of their life cycle in fresh water snail and part in humans
The parasitic worms infect the blood vessels, liver, kidneys, bladder and other organs
It affects 200-300 million people in Africa (including Ethiopia), South America, Asia and parts of the
Caribbean
He made soapberry from local plant known as endod (phytolacca dodecandra) to kill the snail, which
is the intermediate host for flat worm (if the snail can be controlled, the spread of bilharzias can be
reduced)
Soapberry of Dr. Aklilu Lema is cheap and locally available to buy and use for African countries to
eradicate the disease
2. Dr. Tewolde Birhan Gebre Egziabher - an ardent lover of nature
recognized for his work on environmental protection and biodiversity
Works to safeguards the biodiversity and traditional rights of farmers and communities to their genetic
resources
3. Prof. Tilahun Yilma - professor of veterinary virology at the University of California
He has developed vaccine for terrible cattle disease known as Rinder pest using genetic engineering
Render pest is deadly viral disease, which killed millions of cattle in Africa
He works to develop vaccine for HIV/AIDS
His contributions in science and medicine have been recognized by many international organizations.
4. Prof. Yalemtsehay Mekonnen - the first female professor from Addis Ababa University
She works on:
Assessment of impact of chemical pesticides hazards on humans.
research on the use of plant as a medicine against human and animal disease
She has awarded research grant and fellowship from different national and international organization for her
contribution in the area.
5. Dr. Melaku Worede -
He has worked for many years to save the genetic diversity of Ethiopia’s domestic plants.
set up the plant genetic resources center in Addis Ababa 1
developed way of farming to produce high yields without commercial fertilizer
served as the first chair of African committee for plant genetic resources and chair of UN food and
agriculture organization's commission on plant genetic resources
6. Dr. Gebisa Ejeta
has developed high yield and drought resistance strain of sorghum
has awarded national hero award and world food prize for his massive contribution in science and
technology
7. Prof. Beyene petros - a biomedical scientists serving at Addis Ababa University
produced more than 43 publication in journal and books
He won Gold medal award from Ethiopian health association and fellowship from fulbright and center for
disease control and prevention, Atlanta, USA.
8. Prof. Sebsebe Demissew
Plant taxonomist, director of national herbarium and leader of Ethiopian flora project
9. Dr. Zeresenay Alemseged
Paleontologist, who discovered a 3.3 million years old humanoid fossil in 2006
10. Dr. Tsehaynesh Meselle - Leads research in human health, including HIV/AIDS.
11. Dr. Birhane Asfaw - discovered two 160,000 years old human skulls.
- His discoveries were published in famous scientific journal nurture
12. Prof. Legese Negash - pioneer in propagation of Ethiopian indigenous tree
- Founder and leader of the indigenous tree propagation and biodiversity department in Ethiopia
13. Prof. Mogese Ashenafi - works at Addis Ababa University and leads international research into food
microbiology
14. Prof. Ensermu Kelbesa - leading systematic botanist
- He has discovered and named different new plants
1.2. Biological research in Ethiopia
Biologist conducts different research in different area of biological science. To carryout researches, they need
different tool, laboratories and other biologist to discuss idea with and develop theory. Ethiopia has various
institutes which are involved in biological research. Biologist come to these institutes and our biologist also
travel other countries to take part in different research program.
Addis Ababa University (department of biology)
One of the major centers for biological research in Ethiopia
contains much modern and high level equipment that help in their study.
 Palace for many renowned Ethiopian biologists.
It also manage 2 major units
A. The national herbarium which serves as national repository of Ethiopian plant and center for plant
identification in the country
B. The zoological natural history museum (ZNHM) which contains collection of Ethiopian fauna
including endemic species. It provides visual education for general public, students, and tourists. Other research
institution and their focus area of research are summarized in the table below

JOIN ON Telegram @QesemAcademy

2
Institutions Focus area of research
Armauer Hansen Research in first set it carried out research only into leprosy later widened
Institute (AHRI) to tuberculosis, leishmaniasis, malaria and HIV/AIDS
Aklilu Lemma Institute of Microbiology of infectious diseases
Pathobiology (ALIPB) Vectors of disease and how to control them
- previously known as Human parasitic disease
department of pathology at Animal health and disease
AAU Endod and use of other plants as medicines.

Ethiopian Health and  Health and nutrition issues

Nutrition Research institute Other specific area of research includes
(EHNRI) HIV/AIDs vaccine
tuberculosis (TB)
infectious disease
nutritional status of baby and mother
Ethiopian Institute of Crop technology to achieve food security and nutritional quality
Agricultural Research) breeding, feeding and health improvement of livestock
(EIAR) also known as improving soil fertility
institute of Agricultural Forestry (rehabilitation, conserving and restoring forest ecosystem)
research (IAB) Crops for mechanized farming

Institute of Biodiversity Issue of biodiversity conservation, especially endemic plant and

conservation (IBC) animal of Ethiopia
Conserving gene of Ethiopian plant
Ecosystem conservation
Biotechnology and safety
Aquatic plant, medicinal plant, forests etc.

UNIT - 2
CELL BIOLOGY
2.1. The microscope
Microscope is a basic tool for biologist, which is used to see/study very small things that can't be seen by our
naked eyes.
Types of microscope
1. Light microscope is a type of microscope which use beam of light to form image. It can be classified in to
A. Simple light microscope - contains only one lens system. E.g. Hand lens
B. Compound light microscope (CLM) - contains two lens system, eye pieces/ ocular lens and objective
lens. It magnifies the object/specimen twice and produces much better magnification.
The 4 types of objective lenses
Low power objective lens - provide lowest power of magnification 4x
Middle power objective lens, provide 10 x magnifications
High power objective lens, provide 40x magnification
Oil emersion objective lens, provide the highest magnification (100x)
Magnification and resolution
The two important function or abilities of microscope are magnification and resolution.
Magnification - is the ability of microscope to increase the size of an object.
- The total magnification CLM = magnification of eye piece lens x particular objective lens
- Light microscope can magnify an object up to 2000 times
Resolution - the ability of microscope to see detail or scatter parts of an object
Approximately light microscope can resolve things about 200 nanometer (nm) apart
Staining - is a process adding chemical stain or dyes to slide tissues to make the cell or their parts easier to3
see. Some commonly used stains are:
 Types of stain types of cell main organelles stained
Haematxylin animal & plant cell nuclei stained blue (purple or brown)
Methylen blue animal cell nuclei stained blue
Acetocarmine animal and plant sell staining the chromosome in dividing nuclei
Iodine plant cell any material containing starch
Mounting - is a process of preparing an object or specimens to be seen under a microscope. Mounting
process involve the following major steps
having specimen to be seen under a microscope
place the object /specimens/ at the center of clean glass slide
cover the specimens with cover slip
remove excess fluid from slide
place the slide (with specimens) on stage to focus JOIN ON Telegram
Parts of compound light microscope @QesemAcademy

Parts of compound Description and Function

light microscope
Eye piece/Ocular lens A lens closer to viewer and used to look through
Objective lenses Lenses closer to the object which is used to magnify objects
Stage A flat surface on which slide with specimen is placed to be examined
base/foot Support the weight of the microscope
Course adjustment knob used to move the tube up and down for proper focusing
Fine adjustment knob Used to bring the object in to perfect focus (to get real image)
Nose piece Revolving part of microscope that hold objective lens
Diaphragm (Iris) Used to control the amount of light passing through the specimen
Mirror(light source) Reflects light upward through diaphragm to illuminate the specimens
Arms Support the tube and connect it to the base
Body tube Holds nose piece at lower end and eye piece at upper end
Stage clip Used to fix the slide in place

4
Advantage and disadvantage of light microscope

LIGHT MICROSCOPE

Advantage
Disadvantage
- can see living cell
- limited resolving power
- can also be used without electricity
- limited magnification powers
- used anywhere in the world
- portable( relatively small and not very heavy)
- realatively cheap

Advantage and disadvantage of election microscope

Advantage Disadvantage
• can see much more detail • All the specimens are examined in a vacuum
• higher magnification and resolution • impossible to look at living material
• very expensive
• take up a lot of space and are usually kept in a
separate room
• rely on a constant source of electricity

Comparisons between light and electron microscope

Light microscope Electron microscope
- Low magnification and resolution power - Highest magnification and resolution power
- Use beam of light to form an image - Use beam of electron to form an image
- Used to study living and nonliving material - doesn't help to study living materials directly
- It is possible to use it without electricity - Depend on electricity
- Is relatively cheap - Is very expensive
- Simple to use - Require large space
- Easy to move from place to place - Not simple (required professional skills) to use
- Doesn't require large space -is not easy to move from place to place
- Use glass lens - It uses magnetic lens (Electron beams are focused
by magnetic lenses

2. Electron microscope is more powerful types of microscope with highest magnification and
resolution
power. It uses a beam of electrons rather than light to form an image
It can magnify objects up to 2,000,000 times and has resolution power up to 0.3 nanometer (nm)
apart
In electron microscope, the electron behave like light wave
It has shorter wavelength than LM, so it has high resolution power
As the wave length decrease, resolution power of microscope increase
How does an electron microscope work?
Under electron microscope, all the specimens are examined in a vacuum because air would
scatter the electron beam
The electron beam is focused by magnetic lenses.
In EM, Complex electronics produce image on screen that can be recorded as a photograph
known as electron micrograph 5
There are two types of electron microscope
A. Transmission electron microscope (TEM) in which beam of electrons is transmitted through a
specimen/sample and provides detailed three-dimensional images. An image is focused on florescent screen or
photographic plate
B. A scanning electron microscope (SEM) which produces images of an object by scanning the surface with
a focused beam of electrons and shows only the surface of objects. Image is focused on television-like screen.
2.2. The Cell
Cell is the basic structural and functional unit of living organism
It is a smallest unit of life or building block of life
All forms of life made up of one or more cell
Some organism are made up of one cell known as unicellular (e.g. bacteria and protozoans) others made up
of more than one cell known as multicellular organism.

Type of cells
Prokaryotic cell - is simple, unicellular (single celled) cell that lack true nucleus
Eukaryotic cell - is cell that have membrane bounded nucleus (true nucleus)
 Organelles are subcellular structures that have specialized function.
Size and shape of cell
Most cells are very small or tiny and cannot be seen without the aid of microscope
Some cells are large enough to be seen by our naked eyes. The biggest known cell is ostrich egg cell
Different cells have different shape. They may be flat, spiral, tubular, branched, irregular etc.
The shape of cells is mostly depends on their function
Cell theory
Cell were first seen (discovered) and described by English scientists, Robert Hook in 1965.
He observed tiny compartment in the cork, which he called cellulae - from Latin word (meaning - small
room). This term come down to as cell. He observed only dead plant cell.
The first living cell was observed by Anton Van Leeuwenhoek. He observed little organism, which he
called animalcules (meaning - little animal).
- In 1838 Mathias schleidin (German Botanist) states that "all plants are made up of cell".
- In 1839 (German zoologist) Theodore Schwan stated that "all animals are made up of cell".
-In 1859 Rudolf Virchow stated that "cells come from preexisting cell". The work of these three scientists
contributed to the cell theory.
The cell theory in modern form includes
1. All organisms are made up of one or more cell
2. New cells arise only from other living cells (pre-existing cell) by the process of cell division.
3. Cells are the basic structural and functional unit of life.
All living organisms have certain characteristics, which they carry out. The seven life processes that are
common to most living organism are:
1. Nutrition – all living organisms need food to provide them with the energy used by their cells. Plants make their own
food by photosynthesis, whereas animals eat other organisms.
2. Respiration – the process by which living organisms get the energy from their food.
3. Excretion – getting rid of the waste products produced by the cells.
4. Growth – living organisms get bigger. They increase in both sizes and mass, using chemicals from their food to build
new material.
5. Irritability – all living organisms are sensitive to changes in their surroundings.
6. Movement – all living organisms need to move to get near to things they need or away from problems. Animals move
using muscles, plants move more slowly using growth.
7. Reproduction – producing offspring is vital to the long-term survival of any type of living organism.
Cell structure and function
Almost all cells (plant and animal cells) have a nucleus, mitochondria, ribosome, cytoplasm,
endoplasmic reticulum & cell membrane.
Other features that are found in plant cell are cell wall, large central vacuoles, and plastids 6
Animal cell also have some unique features such as lysosomes and centrosome
Structure and function in unspecialized cell
 All of the process of life takes place within a single cell.
Every cell contains sub cellular structure known as organelles
Each organelle has specific functions within the cell
1. The nucleus - it control all activities of cell the (controlling center of a cell)
- It contains genetic material (chromosome) which carries genetic information
2. The cell membrane/Plasma membrane - Is thin living layer of both plant and animal cell
- composed of protein and lipids bilayer (lipo - protein)
- In animal cell, it is the outer most layers whereas in plant cell, it is found next to cell wall
- It is responsible to regulate the movement of material in and out of cell (selectively permeable
membrane or semi - permeable membrane); allow some materials to pass through and not others
3. The cytoplasm - is a jelly-like substance composed of mainly water (about 70%)
- found between the cell membrane and nucleus
- Site of most cellular activities (chemical reactions) JOIN ON Telegram
4. The Mitochondria (singular: mitochondrion)
- are often referred to as the "powerhouse" of the cell" @QesemAcademy
- It is a site of cellular respiration (energy production
5. Ribosome - are small organelles found attached to outer surface of endoplasmic reticulum (ER)
- They can be also found free in cytoplasm
- They are responsible to synthesis protein (site of protein synthesis)
6. Cell wall - is a rigid, non-living organelle lying just outside the cell membrane of plant cell.
- It can also found in fungi and bacteria but not in animal cell.
- In plant cell, it is composed of complex carbohydrates called cellulose
- It provides structural support, protection, and shape of cell.
6. Lysosomes - are small sac-like structures surrounded by a single membrane
- They are needed and found only in animal cell.
- contains digestive enzymes which help to break down and remove old worm out cell parts
- It is also known as "suicide sac (bags)".
7. Plastids - are organelles found in cytoplasm of plant cell
There are three types of plastids
A. Chloroplast - is site of photosynthesis
- It contains the green pigment called chlorophyll, which absorb sunlight
B. Chromoplast - contains red, yellow or orange pigment
- It gives the color of fruit and flowers
C. Leukoplast - it lack pigment (colorless) and serve as storage of starch
8. Vacuoles - are fluid filled organelles enclosed by a single membrane
- It is used to store fluid called cell sap, which contains water, salt, sugar, minerals, and waste products. It
provides turgidity of plant cell when filled with water
9. Endoplasmic reticulum (ER)
- A network of membranous tubules, extending through cytoplasm.
- Connects cell membrane with nuclear membrane and plays a major role in the production, processing, and
transport of proteins and lipids.
There are two types of ER
Rough endoplasmic reticulum (Rough ER) - contains ribosome attached on its surface and
synthesizes proteins
Smooth endoplasmic reticulum (Smooth ER) doesn‘t have ribosome and synthesizes lipids
10. Golgi bodies/Golgi apparatus/Golgi complex - are stacks of flattened membranous.
- It plays a major role in modification, packaging protein for transport.
Cell specialization in human
- In multi-cellular organism, most cells become specialized to carryout particular function
- Cells which adapt to carryout particular function are called specialized cells
- A combination of sperm cell and egg cell form embryo (single cell), which divide many times to form
mass of unspecialized/undifferentiated cells 7
- As the embryo develops, the cell become differentiated /specialized, this can be shown as
Embryonic stem cell → mass of unspecialized →specialized cell
Embryonic stem cells are unspecialized cell from cell early embryo that has potential to form any
specialized cell.
- Specialized cell with similar structure and function are grouped together to form tissue (eg-Muscle tissue,
nerve tissue, etc.)
- Tissues are combined to form organ (e.g. heart, lung, kidney etc.)
- Organs are working together to form organ system (e.g. digestive system).
- A number of system are working together make up organism, this can be shown as
Specialized cell → tissue → organ → organ system → organism
Some example of specialized cell in human
1. Epithelial cells specialized cell that cover and protect the internal and external surface of the body (skin,
gut, throat etc.)
2. Reproductive cell (egg and sperm cell)
- are specialized cell which involve in reproduction process
- They contain only half the number of chromosome of normal body cells
- Their nucleus contains genetic material (chromosome)
A. Egg cell/ova/ - is a female reproductive cell (female sex cell), produced in ovaries.
- Larger in size than male sex cell and have protective outer coat.
B. sperm cell - is a male reproductive cell (male sex cell).
- Have long tail (flagellum) containing muscle like protein that helps to swim towards eggs
- The middle section contains large number of mitochondria which provide energy for tail
- They have structure known as acrosome in head, which store digestive enzyme
- The enzyme is used to breakdown the protective coat of egg cell during fertilization
3. Nerve cell (neurons)
- Specialized cells, responsible to transmit electrical nerve impulse (signal) between different parts of the body and
control your body system
- Part of communication and control center of your body
Parts of neuron (nerve cell)
A. Cell body - structure which contains cellular structure (like mitochondria and nucleus)
B. Dendrite - hair like extension from cell body that communicates with other neurons
C. Axon (nerve fiber) - is long tiny extension of cell body that carry nerve impulse long distance
D. Myelin sheath - is fatty insulating layer of axon which help the nerve impulse to travel fast
4. Muscle cell (myocytes) - are responsible for movements of our body.
- Rich in proteins like actin and myosin, these enable the muscle to relax and contract
- contains large number of mitochondria to provide more energy for muscular movement

2.3. Cell and its environment

Cell obtained Material necessary for life ( (like O 2 & nutrient) from the environment and waste product (like
CO2) must be removed from the cell. materials can move into and out of a cell through its semi-permeable
membrane (cell membrane), which allow some materials to pass through and not others. There are two major
ways by which materials can move in and out of a cell. These are passive transport and active transport.
1. Passive transport (diffusion and osmosis) - movement of materials without the use of energy
2. Active transport - is the movement of materials using energy
A. Diffusion
- Random movement of molecules from area of its higher concentration to area of lower concentration
until the molecules tends to be in equilibrium/distribute uniformly.
- It occurs along concentration gradient (difference in concentration between two areas)
- Rate of diffusion can be affected by temperature, concentration gradient, size of particle etc.
- Diffusion is an important mode of nutrient uptake and gaseous exchange in cells
B. Osmosis - is a special kinds of diffusion in which water (solvent) diffuse (move) from dilute (weak)
solution to concentrated (strong) solutions across semi permeable membrane
NB: Dilute solution is a solution with high solvent/water concentration and relatively low solute
concentration, whereas concentrated solution is a solution with low solvent concentration and high solute
concentration. There are 3 types of solutions (osmotic conditions). These are:
8
1. Hypertonic Solution (hyper - means more)
- If concentration of solution outside the cell membrane is greater than inside
- Water molecule move from inside to outside (loss water) and causes a cell to shrink
2. Hypotonic Solution (hypo - means - less)
- If concentration of solutions inside the cell membrane is greater than outside.
- The cell gain water and causes a cell to swell up due to osmosis
2. Isotonic Solution:
- If the concentration of solutions inside and outside of cell membrane is equal
- There is no net movement of water molecules and no change in the cell
Osmosis in animal cell - osmosis is important for movement of water in and out of the animal cell,
when needed. However, osmosis can affects animal cell
- If animal cell is placed in hypertonic solution, the cell loss water and will shrivel up (shrink). The
condition is called crenation.
- If animal cell is placed in hypotonic solution, the cell gains more water & swell up eventually burst
Osmosis in plant cell - osmosis is important in plant cell to support the stem and leaves. The swelling up of
cell keep stem and leaf of plant rigid and firm.
- If plant cell is placed in hypertonic solution, the cell loss water. Then vacuole shrink and the cell become
less rigid (flaccid), eventually the cytoplasm pulls away from the cell wall. This results in loss of turgor
pressure and is known as plasmolysis
- If plant cell is placed in hypotonic solution, the cell gain water and swell up.
- The swelling up of the cell creates pressure that pushes the cell wall outward.
- This pressure is known as turgor pressure. On the other hand, the cell wall in plant created wall pressure in
opposite to turgor pressure (push inward). This can avoid bursting of cell in plant and make them turgid.
C. Active transport - is a movement of molecules against concentration gradient, molecules move from
area of low concentration to area of high concentration. It required energy.
The importance of active transport: E.g.
1. Absorption of mineral ions from soil by root hair cell. Concentration of mineral in root hair is
greater than in the soil. So it required energy to move against concentration gradient.
2. Translocation of organic materials in plant - organic molecules produced by photosynthesis is moved
from their leaf to other parts of plants (stem and root).
3. Glucose in your gut and kidney tubules moved into your blood against concentration gradient.

Fig. 2.3. Observations of mineral ions by root hairs of plant (active transport)

UNIT 3

HUMAN BIOLOGY AND HEALTH

3.1 Food and nutrition

All living organisms need a source of energy to survive.

Organisms set in different categories depending on their source of food as follows;

9
 Organisms

AUTHOTROPHS = can HETEROTROPHS = can't

make their own food make their own food

Photosynthetic Chemosynthetic Omnivore =

Herbivors = Carnivore =
= use light = use d/t consume both
consume plants consume meat
energy chemicals plant and meat

The human diet

Food: is the source of nutrients and energy for the body
 It has three main use to human
A. To provide energy for our cells to carry out all the functions of life
B. To provide the raw materials for the new biological material needed in our bodies to grow and also to
repair and replace damaged and worn out cells.
C. To provide the resources needed to fight disease and maintain a healthy body.

Nutrient: usable chemical compound found in food

Roughage: indigestible substance that do not provide energy

MACRONUTREINT: needed in large amounts

i. Carbohydrates,
ii. Proteins

Nutrient iii. Lipids(fat & oil).

MICRONUTREINT: needed in small amounts

iv. Minerals
V. Vitamins

i. CARBOHYDRATE:-
 They are made up of carbon, hydrogen and oxygen
 provide us with energy
 broken down to form glucose which is used in cellular respiration to produce energy
 Stores in the from glycogen, which is found in your liver, muscles and brain.
 excess carbohydrate that you eat is converted to fat
 glucose is the sugar made by plants in photosynthesis and it is vital in cells for energy
 starch is more complex carbohydrate stored in plants
 Obtained from food like injera, honey, Potatoes, rice, bread, etc
 They divide into three main types, depending on the complexity of the molecules

JOIN ON Telegram @QesemAcademy

10
 Simple Sugars

Double Comple Sugars

Sugars

The Simple Sugars/Monosaccharide/

 There is 1-oxygen atom and 2-hydrogen atoms for each carbon atom present in the molecule.
 (CH2O)n is general formula
 Example: C6H12O6 is general formula for Glucose.

Simple sugar
Glucose

Fructose

Galactose

The Double Sugars/Disaccharide

 made up of two simple sugars join together
 When two simple sugars join together to form a double sugar, a molecule of water (H2O) is removed
(condensation reaction).
 monosaccharide + monosaccharide → disaccharide

Glucose
Maltose
(malt sugar)
Glucose

JOIN ON Telegram @QesemAcademy

11
 Glucose
Lactose
(Milk sugar)
Galactose

Glucose Sucrose
(sugarcane
Fructose sugar)

 Most simple and double sugars have properties to dissolve in water and they taste sweet.

The Complex Sugars/Polysaccharide

 Many single sugar units are joined to form a long chain.

 properties of complex sugar are;
 very compact molecules (for storing energy)
 physically and chemically very inactive
 sweet test is lost
 do not dissolve in water
 here are some examples of complex sugar
a. Starch: energy store in plants
 The sugars produced by photosynthesis are rapidly converted to starch
b. Glycogen: sometimes referred to as ‘animal starch’
 it is energy store found in animals
 found mainly in muscle and liver tissue
c. Cellulose: important structural material in plants
 the main constituent in plant cell walls
 consists of long chains of glucose
 Human beings cannot break down its linkages and so they cannot digest cellulose.

Test for Carbohydrate

 Starch test
 help to test presence of starch
 reagent → iodine
 result/color change → change to blue black
 Benedict’s test (reducing, glucose) JOIN ON Telegram
 help to test for simple sugars @QesemAcademy
 reagent → benedict reagent/solution
 result/color change → change to yellow

ii. PROTEINS:-
 Made up of the carbon, hydrogen, and oxygen, in addition they all contain nitrogen.
 Some proteins also contain sulphur 12
 Are polymers, made up of many small units joined together called amino acids.
 There are about 20 different naturally occurring amino acids
 The bond found between two amino acid is peptide bond.
  proteins are coil, twist, spiral and fold amino acid
 proteins differ in:
 type
 number of their amino acid
 sequence
 shape

PROTEIN

Water soluble Water insoluble

-antibodies - connective tissue
- enzymes - tendons
- hormones - matrix of bone(collagen)
-muscles
-silk of spider web
- silkworm cocoons
- keratine

 protein make 17-18% of human body

 importance of protein are:
provide less energy than carbohydrate and lipid
for repair and damaged tissue and body building
to make enzymes
 the difference in temperature and PH denature the protein
 lack of protein causes Marasmus and Kwashiorkor
 Meat, fish, dairy product, white pea bean, egg, etc. are protein rich food.

Test for Protein

 Biuret test
 reagent – Potassium hydroxide
 and copper II salphate
 result/color change – purple (mauve) colour

iii. LIPID (FATS AND OILS):-

Fat Oil
Solid at room temperature liquid at room temperature
Mainly Animal product Mainly Plant Product

 lipids are made up of carbon, hydrogen and oxygen, but, lower proportion of oxygen than carbohydrates.
 the simplest form of lipid is Glycerol and fatty acids.
 fatty acids have a long hydrocarbon chain
 One glycerol combines with three fatty acids
 high levels of fat and Cholesterol in our diet are not good for health

Saturated → each carbon atom is joined to another by single bond

Fatty acid

Unsaturated → carbon chains have one or more double bonds

13
 source of energy in your diet and they are the most effective energy store
 they contain more energy per gram than carbohydrates or proteins
  Combined with other molecules, it has vital roles as hormones, in your cell membranes and in the nervous
system.
 All lipids are insoluble in water, but dissolve in organic solvents.
 Meat, oily fish, eggs, butter, beef fat, sesame oil, niger seed oil (nug) and olive oil are sources of lipid.
 Cholesterol: most made in your liver and some come from food we eat
 carried around your body in your blood
 Without cholesterol, you wouldn‘t survive.
 It makes the cells membranes, sex hormones and the hormones which help your body deal with
stress.
 High levels of cholesterol in your blood seem to increase your risk of getting heart disease or
diseased blood vessels.

Test for Lipid

 Reagent: Ethanol
 Place a small sample of fat/oil in a test tube
 add ethanol
 Shake the test tube
 add water
 Result: White cloudy layer formed

Testing for vitamin C

JOIN ON Telegram
 DCPIP (dichlorophenol indophenol) reagent
 Pour about 3 cm3 of DCPIP into a clean test tube @QesemAcademy
 Using a dropper, add orange or lemon juice drop by drop to DCPIP in the test tube.
 Positive result: gradual fading of the blue color of DCPIP

iv. MINERALS:
 minerals are needed in small amount

Mineral Approximate Location or role in body Example of foods Effects of deficiency

mass in an rich in mineral
adult body
(g)
Calcium 1000 Making bones and teeth Dairy products, fish, Rickets
bread, vegetables
Phosphorus 650 Making teeth and bones; part Most foods Improve formation of
of many chemicals, teeth and bones;
e.g. DNA failure of metabolism
Sodium 100 In body fluids, Common salt, most Muscle cramps
e.g. blood foods
Chlorine 100 In body fluids, Common salt, most Muscle cramps
e.g. blood foods
Magnesium 30 Making bones; found inside Green vegetables Skeletal problem; cell
cells chemistry affected,
defects in metabolism
Iron 3 Part of haemoglobin in red Red meat, liver, eggs, Anaemia
blood cells; helps carry green leafy
oxygen vegetables,
e.g. spinach

V. VITAMINS:
Vitamins Food rich in Vitamins Deficiency disease
Retinole (VA) Green pepper, carrot, leafy vegetables, cod Poor sight, poor growth
liver oil
Thiamin (VB1) Cereals, milk, liver, sprouted beans Beriberi, loss of appetite, disease of
muscle
Riboflavin (VB2) Green vegetables, liver, milk, meat, peas Slow growth, eye disease, tongue
inflammation
Niacin (VB3) Milk, meat, vegetables Pellagra
Ascorbic Acid (VC) Green pepper, lemons, orange, vegetables Scurvy, bleeding gum, slow healing 14
Calciferol (VD) Fish liver oils; also made in skin in sunlight Ricket
Tocopherol (VE) Cereal oil, milk, egg, yolk, lettuce, seeds Sterility
Phylloquinine (VK) Green leaf vegetables Prolonged blood clothing time
 v. The role of Water
 your body is 60%-70% water
 it is vital solvent
 Transport substance in the body. example. urea, sweat
 For body temperature regulation. example. sweat
 for removal of waste material
 it is a reactant in many important reaction in the body
 needed for osmotic stability of the body

Balanced diet
 Is taking food from all food groups in order to maintain a healthy body.

Malnutrition: when diet lacking in important elements needed for a healthy body.

Over nutrition: when too much food is eaten

Under nutrition: when too little food is eaten

3.2 The Digestive System

Digestion: breakdown large, insoluble molecules in to smaller, simplest, & soluble molecule

 It provides energy & new biological molecules.

Digestion

Physical (Mechanical) Chemical

 Break down food in to smaller unit peaces -accomplished by enzyme

 bite & chew food in mouth
 squeezes food in stomach

More about enzyme:-

1. enzymes are protein
2. enzymes are catalyst – remain unchanged
3. enzymes are specific – one enzyme catalyze only one reaction
4. enzymes are sensitive to temperature – all human enzymes are best at 37c0
5. enzymes are sensitive to PH – each enzymes have their own range of PH

Intracellular – secreted and work inside the cell

Enzymes Extracellular – different secretion and work outside the cell

Digestion in mouth
 Both chemical and physical digestion occur here
 Ingestion: the act of taking in food
 Mouth: select taste, smell and texture of food
 Bite, chew and chop the food by teeth known as mastication
 mix food with enzyme

Starch + H2O Maltose

The Human Teeth
 there are 4 types of teeth
 Incisors – front teeth
 Canine - long and pointed teeth
 Premolars - flat teeth
 Molars - found at the back

Structure of human teeth 15

 Enamel→ the outer cover
- The strongest part (hardest)
- white color that resist decaying
 - non-living part
 Dentine → found next to enamel
- very hard, similar to bone
 Pulp Cavity → the center of the teeth
- contain nerve and blood vessels
- sensitive to heat, cold and pain
 Cement → keep teeth firm with jaw (set in to your jaw)

Moving the food:-

Bolus: ball shaped saliva coated chunk of chewed food

Peristalsis: wave like muscle contraction to move food along the throat

Epiglottis: the flap that covers the trachea during swallowing so that food does not enter the lungs.

Digestion in Stomach
- Digestion in stomach take 1-4 hours
- Sphincter: ring of muscle found at the first and last parts of the stomach
- open only during swallowing and being sick
- In stomach food mixed with gastric juice

Hydrochloric acid (HCl)

Gastric Juice Mucus Pepsin

Protease enzyme, digest protein
Enzyme Rennin

- HCl: Make the food suitable for action of pepsin

- kill some bacteria
- Mucus: Protect wall of stomach from attack by HCl. JOIN ON Telegram
- Pepsin: the major gastric juice enzyme
- work best in acid
@QesemAcademy
Protein + H2O Pepsin Peptones

- Rennin: Mostly found in mammals

- Curdle milk protein
- Chime: is grey soup like mixture pass to the intestine from the stomach

Digestion in Intestine
Small Intestine: is about 6-8m coiled tube

- Produce protease, carbohydrase and lipase enzyme

Duodenum → the upper part

small intestine Jejunum → middle part
Ileum → Lower part, digestion end here,
both digestion and absorption occur

a. In Duodenum
- it contain bile and enzyme
- pancreas secret pancreatic juice 16

Pancreatic Juice
 Trypsin Lipase Pancreatic amylase

 Peptone trypsin peptide

 fat and oil lipase fatty acid and glycerol
 starch amaylase maltose
- Bile: secreted from liver, has no enzyme
- it is alkaline (base)
- stored in gall bladder
- help to neutralize acid

Fat Bile Fat droplet (emulsify fat)

b. In Jejunum and Ileum

- Intestinal juice is secreted here

Erepsin

maltase Intestinal juice lactase

sucrase

 Peptides Erepsin Amino acid

 Maltose maltase Glucose and glucose
 Lactose lactase Glucose and galactose
 Sucrose sucrase Glucose and Fructose

Absorption: glucose, amino acid and fatty acid and glycerol leave the small intestine by diffusion and go in to the blood
supply.

- Small intestine have finger like projection called Villi that absorbs food
- glucose and amino acid directly go in to the blood
- fatty acid and glycerol, move in to the lacteals
- lacteals is part of lymph system with lymph fluid it goes to blood supply
- Digested food in small intestine move in to the liver through hepatic portal vein then to each individual cell.

Assimilation: taking in and uses of digested food by the cell

Engestion: removal of the faeces from your body

Issue of digestive health

Constipation: compacted, hard and difficult to evacuate faeces, because of loss of water (lack of fiber)

- treated by: eating more fiber

- drinking plenty of water
- taking laxatives

Diarrhoea: very loose and watery faeces

- treated by: drinking water with rehydration salt

17
JION Telegram @QesemAcademy
3.3 The human respiratory system

Structure of human respiratory system

The respiratory system is a vital in order to get oxygen to oxidize food and release energy for
proper functioning of the body.
The human respiratory system consisting of the following structures:
Mouth: is an organ through which the air enters into respiratory structures
Nose/nasal cavity: is additional structure through which the air enters into respiratory tract.
Nose contains the nasal passages, which have:-
a large surface area,
a good blood supply,
Lots of hairs and a lining that secretes mucus.
 The hairs and mucus filter out much of the dust and small particles that we breathe in,
Whilst moist surfaces increase the humidity of the air we breathe into our bodies and the rich blood
supply warms it
 This means that the air we take in is warm, clean, and moist before it gets into the delicate tissue of our
lungs.
Pharynx: is the structure that serves as a common passage for both food and air
Larynx or voice box: the upper part of trachea by directing air leaving the lungs over the vocal cords.
Trachea: is the wind pipe which is made from C-shaped cartilage that supports it and holds it open.
The lining of the trachea secretes mucus, which collects bacteria and dust particles.
The cells that line the trachea are also covered in hair-like cilia that beat to move the mucus with any
trapped micro-organisms and dirt away from the lungs and towards the mouth.
 The opening of trachea is called glottis.
The entrance of food and dust particles into the glottis is prevented by epiglottis.
Bronchi (singular bronchus): are the branches that arise from the trachea, one leading to each lung.
Bronchioles: are small tubes branching from each bronchus in the lung. They are much smaller than bronchi.
Alveoli (singular alveolus): are tiny air sacs which are used for exchange of gases between the lungs and the blood
capillaries, they are called functional unit of the lung.
The lung is the major breathing organ of human; it is surrounded by membranous structure called pleural
membrane.
18
The lung is spongy and elastic organ which is protected by ribs, vertebral column, diaphragm and
intercostal muscle.
Diaphragm: muscle separating heart and lung from abdomen.
Intercostal muscle: are muscles that are found between the ribs and used in breathing.
There are two sets of intercostal muscle in normal quite breathing only external intercostal muscle is
involved, however if we need to breath deliberately internal intercostal muscle is involved

How is air brought into the lungs?

The process of breathing involves the process of inhalation and exhalation.
The breathing movements are brought about by two different sets of muscles that change the
pressure in the chest cavity.
The mechanism of breathing
Structure Inhalation (breathing in) Exhalation (breathing out)
Diaphragm Contract & flatten Relax & become dome shaped
External intercostal Contract Relax
muscle
Internal intercostal Relax Contract
muscle
Ribcage Moves up & outwards Moves down & inwards
Chest cavity Looks bigger Looks smaller
Pressure Decreases Increases
Lung Inflated (filled with air) Constricts(defleats)
The volume of thorax Increases Decreases
The process of gaseous exchange
 breathing in supplies us with the oxygen we need for cellular respiration
 when we breathe out waste carbon dioxide is removed from the body
 When the air is breathed into the lungs, O2 passes into the blood by diffusion along a concentration gradient.
 At the same time CO2 passes out of the blood into the air of the lungs, also by diffusion along a
concentration gradient.
 This exchange of gases takes place in the alveoli, the tiny air sacs with a large surface area that make up much
of the structure of the lungs.
 The movement of O2 into the blood and CO2 out of the blood takes place at exactly the same time
 There is a swap or exchange between the two and so this process is known as gaseous exchange
The mechanism of gas exchange in the alveoli depends on:-
a large surface area
moist surfaces
short diffusion distances
a rich blood supply These maintain steep concentration gradient
Factor affect breathing rate
The breathing rate is determined by the rate of breathing and depth of breathing
The normal rate of breathing in adult human being is 12-14 times per minute
Depth of breathing: is the amount of air inhaled or exhaled per breath
Tidal volume: is the amount of air that one can be breathed in & out at normal
resting situation
Vital capacity: is the maximum amount of air that is breathed in and out:
The rate of breathing can be affected by the following major factors. These are:

A. Exercise
During exercise when muscular activity increases, the breathing rate and depth of breathing increases
to supply more oxygen to release energy for the body.

B. Anxiety
During anxiety the body reacts as it is in danger, extra oxygen needed to more energy in order to
survive danger, therefore the rate & depth of breathing increases.
C. Drugs
Stimulant drugs such as khat and cocaine can increases the rate and the depth of breathing. 19
D. Altitude
At places of higher altitude; the level of oxygen becomes lower &lower. This makes breathing
 difficult thus the rate and depth of breathing becomes higher.
E. Weight
Excess weight can also affect the breathing rate.
It can be difficult to breathe deeply because of the fat around the abdominal organs, which makes it
difficult for the diaphragm & other structures around the lungs to relax properly.
F. Smoking
Smoking is a habit that directly affects your respiratory system as well as other areas of your body
The effect of smoking on The health:
The cigarette smoke consists of around 4000 chemicals that are inhaled into the lungs. some of these
include:

Nicotine: is the addictive drug found in tobacco smoke.

Carbon monoxide: is a very poisonous gas found in cigarette smoke .It takes up some of the oxygen
carrying capacity of the blood.
Tar: is a sticky black chemical in tobacco smoke and causes irritation of nose , throat & lung.
Carcinogenic substances: are cancer causing substances; the most commonly carcinogenic are arsenic
& benzeprene.
Smoking-related diseases
Smoker health may get affected in various ways :
Tar is a sticky black chemical in tobacco smoke that is not absorbed into the bloodstream.
It simply accumulates in the lungs, turning them from pink to grey.
In a smoker, the cilia which move things away from the lungs are anaesthetized by each cigarette and
stop working for a time, allowing dirt and bacteria down into the lungs.

Tar makes smokers more likely to develop bronchitis -inflammation and infection of the bronchi.

The build-up of tar in the delicate lung tissue can also lead to a breakdown in the alveolar structure.

In these chronic obstructive pulmonary diseases (COPD) the structure of the alveoli break down
and much larger air spaces develop.
Cancers of lung, lips, and throat can be caused due to carcinogenic substances
Smoking also affects heart & blood vessels which increases the risk of the heart attack and stroke.
Smoking and the family:
Smoking may have individual, family & the society; some of its effects include:
Economic crisis Increased risk of respiratory diseases
Psychological problems Conflict in the family
Breathing hygiene:
There are mechanisms that can be used to keep the breathing system into a healthy state:
- Good oral hygiene
- Covering the mouth during cough &sneezing
- Consult a doctor for any problems related to respiratory organs
3.4 Cellular respiration
The digestive system, breathing, and circulation systems all exist to provide the cells of the human
body with what they need for respiration.
Respiration: is the process in which energy is released from the breakdown of organic substances in
the body.
The energy that is used by the cells is stored in the form of a molecule known as ATP,
Which stands for adenosine triphosphate. This is an adenosine molecule with three
phosphate groups attached to it.
When energy is needed for any chemical reaction in the cell, the third phosphate bond is broken 20
in a hydrolysis reaction.
ATP+H2O→ ADP +Pi +energy
 ATP is formed by the bond between adenosine diphosphate & a free inorganic phosphate group (Pi)
and the all-important energy needed in the cell.
ADP +Pi →ATP+H2O
The importance of ATP to the body:
to build up large molecules from smaller ones to make new cell material (anabolism). And
also break large molecules down into smaller molecules (Catabolism).
Anabolism + Catabolism = Metabolism
To enable muscle contract and relax
Provide energy for the active transport of some substances across cell boundaries
Types of Respiration
I. Aerobic respiration
during the process of cellular respiration, glucose reacts with oxygen to release energy that can be
used by the cell. Carbon dioxide and water are produced as waste products.
The reaction can be summed up as follows:
Glucose + oxygen → carbon dioxide + water + energy (ATP)
Aerobic respiration takes place in the mitochondria in cells.
These are tiny rod-shaped bodies (organelles) that are found in almost all cells.
Cells that use a lot of energy contain lots of mitochondria

II. Anaerobic respiration

breaking down of food to release energy without oxygen
it is a type of respiration that does not use oxygen.
Anaerobic respiration produces far less ATP than aerobic respiration.
It also produces a different waste product called lactic acid.
Glucose → lactic acid + energy (ATP)
3.5 The circulatory system
 The transport system is required to supply the needs of the body cell & remove the waste products
they produce.
The human transport system is the blood circulation system. It has three elements: the pipes
(blood vessels), the pump (the heart), and the medium (the blood)
A double circulation:
Human circulatory system is called a double circulation.it consists:
i. One carrying blood from the heart to the lungs and back again to exchange oxygen and carbon dioxide with
the air. This is called pulmonary circulation
ii. The other carrying blood all around the rest of the body from the heart and back again. This is called
systemic circulation
A. The blood vessels
 A very important element of any transport system is the pathways along which the transport takes
place.
 In the human body there are three main types of blood vessels:-
Arteries, Veins & Capillaries

Arteries: carry blood away from the heart

The largest artery is called aorta

The smallest artery is called arterioles

It have thick walls that contain muscle and elastic fibres
It have a pulse: the pulse is the surge of blood from the heart when it beats 21
they have no valves
Most arteries carry oxygenated blood ‗except:
  Pulmonary artery which carry the blood away from your heart to your lungs
 Umbilical artery which carries blood away from a foetus into the placenta
Veins: carry blood towards the heart.
The largest vein is called venacava
The smallest vein is called venules
▲ They have much thinner walls than arteries & less elastic wall\
▲ They do not have a pulse but they often have valves
▲ Most veins carry deoxygenated blood except:
 Pulmonary vein, which carry oxygenated blood back from lungs to the left-hand side of
heart
 Umbilical vein, which carries oxygenated blood from the placenta back to the developing
foetus.
Capillaries
▲ They are narrow, thin walled blood vessels
▲ It help to connect arteries with veins and take blood to the tissues & cells
▲ They have no valve
▲ They are site of the exchange of substances within the body.
▲ Blood from the arteries passes into the capillaries, which have thin walls & massive surface area.

B. The Human heart

The human heart is a bag of reddish-brown muscle that beats right from the early days of development
until the end the life, sending blood around the body.
It is made up of a unique type of muscle known as cardiac muscle

The walls of the heart are almost entirely muscle.

These muscular walls are supplied with blood by the coronary arteries (supply oxygenated blood to
cardiac muscle).
The deoxygenated blood is carried away in the coronary veins, which feed back into the right atrium
(atria).
 Human heart is divided into 4 chambers
The two upper chambers are the right & left atria
The two lower chambers are the right & left ventricles
 The walls of the atria are relatively thin, so they can stretch to contain a lot of blood.
 The walls of the ventricles are much thicker, as they have to pump the blood out through the major
blood vessels.
 The muscle walls of the left-hand side of the heart are thicker than on the right. This is because the
left hand side of the heart has to pump blood around the whole body whilst the right-hand side
pumps only to the lungs.
The working of the heart
 The two sides of the heart fill and empty at the same time to give a strong, coordinated beat
Mechanism of blood circulation
Deoxygenated blood, which has supplied oxygen to the cells of the body and is loaded with carbon dioxide,
comes into the right atrium of the heart from the veins of the body. The atrium contracts and forces blood
into the right ventricle. The right ventricle contracts and forces blood out of the heart and into the lungs
where it is oxygenated - it picks up oxygen. Oxygenated blood returns to the left-hand side of the heart from
the lungs and the left atrium fills up. The left atrium contracts forcing blood into the left ventricle. The left
ventricle contracts forcing oxygenated blood out of the heart and around the body
22
Valves
Valves: mechanism in the veins that allows blood to flow in one direction only.
inside the heart there are many different valves.
their names describe their appearance;
bicuspid (two parts): are found between the left atrium & left ventricle
Tricuspid (three parts) are valves between the right atrium & right
ventricles.
Semilunar (half-moon): valve found at the base of aorta and pulmonary
artery
Septum: - wall separating the right and left sides of the heart
Diastole is when the heart muscles relax and it fills with blood.
Systole is when the heart muscles contract and force the blood out of the heart
The pressure at which the blood travels around our arteries varies as the heart beats.

 A normal blood pressure is about 120 mmHg/80 mmHg -the nominator is systolic & the
denominator is diastolic pressure.
 Sphygmomanometer: is an instrument that is used to measure blood pressure.
C. The blood
Blood is a complex mixture of cells and liquid that carries a huge range of substances around the
body
Blood consists of a liquid called the plasma.
Plasma: - is a pale yellow liquid that transports all the blood cells & also number of other things.
There are components of blood cells. These are:

Red blood cells (Erythrocytes)

They are more in number than other types of blood cells
They are disc shaped & non-nucleated cells.
They are made in bone marrow, when they mature they lose their nucleus.
The RBC only live 100-120days so they are constantly being replaced.
They are used to carrying O2 around our body. Because they are packed with a special red substance
called haemoglobin, which picks up oxygen.
Hemoglobin is a special red pigment, a large protein molecule folded around four iron atoms.
23
In a high concentration of oxygen, such as in the lungs, the hemoglobin reacts with oxygen to form
oxyhaemoglobin.This is bright, which is why most arterial blood is bright red.
In areas where the concentration of oxygen is lower, such as the cells and organs of the body, the
 reaction reverses
The oxyhaemoglobin splits to give purple-red haemoglobin (the colour of venous blood) and oxygen
The oxygen then passes into the cells where it is needed by diffusion.
White blood cells (leukocytes)
They are much bigger than the red cells but they are fewer of them.
They have a nucleus and form part of the body‘s defense system against microbes
They can be classified as:
Lymphocytes- form antibodies against microbes
Phagocytes-engulf invading microorganisms
Platelets (thrombocytes)
They are small fragments of cells and very important in helping blood to clot at the site of a wound.
Platelets have thread like protein fiber called fibrin for blood clotting to trap blood cells, platelets and
fluid through a complex series of enzymes controlled reactions.
The clotting of the blood prevents from bleeding to death from a simple cut
It also protects the body from the entry of bacteria and other pathogens
Human blood groups
There are special proteins called antigens are found on the surface of all cells.
They allow cells to recognize each other and also to recognize cells from different organisms
If the cells of an immune system recognize a foreign antigen on a cell in the body, they will produce
antibodies & it destroy the foreign cells.
A number of different antigens are found specifically on the surface of the RBC, which gives different
human blood groups.
The blood grouping system is called ABO system.
Based on presence and absence of these antigens , there are four types of blood groups
There are two possible antigens : Antigen A & antigen B
There are also two types of antibodies:- antibody A & antibody B
 The below table describe the compatibility of Different blood groups
Blood group Antigen on RBC Antibody in the plasma Donate to Receive from
A A B A & AB A& O
B B A B & AB B&O
AB AB None AB only All groups
O None A and B All groups O only
Blood group ‗O ‗is called universal Donor, because it has no antigens so, it can be given to anyone.
Blood group ‗AB‘ is called universal recipient , which has no antibodies can receive any type of blood
If the blood from different blood groups is mixed together, there may be a reaction b/n the antigen & the
complementary antibody which makes the red blood cells stick together, this is called agglutination.
Two common problems of the circulatory system:
A. Anemia: it is caused when there are:
 too few red blood cells in the body, or too low levels of hemoglobin in the blood.
 It is most commonly due to lack of iron in the diet so it is treated by iron rich diet.
B. Hypertension (High Blood Pressure):
Is considered high if the systolic pressure is >140mmHg or the diastolic pressure is >90mmHg
There are a number of factors that can increase the risk of hypertension.
Many of these factors mean that blood vessels are likely to be getting narrower, or becoming
more rigid
These factors include: - sedentary (inactive) lifestyle,
Increasing age, smoking, 24
being overweight, kidney diseases, diabetes and
Excessive salt intake, certain medicines such as steroids
 Excessive consumption of alcohol,
Treatment of hypertension
Losing weight Lower salt level in diet
Life style adjustment using medicines like:

Diuretics: which increase frequency of urination to decrease the blood volume and
Beta blockers: - these blocks the nerves w/c narrows the arteries
UNIT: 4
MICROORGANISMS AND DISEASES
4.1. Micro-organisms
Micro-organisms are tiny living organisms that are usually too small to be seen with the naked eye,
these includes bacteria, viruses, yeast and mould
Many of microorganisms are very useful while other cause diseases.
Bacteria
 Are single celled organisms
 They are much smaller than the smallest plant& animal cells.
 They contain cytoplasm surrounded by a membrane
 They have non cellulose cell wall
 Some bacteria have flagella to help to them move
 They also come in a variety of different shape and size
Viruses
 are even smaller than bacteria
 They usually have regular geometric shapes, and
 They are made up of a protein coat surrounding genetic material containing relatively few
genes.
 They do not carry out any of the functions of normal living organisms except reproduction
 They are obligate intracellular parasites
 They have either DNA or RNA as genetic material
Fungi (Yeast and mould)
 Yeast are single -celled organisms
 Each yeast cell has a nucleus, cytoplasm, and a membrane surrounded by a cell wall.
 They reproduce is by asexual budding - splitting to form new yeast cells.
Moulds
 They are made up of, threadlike structures called hyphae.
 The hyphae are not made up of individual cells - they are tubes consisting of a cell wall containing
cytoplasm and lots of nuclei.
 They reproduce asexually by spore formation.
The germ theory of disease
Germs are micro-organisms responsible for cause of some diseases
The development of microscope Anton van Leeuwenhoek in 17th century helped different biologists
to explain the relationship between infectious diseases & micro organisms
The development of knowledge about micro-organisms is actually related to the theory of spontaneous
generation.
The theory of spontaneous generation
States that living things could arise from non-living things spontaneously. This theory is opposed by
many biologists & a French biologist Louis Pasteur disproved it finally by using an S- shaped flask
that traps dust & microorganisms.
Pasteur was convinced that any growths that appeared -for example, mould on food as it decayed -
came from microscopic organisms already present in the air.
25
First he showed that the theory of spontaneous generation was wrong. Then he showed that if he boiled
broth and sealed the container, the broth would stay clear until he introduced material which had been
exposed to the air.
At this point micro-organisms grew and the broth turned cloudy
 Pasteur went on to identify the micro-organisms that caused a number of diseases including anthrax,
rabies, and diphtheria.
The immune system
Immune system:- the system in the body which protects the body against invading microorganisms
and foreign proteins.
Like all living cells, pathogens carry unique protein molecules called antigens on their cell surfaces.
When a pathogen gets into the body the antigens on the surface stimulate a response by the immune
system.
White blood cells (lymphocytes) produce antibodies to disable the pathogen. Other white blood cells
(the phagocytes) then engulf and digest the disabled pathogens.
Once someone have had a disease, the immune system ‗remembers‘ the antigen and the right
antibody to deal with it.
Control of microorganisms
Sterilization is the killing of all micro-organisms in a material or on the surface of an object,
making it safe to handle. These include the use of:
High temperatures or heat
It is highly efficient means of sterilization
 Autoclaving: it involves the killing of microorganisms by boiling in water at 121 °C. under
high pressure for 15-45 minutes of ‗cooking‘ at these temperatures
 Ultra high temperature (UHT) is a way of treating food to kill all the micro-organisms on
it. The temperatures used range from around 135 °C to 150 °C
 Dry heat sterilization: Dry heat, over a long time, kills all micro-organisms. Special ovens
used in microbiology use temperatures of 171 °C for an hour, or 160 °C for 2hours,.
 Incineration - burning substances at high temperatures in the air - also kills micro-organisms
 Pasteurization: it involves boiling or heating of milk, beer and other foodstuffs at 71.6 °C for at least
15 seconds or 62.9 °C for 30 minutes.
A chemical approach to controlling micro-organisms
 Possible pathogens can be attacked chemically in a number of ways .for e.g.
1. A disinfectant is a chemical or physical agent that is applied to an inanimate object to kill micro-
organisms. Disinfection means reducing the number of living micro-organisms present in a sample
This method discovered by Joseph Lister. some of example of disinfectant include: house hold
bleach, Dilute bleach and calcium hypochlorite
2. Antiseptics: are chemical agents that are applied to living tissue to kill micro-organisms -disinfectants for
the skin.
it help to protect entrance of germs if the skin is cut or wounded.
Growing of microorganisms
Micro-organisms can be grown in laboratories under controlled condition.
It is important for various purposes; these include:
To know how to killed them
To develop vaccines
To identify their useful & harmful aspects
For growing microorganism‘s biologist need to fulfill the following precondition:

Isolating type of microorganisms to be studied

developing suitable nutrient like agar and broth
Agar: is a solid nutrient medium which is extracted from red algae
Broth: is a liquid nutrient medium 26
Antibiotics
 Drugs which kill bacteria but do not harm human cells
 Penicillin was the first antibiotic to be discovered
 Artificial immunity
Our body has its own natural ability to protect itself against artificial disease, however if the immune
system of the body fails to defend some dangerous disease it will be treated by artificial immunity.
Artificial immunity is given in the form of vaccine
Artificial active immunity: involves introduction of weakened or dead pathogen in the body which
stimulates the body to produce its own antibodies.
It can be natural from mother to child (natural passive) until the child produces its own natural
active immunity
Artificial passive immunity: it involves giving specific antibodies in the form of infection. It
provides a high type of resistance but last only for short time.
Natural active immunity;- acquired from exposure to the disease organism through
infection with the actual disease.
Vaccination (immunization):
 is the use of dead or weakened strains of pathogens to produce immunity to dangerous
diseases
 the vaccination work through the following ways
a weak or dead form of the infecting organism is put into the body by injection or by mouth
once in the body, the white blood cells respond by producing antibodies
If the living micro-organism enters the body in the future, antibodies are produced very rapidly
to destroy it and so the disease does not develop.
4.2. Diseases
Disease is any form of disorder in or on the body distorts its normal functioning
Some of the most commonly known diseases which are caused by pathogenic organisms
among them include:
i. Tape worm (cestoda)
Flat shaped worm that parasitizes the wall of intestine of humans
They have no digestive system & but have cuticle to absorb nutrients
The most common are beef tape worm(Taenia saginata) & the pork tapeworm(Taenia solium)
They have complex life cycle which involves at least two different hosts.
Transmission: eating improperly cooked or raw meat
Symptoms: feeling weakness, weight loss, segments of tape worm in feaces
Control & prevention: avoid eating raw meat, use antiworm drug & proper disposal
of feaces
Life cycle of beef tape worm
Cows raised in unsanitary conditions may contain cysticerci ‗bladder worms‘ embedded in their muscles.
These consist of a capsule containing a scolex. When a bladderworm is ingested (e.g. in undercooked
beef), The scolex turns inside out and attaches by suckers and hooks to the wall of intestine.
It then begins to produce buds, called proglottids, which remain attached to each other for a time and, as
they mature, each develops both male and female sex organs.
The most mature proglottids eventually break loose and are passed out in the faeces. If conditions are
such that cows get access to the human faeces, they take in the eggs and the whole cycle starts again.

ii. Tuberculosis
 It is caused by a bacterium called Mycobacterium tuberculosis
 It can affect anyone of any age, but People with weakened immune systems (such as people
suffering from HIV/AIDS) are at increased risk 27

Transmission :
 Droplet infection, but need prolonged exposure to someone with TB for infection to
 occur. work in overcrowded conditions
Symptoms
 Some people may not have obvious symptoms (asymptomatic), however the symptoms of TB
include:

a low-grade fever fatigue a persistent cough

Night sweats weight loss and
Control and prevention
In social terms avoiding overcrowded conditions Covering the nose &mouth during coughing
Good ventilation vaccination
Treatment
People with active TB disease must complete antibiotic for four months or more
The role of vectors in disease:
A vector is an organism that transmits disease-forming micro-organisms from one host to another
well-known example is the Anopheles mosquito, which carries the malarial parasite
iii. Mosquitoes and malaria
Malaria is a disease where mosquitoes are the vector
The mosquito vector is the female Anopheles mosquito
The disease itself is caused by the single-celled parasite Plasmodium
It spends part of its life cycle in a mosquito and part in the human body
Life cycle
√ Female needs two meals of human blood to provide protein for her developing egg and this
is when she passes on her load of malarial parasites.
√ If the first feed the mosquito takes is from someone infected with malaria, the Plasmodium
parasites called Plasmodium falciparum remain in her mouthparts
√ the next time she feeds, the Plasmodium parasites pass into the blood of the victim along
with the saliva - and someone else is infected with malaria
Symptoms: These include fevers, chills, and sweats
Control and prevention: Methods of controlling malaria must involve controlling the Anopheles
mosquitoes. This can be done by: Using mosquito repellents
having screens on doors and windows
insecticide-treated mosquito nets
Proper disposal of sewage‘
Minimize any opportunities for the mosquitoes to breed

iv. Gastroenteritis/acute watery diarrhea (AWD)

Intestinal infection causing acute watery diarrhea
Some of the causative organisms include rotaviruses, the bacteria Salmonella and
Escherichia coli (E. coli), or the protoctists Giardia and Amoeba.
Transmission
eating contaminated food or water
prepares or handles food without washing their hands after going to the toilet
poor sanitation
poorly cooked and raw eggs if they are infected with bacteria such as Salmonella
symptoms
28
violent abdominal cramps and pain
feeling nauseous, vomiting or often both
watery diarrhoea which does not usually have blood in it
 slight fever
general muscle aches and headache
Control and prevention
Good personal hygiene Avoid eating undercooked or raw food
v. Cholera
√ It is caused by bacteria called Vibrio cholera & it infects intestine
Transmission: eating or drinking food or water contaminated by the faecal waste of an infected person
Symptoms: include the pale, watery diarrhea, vomiting and dehydration, muscle cramps
Treatment: taking more fluid to replace the lost through diarrhea &antibiotics, rehydration salt (ORS)
Control and prevention: avoid consumption of uncooked food
Proper disposal of feaces ,
Good personal hygiene and environmental sanitation
Taking cholera vaccine
vi. Typhoid (Typhoid fever)
is a bacterial infection caused bacterium called Salmonella typhi - typhoid only affects humans
transmission : Like other diarrhoea diseases they are spread by eating foods or drinking water
contaminated by faeces from an infected individuals
symptoms: it may include :A very high fever - 39-40 °C, A painful abdomen
Sore throat and headache, an enlarged spleen and liver , Constipation or diarrhoea
Treatment: antibiotics are used as a very effective treatment. Plenty of fluids to replace the ones they
lose
Control and prevention: careful hand washing after toilet visits,
clean drinking water and good sewage disposal
good food hygiene in kitchens and care in eating raw or lightly cooked foods
vii. Sexually transmitted diseases (STDs)
STDs are Infectious diseases spread by sexual contact it is also known as venereal diseases (VD)
are a growing problem in Ethiopia -partly because sexual activity often starts relatively young
the most commonly known STDs are:
A. Gonorrhea (gonococcal infection)
o Is caused by the bacterium Neisseria gonorrhoeae.
o Gonorrhea germs are found in the mucus areas of the body (the vagina, penis, throat and rectum).
o Transmission :It is spread through sexual contact, Having unprotected sex, having many sexual partner o
Symptoms: burning sensation while urinating and a yellowish-white discharge from the genital organ
 If a pregnant woman has untreated gonorrhea, she can pass the infection on to her baby result in
blindness
Treatment: it can be treated effectively in the early stages using antibiotic o
Prevention& control:
Infected individual do not have sex until your course of treatment is completed.
Use a male or female condom
Be faithful to sexual partner.
B. Syphilis
√ Is bacterial infection, caused by the spiral-shaped Treponema pallidum
√ Any sexually active person can be infected
Transmission: like gonorrhea It is spread through sexual contact
It is congenital syphilis, which is spread from mother to foetus. This can cause very serious problems
29
for the baby when it is born.
Structure of Treponema pallidum
Symptoms: Syphilis progresses in distinct stages
The symptoms occur in stages called primary, secondary and tertiary (late)
Primary stage (the first six weeks): painless sores around reproductive organ, rectum, & mouth
Secondary stage (six weeks after): The most common symptom during this stage is a rash.
Other symptoms can include:
Tiredness sore throat hoarseness patchy hair loss
Fever headaches loss of appetite
swollen glands
Untreated the disease then goes into a long quiet phase
Tertiary stage (late syphilis):
Involve illness in the skin, bones, central nervous system and heart.
It causes severe and irreversible problems that cannot be treated successfully.
If a pregnant woman has untreated syphilis she may transmit the disease to her unborn child. This may
result in death or deformity of the child.
Treatment: It is treated easily with antibiotics such as penicillin or tetracycline
Pregnant women can be treated with antibiotics to cure them and protect their baby
Prevention& control: similar with gonorrhea
C. Chancroid
It is a bacterial STD that is caused by the bacterium Haemophilus ducreyi
It is more commonly seen in men than in women.
Transmission: having sex with an infected person & increase risk of becoming HIV-positive
Symptoms:
The first symptoms of chancroid are sore ulcerations on the genitals, particularly penis, it is soft and
filled with pus.
The second stage of the infection is that the lymph glands in the groin also become infected,
Permanent loss of penis
Treatment: it can be treated easily with a dose of antibiotics
Prevention & control:
be faithful sexual partner
Use a male or female condom
Good genital hygiene & male circumcision
Using medicines correctly
Traditional medicines are very &alternative form medicine in developing countries like Ethiopia
o It is often holistic, based on treating the whole patient, but limiting their dose is very important.
o It is based on extracts of plants including herbs and spices.
Modern medicines: are responsible for cure various diseases &made in very carefully controlled doses
The most common include: antibiotic & vaccine
However care should be taken while using modern medicine: so the following precaution should
be considered: 30
Do not take more than you are prescribed,
Do not take less than you are given
 Make sure you finish taking all the medicine
Follow the instruction if not antibiotic-resistant bacteria may evolve which can be very
serious indeed
4.3. HIV and AIDS
Acquired Immune Deficiency Syndrome (AIDS) is the medical term for a combination of illnesses
that result when the immune system is weakened or destroyed.
It is caused by Human Immuno deficiency Virus (HIV), a virus that attacks the immune system.
Transmission:
 sexual intercourse which is un protected
 It can pass from a mother to her baby in the womb, during birth or when she breastfeeds
 Infected blood on needles used for injecting illegal drugs, or knives used for female genital
mutilation.
Symptoms
Patients often have few symptoms to begin with but eventually their weakened immune system means
they get many diseases.
Treatment
Antiretroviral drugs can slow down the progress of HIV/AIDS and protect unborn babies from
infection.
 The sooner people can start taking antiretroviral after infection, the longer they will stay healthy.
Prevention & control
It can be controlled by ABC rule means that:
A: abstain from sex
B: be faithful to sexual partner JOIN ON Telegram
C: condom use
@QesemAcademy
HIV and the immune system
How does HIV attack the immune system?
There are two main types of white blood cells in the immune system. These are:
1. T-cells actually bind to the antigens on the invading micro-organism and destroy it.
2. B-cells make antibodies which bind to the antigen and destroy it.
HIV attacks the T-cells of immune system. It gets inside them and so they can no longer work.
As more T-cells are invaded by the virus, the immune system is less and less effective.
This is why people with HIV/AIDS get so many other infections
Stigma and discrimination
Stigma is a mark of disgrace on people with HIV, while discrimination is an act of
neglecting some from the group or other.& are the most serious cases that affects people living
with HIV/AIDS
Care and support
It is important for people living with HIV/AIDS since it helps them live longer & healthier
Unit 5:
Classification
5.1. Principles of classification
On Earth today there are many types of living things. This great variety of life is called biodiversity.
Classification: is grouping of similar living things.
Taxonomy: is study of classification of organisms (Greek, taxis-to arrange, nomos-law) 31

Need for classification

Biologists classify living things for the following reasons:
 To simplify their study
To bring order out of chaos or confusion
To try to understand how life originated
What is a species?
 A group of organisms that can breed successfully with one another to produce fertile offspring.

How are living things classified?

Living things are classified according to how similar they are
One example is animals that are put in a group together because their limbs are built on the same basic
plan.
The limbs of a bat, horse, bird, human and whale all have the same basic pattern though they are used in
different ways these limbs are called homologous structures. (Similar structure with d/t function)
Today there are more sophisticated ways of comparing organisms. The fundamental chemicals of life -
such as DNA, RNA and proteins - are found in almost all organisms
The classification system
▲ Taxonomy: is the process of classifying living organisms‘
▲ Taxa: category in classification
▲ The main taxonomic categories are kingdom, phylum (or for plants, division), class, order,
family, genus and species.
The largest groups into which living organisms are divided are the kingdoms.
Kingdoms are subdivided into phyla,
Each phylum into classes, each class into orders,
Each order into families, each family into genera and each genus into species.
The species is the smallest unit of classification
Naming living things
Different method of classification was introduced by different biologists at different times:
Aristotle: Greece a philosopher .who tried to create a classification system for the living world, and
grouped animals by: animals that live on land‘ and ‗animals that live in water
The modern classification method is introduced by Swedish botanist Carl Linnaeus in 18th century.
He developed the binomial system of nomenclature for organisms
He published in a book called The System of Nature
Binomial means two names. The two names of an organism are in Latin
Simple rules for writing scientific names
The first name is the name of the genus name & it is starts with capital letter. e.g. Homo sapiens,
The second name is the name of a species & it is written with a small letter.
The two names are underlined when handwritten or in italics when printed.
Table 5.1 Examples of scientific names of some common organisms

common name Scientific name

Human beings Homo sapiens
A dog Canis familiaris
A housefly Musca domestica
Domestic cat Felis domesticus
Maize Zea mays
Bean Phaseolus vulgaris
Lion Panthera leo
Living things are classified and named for the following main reasons.
To create an internationally accepted way of referring to a particular living thing. 32
To avoid confusion created by different languages.
To help in simplifying classification and study of living things.
 Human Honeybee Teff Mushroom
Kingdom Animalia Animalia Plantae Fungi
Phylum Chordata Arthropoda Angiospermophyta Basidiomycot
Class Mammalia Insecta Liliopsida Basidiomycetes
Order Primates Hymenoptera Cyperales Agaricales
Family Hominidae Apidae Poaceae Agaricaceae
Genus Homo Apis Eragrostis Agaris
Species sapiens mellifera teff campestris
Table 5.2 Hierarchy of groups
5.2. The five kingdoms
▲ A kingdom is the largest taxon and consists of all the other taxa. In the modern classification, there
are five kingdoms namely:

1 Kingdom Monera 4 Kingdom Plantae

2 Kingdom Protista 5 Kingdom Animalia
3 Kingdom Fungi
This system of classification is known as the five-kingdom system
Viruses are not classified in any of the above kingdom. This is because viruses do not have all the
seven characteristics of life, although most scientists now classify them as living organisms.
1. Kingdom Monera
The representative groups are Eubacteria (true bacteria) & the blue-green algae (Cyanobacteria).
They are unicellular & prokaryotic (have no distinctive nucleus).
They are all microscopic and they reproduce by simply splitting in two (binary fission)
They have either autotrophic or heterotrophic mode of nutrition
Examples include Mycobacterium tuberculosis and Haemophilus ducreyi which are pathogenic while
others are useful.
2. Kingdom Protista
Consists usually unicellular & eukaryotic (do have nucleus)
They include plant-like organisms that can move around and animal-like organisms that cannot move
Representative groups of this kingdom are subkingdom protozoa& subkingdom algae
A. Subkingdom protozoa
They are microscopic & have no chloroplasts
They live as parasite or free living
Have locomotory structure. e.g. Amoeba- pseudopodia , Paramecium:-cilia
B. subkingdom algae
They are photosynthetic & eukaryotic
They live either in aquatic habitat or on land
They have undifferentiated body called thallus.
E.g. Dinoflagellates, red algae, & green algae
3. Kingdom Fungi
Fungi are eukaryotic and usually multicellular.
They are heterotrophic
Many fungi are saprotrophs, which means they feed on dead material.
They play a vital role within ecosystems as decomposers
Examples of this type of fungus are Rhizopus ,Mucor and Penicillium 33
They can be parasites, feeding on living organisms. Such as Candida albicans (thrush) and
Tinea pedis (athlete‘s foot) affect people and other animals.
Some fungi are mutualists. This means they live in close association with another organism
 and both benefit. Examples are lichens, which are a combination of a fungus and green algae
Mycorrhizae, an association between a fungus and the roots of a plant.
There are also single celled fungi like yeast.

4. Kingdom Plantae

The plants - includes a great variety of organisms, which range from tiny mosses to giant trees &
80% of these are flowering plants
The main characteristics of all plants include
They have eukaryotic cells.
They are multicellular organisms
They contain chlorophyll and carry out photosynthesis.
They are predominantly land dwelling.
Their cell wall composed of cellulose
Most have a waxy cuticle that helps to prevent drying out
The kingdom is split into a number of divisions. Plant divisions are the same as animal phyla. The
four most important divisions are:
A. Division Bryophyta (mosses and liverworts)
They are the simplest land plants.
They do not have a true leave , stem & root system
They are non-vascular (do not have xylem and phloem).
The best examples of bryophytes are mosses like Etodon concinnus,and Funaria species.
A moss plant:
has a simple, slender stem.
They also have thin simple leaves
also have simple root-like structures called rhizoids and attach the mosses to the
soil & used for absorption of water.
The other example is the liverworts, which only grow in very wet places.
Bryophytes are commonly found in rainforests and at high altitudes on mountains

B. Division Pteridophyta (Filicinopyta)-ferns

 They have true leaves, stems, and roots.
 Fern stems have rhizomes, which grow horizontally just below the surface of the soil.
 They have vascular tissue
 They have large prominent leaves called fronds
 Their spore produced in the fronds &dispersed by wind 34
 They reproduce by alternation of generation(the sporophyte is well developed their gametophyte
stage is reduced)
 most ferns live in damp, shady places - they are very common in tropical rainforests
  However, some ferns - such as Pteridium spp (commonly known as bracken) can grow and do well in
full sunlight.
 Another example of a pteridophyte is the fern Dryopteris spp.

Ferns

C. Spermatophytes(seed-bearing plants )
They are the most successful because of the following characteristic features that they possess:
They have well-developed roots, stem and leaves.
They have well-developed vascular tissues.
The male gametes are contained within pollen grains and female gamete is contained within the
embryo sac.
The product of fertilisation in sexual reproduction is a seed that may or may not be enclosed in a
fruit.
The spermatophyta are divided into two divisions. These are:
i. Division Gymnospermae(coniferopyta)- non-flowering plants
ii. Division Angiospermae(flowering plants
i. Division Gymnospermae(coniferopyta)- non-flowering plants
These are more commonly known as the conifers or ‗naked seed plants‘. Pine trees, spruces and
cedars
▲ The main characteristics of the gymnospermae are:
Their seeds are not enclosed in fruits.
They have small needle-shaped leaves with a thick waxy cuticle that reduces water loss and
minimises damage by excess heat or cold.
They are evergreen so they can photosynthesize all year long
The reproductive structures are found in cones.
They different types of cone. The male cone forms huge numbers of pollen grains that are blown by
wind to a female cone.
Fertilisation results in a small winged seed.
The genus Pinus (for example, Pinus sylvestris, Pinus resinosa,) is a good example of a conifer

35
 ii. Division Angiospermae(flowering plants)
 They are the biggest group of land plants on the Earth.
The main characteristics of the angiosperms are
They have flowers as reproductive organs.
They have their seeds enclosed in a fruit.
They have well-developed xylem and phloem tissue
Angiosperms are subdivided into two main classes according to the number of cotyledons they have
in their seeds. These are:
I. Class Monocotyledons (monocots)
 are a group of enormous importance because they are cereal plants that form the staple diet
The main characteristics of the monocotyledons are:
The embryo has a single seed leaf (cotyledon).
Leaves are generally long and thin with parallel veins.
The stem contains scattered vascular bundles.
They do not reach great sizes (palms are the exception to this).
They are often wind pollinated
Example grasses, orchids and maize. Maize& Teff

II.Class Dicotyledons (dicots)

They make up most of the trees, as well as many vegetable plants.
The main characteristics of the dicotyledons are:
The embryo has two seed leaves (cotyledons).
The leaves are often relatively broad and have a network of veins.
The stem contains a ring of vascular tissue.
Some dicots reach great sizes.
They are often insect pollinated.
 Some common examples of dicots include sunflowers, peas, roses and beans. Most trees, such as
Jacaranda, Eucalyptus, Cassia and mangos are dicotyledons. Shrubs include Hibiscus, Lantana camara,
Bauhinia and oranges
5. Kingdom Animalia
This kingdom includes the animals. There are at least two million species of animals alive today.
They are multicellular, eukaryotic and heterotrophic 36
They exhibit locomotion, that is, can move their bodies from one place to another, and
Their cells do not have cell walls.
 They have nervous systems so they are sensitive to their surroundings.
They are either invertebrates (not have a backbone.) or the vertebrates( - all
the animals which have a spinal cord enclosed in a backbone of vertebrae)
There are33 animal phyla but the main ones are
1. Phylum Porifera (the sponges)
They are the simplest invertebrates. Most of them are hermaphroditic
They have hollow filter feeders, and the body cavity is connected to its external environment by pores.
There is little co-ordination or control.
They range in size from a few millimetres to two metres and are supported by a calcareous spicules.
 Sponges are an evolutionary dead end and have no other close living relatives

2. Phylum Coelenterata(cnidaria)
They include some exceptionally beautiful creatures and also
Some very poisonous ones. Sea anemones, hydra, jelly fish and coral are among the members of this
phylum.
They have soft bodies with a ring of tentacles for capturing prey.
They have stinging cells on their tentacles for poisoning or immobilising prey and predators.
They have two layers of cells in their bodies that surround a central cavity.
They have only one opening, the mouth, and their bodies have radial symmetry
Radial symmetry : is a body that can be divided into many halves.
3. Phylum Platyhelminthes - flatworms
 They show a relatively high level of organization
 They have flattened bodies with a mouth but no anus.
 They have no body cavity and rely on diffusion for everything.
 They are hermaphrodites
 They live in other animals as parasites or are free-living in fresh water.
Examples of Platyhelminthes include Planaria spp, which live in fresh water, tapeworms and liver flukes
like Fasciola hepatica
4. Phylum nematoda(round worm)
They have narrow, thread-like bodies,
Their bodies are not segmented and are round in cross-section.
They don’t have a circulatory system but they do have a complete digestive system.
Bilaterally symmetrical.
They contains many important parasites, such as Ascaris, which infects the guts of both humans and pigs, and the
family Filariidae -which cause elephantiasis
5. Phylum Annelida(segmented worm)
They have segmented body.
They have a closed blood circulatory system.
They are hermaphrodites, with male and female reproductive organs and
37
They have bristle like structures called chaetae to help them move.
They are found in moist soil and water and most are free-living.
The common earthworm, Lumbricus terrestris,& leech
 Earthworm Snail (mollusc) e.g. of Echinoderms
6. Phylum Mollusca
The most intelligent of the invertebrate species.
Octopi and squid have well developed brains.
They may have shells or be shell-less, live in the sea, or in fresh water or on land.
They have a soft muscular foot with a soft body
Their bodies are divided into head, foot and visceral mass and they are not segmented.
They breathe through gills. Examples of molluscs include slugs and snails.
7. Phylum Echinodermata
They are spiny skinned animals
they have a mouth, a gut and an anus
They are all marine animals, and move around using tube feet.
The adults have five arms, but the larval stages do not.
Examples include Asteris, the common starfsh, Echinus, the common sea urchin and
Paracucumana tricolor, a brightly coloured sea cucumber known as a sea apple.
8. Phylum Arthropoda
This phylum gets its name from two Greek words, arthron - joint, and podos - foot.
They have an external exoskeleton made of chitin that prevents excessive water loss.
They are animals with segmented bodies and jointed limbs.
They have a well-developed nervous system and a complete gut from the mouth to anus.
They divided into a number of classes according to the number of limbs, presence and number of
antennae and number of body parts.
Class insecta
They live almost everywhere although most are land-based.
They have a body divided into three body parts; head, thorax and abdomen.
They have three pairs of jointed legs on the thorax along with one or two pairs of wings.
On their head they have a pair of antennae and one pair of compound eyes.
Insects include flies, butterflies and moths, beetles, wasps and bees and many other common groups.

Class crustacea
They are mainly aquatic.
They vary in size from very small, for example water fleas, to quite large, for e.g. lobsters and crabs.
Their body is made up of two parts - a cephalothorax (head fused with thorax) and abdomen.
The body is often protected by a tough covering called a carapace.
They have more than four pairs of jointed legs, two pairs of antennae and simple eyes.
They include Daphnia, crab, prawn, shrimp, barnacle, water flea, lobsters, woodlice and crayfish.
38
Class chilopoda ( the centipedes )and the diplopoda (the millipedes)
They both have long bodies with many segments and lots of leg
 Centipedes Millipedes
Have flattened bodies Cylindrical bodies
Have brightly coloured bodies Dull-coloured bodies
Have few or less segments Have more segments
Have one pair of limbs per segment Have two pairs of limbs per segment
Carnivorous (feed on other animals) Herbivorous
Have poisonous claws for paralysing their prey Have claws for biting and chewing plant material
Table 5.3 Differences between centipedes and millipedes
Class Arachnida (the spiders)
They are mainly terrestrial although some are aquatic.
They have two body parts - a cephalothorax and the abdomen - with no antennae.
They have eight legs in four pairs.
They have simple eyes
Spiders spin silken webs. Examples of arachnids include spiders, ticks, scorpions, and mites.
9. Phylum Chordata
The term Chordata is derived from the term notochord
Notochord flexible rod like structure of cartilage running along the dorsal side of the body.
They have the following three features in common:
They have a notochord at some stage of their lifecycle.
They have a hollow nerve cord
They have gill slits during early stages of development that are later replaced by lungs and gills.

Vertebrates
The chordates, the best known of which are the vertebrates (animals with vertebral
column/backbone)

In addition, they also have the following features:

An internal skeleton (endoskeleton) made of bone or cartilage.
JOIN ON Telegram
A closed blood circulatory system consisting of blood vessels. @QesemAcademy
A well-developed nervous system.
Two pairs of limbs.
Kidneys as excretory organs
Phylum Chordata divided five classes

i. Class pisces- fishes

They are aquatic
They have streamlined bodies with scales on their skin.
They use gills for gaseous exchange and have fins for swimming
They are ectothermic - they rely on heat from their environment to regulate their body temperature.
Table 5.5 Differences between bony fish and cartilaginous fish
Bony fish (teleosts) Cartilaginous fish(elesmobranches)
Have bony skeleton Have cartilaginous skeleton
Have round-shaped scales Have scales that are not round shaped
Have opercula (gill covers) covering their gills Have no opercula (gill covers) but have gill slits
Have homocercal tails (even size fins) Have heterocercal tails (one part is larger than the other)
Are usually smaller in size Are usually larger in size
e.g. Tilapia, Nile perch, mackerel and catfish E.g. Sharks, skates and rays.
ii. Class Amphibia
 Spend part of their lives in water and part of it on land.
 They were the first vertebrates to colonise the land. 39
 They have simple sac-like lungs (which are not very efficient) and smooth, moist skin
 Their lifecycle includes metamorphosis, and they need water for successful reproduction as fertilization
is external and the larval form (tadpole) is aquatic.
  Gills are only present in the larval forms & they are ectothermic Example: frogs, toads, newts and
salamanders
Frog Toad
Has a smooth skin Has a rough skin
Has a moist skin Has a dry skin
Has more webbed feet Has less webbed feet
Has a brightly coloured body Has a dull-coloured body
Has a more streamlined body Has a less streamlined body
Has extra-long hind legs Has hind legs that are not extra long
Table 5.6 Differences between a frog and a toad
iii. Class Reptilia
The reptiles are mainly terrestrial animals
They have bony skeleton
They have dry skin with scales and their gas exchange takes place exclusively in the lungs
They have developed internal fertilisation
Some reptiles even keep the eggs within their body and give birth to fully developed young.
They are poikilothermic (ectothermic) & have no external ears
Examples , snakes, crocodiles
Two pair of pentadactyl limbs usually present

iv. Class Aves(birds)

Have skin that bears feather & scales on legs.
Have bony skeleton
Two pairs of pentadactyl limbs, front pair forms wings
They are homoeothermic (endothermic)
Example: domestic fowl, the wattled ibis, white collared pigeon and the Ethiopian eagle owl.
v.Class Mammalia
They are the best known of all animals
Their skin bears hair , the skin consists of glands like sebaceous& sweat
They produce live young which have developed for a time within the body of the
mother in a structure called the uterus
They have bony skeleton & Have external ear
Have two pairs of pentadactyl limbs
They use lungs for gas exchange
A true mammal produces milk for its young in mammary glands
Subdivisions of mammals
Mammals are classified according to the way their young are produced. There are three sub-classes of
mammals:
i. Egg-laying mammals - lay eggs, e.g. duck-billed platypus.
ii. Marsupials - produce immature young, which are nourished by milk in the pouch,
E.g. Kangaroo, koala bear, opossum
iii. Higher mammals - produce fully developed young, which are nourished by milk from the mammary
glands, e.g. cows, elephants, cats, monkeys, and humans.
 There are even flying mammals, as bats have been adapted to fly through the air on their
leathery wings!
UNIT 6
ENVIRONMENT
6.1. Ecosystems
Ecosystem: all the animals and plants that live in an area along with the things that affect them. It is the
home or habitat of the living organisms within it
 Habitats may be on land - when they are known as terrestrial habitats 40
or they may be in water, when they are called aquatic habitats.
  There are two main types of aquatic habitat - the marine habitat, which is the salt water of the seas and
oceans, and the freshwater habitat of lakes, ponds, rivers, and streams
- They are affected by both the abiotic components and the biotic components of the ecosystem
A. Abiotic components
o Abiotic factors are the non-living elements of an ecosystem
o The climate and weather produce several important abiotic components. They include the amount of
sunlight, and the amount of rainfall.
o Temperature is a factor which often affects whether animals and plants can survive in an ecosystem.
o Other abiotic factors include the type of soil and rocks, the drainage of the soil and the pH (acidity).
B. Biotic components
o Are factor of the living organisms within an ecosystem which affect the ability of an organism to survive
o Each organism is the part of another organisms environment thus they interact in various ways: these are:
I. Intraspecific: occur between members of the same species, such as Competition for food,
territory, & finding mate.
II. Interspecific f: occur between members of different species. This include predator-prey relationship
& symbiosis
Predator-prey relationship (predation): in which predator animal like lion, tiger feed on other animal
(prey) like buffalo, rabbit, etc.
Symbiosis: is relationship between two organism of different species in which one or both get
benefited from the relationship: this can classified as:
Commensalism: is the relationship in which one organism is benefited while the other is
neither benefited nor harmed. E.g. The r/ship between big trees& epiphytes
Mutualism: is relationship in which get benefited & it‘s an obligatory relationship
For example: lichen (algae & fungi).
Parasitism: is the relationship in which one organism is benefited (the parasite) & another
organism is harmed (host). e.g. R/ship between human & parasite like tape worm.
Protocooperation: the relation which both organism are benefited but it is not an obligatory
relationship. e.g. the r/ship between teeth cleaning bird & crocodile
6.2 Food relationships
According to their mode of nutrition organism can be classified as: autotrophs and heterotrophs
A. Autotrophs: organism that can synthesize their own food to release energy from the raw material
in their surrounding environment. they can be classified as :
▲ Phototrophs: organisms that feed off light to synthesize their organic food .This group of
organisms are called producers. E.g. green plants, algae,& photosynthetic bacteria.
▲ Chemotrophs: organisms that get energy from the breakdown of inorganic chemical
E.g . Nitrifying bacteria
B. heterotrophs: organisms that rely on eating other organisms. They cannot produce their own
food so they are called Consumer. They can be grouped as:
Herbivores: animals that eat plants only. E.g. cow, buffalo, sheep, etc.
Carnivores: animals that feed on other animals only. e.g. tiger ,lion
Omnivores: animals whose diet includes both plants and animals. e.g., human
Decomposers: organism that break down the remains of animals and plants and return the
mineral nutrients to the soil e.g. bacteria & fungi
Food chains
Food chain: is simple & direct feeding interrelationship which involves transfer of energy & nutrients
from one organism to another.
41
in a food chain energy flow is unidirectional (from producer to consumer)
Each organisms occupies particular tropic level within a food chain
 Trophic levels: levels in a food chain to which an organism belongs.
The main tropic levels are:
i.Producer (first tropic level): are green plants & algae.
All organisms depend directly or indirectly on producer.
The sun is ultimate source of energy for all food chains.
ii. Primary consumers (second trophic level): includes herbivores & omnivores.
iii.Secondary consumers (third tropic level): are carnivores which mostly eat herbivores &omnivores.
iv. Tertiary consumers (fourth tropic level): are carnivores (sometimes called top carnivores) which
mostly eat other carnivores
 Decomposer are found at the of each food chain
 Many aquatic food chains start with the microscopic photosynthetic organisms known
as phytoplankton (plant plankton).
 These tiny organisms are eaten by the equally microscopic zooplankton (animal plankton) and
these two groups of organisms underpin food chains which involve almost every animal in the water,
from tiny shrimps to enormous whales.
Examples food chain
Oak (Leaves) → grasshopper → rodent → leopard
ndary
Producer primary consumer 2 consumer tertiary consumer
Grass → zebra → lion
Phytoplankton → zooplankton →fish →man
Food web
 Food web is network of food chains
 In a food web the interactions between many different food chains can be shown
Example of food web

Pyramid of Biomass
Biomass: Is a term that describes all the organic material produced by living organisms.
It all comes originally from plants as they photosynthesize at the beginning of all food chains.
 This biomass is then passed on through a food chain or web into the animals which eat the
plants and then on into the animals which eat other animals.
 The total amount of biomass in the living organisms stage of the food chain can be drawn to
scale and shown as a pyramid of biomass
 The biomass supported at each trophic level decreases as it goes from one tropic level to the
next.
 At each tropic level biomass is lost in various forms: heat from respiration, urine, feaces, to 42
provide energy
Pyramid of numbers
 The number of organism decreases it moves from one tropic level to the next.
  In most ecosystems producers contain large number of organisms than consumer,
however sometimes this may not work
For e.g. the breadfruit tree can grow to around 20 m tall, yet it can be attacked by mealybugs. They in
turn are eaten by ladybirds. However, the pyramid of numbers for this food chain doesn‘t look like a
pyramid at all.
Pyramid of energy
 In ecosystem there is always be transfer of energy from one tropic level to the next tropic level
 There is progressively less energy available for organisms further down a food chain.
Energy is cannot be recycled in an ecosystem; it always flows in one directly.

6.3 Recycling in nature

 Living things are constantly removing materials from the environment.
 The recycling of substances provide an important link between the biotic and abiotic component.
 The materials are returned to the environment from the waste products of animals and the dead
bodies of plants and animals.
 Nutrient in organisms are back into the soil by action of group of organisms known as the
decomposer. Decomposer(bacteria & fungi) play a huge role in recycling of nutrients :
Important of decomposers
They are important in various ways to the environment:
Break & digest dead bodies of plants, animals & waste materials or dropping of animals & add them
into the soil. This increases the fertility of the soil which is useful for plants.
Removes unpleasant waste materials from an environment
Used to make compost in garden
Recycling of substances in an ecosystem includes chemical, physical, & biological processes.
i. The nitrogen cycle
▲ Nitrogen is a vital part of the structure of amino acids and proteins, DNA and RNA
▲ It involves the conversion of nitrogen gas by various processes into usable form by plants
▲ Green plants absorb nitrogen in the form of nitrates dissolved in the soil water.
▲ They use these nitrates to make proteins, and then this protein is passed along the food chain.
▲ The atmospheric nitrogen is fixed by microorganisms living in a symbiotic relationship certain plants,
specially legumes, it includes pea, beans and clover - have nodules on their roots which are full of nitrogen-
fixing bacteria
The nitrogen cycle involves the following bacteria
A. Nitrogen fixing bacteria-convert free atmospheric nitrogen into nitrate
Note: lightning has also a role in fixing atmospheric nitrogen
B. Nitrifying bacteria : convert ammonium to nitrite then to nitrate
Ammonium Nitrite
Nitrite Nitrate
C. Putrefying (amonifying) bacteria: they convert protein in the dead bodies & decay of plants into
ammonium compounds.
D. Denitrifying bacteria -are bacteria that convert nitrates into free atmospheric nitrogen
ii. The carbon cycle
Carbon cycle: cycling of carbon compounds between the living and the nonliving world.
 The main molecules of life are based on carbon atoms.
 It mainly involves the conversion of the inorganic molecule carbon dioxide to form organic
molecules which are formed within the tissues of organisms.
 Carbon dioxide is removed from the air by green plants in the process of photosynthesis.
 Then when the plants are eaten by animals the carbon is passed on and becomes part of the
animal bodies
 when animals respire they release carbon dioxide as a waste product into the air 43
 Finally when both plants and animals die, their bodies are broken down by the action of
decomposers.
 Carbon dioxide is also released into the atmosphere in the process of combustion.
  This build-up of carbon dioxide gas in the atmosphere is generally believed to contribute to the
greenhouse effect, also referred to as global warming
 Methane is another greenhouse gas which causes air pollution and the levels of this gas are rising
too.
6.4 Adaptation
 Features organisms develop which make it possible for them to survive in particular habitats.
 Organisms in different climatic condition have different adaptation mechanisms to survive in their
ecosystem.
I. Animals in cold climates
Animals in very cold climates have other adaptation:
 Thick layer of fat under the skin to keep to store more internal heat &a thick fur coat on the outside
 Reduced surface area to volume ratio
 Usually have Very small ears
 camouflage of an Arctic animal in summer would stand out against the snow in winter
 E.g. Arctic fox change the greys and browns of their summer coats for pure white in the winter.
II. Adaptation in dry climates
Many animals which live in hot or dry conditions have other adaptations for cooling down
They are often most active in the early morning and late evening
They often have large, thin ears as well to increase their surface area for losing heat
They don‘t have much fur & relatively little body fat stored under the skin.
III. Some adaptation of plants
Plants take in water through their roots in the soil & lose water all the time through their leaves.
There are small openings called stomata in the leaves of a plant. These open to allow gases in and
out for photosynthesis and respiration.
When it is hot and dry, photosynthesis and respiration take place fast
most plants that live in dry conditions have reduced the surface area of their leaves so they lose less
water e.g. cacti
plants can cope with dry conditions to store water in their tissues
Plants which store water in their fleshy leaves, stems or roots are known as succulent
Animal dispersed plants have seeds which have hocks & spines
IV. Some animal adaptation
Carnivores animals have sharp & pointed canines to tear flesh.
Porcupine has skin surface which is covered with long stiff parts like needle called quills,
which it can raise to protect itself when it is attacked by enemy
6.5 Tree-growing project
Ecosystem our country has been changing dramatically because of deforestation. Now Only 3% of land
is covered with forests.
Trees produce oxygen and remove carbon dioxide from the air. They help to reduce the effects
of air pollution and also reduce global warming.
It hold the soil in place and without them our soil is becoming unstable and blowing away.
it also help absorb water - they prevent soil erosion and help to prevent the formation of great areas of
Desert
Tree planting procedure
To plant a tree successfully:-
I. The soil must be prepared,
II. a big hole must be dug and
III. Water must be put into the hole before the tree is planted.
IV. Once the sapling is in place, the soil must be pressed very firmly around it and
V. Often a stake is used to support the young tree as it starts to grow and get established. 44
VI. The young trees need to be cared.
BIOLOGY GRADE 10
UNIT 1
1. BIOTECHNOLOGY
1.1. What is biotechnology?

Biotechnology is the use of micro-organism to make things that people want

Or the use of living organisms to make what people want, often involve industrial production.
-It helps to make and preserve food and alcoholic drinks.
Example: - - brewing beer
-making wines Traditional application of
-Making bread biotechnology
-making cheese (ayib)
- making yoghurt (irgo)
-Change gene of crop and animals
-produce new medicine Modern application of
-produce new energy sources biotechnology
→Biotechnology is based on microbiology. i.e. the study of micro-organisms and their effects on human.
-Bacteria and fungi are the main micro-organisms used in biotechnology.

1.2. TRADITIONAL TECHNOLOGY USING YEAST.

Yeast: - Is the single cell.

-Has nucleus, cytoplasm, cell membrane, and cell wall.

- 1gram of yeast contains about 25 billion cells. This expresses that how much they are small.
-Yeast can respire aerobically and anaerobically.
-yeast reproduces by asexual budding (split in to two)

Aerobic -which uses oxygen to

break down food
Cellular
respreation
Anaerobic - which break
down food without oxygen

Aerobic respiration of yeast – produce more energy.

Sugar + oxygen → water + carbon dioxide + energy.
Anaerobic respiration of yeast- it is called Fermentation (anaerobic).
Fermentation converts sugar into acid such as lactic acid, alcohol, and co2 using yeast and bacteria, under anaerobic
conditions.
Sugar → ethanol + Carbon dioxide + energy
→ Yeast can respire aerobically in bread making, but must respire anaerobically to make alcoholic drink.
-too much alcohol kills yeast and stops fermentation. 45
- Yeast is used in making – injera, bread, tell, tej …etc.
Food production using bacteria
Making yoghurt (irgo):- Formed by the action of bacteria on lactose (Milk sugar).
Lactose fermentation lactic acid.
-It is fermented (anaerobic) milk.
-The bacteria grow, reproduce and fermented in milk.
- If you add starter culture, yoghurt can be produced quickly.
-The lactic acid in yoghurt makes it sharp, tangy taste, clot milk, solidify smooth and thick
texture.
- Additionally, the bacteria in yoghurt prevent the growth of other bacteria that goes yoghurt bad.
Cheese making (ayib):- Like in yoghurt the bacteria in cheese converts lactose in to lactic acid, but much more lactic
acid is produced.
- It is more curds (solid)
- Enzymes from the stomach of calves also produce liquid whey (aguat).

1.3. New application of biotechnology

What is genetic engineering?

-Genetic engineering helps to change an organism and gives it new characteristics
- It involves changing genetic material of an organism to specific and desirable characteristics.
Genetic material→ carry the instruction.
- Found in nucleus of every cell.
Example: - a gene (information) that helps to make protein in human cell may transfer to bacterium cell, so does the
bacteria cell.

Application of biotechnology in agriculture

-Using genetic engineering you can introduce new characteristics in agriculture.
- It helps to improve growth rate of plants and animals.
- Produces disease and drought resistant crop.
-Also produces plants that make their own pesticide chemicals.
Problems with new biotechnology are:-
i. Insects may become pesticides resistance.
ii. Genetically modified plant gene may affect/harm wild life.
iii. Genetically modified crops are often not fertile.
iv. It can become expensive and time consuming to farmer.

Application of biotechnology in food

-In food and drink production enzymes are produced by genetically engineered bacteria.
Then the enzymes are used to:-
i. Clarify beer
ii. Breakdown starch in to sugar ( syrup )
iii. Make meat more tender.(make easy to bite and cut)
iv. Make commercial baby food.
v. Create complete new food. Example: - mycoprotien.

Application of biotechnology in medicine.

Biotechnology is used to: - develop new vaccine.

-Create new medicine.

Example: - penicillin; discovered by Alexander Fleming.
-Produce lifesaving protein from mammal‘s milk (blood clothing proteins in sheep‘s).
- Produce pure human insulin for diabetes.

Application of biotechnology in new energy production 46

-Biotechnology produces renewable forms of energy (direct or indirect energy).

Biogas:- Supply energy from animals and humans wastes.
- It is flamed mixture of gases when bacteria break down plant materials or animal anaerobically.
-it mainly produces methane.
To produce biogas:-
1 collect dung or plant material
st

2nd put in to biogas generator/digester

3rd add many different population of bacteria
Finally the biogas produced is passed along a pipe in to your home to produce heat, light, refrigeration…etc.
- Biogas works best in hot countries (30C0)
- Biogas is an exothermic process.
The components of biogas:
Components % of the mixture by volume
Methane 50-80
Carbon dioxide 15-45
Water 5
Hydrogen sulphide 0-3
Other gases 0-1

Biogas
Advantage disadvantage
 Renewable resources -production is restricted based on climate or available land
 Non-pollutant

More biofuel

Ethanol-based fuels

-Sugar-cane and maize are fermented with yeast to give ethanol.

-Ethanol extracted by distillation and used in vehicles and industries

Ethanol

Advantage Disadvantage
-Efficient -take lot of plant material
-Does not produce toxic - leave large amount of cellulose
- Much less pollutant (carbon neutral)
- Can mix with petrol to make gasohol.
Sugar-cane Fermentation ethanol
Maize enzymes break down of starch + fermentation ethanol

UNIT 2

HEREDITY

Definition:-Heredity is the transmission of genetic characters from parents to offspring.

Or the passing of traits to offspring from its parent
Nucleus: - Contain information needed to build a whole new animal, plant, bacterium, fungi…etc.
Chromosomes: - means colored body
47
- Thread like structure found inside nucleus.
-made up of DNA (Deoxyribonucleic acid), which carry the instruction needed to make all the
protein (enzyme) in your cell.
 -Consists of genes which carry instruction.
- Different organism has different number of chromosomes.
Example:-Human has 46 chromosomes in each cell.
- Tomatoes have 24 chromosomes in each cell.
- Elephant has 56 chromosomes in each cell.
Homologous chromosomes: - pair of chromosomes is having the same gene sequences.
Diploid chromosome contain two sets of chromosomes
Haploid chromosome contain one sets of chromosome
Example: - human has 23-pair of chromosomes, 22-pair is Autosomal/somatic/body cells chromosomes,
while 1-pair is sex determining chromosomes (determine male/female).
-Chromatids: - are the two strands of a chromosome
→ Autosomal chromosomes determine all what you look like.
‘X‘ chromosome represent girl and
 ‗Y‘ chromosome represents boys.
Karyotype: -Is a Photograph of human chromosomes.

2.1. Chromosomes, gene and DNA

Gene: - a unit of hereditary material located on the chromosome.

-made up of repeated pattern of base in DNA.

DNA: - is long protein complex molecule.
-Two strands twisted together.
- make spiral called double helix.
- contain small molecule called nucleotide join together.
Nucleotides:-

Nucleotides
consists

phosphate
sugar a bases
group

-there are four (4) types of base pair.

- Bases appear in pair, in different order, always pair up in the same way and link the two strands of DNA.
- These bases are: i. Adenine (A) ii. Thymine (T)
iii. Guanine (G) iv. Cytosine (C)
N.B Always Adenine pair with Thymine.
Guanine pair with Cytosine
There are about 3 billion bases in human body
- Base + sugar + phosphet → nucleotide.
- Nucleotide + nucleotide + nucleotide + nucleotide…. → Polynucleotide
→DNA is a polynucleotide‘s.

2.2. Mitosis and Meiosis.

Cell division is the process of a parental cell divide in to daughter cells.

2.2.1. Mitosis 48
It takes place in normal body cell/somatic cell.

-it produces identical cells.

 - used to replace worn out cells, dead cells and injured cells.
- Mitosis has five (5) stages, these are:

1. Inter Phase

5. Telophase 2. Prophase

4. Anaphase 3. Metaphase

1. Interphase: - a preparation period.

- DNA replications occur.
- Chromosomes of the cell are not visible.
2. Prophase: - chromosomes condense, thicken, and shorten.
- The longest phase
- Nucleus and nuclear membrane disappear.
- The centrioles divide and move to opposite side to form spindle fiber.
- Sister chromatid forms.
- Centromere held the two chromatids.
3. Metaphase: - Chromosomes line up at the center.
4. Anaphase: - centromere separate
- spindle fiber shorten and pull the chromatids
- Chromatids move to opposite side.
5. Telophase: - the nucleus and nuclear membrane re-appear.
- Two new nuclei form at the pole.
- Two identical daughter cells formed.
- The daughter cell goes back in to interphase.

Gametogenesis
Gamete: - male/female reproductive structure (sex cell). 49

Gametogenesis: - is the process of gamete formation.

- Has different version in male and female.
  Gamete formation in male is called Spermatogenesis
 Gamete formation in female is called Oogenesis.

GAMETOGENESIS

OOGENESIS - 1st stage before birth. SPERMATOGENESIS- does not start

-2nd stage during monthly cycle when until puberty.
egg matured. - carried out throughout the male life.

No two egg/sperm cell are the same, each gamete you produce is slightly different

2.2.2. Meiosis

-It is the division of sex cell

- It is the reduction division (chromosome number reduces in half).

Example: - Human
-Chromosomes reduce from 46 to 23.
-results four (4) daughter cells.
- Meiosis has two (2) successive stages

Meiosis-I Meiosi-II
separate homologous chromosomes Separet chromatids

MEIOSIS

Phases of Meiosis - I

Interphase Prophase -I Metaphase-I Anaphas -I

Telophase-I

Phases of Meiosis - II

Prophes - II Metaphase-II Anaphase-II

Telophase-II

Prophase-I:-Chromosomes appear in pair with two chromatids.

- The longest phase
-nucleus and nuclear membrane disappeared.
- Crossing over occurs. 50
Metaphase-I: - Chromosomes line up at the center
Anaphase-I: - One chromosome moves to the opposite side.
 - Chromosome number in each cell reduces to half.
Telophase-I: - spindle fiber is disappeared
 Nucleolus re-formed
 Nuclear membrane re-formed
 The nuclear membrane reforms and the cells begin to divide.
Prophase-II:

 chromosomes condensed & shortened

 Nucleolus and nuclear envelope disappeared
 Spindle fiber is formed

Metaphase-II: - -chromosomes line up on metaphase plate

Anaphase- II: - the centromere divide
-chromatids move to the opposite side
Telophase – II: - nuclear membrane reappears
-chromosome return to interphase
-four (4) daughter formed with half number of chromosomes.

2.3. omparison of mitosis and meiosis

No. Mitosis Meiosis

1 Take place in somatic cell Take place in germ cell(sex cell)

2 Same number of chromosomes in daughter cells Chromosome number reduce in half
3 Daughter cell is identical to parental cell Daughter cell different from parental cell
4 DNA replication occur always DNA replication varies in boys and girls.
5 Depends on cell type from few hours to every few years
6 Occur in all organism Occur only in sexually reproduce organisms
2.4. MENDELIAN HEREDITY
-Gregor Mendel was a father of genetics.
- he was a monk at a monastery in Brun in Austria.
- he was done an experiment on garden pea plants.
- he was breeding patterns of the peas carefully, he breed different pure strains of peas.
-Normally pea pollination is self-pollination, but Mendel carefully pollinate them by,
1st open the bud of the flower before the pollen matured
2nd fertilize the stigma by brushing it with ripe pollen.
- Mendel chooses seven (7) pure-breed traits.
- He categorizes these traits as Dominant and Recessive.
Dominant trait: the character is expressed in phenotype even one copy of the allele is present or
- A trait that mask another trait.
- It represent by 1st capital letter of the trait name.
Example: Tall trait represent by the 1st letter ‘T’. 51
Red flower trait represent by the 1st letter ‘R’.
Recessive trait: the character is expressed in the phenotype if two copies of the allele is present or
- A trait that masked by another trait.
 - It represent by 1st small letter of the opposite dominant trait name.
Example: Short trait represents by small & 1st letter of the opposite trait (tall)‘t’.
White flower trait represents by small & 1st letter of the opposite trait ‘r’
The recessive gene have no effect on the phenotype of the offspring unless they are in homozygous.

Table 2.1 dominant and recessive trait of pea plant Mendel select during his experiment.
- Mendel crosses/pollinate one dominant trait with its opposite recessive trait.
Example: pure Tall stem cross with pure short stem. → parent/P

T X t, T X t, T X t, T X t → gamete
The offspring are all Tall (Tt) → First filial/F1
o In other hand Mendel states also the basic law of genetics.

- To understand how inheritance works first let you understand these terms below.

Alleles: different forms of the same gene or

- The particular form of information on the chromosome.

Example: - eye color

-Nose shape traits that controlled by many genes.

-Dimples traits that controlled by single gene.

JOIN ON Telegram
-Ear lobes @QesemAcademy
Homogenous/Homozygous: having two identical alleles for particular feature.
Example: - tall (TT), Short (tt), Red (RR), White (rr) Dangle ear lobe (DD)…
Heterogeneous/Heterozygous: having two different alleles for a particular feature.
Example: Tall (Tt), Red (Rr), dangle ear lobe (Dd)…
Genotype: a description of the allele of an individual for a given genetic trait.
Phenotype: a description of physical appearance of an individual‘s relating a given genetic trait.
2.5.1. Monohybrid inheritance
It is inheritance of different forms of one gene.
- Homozygous breed is the true breed and heterozygous breed is not.
- The first generation/offspring of any cross is called the first filial (F1).
- The second generation/offspring of any cross is called the second filial (F2).
Example; Pure Tall pea plant cross with pure Short pea plant.
-TT X tt→ parent (P)
All (100%) offspring will be heterozygous Tall (Tt) → F1,then to find f2
- F1 X F1 (Tt X Tt)
¼ Pure tall (TT), 2/4 heterozygous tall (Tt) and ¼ Heterozygous short (tt) → F2
Genetically crosses can be shown with the use of simple genetic diagram called Punnet square/test cross

Heredity and breeding

In Ethiopia we have 25 types of cattle, 13 types of sheep, 15 types of goat, 4 types of camel, 5 types of chickens, 4 types
of donkey, 2 types of horse, and 2 types of mule.

- All of these have come about carful breeding.

There are different types of breeding. 52
Selective breeding

- Use to breed for particular trait.

 - Choosing certain trait and breed only individuals that produce the desire trait.
- You need to select ‗true breeding’ (homozygous recessive/homozygous dominant).
- Only best animal/plant with wanted characteristics must breed and other must castrated.

Example; animal selected for meat, strength, milk, fast growing, etc.
- The Borena breed cattle’s are the best example.

Cross breeding/combination of trait

- Combine good trait from two different breeds.

- It takes long period to find new true breeding strain.
Example; high milk, less resistant goat X low milk, high resistant goat may give high milk and high resistant offspring.
UNIT 3
HUMAN BIOLOGY AND HEALTH
 All living organisms including human being need some level of awareness of their external
environment (surrounding) to do something like: -
 To avoid danger
 To find food
 To find a mate
 To go to religious place
 This awareness (information) had to be exchanged between cells inside the body.
 This means coordination is required to respond to the external environment.
 The information about the external environment must be received and then transmitted to the cells
(body) to respond to the external environment.
 Awareness of changes in our surrounding is only useful if our body coordinates and takes advantage
(respond) to the external environment.
 The whole activity of the body is coordinated and controlled by two principal coordination systems.
These are: -
Nervous system
Endocrine system

Nervous system Endocrine system

Use nervous coordination system which is made Use chemical coordination system
up of nerve cells.
Uses electrochemical impulse Uses a hormonal system (chemical message)
Nerve impulse is transmitted through nerve cells Hormones are transmitted through the blood
Origin of message are receptors Origin of message are endocrine gland
The destination of message are effectors (muscle The destinations of messages are target
and other organs) organs.
Provide quick response Provide slow response
Have short term effect Have long lasting effect
Act like the telephone system (rapid) Act like the postal system
Much of the function of the body is coordinated by endocrine system

3.1. The nervous system

-Help organisms for body Coordination (arrange):
 Body Integration(put together/assemble) and
 Body Control 53
- Very rapid response.
-Fast acting control system that triggers muscle contraction or gland secretion.
- Uses electro-chemical to co-coordinate various functions.
-Has three main functions;
 Sensory input: - when the body gathers information/data by sensory receptors.
 Integration of data: -processed in the brain.
 Motor output: - conducted from brain and spinal cord to muscle and glands.
-The nerve system of human is organized as below figure;

Nerve system

Centeral nerve system Peripheral/body/ nerve

(CNS) system (PNC)

somatic(cranial Autonomic Nerve

Brain Spinal cord and spinal) nerve system

Symphathetic
Parasymphathetic
nerve system nerve system
- activate body to -oversees digestion,
cope with some elimination,
stressors(fight or glandular function...
flight)

.Nerve Coordination

-Single-celled organisms and plants do not have nerve system.

-Nerve co-ordination works as follow

Effector neuron
affector neuron
•stimulus picked
•Information •effector organ
up by sensory •Instruction sent act up on
reseptorse processed in
• information passed CNS out to the body stimulus
out through from CNS
sense organ affector neurons to CNS muscle/glands
CNS

Neurons

- are the basic structure of the nerve system.

- Specialized to transmit electrical impulse.

A. Afferent/affector/receptor/Sensory neuron
-carry information from receptor to CNS
B. Efferent/effector/motor neuron
- carry impulse from CNS to different effectors organ (muscle/glands
C. Relay neuron /interneuron/intermediate neuron/associate neuron
- passes signals between afferent neuron and efferent
Relay neurons are only found in the brain and spinal cord
54
Neurons are made up of four major structures:-
1. Cell body: -contain nucleus, mitochondria, and other organelles
- provide energy and control cell
 2. Dendrite: - finger like projection at the tip
- connect to neighboring nerve cell (receive impulse)
3. Axon: - the most distinct, long and thin part.
- transmit electric impulse within the neuron.
4. Myelin sheath: - fat insulating layer around the axon.
- so the impulse travel fast along the axon.

Fig. neuron
- The nerves are bundle of neurons.

How neural impulses transmit?

 Resting potential:- neuron that do not transmit impulse ( at rest )

-Electrically polarized /opposite charge inside membrane outside/ because of Na+ the outside axon
membrane and it is called resting potential.
 Action potential: - neuron that transmitting impulse.
-electrically depolarized /mixed charge/
-the wave of positive charge inside the axon membrane
Synapse: - a junction between two neurons

Neurotrasmiters:- chemical released and picked up by the next neuron.

-help to pass electric impulse through the synapse..

Neuromuscular junctions: - the special synapse between effector neuron and muscle

55
 Fig. cranial and spinal nerves

Brain:
- Very complex structure made up of delicate mass of nerve tissues
- Protected by three membrane called meninges and skull bone in the space called cranium.
The three layer of meninges:

Duramater
-outer
-Attached to the
skull
Arachnoid
-Tough

-middle
membrane
Pia
mater
-inner
membrane
-Direct cover the
nerve tissue
- delicate

The internal region and external region of brain is made up of;

A. Grey matter: - grey colored bulk of the brain.
- Outer Surface
- composed of cell bodies and relay neurons of neuron and the synapses.
B. White matter: - white colored interior region.
- composed of axon covered with myelin sheath.
The brain can differentiate in to three main regions with different section as shown on bellow figure.

56
 Main Regions Functional Regions Functions
Cerebrum -control conscious awareness of sense organ
-the largest hemisphere -interpret sensory information(perception)
-coordinate voluntary movement of the body muscle
-control memory, speech, thought, intelligence, learning, etc.
Fore-brain
-the largest frontal area Thalamus -direct impulse from the sense organ to the appropriate part of the cerebrum
and vice versa.

Hypothalamus -Control the homeostatic center and centers which cause feeling of hunger
and thirst.

Mid-brain -Control wakefulness and sleep

-distribute nervous impulse to forebrain and hind brain
-concern with vision
Cerebellum -control posture and balance
-control delicate movement like writing or playing music
Hind-brain instrument(coordinate muscle activities)

Medulla oblongata -Control involuntary action such as respiration, circulation, salivation,

and peristalsis.
Pons Controls sleep-wake cycle and breathing
Each side of our body controlled by the opposite side of your brain

Mental illness: - general term refers a wide variety of disorders and disease to psychological, emotional, or behavioral.
-It may range from mild depression to serious effect.

-result from an imbalance of the chemical transmitters in your brain.

Spinal Cord

-Extends out from your brain down your body.

-Incase and protected by the vertebrae making up your spine.

-Nerves come out of spinal cord are known as spinal nerves.

Unlike the brain it has the grey matter inside surrounded by white matter on the outside.
57
.
 VOLUNTARY AND REFLEX ACTIONS.

Voluntary action: - you choose to do them.

- Is normal, conscious action

- You have an awareness of those action
Examples: crossing road,

-Greeting friends

-Eating

- Working your homework etc.

-The pathway of voluntary action is as follows;

 Receptor Cell →Affector Neuron →CNS→ Effector Nerves→ Muscles/glands

Involuntary action: - you do not choose to do them

- It is without conscious thought

- Have not aware about the action
Example: breathing, digestion, and etc.

A reflex action:

It is sudden, automatic, uncontrolled, instinctive, unlearned, response to stimuli.

-You do not have to think about it.

-Helps to avoid danger or damage.

- The massage does not reach a conscious area of your brain before instruction is sent out to take action.

-Many involve spinal cord while others involve the brain.

Examples: breathing

-blinking eye

-dilate/constrict pupil

-Three types of neuron involves

1. Affector neuron

2. Associate/relay neuron; connect affector and effector neuron in CNS. Reflex arc.

3. Afector neuron

- Doctors use the reflex jerk of your knee to check that your reflexes are working.

The path of reflex action is as follows;

 Stimulus →receptors→ affector neuron→ co-coordinator →

→effector neuron → effector → response.

Conditional reflexes

This are learned reflex action.

Example: Pavlove experiment on dog salivation hearing the bell ring.

DRUG ABUSE

Drug: - is a substance which alter the way in which your mind or body, or both works.
58
- It is harmful or useful ( for pleasure and medicine)
Example; medicine is useful but cannabis is harmful.
 Legal drug: Illegal drug
- socially acceptable -socially do not acceptable
Example; caffeine, nicotine, khat, alcohol, tobacco
Example; heroin, cocaine, LSD, cannabis
-used for pleasure and to be sociable, become habit-highly affect human health
-turn to crime and lead to prostitution
Drug dependence: - is when you use a drug again and again and become addicted, because it changes the chemical
process in your body.

Addicted:- compulsively or physiologically dependent on something habit-forming.

-when an addicted person tries to stop the drug they will feel very unwell, often experiences combination of
aches and pain, shaking, sweating, headaches, craving for drug, fever these are known as withdrawal symptom.

Common features of drugs:

1. addicted
2. Affect brain function and alter behavior.
3. Damage health
4. Adversely affect individual, family, community, and country.

Smoking cigarette

-have 3 types of chemicals that affect human this are nicotine, tar, and carbon monoxide.

-addictive drug in cigarette is Nicotine.

-Smoking increases your risk of;

A/ Coronary heart disease- is the heart disease.

 Affects the wall of you artery.

 Make the blood vessels supplying blood to the heart narrow.
 These reduce the supply to the heart and other area.
 May damage the smooth lining of the heart which causes atherosclerosis.
B/ Stroke

 is damage/blocked of blood vessels taking blood to the brain.

 An area of brain damage which may lead to;
-Paralysis
-Memory loss
-Death

C/ Lung disease

 Tar and smoke (other chemical) in tobacco damage the lung tissue and lead to risk of chronic obstructive
pulmonary disease (COPD) and lung cancer.
D/ cancer (lip, mouth throat, pancreas, bladder, and kidney)

 Chemicals in cigarette are carcinogenic (cancer causing).

 Passive smoker: - second person who affected by smoke indirectly.
- inhaling smoke around you.
Example; Pregnant women and the baby

Alcohol

- Most common drug.

- It is very addictive and it is very poisonous.
- Alcohol acts quickly because it is readily absorbed in to the blood stream.
- Liver can break down the alcohol before it damage your tissue
 Alcohol dilate the blood vessels
 Produce feeling of warmth and well-being.
 Increase heart rate and hunger
 Slow down your reaction
 Make you lose your self-control 59
 Poor muscle co-ordination.
 Slurred speech and lose of balance
 Make to lose water from your body(diuretic)
 Can cause headache, dehydration, and nausea.
 Leads to have unprotected sex(which may cause HIV/AIDS)
 Finally is can lead to unconsciousness, coma, and death.

Khat

-it is shrub plant.

-made in to tea or chew fresh khat leaves.

-it is mild stimulant.

- it contains cathinone chemical that addict and acts quickly within 30 minute.

-when people cannot gate it they feel depressed, tired, and unable to concentrate.

Cannabis (marijuana/ganja/weed)

-contain 400 known chemicals and 60 of which called cannabinoids are unique to plant.

-the most potent is delta-9-tetrahydrocannabinoid (THC) that affects memory, emotion, and motivation.

-it can be eaten or smoked.

-it is mild hallucinogens; i.e. affect the mind in a way that produces distorted sensations abnormal in content.

-its effect is variable from person to person.

- Cannabis can mix with tobacco this increase its effect.

- a survey showed that 43% of the people in mental hospital had abused alcohol, khat or cannabis.

LSD (Lysergic acid diethylamide)

-Made in the laboratory from the fungi.

-it is hallucinogenic

-it makes you feel you can fly.

Cocaine

-it is an extremely addictive drug and also quite expensive.

- make you feel powerful and get rush of energy by;

 Rises blood pressure

 Rises heart rate
 Rises body temperature
 It may kill people.
- You can end up feeling paranoid and depressed afterward.

Heroin.

- made from opium poppy tree.

- use as painkiller and recreational drug.

- prepared as white/brown powder that can dissolve in water.

- it can take as injection, snorted in to nose, smoked, eaten, inserted through rectum.

- it block pain, do not feel hunger and sex.

3.2 Sense organ

60
 Sense organ contain sensory receptor that detect a particular stimulus,

 A sense organ is an organ that contains a large number of sensory receptor cells
Receptor Energy

Eye (retina,provides vision) Light

Ear (cochlea, organ of hearing) Sound

Ear (semi-circular Movementcanals,

(kinetic) organ of bala

Tongue (taste buds, enable us to taste) Chemical

Nose (olfactory organ Chemical or organ of smell)

Skin (touch, pressure and pain) Movement (kinetic)

Skin (temperature receptors) Heat

Muscles(stretch receptors) Movement (kinetic)

Arteries and brain (chemo receptors responding to pH and carbon dioxide levels) Chemical

1. The human eye

Eye protection:

 Sockets the cavity in the skull in which eye is situated.

 Eyelids, eye brow, eye lash protect the eye from the entry of material like dust, sand

 The conjunctiva; transparent mucus membrane covering the front of eye ball

 Tear; a salty solution contain an enzyme called lysozyme that kill some bacteria. Tear is secreted by tear gland
or lachrymal gland.

Parts of the eye

 The sclera The tough, opaque external covering of the eye. Important to protect and maintain the shape of eye
ball , white part of eye
 Cornea transparent front part of sclera , important to bend light ray toward retina
 Choroid the middle pigmented layer of the eye. rich in blood vessel that supply nutrient and oxygen to the cell
of retina
 Pupil; is a hole in the center of the iris, through which light enter the eye

61
 Iris is the colored part of the eye.
 It contain two set of muscle called circular and radial
 responsible for controlling the amount of light entering the eye
In dim light
 the radial muscles contract
 the circular muscles relax
 The pupil is pulled open wide (it dilates).
In bright light,
 the circular muscles of the iris contract
 the radial muscles relax,
 Pupil very small (it constricts).

The lens, a flexible disc that helps focus light on the retina
 The lens is held in place by suspensory ligaments and the ciliary muscles.
Suspensory ligaments elastic-like structures that suspend the lens and pull lens into shape for focusing distant objects
onto the retina
Ciliary muscles eye muscles that automatically contract and change the shape of the lens by changing the tension of
suspensory ligaments
Retina: the inner layer of the eye it contains special light-sensitive photoreceptors called rods and cones

Rods
 respond to relatively low light levels,
 do not give a very clear image
 They do not respond to different colors, everything looks black and grey
 Distributed evenly on retina except fovea
 Fewer in number on retina
The pigment in the rods that responds to light is based on vitamin A. a lack of vitamin A in the diet causes night
blindness

Cones
 Responsible for bright light color
 They give a very clear, defined image
 Responsible for color vision
 More concentrated in and around fovea
 Occur greater on retina
 Color blindness; the genetic disorder inability to distinguish colors red, blue and green
Fovea ( yellow spot)
 The most sensitive part of retina
 It contain cones, Most light ray are focused on it
Blind spot
 The point where light optic nerve leave the eye
 There is no cones and rods on blind spot
 The light ray falls on blind pot do not form image
Aqueous humor; is a watery fluid that fill the front chamber of the eye, maintain the shape of eye ball 62
Vitreous humor; is jelly like (semi solid) substance that fill the area behind lens. It also maintain the shape of eye
ball
Optic nerve; the bundle of nerve fibers that transport nerve impulse from retina to brain
Accommodation; the ability of the eye focusing near and distance object

a) Focusing on a distant object

 Ciliary muscles relax
 Suspensory ligaments pulled tight
 lens ‗flat‘ and less convex (flatter)
b) Focusing on a nearby object
 Ciliary muscles contract
 Suspensory ligaments slack
 Lens more rounded and more convex (rounded)
Summary of sense of sight
Light rays → Cornea → Aqueous humor → Pupil → Lens → Vitreous humor → Retina → Optic nerve → Brain →
Sense of sight
Common eye defects

Short sight (myopia)

 The condition where the eye can only sea near object

 Cannot see object from long distance

 Image of far object formed in front of retina

Caused by

 Longer eye ball than normal

 Lens is ‗too strong‘ and curved while cillary muscle relaxed

Corrected by wearing diverging (concave) lens

63
Long sight ( hypermetropia)

Long sight A condition where the eye an only see far object
 Nearby object cannot seen clearly
 Image of near object focused behind retina
Caused by
 Short eye ball than normal
 A lens is ‗too weak‘ and flat while cillary muscle Contracted
Corrected by; wearing diverging (convex) lens

Astigmatism

 Astigmatism: is a type of refractive error in which the eye does not focus evenly on retina
 Caused by; The egg shaped eye instead of round
 The cornea is curved asymmetrically and this affects the way light is focused
on retina.
 Corrected by; cylindrical and equally curved lens
2. The ear
The human ears are responsible for
 Hearing
 Balance and position
The ear divided into three regions
1. Outer( external ear)
Pinna; direct sound wave into ear canal

JOIN ON Telegram
@QesemAcademy 64
  Helps to know the direction of sound
Ear canal
 Used to direct sound wave to eardrum
 Have gland to produce wax inside ear canal
 Wax use;
 Trap dust and germs
 Lubricate the ear drum
Ear drum (tympanum)
 A tiny and delicate membrane
2. The middle ear (air filled cavity)
 It contain three tiny bones (ossicles)
 Hummer /malleus/ attach to ear drumHqammer
 Anvil /incus/
 Stirrup /Stapes/ attach to oval window
 Eustachian tube; helps to equalize air pressure between outer and middle ear
3. The inner ear / fluid filled cavity/ consists;
 Cochlea a coiled tube
 Contain nerve ending of auditory nerve
 It is sensitive to sound vibration
 Semi circular canal; consists of cell that are sensitive to the motion of body
 Utricullus and sacculus; are concerned with the balance and posture
Summary of sense of hearing
Sound wave → Pinna → Ear canal → Ear drum → Hammer → Anvil → Stirrup → Oval window →
Cochlea → Auditory nerve → Brain → Sense of hearing
Common disorder of the ear
 The total loss of hearing is called deafness
 Partial hearing loss is called hearing impairment
 Some of the common hearing impairment and deafness are;
 Obstruction of auditory passage
 Inflammation
 Infection
3. Taste and smell

Tongue
 Have sensory receptors sensitive to dissolved substance
 The sensory receptors of taste are located on the upper surface of the tongue known as
taste bud.
 The five different types of taste buds spread evenly across the tongue
 The receptors for smell are located in the upper parts of the nasal passages.
 There are five basic taste sensations are sweet, sour, bitter and salt recently discovered a
fifth taste called umami .
 Umami is a very savory flavor found in foods such as meat, cheese, broth and mushroom.
The nose
 Smell is caused by chemical stimuli
 Smell receptor are called olfactory cells which are located in the roof of nasal cavity
 The specialized cell of smell are similar to taste however, nose detects dissolved chemical
at distance
4. The skin as a sense organ

65
  Human skins are sensitive to different type of stimuli such as touch, temperature, pain and
pressure. Due to the following receptors
I. Meissners corpuscles; Touch
II. Pacinin corpuscles; pressure
III. Thermo receptors; Temperature
IV. Nocireceptors; pain
Importance of the skin
 It forms a waterproof layer around body tissues,
 It protects from the entry of bacteria and other pathogens.
 It protects from damage by UV light from the sun.
 It is an excretory organ (nitrogenous wastes are lost in your sweat).
 It is vital in controlling body temperature.
Skin has three main layers.

Hypodermis; the lower layer,

 Contains fatty tissue which helps to insulate the body against heat loss.
Dermis; the middle layer
 Contains the blood vessels, the sweat glands, the sensory receptors, and the hair follicles.
 Closely involved in temperature control in homeostasis and in sense of touch.
Epidermis; the upper layer or is made up of dead cells.
 Stop water loss and also protect against the entry of pathogens.
 particularly involved in the homeostatic mechanisms of the skin

3.3 Endocrine glands

Glands in our body can be grouped in to:-
A. Endocrine: - ductless; less in number
B. Exocrine: - have duct; many in number
Exocrine glands release their secretion in to the duct or tube which carry to
target organ Ex. -Sweat
-mammary glands

66
 - Salivary
Endocrine gland release their secretions (hormone) directly in to the blood
Endocrine system is the system of glands which produce chemicals called hormone to co-
ordinate our body.
- Most hormones only affect certain tissues or organs
They can act very rapidly, but often their effects are slower and longer lasting than the results of
nervous control.

1. Pituitary Gland
Where it found:- in the brain
- Its size: - a pea sized
The alternative name:- master (controller) of glands
Main role:- secrete d/t hormones that controls the secretion of other hormones
Other role:- co-ordination between the nervous and hormonal systems of control
2. Thyroid Gland
It is found in the neck
It uses iodine from diet to produce thyroxin.
Thyroxin: - controls the metabolic rate of your body
-how quickly substances are built up and broken down
-how much oxygen your tissues use and how the brain of a growing
child develops
If overactive thyroid, it makes too much thyroxin
- Metabolism starts to go very fast
- losing a lot of weight
-Sweating a lot symptoms
-becoming irritable
If the thyroid doesn‘t make enough -
-feel tired
-lack energy
Low levels of thyroxin can cause problems in:-
-getting pregnant
-miscarriages
-still births
If small children do not make enough thyroxin:-
-their growth is stunted
- do not develop normally this is called cretinism
-have difficulties in learning
The most common reason for not making enough thyroxin is a lack of iodine in the diet
without iodine, the thyroid gland works very hard to make more thyroxin
Thyroid will grow and enlarge to make right amount of thyroxin
This is celled Goiter
Women and children are more affected than men
3. Parathyroid gland
It is a butterfly shaped gland located at the thyroid gland.
 Produces a hormone called parathyroid hormone.

67
  Parathyroid hormone is responsible for controlling the level of calcium and phosphorus in
the blood.
4. Insulin
It controls the blood sugar level
So, it prevents diabetes
Our cells need constant supply of glucose for respiration
Glucose is transported around the body to all the cells by blood
Level of sugar in our blood is controlled by hormones produced in our pancreas
without this control mechanism, blood glucose level varies
i.e. it increase after meal and decrease with no meal
5. Pancreas
It is a small pink organ found below our stomach.
It is used to prevent the internal disturbance
It constantly monitors blood glucose concentration by releasing:-
A. Insulin
B. Glucagon
Insulin and Glucagon act antagonistically
When blood glucose level is raised above an ideal after meal, insulin is released and stimulates
liver to convert remove any glucose not needed.
The soluble glucose is converted to an insoluble carbohydrate called glycogen and stored
in your liver.
And when blood glucose concentration falls below the ideal range, glucagon is released w/c
stimulate liver to break down glycogen, converting it back into glucose
This control mechanism of pancreas is used to maintain blood glucose concentration
fairly constant at about 90 mg glucose per 100 ml of blood
The causes and treatment of diabetes
Sometimes, pancreas does not make enough - or any insulin
Without insulin, blood sugar levels get higher and higher
after you eat food
As a excess glucose in the blood and kidneys produce
glucose in your urine
This condition is called Diabetes
Its symptoms include:-
1. Lot of urine produced w/c cause thirsty all the time
2. Because glucose can‘t get in to the cell, lack of energy and filling tired
3. Fats and protein used instead, w/c
cause loss of weight
There are two type of diabetes
Type I
Type II
TYPE I diabetes
appears in children and young people
it is inherited
cannot avoided
TYPE II Diabetes
appears later in life

68
 it can be linked to being obese or possibly very underweight
6. Adrenaline
It is produced by adrenal glands
Adrenal gland is found on the top of kidneys
Adrenaline is the hormone of fight or flight During: -
- Stress
- Angry adrenal gland secretes a lot of adrenaline which rapidly
- Fright carried in to blood stream
- excite
Adrenaline prepares your body for action
So that, you can run fast to escape or fight successfully
7. The gonads
Are the endocrine glands which produce some of the sex hormones.
These are the testes and the ovaries
They become active at the time of puberty
The role of the testes
Puberty in boys usually begins between the ages 9-15
The time is not common to all individuals
No two people experience puberty in exactly the same way
The chemical changes which trigger puberty are unseen
The pituitary gland starts to produce increasing amounts of FSH
This in turn stimulates the male gonads (testes) to begin developing and producing the male sex
hormone testosterone
The menstrual cycle
The menstrual cycle is a sequence of events which takes place approximately every four weeks
throughout
the fertile life of a woman, from the age of puberty to around 50 years of age
At the puberty stage, pituitary secretes two different hormones called:-
A. FSH (follicle stimulating hormone)
B. LH (luteinizing hormone)
FSH-stimulates the growth and maturation of graafian follicles in females
FSH also affects the ovary itself which starts making the female hormone oestrogen
This in turn stimulates the uterus to build up:-
- a thick lining with lots of blood vessels ready to
--spongy support a pregnancy
About 14 days after the ova start ripening, one of them bursts out of its follicle
This is called ovulation
When it happens the hormone levels from the pituitary begin to drop dramatically
After ovulation the remains of the follicle forms the corpus luteum(a yellow body)
corpus luteum:- the cell mass that remains after the release of an egg.
It secretes both progesterone and oestrogen
Progesterone makes sure that for some days the uterus lining stays thick and spongy and
stimulates the growth of more blood vessels, ready to receive a fertilized ovum.
If a pregnancy occurs the embryo will immediately get a rich supply of food and oxygen.
About ten days after ovulation (when no pregnancy has occurred) the ovary reduces the levels of
both oestrogen and progesterone

69
 As the chemical messages change again the blood vessels which are supplying the thick spongy
lining of the uterus close down
The lining detaches from the wall of the uterus and is lost through the vagina as the monthly
period or bleeding
However, if the ovum has been fertilized it will reach the uterus and sink into the thick, spongy
lining, attach itself (implant) and start to develop
3.4 Reproductive health
The pathway of sperm cell from testes to oviduct:
Testes → epididymis → Vas deferns → Ejaculatory duct → Urethra → Vagina
→cervix → uterus → Oviduct (Fallopian tube)
Pregnancy to be formed:-
- Sperm should be successfully joined with ovum
The sperm gets inside the body of the woman during sexual intercourse
Sperm can live for up to three days inside a woman’s body
But once an ovum is released from the ovary, it is fertile for only a few hours - 24 at most
The erectile tissue in the penis fills with blood so that it becomes erect and can be placed inside the
vagina
The sperm move from the testes through the urethra, and semen containing millions of sperm is
released inside the vagina
This process known as ejaculation
The sperm move through the cervix into the uterus then to the Fallopian tube
It is in the fallopian tube where sperm and ripe ovum mix each other(fertilization)
Out of the millions of sperm released, only a few hundred to a few thousand actually reach the ovum
-and only one of those will actually fertilize it
Sperm manage to reach the Fallopian tubes only around half an hour after they are released
The ovum which bursts from the follicle at the moment of ovulation has no way of moving itself
It is then moved along the tube by the beating of the cilia, which carry the ovum towards the uterus.
Fertilization( joining of single sperm with ovum) in human it is also called conception

Contraception
It the method of controlling fertility
Contraceptive method can be:-
A. Traditional
B. Modern
Traditional Modern
vinegar-soaked sponges - condoms
Mixtures of camel dung - Different hormones
Herbs placed in the vagina
Many of these traditional methods were harmful and did not work, they were not scientific at all
Contraception means ‗against pregnancy‘
It describes ways in which pregnancy can be avoided
The effectiveness of contraceptive methods is measured per ‘100 woman years
There are two types of contraceptive methods
A. Natural
B. Artificial
i. Natural method

70
The natural birth control (contraceptive) method is carried without using any physical
or hormonal materials. This involves:
a. rhythm or calendar method - based on the understanding Of the
menstrual cycle and prediction of the ovulation time.
b. Breast Feeding - woman do not ovulate while she is feeding breast.
ii. Physical or barrier methods of contraception
 Involve physical barriers which prevent the meeting of the ovum and the
spermatozoa.
1. Male and Female Condoms
 A thin latex sheath is placed over the penis and vagina during intercourse to collect sperm
 Gives better protection against pregnancy when combined with spermicide
2. The diaphragm or cap
 A thin rubber diaphragm is inserted into the vagina before intercourse to cover the cervix and
prevent the entry of sperm
3. The IUD or intrauterine device:- does not prevent conception – the ovum and the sperm may
meet – but it interferes with and prevents the implantation of the early embryo. An IUD is a device made
of plastic and a metal, frequently copper, which is inserted into the uterus by a doctor and remains there
all the time.
iii. Hormonal methods of contraception
Use natural hormone to prevent conception
1. The mixed pill
 One of the most reliable methods of contraception.
 The pill contains the female hormone oestrogen
 This raises the level of oestrogen in the blood
 This is detected by pituitary gland
 This in turn slows the production of FSH
 Without rising FSH levels no follicles develop in the ovary and no eggs mature to be released
 without mature ova there can be no pregnancy
 the pill also contains progesterone
Hormonal method can be used in different forms like:-
A. hormonal injection
B. hormonal implant
The basic principle of these methods is the same, using natural hormones in different forms.
iv. Sterilization or surgical method of contraception
is the ultimate form of contraception
By cutting or tying the tubes along which eggs or sperm travel Sterilization (surgical) may be:-
Vasectomy:- the sperm ducts (vas deferens) are cut, preventing sperm from
getting into the semen.
Tubectomy:- the Fallopian tubes are cut or tied to prevent the ovum reaching the
uterus or the sperm reaching the ovum.
Human Immunodeficiency Virus and Acquired Immune Deficiency Syndrome (HIV/AIDS)
AIDS is the medical term for a combination of illnesses that result when the immune system is
weakened or destroyed.
HIV is a virus that attacks the immune system, making the sufferer susceptible to other diseases.
HIV attacks immune system so you cannot fight off infections such as TB or even a cold
It can be spread in four body fluids:-
-Blood - breast milk.

71
 -Semen - vaginal secretions
The virus can only spread if bodily fluids from infected person enter the bloodstream of an
uninfected person.
It is most commonly spread through unprotected sex with an infected partner
An HIV-infected mother can infect her baby during:-
-Pregnancy
- Birth
-Breastfeeding.
HIV can also be passed on by an infected blood transfusion
By sharing non-sterilized sharpen materials
HIV targets T-lymphocyte which is the part of our immune system that fights against infection
As HIV progress to AIDS, it lowers the number of free T-helper cells which results in more infection
Finally the T-helper cells severely reduced, which means the body of infected individual cannot fight
against other opportunistic infections
There is no vaccine and no cure for HIV/ AIDS
But there are drugs called antiretroviral that reduce the progress of HIV to AIDS
They are very effective if they are used in combination called HAART (highly activity anti-retroviral
treatment
3.5 Homeostasis
The word homeostasis comes from two Greek words: -
homoios which means ‘like’ or ‘the same’
Stasis, which means state
And when we combine the two word:- keeping the conditions in the inside of your body (the internal
environment) in the same state all the time
The nervous systems play an enormous role in
Hormonal maintaining this important balance
Feedback m isms involving both the nervous system and hormonal systems play a very important
part in maintaining homeostasis.
Most of these control systems in the body are examples of negative feedback
This means that when levels of a substance in your body rise, changes are made which lower
the levels again.
Similarly, when levels of a substance fall, changes are made so that it rises again to the
original levels.

Controlling temperature
One of the most important factors which should be controlled
Temperature is a way of measuring hotness or coldness
Internal or core temperature is maintained at the temperature (around 37 °C)
Living organisms are continually gaining and losing heat from:-
-Cellular respiration
- Conduction
-Convection
- Radiation from their surroundings

72
 It is the balance of these gains and losses that gives the core temperature
Not all animals need to control their core body temperatures.
EX. Protista and small animals living in big bodies of water like the sea have no means of temperature
regulation because they do not need them
Larger animals must be able to regulate their body temperatures so they can avoid cell damage from
overheating
But they also gain enough heat to have an active way of life.
There are two types of animals:-
-Poikilotherms
-Homoiotherms
Poikilotherms:-
Animals whose internal temperature varies along with that of the environmental temperature
Their body temperature is governed by the external temperature
They rely largely on the environment for their body heat
Their body temperature can vary over a wide range
EX. Fish and Reptiles
Homoiotherms:-
Organisms with a relatively constant internal body temperature
Their temperature is independent of the environmental temperature
Their body temperature is usually higher than the external temperature
EX. Birds and Mammals
Humans are a well-known example of homoiotherms
Temperature control in poikilotherms
Poikilothermic animals have to rely on changes to their:-
-Behavior To use the heat in their environment to
-Body structure maintain steady & useful body temperature
A. When they are cold they may:
-bask in the sun
- press their bodies close to a warm surface
- erect special sails or areas of skin which allow them to absorb more heat from the sun
B. When they are getting too hot they may:
-move into the shade
-move into water or mud
Temperature control in homoiotherms
There are two main methods
1. Physiologica methods of T° regulation
2. Behavioral
1. Physiological methods of temperature regulation
Sweating:- when you are hot sweat oozes out of the sweat glands and spreads over the surface of the
skin.
-As the water evaporates it cools the skin, taking heat from the body
Vasodilation: - If body temperature raises, the blood vessels supplying the capillaries in the
skin dilate
So that, more blood flows through the capillaries. As a result, skin flushes
and more heat is lost through radiation from the surface
Panting and licking:-Some animals such as:-
- Dog only have sweat glands in small areas of

73
 -Cats the skin such as the feet
These animals may lick themselves, coating parts of their bodies with Body temperature (°C)
saliva which evaporates and cools them down. They also pant, which allows water to evaporate
from the moist surfaces of the mouth and this also cools them down
Vasoconstriction:- When core temperature begins to fall, the blood vessels which supply skin capillaries
constrict. This to reduce the flow of blood through the capillaries. This again reduces the heat lost
through the surface of the skin, and makes people look paler
Piloerection (pulling the hairs upright):- human beings, like other mammals, have a layer of hair over
their bodies. The hair erector muscles contract. This pulls the hairs upright, trapping an insulating layer
of air which is very effective at conserving heat.
Shivering and metabolic responses: - If the core body temperature drops, metabolic rate speeds up.
This produce more heat energy, so body temperature starts to go up. As result, boy may start to shiver
When you shiver your muscles contract rapidly, this involves lots of cellular respiration.
This releases some energy as heat which is used to raise the body temperature
Fat layer under the skin (subcutaneous fat):- Homoiotherms only lose or gain heat when they really
need to. Under the surface of the skin is an insulating layer of fat. This prevents unwanted heat loss
It very common in animals which live in very cold conditions
EX. - seal he very thick layer of fat under
- whales their skin is known as blubber

3, Behavioral methods of temperature control

Homoiotherms do not only rely on physiological methods to control their internal body
temperature Like poikilotherms, they use behavioral method
Clothing:-Choosing suitable clothes depending on the weather condition. Human being do not have
much fur or feather
Seeking shade or shelter:- people look for shade to keep them cool when it is hot and sunny
condition
Taking high-calorie food in cold conditions:-People need to use more metabolic energy to keep warm.
They eat high-calorie food in cold conditions.
Hibernation:-In countries which have very cold winters, some homoeothermic animals will hibernate.
They go in to deep sleeping. These animals eat a lot and gain a lot of fat before hiding away in a
warm nest or burrow and going into a very deep sleep. Their metabolic rate falls and so does
their body temperature. They do not wake up until the warmer weather of spring arrives with
more food for them to eat
EX. Dormice and Hedgehogs in the UK.
Aestivation:-In hot countries, some animals ‗hibernate‘ through the hottest weather as they
cannot keep their bodies cool enough. These animals usually hide themselves underground or
under a layer of mud and go into a deep sleep until conditions cool down again
For example:-East African land snails
Wallowing or bathing:- some animals cannot lose enough heat through sweating alone to keep their
bodies cool enough in hot weather. This is a particular problem for some larger animals. By wallowing in
mud or bathing in water, the animals cover themselves in water. The water evaporates from the
surface of their skin, cooling them down
EX. Elephants and Pigs
Homeostasis and the kidney

74
Excretion: - Getting rid of the waste products which could build up in our body and damage our cells.
There are two main metabolic waste products which would cause major problems in our body if the levels
rise
These are: - carbon dioxide and urea. The organs which are involved in getting rid
of these metabolic wastes are known as excretory organs.
The main excretory organs in our body are:-
-lungs
-kidneys
- Skin
 The CO2 produced during cellular respiration is almost all removed from the body via
the lungs when we breathe out.
 The lungs are not only the site of gas exchange for respiration, they are also an
excretory
 Increased level of CO2 due to exercise is picked up by sensory receptors in our arteries
and brain, which send electrical impulses to stimulate the breathing centers in our
brain.
 Brian send impulses to make we breathe faster and deeper. As a result, the carbon
dioxide levels fall.
 Low level of CO2 is also detected by the same receptors and so the stimulation of the
breathing centers is reduced which in turns reduce breathing rate.
 This is an example of a feedback mechanism - as the CO2 levels go up, the breathing
rate goes up which makes the CO2 levels fall, so the breathing rate returns to normal.
 Another metabolic waste which can cause serious problems is urea.
 Urea is produced in our liver when excess amino acids are broken down.
 These excess amino acids come from protein in the food we have eaten and from the breakdown
of worn-out body tissue.
 Our body cannot store excess protein or amino acids, so any excess is always broken down.
 The amino acids are converted into carbohydrate (which can be stored or used) and ammonia.
The ammonia is then combined with CO2 to make urea.
 The urea which is produced is a form of nitrogenous waste and it leaves our liver via the blood.
 The urea is then filtered out of the blood by the kidneys and removed in the urine Kidney are the
main excretory organ as well as organ of homeostasis(regulating water and salt balance)
 Regulation of water and salt concentration by kidney is called osmoregulation.

The kidneys
 control the levels of water and ions in your body
 Blood flows into the kidney along the renal artery.
 The blood is filtered, so fluid containing:-
-Water and many other substances is forced out
- Salt into the kidney tubules.
- Urine
-glucose
 Then everybody needs is taken back (reabsorbed) including all of the sugar and the mineral ions
needed by the body
 The waste product urea and excess ions and water not needed by the body are released as urine
 Each kidney has a very rich blood supply and is made up of millions of tiny microscopic tubules
(nephrons) which are where all the filtering and reabsorption takes place

75
Bowman’s capsule:-
 The site of the ultrafiltration of the blood
 several layers of cells - the wall of the blood capillaries and the wall of the capsule - act as a
filter
 water, salt, glucose, urea and many other substances are forced out into the start of the tubule
 This process is known as ultrafiltration - filtration on a very small scale
Glomerulus:-
 The knot of blood vessels in the Bowman‘s capsule where the pressure builds up so that
ultrafiltration occurs.
First coiled (convoluted) tubule: -
 The liquid which enters this first tubule is known as the glomerular filtrate.
 The first tubule is where much of the reabsorption takes place
 All of the glucose is actively taken back into the blood along with around
 It has many microvilli to increase the surface area for absorption
Loop of Henle:-
 Where the urine is concentrated and more water is conserved. Second coiled (convoluted)
tubule:-
 Where the main water balancing is done. If the body is short of water, more is reabsorbed into
the blood in this tubule under the influence of the anti-diuretic hormone or ADH
 Diuresis means passing urine, so anti-diuresis means preventing or reducing urine flow
 Also ammonium ions and some drugs are secreted from the blood into this tubule to get rid of
them
Collecting duct:-
 Where the liquid (essentially urine) is collected.
 It contains about 1% of the original water, with no glucose at all
 Urine is formed constantly in our kidneys, and it drips down to collect in our bladder.
 We can control the opening of the bladder by a strong ring of muscle known as a sphincter at the
entrance to our urethra, the tube that leads from the bladder to the outside world
 The amount of water lost from the kidney in the urine is controlled by a sensitive feedback
mechanism involving the hormone ADH
 A hormone produced by the pituitary gland that reduces the production of urine in the kidneys
and thereby prevents water loss
 The changes in urine concentration is detected by a special area called osmoreceptors in the brain
The liver and homeostasis
-Kidney are not the only the organ of homeostasis
- Skin but our Liver also play a role in maintaining internal environment constant condition
It is the largest individual organ in your body
 The liver cells are very active - they carry out a wide range of functions, many of which help to
maintain a constant internal environment
 The liver has a very special blood supply.
 In addition to the hepatic artery and vein, there is another blood vessel which comes to the liver
directly from the gut.
 This is the hepatic portal vein and it brings the products of digestion to the liver to be dealt with
A large number of reactions take place in the liver. Many of them are involved in homeostasis
in one way or another. It plays a part in all of the following functions:
 Control of the sugar levels in the body
 Controlling and balancing the fats that you eat and the cholesterol levels in your blood
 Protein metabolism
 The breakdown of worn-out red blood cells
 The formation of bile

76
  Control of toxins
 Temperature control
UNIT 4
FOOD MAKING AND GROWTH IN PLANTS
The leaf
The flowering plant is a complete organism with organs carrying out particular functions. There are
four main organs of a flowering plant
A. Flowers: - which contain the reproductive organs.
B. The leaves:-use light energy, CO2 and H2O to make food by photosynthesis.
C. The stem: - provides support and a transport system for water and minerals to
the leaves and flowers. It also transports food from the leaves to the roots and
flowers.
D. The roots which anchor the plant to the ground and absorb water and minerals
A photosynthesizing machine
Plants take the inorganic molecules CO2 and H2O and use them to produce the organic
molecule glucose along with inorganic O2 in the presence of light energy
photosynthesis is the basis of all life on Earth - it provides the food we eat and the oxygen
we breathe
Plant leaves are perfectly adapted to allow the maximum possible amount of photosynthesis
to take place
Adaptations of a leaf for photosynthesis
The leaf is flat and wide, giving a large surface area to collect light and short distances for gases to
diffuse.
The veins bring water from the soil to the cells
The waxy cuticle is a waterproof layer found on the surface of many leaves to help prevent
water loss
The palisade mesophyll is the main photosynthetic tissue of the plant. There are many cells,
closely packed together near the surface of the leaf to get as much light as possible. Each cell
has many chloroplasts - hundreds of them - which are spread out through the cytoplasm of
the cell when light levels are high but which cluster at the top of the cell when light levels are
low. Each chloroplast contains stacks of membranes and chlorophyll to give an increased
surface area for photosynthesis to take place.
The spongy mesophyll has fewer cells with fewer chloroplasts. However, there are lots of
air spaces and a big surface area for gas exchange. Some photosynthesis takes place here but
more importantly it is where the Co2 needed for photosynthesis moves into the cells, and the
O2 moves out. The water lost in transpiration evaporates from the cells here as well.

The lower epidermis has openings known as stomata which allow Co2 to diffuse into the leaf and O2
- lower epidermis- surface layer of a leaf containing stomata
Stomata:- pores mostly on the lower surface of leaves that can be opened or closed to control gas
exchange and water loss and water vapor to diffuse out.

77
 The guard cells open and close to control the entry of Co2 into the leaf and also to control the loss of
water by transpiration
Waxy cuticle:- waterproof upper surface layer found in many types of leaf
Guard cells:- pairs of cells which surround and control the size of stomata by altering their
shape
The vascular bundles contain the xylem, dead tissue and the phloem, living tissue
Xylem:- the hollow cells of a plant that transport water and minerals to plant cells
Phloem:- the food conducting living tissue of a plant chloroplast the organelle in the cytoplasm of
plant cells where chlorophyll is stored, and photosynthesis takes place
Photosynthesis
Plants need food to provide them with the energy for respiration, growth, and reproduction
Other organisms (animals) feed on others, i.e. cannot make their own food, heterotrophs
Plants produce their own food in a process known as photosynthesis. They are known as autotrophs
(feeding themselves)
Photosynthesis takes place in the green parts of plants, especially the leaves, in the presence
of light

During photosynthesis light energy from the sun is absorbed by a green substance called chlorophyll
that is found in the chloroplasts of some plant cells.
The energy that is captured is used to convert CO2 from the air and water from the soil into a simple
sugar, glucose, with oxygen as a by-product
Some of the glucose produced during photosynthesis is used immediately by the cells of the plant for
respiration to provide energy
What is needed for photosynthesis
For photosynthesis to occur successfully:-
-carbon dioxide
- Water
- Supply of light energy are needed
- Chlorophyll
The need for light
It is known that plants need light during photosynthesis. But this is not to mean that, all
photosynthetic reactions depend on the presence of light
Regarding this, reactions can be:-
A. Light dependent
B. Light independent reaction
 The light-dependent reaction cannot take place without light energy.

78
 JOIN ON Telegram @QesemAcademy
 the light energy is absorbed by chlorophyll molecules through activation of their electrons and
used to split water molecules into hydrogen and oxygen.
 ATP for energy is produced as well.
 The O2 is given off as a gas.
Transport
 Osmosis plays a very important role in plants
 The transport systems rely heavily on osmosis, diffusion and active transport
 Trees are supported by their woody trunks. But many plants do not have woody tissue, and so
they have no structural support. They rely on having cells which are rigid and firm. These firm
cells are maintained by the movement of water into the cells by osmosis to create turgor.
 This is one reason why osmosis is so important for plants. Osmosis very important for moving
water around within the plant itself
 Water moves into the plant root cells across the cell membrane along a concentration gradient.
 The roots are covered with special cells, which have tiny hair-like extensions called the root
hairs.
 These root hairs increase the surface area for osmosis to take place.
 Once water has moved into the root hair cells, the cytoplasm of the root hair cells is more dilute
than the cytoplasm of the surrounding cells.
 Water moves into the neighboring cells by osmosis. These cells now have more dilute cytoplasm
than the cells next to them, and the water moves on by osmosis until it reaches the xylem and the
transpiration stream.
Active transport in plants
 Mineral ions in the soil are usually found in very dilute solutions - more dilute than the solution
within the plant cells. By using active transport plants can absorb these mineral ions, needed for
making proteins, and other important chemicals from the soil, even though it is against a
concentration gradient
 Active transport like this involves the use of energy produced by respiration in the cells.
Transport of materials around the plant
 Food is prepared in the leaves by photosynthesis and transported to other parts of plants
 Water is absorbed by root and move to all parts
 Therefore, plants need a transport system to move substances around their bodies
A double transport system
1. Phloem Are the transport system in plants
2. Xylem
The phloem:-
 It is made up of living tissue and it is involved in the transport of organic food made by
photosynthesis -from the leaves to the rest of the plant.
 Phloem cells are thin walled and are regularly replaced when they are worn out
Transpiration: - the process by which water absorbed by plants, through the roots, is evaporated into the
atmosphere from the plant surface, from the leaves
The transpiration stream
Water is taken into a plant through the roots and moves by osmosis to the xylem tissue
There is no active transport in the xylem
The transport of water through a plant is the result of the transpiration stream
Plants lose water vapor from the surface of their leaves. This loss is known transpiration
Most of the transpiration takes place through the tiny holes in the surface of the leaf known as
stomata.
The stomata are there to allow air containing CO2 into the leaf for photosynthesis.

79
 They can be opened and closed by the guard cells which surround them
losing water through the stomata is a side effect of opening them to let CO2 in, but it is vital for
transpiration.
Most of the stomata are found on the underside of the leaf
unlike the other cells in the epidermis layer, Guard cells contain chloroplasts so they
can photosynthesize
when there is sunlight, the concentration of sugar in the guard cells goes up as a result
of photosynthesis
Water then moves into the guard cells by osmosis from the epidermal cells around them
The sausage-shaped guard cells become very turgid, and as they swell up they bend,
opening a gap - the stoma - between them
The pore closes when water moves out of the guard cells by osmosis into the surrounding cells
and as the level of turgor in the guard cells falls, the stoma closes.
Moving water through the plant
As water evaporates from the surface of the leaves, water is pulled up through the xylem
to take its place
There is pressure pushing the water up from the bottom - the root pressure - as water
moves in by osmosis
In the xylem, two physical forces help the water to move upwards.
These are:- A. Adhesive forces
B. Cohesive
A. Adhesive force: - Forces of attraction between different types of molecule (Ex. Water & wall
of xylem)
-It support the whole column of water
B. Cohesive force:- Forces of attraction between similar types of molecule( Ex. Between water
molecules )
-The water molecules tend to stick together and get pulled upwards like a string
of beads
When water reaches the xylem in the leaves, the concentration of water in the solution of xylem
become higher than the solution in the mesophyll cells in the leaf
Water moves out from the xylem into the mesophyll cells and so across the leaf by osmosis
When it reaches a mesophyll cell which is surrounded by air, water evaporates from the surface into
the air and diffuses out through the stomata along a concentration gradient.

Adaptations of plants to reduce water loss in difficult environments

Different environmental factors have different effect on the opening and closing of stomata, so
on photosynthesis Plants which live in very hot areas, where there is relatively little water have
adaptations:-
A. They may have very thick, waxy cuticles to reduce any water loss through the overall leaf
surface
B. Others have very hairy leaves, which trap a micro-atmosphere around the stomata and
reduce water loss
C. Other plants have reduced their leaves to very narrow spikes to reduce the surface area over which
water may be lost
D. On some plants the stomata are sunk into pits
Response in plants

80
All living organisms need to be able to respond to their surroundings through coordination. This
may be to find food, move towards the light or avoid danger
Plants achieve their co-ordination and responsiveness through a system of hormones
Hormones are chemical messengers which are produced in one part of an organism and have an
effect elsewhere. Plant hormones (phytohormones) have several effects on plants:-
For example, they co-ordinate:-
 Flowering
 Cell division
 Cell elongation
- These are essentially growth processes and plant responses of this type are called growth
responses.
- Since growth is a slow process, most plant responses are slow
The germination of seeds
 In most flowering plants, growth starts when the seed begins to germinate
 Seeds may have different sizes and shapes, but the basic structure of seeds always
contains certain things: Food storage tissue is called endosperm.
 An embryo plant made up of three main parts: -
a. the plumule (embryonic shoot)
b. the radicle (embryonic root)
c. the cotyledons (embryonic leaves)
 The testa (the seed coat) which may be thin and papery like the covering on a groundnut or very
strong and hard like the shell of a nut
 The number of these embryonic leaves that are present used to group a division of the
angiosperms into: -
A. Monocotyledons (one seed leaf)
B. Dicotyledons (two seed leaves)
Endosperm- the nutritive tissue of a seed, consisting of carbohydrates, proteins, and lipids
Plumule- the bud, or growing point, of the embryo, above the cotyledons
Radicle -the first part of a seedling (a growing plant embryo) to emerge from the seed during the
process of germination
Cotyledons- the first leaves sent out by the germinating seed -
the seed leaves Testa- the hard external coating of a seed
Hypocotyl- the first leaf-like structure that appears on a germinating seed
 Grows upward in response to light Epigeal germination- cotyledons are carried
above the ground.
 Hypogeal germination- cotyledons remain below the ground
- Once a seed is mature and conditions are right - it needs
water
Warm the seed begins to germinate
Oxygen
√ As the seed absorbs water, the large insoluble food molecules stored in it
undergo chemical changes
√ They are broken down (hydrolyzed) into soluble food
√ The main food storage material in seeds is starch, and it is stored either in
the cotyledons or in the endosperm.
√ This starch store is converted to sugars by the action of the enzyme diastase
√ In some seeds fats and oils are stored. In these seeds the enzyme lipase catalyzes the

81
 hydrolysis of fats to fatty acids and glycerol
Proteolytic enzymes present in the seeds catalyze the hydrolysis of proteins
to amino acids.
 A lot of energy is needed during germination.
 The seed cannot make its own food by photosynthesis while it is underground, so the energy
needed comes from the stored food materials
 As a seed germinates its weight decreases as the stored food is used up.
 The decrease in weight continues until the seedling is capable of photosynthesizing
Plant hormones and growth
 Growth in plants is controlled by chemical messengers called plant hormones. Examples of
plant hormones are:-
 Auxins (indole-acetic acid, IAA)
 Gibberellic acid
 Cytokinin,
 Ethylene
 Abscisic acid
 Some of these hormones promote growth, others inhibit it
 Some of them will promote growth in one type of plant tissue and inhibit it in others
Auxin (IAA):- is the best-known plant hormone. It is involved in general plant growth.
- It stimulates the elongation of the new plant cells, so they get longer and bigger.
- It is also involved in apical dominance. IAA is made at the tip of the main shoot
and as it moves down the stem it slows down the growth of side shoots.
- So the main shoot dominates the whole plant
Apical dominance: - growth concentrated in the terminal bud, allowing it to grow taller,
thereby increasing its exposure to sunlight. Auxin also stimulates the growth of roots. If
auxin is applied to a cut stem it will stimulate new roots to grow
 The best-known function of auxins is in the responses of plants to the world
around them.
 The responses of plants towards things such as light and gravity are called
tropisms
Gibberellins:- These hormones stimulate the growth of plant stems. If you take a dwarf plant and give it
Gibberellins, the stems will grow until the plant is a normal size.
Gibberellins also help seeds to break their dormant period and start to grow. They
do this by stimulating the production of the enzymes needed to break down the food stores in the
seeds.
Cytokinins:- are hormones that stimulate cell division in plants so they are very important in
plant growth
Ethylene:- a gaseous plant hormone that stimulates fruit ripening and the dropping of leaves
Abscisic acid (ABA):- It inhibits growth and plays a major role in leaf fall. It is also involved in
seed dormancy
It may be involved in geotropisms, but it plays a small part compared to IAA.
Tropic responses:-
 This is a response of plants to different stimulus coming from one direction.
 There are different types of tropic responses
Ex. Plants need light to photosynthesize. They (shoot) grow towards the light to absorb
the maximum light. This is called positive photo-tropism phototropism is responding to
light

82
  When seedlings are placed horizontally, their:-
- Roots grow downward this is affected by the force
- Shoots upwards of gravity
 Movement in response to the stimulus of gravity is called geotropism.
 Roots are positively geotropic and shoots are negatively geotropic
 Hydrotropism: - the tendency of plants to move or grow towards water

H are tropic responses brought about?

Maize grains germinate to produce a straight shoot called a coleoptile
The growth region of a shoot is some distance below the tip.
This fact suggests that removal of the tip would not affect the growth of the shoot
When the tips of the coleoptiles are removed (they are decapitated), they don‘t grow
The growth of a shoot is promoted by auxins, failure of decapitated seedlings to
grow suggests that the auxins are probably produced in the tip
The growth hormone, auxin, produced in the tip is indole-3-acetic acid (IAA).
IAA diffuses from the tip to the growth region to initiate growth
UNIT 5
CONSERVATION OF NATURAL RESOURCES
Natural resources:- are resources that supplied by nature. There are two types of natural
resources
A. Renewable Natural resources
B. Non renewable
Conservation and biodiversity
Biodiversity:- the diversity of plants and animals in a particular habitat or in the world as a whole Why is
biodiversity so important? It increases:-
- Food chain and food web
- Health of planet
- The genetic diversity
Conservation:- the preservation and wise management of the environment and of a natural resources
Vegetation
Vegetation is the plant life in a particular region. There are rich and varied vegetation in Ethiopia
We have ecosystems which vary from desert to tropical rainforests. The vegetation across our country
changes dramatically with the conditions
Different vegetation that is found in Ethiopia includes: -
 Tropical rain forest
 Savanna grass land
 Deciduous woods
 Tropical bush
Human effect on vegetation :-
Human beings have influenced vegetation in different ways. This include:-
-Deforestation- removing tree for different reasons
-Agricultural expansion
-Fire wood collection
- Grazing
 This all reduce the biodiversity of the vegetation and often destroys the structure of the soil.
This again may result in different environmental problems like:-
-Desertification
-Global warming

83
- poisoning of environment
Endemic species
Endemic species:- are species which are native or confined to a certain region
Ethiopia is a country which is internationally recognized for its rich diversity of plant species. There are
around 800 endemic plants Ethiopia.
Examples of our endemic species include:-
- Teff (Eragrostis teff) -kererro
- Euphorbia spps -sembo trees
-Noug or Niger seed (Guizotia abyssinica) -Zigba
-Enset (Ensete ventricosum) -Juniper (Tid)
-Ficus vasta Forssk
Wildlife:
 Are all animals (except people) that are not domesticated. The wildlife of Ethiopia is some of the
richest in the world. We have 242 listed mammalian species. There are around 862 species of
birds.
 Insects are another important aspect of Ethiopian wildlife. Wildlife is useful to people in a
number of ways:-
- Insects used as pollinators
- Bees provide the hone
- Acts as a genetic bank for our domestic animals
- Generate income from tourism
 There are a high number of endemic species of different types of wildlife in Ethiopia
Ex. there are 28 species of mammals, which include:-
-Gelada Baboon
- Walia ibex
- Menelik’s Bushbuck
- Mountain Nyala
- Swayne’s Hartebeest
- Ethiopian wolf
Endemic bird species include:-
- heavy-headed - wattled ibis
- thick-billed raven - black winged lovebird
- white-collared pigeon -Prince Ruspolis Turaco

Conservation of wildlife
 There are different ways of conservation of wildlife Conservation involves:-
-protecting habitats and managing populations
-preventing the spread of disease
 Wild life also conserved in Parks or Sanctuaries. There are a number of National Parks in
Ethiopia.
A National Park is a relatively large area of land which is owned by the Government and is set
aside for the protection of vegetation and wildlife and for their appreciation by human beings.
National Parks contain several ecosystems which are not affected by human activities.
The main National Parks of Ethiopia are:-
-Abijatta-Shalla Lakes National Park -Awash National Park
-Bale Mountain National Park -Gambela National Park
-Rift Valley Lakes National Park -Mago National Park
-Omo National Park -Nechisar National Park

84
-Simien Mountains National Park -Yangudi Rassa National Par

National park Regional state Animal found

Abijatta -Shala Oromia Flamingos,Great White Pelicans,
rant's Gazele, Oribi Warthog &
Golden jackals
Awash Afar Beisa oryx, Soemmerrings Gazelle,
Wild pigs Cheetahs, Leopards, and
Ostrich, secretary birds Carmine
Bee-eaters and Abyssinian Roller
Bale Mountains Oromia Gelada Baboon, Mountain Nyala,
Ethiopian Wolves and Meneliks
Bushbucks,Giant Mole Rat,
Klipspringer warthogs.
Gambella, It Gambella, Nile perch, Crocodiles, Hipos,
includes baro river Elephants, Buffalos and Lions
waterbuck, Roan Antelope, hyena,
buffalo, zebra, Vervet Monkeys
and black-and-white colobus
monkeys.
Mago SNNP Girafte, Elephants, Lions, Buffalo,
Cheetah and Zebra, leopard
and oryx. rare Black Rhinos may
be found. Vultures
Nechisar SNNP Red-billed Hornbills, fish eagles,
the Abyssinian Ground-hornbill
and the Kori Bustard, crocodiles,
Burchell’s Zebra, bushbucks,
Grey Duiker, Grant’s Gazelle,
Greater Kudu, Swayne’s
Hartebeest.
Omo SNNP kudu, hartebeest, oryx, Anubis
Baboons, lions, cheetahs, buffalo,
giraffes and elephants
Simien mountain Amara Walia ibex, Ethiopian wolves and
Gelada Baboons
Yangudi Rassa Afar wild-ass, Greater and Lesser Kudu,
Grevy’s Zebra and
Cheetah,
Rift Valley Lakes Oromia Grant’s Gazelle, warthogs, Greater
(chain of seven and Lesser Flamingos, a huge
lakes) colony of Great White Pelicans,
fish eagles, spoonbills, Abdim’s
Storks and ibises.

85
  Ethiopia also has a number of wildlife sanctuaries which are similar to National
Parks but focus on the conservation of particular species
These include:-
-Harar Wildlife
- Kuni-Muktar Mountain Ny
- Senkelle Swayne‘s Hartebe sanctuary

Sanctuary Regional Animal found

state
Harar Wildlife Sanctuary Oromia native elephant sub-species,
Loxodonta Africana oleansie.
The area is also home to the
black-maned lion.
Kuni-Muktar Mountain Nyala Oromia Mountain Nyala (Tragelaphus
Sanctuary nyala), an extremely rare
endemic animal in Ethiopia.
Senkelle Swayne‘s Hartebeest Oromia Swayne‘s Hartebeest
Sanctuary

Air
 Clean air is essential for our bodies to live as it supplies the oxygen for cellular
respiration
 We breathe air into and out of our lungs all the time from our birth to our death.
 But air we breathe in is not always clear. There are other substances released that pollute the
air and are harmful to humans, plants and animals.
 These are called pollutants. Pollution is the contamination of the natural environment by
harmful substances as a result of human activities

What is in air pollution?

 It is a contamination of air by different pollutants.
 One type of air pollution is smoke produced by burning fossil fuel for energy.
 Fossil fuels contain chemicals known as hydrocarbons
 When fuels are burned, small particle are released into the air causing local air pollution.
 Smoke pollution worldwide is thought to be causing global dimming, blocking out some
of the light from the sun. Another is production of CO2.
 It is produced from burning of wood and fuels or from respiration of living
organisms. This result in increase of CO2 in the air.
 Increased level of CO2 with methane, act as blanket and trap heat close to the surface of
the earth. This result in Global warming
BIOLOGY GRADE 11
UNIT ONE
THE SCIENCE OF BIOLOGY
Biology
√ Is the science of life and living organism
√ It derived from two Greek words
o Bios- means life i.e. is set of characteristics that distinguish living organism from
nonliving objects (including dead organism)

86
 o Logos- means study
Organism- is a living being made from one cell or many cells

√ Example for one cell organism-bacteria, unicellular algae

√ Example for many cells organism- animal, plants and most fungi
Few areas of biological study
Astrobiology
 It try to find evidence of life on other planets
 Is the investigation of the possibilities of life on other planets
Biomedical research
 Research into development of new drugs and vaccine
 Study the way in which diseases develop
Microbiology
 Study how microorganisms of all kinds function
 Study micro-organisms
 Study HIV to get a better understanding of how AIDS develop and how it can be treated
Pale biology
 Is the study of the origin and evolution of life
 Try to find the way in which life began on earth
 Study how life has evolved from simple life forms into more complex ones
Evidence of paleo biology study to estimates of when and how new life forms appeared on the
planet

√Fossils
√Study on chemistry of ancient rocks
Human genome project

√ it produced the first ever map of the 46 chromosomes found in human cells
√ determine exact structure of each chromosomes
Ecology
√ study the interaction of organism with each other and with their environment

Beside these biologists there are others who are perhaps more recognizable.
Doctors: Who maintain or restores human health through the practice of medicine.
Dentists: Physician whose practice is in the field of dentistry, .involves mouth, teeth, and
gums.
Veterinary: deal with prevention, diagnosis, and treatment of disease, disorder and
injury in animals.
Surgeons: physician who performs surgical operation.
Biochemists: Scientists that are trained in biochemistry.
Ecologist: Study the interrelationship b/n organisms and their environment.
Ethnologists: Scientists those study animal behavior under natural condition.
Geneticists: Who study about genetics (science of genes, heredity and variation of
organisms).

87
 Oncologists: Who treats cancer and tumor provides medical care for a person diagnosed
with cancer.
Neurobiologists: Concerned with the anatomy and physiology of the nervous system.
Parasitologists: Who Study the lifecycle of parasite and their hosts.
Physiotherapists: a healthcare professional that helps patients achieve maximum range
of movements and physical ability.

Science
√ Is a unique system of acquiring knowledge based on the scientific method
√ Is an ongoing effort to find new information and principles
√ It derived from Latin word scientia-means knowledge
√ It sometimes called experimental science
Experimental science
 Is science that use experiments to obtain information
 It depends very heavily on experimentation to obtain the information
 It differ from applied science (is the use of scientific research to meet certain human needs)
Important ideas in science

 Any suggestion or explanation has capable of being proved wrong

 Science is tangible
Science developed as a result of:-
1. Observation
2. Experimentation
3. study
Observation
√ For centuries, it was base for peoples for their explanation of what they saw going on in the world
around them without testing
Example –spontaneous generation
Spontaneous generation theory

- Suggests that certain nonliving material can change directly in to living organisms
Example of reasons for emerging of the theory that suggests nonliving object can give rise to
living organisms are observation of peoples when:-
 swarms of bees flying from a bull‘s carcass
 Mice emerging from containers containing dirty cloths and cereals
The theory of Spontaneous generation disproved by French biologist Louis Pasteur by using scientific
methods

Scientific method
 is the process by which scientists approach their work
 it determine if something is true or false
 is procedure by which scientists explain occurrences in a logical and sensible way
Importance of scientific methods
o knowledge acquiring
o theories and law formulation
o to set solution for problems

88
 o
to set and discover principles and facts
Importance of determining an idea using scientific methods

- avoid spreading of unreliable information

- makes it possible to further study an idea or occurrence
- determines validity and accuracy

Steps of scientific methods

JOIN ON Telegram @QesemAcademy

89
 1. Ask question (questioning)
√ Ask a question something catches our imagination
√ It is identifying of problem
2. Background research
√ before trying to do the whole investigation collect and gather information from different
sources about the problem that we identify
3. Construct hypothesis(hypothesis)
Hypothesis
√ Is theory or an idea that is not proven but that leads to further discussion or study
√ Is an educated guess
√ It used to make prediction
√ it must be stated in a way that it can be tested by an experiment
√ Prediction- is the estimation of scores on one variable from information about one or
more other variables
4. Carry out an experiment (experimentation)
√ it is practical activity to test the hypothesis
√ seek to establish cause and effect
√ it consists of two groups
1. control group
2. experimental group
Control group

90
  it provides a standard comparison with which to confirm or rule out error in an experimental
observation
 group that does not receive the treatment
 it used to isolate the factor we are investigating and show that changes are due to this factor

Experimental group

 is the group in an experiment which is being experimented on in order to compare with the
control group
 is group that receives the treatment in an experiment
 is a scientific test in which all conditions are kept constant except for the variable being tested
Variables

√ a factor in a scientific experiment that may be subject to change

Independent variable (IV)

√ is factor that the scientist change or manipulate

√ it manipulated to influence dependent variables
√ is the thing you are testing
Dependent variable (DV)

√ is the factors that the scientist measures to see if it changes when the IV is changed
√ it change when IV changes
√ is the thing that we are measuring
√ is factor that the scientist has no control
Controlled variables
√ are factors other than the IV that are kept constant in order to avoid influencing results
√ can affect experiment results or outcomes
Example
 Temperature
 Number of seeds per dish
 Lighting conditions
 Volume of liquid etc
Confounding variables

91
 √ Are variables that we can‘t control but that might influence the results
Example
If you measure the CO2 uptake by wheat plants as the light intensity changes over the day, you can‘t
control the effect of change in temperature. it could be a confounding variable.

5. Analyze results and draw conclusion

 Record observation and analyze the meaning of the data. Often, you will prepare a table
or graph of the data
6. Accept or reject the hypothesis
 Conclude whether to accept or reject your hypothesis

7. Report results

 Communicate your results.

 The result may be compiled into a lab report or formally submitted as a paper.
 We must now decide whether or not to report the results to other biologists.

8. Publication
The action of making the report generally known in journal
Terms that are important to know how well an experiment is received by other scientists

1. Accuracy

2. Reliability

3. Validity

1. Accuracy- true value

√ Refers to how precisely you measure or count something

√ Degree of measure to a true value
Example

 Measuring time with a clock

 Measuring minutes by stop-clock
 Measuring of how much light pass through a liquid by colorimeter
 Measuring volume by syringe, measuring cylinder, pipette and burette
 To Measure 2.5 cm3 volume-pipette is best
 To measure 300 cm3 volume- measuring cylinder is best

1. Reliability-repeatability
√ Is a measure of how dependable our results are
√ it concerns gaining of the same results for repeated investigation
To increase the reliability of experiment we can do the following:-

Standardize procedures
Try to avoid personal judgment
Repeat the experiment many times to:-
a. Calculate average result
b. Spot any anomalous results
N.B Anomalous results-means odd results that do not fit the general pattern

92
 3. Validity

√ Are we measuring what we are intended to measure?

√ Concerns whether an experiment really measures what it says it is measuring

Writing reports of scientific experiments

Scientific experiments should be understandable and repeatable to other researchers in the area. Scientific reports are
written in a way that reader can get full and understandable information. Although the guidelines vary from one
publisher to another, the basic components are usually the same. The basic components are the following.
Title
Hypothesis/ research question
Experimental procedures - materials and methods
o Apparats used
o Details of chemicals used- volume, concentration or mass
o Details of experimental animals, if used.
o Details of control used
Summary of the results
Conclusion
Evaluation of the procedures
Acknowledgment

1.2 The tools of a biologist

Depending on the type of their activity, biologists use different types of tools both in the laboratory
and in the field
Common laboratory tools include the following
o Microscopes- for magnification
o Dissecting equipment - for dissecting specimens
o Petri dishes- for culturing microorganism
o Pipettes and syringes - measuring volume of liquid
o Centrifuge - to separate solid particles from liquid medium
o Measuring cylinder - measuring volume of liquid
o Balance - measuring mass
Common field tools
o Quadrats - to estimate species abundance in a small portion of land or water body.
o Nets and pitfall traps - to catch insects
o Plastic bags or plastic jars -to collect and keep plant samples for short time
o Insect killing jars - to keep small animals
o Data logger- tor record data online
o PH meter, oxygen meter, thermometer
o Theodolite - to measure the height o trees
o Field microscope - to observe specimens in the field

93
1.3 The relevance and promise of biological science
The study of biology has immense relevance almost in all aspects of life. Biology played significant roles
in the past, is playing and will play key roles in any activities of life in the future.
Biology and agriculture
One of the major challenges posed to the globe is feeding the alarmingly increasing population. Hence,
many streams of biology are currently working on how to produce more food, mainly focusing on genetic
modification of the existing crop plants. The major focus include producing plants that
o will be adapted to the new conditions - adaptive to climate change
o capable of producing their crops quickly so that more than one crop can be obtained per
year from a field
o disease resistant
o drug resistant
Biology and Medicine
Biologists are also involved in the designing ways to optimize rate of population growth by reducing birth rate
through advising different concerned bodies. For example, advising the government or community or individuals
on effective methods of contraceptive methods.
Biology and environment
Biology involved in many efforts to maintain balanced environment to make our world safe haven to all creatures.
Biotechnology is a recently evolved stream of biology, dealing with the use of microorganisms and enzymes for
the benefit of mankind. The promises in the field of biotechnology include the following.
Treatment for degenerative diseases such as Parkinson‘s diseases and alzheimer‘s disease
Cures for genetic diseases
Production of drugs that are tailor-made to suit an individual‘s needs
Establishing biologically-controlled industrial processes to produce huge biological products such
as insulin
cloning of productive animals and plants
Production of monoclonal anti-bodies that can deliver a drug to cells which need treatment (e.g.
Cancer cells)
Genetically modifying plants to meet specific needs
Using stem cells to repair damaged cells in an organ
1.4 Biology and HIV/AIDS
AIDS is a short name for Acquired immune-deficiency Syndrome and is caused by
Human Immunodeficiency Virus (HIV). HIV attacks cells in human immunity systems, called T-helper cells
that enable human immunity system to fight other diseases. Thus, HIV infected individuals are usually
suffered by opportunistic infections that normally human body defends. IHV is largely sexually transmitted
disease (STD), there are four major ways.
 Making homosexual or heterosexual intercourse with an infected person
 Transfusion of blood or blood products

94
  Sharing infected needles
 From mother to child during pregnancy
The role of biology the fight against HIV/AIDS
 Break the transmission pathway
 Produce drugs that kill the virus or stop it from reproducing
 Produce a vaccine against the virus

Biologists have developed several drugs, called anti-retroviral drugs, targeting the different stages of this life
cycle which usually used together. Such combination of treatment is called highly active anti -retroviral
therapy, HAART. No drugs give lasting immunity for HIV
The huge effort to develop a vaccine for HIV is challenged by the rapid mutating behavior of the virus.
However, based on the finding that all strains of HIV have common part, they are developing the vaccine.
Other biologists are searching for a vaccine taking the antibodies found in repeatedly exposed persons but
not infected.
The role of everyone in the fight against HIV/AIDS
Recognize that people with AIDS are simply sick people who need medical care, support and love
Tolerate and understand the reality
Restrict sexual partners
Avoid sharing infected needles and sharp items
Awareness and practice by mobilizing the community
UNIT 2
BIOCHEMICAL MOLECULES
2.1 Inorganic and organic molecule
Biological molecules can be classified into two main types: inorganic molecules and organic molecules
 Organic molecules are molecules that always contain both carbon and hydrogen.
 Inorganic molecules may contain one or the other (or neither), but not both.
Elements are used to build biological molecules, for example in humans;
 Calcium (Ca) for bones, teeth and muscles,
 Chlorine (Cl) for digesting food

95
  Fluorine (F) for tooth enamel and iron
 (Fe) to help blood carry oxygen.
Atoms of elements;
Can join together to form molecules with forming a chemical bond.
two atoms of same element join to form a molecule of that element example, oxygen gas is O2.
Atoms of one element can join with atoms of another element to make a molecule of a compound.
The atoms are always present in the same ratio in all the molecules of the compound.
Each atom can make a certain number of bonds with other atoms; this is called its valiancy
Water
Water covers three-quarters of the planet and remaining one-quarter, is land;
Water is not very far away. It may be in streams, rivers, ponds, lakes or in underground
aquifers.
It is in all living things. Most cells are about 70% water and some are as high as 90%.
What is water?
The chemical formula for water is H2O.
Water is made of molecules contains two hydrogen atoms bonded to one oxygen atom.
Notice that the molecule is not ‗straight‘ it is bent into a ‗v‘ shape.
The molecule forms a ‗dipole’. Part of the molecule has a slight negative charge (δ-) and other
parts have a slight positive charge (δ+).
All water molecules are interlinked! The bonds joining the hydrogen atoms to the oxygen atom,
there are very weak bonds called hydrogen bonds that join oxygen in one water molecule
(Slightly negative part) to hydrogen in another water molecule (slightly positive part)
it is the only substance that exists in three states
Solid, Liquid and Gas - at temperatures commonly found on Earth.
Solid water is ice, liquid water we call water and gaseous water is steam
The hydrogen bonds in water keep breaking and reforming as the molecules move around,
but there is always some bonding between the molecules in a mass of water.
One water molecule can possibly make bonding with four other molecules.
Why is water so important to living things?
The very first cells on Earth evolved in water about 3.5 billion years ago. Water has many properties that
make it important to living things, such as:
A transport medium
A reactant in many chemical reactions
A place for other reactions to take place
• Water is a vital chemical constituent of living cells
A place to live in. Many organisms live in water. Plants, algae, and different animals
Water is Transparent.
- Means light can pass through the water and allow the plants and algae to photosynthesize.
96
 - So aquatic animals can see where they are going.
- However, water does not allow all light to pass through it, as we go deeper less light penetrates.
- Different wavelengths of light penetrate to different depths. Red and indigo are soon lost.
- Blue and green wavelengths penetrate deeper than others.
Water has a high specific heat capacity
Specific heat capacity the amount of energy needed to raise temperature of 1 g substance by 1 oC
It takes quite a lot of energy to heat water up. Water also loses heat quite slowly.
The overall effect that water stays more or less the same temperature particularly large masses of
water, such as oceans and lakes.
This is important as the functioning of enzymes in living cells is affected by temperature.
Too hot or too cold and the enzymes do not function efficiently and the reactions in the cells
controlled by the enzymes are not carried out efficiently.
Ice is less dense than liquid water.
It is unusual for solid form of a substance to float on liquid form of same substance. But ice floats
on water. Because water expands when it freezes. So, in cold weather, water freezes from top to down.
The ice on the surface acts as an insulator and slows down heat loss from liquid water underneath.
So life can continue in relatively warm water underneath the ice all through the cold weather.
Water has a high latent heat of vaporization.
Latent heat of vaporization is the energy used in converting a liquid to a gas
This means that it takes a lot of energy to turn liquid water into water vapor (or steam).
Means water doesn‘t vaporize too easily and that ponds don‘t dry up too quickly in hot weather
and the organisms in the pond have a better chance of survival.
Important in temperature control. When we sweat, the energy needed to vaporize the sweat comes
from our bodies. This heat is then lost from our bodies and so we cool down.
If water vaporized easily, sweating wouldn’t be as effective in controlling our body temperature.
Different wavelengths of light penetrate to different depths. Red and Indigo soon lost.
But Blue and green wavelengths penetrate deeper than others.
Water has a high surface tension
Water molecules in main body of a mass of water H bonded to other water molecules on all sides.
But at the surface, there is no H bonding above. So the ‘pull’ from the sides is stronger than it
would otherwise be and the molecules at the surface are held together more strongly.
This is why some animals can ‘walk on water’ and others attach themselves to surface of water.
Water strider one, example of an insect is so light that force of surface tension support insect
weight.
Water is a good solvent for many substances
– Many organic and inorganic substances important to life dissolve in water, but don‘t dissolve
either at all or as well in other liquids.
- Water is very versatile. Substances dissolve in water, transported in a water-based medium.
- Biological mechanisms such as Active transport, Diffusion, and Facilitated diffusion move
substances in and out of the water (transport medium).
- In mammals, the plasma of blood is 90% water.
- In plants water carries dissolved minerals upwards from roots to other parts of plants in xylem.
- Water in the phloem tubes carries dissolved organic substances all over the plant.
Water has the ideal viscosity for a transport medium.
97
 Viscosity is a measure of how fluid a liquid is, how easily it flows.
If water more viscous (less fluid) than think of tar! Heart not moves it through blood vessels.
If it were more viscous, it would damage the delicate organelles in the cells.
If water were less viscous (more fluid) than it is, it would flow too easily and, inside cells, the
organelles would not be supported.
Plant cells absorb a lot of water, they swell until cellulose cell wall won‘t let them swell any
more. In this condition, we say they are turgid.
Turgid cells press against each other and this pressure helps to support the plant.
Water as a reactant;
Many reactions in living things need water as a raw material.
Photosynthesis is process of energy transfer requires water as reactants.
Water is also involved in digesting large food molecules into smaller ones.
Reactions use water to split large molecules called hydrolysis. Hydro = water; lysis =
splitting.
Water molecules are used to split large food molecules into smaller
Water as a medium for chemical reactions
Cell function because of the many chemical reactions that are continually taking place in them.
Take place on membrane systems of the cell, but others in e liquid ‗cytosol‘ of cytoplasm.
Photosynthesis and respiration take place in liquid inner of chloroplasts and mitochondria.
Water is an ideal medium for these reactions
It can dissolve many substances; the reactions will only take place effectively in solution.
It has a low viscosity; particles can move around and come easily into contact with each other.
2.2 Organic molecules
Carbohydrates
What are carbohydrates and why do we need them?
All carbohydrates contain carbon, hydrogen and oxygen. The ratio of H to O atoms is 2:1.
Carbohydrates have a range of functions:
 Used to release energy in respiration glucose is the main respiratory substrate of most
organisms.
 Carbohydrates are a convenient form to store chemical energy; storage carbohydrates include:
- Starch in plants
- Glycogen in animals
Some carbohydrates are used to build structures; structural carbohydrates include:
- Cellulose, is the main constituent of the primary cell wall of plants
- Chitin, occurs in the cell walls of fungi and in the exoskeletons of insects
- Peptidoglycan occurs in bacterial cell walls
What different types of carbohydrates are there?
Based on the number of sugar molecules carbohydrates are grouped in to three groups.
These are Simple, Double and Complex carbohydrates
1. MONOSACCHARIDES
98
 Are the simplest carbohydrates.
Monosaccharaides are carbohydrates with atoms that are arranged in a single ring-like
structure.
A monosaccharide molecule can be thought of as a single sugar unit.
Monosaccharaides can be classified according to how many carbon atoms are present in the
molecule.
Triose monosaccharide has 3C atoms, C3H6O3. Glycerate phosphate is important in photosynthesis.
Pentose monosaccharide has five C atoms, C5H10O5. Ribose is found in RNA nucleotides.
Hexose monosaccharide has six carbon atoms - formula C6H12O6. Glucose is the hexose
There are several different Trioses, Pentoses and Hexoses.
 Isomers; the same number of each kind of atom but atoms are put together in a
different way. Example pentoses and hexoses.
Monosaccharide; classified based on functional group they possess. Aldehyde and Ketone groups
 Aldehyde with CHO (carbonyl group) at end of carbon chain (monosaccharide are Aldoses)
 Ketone; with C=O (carbonyl group) in middle of carbon chain (monosaccharide are ketoses). .
2. DISACCHARIDE
 Carbohydrate molecules that are made by two monosaccharide molecules joining together.
 Maltose(malt sugar) is derived from two α-glucose molecules
 Sucrose is derived from an α-glucose molecule and a fructose molecule
 Lactose (milk sugar) is derived from a β-glucose molecule and an α-galactose molecule.
 The formula of the disaccharides to be C12H22O11.
 H2O is formed from a hydroxyl group from one monosaccharide and a H atom from the other
 The two monosaccharide units bonded to make a disaccharide in condensation.
 The bond that holds the two monosaccharide units together is a glycosidic bond.
3. POLYSACCHARIDES:
Are complex carbohydrates. Built as many monosaccharide join together by condensation links.
Some polysaccharides are storage molecules that will not interfere with the metabolism of cells
Structural carbohydrates build structures - like plant cell walls and insect exoskeletons.
Examples include, starch, cellulose, glycogen, chitin, pectin, lignin
 A polymer molecule is made from many smaller, usually identical, molecules called
monomers.
 Chitin is the main structural components of exoskeletons of invertebrate like insects
and in fungi
 Pectin extracted from plants and serve as gelling agent in food industries for
preserving
Starch
 Starches are plant storage form of carbohydrates and polymers of α-glucose,
 Starch is not a single compound but a mixture of Amylose (linear) and Amylopectin (branched).
 Both are polymers of α-glucose, but the arrangement of the α-glucose monomers is different.
 Amylose is a linear molecule containing many hundreds of α-glucose molecules joined by α-1, 4-
glycosidic bonds. As it is being formed, this long chain winds itself into a helix.
 Amylopectin is a linear ‗backbone‘ of α-glucose joined by α-1, 4-glycosidic bonds and side
branches bonded with α-1, 6-glycosidic bonds.
 An α-1, 6-glycosidic bond with another glucose as well as the usual α-1, 4-glycosidic bond.
 The branched nature of amylopectin means that there are many ‗ends‘ to the molecule.
 This allows it quickly hydrolyzed by enzymes at ends of chains to release glucose for respiration.

99
Why starch stains blue or black or blue-black with iodine?
Amylose molecule winds itself into a helix when in contact with water.
This allows a reaction to occur between the starch and the iodine solution.
Rows of iodine atoms sit inside the amylose helix.
This changes light-absorbing properties of both, so that the amylose iodine complex
appears blue.
Starches in different plants have different proportions of amylose and amylopectin.
This results in different shades of blue-black iodine test, because only amylose reacts
with iodine.
How the structure of starch is suited to its function?
Starch is a plant storage carbohydrate. Both Amylose and Amylopectin are;
√ Compact molecules, so many α-glucose stored in small space, without affecting cell metabolism.
√ Insoluble. If soluble glucose stored (instead of converted to starch), it draw water, by osmosis,
from neighboring cells and organelles within cell. Insoluble starch produces none of these effects.
√ Insoluble, the molecules cannot move out of cells - they remain in storage organs.
Glycogen
Glycogen is a storage carbohydrate in animal liver and muscles cells and polymers of α-glucose similar
structure with amylopectin but more α-1, 6 links, making it more highly branched.
Because of this, it can be hydrolyzed even more quickly to release glucose for respiration.
This is important because animals have a higher metabolic rate than plants and need to release energy
more quickly to ‗drive‘ their metabolic processes.
Glycogen is more branched and a protein at the heart of every glycogen called glycogenin
Cellulose
 Cellulose is a polymer of β-glucose.and most abundant organic molecule in the biosphere
 Polymer of β-glucose joined by β-1,4glycosidic bonds, formed by condensation reactions.
 However, different position of H and OH groups on carbon atom 1 compared to α-
glucose. Many cellulose molecules lay side by side and hydrogen-bond to each other
results formation of cellulose micro fibrils. Micro fibrils bond together to form bigger
fibers or fibrils make up of cell walls structure.
How the structure of cellulose is suited to its function?
The cellulose molecule is;
 Unbranched this allows hydrogen bonding and the formation of micro fibrils.
 If it were branched, micro fibrils could not form.
 The fibrous nature gives the cell walls their strength, but also gives them some flexibility.
Lipids( fats and oils)
What are Lipids?
 Lipids contain C, H and O, but much less oxygen than carbohydrates. Varied lipids group that
include:
 Triglycerides formed from; Glycerol and three fatty acids
 Phospholipids formed from, Glycerol, two fatty acids and a phosphate group
 waxes formed from Fatty acids and long-chain alcohols
 Whilst some lipids have quite large molecules, they are not polymers and, in many cases, their
molecules are relatively small. ‗
 The feature that they all share is that are all made from fatty acids and alcohols. Because of
their varied nature.
 lipids have a range of functions:
 Waxes are so insoluble in water that they make excellent water repellents, for example, in coating
birds‘ feathers and the epidermis of the leaves of plants (the waxy cuticle).
100
  Phospholipids are one of the basic components of all cell membranes.
 Triglycerides have functions including:
- Respiratory substrate a molecule of triglyceride yields over twice as many molecules of
ATP (twice as much energy) as a molecule of glucose
- Buoyancy - lipids are less dense than water (oil floats on water), so the presence of large
amounts of lipid reduces the density of an animal, making it more buoyant
- Waterproofing-the oils secreted by some animals onto their skin are triglycerides
- Thermal insulation the cells of adipose tissue found under the skin of many animals contain
large amounts of triglycerides, which give good thermal insulation

Triglycerides:
o A triglyceride is an ester formed from one molecule of glycerol and three fatty acid molecules.
o A fatty acid molecule consists of a covalently bonded hydrocarbon chain, at the end of which is a
carboxyl group, which has acidic properties.
o The hydrocarbon chain is non-polar (this means that it has no charge).
o Carboxyl (functional group of fatty acid.) is ionic and dissociates in solution to form COO- and
H+.
o The hydrogen ions released make the solution acidic.
o When triglyceride formed, condensation reactions join 3 fatty acid molecules to glycerol.
o The bonds formed are ester bonds broken by hydrolysis to give glycerol and fatty acids
The nature of the hydrocarbon chains in fatty acids can differ in two main ways: These are;
1. The number of carbon atoms in the chains can vary.
2. Hydrocarbon chains with same number of C atoms can have different numbers of H atoms
This is because of the nature of the bonding between the carbon atoms in the chain.
 If all the C-C bonds in hydrocarbon chain are single bonds, the fatty acid is a saturated fatty acid.
 If one of the carbon-carbon bonds is a double bond, then it is a monounsaturated fatty acid.
 If more than one C-C bond is a double bond, then the fatty acid is a polyunsaturated fatty acid.
Phospholipids
Phospholipids are formed when two fatty acid molecules are bonded to the glycerol and the place of the
third is taken by a phosphate group. Since the phosphate group is ionic and the hydrocarbon chains of
the two fatty acids are covalently bonded, there are two distinct regions to a phospholipids molecule:
1. Hydrophilic (water-loving) region, consisting of the phosphate ‗head‘
2. Hydrophobic (water-hating) region, consisting of the hydrocarbon ‗tails‘
In water, phospholipids become organized into a bilayer (two layers sandwiched together). In this
configuration, the hydrophilic heads face outwards into the water and the hydrophobic tails face
inwards, away from the water. Phospholipids bi layers are the basis of plasma membranes. The
phosphate head is shown as a ball and the fatty acids as two tails.

Proteins
Why do we need proteins?
 The word protein comes from the Greek word proteios, meaning ―first or ―primary.
 Proteins account for more than 50% of the dry mass of most cells, and they are instrumental in
almost everything organisms do.
 A human has tens of thousands of different proteins, each with a specific structure and function;
proteins, in fact, are the most structurally sophisticated molecules known.
 Each type of protein having a unique three dimensional shape. Proteins are all constructed from
the same set of 20 amino acids. The bond between amino acids is called a peptide bond, so a
101
 polymer of amino acids is called a polypeptide. A protein is a biologically functional molecule
made up of one or more polypeptides; each folded and coiled into a specific three-dimensional
structure.
 Protein molecules are polymers of amino acids and so are macromolecules also.
 Protein molecule contains the element carbon, hydrogen and oxygen (like carbohydrates
and lipids), but they also contain nitrogen and most contain sulphur.
 It vary in size,
 the smallest protein molecule contain fewer than 100 amino acids,
 The largest contain several thousand.
Function of protein
 The structure of plasma membranes.
 Form ion channels, transport proteins and surface receptors for hormones,
neurotransmitters and other molecules.
 The immune system- antigen and antibody molecules are proteins.
 All enzymes are proteins – control metabolism.
 The structure of chromosomes- DNA is wound around molecules of the protein histone to form
chromosome.
All amino acids molecules are built around a carbon atom (the alpha carbon) to which is attached
 A hydrogen atom
 An amino group (_NH2)
 A carboxyl group (_COOH)
 An R group- which represents the other atoms in the molecule, such as a single hydrogen atom, a
hydrocarbon chain, or a more complex structure.
Two amino acids can be joined together by condensation to form a dipeptide. During the reaction:

 the H is lost from the amino group on one amino acid and
 The OH is lost from the carboxyl group on the other amino acids to form water molecule.

Protein Structure

A. Primary structure

 Polypeptide chain of amino acid.

B. Secondary structure

 Folding of polypeptide chain either an alpha helix or a beta pleated sheet.

 The structures are held in place by hydrogen bonds that form between peptide bonds in
adjacent parts of the amino acid chain.

 Secondary protein structure occurs when the sequence of amino acids are linked by
hydrogen bonds.

 Both types of secondary structure can exist in different regions of the same polypeptide
chain.

C. Tertiary structure

 Involves the further folding of the secondary structure and the formation of new bonds to
hold the tertiary structure in place.

 Occurs when certain attractions are present between alpha helices and pleated sheets
102
These new bonds include:

 More hydrogen bonds- between the R- groups of some amino acids.

 Disulphide bridges- between amino acids that contain sulphur

 Ionic bonds- between amino acids with positively charged R-group and those with
negatively charged R- group.

The tertiary structure of a protein is unique and this gives each protein a specific function. For example

 The shape of active site- which only binds with only one substrate and catalyzes only one
reaction.

 The shape of a hormone receptor plasma membrane.

 The shape of an antibody means it can bind with and destroy just one antigen.

D. Quaternary structure

Two or more polypeptide chain folded into a tertiary structure become associated in the final structure of
the protein

Eg haemoglobin – oxygen carrying molecule found in RBC. Four polypeptide in it ( two alpha and two
beta)

Collagen: - Fibrous protein found in many tissues in mammals

i. Fibrous protein- that have tertiary structure that resembles a long string or fiber (e.g. collagen and
keratin).

ii. Globular protein-that have a tertiary structure that resembles a globule or ball (e.g. enzymes and
receptor protein)

Nucleic Acid (DNA and RNA)

What are nucleic acids?
 Nucleic acid molecule contains the element carbon, hydrogen and oxygen (like
carbohydrates, proteins and lipids), but they also contain nitrogen and
phosphorus
 Nucleic acids are macromolecules that exist as polymers called polynucleotides.
 As indicated by the name, each polynucleotide consists of monomers called
nucleotides.
 A nucleotide, in general, is composed of three parts:
 a five-carbon sugar (a pentose),
 a nitrogen-containing (nitrogenous) base, and
 One phosphate group.
 The portion of a nucleotide without any phosphate groups is called a nucleoside.
 To understand the structure of a single nucleotide, let‘s first consider the
nitrogenous bases.

103
  Each nitrogenous base has one or two rings that include nitrogen atoms. (They are
called nitrogenous bases because the nitrogen atoms tend to take up H+ from
solution, thus acting as bases.)
 There are two families of nitrogenous bases: pyrimidines and purines.
 A pyrimidine has one six-membered ring of carbon and nitrogen atoms.
 The members of the pyrimidine family are cytosine (C), thymine (T), and
uracil (U).
 Purines are larger, with a six-membered ring fused to a five-membered ring.
 The purines are adenine (A) and guanine (G).

Food Test

 Reducing sugar (glucose, fructose, maltose, and lactose) react with benedict‘s solution
when heated to give a yellow/orange/red precipitate.
 Non reducing sugar (sucrose) must first be hydrolyzed by boiling with HCL and then
neutralized before they will react with benedict‘s solution; they then give the same
yellow/orange/red precipitate as reducing sugars.
 Proteins react with biuret reagent to give a mauve/purple color.
 The emulsion test for lipids produces a milky-white color in water.
 The iodine test for starch produces a blue-black color.
UNIT 3
ENZYMES
What is enzyme?
 In 1877, German physiologist Wilhe kuhne first used the term enzyme, which comes
from Greek "leavened" or "in yeast".
 Eduard Buchner submitted his first paper on the study of yeast extracts in 1897.
 He found that sugar was fermented by yeast extracts even when there were no living
yeast
cells in the mixture.
 He named the enzyme that brought about the fermentation of sucrose zymase.
Structure and properties of enzyme
Enzymes are life‘s great facilitators.
They create the conditions needed for biochemical reactions to happen fast.
104
 The general name that chemists use for a chemical entity that increases the speed of a reaction is
a ―catalyst.‖
Enzymes are biological catalysts as they catalyze the chemical reactions inside living things.
A catalyst speeds up a chemical reaction with no effect on:
 The products formed
 The energy change
 The nature of the catalyst itself
 Course (equilibrium) of the reaction.
Nearly all biological catalysts are enzymes. They are globular proteins with a specific tertiary
shape, part of which forms an active site.
Enzymes are globular proteins with a complex 3-D structure. The shape and the chemical
environment inside the active site permit a chemical reaction to proceed more easily.
The substrates of enzymes are the reactants that are activated by the enzymes. A
substrate molecule binds with the active site to form an enzyme-substrate complex. This then
forms the products.
 An enzyme's activity decreases markedly outside its optimal temperature and pH, and many
enzymes are (permanently) denatured when exposed to excessive heat, losing their structure and
catalytic properties
 Enzyme activity can be affected by: inhibitors molecules that decrease enzyme activity and
activators molecules that increase activity.
Examples: therapeutic drugs and poisons are enzyme inhibitors
Enzyme can be used over and over, because it is unaltered by the reaction.
Enzyme are effective in small amount, of enzyme can affect a large amount of substrate.
Functions of Enzyme
 Enzymes are known to catalyze more than 5,000 biochemical reaction types.
 Other biocatalysts are catalytic RNA molecules, called ribozymes.
Enzymes' specificity comes from their unique three-dimensional structures.
 Like all catalysts, enzymes increase the reaction rate by lowering its activation energy.
Example: orotidine 5'-phosphate decarboxylase, which allows a reaction millions of
years to occur in milliseconds.
 Some enzymes are used commercially, for example, in the synthesis of antibiotics.

Some household products use enzymes to speed up chemical reactions:

Example: In biological washing powders break down protein, starch, or fat stains on
clothes, and enzymes in meat tenderizer break down proteins into smaller molecules,
making the meat easier to chew.
In order for molecules to react, they must have sufficient energy.
Activation energy (or Ea), is minimum energy needed to start off the reaction.
The reactant must ‗climb an activation energy hill‘ before anything happens.
under normal conditions, very few molecules have sufficient kinetic energy to ‗climb the
activation energy hill‘, so the reaction proceeds slowly.
105
 More reactant molecules can meet this lower energy requirement and so the reaction
proceeds more quickly.
Enzyme Nomenclature and Classification
Different enzymes are named in different ways. This includes:
 By adding ‘ase’ to part of the name of the substrate.
Example: Lipase (lipid hydrolyzing enzyme), Sucrase (sucrose hydrolyzing enzyme).
 On the basis of the reaction that they catalyze.
Example: polymerase (aids in polymerization - joining similar units together), dehydrogenase
(removal of hydrogen atoms or ions).
 On the source from which they were first identified. E.g. papayin from papaya.
 According to their site of action. E.g. intestinal protease acts on proteins in the
intestine.
 Some enzymes end with ‘in’, indicating that they are basically proteins.
Example: pepsin, trypsin, etc.
Because of the varied ways in which enzymes had been named, biologists at the Enzyme
Commission decided to produce a systematic way of naming enzymes, based on the ways
in which the enzymes act. The enzyme omissions (EC) divide enzymes into six main groups according
to the type of reaction they catalyzed

Class Reaction catalysed Examples

1. Oxidoreductases Transfer of hydrogen and oxygen atoms or Dehydrogenases,
electrons from one substrate to another Oxidases
2. Transferases Transfer of a specific group (a phosphate or Transaminase,
methyl, etc.) from one substrate to another Kinases
3. Hydrolases Hydrolysis of a substrate Esterases,
Digestive enzymes
4. Lyases Nonhydrolytic removal of a group or addition of Decarboxylases,
a group to a substrate Aldolases
5. Isomerases Change of the molecular form of the substrate Phosphohexoisomerase,
Fumerase
6. Ligases Joining of two molecules by the formation of Citric acid synthetase
(Synthetases) new bonds

International Union of Biochemistry (1984) classified Enzyme. This enzyme commission assigned
each enzyme name and four distinguishing number.

Example: in Enzyme EC 3.4.11.1 is:

EC stands for Enzyme Commission
The first number shows to which of the six main classes the enzyme
belongs
The second figure indicates a subclass
The third figure gives a sub-subclass
The fourth figure is the serial number of the enzyme in its sub subclass.
A Hydrolase - all the enzymes in class 3 hydrolyse some kind of bond.
A peptidase - all the enzymes in subclass 4 of class 3 are peptidases and

106
 hydrolyse peptide bonds
An amino-peptidase - all the enzymes in sub-subclass 11 of subclass 4 are
amino-peptidases; they hydrolyse peptide bonds at the amino end of a polypeptide
chain
Leucyl-amino-peptidase - this particular amino-peptidase is number 1 of this sub
subclass

Sector Application area Benefits

Supplies of natural rennet from
Biochymosin to produce cheese.
Dairy calves livers are limited.
Lactase to produce lactose-free
Lactose-intolerant people suffer
milk
fewer cramps
Many biological stains are removed
Use of proteases, lipases and
efficiently at low temperatures
amylases in biological washing
Detergents (saving energy).
powders.
Remove food particles at lower
Use of proteases and amylases in
temperatures and require fewer.
dishwasher detergents
bleaching products to be added
Proteases to remove hair and Process is carried out much quicker
lipases to degrease animal hides. than by traditional methods.
Textiles Use of cellulase to ‗bio-polish‘ Produces a smoother and glossier
cotton fabrics. finish.
Use of cellulase to ‗bio-stone‘ The enzyme gives the ‗stone-
denim washed‘ effect much more easily
Clarifies fruit juice
Food Pectinase to process fruit juice.
Sucrose paste in the chocolate is
processing Inverase to produce liquid-
made liquid by injection of the
centre chocolates
enzyme

Amylases used in starch

Reduces the quantity of starch in the
conversion
paper and improves quality.
Pulp and Use of xylanase enzymes in pre
Produces a whiter paper.
paper bleaching the pulp.
Stickies would otherwise clog the
Use of esterases in control of
machinery and reduce the quality of
‗stickies‘ (glues introduced
the paper
during paper recycling)
Allows easy diagnosis of diabetes
Glucose oxidase in clinistix
by testing urine.
strips, tests for glucose.
Medicine Testing for high levels of these in
Liver enzymes.
the blood confirms liver damage.
Pulmozyme to treat cystic
Reduces viscosity (stickiness) of
fibrosis
mucus

107
 Streptokinase to dissolve clots Restores blood supply to area of
Pharma of heart-attack patients. heart muscle.
ceutical Production of abacavir sulphate Abacavir sulphate is an important
is controlled by enzymes anti-AIDS drug
THE TWO MODELS OF ENZYME ACTION

Both of these models suggest that the enzyme catalysis the reaction by lowering the activation
energy. However, they differ in explaining how the substrate binds to the active site of the
enzyme.

A. The lock-and-key model

√ Proposed in 1894 by a German biochemist named Fischer.

√ This model proposes that the shapes of the substrate molecules are complementary
to that of the active site, rather like the shape of a key is complementary to that of the
lock it fits.
√ Fit between the substrate and the active site of the enzyme is exact.
√ Like a Key fits into a lock very precisely Enzyme-substrate complex formed.
√ Products have a different shape from the substrate and Products are released from the
active site leaving it free for another substrate molecule.
√ The complementary substrate molecule binds with the active site of the enzyme to
form the enzyme-substrate complex.

Reactant A + Reactant B + enzyme ➞ ES complex ➞ EP complex➞Product AB + enzyme

√ The complex causes the reactants to enter a transition state in which the activation
energy of the reaction is lowered.
√ The reaction takes place and the products formed are released.
√ The lock-and-key model of enzyme action suggests that the enzyme lowers the
activation energy by providing an alternative pathway for the reaction.
√ This model sees the enzyme-substrate complex as the intermediate, which is
part of a pathway that requires less energy than the normal pathway. However,
a weakness of this
Model is that it does not explain how the intermediate reduces activation energy.
B. The induced-fit model
 Proposed in 1958 by Koshland. This model suggests that the active site and the substrate
aren‘t naturally complementary in shape, but the binding of substrate molecules produces a
conformational change in the active site. This allows the substrate and active site to bind fully.
 The conformational change also puts the substrate molecules under tension, so they enter a
‗transition state‘ and are able to react because of the lowered activation energy.
 In the transition state, bonds in the reactants are put under strain and break more
easily and rejoin with other bonds to form the products.
 Most biologists now prefer the induced-fit model over the lock and-key model:
As it explains other properties of enzymes, such as enzyme inhibition,
The rate of a chemical reaction is the rate at which reactants are converted
into products.
108
  In the case of an enzyme-controlled reaction, this is determined by how many
molecules of substrate bind with enzyme molecules to form enzyme-substrate
complexes.
 The turnover rate of the enzyme, the number of molecules of reactants that form
enzyme-substrate complexes with each molecule of an enzyme, per second.
Cofactors

 An active enzyme made from two molecules, neither of which has enzyme activity
without the other. The two parts are the apoenzyme and the cofactor.
 Apoenzyme - a protein that combines with a cofactor, to form an active enzyme.
 The protein (apoenzyme) is inactive on its own.
 Cofactor - a small non-protein particle essential for the activity of some enzymes.
 Holoenzyme - Where an active enzyme molecule comprises an apoenzyme and a
cofactor, the whole is sometimes referred to as the Holoenzyme.
 Cofactors include: coenzymes and mineral ions.
 Coenzymes are organic molecules and many are derived from vitamins.
 They bind with the enzyme to give catalytic activity
Factors affecting the functions of enzymes
The turnover rate and, therefore, the activity of the enzyme are influenced by a number of
external factors
A. Temperature
 Usually, the reaction rate increases with temperature, but with enzyme reactions, a point is
reached when the reaction rate decreases with increasing temperature.
 When the temperature is raised, particles are given more kinetic energy.
 This has two main effects: ‗Free‘ particles move around more quickly.
 This increases the probability that a substrate particle will collide with an enzyme
molecule.
 Particles within a molecule vibrate more energetically.
 This puts strain on the bonds that hold the atoms in place.
 Bonds begin to break and, in the case of an enzyme, the shape of the molecule
and the active site in particular, begin to change. The enzyme begins to lose its
tertiary structure and denature.
 The activity of an enzyme at a given temperature is a balance between these
two effects.
 If the raised temperature results in little denaturation but a greatly increased
number of collisions, the activity of the enzyme will increase.
 If the higher temperature causes significant denaturation then, despite the extra
collisions, the activity of the enzyme will probably decrease.
 Above the optimum temperature, the enzyme denatures very quickly to the
point at which the shape of the active site has changed so much that an enzyme-
109
 substrate complex cannot form. At this point the reaction rate is zero.
 For most enzymes the optimum temperature is about 30-38°C
 Many are a lot lower, cold water fish will die at 30°C because their enzymes
denature
 A few bacteria have enzymes that can withstand very high temperatures up to
100°C.
B. The PH
 PH also affects the rate of enzyme-substrate complexes.
 As the PH is decreased or increased, the nature of the various acid and amine groups
on side chains is altered with resulting changes in the overall shape structure of the
enzyme.
 The majority of enzymes in most mammals function most efficiently within the pH range
6.0 - 8.0, although the optimum PH of pepsin (an enzyme found in the stomach) is
between PH 1.0 and PH 3.0.
 Significant changes in pH can affect an enzyme molecule by:
 Breaking ionic bonds that hold the tertiary structure in place; this leads to
denaturation of the enzyme molecule.
 Altering the charge on some of the amino acids that form the active site; this
makes it more difficult for substrate molecules to bind. Most enzymes have an
optimum pH of around 7 (neutral). However, some prefer acidic or basic conditions
C. Substrate concentration

 The activity of an enzyme depends on the number of substrate molecules per second
that bind to form enzyme-substrate complexes (Turnover rate).
 A small number of substrate molecules mean few collisions and so only a few
enzyme-substrate complexes form.
 Increasing the concentration of the substrate means more collisions and more enzyme-
substrate complexes. So, the overall rate of reaction is increased.
 Eventually, because of the high substrate concentration, each enzyme molecule could
be working at maximum turnover - that is, each active site is binding with substrate
molecules all the time and there is no ‗spare capacity‘ in the system.
 Increasing the substrate concentration beyond this point will have no effect on the
activity of the enzyme because all the active sites are occupied all the time.
D. Enzyme concentration
 Assuming a constant large supply of substrate molecules, each enzyme molecule will
work at maximum turnover. Therefore, the reaction rate will be directly
proportional to the number of enzyme molecules - the concentration of the enzyme.
 Increasing the concentration will increase the reaction rate. However, increasing
the concentration of the enzyme will not increase the activity of the enzyme. Each
enzyme molecule will be working at maximum turnover, so the activity of the enzyme
is likely to remain constant.
110
E. Enzyme inhibitors
Enzyme inhibitors are molecules that interact in certain ways with the enzyme to prevent it from
functioning in a normal manner.
They can alter the catalytic action of the enzyme and consequently slow down, or even
top catalysis. Poisons and drugs are examples of enzyme inhibitors.
1. Irreversible Inhibitors
Form strong (permanent) covalent bonds with an enzyme. The structure of the
enzyme is modified to the degree that it ceases to work.
These inhibitors may act at, near, or remote from the active site. Consequently, they
may not be displaced by the addition of excess substrate.
Since many enzymes contain sulfhydral (-SH), alcohol, or acid groups as part of their
active sites, any chemical which can react with them acts as an irreversible inhibitor.
Heavy metals such as Ag+, Hg2+, Pb2+ have strong affinities for -SH groups.
Nerve gases such as di isopropylfluorophosphate (DFP) inhibit the active site of
acetylcholine esterase by reacting with the hydroxyl group of serine to make an ester.
Oxalic and citric acid inhibit blood clotting by forming complexes with calcium
ions necessary for the enzyme metal ion activator.
2. Reversible inhibitors
 Reversible inhibitors bind to enzymes only weakly (temporarly) and the bond that holds them
breaks easily releasing the inhibitor and allows the enzyme to become active again.
 There are two main kinds of reversible inhibitors:
 Competitive inhibitors and
 non-competitive inhibitors
A. Competitive inhibitors
 A competitive inhibitor could be any compound that closely resembles the chemical
structure and molecular geometry of the substrate.
 The inhibitor competes for the same active site with the substrate molecule. A
competitive inhibition is usually temporary and reversible.
 Therefore, the level of inhibition depends upon the relative concentrations of the
substrate and inhibitor.
Methanol poisoning occurs because methanol is oxidized to formaldehyde and formic acid which
attack the optic nerve causing blindness. Ethanol is given as an antidote for methanol poisoning
because ethanol competitively inhibits the oxidation of methanol. Ethanol is oxidized in
preference to methanol and consequently, the oxidation of methanol is slowed down so that the toxic
by-products do not have a chance to accumulate.
B. Noncompetitive Inhibitors:

Non-competitive (allosteric) inhibitors bind to a region away from the active site, producing
a conformational change in the enzyme that prevents the substrate from binding; the extent
of the inhibition is independent of the substrate concentration.
Allosteric inhibition can control metabolic pathways.

The final product of a series of reactions inhibits the enzyme controlling the first reaction in
the series; this is also known as end-product inhibitio

111
 Application of the Enzyme Inhibitors

 Enzyme inhibitors play important roles in pharmaceutical and biochemical industries.

 They can be widely used in metabolic control, as metabolic poisons and medicines.
 For example, many poisons work by inhibiting the action of enzymes involved in
metabolic processes, which defends a plant or animal against predators.
 In addition, some enzyme inhibitors can be used as drugs in the treatment of various
diseases.
 Some antimicrobial drugs are enzyme inhibitors that deactivate the enzymes that
are needed for the survival of pathogens.
UNIT 4
CELL BIOLOGY
4.1 Cell theory
 It may seem obvious now that we, and other living things, are made up of cells.
 Prior to the 1600s, however, it wasn‘t obvious at all, for the simple reason that no one
had ever seen a cell up close and personal.
 To distinguish individual cells in a piece of tissue or individual bacteria in a sample of
liquid required the development of relatively high-powered microscopes, instruments
used for magnifying objects otherwise too small to be seen.
 The first person to observe cells as microscopic structures was the British scientist
Robert Hooke. In fact, he was the person who gave cells their name.
 In his book Micrographia, he used the term cell to refer to the box-like structures he
saw when he looked at dead cork tissue through a simple microscope.
112
 JOIN ON Telegram @QesemAcademy
 He chose cell as the name because these boxes reminded him of the cells of a
monastery, the simple rooms in which monks slept.
 The cells that Hooke observed, however, were in dead tissue, and were in fact cell
walls left behind after the death of the real cells.
 The first person to observe living, moving cells was Anton van Leeuwenhoek, a
Dutch shopkeeper and crafter of lenses.
 In the 1670s, inspired by Hooke‘s book, he began to build his own, more
powerful microscopes with these; he was able to observe living single-celled
organisms—such as bacteria—and sperm cells, which he collectively called
animalcules
A timeline for the development of the cell theory
Robert Hooke (1665)
 He makes drawings of cork and sees tiny structures that he calls ‗cells‘. Also, Hooke saw only
dead cells.
Anton van Leeuwenhoek (1674)
 Sees living, moving unicellular organisms (protoctistans) in a drop of water.
 He is using a simple microscope with only one lens.
 However, van Leeuwenhoek is very skilled at grinding lenses and so his microscope can
achieve magnifications of 300×. He calls the moving organisms ‗animalcules‘.
 He also sees bacteria (from his teeth), which he also calls ‗tiny animalcules‘.
Rene Dutrochet (1824)
 The French biologist Dutrochet states the cell theory by recognizing that all organisms are
made of cells.
 He also discovers:
• The stomata in the epidermis of leaves
• The process of osmosis
• Chlorophyll is needed for photosynthesis to occur
• Respiration occurs in both animals and plants
Matthias Schleiden and Theodor Schwann (1839)
 Matthias Schleiden and Theodor Schwann put forward the first clearly stated cell theory.
 the cell is the unit of structure, physiology and organization in living things
 the cell retains a dual existence as a distinct entity, and a ‘building block’ in the formation of
organisms
 Cells form by free-cell formation (spontaneous generation)
 Although we still accept the first two ideas, the final idea of spontaneous generation
has now been proved false.
Rudolf Virchow (1858)
Rudolf Virchow, a German doctor who develops many surgical techniques and promotes several
fields of modern medicine, declares that: ‗Omnis cellula e cellula‘, which means that a cell can only arise
from another cell like it.(cell come from preexisting cell)
With this Virchow completes the first accepted version of the cell theory:
 All organisms are made up of one or more cells
 All cells come from pre-existing cells
 The cell is the unit of structure, physiology and organization in living things
 The cell retains a dual existence as a distinct entity and a building block in the
construction of organisms.
Modern cell theory
113
 All known living things are made up of cells
 The cell is a structural and functional unit of all living thing
 All cells come from pre-existing cells by division (no spontaneous generation of cells).
 Cells contain hereditary information which is passed from cell to cell at cell division.
 All cells have basically the same chemical composition
 All energy flow (the metabolism and biochemistry of life) occurs within cells
Cell size
 Most cells fall within a much narrower range of sizes than the unfertilized ostrich’s egg cell and
the smallest bacterium.
 The length of most animal and plant cells fall within a range of 10 μm to 100 μm.
 Most bacteria are about one-tenth of this length.
 The animal cell may be just ten times as long - but it is also ten times as wide and ten times as
deep. This makes it 1000 times bigger than the bacterium!
What units shall we measure cells in?
 It all depends on which cells, but first we should understand which units are available
and which ones would be convenient to use.
 Example: to size of RBC measure cells in metres, it would be approximately
0.000007m.
Counting all these zeros is very confusing, so we use other, smaller units to
measure the size of cells and molecules.
 There are three smaller units commonly used:
Millimeters (mm) - 1/1000 of m
micrometres (μm) - 1/1000 of a millimeter, and 1/1 000 000 m
Nanometres (nm) - 1/1000 of a micrometer,
1/1 000 000 of a millimeter, and 1/1000 000 000 of a meter.
We can convert the units from one to another as shown below:
Calibrating the eyepiece graticule
A stage micrometer - this is really a microscope slide with a very precise scale etched onto it.
An eyepiece graticule - this is a piece of plastic with a less accurate scale than the graticule that fits
inside the eyepiece of the microscope
Types of cell
There are two main types of cells: prokaryotic cells and eukaryotic cells; the table shows the
differences between them

Feature Prokaryotic cells Eukaryotic cells

Size 1-10 μm 10-100 μm
Nucleus No membrane-bound nucleus Nucleus surrounded by nuclear envelope
DNA In a continuous loop ,not associated Linear DNA associated with histone
with protein to form chromosomes proteins in chromosomes
Mitochondria Absent Present
Absent (but some prokaryotic cells
Chloroplasts contain a kind of chlorophyll and Present in some cells (some plant cells and
some algal cells)
can photosynthesise)
Present, but smaller than Present, but larger than in prokaryotic
Ribosome
in eukaryotic cells (70S) cells (80S)
114
 •Always present • Present in plant cells, algal cells and
Cell wall fungal cells
Not made from cellulose (often made • Cellulose in plant cells, various
from peptidoglycan) materials in other cells

Parts of the cell and their functions

Cell membrane /plasma membrane/
The membrane that surrounds and encloses a cell is sometimes called the cell surface
membrane, but biologists now refer to it as most the plasma membrane.
Cell membrane plays a crucial role:
 To enclose organelles and other contents in cytoplasm.
 To protect the cell.
 To allow substances into and out of the cell
To have metabolic reactions on its surface:
 Cell signaling; various molecules in the membrane allow the cell to be
recognized by hormones and the immune system (in animals) and (in
plants) growth regulator substances, such as auxins.
 The plasma membrane clearly has a vital role in isolating the cell from its
environment, whilst allowing necessary exchanges with that environment.
Models of plasma membrane
A. The Davson-Danielli model / sandwich model of cell membrane/
In 1935, Davson and Danielli knew that both proteins and phospholipids were involved in the
structure of plasma membranes. Without any direct observational evidence to assist the
Davson and Danielli suggested a kind of ‗sandwich‘ of protein and phospholipid. The protein
was to form the ‗bread‘ of the sandwich with the phospholipid forming the ‗filling‘.
In 1954 they proposed a revised model in which they included protein-lined pores.
B. The fluid mosaic model of cell membrane
 In 1972, Singer and Nicholson suggested that the arrangement of proteins and phospholipid
bilayer was not static, but was fluid and constantly changing.
 Our current idea of membrane structure still assumes this fluid-mosaic nature.
The key features of the model as we currently understand it are:
 The phospholipid bilayer as the basis for the membrane
 Integral proteins (also known as intrinsic proteins and transmembrane proteins) that
span the membrane.
 Some of these proteins play an important role in moving substances across the membrane.
There are two main types of these transport proteins:
1. Channel proteins - these proteins have a channel through them along which a specific ion
can pass; there are different channel proteins for different ions.
2. Carrier proteins - these proteins act in a more sophisticated way to move
larger molecules through the membrane by facilitated diffusion or active transport;
the ones involved in active transport are often referred to as pumps.
115
  Peripheral proteins (also known as extrinsic proteins) that span only one layer (or sometimes
less) of the membrane. They have a range of functions; some are enzymes, others
anchor integral proteins to the cytoskeleton.
 Glycoproteins and Glycolipid - protein and lipid molecules that have carbohydrate
chains attached to them and often serve as signals to other cells. They also act as
receptor sites for hormones and drugs. The carbohydrate component of each can be
cell specific and so allow identification of the cell by the immune system.
 Cholesterol - reduces the fluidity of the membrane.
How do substances cross the plasma membrane?

The Passage of substance across the plasma membrane occurs in two ways

 Passive process: rely only on the kinetic energy of the particles and the concentration
gradients
 Active process: require energy from the cell‘s metabolism in the form of ATP

1. Passive process
A. Simple diffusion
 To pass through the plasma membrane by simple diffusion particles must be:
- Small sized
- Lipid soluble and
- Non-charged
 Small, hydrophobic, or fat-soluble molecules, such as oxygen, cross the cell membrane
quite readily because of "fat dissolving fat" interaction.
 Small, uncharged, hydrophilic, or water-soluble molecules, such as water and carbon
dioxide, would also be able to cross the cell membrane although there is no "fat
dissolving fat interaction.
 When particles diffuse across a plasma membrane, there must be a concentration
difference between the two sides of the membrane (a concentration gradient) to drive the
process.
 As diffusion proceeds, the high concentration will decrease and the low concentration
will increase until the two concentrations are the same
The rate at which diffusion across a membrane takes place is influenced by:
 The concentration gradient - a bigger difference in concentration results in
faster diffusion than a smaller gradient
 Distance - a shorter distance results in faster diffusion
 The surface area of the membrane - clearly if there is more membrane
where diffusion can take place, diffusion will happen faster
 Temperature. Diffusion occurs faster at higher temperatures because the

116
 particles have more kinetic energy and so move faster.
B. Facilitated diffusion
 Facilitated diffusion is essentially the same process as diffusion but it allows large,
hydrophilic molecules to cross the cell membrane.
 Note in both cases that the particles are moving from a high concentration to a
low concentration (as with simple diffusion).
 however, also note that whilst the ions can simply move straight through the ion pore
of a channel protein, but the carrier protein must undergo a conformational change
(change in Shape) to move particles through the membrane
 The rate of facilitated diffusion depends largely on the number of protein carriers
available; when all proteins carriers are bound "saturation" occurs and the diffusion rate
stabilizes.
C. Osmosis

 Osmosis is the movement of water from a system with a high (less negative) water
potential to one with a lower (more negative) water potential, across a partially
permeable membrane.
 Water moves across a partially permeable membrane. It is the diffusion of
water.
 The symbol for water potential is the Greek letter Ψ (psi). Water potential is
measured in units of pressure: Pa, kPa or MPa.
 Pure, liquid water has a higher water potential than any other system. Ψ (pure water) = 0
Pa
 All other systems (cells, solutions, and suspensions) have a water potential that is
lower than that of water which is negative value.
 The rate at which osmosis proceeds is influenced by the same factors as simple
diffusion:
Surface area of the membrane
Difference in water potential
Distance the molecules must travel
 When comparing the water potential of a solution to that of a cell, we could describe it
as:
 Isotonic - having the same water potential as the cell
 Hypertonic - having a lower (more negative) water potential than the cell
 Hypotonic - having a higher (less negative) water potential than the cell
Animal cells
 In the hypertonic solution, the cells lose water by osmosis and shrink. This is called
Crenation
 In the hypotonic solution, the cells gain water by osmosis and swell.
 The pressure will eventually burst the weak plasma membrane: this is called haemolysis.
 There is no change in the isotonic solution.
Plant cells
117
 In the hypertonic solution:
 The cytoplasm of the cells loses water by osmosis and shrinks. Because of this, there is
no pressure from the cytoplasm on the cell wall.
 The cell is said to be flaccid. If the cytoplasm shrinks too much, it loses contact
with the cell wall and we say the cell has been plasmolysed.
In the hypotonic solution,
The cells gain water by osmosis and swell. However, because of the cell wall, the cell
cannot become much larger. Plant cells in this condition are turgid.
Isotonic solution; There is no change as same amount enter and leave the cell.
Turgidity is important in supporting young, non-woody plant stems. If the plant is kept well
watered, the cells will remain turgid.
The turgid cells will press against each other and this pressure will keep the plant upright. If
the plant is not watered, the cells will be plasmolysed and become flaccid.
They will no longer press against each other and the support will be lost. The plant will wilt.
2. Active process

A. Active transport

 Substance must be moved against the concentration gradient

 From low concentration to high concentration which need metabolic energy (ATP)
 The protein used to actively transport substance across the plasma membrane is called
pumps.

B. Endocytosis

 large particles are engulfed by the cell

 during this movement parts of the plasma membrane surround the particles to form
vesicles
 they can occur in a number of ways
 phagocytosis
 pinocytosis
 receptor-mediated endocytosis

i. Phagocytosis:

 also called cell eating

 large solid particles are ingested into the cell by forming pseudopodia(extension of
plasma membrane)
 then they can form internal vesicles which is then moved inside the cell

ii. Pinocytosis

 also called cell drinking

 ingestion of small liquid particles
 not require the formation of pseudopodia

iii. Receptor-mediated endocytosis

118
  membrane in folds to form vesicles when particles have bounded to specific
receptor on plasma membrane
 the binding stimulate the in folding of plasma membrane

C. Exocytosis

 in this process substance are moved from inside to outside of the cell
 it is effectively, the reverse of endocytosis
 it is the process by which enzymes and hormones are secreted
 also ATP is used to alter the configuration of the membrane

Other organelles of the cell

Nucleus

It has several components

 Nuclear envelop: -the double membrane that surround the nucleus which contain
nuclear pores allows the passage of some molecules between the nucleus and
cytoplasm.
 Nucleolus: - an organelles with in the nucleus, is not membrane bounded
 Its function is to synthesis the components of ribosomes
 Chromatin: - consists of DNA molecules bound with protein called histones
 During the cell division the chromatin condenses in distinct recognizable
structures called chromosomes

Mitochondria

 Are the site for most of the reaction of aerobic respiration

 They are surrounded by double membrane
 The inner membrane is folded in to cristae to increase the surface area for reaction of
respiration and for electron transport system.
 Some of the reaction of aerobic respiration take place in the fluid matrix

Ribosomes

 Is the site for protein synthesis

 They are found free in cytoplasm and also in membrane system of endoplasmic
reticulum
 Forming rough endoplasmic reticulum
 Each ribosomes comprises two sub units that are made from RNA and protein

Endoplasmic reticulum (ER)

 Membrane system found throughout cytoplasm of eukaryotic cells

 They are two main types

119
  Rough ER –has ribosomes on its surface and responsible for manufacture and
transport of protein
 Rough ER is extensive in cells that manufacture a lot of protein
such as cells that manufacture enzymes i.e. lumen of intestine
 Smooth ER-has no ribosomes
 But concerned with the synthesis of lipids
 Carbohydrate metabolism and detoxification

Golgi apparatus (Golgi body)

 Consists of number of flattened membrane bound sacs in which protein are modified
 Modification acts as a ‗tag‘, which determines the final distinction of the molecules
 Think of Golgi body as cellular post office that labels, pack and then distribute molecules
 Many of the modified molecules are released from the Golgi apparatus in vesicles to be
carried to other parts of the cell or to the plasma membrane to pass out of the cell by
exocytosis to be used elsewhere. Some vesicles form the lysosomes.

Lysosomes

They contain digestive enzymes that break down cellular wastes and debris.

 Has no specialized internal structures and surrounded by single membrane

 They are abundant in phagocytic white blood cell that digest foreign cells that have been
engulfed

Organelles in plant cells

Cell wall

 Formed from cellulose fibers, which freely permeable to substance and gives both
strength and elasticity for plant cells

Vacuole

 Fluid filed sac that store range of solutes in plants

 Maintain turgidity or turgor of the cell

Chloroplast

 Surrounded by double membrane

 Membranous region called Grana each of which is stack of thylakoids where the light
dependent reaction occurs.
 Fluid stroma –where light-independent reaction occur.

What is cell fractionation?

120
  Is a technique used to study different organelles of the cell
 The technique is based on the masses of the organelles and their sizes.
 They separate the components of a cell by centrifugation.
 When the mixture of the organelles is spun in a centrifuge, the various types settle out at
different speed of spinning
 The large nucleus require relatively low centrifuge speed to make it settle out
 Much smaller ribosomes require much higher spinning speed to settle at the bottom of
spun.

UNIT FIVE
ENERGY TRANSFORMATION
5.1 Respiration
Respiration- is the metabolic process which produces cellular energy (ATP) inside a cell from biological
molecules (Food).
There are two types of respiration
Aerobic respiration: - cellular energy production from food (Glucose) in the presence of oxygen.
Anaerobic respiration: - cellular energy production from food (Glucose) without oxygen.
What ATP molecule?
ATP an abbreviation which means Adenosine Tri-Phosphate
 ATP is a nucleotide
All nucleotides composed of:
- Nitrogen base
- Pentose sugar
- Phosphate group
One ATP molecule is composed of:
 Nitrogenous base (contains adenine)
 1- pentose sugar (Ribulose)
 3- phosphate group
ATP is sometimes described as a phosphorylated nucleotide, it is a nucleotide formed by the addition of
phosphate group.
Phosphorylation means addition of phosphate group to a molecule.
ATP is adenine nucleotide with two extra phosphate groups.
 Adding the extra phosphates requires energy, particularly when the third phosphate is added.
As a result, energy is stored in the ATP molecule and when the bonds that hold this third
phosphate are broken, the energy is released again. When the third phosphate is removed
from ATP.
ATP-------------------------------> ADP + Pi + Energy
How is ATP adapted to its role as an energy transfer molecule in cells?
 The energy from sunlight or glucose cannot directly used to drive available cellular
process
rather used to produce ATP. We say that it is coupled processes as the process takes
place simultaneously at the same time.
 ATP is adapted to its role because of the following:-
 It releases energy in small amount that matches biological process of the cell.
 It releases energy only in single step only, Hydrolysis.
 It able to move around the cell easily, but not escape from the cell

121
  The following major process requires energy from ATP:
- Synthesis of macromolecules E.g. Protein, polysaccharides
- Active transport across plasma membrane
- Muscle contraction
- Conduction of nerve impulses
- Initial step of respiration, Glycolysis
How ATP is produced in the cell?
Almost all ATP produced in the cell is the same way:
 Involving ADP and Pi joining to form ATP that requires input of energy
 it involves enzyme ATP synthase (in chloroplast and mitochondrial membrane)
ADP+Pi ATP + H2O
How ATP synthase work?
1. When rotor spin by hydrogen ion passing through it.
2. Energy of spinning activate catalytic knob that converts ADP and Pi to
ATP. Compare and contrast aerobic and anaerobic respiration.
How ATP produced in respiration?
Aerobic pathway
 usually takes place in higher animals
 Occur in mitochondria and involves oxygen
 Involves Glycolysis, Kreb cycle and Electron transport chain
 Generate more ATP per oxidation of single glucose molecule
 End with water and carbon dioxide
Anaerobic pathway
 Usually takes place in microorganisms.
 Occur in cytoplasm and no oxygen requirement.
 Only involves Glycolysis
 Generate two ATP oxidation of glucose molecule
 Ends with different end products E.g. alcohol, CO2, and lactic acid.
How is ATP produced in aerobic respiration?
A. Substrate level phosphorylation (SLP)
 Is catalyzed by enzyme, but not ATP synthase.
 It produces small amount of ATP produced by aerobic respiration (10%).
 It can takes place in cytoplasma and mitochondrial matrix
 Example Phosphoenol pyruvate (PEP) is a substrate that able to transfer attached
phosphate group directly to ADP, Phosphorylation.

122
 E.g. ATP produced in glycolysis and Kreb cycle
B. Oxidative phosphorylation (OLP)

 Is an oxygen dependent production of ATP, phosphorylation.

 It produces about 90% of ATP produced by aerobic respiration.
 The process is catalyzed by enzyme that is based on proton spinning through rotor spin of ATP
synthase.
 Occur in mitochondrial inner membrane
E.g. Electron transport chain and chemiosmosis
How are hydrogen ions transferred from glucose to ATP synthase?
 Two molecules are important in this transfer process NAD (nicotine Adenine Dinucleotide)
 FAD (Flavin Adenine Dinucleotide)
 They are coenzymes and capable of accepting hydrogen ions and get reduced.
That is written as NADH (red.NAD) and FADH2 (red.FAD.)
 They can release their hydrogen ion and oxidized where hydrogen ion used in rotor
spin of ATP synthase.
Redox (coupled) reaction; is state when both oxidation and reduction reaction
happen together simultaneously. This means when one compound loss an
electron another compound accepts.

 A compound is get oxidized when it loses hydrogen, loss electron, gain oxygen
and increases in oxidation number and reduced when compound gain hydrogen, gain
electron, loss oxygen and decreases in oxidation number
Stages of aerobic respiration of glucose
There are four stages in the aerobic respiration of glucose. These are:
123
  Glycolysis
 Link reaction
 Krebs cycle
 Electron transport and chemiosmosis
A. Glycolysis
 The first stage glycolysis, takes place in the cytoplasm.
 It does not take place inside the mitochondria because the glucose molecule cannot diffuse
through the mitochondrial membranes ‗
 It is medium-sized molecule
 not lipid soluble
 No carrier proteins
 Glycolysis means glucose splitting, glucose converted into a smaller molecule containing only
three carbon atoms – pyruvate.
 Pyruvate can enter the mitochondria and so all the other stages take place inside the
mitochondrion.
C6H12O6-----------------------------> 2 C3H6O3
 The released hydrogen ions during glycolysis collected by NAD (Reduced NAD).
The main processes in glycolysis
 2- ATP is used to ‗phosphorylate 1- glucose molecule.
 Glucose converts to Fructose 1,6-bisphosphate(6C sugar)
 Fructose 1,6-bisphosphate is split into 2- molecules of the glyceraldehyde 3- phosphate (GP) 3C
sugar
 2-glyceraldehyde 3- phosphate then converted into pyruvate, by releasing small amount of
energy, 2- phosphate and 2- hydrogen ions
 Totally 4- ATP produced ( production of 2- ATP by substrate level phosphorylation) and 2-
ATP produced from 2- ADP and 2- Pi
 2- Hydrogen ions collected by NADH2- reduced NAD formed.
 2- Pyruvate molecule is also formed.
Glucose + 2 ATP --------------------------> 2 Pyruvate + 4 ATP + 2 reduced NAD
B. Link reaction
√ These stages of respiration take place in the fluid matrix of the mitochondrion.
√ The output of glycolysis i,e. pyruvate becomes input in the link reaction.
√ 2- Pyruvate reacts with 2- molecule of Coenzyme-A (CoA), and forms 2- molecule of acetyl
coenzyme A(acetyl CoA), by undergoing decarboxylation and dehydrogenation.
√ dehydrogenation;- removing hydrogen from a molecule in the reaction: hydrogen is lost and
reduced NAD is formed;
√ Decarboxylation; - removing carbon from a molecule. a carbon atom is lost to form carbon
dioxide;
√ coenzyme A coenzyme derived from pantothenic acid needed for respiration
√ acetyl coenzyme A produced by the reaction of coenzyme A with a molecule of pyruvate
C. Krebs cycle
 The output of link reaction becomes the input in Krebs cycle
 It takes place in the fluid matrix of mitochondria.
 It starts and ends with Oxaloacetate
124
  In this cycle energy are released from the system.
What happens in the Krebs cycle?
Two-carbon group acetyl-coA reacts with the four-carbon compound oxaloacetate to form
a six-carbon compound called citrate.
Citrate decarboxylated to form a five-carbon compound and CO2
Five-carbon compound further decarboxylated to form a four-carbon compound and
CO2, ATP molecule by SLP
Four-carbon compound regenerate the original four-carbon compound (oxaloacetate)
and begin reacting with another molecule of acetyl CoA.

D. ETC (Electron Transport Chain) and Chemiosmosis

Take place in the inner membranes of mitochondria (cristae)
Electron transport chain and chemiosmosis make up the process of oxidative
phosphorylation.
 the hydrogen atoms carried by reduced NAD and reduced FAD are released and split into protons
(hydrogen ions) and electrons
Reduced NAD----------------------------> NAD + H+ + e-

Reduced FAD ----------------------------> FAD + H++ e-

 The electrons pass along a series of electron carriers that form the transport chain; they lose
energy as they pass from one carrier to the next carrier.
 three of the electron carriers are proton pumps that move protons from the matrix of the
mitochondrion to the inter-membrane space
 as the electrons are transferred through these three proton pumps, the energy they lose powers the
pumps which move the protons into the inter-membrane space
 Electrons from reduced NAD make this happen at all three pumps.
 The names of electron carrier or proton pumps electron transport chain are:
• reduced NAD dehydrogenase
• Ubiquinone
• Cytochromes complex
 At the end of the electron transport chain, the electrons combine with protons and with oxygen to
form molecules of water. Because of this, oxygen is known as the terminal electron acceptor.
 Reduced NAD is dehydrogenated by the three electron carrier (Reduced NAD dehydrogenase,
ubiquinone, and cytochrome complex).
 Reduced FAD is dehydrogenated by two electron carrier ubiquinone and cytochrome complex
 When 1- reduced NAD is oxidized able to pump 6H+ from the fluid matrix to the cristae, and this
6H+ pass through the ATP-synthase enzyme which found in the cristae produces 3- ATP.
 When 1- reduced FAD is oxidized able to pump 4H+ from the fluid matrix to the cristae, and this
4H+ pass through the ATP-synthase enzyme which found in the cristae produces 2- ATP.
 Since this phosphorylation is supported by oxygen it is called Oxidative level Phosphorylation.

125
The events in the aerobic breakdown of glucose molecule
Process Location Goal Input Output(end
product)
-Glycolysis Cytoplasm Split of glucose 1 Glucose 2 Pyruvate
to pyruvate 2 NADH
4 ATPs, net 2ATPs

-Link reaction Mitochondrial Convert pyruvate 2 pyruvate 2 CO2

(Preparation for matrix to acetyl CoA 2 Acetyl CoA
citric acid cycle) 2 NADH

Mitochondrial Take Acetyl CoA 2 Acetyl CoA 4 CO2

-Citric acid cycle matrix to kreb cycle 2 ATP
(Creb cycle) 6 NADH
2 FADH2

-Electron transport Mitochondrial Use energy in 10 NADH x 3 ATPs 34 ATPs

and chemiosmotic cristae NADH and 2FADH x 2 ATPs
ATP synthesis FADH2 to create O2 H2O
gradient of H+

Respirometer:- an instrument which is used to detect (measure) the presence and the amount of oxygen
used in aerobic respiration and carbon dioxide produced.
Anaerobic pathway
 Anaerobic respiration takes place in the cytoplasm without oxygen.
 Anaerobic respiration also called alcoholic fermentation.
 If there is no oxygen present, the final reaction of oxidative phosphorylation, where
electrons and protons react with oxygen o form water, cannot take place.
 As a result, the electron transport chain comes to a halt. No protons are pumped and the
action of ATP- synthase also stops.
 If the ETC does not function, NAD is not regenerated from reduced NAD and FAD is not
regenerated from reduced FAD.
 The Krebs cycle and the link reaction come to a halt.
 But Glycolysis continues in anaerobic respiration pathway, the reduced NAD formed
during glycolysis can be regenerated under anaerobic conditions by converting the pyruvate into
another product (molecules like lactate and ethanol) in a reduction reaction.
Reduced NAD supplies the hydrogen for this reduction and becomes oxidized itself.

 Animals don‘t prefer anaerobic respiration, but during stress exercise the body faces
oxygen deficiency the body metabolites glucose without oxygen. Only 2-ATP will be produced.
 Plants undergoes anaerobic respiration during some conditions, conditions like
germination (when seeds covered by water and soil), during flooding (when plants covered by
rain water)
 Different organisms produce different fermentation end products.

126
 Animal cells produce lactate (lactic acid) when they ferment glucose.
C6H12O6 ------------------------------------------.>2C3H6O3 + 2ATP
Glucose Lactate (lactic acid)
Yeast cells produce ethanol (ethyl alcohol).
C6H12O6---------------------------------------> 2C2H5OH + 2CO2 + 2ATP
Glucose Ethanol (alcohol)

Anaerobic respiration in animals (Lactate formation during exercise):-

 During exercise, the energy demand of muscle cells increases greatly. More glucose
is respired to meet the demand.
 Sometimes, aerobic respiration is insufficient to meet this energy demand.
 Fermentation of glucose supplies the extra energy. But it also forms lactate and as
this accumulates, it leads to muscle fatigue. And only yields 2 -ATP per molecule of
glucose whereas aerobic respiration yields 36/38- ATP.
 Fermentation is a much faster process and can produce a lot of ATP quickly, over a
short period of time. The ATP used in sprints and short-distance runs is nearly all
generated anaerobically. But, due to muscle fatigue, this cannot be sustained. Longer
races must be run slower to allow aerobic respiration to produce the ATP at its
slower rate.
 Lactate, once formed, can be used to regenerate glucose or be metabolized as an
energy source by the liver. By the process called Cori cycle makes.

127
 Other organisms produce other fermentation products, many of which are made use of in
different industries.

Respiratory Intermediate Organisms Fermentation Industry product

molecule product product

Propionicbacterium Propionic acid and Swiss Cheese

CO2

Bacillus, Lactic acid Cheddar cheese,

Lactobacillus, Yogurt,
Streptococcus Soy sauce
Glucose Pyruvate
(Pyruvic acid)

Yeast Ethanol and CO2 Wine, beer

Clostridium Acetone isopropanol Nail polisher

remover,
Rubbing alcohol

Escherichia, Acetic acid Vinegar

Acetobacter

128
Respiratory substrate
What substances can be used as energy sources?
 Carbohydrates are the best respiratory substrate, especially glucose
 Lipids and proteins can also be used as respiratory substrates.
 Lipids and proteins are converted into substances that can enter the aerobic respiration
pathway at some point.
 The metabolism of proteins, lipids, and carbohydrates converges on the Krebs cycle.

129
5.2 Photosynthesis
 In photosynthesis, light energy is used in a series of reactions that lead to the synthesis of
a range of organic molecules.
 The energy that entered the system as light is now held in the organic molecules
produced (glucose). It is now chemical energy.
 When energy is changed from one form to another, energy is transduced.
 Energy transduction takes place in a series of reactions called the light-dependent
reactions.
 Light energy is absorbed by special photosensitive pigments such as chlorophyll in the
chloroplasts.
 The light-dependent reactions take place in the membranes of the thylakoids (Grana) in
the chloroplasts.
 The liquid stroma is the site of the light-independent reactions, in which carbohydrates
are synthesized.
 Chemical reactions like these take place most effectively in solution, than in membrane.
Transduced:-conversion of energy from one form to another
Light-dependent reactions:-reactions of photosynthesis dependent on light
Photosensitive pigments: -pigments having a response to light
Chlorophyll: -green pigment that absorbs blue and red light

Thylakoids: - flattened sacs inside a chloroplast on which light-dependent reactions of photosynthesis

take place
Structure of chloroplast
The chlorophyll and other photosensitive pigment molecules are arranged in special
photosystems that are linked to electron transport chains (ETCs).
The molecules of the photosystems and the electron transport chains are fixed in the
membranes of the thylakoids. This makes the process much more efficient.
There are two different photosystems, each sensitive to light of a different wavelength
and linked to a different electron transport chain.
These are called photosystem I and photosystem II.
Photosystems:-biochemical mechanism by which chlorophyll absorbs light energy
Photosystem- I: - photosystem in photosynthetic light reactions. Discovered before
photosystem II
Structure of a photosystem
A photosystem consists of a number of pigment molecules all clustered around one
particular chlorophyll molecule called the reaction center molecule
This cluster of pigment molecules is called an antenna complex. Only the reaction center
molecule is positioned next to the ETC.
The Energy absorbed by the photosensitive pigments in the photosystem is transferred to
the reaction center molecule, where the light-dependent reactions begin.
Different pigment molecules in the antenna complex can absorb different wavelengths
of light, making the whole system more efficient.
The pigments in the antenna complex include chlorophyll a, chlorophyll b, and
carotenoids.

130
 The reaction center molecule is always chlorophyll a.
The range of wavelengths each molecule absorbs is its absorption spectrum.
Chlorophyll a, chlorophyll-b and carotenoids, they absorb most wavelengths of visible
light – except 500 nm to 600 nm – green.
Plants are green because these wavelengths are reflected, not absorbed;
Reaction center molecule: -where light-dependent reactions begin
Antenna complex: - an array of protein and chlorophyll light harvesting molecules embedded in the
thylakoid membrane
Absorption spectrum: - the range of wavelengths a molecule absorbs
Action spectrum: - the photosynthesis effectiveness of each wavelength
A. The light-dependent reactions of photosynthesis.
 The light-dependent reactions use light energy to ‗drive‘ the synthesis of two molecules
 These two molecules are:
1. ATP
2. Reduced NADP
 ATP – this provides the energy for the reactions, and
 Reduced NADP – provides the hydrogen ions for a key reduction reaction. NADP is very
similar to NAD that is used in respiration and it has the same function – transporting hydrogen
ions.
 ATP and reduced NADP that will, in turn, drive the light-independent reactions.
Photosystem I and photosystem II
1. Electrons (e–) in chlorophyll molecules in photosystem II are excited by the energy in photons of
light, they become more energetic. Because of the extra energy, they escape from the chlorophyll
and pass to an electron acceptor (the primary electron acceptor).
2. The conditions created in the chloroplast cause the following reaction to occur:
2H2O -------------→ O2 + 4H+ + 4e–
Light-dependent splitting of water is called photolysis. The electrons replace those lost from the
chlorophyll molecule.
3. The primary electron acceptor passes the electrons to the next three molecules of electron carrier
in an ETC these are plastoquinone (Pq’), cytochromes complex and plastocyanin (Pc)
4. One of the molecules in the cytochromes complex is a proton (hydrogen ion) pump. The energy
they lose powers the pump which moves protons from the stroma of the chloroplast to the space
inside the thylakoid. This leads to an accumulation of protons inside the thylakoid, which drives the
chemiosmotic synthesis of ATP.
5. Electrons in chlorophyll molecules in photosystem- I, is obtained from sunlight and photosystem
–II.
6. The electrons then pass along a second ETC involving two ferredoxin (Fd) and NADP reductase.
At the end of this electron transport chain, they can react with protons (Hydrogen ions) and NADP
in the stroma of the chloroplast to form reduced NADP.

131
 √ The arrangement of molecules capable of carrying out all the reactions in the light
dependent stage of photosynthesis is called photosynthetic unit.
√ A photosynthetic unit is a unit of pigments, electron carriers, and ATP synthase
that is in the light-dependent stage of photosynthesis.
√ The ATP formed in photosystem II of light dependent reaction is called non-
cyclic photophosphorylation. This is because: the phosphorylation (formation of
ATP) is light dependent and the electrons lost from the chlorophyll are not
recycled in any way.
√ Plants sometimes generate ATP by cyclic photophosphorylation. In cyclic
photophosphorylation, only photosystem I is used. No oxygen and no reduced
NADP are formed. Electrons lost from the chlorophyll molecule are returned to it.
This process usually only happens when sugars cannot be synthesized for some
reason – such as lack of carbon dioxide.
B. The light-independent reaction of photosynthesis
 The light-independent reactions of photosynthesis occur in the stroma of the chloroplasts.
 The light independent also called the Calvin cycle. Named after Melvin Calvin, who discovered
the light independent reaction of photosynthesis. In the 1950s Melvin Calvin experimented with
unicellular algae called Chlorella by exposing them to radioactive carbon dioxide
The main stages of the light-independent reactions are:
 Carbon dioxide reacts with ribulose bisphosphate (RuBP) – a 5C- compound in the
stroma; the reaction is catalyzed by the enzyme called Rubisco.
 Two molecules of the three-carbon compound glycerate phosphate (GP) are formed.
 2- GP is converted to triose phosphate (TP)–another 3C- compound formed; this is a
reduction reaction uses ATP and hydrogen ions from reduced NADP.
 Some of the TP formed is used to regenerate the RuBP (ATP is again required), whilst
some TP is used to form glucose and other useful organic compounds.
In light-independent reactions of photosynthesis:
It shows how three ‗turns of the cycle‘ result in an output of one molecule of TP.
Six turns of the cycle would give an output of two molecules of TP enough to make one
molecule of glucose.
TP can also be converted to lipids, amino acids and from these into nucleotides and all
the other organic molecules found in plants.

132
 TP is the basis for the synthesis of all organic molecules.

Factors affect the rate of photosynthesis

A. Light intensity
 Low light intensity can limit the light-dependent reactions by reducing the number of
electrons in chlorophyll molecules that are photo-excited.
 very low light intensities – respiration is still occurring and is taking in oxygen faster than
photosynthesis is producing it
 medium light intensities – photosynthesis is producing more oxygen than respiration
uses, the rate of photosynthesis increases with increasing light intensity
 very high light intensities – the rate of photosynthesis is beginning to level out, even
though the light intensity is still increasing; some other factor is probably limiting the rate
B. Carbon dioxide concentration
 CO2 concentration limits the light-independent reactions by influencing the rate of the
initial reaction with RuBP.
 At very low concentrations of carbon dioxide, little photosynthesis takes place, although
respiration is still using up oxygen.
 As the carbon dioxide concentration increases, the rate of photosynthesis increases too.
 If the concentration of CO2 increases continuously, no more increment on the rate of the
reaction, because Rubisco do not have spare capacity.
C. Temperature
 Temperature can limit the rate of photosynthesis by affecting enzyme action
 E.g. ATP-synthase (light-dependent reactions) and Rubisco (light-independent reactions).
 Many of the reactions in both the light-dependent stage and the light-independent stage
are controlled by enzymes, which are affected by temperature.
 Once the temperature exceeds the optimum, the enzyme denatures and the rate of
photosynthesis decreases rapidly.
Other ways of photosynthesizing
1. C3- photosynthesis and photorespiration
 The photosynthesis which takes place in temperate plants (temperate environments), such
as those found in Europe,
 The plants called C3 plants, plants which grow in low light intensity and low water.

133
 The photosynthesis is called C3 photosynthesis– because the first compound formed in
the light-independent reactions (Calvin cycle) is GP, which contains three carbon atoms.
 C3 plants have leaves that are adapted to this method of photosynthesis.
 The leaves structure:
Broad
Palisade cells arranged on the upper surface
Smaller number of stomata
Stomata found in the lower surface
 These leaves are generally broad, to catch as much sunlight as possible. The cells that
contain most chloroplasts (the palisade cells) are nearest the upper surface of the leaf to absorb as
much light as possible. The stomata are mainly on the lower surface, to minimize water loss.
 During the day, the stomata are open for most of the time to allow the entry of carbon
dioxide, but they can be closed if the water loss is too great on a hot day.
 To prevent water lose the stomata closes and this leads to CO2 shortage.
 When the concentration of CO2 falls and the enzyme Rubisco starts to behave in an
unusual way. Rubisco binds with oxygen, instead of CO2. This means that RuBP is oxidized to 1-
GP (not 2 GP) and a molecule of phosphoglycolate.
 Also, carbon dioxide is produced in the process. The processes called photorespiration
because it involves oxidation of carbon.
 Rubisco function unusually, most enzymes catalyze on types of reaction.
 The 1 GP formed in photorespiration can re-enter the Calvin cycle, but the
phosphoglycolate must be converted into GP for use in the Calvin cycle by a complex series of
reactions. Phosphoglycolate can‘t join the Calvin cycle directly.
 To change phosphoglycolate in to GP (Glycerate phosphate) the reactions involves three
different organelles chloroplast, peroxisome, and a mitochondrion.

134
  Photorespiration reduces the efficiency of photosynthesis for several reasons, including:
the carbon is oxidized, which is the reverse of photosynthesis
The RuBP must be resynthesized and the phosphoglycolate removed
ATP is used in the resynthesize of RuBP
2. C4 photosynthesis
 The photosynthesis which carried by plants that grow in tropical areas like
Ethiopia (such as maize, crabgrass, sorghum, and sugarcane)
- No photorespiration in C4 plants.
 The first compound formed in the light-independent reactions is a C4 compound
called oxaloacetate.
 The light-dependent reactions are the same as in the C3 plants, but there is a
difference in how glucose is synthesized in the light-independent reactions.
 The leaves of C4-plants have special features or adaptation
The chloroplast don‘t contain thylakoid
Mesophyll cells carry the light dependent reaction
 The cells of the bundle sheath contains chloroplasts, but have no thylakoids
means that the light-dependent reactions cannot occur here and so oxygen is not produced
in these chloroplasts. This helps to prevent photorespiration and allows only the Calvin
cycle to take place in these cells.
 The light-dependent reactions in the C4 pathway take place in the mesophyll
cells, which have chloroplasts with thylakoids. But they do not have the enzymes to
catalyze the reactions of the Calvin cycle.
The main process in C4- photosynthesis:
1. Carbon dioxide reacts with a C3 compound called PEP (Phosphoenolpyruvic acid) to form the C4
compound oxaloacetate. This is catalyzed by the enzyme PEP carboxylase (PEPC)
PEP Carboxylase

CO2 + PEP (3C) ----------------------------------> Oxaloacetate (4C)

2. Oxaloacetate is converted into another C4 compound called malate, which then passes from the
mesophyll cell into a bundle sheath cell.
Oxaloacetate (4C) -----------------------------> Malate (4C) + H+
3. Malate is converted to pyruvate in the bundle sheath cell with the release of a molecule of carbon
dioxide, the CO2 which starts the reactions of the Calvin cycle by binding with RuBP.
Malate (4C) -----------------------------> Pyruvate (3C) + CO2
4. The pyruvate is converted back to PEP; this reaction requires ATP
Pyruvate (3C) + 2ATP -----------------> PEP (3C)
C4 photosynthesis is most efficient in conditions of:
• Low carbon dioxide concentration
• High light intensity
• High temperature

3. CAM –Photosynthesis
 CAM- Crassulacean Acid Metabolism

135
  CAM photosynthesis – is a type of photosynthesis in which CO2is fixed at night into 4C
compound during the day the stomata closed and the carbon is fixed via the Calivin cycle.
CAM helps plants conserve water and is often characteristics of xerophytes plants.
 CAM plants are those growing in desert e.g. Cacti
 In the extreme heat, if stomata open during the day is a sure path to desiccation and death
for the plants.
 Plants open their stomata at night when temperatures fall.
 CAM photosynthesis is effective in desert plants because it separates the light-dependent
and light-independent stages in time; the leaves only open their stomata to allow the light
independent reactions to take place during the night, saving precious water.
The CAM photosynthesis cycle
1. At night, the plants open their stomata to allow in CO2, which then reacts with PEP in
mesophyll cells to form oxaloacetate, and then malate just as in the C4 pathway.
2. The malate is then stored in the vacuoles of these cells overnight.
3. During the day, the light-dependent reactions generate ATP and reduced NADP so that the
Calvin cycle can continue.
4. Malate is released from the vacuoles and is broken down to glycerate, releasing CO2 for the
reactions of the Calvin cycle.
BIOLOGY GRADE 12
UNIT 1
MICROORGANISMS
1.1. Bacteria
Types of microorganisms
Microorganism- literally means a very small (minute) organism.
-are organisms that are too small to be seen by our naked eye but can be
seen with aid of microscope.
Microorganisms can be, i. unicellular organisms that made only one cell.
ii. Multicellular organisms that have more than one cell.
Microorganisms are subject of microbiology.
Microbiology is the branch of biology that deals with microorganisms.
There are five main groups of microorganisms, each groups can be subdivided.
1. Protozoa- studied by protozoology
2. Algae - >> >> phycology.
3. Bacteria - >> >> Bacteriology
4. Fungi- >> >> Mycology.
5. Viruses- >> >> Virology.
Protozoa, Fungi and Algae
Protozoa: - are found in kingdom of protista
- Consists of unicellular organisms that lack cell wall and chloroplast.
- Can‘t makes their own food, i.e. all are heterotrophic organisms.
- Most of them are motile(able to move).
Protozoans are subdivided into four based on their locomotary structure.
i. Amaeboids;- have locomotary structure called pseudopoda or ‗false foot‘.
Pseudopoda is protrusion of cytoplasm, sometimes used for feeding through
phagocytosis.
Eg. Entamaeba hisolytica - cause amoebic dysentery
ii. Flagellates;- have flagella as locomotary structure that made of microtubules.
Eg. Gardia lambella- cause Gardiasis
136
Trypanosoma spp- causes sleeping sickness.
iii. Cilliates;- move by means of locomotary structure called Cillia which also
made of microtubules. E.g. Paramecium
iv. Sporozoa;- have no locomotary structures.
Eg. Plasmodium species.-cause malaria
Fungi :- found in kingdom mycota.
- Have cell wall that made of chitin.
- But have no chloroplast, so they can‘t make their own food.
- They are heterotrophic ---some are saprotrophic (saprobionts).
--- Some are parasitic.
The saprotrophic - release enzymes to digest dead matters or substrate on w/c they grow, and the
products of digestion are then absorbed into fungus to help it grow and reproduce.
The parasitic - live on other living things, absorbing food w/c are digested by others. Fungi- consist of
organisms from unicellular to multicellular.
Unicellular fungi:- are like yeast, candida and Tenia pedis.
Yeast (saccharomyces)- used in bread(e.g. bakery saccharomyces) and alcoholic drink (eg.
brewery saccharomyces ) making process. Candida- is yeast like fungi that causes thrush in humans
as opportunistic infection, called Candidiasis.
Multicellular fungi- some are visible and others are microscopic. Microscopic multicellular fungi
eg. Bread molds
Molds are made of hyphae w/c is microscopic strand slender (filamentous) cell of fungi that branches
to form network mass called mycelium.
Mode of reproduction of fungiAsexual reproduction:-
i. Budding -in yeast
ii. Sporulation-reproduction by producing asexual reproduction structure called spores.
iii. Fragmentation- breaking of hyphae into pieces.
Sexual reproduction:-
- Conjugation (simplest form of sexual reproduction), eg. Molds
Algae:- Found in kingdom protistae
- Consists of unicellular and multicellular eukaryotic organisms.
- They have cell-wall, that made of cellulose.
- They have chloroplast, so that they can photosynthesize food.
- They live in fresh and marine water body, so that they are phytoplankton or
‗sea weeds‘, i.e. they are sources of food for other aquatic organisms and also sources of O 2 to
aquatic environment.
They are classified into six groups
i. Dianoflagelata
ii.Euglenophyta; only algae that lack cell wall,
iii. Diatoms.
iv. Chlorophyta- green algae
v. Phaeophyta;- brown algae from w/c cosmetics are made
vi. Rhodophyta;-red algae from w/c Agar is extracted
. Excerpt phaeophyta, others are microscopic.
Bacteria
-Are unicellular prokaryotic organisms.
-In prokaryotic cells, there is no true nucleus and membrane bounded organelles. Bacteria do not
contain mitochondria, chloroplast, endoplasmic reticulum, etc.
Structure of Bacteria
137
(What are bacteria looking like?)
- Most have capsule or glycocalyx, which is protective slime layers.
-Some bacteria have flagella; w/c is simple type.
-Most bacteria contain pili (fimbrae) around the surface of the cell, w/c use to attach on
other surfaces.
-All bacteria have cell membrane, cell wall (that made of peptidoglycan), cytoplasm, ribosome (70’s),
and DNA (looped and naked).
-The region where DNA is found in the cytoplasm is called nucleoid.
-Some bacterial cells have small circular self-replicating DNA called plasmids
Shapes of bacteria
(Are all bacteria the same shape?)
Bacteria have different size, shape, and arrangement.
Size
Bacterial cell vary greatly in their size and usually much smaller than eukaryotic cells. Their length is
between (0.1) 1µm to 10µm.
Shape
Bacterial shapes come in three main shapes.
1. cocci(sing. Coccus):- spherical bacteria
2. Baccilli(sing. baccillus):- rod shape bacteria
3. spirochates:-spiral or corkscrew-shaped bacteria
(Vibro: rod when curved into coma shape. eg. Vibro cholerae)
Other way of classifying bacteria Arrangement
i. Coccus ii. Bacillus iii. Spirochates
1. Single(coccus) 1. Single(bacillus) 1. Spirochates
2. pair(diplococcus) 2. Pair(diplobacillus) 2. Borella
3. chain(streptococus) 3. Chain(streptobacillus) 3. Treponema
4. cluster(staphylococcus 4. Flagellates 4. Spirilla
Based on differential stain:
Differential stain- is a test that uses staining to classify organisms or organic material. Types of
differential stain
1. Gram stain
2. Acid fast stain
3. Special stain- used to stain flagella and endospores.
Gram staining; - is a test for classifying bacteria and it named after Hans Christian Gram.
Gram staining produces different result with different types of bacteria based on thickness of cell
wall.
1. Gram positive bacteria: - bacteria that stained purple and have thick cell wall.
2. Gram negative bacteria: - bacteria that stained pink and have thin cell wall.
Procedures in gram staining technique
1. Fixation
2. Simple staining by crystal violet, then all bacteria turn to purple.
3. Treating with iodine to form violet-iodine complex.
4. Decolorizing by washing off with 95% ethanol.
5. Counter stain using secondary stain called safranin.
 At the end some bacteria stain as pink, called gram negative. And others stained as
purple, called gram positive.
Gram-positive bacteria
-have more peptidoglycan in the cell wall.

138
 - No outer membrane surrounding the cell wall.
- Not harmful except bacterium that cause tuberculosis.
E.g. Lactobacilli (makes yogurt & buttermilk), Streptococcus, Staphylococcus
Gram-negative bacteria
-have much less peptidoglycan in their cell wall.
- Have membrane out- side peptidoglycan cell wall.
- The outer membrane secretes endotoxin-which is resistant to many antibiotics.
- Almost all cause more serious disease, and more difficult to treat.
Eg. Rhizobacteria grow in root nodules of legumes, Vibrio cholerae,
Bordetella pertussis, Neisseria gonorrhoeae, Neisseria meningitides
Mode of nutrition of Bacteria
i. Autotrophic - is two type
1. Chemosynthetic -use energy from exergonic chemical reaction.
2. Photosynthetic - use energy from light to make food.
 Photosynthesis (photophosphorylation) takes place along the plasma membrane of
bacterial cell.
ii. Heterotrophic - which are two types: 1. saprotrophic
2. Parasitic
Mode of reproduction of bacteria
1. Binary fission 2. Conjugation
The ecology and importance of bacteria
The ecology of bacteria
Bacteria are adapted to live everywhere inside and outside living organisms. Bacteria live in various
physical parameters based on the availability of light and O2, as well as the pH, temperature and salinity
of the environment.
On basis of O2 availability - bacteria can be:
-Obligate aerobes- that require O2 for growth
-Obligate anaerobes- those which are inhibited or killed by O2, and which grow only in its absence
- Facultative anaerobes- which grow either in the presence or absence of O2.
On basis of temperature availability - bacteria can be:
- psychrophiles- that live at very cold temperatures
-mesophiles- Those which flourish at room temperature (250C) or at the
temperature of warm- blooded animals (370C )
-thermophiles- those that live at high temperatures (greater than 45 0C)
On basis of PH: bacteria can be:
 Acidophiles: prefers an acid medium eg. Lactobacillus acidophilus, present in the vagina
of post-pubescent females. Helicobacter pylori, cause gastritis in human.
 Alkilophiles: bacteria grow best at high alkaline pH. E.g. Vibrio cholerae, the cause
of cholera
Large intestine of human contains large number of bacteria. Eg. E.coli
 There are about 10 bacterial cells for every cell of human body.
1.2 The ecology and uses of bacteria
Importance of bacteria:
-cause disease in plants or animals. Human diseases caused by bacterial pathogens
include tuberculosis, whooping cough, diphtheria, tetanus, gonorrhea, syphilis,
pneumonia, cholera and typhoid fever, to name a few.
- used in many biotechnology (industrial processes). The biotechnology industry uses bacterial
cells for the production of biological substances that are useful to human existence, including fuels,

139
foods, medicines, hormones, enzymes, proteins, and nucleic acids.
-have great role in recycling of nutrient or biogeochemical cycling.
The role of bacteria and other microorganisms in infectious diseases
Some diseases are caused by invasion of body by microorganisms. Organisms that cause disease are
called pathogens. A disease that is caused by microorganisms infecting the body is called infectious or
communicable disease.
The bacteria that cause these diseases have special structural or biochemical properties that determine
their virulence or pathogenicity. These include:
1. Ability to colonize and invade their host;
2. Ability to resist or withstand the antibacterial defenses of the host;
3. Ability to produce various toxic substances that damage the host.
-Germ theory of disease states that diseases can be caused by microorganisms, which proposed by Louis
Pasteur. Robert Koch and Joseph lister are also involved on the development of this theory.
Contribution of Louis Pasteur
-disproved the spontaneous generation theory once and for all.
-Discovered fermentation process.
-Discovered pasteurization process.
-Discovered vaccines.
-identified some microorganisms.
Contribution of Joseph lister
-Discovered disinfection processes. He showed carbolic acid (phenol), disinfectant that
prevent infection in bones during surgery.
Contribution of Robert Koch
-He is called father of bacteriology.
- identified many microorganisms that cause diseases.
- provided koch‘s postulate.
koch‘s postulate:
i. The microorganisms must always be present, when the disease present. Should notbe present if the
disease is not present.
ii. The microorganisms can be isolated from infected animals (host), and grow in cultures.
iii. Injecting such cultured microorganisms into healthy host should result in the same disease.
iv. It should be possible to isolate the microorganisms from this newly diseased host and grow it in
culture.
How microorganisms cause diseases?
Different microorganisms cause diseases in different ways.
Bacteria- cause disease by
i. releasing toxin as they multiply to cause disease in the region of infection or other.
ii. Invading and physically damaging tissues.
-Bacterial diseases can be treated with antibiotics.
Viruses- causes by
-Disrupting the metabolic system of the cells, the genetic material of the virus become incorporated
with the cell and instruct the cell to produce more viruses and finally lyses the cell as they released.
- Viruses cannot be treated with antibiotics because they are not true cells and live inside the immune
cells where antibiotic cannot enter.
Fungi- Causes disease by
i. releasing enzyme that digest the substances in the tissues.
ii. Physically damaging the tissue as hyphae grow.
iii. Secreting toxins.
140
 iv. Causing allergic reaction.
Protozoans
-Cause diseases in many different ways.
Transmission of diseases causing microorganisms
-The origin of microorganisms that infect other people is called the reservoir of infection.
-Reservoir of infection- is any person, animal, plant or soil or substance in which an infectious agent
normally lives and reproduces.
Reservoirs of infection include:
1. Human beings- are reservoir of many diseases, such as commen-cold, diphtheria, etc
2. Animals- eg. Chickens- reservoir of salmonella, Mosquitoes- reservoir of malaria
3. soil- reservoir of tetanus
4. water- reservoir for amoeba, cholera, leginnarie‘s disease, etc
5. Food- reservoir for thypiod, etc
6. Air- reservoir of pneumonia, TB, etc
7. Contaminated objects- reservoir of HIV/AIDS and trachoma
Because there are different reservoirs of disease causing organisms, there are many ways by which
disease can be transmitted;
1. Droplet infections (Transmit Cough and sneezing). Eg. Respiratory diseases
2. Drinking contaminated water; cholera, typhoid, etc.
3. Eating contaminated food; salmonella, listeriosis, etc.
4. Direct contact; Athlete‘s foot and ring worm
5. Sexual contact; candidiasis, STDs, hepatitis B, etc
6. Blood to blood contact; AIDS and hepatitis B when drug users share needles.
7. Animal vectors; malaria, sleeping sickness
What other types of diseases are there?
According to WHO’S definition:
Health is a state of complete ‘’physical, Mental, and social well-being.’’
Disease is the absence of perfect health, or is a condition with specific case in which parts or all of the
body made to function become non-normal or work in less efficient manner.
1. Human induced diseases- disease that arises as result of a person’s life style or working condition.
Eg. Heart disease and fibrosis
2. Degenerative diseases- results from aging process during which the affected tissues deteriorate
overtime due to simple ‘wear and tear’.eg. Artheritis and Alziamers
3. Genetic diseases- are diseases that result from action of mutated gene.
Eg. Hemophilia and sickle cell anemia
4. Social disease- disease that result from social activities and may lead to socially unacceptable
behavior. E.g. Drug addition, STDs, culture shock, etc
5. Deficiency disease- results from lack of nutrients in our diet
Eg. Scurvy and kwashiorkor (caused by a lack of protein)
Other categories of diseases
1. Multifactorial diseases-condition that affected by the interaction of many
factors. Eg. Artheriosclerosis- caused by aging, or deposition of fats on arteries and stress
and depression.
2. Functional diseases- caused by malfunction of an organ or system without any damage or
physical sign of disease in an organ.
Eg. Heart disease, IBS (irritable bowel syndrome), ME (Myalgic Encephalopathy), or chronic
fatigue syndrome.

141
How are bacteria used in industrial process (biotechnology)?
-food and beverage industry
-production of vinegar
-production of antibiotics
-sewage treatment
Food and beverage fermentation
Bacteria and other microorganisms have been used in manufacturing process of:
-bread, alcohol, Irgo(yogurt), cheese, etc.
Production of vinegar
-Vinegar is a dilute solution of ethanoic acid in water.
- It is used in two main ways -to flavor food
-to preserve food
-Vinegar is too acidic for microorganisms to grow and multiply, keeping food in vinegar is good way of
preserving, w/c is called pickling.
- Vinegar is produced by fermenting beer, wine, and cider for second time.
- Acetobacter bacteria are used to oxidize alcohol in beer, wine, and cider to ethanoic acid.
-Vinegar is made in special fermenter w/c is filled with wood shaving and alcohol source is sprayed from
the top.
-the alcohol trickles down through the wood shaving, w/c are covered with acetobacter bacteria.
-As the alcohol flow down, the bacteria oxidize it in to ethanoic acid.
- Air is blown in at the bottom to supply oxygen that bacteria need.
- Vinegar produced at the bottom of wood shaving.
Production of antibiotics
-First antibiotics is pencillin, made from fungi called pencillium notatum
-Antibiotics can be produced using genetically modified bacteria in huge special fermenter.
- Genetically modified bacteria are also used to produce
-human insulin
- Human growth hormone
- Enzymes for d/t industries
- Vaccines, for hepitis B
Fermenter: is the bioreactor or vat/ tank, vessel in which fermentation occurs.

142
How bacteria are genetically modified?
- By genetic engineering
- Genes are section of the DNA of an organism that code for a particular protein.
- Gene can be transferred successfully from one organism into bacterium, then genetically modified
bacterium will now make the protein that its new gene code for
-Genetic engineering become possible because of the development of three techniques
i. cutting gene out of DNA molecule using enzymes called restriction endonuclease.
ii. Inserting and tie gene into another molecule using ligase enzyme.
iii. Transferring gene into another cells using Vectors, such as plasmids, viruses, and gene gun.
Once a gene has inserted into bacterium, the bacterium become transgenic or genetically modified
bacterium.
How plants can be genetically modified?
Many crop plants can be genetically modified by inserting foreign gene into them. This gives the
plants new traits, such as: - resistant to diseases:
- Resistant to pest
- Longer shelf life
- Faster growth rate
- increase food quality
- Plants can be genetically modified in cellular levels during cell (tissue) culturing in laboratory under
controlled conditions.
- Genetic engineering of plants becomes difficult to biologist because plant cells do not accept plasmid, as
bacteria.
- Biologists discovered Agrobacterium tumefacein bacteria that regularly infect plant cells.
- Agrobacterium, acts as vector to carry genes that have been inserted into bacterium to cells of plants.
- But agrobacterium cannot be used to genetically modify all types of plants.
I.e. agrobacterium cannot infect cereals, such as maize.
- To solve this problem, biologists developed a gene gun that used to shoot the gene in to cells of plant.
143
- Gene gun shoots bullets ‗tiny pellets of gold‘ that are covered in DNA.
- Gene gun has made possible to genetically modify some plants such as maize, tobacco, potato, carrots,
apple, soya been, etc.
Sewage treatment
 All types of sewage treatment depend on the action of microorganisms to oxidize
polluting organic present in sewage.
There are two main methods
1. Percolating filter methods
2. Activated sludge methods
1. Percolating filter methods
- First sewage is screened to remove large pieces of debris and then stand in large
settlement tank to allow suspended matter settle out.
- The sewage is allowed to trickle through beds of stones, which covered by large
number of microorganisms (bacteria, fungi, and protozoa).
- As the sewage trickles through the filter beds, the microorganisms digest the organic
matter and absorb the products.
- When the liquid reaches the bottom of the filter bed, polluting organic matter has
been removed.
- The treated sewage can be discharged into river.
2. The activated sludge method
- First the sewage is screened and allowed to stand in settlement tank, as in percolating filter
method.
- The this is pumped into treatment tank, where
i. activated sludge, rich in microorganisms is added
ii. Oxygen is blown through mixture.
- In oxygenated mixture, the microorganisms from added activated sludge oxidize the polluting organic
matter.
- Some of the sludge formed is recycled to seed tanks.
The role of bacteria in an ecosystem
 Bacteria play role in recycling of minerals in ecosystem.
 Many bacteria are decomposers (they breakdown complex molecules into much smaller
molecules).
 Some simpler molecules are absorbed for bacterial metabolism, the other are released to the
environment.
 Elements that recycled, are carbon, Nitrogen, sulphur, and phosphorous
1. Nitrogen cycle
 The element nitrogen is found in many important organic molecules in all living
organisms such as Protein, nucleic acids, and ATP.
 When organisms die, nitrogen contained by them made to other organisms
 Several different types of bacteria are involved in the recycling of nitrogens. The role of bacteria
in Nitrogen cycle
1. Nitrogen fixation- nitrogen gas is fixed into NO3 that needed by plants to make protein.
Eg. Rhizobium
2. Ammonification- protein in dead organism and waste of animals are breakdown
to release Ammonium (NH4). Eg. Ammonifying bacteria
3. Nitrification: Occur with two steps.
Eg. Nitrifying bacteria i. NH4 Nitrosomonas NO2
ii. NO2 Nitrobacter NO3
4. Denitrification - reduce NO3 into Nitrogen gas returning nitrogen into air and reducing the amount of
nitrogen in the soil.
144
Eg. Denitrifying bacteria - Pseudomonas
2. Sulphur Cycles
Sulphur is found in fewer types of organic molecules than nitrogen.
- is found in many protein
The role of bacteria in sulphur cycles:
i. Decomposition- sulphur is released from protein of dead matter as H2S, which give ‗the rotten egg’
smell.
Eg. Desulphovibro(Anaerobe)
ii. Oxidation of Hydrogen sulphide- H2S is oxidized to release sulphur
Eg. Photosynthetic sulphur bacteria (anaerobe)
iii. Oxidation of sulphur - suphur is oxidized to sulphate ion.
Eg. Non-photosynthetic sulphur bacteria(aerobes)
If the population of bacteria that involved in Nitrogen and sulphur cycle were
reduced, then the cycling of these elements could not occur.
1.3 What are Viruses?
Viruses: are acellular or non-cellular particles (virion) consisting of DNA or RNA surrounded by a coat of
protein or sheath called capsid.
 They infect all cellular life including: Bacteria, protests, Fungi, Plants, and Animals.
Virion: is particle of viruses.
Virions lack nucleus, cytoplasm, mitochondria, chloroplast, and ribosome.
Because of lack these organelles, they cannot carry out:
 Respiration and photosynthesis.
 DNA replication and protein synthesis.
 Transport (active and passive).
 Facilitated diffusion

 To carry out such process, when they hijack biochemical machinery of host cell.
 They multiply only inside host cell (obligatory) intracellular parasites.
 They are not cell like:
 Neither prokaryotic nor Eukaryotic.
 Their size is between 0.01-0.1 micro meters.
 Some of them have lipids and proteins made membrane outside capsid
 Others have proteins and enzymes inside capsid.
a. Viruses that contain membrane around capsid are called enveloped viruses. Envelope is
derived from host cell membrane during viral multiplication. It provides protection from
dryness, and helps to attach them to host cell membrane by spike.
 E.g. Herpes virus, Retrovirus.
145
 b. Viruses lack envelops are non-enveloped viruses. E.g. Adenovirus, Bacteriophage.
Note: Envelope is additional layer surrounding protein coat.
Host Range: is a virus host range of cell type or host sps w/c virus is able to infect,
including human, bacteria, fungi, protists and plants.
However, most viruses are able to infect specific types of cell only one host (host cell
specificity).
They are often rely on specific attachments to host cells and binding to specific receptor.
Classification of viruses
 Classified based on morphology (shape), type of organisms they infect and nature of their
genetic material.
 Based on type of organisms they infect, viruses classified into:
1. Animal –infecting viruses: e.g. Chickenpox.
2. Bacteria-infecting viruses: e.g. Bacteriophage
3. Plant-infecting viruses: e.g. Tobacco mosaic virus.
 Based on types of nucleic acid and strategy for replication, 3 major groups of viruses are:
1. DNA VIRUSES
 Have DNA as genetic material. E.g. Herpes simplex w/c causes cold sore,
chickenpox, smallpox, adenovirus, and bacteriophage.
2. RNA VIRUSES
 Have RNA as genetic material. E.g. H1N1, Ebola, Influenza, Hepatitis, Polio,
measles etc.
3. Retroviruses: have RNA as genetic material, but RNA reverse-transcribe into
DNA after entering a host cell. The retroviral DNA can then integrate into
chromosomal DNA of host cell. E.g. HIV, Human T-cell leukemia virus (blood
cancer), Rous sarcoma virus w/c cause tumors in chickens.
Viral multiplication: nucleic acid in virus contains genes for virion‘s structural components and genes
for few of enzymes needed for synthesis of new viruses. However, enzymes needed for protein synthesis,
ribosome, tRNA, & energy production supplied by host cell & used for synthesizing of viral proteins &
enzymes. To multiply, they invade host cell & take over host‘s metabolic machinery.

Multiplication of Bacteriophage

 Bacteriophages multiply by 2 mechanisms:

a) The lytic cycle
b) Lysogenic cycle
A. The Lytic Cycle or T-4 Bacteriophages
 It leads to death of bacterial cell & replication of virus.
Stages:

I. Attachment: virus attaches to host cell membrane through viral spikes.

II. Penetration: virus injects its DNA into bacterium releasing phage lysozyme enzyme to breaks
down a portion of cell wall. The capsid remains outside bacterial cell.
III. Biosynthesis: synthesis of viral nucleic acid and proteins. Host protein synthesis is stopped by
virus-induced degradation of DNA.
IV. Maturation: bacteriophage DNA & capsids are assembled into complete virus.
146
V. Release (lysis): host cell lyses & new virions are released.
B. The lysogenic cycle:
_It does not cause lyses & death of host cell when they multiply.
-Viral DNA is incorporated into host cell‘s DNA & phage remains latent
-The latent virus multiplies along with host cell until environmental factors trigger
viruses.
-when environmental factor triggers virus, viral DNA begins producing viral proteins.
-The whole viruses then assembled.
- Assembled virions leave bacterial cell either by chronic exocytosis from plasma
membrane or by lytic process.

HIV AND AIDS

 HIV is retrovirus which has RNA as genetic material.
 Surrounded by a coat of fatty acid said to be viral envelop or membrane.
 Made from different type of component. Such as:
 Enzymes, Glycoprotein, Antigen, Genetic material (RNA), Protein shell, Lipid
membrane.
 The spikes structure on the surface of HIV particles are made from:
 3 molecules of GP120 & 1 molecule of GP41.
 HIV infects parts of immune system said to be T-helper cells.
 GP120 of HIV particles bind with CD4 of T-helper cell to release their RNA
HIV MULTIPLICATION
 After HIV particles has bound to CD4 receptor of T-helper it can be reproduced with in
T-cells.
 Three enzymes are required for HIV multiplication.
1. Reverse transcriptase: used to convert viral RNA to DNA.
RNA----------------------DNA
2. Integrase enzyme: used to insert viral DNA into host‘s DNA.
3. Protease enzyme: used to assemble viral components into new HIV.
 Their Genome replication is:
RNA DNA RNA VIRAL PROTEIN VIRAL ENZYME NEW VIRUS

Stages of HIV infection

 There are 3 d/t stages of HIV infection.
I. Acute stage: is the initial stage of HIV infection. After HIV infection, the WBC start
producing antibody can be used in diagnosis of HIV.
II. Latency period: is the stage when the body replaces the CD4 lymphocyte of T-helper
cell as fast as they are destroyed.
III. Disease period (AIDS): AIDS related complex (ARC) can appear. Final stage of HIV
infection.

147
  Number of T-helper cells & antibody production decline when the number of HIV
particles increases.
 Because of the reduction in number of T-helper cells, the immune system function
reduced & many opportunistic infection including; Pneumonia & TB together
cancer like Kaposi’s sarcoma.

Effect of antiretro viral Drugs

 AIDS has no cure or vaccines. But, anti-retro viral drugs can be used in slowing down the
progression of infection of HIV to AIDS. These drugs are:
1. Entry inhibitors: drugs attach to CD4 of T-helper or GP12O of HIV & prevent their
binding together.
2. Nucleotide reverse transcriptase inhibitors: drugs that attach to the nucleotide &
prevent reverse transcription to be used by HIV to convert the viral RNA into viral DNA.
3. Non-nucleotide reverse transcriptase inhibitors: drugs that attach to enzyme &
prevent the reverse transcription used by HIV to convert viral RNA to viral DNA.
4. Protease enzyme inhibitor: drugs that prevent HIV‘s protease enzymes from the
assembling of viral components into new HIV.

Highly Active Antiretroviral Treatment (HAART)

Uses antiretroviral drugs in combination to make an effective treatment against HIV
even if it has side effect.
HIV mutates (change) into different strain from time to time. Here of it has been difficult
to develop the preventing vaccine & curative drug against.
Impact of HIV/ AIDS
HIV has social and economic impact on:
 An individual
 Family
 country

Control and prevention of HIV /AIDS

The spread of HIV can be reduced by:
 Responsible sexual behavior
 Limiting the number of sexual partners
 Using ABC method-abstain, be faithful, use condom
 Male circumcision-reduces the risk of males acquiring the disease.
UNIT 2
ECOLOGY
2.1 Cycling matter through ecosystems
Why is it important that materials are recycled?
 All the organisms in the ecosystem are interdependent and interact with their physical
environment.
148
  Ecology is the branch of science that describes the interaction between different species
with each other and with the nonliving environment.
 Ecosystems look unchanging, but they are in fact always changing.
 Materials are always being ‗moved around‘ within an ecosystem when organisms are:
• feed
• excrete
• respire
• breathe
• die and are decomposed.
 The molecules that are moved, store large amounts of energy in the bonds holding the
atoms together.
 So, as materials are moved, energy is transferred also.
 Decomposers (bacteria and fungi) have key role in returning nutrients to the ecosystem.
 Decomposers feed by a method known as saprobiotic nutrition(feed on dead matter)
 They secrete enzymes onto the dead matter that digest the complex organic molecules
into simpler, smaller ones.
 But, unlike you, their extracellular digestion does not take place in a gut, it takes place in
the soil, or wherever the dead matter happens to be.
 Micro-organisms absorb these products their extracellular digestion.
 However, besides hydrolytic enzymes that break down complex organic molecules
have many enzymes for other purposes.
 E.g. many of the decomposers have an enzyme that releases the amino group from amino
acids and converts it to ammonia, by the process of Ammonification.
 The main stages in the carbon cycle
The main processes involved in cycling carbon through ecosystems are:
• Photosynthesis – the process that fixes carbon atoms from carbon dioxide into organic
compounds (e.g., glucose)
• Feeding and assimilation – feeding passes carbon atoms in complex molecules to the
next trophic level in the food.
- Assimilated:- become part of the body of that organism
• Respiration – releases inorganic carbon dioxide from organic compounds
• Fossilization – forming of fossil fuels (e.g. coal, oil, and peat).
• Combustion – fossil fuels are burned, releasing carbon dioxide into the atmosphere.
 The main stages in the nitrogen cycle
 Nitrogen is found in many biological compounds of proteins, amino acids, DNA, RNA
and ATP.
 The main processes in the Nitrogen cycle are:
• Plants absorb nitrates from the soil.
• The nitrates are then used to form amino acids to synthesize proteins.

149
 • The plants are eaten by animals, and then the proteins digested and assimilated into
animal proteins.
• Both plants and animals die, & decomposers decay the excretory products and
detritus, to release NH4 + by Ammonification into the soil.
• Nitrifying bacteria oxidize the ammonium ions to nitrite (NO2–) by Nitrosomonas
and then to nitrates (NO3–) by Nitrobacter by the process called nitrification.
• Denitrifying bacteria reduce nitrate to nitrogen gas that escapes from the soil.
• Nitrogen-fixing bacteria ‗fix‘ nitrogen gas into ammonium ions, in two ways.
 Nitrogen-fixing bacteria free in the soil reduce nitrogen gas into ammonium ions
in the soil (Azotobacter and Klebsiella).
 Nitrogen-fixing bacteria in nodules on the roots of legumes form ammonium ions
to synthesize amino acids (Rhizobium).
 phosphorus cycle
 Phosphorus is present in organisms in the form of phosphates.
• Phosphate is absorbed from the soil (or water) by plants
• These are passed along food chains to various herbivores and carnivores.
• Their dead bodies are decomposed and phosphate ions are released from phospholipids,
ATP, DNA and RNA and returned to the soil or water
• Phosphates also enter the soil (or water) as a result of the weathering of rocks and form
fertilizers.
• Over millions of years, phosphate ions can leach into the seas and become part of newly
forming sedimentary rock.
 Sulphur recycles
 The core cycle is between the soil, plants, animals, and special decomposers.
• Sulphate ions in the soil are taken up by plants (sulphur-containing amino acids, such
as methionine and cysteine).
• these are passed to animals by feeding and digestion
• On death of the plants and animals, Desulphovibrio bacteria release the sulphur in the
proteins in the form of hydrogen sulphide (H2S) in anaerobic conditions.
In some aquatic environments the H2S is oxidized to sulphur(S) by photosynthetic sulphur
bacteria [2H2S+CO2→ (CH2O) +H2O+2S
• Sulphur bacteria, (Thiobacillus), oxidize the hydrogen sulphide (sulphur) to sulphate
(SO42–), with an intermediate sulphite (SO32–) in aerobic conditions.
• Sulphur can also become incorporated in rocks that yield fossil fuels.
• Combustion of fossil fuels oxidizes the sulphur to sulphur dioxide (SO2) for pollutant
atm and the formation of acid rain.
• in the atmosphere, the sulphur dioxide becomes oxidized to sulphite and sulphate which
dissolve in rainwater to form a mixture of sulphurous and sulphuric acid: acid rain
 The water cycle
 Water is essential to all living organisms in all kinds of ways:

150
  It makes up 70% of all cells.
 It is an essential requirement of photosynthesis.
 It is the basis of all transport systems in organisms.
 It provides a means of removing excretory products.
 In addition, in our daily lives:
 To wash our clothes &others
 To flush away waste
 To make products such as paper, steel and beer.
 To generate electricity.
 In a system, called ‗hydroponics‘, to grow plants in a soil-free medium.
2.2 Ecological succession
 Succession the process where one ecosystem replaces another ecosystem.
 The ecosystems that exist today did not always exist.
 They have developed from other previous systems by succession.
• First began on completely bare ground (Bare rock).
• Very soon, lichens can be seen growing on the surface of the rock & resilient organisms (are
able to recover easily & quickly) called pioneer species.
• The living lichens grow into the rock causing it to crumble.
• When the lichens die, decomposers act on the remains to release mineral ions into the
crumbled rock.
• The mixture of dead remains, crumbled rock, and mineral ions forms a primitive soil.
• This less harsh environment is suitable for mosses.
So, spores of mosses can now ‗germinate‘, grow, and continue.
• Bare → lichen, mosses → annual herb→ perennial herb→ scrubs →forest
Rock stage stage stage stage stage
 The various stages in a succession are called seres.
 The final, most complex, state of a succession is the climax community.
 The essence of succession:
 Organisms colonize an area.
 They change the abiotic conditions in the area.
 This allows other species to colonize the area.
 The new species compete with there before and become dominant.
 They also then change the abiotic conditions, and the process continues.
 The following trends occur in any succession
 The total biomass of the community increases.
 The species diversity increases.
 The number of ecological niches increases.
 Food webs become more complex.
 The community becomes more stable
151
  A lake or pond can undergo a succession that results in the water being replaced by
sediments allowing land plants to grow.
 Both successions end with the same climax.
 Because the first takes place from rock it is called a xerosere.
 The second, starting from water, is a hydrosere
 Where a succession starts from bare, ground, or from a newly formed pond with no life,
called a primary succession.
 Sometimes, communities are destroyed by fire or a farmer or some other human
intervention, then a new succession in such area is said to be a secondary succession.
 Secondary successions to the original climax are usually much quicker than primary
successions. because:
 the succession is not starting from bare rock/open water
 the soil is already present
 Different areas have different climax communities
Factors that could influence the type of climax community formed include:
• Temperature
• Precipitation (rainfall)
• The presence of grazing animals
• Soil type
• Soil depth.
2.3 Biome
Biome: Is geographical or regional area with specific:

_climate, plants, soil, and animals

_is a region of the earth characterized by distinct zone of life

Temperature & Precipitation: is the most significant factors of climate in determining biome types.

_ There are 2 major types of biomes such as:

1. Terrestrial biomes &

2. Aquatic biomes
I. Terrestrial biomes: are biomes that consisting of an area of lands defined by several
factors:
_ Temp., precipitation (rainfall), Plants (flora), Animals (Fauna), Soil type (edaphic factor).

152
Characteristics of terrestrial factors

No Biomes Precipitation Temp Soil Plant Animal

1 Hot desert Almost none Hot Poor Sparse-succulents Sparse-insects,
(cacti), sage brusharachnids, reptiles &
birds
2 Cold desert Almost none Cold Poor Sparse- Sparse-polar bears,
microorganisms & seals
some Lichens
3 Thorn forest _Dry Hot summer, Poor Shrubs, some Drought-& fire
(shrubs) summer, cool winter woodland like adapted animals
rainy winter scrub oak
4 Tundra Dry Cold Permafrost Lichens & mosses Migrating animals
(frozen soil)
5 Boreal(Taiga) Adequate Cool year Poor, rocky Conifers Many mammals,
Forest round soil birds, reptiles insects,
arachnids
6 Temperate “ Cool season Fertile soil Deciduous trees Many mammals,
deciduous & warm birds, reptiles, insects
forest season etc.
7 Tropical 8_9 wet Always warm Fertile soil Ferns, large Many animals
Montane forest months, air deciduous trees,
always epiphytes
humid
8 Tropical Very wet Always warm Poor, thin Many plants, Many animals
rain forest soil epiphytes
common

 The moisture portion of western high lands consists of the tropical montane vegetation
with:
- Dense, Luxuriant forest, rich under growth.
- Higher annual rainfall but lower Temperature.
 The drier sections at lower elevation of western & eastern elevation of montane forests
are mixed with grassland.
 However the temperate grass land covers the higher altitude of western & eastern high
lands.
 The tropical dry forest found in rift valley & low land together with some dry grass land
contains the portion of Danakil. The reason why high species richness of plants & animals
are observed in Ethiopia b/c there are several biomes with in country.
2. Aquatic Biomes: are biomes where life exists from the top of the sea to bottom of sea.

Can be classified as:

a) Marine biomes
b) Fresh water biomes

153
 Biome Salt content Moving or Other feature Animals and plants
standing
Marine:
oceanic, High Moving The region of the ocean Many fish, mammals and
pelagic where light penetrates plankton
oceanic, High Less The region of the ocean Angler fish, sulphur bacteria at
abyssal movement where no light penetrates vents
Coral reef High Moving Most diverse of all marine Corals, many fish, many
habitats. Have many strata seaweeds
like a rainforest.
Estuarine Intermediate Extreme Unique habitat due to Shore birds, fish, crabs,
movement mixing of saltwater and mangroves, kelps, sea grass
fresh water

Fresh water:
Ponds and Fresh water Standing Are stratified as top layer Large numbers of plankton,
lakes absorbs more heat and light plants and animals in top
layer

Streams and Fresh water Moving Water is highly oxygenated Algae, plankton, plants and
rivers fish

Wetlands Fresh water Standing Water is very nutrient rich Many plants and animals –

highest of all aquatic biomes

2.4 Biodiversity
Biodiversity: refers to the number, variety, & variability of living organisms (plants, animals, &
microbes).
 Is the species richness.
 It is seen at level of Gene, species, culture & ecosystem.
 Can increase when:
 New species created
 New genetic variations of species produced.
 New ecosystem formed.
Components of biodiversity:

 It is measured by 4 elements such as:

1) Species diversity: is refers to the variety of species in a region.
 Can be measured by elements such as:
a. Species richness: is the total number of species in a defined area.
b. Species abundance: is the relative number among species.
c. Taxonomic diversity: is the variation of species from each other in their distribution
like family, order, classes, genera, & phyla.
2) Genetic diversity: is the variation of genes of species based on the DNA.
154
 3) Culture diversity: is manifested by diversity in terms of:
 Language
 Land management practice
 Social structure etc.
Ecosystem diversity: is the broad difference between ecosystem type, diversity habitat, &
ecological processing occurring with in an area.
Index of diversity: is the number indicating biodiversity of an ecosystem
It used to calculate species diversity. One index of diversity (d) is Simpson’s index diversity. It can be
calculated by formula:

d= N(N-1)

∑n(n-1) where d= index of diversity

N= Total number of organisms in an area

n = total number of organisms of each species in an area

The higher value of index of diversity shows that:

 high species diversity

 A number of successful species to formed.
 Ecosystem becomes more stable.
 The environmental factor is likely to be less hostile
 More ecological niches to be found.
The low value of index of diversity shows that:

 Low species diversity.

 Ecosystem become less stable, only in-dominant species.
 The environmental factor is likely to be more hostile.
 Less ecological niches to be found.

Human influence on biodiversity

 Human affected biodiversity in two ways such as:
Deforestation
Agriculture
Deforestation: is the process of destruction of forests.
 Forests are cleared to make land ready for:
Mining
Agriculture
Construction
 They are also needed to obtain timber from forest to make:
Paper, furniture, charcoal
Tropical rainforest: is the most complex & species richness of ecosystem.

155
  Even though many trees are very tall, the root systems are shallow & trees can easily fall.
 The root systems grow shallow in nutrient poor soils.
 Soils are poor in nutrients because many mineral ions from soils remain locked up in the
huge trees.
 The only recycling of nutrients that occur on a regular basis takes place when leaves fall.
 There is no accumulation of detritus as decomposers rapidly break down the leaves to
release the mineral ions they contain.
 The roots take up most of mineral ions & leaving few mineral ions in the soil

Effect of agriculture on biodiversity

 The large areas of land are given over to the production of one crops plant.
 This brings about the reduction of biodiversity for several reasons.
These are:

 The area is dominated by one species reduces the number of niches for organisms to fill.
 The organisms that lives there are considered as pest as they reduce the productive yield.
 They are controlled by use of pesticide.
 Hedgerows are removed from area to create bigger & more productive yield. This causes
the production of the number of habitat, niches, & biodiversity of an area.
Biodiversity in Africa
There are high floras & fauna in Africa as plants provide the number of habitat & niches for mammals.

Africa has:

 1/4th of the world‘s mammal species about 1229 out of 4700.

 900 mammals species found in SSA (sub-Saharan Africa).
 137 mammals species found in Madagascar.
 79 antelope species found in eastern & southern Africa.
 1/5th of world‘s birds species in Africa 2000 out of 2000.
 1600 birds are endemic to SSA.
 950 Amphibian species found in Africa.
 Therefore, Africa & South America is the continent of the highest number of
Amphibians.
 Ethiopian has better biodiversity than most of African countries except Kenya &
Democratic Congo.
 Different climate & altitude give different biomes which lead to high biodiversity.
 Ethiopia is one of the 12 centers of the origin of some cultivated crops called Vavilov‘s
centers.
 11 of them have genetic diversity centers in Ethiopia. These are:
1. Coffea Arabica- coffee
2. Eragrostis teff – Teff
3. Ensete ventriculum- Enset
4. Coccinia Abyssinica- Anchote
5. Guizotia Abyssinica- Niger seed-Nug
6. Brassica carinata – Ethiopian rape -Gomenzer.
7. Carthamus tinctures – sunflower- suf.

156
 8. Ricinus communis- Castor bean – Gulo.
9. Sorghum Spp. – sorghum
10. Hordeum Spp. – Barley
11. Linum usitatissimum- Linseed – Telba.
Forage plants or crops: are used as animal feed in Ethiopia.

 46 endemic species of legumes are important as forage plant used to increase fertility of
soil.
 6500-6700 plant species found in Ethiopia out of these 1156 (10- 12%) are endemic.
Vertebrate diversity of Ethiopia

Vertebrate Order Family Genera Species Endemic

group
Mammals 12 40 144 277 22

Birds 24 87 306 861 27

Reptiles 4 15 36 78 3
Amphibians 5 7 19 63 17

Fish 5 14 33 101 4
Direct effect of humans practice on biodiversity

 Deforestation, fuel wood collection, & illegal logging.

 Over grazing by stock mammals.
 Over hunting reduces number of species hunted.
 Introduction of improved variety decreases genetic diversity as the only improved variety
is used.
 Introduction of alien invasive species- these often out compete native species for the
available resources & make themselves extinct locally.
Indirect effect of humans practice on biodiversity

 High population growth.

 Under valuation of biodiversity resource by governmental body.
 Promotion of unsustainable exploitation resource by legal & institutional system.
 Disregard of traditional communal land management system.
Biodiversity loss concern

According to millennium assessment findings, biodiversity loss contributes to:

 Worsening health,
 Decreasing food security
 Worsening social relation.
 Increasing of vulnerability.
 Less freedom of choice & action.

157
  Low material wealth.
The important of ecosystem for humans

 Supporting of recycling nutrient, soil formation, & primary production.

 Providing food, fresh water, wood, fibers, & fuel.
 Regulation of climate, floods, & disease.
 Supporting of culture value like spiritual, educational, & recreational.
Conservation of biodiversity:

Conservation: is the maintenance & sustainable use of resources including preservation & restoration of
ecosystem. However, we are losing 10% of our biodiversity in every 50years.

Action is needed at individual, local, regional, national, & international level to conserve biodiversity.

In 2005, the Ethiopia institution of biodiversity conservation in Addis Ababa put forward a national of
biodiversity action plan based on,

 Ecological consideration
 Socio-economic
Types of conservation

They are two major types of conservation.

A. In situ conservation: is the conservation of genetic resources with in natural ecosystem

in w/c they occur. E.g. National parks, biosphere, reserves, Sanctuary managed resource
of nature.
B. Ex-situ conservation: is the conservation of genetic resource outside of natural
ecosystem in w/c they occur. E.g. Zoo, captive breeding, aquarium, botanical garden, and
gene bank..
There are 3 guiding ideas of conservation:

 Research
 Minimum intervention
 Repair rather than replace.
Ecological principles of conservation:

 Biodiversity is supported by protection of any species. Habitat maintenance is

fundamental to species conserved.
 Large areas contain more species than smaller areas with similar habitat.
 Disturbance of habitat is reshaping of ecosystem.
 Climatic change will affect all of ecosystem.
 Person who is planted a key stone indigenous of trees called Ficus vasta Forssk at his
center indigenous of tree propagation to enhance biodiversity development in Ethiopia is
said to be Professor Legesse Nagesh.
2.5 Population
Population: is the groups of closely related organisms that can be freely interbreed & live together.
158
  Consists of all individuals of a species in particular habitat at specific time.
 Habitat is place where population lives & obtains resources it need within its
geographical range.
 Geographical range: is the part of earth where a species live.
 Ecological niches: is the role of population with in its habitat.
 Several populations can live together in the same area because each exploits different
habitat & different niches.
E.g. - Phytoplankton exploits open H2O of pond.
-Decomposers inhabit detritus found at the bottom of pond.
 Basically, two species cannot occupy the same niches.
 If they do so, one species compete with another & makes it extinct is said to be
competitive exclusive principles.
Factors affecting population size

The number of population affected by:

 Natality – refers to birth rate

 Mortality – refers to death rate
 Migration – movement of population from an area to another. Divided into 2.
a) Immigration – is the movement of population into an area.
b) Emigration – is the movement of population out of an area.
Other factors controlling population sizes

1. Abiotic factors: are physical or environmental factors including

-Light -CO2 & O2 concentration. – Physical space & nutrient
-Temp - soil type

2. Biotic factors: refers to the effects onto a given population from other organisms of the same
or d/t species. Some of them are:

a. Predators: are the presences of carnivores for animals or herbivores for plants.
 Are larger sizes of organisms hunting the smaller sizes of organisms (prey).
b. Disease: causing organisms or pathogen can reduce the productivity age of population by
causing fatal.
c. Intra-specific competition: is the competition between the members of the same species
for the same resources in the same habitat. E.g. many human families occupying in a small
plot land.
d. Inter-specific competition: is the competition between the different members of the same
species for the same resources in the same habitat. E.g. Ethiopian wolves & domestic dogs
hunting rats.
Population Growth
- All population shows the same pattern of the growth rate.
- There are two types of population growth rate, such as
1. Arithmetic growth rate: number of population increases by fixed amount in each period of times.
E.g.: 5, 10, 15, 20, 25…
- Produces the uniform growth rate over time.
2. Exponential growth rate: number of population‘s double in each period of times.
E.g. 10, 20, 40, 80--which producing an ever-increasing rate over time.

159
Phases of population growth curve

There are 4 phases of population growth

a. Lag-phase: population is adapted to the environment to reproduces but some organisms are not
adapted to environment & then die.
- Numbers of populations are static or slow or increase.
b. Log- phase: all population is adapted & they reproduce rapidly due to plentiful resources.
- Numbers of population are increasing rapidly.
- Number of birth is rate of population is greater than the number of the death rate.
c. Stationary phase: carrying capacity is reached.
Carrying capacity- is the stability of the population sizes at a certain time.

- Is determined by biotic & abiotic factors of environment.

- Limiting factors- decreased nutrients accumulation of toxic waste products & restricting
living space begins to slow growth rate.
- Number of birth rate & death rate are equal.
d. Decline phase: over uses of resources & highly accumulation of toxic substance cause decline in
number of population.
- Number of death rate is greater than the number of birth rate.
Human population
- Their stages of development of human population of a country can be denoted in the
demographic transition in which it changes from the pre-agriculture society to
Industrial society
Post-industrial society
Human populations are subjected to factors affecting its development
These include the points at which the country or region develops
agriculture & industrialization that affect:
 Birth rate
 Death rate
 Life expectance
- Demographic transition: model that explains the transformation of the country from
having:
 High birth rate & death rate
 Low birth rate & death rate
Age pyramids of populations:
- Are pyramids that show the % of males & females in each age group of population.
- Can include:
 Expanding age pyramid
 Stationary age pyramid
 Contracting age pyramid
- Rapid population growth can be controlled by:
 Contraception programmed
 Education about sex
 Best provision of resources to agriculture
UNIT 3
GENETICS
3.1 Genetic crosses
Genetics: is a science of inheritance which study about variation & heredity among the offspring
& their parents.
160
Variation: is the difference among offspring & their parents.
Heredity: is the similarity among offspring & their parents.
The elements of variation & heredity of the living organisms said to be genes.
 Genetics determine the way in w/c traits are transmitted from one generation to next.
 It concerned with the unit of inheritance or genes.
The relationship between alleles, genes, DNA & chromosomes
 Alleles:- are alternative form of gene.
-are d/t version of the same genes.
-occupy the same locus on the homologous chromosomes.
 Locus: is the position or location of the genes on the chromosomes.
 Genes : is the section of DNA or chromosomes to determine the characteristic of
organisms - is the sequence of base or nucleotide in DNA or RNA molecules.
 Chromosomes: -are long threads like structure which is responsible for transmission of
genetic information
– are wrapped around histone protein.
 Made of DNA & histone protein.
 Store genes
DNA + Histone protein Chromatids chromosomes

Maternal and Paternal Chromosomes

 Sexually reproducing organisms receive one set of chromosomes from their parents (male
& females). E.g. in each human cell, there are 46 number of chromosomes, 23
chromosomes are coming from mother and called maternal chromosomes & 23
chromosomes are coming from father called and Paternal chromosomes.
 The maternal & paternal chromosomes come together during fertilization to form
homologous pairs.
Homologous and Non- homologous chromosomes
1) Homologous Chromosomes:
 Are chromosomes come in pair
 Are structurally & functionally similar chromosomes because they carry the same gene at
the same locus on the chromosomes.

2) Non- homologous chromosomes:

 Are structurally & functionally different chromosomes because they carry different
genes at the same locus on the chromosomes.
 Homozygous organism: have similar alleles for a particular gene on the homologous
pair.
161
  Heterozygous organisms: have different alleles for a particular gene on the
homologous pair.
Genotype and Phenotype

Genotype: is genetic composition or internal expression of organisms for a given trait.

 Is an internal appearance of organisms

E.g. AA, BB, Aa, Bb, DD, Dd etc.

Phenotype: is the physical or external appearance of organisms.

 Is an observable characteristic of organisms resulting from an interaction between

genotype and environment
E.g. Phenotype = shape, height, color etc.

How do we predict ratios in a monohybrid cross?

-Monohybrid cross- is a genetic cross or breeding situation that relates to just one trait or
feature.

Gregor Mendel

Gregor Mendel is said to be the father of genetics because he showed the law & mechanisms of
inheritance in eukaryotic organisms. He discovered rules by which genes are inherited

- He used garden pea plant & breed to show mechanism of inheritance in his monastery garden.

- When he conducted his experiment, Mendel selected the pea plants due to their 5 major
characteristics such as:

 Produce large number of seed.

 Easily cultivated.
 Have short life cycle or short period of generation.
 Are self & cross-pollinated plants.
 Have several contrasting traits.
Techniques of Mendel breeding

-Mendel allowed self-pollination & fertilization of different lines of garden pea plants.

-Pure (true) breeders- are organisms that are homozygous for any given genotype which produce the
same phenotype.

162
E.g. - Parent phenotype: Tall x Short

-P1 genotype TT x tt x T T

-P1 gametes T T t t t Tt Tt

t Tt Tt

 All F1 -first filial generation produced from P1- Phenotype- all (100%) are tall
- Genotype -all (100%) are Tt

- Mendel used the same producers for all contrasting traits or characters which include:

1. Removed stamen from purple flowered plant to prevent self-pollination.

2. Used a paint brush to transfer pollen grain from white flowered to carpel of purple flower.

3. Then, pollinated carpel produces the pea pod containing several pea seeds.

4. He collected & grew all seeds from all pods.

5. When plants were mature. He noted the color of their flower.

- He also carried out reciprocal crosses. In this case he also pollinated white-flowered plants with pollen
from purple-flowered plants.

- When he analyzed his data, he formulated four concepts such as:

a) Concept of unit character or trait

b) ― ― Dominance and Recessive
c) ― ― law of Segregation
d) ― ―Law of independent assortment.
1. Concept of unit character
-Every trait such as seed shape, color, flower color, position, pod shape, color, & height tall or short are
controlled by heritable factors called genes.

-Mendel factors or unit character is called genes.

Unit character Dominant trait x F1 generation F2 generation

Recessive trait
Seed shape Round x Wrinkled All round 3:1
Seed color Yellow x Green All yellow 3:1
Flower position Axial x Terminal All axial 3:1
Flower color Purple x White All purple 3:1
Pod shape Constricted x Smooth All constricted 3:1
Pod flower Green x Yellow All green 3:1
Height Tall x Short All tall 3:1
2. The concept of dominance and recessive
 Dominant traits: traits that mask the effect of other and express itself in organism‘s
appearance.
 If two alleles in organisms are different one is dominant & the other is recessive.
e.g. Tt- T- is dominant allele and t- is recessive allele.
163
 - Dominant alleles represented by capital letter & recessive alleles represented by small letter

 Recessive traits: traits that is controlled by recessive alleles. Expressed only when appear
together in homozygous E.g. tt
3. The concept of law of segregation:
 Law of segregation: states that contrasting of factors or alleles separate to produce gamete or sex
cell. Segregation means separation of gametes.
 Any single gamete receives only one allele for trait.
 Physical link between generation is said to be gamete.
 Is applied only for monohybrid cross.
e.g. Considering cross-breeding of one trait of flower position
- P1-phenotype-of F1- Axial x Terminal
- P1- genotype of F1- AA x aa
- P1- gamete of F1 A, A a, a
x A A
-All Phenotype of F1- axial 100%
a Aa Aa
-Genotype of F1- Aa (100% Aa)
a Aa Aa
Dihybrid test cross
Round, yellow seed X Wrinkled, green

RRYY X rryy

Gametes RY, ry, Ry, rY

RY ry Ry rY
RY RRYY RrYy RRYy RrYY
ry RrYy rryy Rryy rrYy
Ry RRYy Rryy RRyy RrYy
rY RrYY rrYy RrYy rrYY
Round and yellow 9

Round and green 3

Wrinkled and yellow 3

Wrinkled and green 1

Phenotypic ratio = 9:3:3:1

Genotypic ratio = 1:4:2:2:1:2:2:1:1

 There are more possibilities than in monohybrid inheritance
 homozygous for both features – RRYY
 heterozygous for both features – RrYy
 heterozygous for one feature but not the other – RRYy or RrYY
Back cross with rryy

164
  If the plants produced show all four possible phenotypes, the original was heterozygous
for both features.
 If the plants produced all had round, yellow seeds, the original was homozygous for both
features.
 If the plants produced all had rounds seeds but some had green and some had yellow
seeds, the original was heterozygous for seed color only.
 If the plants produced all have yellow seeds but some are round and some wrinkled, the
original was heterozygous for seed shape only.
 Are alleles always simply dominant or recessive?
 The short answer is no.
 it may be co-dominant or incomplete dominant
 Incomplete dominance: when the heterozygous shows an intermediate phenotype
 Co-dominance: a type of inheritance in which two versions (alleles) of the same
gene are expressed separately to yield different traits in an individual.
 Example incomplete dominance in the flower color of snapdragons(sweet pea plant)
 The possible genotypes are:
 RR – plants with red flowers.
 rr – plants with white flowers.
 Rr – plants with pink flowers.
 The genotype & phenotype have the same 1:2:1 ratio.
 Are there always two alleles of a gene?
 Some genes have more than two alleles called multiple allele inheritance. Basic rules
are just the same. These alleles can be dominant or recessive or co dominant.
 An example of multiple allele inheritance occurs in the inheritance of the ABO blood
groups.
 In the ABO blood grouping system, there are four blood groups, determined by the
presence or absence of two antigens (A and B) on the surface of the red blood cells.
 There are three alleles involved in the inheritance of these blood groups:
•IA, which determines the production of the A antigen
•IB, which determines the production of the B antigen
•IO, which determines that neither antigen is produced
Alleles IA and IB are codominant, but IO is recessive to both
 The possible genotypes and phenotypes (blood groups) are shown below.
Genotype Blood group
IAIA, IAIO A
B B B O
I I ,I I B
IAIB AB
IOIO O
It is possible for two parents, with blood groups A and B, to have four children, each with
a different blood group!
Father Mother
A O
Parents I I IB IO Both are heterozygous, but for different blood groups
Sex cells IA or IO IB or IO Parents can make two types of gametes in equal

165
 numbers, each with one allele

Male sex cell

IA IO
1/2
1/2
I B IO IA IB IB IO
Female (1/2) ( 1/4) (1/4)
IO IA IO IO IO
sex cell (1/2) ( ¼) ( ¼)

Figure 3.16 how the four offspring of parents with blood groups A and B can all
have different blood groups
Did you know? Although the gene may have more than two alleles, because they are
alleles of the same gene, any individual will still only have a maximum of two of the
alleles. This is because the different alleles are found at the same locus (position) on
homologous chromosomes. Because there are only two copies of each chromosome, the
person can only have two alleles of the gene
Other examples of codominance when ‘red’ cattle (homozygous for the red allele) are
bred with white cattle (homozygous for the white allele), the offspring are heterozygous
and have patches of red and patches of white skin. They are called roan cattl.e
Two of the alleles that determine our ABO blood group are codominant.
What is the physical basis for these patterns of inheritance?
We began this chapter by pointing out that a gene is a part of a chromosome. For gametes to be formed,
special cells in the sex organs of the organism divide by a process known as meiosis. When a cell divides
in this manner, there are three key outcomes:
 It produces four ‗daughter‘ cells
 These daughter cells have only half the number of chromosomes of the original cell; they
have one chromosome from each homologous pair
 the daughter cells show genetic variation
 meiosis- the process by which a cell divides to form haploid gametes
 homologous chromosomes- chromosomes that carry genes for the same feature at the same
loci (in the same places)
 chromatid- when a eukaryotic cell divides during meiosis, each of its chromosomes divides
into two chromatids
 haploid- a haploid cell, usually a gamete, has a single set of chromosomes instead of
homologous pairs
 diploid- a diploid cell has homologous pairs of chromosomes
 bivalent- a pair of homologous chromosomes
166
 A cell does not normally divide to produce four cells – it produces two.
 Therefore, meiosis must entail two divisions called meiosis I and meiosis II
 at the start of the process, each chromosome is a double structure; it is made of two
chromatids held together by a centromere
 Synapsis: pairing of homologous chromosomes
 This is because the DNA in each chromosome replicated prior to meiosis commencing.
 Before any division takes place, chromatids from different chromosomes in the homologous
pair undergo ‗crossing over’ and exchange sections of DNA.
 Meiosis I follow and the two chromosomes that make up the pair are separated into different
cells.
 In meiosis II, the two chromatids that make up each chromosome are separated into separate
cells.
 Because of crossing over, none of these chromatids are the same.
 There is genetic variation in the daughter cells,
 Four haploid cells produced
 With just two bivalents, there are two possible arrangements and two different sets of
gametes. With 23 pairs of chromosomes, there are 222 different combinations
 Each bivalent aligns itself independently of the others. This is called independent
assortment and is an important source of genetic variation in the gametes produced by
meiosis.
 Sister chromatid -chromatids from the same chromosome; they have the same alleles in the
same sequence
 Non-sister chromatid -chromatids from different chromosomes of a homologous pair;
although the genes are the same and at the same loci, the alleles may be different
 Cytokinesis -the process that leads up to the cell dividing into two during meiosis
The main stages of meiosis
Meiosis I: It is divided into four phases:
 Interphase- chromosomes duplicate
• Prophase - homologous chromosomes pair and exchange segments
• Metaphase - tetrads line up
• Anaphase- pairs of homologous chromosomes split up
• Telophase- two haploid cells form; chromosomes are still double
After telophase there is cytokinesis.
Cytokinesis: the process that leads up to the cell dividing into two during meiosis
Meiosis II: It is divided into the same four phases, but there are some important differences:
 there is no crossing over in prophase
 the chromosomes line up side by side in metaphase
 chromatids are separated in anaphase
167
What about alleles that don’t segregate at gamete formation – genetic linkage
 Mendel was very fortunate in his choice of organisms with which to experiment.
 All the alleles of all the genes did segregate.
 But this does not always happen; some genes inherited together with other genes – they
exhibit linkage. The genes are linked and inherited together because they are on the same
chromosome.
 The earliest 1900s study of linkage was carried out by two British geneticists, Bateson and
Punnett (who also devised the Punnett square).
 William Bateson and R. C. Punnett were studying inheritance in the sweet pea. They studied
two genes: one affecting flower color (P, purple, and p, red) and the other affecting the shape
of pollen grains (L, long, and l, round).
-They crossed pure lines P/P · L/L (purple, long) × p/p · l/l (red, round),
PL/PL X pl/pl
PL X pl
-and selfed the F1 PL/pl heterozygotes to obtain an F2 and shows the
proportions of each phenotype in the F2 plants.

PL pl
PL PL/PL PL/pl
Purpl long Purpl long

pl PL/pl Pl/pl
Purple long Red round
 We now predict not a 9:3:3:1 ratio, but a 3:1 ratio of purple-flowered, long-seeded
plants to red-flowered, round-seeded plants.
What we might have expected from a 9:3:3:1 ratio is:
 215 purple, long
 71 purple, round
 71 red, long
 24 red, round

and from a 3:1 ratio:

 286 purple, long

 95 red, round

-The reason we do not get either is because the genes are

linked,
-but there is some crossing over between them during
prophase of meiosis I.

168
-This produces the types we would not expect from linked inheritance. These types are called
recombinant types.

 Early research on crossing over and recombination was carried out using fruit flies. They
are convenient experimental animals because:
▪ small animals with a short life cycle (just two weeks)
▪ cheap and easy to breed and keep in large numbers
▪ they have only 4 pairs of chromosomes, per cell
▪ the chromosomes, are large and easily observed
▪ staining reveals dark bands which correspond to particular genes
Early 1900s, Thomas Morgan was able to prove, that genes carried on chromosomes are the
physical basis of inheritance.
 A H Sturtevant, worked on linkage and crossing over in Drosophila.
 He made predictions about what offspring to expect:
- if there was no crossing over and then counted the number of expected
- And recombinant types to find the percentage of recombinant types.
-This percentage of recombinant types is called the crossover value and is a measure of how far
apart the genes are on a chromosome.
-A low crossover frequency indicates that the genes are close together;
-A high one that they are further apart-crossing over will occur between them
-Gene mapping has been used to ‗track down‘ genes that cause disease (for example, cystic
fibrosis and Huntington‘s disease)
How is knowledge of genetics important in crossbreeding and inbreeding
crops and stock?
Inbreeding- involves breeding animals or plants with close relatives. This can cause problems
such as infertility in the resulting offspring
Hybrid vigor- the increased vigor or productivity of organisms resulting from crossbreeding
different varieties of the same species
Selective breeding: where organisms are chosen to breed with a specific outcome in mind.
Cross-breeding- is an established breeding method used in breeding to increase overall
productivity.
Cross-breeding, natural or planned, has been important in producing many of the high-yielding
crop plants we now grow
Commercial cattle farmers may cross-breed animals for two related reasons:
• To take advantage of hybrid vigour

169
 • To take advantage of the good qualities of two or more breeds and to combine these
qualities to improve market suitability
-Because it is the result of increased heterozygosity, the term hybrid vigour is sometimes replaced
by heterosis.
What about genes on the sex chromosomes?
Sex determination
 Sex is determined by the X and Y chromosomes.
 Males have one X chromosomes, and one Y , chromosomes and have two different sex
chromosomes they are called the heterogametic sex,
 Females have two X chromosomes and are the homogametic sex.
 They both have 44 (22 pairs) autosomes – non-sex chromosomes
 In any family, or in any mating in mammals, the predicted ratio of males to females is
1:1,
 The Y chromosomes that appears to determine a person‘s sex, the action of one gene on
this chromosomes, the SRY gene that determines the formation of testes.
 SRY gene the dominant gene on the Ychromosomes that causes a mammal to develop as
a male
 In the early development of the embryo, a region called the urogenital ridge develops
into a ‘bi-potential gonad’
 The same structure can develop into either ovary or testis.
 When the SRY gene is activated, the bi-potential gonad develops into a testis, and the
embryo is male.
 If the SRY gene is absent (or inactivated for some reason), genes on the X
chromosomes , and on the autosomes cause the bi-potential gonad to develop into an
ovary, and the embryo is female
 Individuals with only one X chromosomes , and no Y chromosomes , (written X–)
develop into females, but with slightly masculinised features abnormal(Turner
syndrome), sterile
 Similarly, individuals with two X chromosomes, and one Y chromosomes, (XXY)
develop into males, but with feminized features. abnormal (Klinefelter syndrome),
sterile
 These individuals are also sterile, the abnormal number of chromosomes, arises as a
result of nondisjunction of the sex chromosomes, during meiosis. the chromosomes , do
not segregate properly into the gametes,
Other systems of sex determination
 In birds it is females are heterogametic sex and males the homogametic sex! But they
don‘t have X and Y chromosomes,
 They have W and Z. Females are ZW and males ZZ.
 In some reptiles, such as alligators, sex is determined by the temperature at which the
egg is incubated.
 Some snails start out male, and then become female!

170
  In tropical clown fish, the dominant individual in a group becomes female while the other
ones are male, and in blue wrasse fish the reverse.
 Some species have no sex-determination system – they are hermaphrodite (have both
male and female sex organs).
 Hermaphrodites include the common earthworm and some species of snails.
The genes on the sex chromosomes
 Genes found only on the X chromosome or on the Y chromosome are said to be sex-linked.
Genes found only on the Y chromosome include those that determine:
• One form of the degenerative condition retinitis pigmentosa (in which eyesight becomes
progressively weaker and may lead to blindness)
• One form of deafness, these particular conditions can only be inherited by males, as only
males have the Y chromosome.
 Genes found only on the X chromosome include those that determine:
• Red-green color blindness
• One form of hemophilia
 These conditions can be inherited by females and males as both possess at least one X
chromosome.
 Many of these conditions are determined by recessive alleles, including both red-green color
blindness and hemophilia.
 These conditions are more common in men than in women because:
• Men only have one X chromosome
• If this chromosome carries the recessive allele for hemophilia, there is no corresponding
dominant allele on the Y chromosome to mask its effect
• Women have two X chromosomes
• Both these need to carry the recessive allele for hemophilia for a woman to suffer f
conditions as, if only one of them did, the dominant allele on the other X chromosome would
mask its effects
• A man needs to inherit only one X chromosome with a recessive hemophilia allele to
suffer from the condition, whereas a woman must inherit two; this is less likely to happen
 karyotype a photograph of all the chromosomes in a cell arranged in homologous pairs
 Even though the X and Y chromosomes are very different, but they have homologous
regions

171
  This region follows the same pattern of inheritance as genes on the autosomes and is
concerned with control of metabolic activities in cells.

Sex-linked features determined by recessive alleles on the X chromosome share the following
characteristics:

• They are much more common among males (because females must inherit two chromosomes
carrying the recessive allele, whereas males must inherit only one)
• Affected males inherit the allele from their mother
• Affected females inherit one allele from each parent (so the father will be affected)
• Females who are heterozygous for the condition are called carriers
• They may ‗skip‘ a generation and then appear in the males only
Genotypes of sex-linked features include the appropriate sex chromosomes as well as the alleles
E.g.;-for red-green color blindness, B represents the allele for normal vision and b represents the
allele for red-green color blindness.
The possible genotypes and phenotypes are:
• XBY – normal male
• Xb Y – affected male
• XBXB – normal female
• XBXb – carrier female (is not color blind)
• Xb Xb – affected female.
If you were not told that this was a sex-linked feature, there are several hints:
• It clearly skips a generation
• It is more common in the males
• The only affected female has an affected father

3.2 Molecular genetics

 The nucleotides are held together by bonds between the sugar in one nucleotide and the
phosphate group in the next.
 The nucleotides in one strand are paired with nucleotides in the other according to the base-
pairing rule. This states:
 Adenine-containing nucleotides will always be opposite to
Thymine-containing nucleotides

172
 Cytosine-containing nucleotides will always be opposite to

Guanine-containing nucleotides

 Base-paired on the two strands, sequences of bases are complementary.

 Hydrogen bonds that hold the two strands together are quite weak,
 The bonds hold the nucleotides in each strand are much stronger than the hydrogen
bonds.
 The stability of the DNA is important in ensuring the genetic code – does not become
corrupted
 The amount of adenine is equal to the amount of thymine, the amount of guanine is equal
to the amount of cytosine

How does the DNA molecule replicate itself?

 The ability of a DNA molecule to make an exact copy of itself is the basis of all methods of
reproduction and the basis of passing on genetic information from one generation to the next.
 Even though they did not know the details, in 1953, Watson and Crick discoverers of the
structure of DNA proposed that DNA must replicate semi-conservatively.
 This means that the DNA molecule replicates in such a way that:
 each new DNA molecule formed contains one strand from the original DNA
 both new DNA molecules formed are identical to each other and to the original molecule
 DNA replication involves enzymes and proteins, but the key stages are as follows:
 Molecules of the enzyme DNA helicase break hydrogen bonds and ‗unwind‘ helix
revealing two single-stranded regions.
 Molecules of DNA polymerase follow the helicase along each single-stranded region,
which acts as a template for the synthesis of a new strand.
 The DNA polymerase assembles free DNA nucleotides into a new strand alongside each
of the template strands. The base sequence in each of these new strands is complementary
because of the base-pairing rule, A-T, C-G.
 The processes of unwinding followed by complementary strand synthesis progresses
along the whole length of the DNA molecule.
 The result is two DNA molecules that are identical to each other (and to the original
molecule); each contains one strand from the original DNA molecule and one newly
synthesized strand that is complementary to this.
 DNA helicase the enzyme that initiates the separation of the polynucleotide strands during
DNA replication
 DNA polymerase the enzyme that initiates the building of a new complementary
polynucleotide strand of DNA following separation of the original two strands
Gene cloning means making multiple copies of a gene. The principal methods are divided
into two main categories; these are:

• In vivo cloning – the gene is introduced into a cell and is copied as the cell divides
173
 • In vitro cloning – this does not take place in living cells but the DNA is copied many times
over using the polymerase chain reaction (PCR).

 This process mimics the natural semi-conservative replication of DNA in a machine called
a PCR machine.

How are organisms cloned?

 There are advantages and disadvantages to both methods of gene cloning.
 In vitro cloning using the PCR is both quicker and cheaper. Billions of copies of a gene can
be made within a few hours at low cost.
 However, if the gene is to be used by an organism to make a product – for example, by a
bacterium to allow it to make insulin – then in vivo cloning delivers the gene already in the
organism.
A clone of organisms is a group of organisms produced asexually from one parent.
 The members of the clone are genetically identical to each other and to the parent organism.
 Genetically modified organism an organism created using genetic engineering which
contains a transferred gene or genes
 Cloning of plant practiced for thousands of years. More recently the technique of micro
propagation made it possible to produce a clone of thousands of identical plants from just
one parent plant
 Micro propagation is the rapid vegetative propagation of plants under in vitro conditions
of high light intensity, controlled temperature and a defined nutrient medium. The technique
has been applied to a substantial number of commercial vegetatively propagated plant
species.
E.g.-These small groups of a few hundred cells are placed in test tubes containing a special medium
with hormones that induce root growth. They are then transferred to another medium containing
hormones to induce shoot growth. When they have grown sufficiently, the small plantlets transferred to
a compost and grown on. In this way, thousands of identical plants can be produced.
Most of the world’s bananas are now produced by micro propagation.

 You cannot just cut pieces of animals however animals have been cloned. The first mammal
to be cloned, and still the most famous, was Dolly the sheep.
E.g.-Dolly’s genetic mother was a type of sheep called ‘Finn-Dorset’. Dolly was produced by
transferring a diploid nucleus to an egg cell that had been enucleated (had its nucleus removed). Once
the nucleus had been successfully transferred, the egg cell was stimulated to divide by a small electric
current. When development had reached a stage called a blastocyst, the embryo was implanted into a
surrogate ‘mother’ ewe. Seven months later, Dolly was born. She was genetically identical to the Finn-
Dorset ewe (female sheep) from whom the genetic material had been obtained
 A Finnish Dorset is a crossed-breed sheep, half Finn sheep, and half Dorset breed.
 Dolly the sheep, first mammal to be cloned from an adult somatic cell, was a Finnish
Dorset

174
What is genetic engineering?
 Genetic engineering is a process in which the genome of an organism is altered, usually
by having an extra gene from a different organism added.
 The organism is then a genetically modified or a transgenic organism.
 Transgenic organism a genetically modified organism that contains a gene or genes
transferred from another organism belonging to a different species
 Much of the early work on genetic engineering was done to genetically modify bacteria.
 One of the first of these products to be produced by transgenic bacteria was human insulin.
 The gene that controls the production of human insulin was extracted from human
pancreas cells
 And transferred to the bacteria.
 Once modified, the bacteria were then cultured on a massive scale in a fermenter
 And the insulin harvested and purified before distribution.
 Genetically modified bacteria produce a range of products, including:
• Enzymes for the food industry

• Thermo stable enzymes for washing powders

• Human insulin

• Human growth hormone

• Vaccines (for example, for prevention of hepatitis B)

• Bovine somatotrophin (to increase milk yield and muscle development in cattle)

 Plants have also been genetically modified so that they:

• are disease resistant

• have an improved yield

• produce a specific product (for example, golden rice is genetically modified rice that
produces beta-carotene – important in the formation of vitamin A, which prevents night
blindness)

Genetic engineering has many potential benefits. Some of these are described below:

• Disease could be prevented by detecting people/plants/animals that are genetically prone to

certain hereditary diseases,

• treat infectious diseases by implanting genes that code for antiviral proteins specific to each
antigen.

• Genetically engineered plants and animals can be produced to give increased growth rates and
reduced susceptibility to disease

175
• Animals and plants can be ‗tailor made‘ to show desirable characteristics.

. Genetic engineering could increase genetic diversity, and produce more variant alleles
• Genetic engineering is a much quicker process than traditional selective breeding

How can gene technology be used in forensic science?

 Fingerprints have been used for many years to help place a suspect at the scene of a crime,
with the exception of identical twins,
 An individual‘s fingerprints are unique.
 genetic fingerprinting a forensic technique that is used to try to solve crimes by matching
DNA found at crime scenes with the DNA of suspects
 Genetic fingerprinting has nothing to do with actual fingerprints. It is a technique for
comparing the DNA of different people
 DNA in the cells of the body is known as non-coding DNA.
 The non-coding DNA is found between genes and contains base sequences that are
repeated,
 These repeating sequences of non-coding DNA are called mini-satellites
 Mini-satelites form the basis of a genetic fingerprint.
 The mini-satellites are inherited along with the coding DNA from one or other parent.
 The DNA used for analysis obtained from any type of cell that has a nucleus. Eg- blood
(white blood cells could supply the DNA), skin or semen
 The main stages in preparing a genetic fingerprint are:
 DNA is isolated from the cells.
 The DNA cut into fragments using restriction enzymes. The fragments that are obtained are
treated with alkali to separate the strands of each DNA fragment.
 The fragments are separated by gel electrophoresis. Smaller fragments (with a lower
molecular mass) move further than larger fragments.
 The invisible pattern of separated DNA fragments is transferred from the gel to a nylon
membrane. The membrane is placed over the gel in a tray of ‗flow-buffer‘ and is held in
place by paper towels and a weight. The buffer soaks up through the gel, carrying the
fragments of DNA with it. The buffer can pass through the membrane (to be absorbed by
the paper towels), but the DNA cannot. It remains in the nylon membrane in the same
relative position as it was in the gel.
 A radioactive gene probe is applied to the membrane. This is made of single-stranded
DNA (called c-DNA) and binds with base sequences in the mini-satellite regions.
 The membrane is placed over a piece of X-ray film to reveal the positions of those
fragments that have bound to the probe.
 Gel electrophoresis is a technique that uses a thick block of gel (jelly-like material) to act as
a ‗molecular sieve’
 The size of DNA molecules is usually measured in kilobase pairs (thousands of pairs of
bases).

176
 The fragments used in a genetic fingerprint are single stranded, so there are no base pairs.
Their size is measured in kilobases.
 The chance of two people having the same genetic fingerprint (unless they are identical
twins) is about 1 in 1 000 000.
 This means that a genetic fingerprint provide strong evidence of involvement in or
innocence of a crime.
3.3 Protein synthesis
How does a cell ‘know’ to make a protein?
 The code for a protein is specified by DNA
 Has to be carried to the ribosomes and can assemble the amino acids in the correct sequence
to form the protein.
 DNA is a huge molecule and remains in the nucleus at all times.
The following events occur:
• The DNA code for the protein is rewritten in a molecule of messenger RNA (mRNA); this rewriting o
the code is called transcription.
• The mRNA travels from the nucleus through pores in the nuclear envelope to the ribosomes.
• Free amino acids are carried from the cytoplasm to the ribosomes by molecules of transfer RNA
(tRNA).
• The ribosome reads the mRNA code and assembles the amino acids carried by tRNA into a protein; this
is called translation.

 mRNA (messenger RNA) is a nucleic acid that transmits the genetic code from DNA to
ribosome
 transcription process converts genetic information from a DNA code into an mRNA code
 tRNA (transfer RNA) transfers individual amino acids during translation
 ribosome the part of a cell that makes proteins
 translation process in which the mRNA code is converted into a sequence of amino acids
What is the genetic code like?
 The genetic code is held in the DNA molecule.
 A gene is a sequence of base triplets (sequence of three) in the DNA molecule that carries
the code for a protein.
 With four different bases to work with (adenine, thymine, cytosine and guanine),
 There are 64 possible triplet codes, but only 20 amino acids are used to make all the
different proteins.
 What is the purpose of the other 44 codes? In fact, none of these is spare or redundant.
 only one of the strands of the DNA molecule carries the code for proteins. This is called the
coding strand or the sense strand.
 The other strand is the non-coding or antisense strand.
 Most amino acids have more than one code.
 Only methionine and tryptophan have just one triplet that codes for them; arginine has six.
 Three of the triplets (TAA, TAG, and TGA) do not code for amino acids at all. They are
‗stop‘ codes that signify the end of a coding sequence. Because there is this extra capacity in
the genetic code, over and above what is essential, it is said to be a degenerate code.
177
 Besides being a triplet and degenerate code, the DNA code is a non-overlapping code.
 This means that each triplet is distinct from all other triplets. The last base in one triplet
cannot also be the first base (or second base) in another triplet.
 The genetic code is also a universal code.
 This means that the triplet TAT is the DNA code for the amino acid tyrosine in a human, a
giant redwood tree, a bacterium or in any other living organism
 codon a triplet of mRNA bases that has the code needed to make one protein

How does transcription take place in eukaryotic cells?

 During this process, the coded information in the DNA of one gene is used to synthesise a
mol of mRNA that will carry the code to the ribosomes.
 mRNA is similar to DNA that built from nucleotides; however, it is different from DNA in a
number of ways:
• It is a much smaller molecule

• It is single stranded

• The base thymine is replaced by uracil

• The sugar in the nucleotides is ribose, not deoxyribose

 The triplets of bases in mRNA that code for amino acids are called codons
 anticodon a triplet on tRNA complementary to a codon in mRNA
 The mRNA codons are identical to the DNA triplets that code for specific amino acids,
except that U (uracil) is substituted for T (thymine).
 To form the single-stranded mRNA when transcription takes place, only the antisense strand
of DNA is transcribed.
 Transcribing this would produce a complementary sequence of bases, similar to those in the
antisense strand, which would not code for anything.
In eukaryotic cells, transcription takes place in the following way:

 The enzyme DNA-dependent RNA polymerase (RNA polymerase) binds with a section of
DNA next to the gene to be transcribed.
 Transcription factors activate the enzyme.
 The enzyme begins to ‗unwind‘ a section of DNA. RNA polymerase moves along the
antisense strand, using it as a template for synthesizing the mRNA.
 The polymerase assembles free RNA nucleotides into a chain in which the base sequence is
complementary to the base sequence on the antisense strand of the DNA. This, therefore,
carries the same triplet code as the sense strand (except that uracil replaces thymine).
 The completed molecule leaves the DNA; the strands of DNA rejoin and re-coil.
 The mRNA molecule now contains the code for the protein that was held in the DNA of the
gene.

178
How does translation take place?
 All tRNA molecules have the same basic structure.
 The ‗cloverleaf‘ configuration of the molecule has at one end a triplet of bases called an
anticodon.
 This anticodon will be complementary to one of the mRNA codons.
 The other end of the tRNA molecule has an attachment site for the amino acid that is
specified by the mRNA codon.
 Ribosomes are made from ribosomal RNA (rRNA) and proteins organised into a large and a
small subunit.
 Within the ribosome, there are three sites that can be occupied by a tRNA molecule, called
the A, P and E sites

The following events take place:

 The first two codons of the mRNA enter the ribosome.

 tRNA molecules (with amino acids attached) have complementary anticodons to the first
two codons of the mRNA bind to those codons.
 A peptide bond forms between the amino acids carried by these two tRNA molecules and
the dipeptide is transferred to the tRNA in the A site.
 Ribosome moves along the mRNA by one codon, bringing third codon into the ribosome; at
the same time the ‗free‘ tRNA exits ribosome and tRNA with dipeptide moves into the P
site.
 A tRNA with a complementary anticodon binds with the third codon, bringing its amino
acid into position next to the second amino acid.
 A peptide bond forms between the second and third amino acids.
 Ribosome moves along the mRNA by one codon, bringing the fourth mRNA codon into the
ribosome, and the whole process is repeated until a ‗stop’ codon is in position and
translation ceases.
 The translation of mRNA code into a protein molecule requires energy. However, this does
not come from the hydrolysis of ATP as is usual in a cell, but from the hydrolysis of a similar
molecule, GTP – Guanosine Triphosphate. It is hydrolyzed to GDP and Pi

How is protein synthesis different in prokaryotic cells?

 The process of protein synthesis is essentially similar in both eukaryotic and prokaryotic
cells, with DNA being transcribed to mRNA, which is then translated to a polypeptide chain.
 However, there are some differences and these are linked to the fact that:
• Prokaryotic cells do not have a nucleus

• Prokaryotic mRNA does not need post-transcriptional processing

179
• Prokaryotes: transcription and translation are coupled; mRNA can be translated by ribosomes at
one end of its molecule while it is still being transcribed from DNA at the other end

 Eukaryotes: transcription and translation are separated

• Transcription occurs in the nucleus

•translation occurs in the cytoplasm

• Eukaryotic mRNAs are modified before leaving the nucleus

What becomes of the proteins that are synthesized?

 All our proteins are synthesised,
 But all our cells do not synthesise all our proteins.
 are alanine, arginine, asparagine, aspartic
acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine,
methionine, phenylalanine, proline, serine, threonine, tryptophan, tyrosine and valine
 The average adult protein requirement per day is about 50 grams.
 The proteins are hydrolyzed to amino acids in our gut and absorbed into the blood plasma by
active transport.
 they are then transported to the cells where they are used to synthesise
 Some amino acids can be made in our bodies by a process called transamination,
 the amino group of an amino acids is removed and transferred to a keto acid.
 The keto acid then becomes a different amino acid.
 Some amino acids not made from transamination, but from our food like fish, meat cereal,
milk etc.
What controls gene expression?
 The fact that some genes are sex-limited tells us that all genes aren‘t active all the time.
 e.g. – the genes that control the colour of your iris are present in all your cells, but all your
other cells aren‘t this colour – just the iris.
 Somehow, we can control which genes are active where.
How are genes switched on?
 Very often, genes are switched on by ‗transcription factors‘ that are present in the cell. These
transcription factors are usually proteins that bind to a regulatory sequence of DNA near to
the gene they influence.
 The transcription factors bind to a promoter
 The RNA polymerase transcribes the antisense strand of the DNA as it moves along; the
gene is now being expressed.
 Some cancers are caused by hormones acting as transcription factors
 Oestrogen is a steroid hormone it binds with a receptor in the cytoplasm.
 The oestrogen-receptor complex moves into the nucleus and binds with and activates specific
genes.
 In the breasts, and lining of the uterus, the activated genes cause cell division.

180
 Many breast cancers are said to be oestrogen-receptor positive, and cancer cells have
osterogen receptore hormone can bind, causing the same increase in cell division as it does in
normal breast tissue.
 The anti-cancer drug tamoxifen can bind with the oestrogen receptors
How are genes switched off?
 Transcription factors that promote the expression of genes.
 Other factors (group of substances) can act to repress gene action is known as short
interfering RNA (siRNA).
 siRNA are unusual because they are very short only about 21 to 23 nucleotides long and are
double stranded.
 They don‘t act on the gene itself, but they ‗interfere with‘ or ‗silence‘ the mRNA once it has
been transcribed from the DNA. This is called posttranscriptional interference
 the action of siRNA is as follows:
• Double-stranded RNA (dsRNA) is produced in the nucleus from a range of genes.

• Then split into the very short lengths that characterise siRNA by an enzyme called ‘Dicer’.

•The antisense strand of the siRNA then binds with a complex of molecules called RISC.

• The siRNA binds with mRNA allows RISC to degrade/cleave the mRNA into small fragments.

 Researchers have already shown that they can use siRNA

 to treat HIV by prevent the replication of HIV by silencing
 Can silence genes associated with cancer.

Mutation
What are mutations?
 Mutation is any spontaneous (random) change in the genetic material of an organism
 There can be -large structural changes involving
-whole chromosomes or parts of chromosomes,
-or changes that involve only a single base are called point mutations
 There are several types of point mutation that the bases in the DNA sequence of a gene is
altered by being copied wrongly when the DNA replicates.
 The different point mutations are:
• Substitution
• Addition
• Deletions

181
 The change to the gene can be dramatic and the result can be that the protein the gene should
code for is not made at all or a different protein is made
A) Substitution one base is replaced by a different bases
GAC GGG ATT GAG GAG GAC GGG A TG GAG GAG
Original sequence Mutated sequence
 The triplet ATT has been changed to ATG (no other triplet is affected). The original triplet,
ATT, codes for the amino acid isoleucine. However, the new triplet, ATG, codes for
methionine and the same protein would have been synthesized.
 Other substitutions can result in a ‗stop‘ triplet. In this case transcription ceases when it
reaches the stop code and a non-functional mRNA results.
Original sequence for an amino acid sequence

C A G C A G C A G C A G C A G C A G C A G

GIn GIn

C AG C AG C AG T AG C AG C AG C AG

GIn Stop

Incorrect sequence causes

shortning of protein

 Mutation causes sickle cell anemia abnormal hemoglobin that causes the red blood cells to
collapse into sickle-shaped cells under conditions of low oxygen concentration. The sickled
cells often fracture and stick together and block capillaries.
B. Addition and deletion

 Deletion mutation a base is ‗missed out‘ during replication one DNA nucleotide being
omitted from the sequence
 Addition: an extra base is added.
 Both these are more significant mutations than substitutions.
 Substitutions affect just one triplet and, because the DNA code is degenerate, may well have
no overall effect
 Because there is one fewer or one extra base, the whole sequence after the point of the
mutation is altered and these are frame shift mutations.
 A totally different mRNA is produced (if one is produced at all) and a non-functional protein
or no protein at all

182
What causes point mutations?

 Mutations occur spontaneously and randomly they are accidents that occur when DNA is
replicating. Mistakes happen.
 Mutations are rare events, surprising when you consider each cell contains 6 × 109 (six
billion) base pairs that might mutate!
 Biologists estimate mutations arise at rate of 1 in 50 × 106 (one in fifty million) base pairs.
 Each new cell will have, on average, 120 mutations.

This sounds rather worrying, but you should remember two things:

• Most of these mistakes (mutations) are detected and repaired, and

• Because 95% of our DNA is non-coding, most mutations are unlikely to affect coding genes.

Rate of mutation can be increased by a number of factors including:

• Carcinogenic chemicals, for example, those in tobacco smoke

• High-energy radiation, for example, ultraviolet radiation, X-rays

What are the consequences of gene mutations?

 There are a number of factors influence the answer to this, but, really, two important ones:
 which cells, and
 Which genes?
 Mutations that occur in a normal body cell (a non-sex cell) will have one of four possible
consequences:

• It will be completely harmless.

• It will damage the cell.

• It will kill the cell.

• It will make the cell cancerous, which might kill the person.

 The mutation will affect no other person; it will not be passed on to the next generation.
 However, if the mutation occurs in a sex cell, or a cell that will divide to give rise to a sex
cell, then it may be passed on to the next generation.
 Two types of genes are really important genes called proto-oncogenes and tumour
suppressor genes play important roles in regulating cell division and preventing the
formation of a tumour.
 When proto-oncogenes mutate, they become active oncogenes, which stimulate the cell to
divide in an uncontrolled manner.

183
 Tumour suppressor genes recognise uncontrolled cell division and act to suppress cell
division. If these genes mutate and become inactive, a tumour will form as uncontrolled cell
division continues.
 Tumor is a mass of cells created when cell replication gets out of control. Tumours cause the
disease cancer

Can mutations benefit an organism?

 Mutations produce harmful effects, but mutations are the raw material of evolution.
 Mutation is the only process that creates new genes.
 Crossing over, segregation, and random assortment in meiosis together with random
fusion in fertilization: reshuffle existing genetic material, but only mutation produces
new genetic material.
 Mutations in the DNA of bacteria can give them resistance to a specific antibiotic, such as
penicillin or ampicillin. These mutations arise spontaneously, as do all mutations.
 In 1947, four years after penicillin was used widely in the USA, the first penicillin-resistant
bacterium was found – it was a bacterium called Staphylococcus aureus.
 Bacteria can also ‗swap’ antibiotic resistance genes with each other.
 confer resistance genes are found in the plasmids – the ‗extra‘ small circular pieces of DNA

They can transfer these plasmids to other bacteria by:

• Conjugation- plasmid passes through special ‗conjugation‘ tube from one bacterium to another
• Transduction – a virus carries the plasmid from one to another
• Transformation – the plasmid is absorbed from a dead bacterium
 Antibiotic resistance the evolution of strains of bacteria that are not affected by antibiotics.
It is caused by the overuse of antibiotics
Chromosome mutations
 Chromosome mutations occur when there is any change in the arrangement or structure of
the chromosomes occur during meiosis at crossing over in prophase 1
 They are much bigger events than point mutations and result the death of a cell.
 They also affect the whole organism. For example, if essential parts of the DNA are affected
by chromosomal mutations, a foetus may be aborted

Inversion

184
 occurs when an area of DNA on a chromosomes, reverses its orientation on the
chromosomes,
 Just one inversion on chromosome 16 can cause leukemia.
 It is an inversion that leads to an embryo having too few or too many copies of genes, can
cause the embryo to miscarry, fail to grow, or be born with substantial medical problems.
 Chromosome 16 one of the 23 pairs of chromosomes in humans. It spans about 90 million
base pairs and accounts for nearly 3% of DNA in cells
 Chromosome 21 one of the 23 pairs of chromosomes in humans. It is the smallest of the
chromosomes
Deletion
o Cause of mutation, decrease number of genes occurs due to deletion of large section of a
chromosome.
o Deletion can result in a variety of genetic disorders, such as Prader-Willi syndrome results
from a malfunction of the hypothalamus (a small endocrine organ at the base of the brain),
which plays a crucial role in many bodily functions, including hunger and satiety,
temperature and pain regulation, fluid balance, puberty, emotions and fertility.
Insertion
 This mutation describes an increase in the number of genes caused when an unequal
crossover happens during meiosis. The chromosomes, become abnormally long or short
and stop functioning
Duplications
 genes are duplicated results in them being displayed twice on a single chromosome
 Duplication of the whole chromosome is more serious. Having three copies of chromosome
16, known as trisomy 16, trisomy 16 leads to babies being born with a range of medical
issues, such as
-poor fetal growth,
-muscular and skeletal anomalies,
-congenital heart defects and underdeveloped lungs

Chromosome non-disjunction
 Homologous chromosome, do not separate successfully to opposite poles during meiosis,

185
 the result is one of the gametes lacking a chromosome and the other having an extra
chromosome
 If this happens with chromosome 21, Down’s syndrome results. Those condition will have
47 chromosomes, in every cell chromosome, 21 cause -mental retardation, heart defects
and stunted growth.
Translocations
 A piece of one chromosome is transferred to another non-homologous chromosome
 This type of chromosome mutation is often responsible for chronic myelogenous leukemia.

UNIT 4
EVOLUTION
Evolution: is the change in genetic composition of a population over successive generations,
which may be caused by meiosis, hybridization, natural selection, or mutation. This leads to a
sequence of events by which the population diverges from other populations of the same species
and may lead to the origin of a new species.
Evolution - is the gradual and heritable change of population through time.
- is the most comprehensive science in biology.
- defined as the accumulation of inherited changes within populations over time.
- describes how life originates and develops into various forms
4.1 The Origin of Life
The 5 main theories are:

1. Special Creationism
2. Spontaneous generation
3. Eternity of life
4. Cosmozoan theory
5. Biochemical origin
1. Special creation theory: attributes the origin of life to a divine event that was masterminded by the
supernatural being God.
 It is nearly linked to religions.
 Science relies on provable events
 Religion relies on believing in that which cannot be proven, mainly focuses on spiritual
matters, philosophical matter that relates to morality
- concerns between humans and their God
- Less concerned with empirical observable facts and testable hypotheses but rather
with faith, the belief in things that cannot be proven.
 Religion mainly focuses on spiritual matters that, by their very nature, cannot be seen, touched,
or measured effectively. It has the following versions
a. young earth creationism- earth is only few thousand years and created in six 24 hours days.

186
  Agree that the Earth is round and moves around the Sun, they interpret all geology in the light of
Noah’s flood.
b. old earth creationism – genesis account creation of all living things through power of God.
- Suggest earth is very old.
c. Day – age and gap creationism- suggest that a large gap between formation of the earth and creation
of all animals and humans.
d. Progressive creationism- accepts big-bang as the origin of universe.
e. Theistic evolution/ evolutionary creationism - God invented evolution.
f. Intelligent design- God‘s handiwork can be seen in all creation
2. The theory of spontaneous generation (Abiogenesis): states that life has originated from non- living
organic matter abiogenetically (spontaneously).
e. g. - rotting meat........ Flies
- Sour wine ............ bacteria etc.
 Some of the supporters of abiogenesis were Aristotle, Needham, Van Helmont etc.
 The theory of spontaneous generation was first disproved by Francesco Redi.
 Louis Pasteur by his advanced experimental settings disproved the theory for the last time in the
way that can convince scientists to accept biogenesis and to reject abiogenesis.
3. Theory of eternity of life (Biogenesis): - regards life as eternal as matter itself.
- Life only changes its form but never created from dead (non-living) substance
- has no origin and has always existed. According to this theory life comes from
life never from lifeless things, and different types of organisms have always
existed on earth and shall continue to exist. However, the theory does not explain
how life originated in the beginning.
- Life is an inherent property of the universe.
- Albert Einstein was also one of the supporters of this theory.
4. Cosmozoan (Panspermia) Theory: hypothesize that meteorites or dust brought microorganisms to
earth which then evolved to the diversity of life we see today.
- Proposed by Richter in 1865 and supported by Arrhenius (1908)
- But this theory lack significant support as it lacks evidence.
- It is linked to eternal theory of life.
Version l
-Richter explained that life propagate from one place to another in the universe via Cosmozoa
(germs of cosmos).
Version 2
- In 1908 the Swedish physical chemist S. Arrhenius explained this cosmozoa and gave it the
name pansmermia . Life like bacteria propelled by radiation pressure through inters planetary
space to arrive earth.
- According to this theory air friction helped against heat for organisms to arrive Earth.
Version 3
- Pseudopanspermia(weak panspermia)
- According to this view, Organic molecules came to earth and reacted with other molecules on
Earth to produce the first life.
 All forms of the cosmozoan (panspermia) theory suggest that other celestial
bodies have been important in the origin of life on Earth
5. Biochemical theory of evolution (Oparin’s theory): states that the first life is the result of a set of
simple chemicals existed in the primitive Earth‘s atmosphere.
- linked to the work of two biologists:
1. Aleksander Oparin, a Russian biologist who first put forward his ideas in 1924, and
2. John Haldane, an English biologist independently put forward almost identical ideas in 1929 (before
Oparin‘s book had been translated into English).
187
They both suggested that:
• The primitive atmosphere of the Earth was a reducing atmosphere with no free oxygen – as opposed to
the oxygen-rich atmosphere of today
• There was an appropriate supply of energy, such as lightning or ultraviolet light, and
• This would provide the energy for reactions that would synthesis a wide range of organic compounds,
such as amino acids, sugars, and fatty acids.
Oparin suggested that the simple organic compounds could have undergone a series of reactions leading
complex molecules.
He proposed that the molecules might have formed colloidal aggregates, or ‗coacervates’, in an aqueous
environment. The coacervates were able to absorb and assimilate organic compounds from the
environment in a way similar to the metabolism of cells.
Haldane’s ideas about the origin of life were very similar. He proposed that the primitive sea served as a
vast chemical laboratory powered by solar energy. As a result the sea became a ‗hot dilute soup‘ of
organic monomers and small polymers.
In 1953, Stanley Miller conducted his now-famous spark-discharge experiment. He passed electric
sparks repeatedly through a mixture of gases that were thought to represent the primitive atmosphere of
the Earth. These gases were methane (CH4), ammonia (NH3), water (H2O), and hydrogen (H2).
Stanley Miller’s spark-discharge experiment analyzed the liquid in the water trap; he found a number of
simple organic molecules – like hydrogen cyanide (HCN)
He found a larger variety and more complex organic molecules were formed including:
• Amino acids – essential to form proteins
• Pentose sugars – needed to form nucleic acids
• Hexose sugars – needed for respiration and to form starch and cellulose
• Hydrogen cyanide again – but it has been shown that the nitrogenous bases found in nucleotides can be
synthesized in the laboratory using HCN as a starting point
 The biologist John Desmond Bernal suggested that there were a number of clearly defined
‗stages‘ in explaining the origin of life:
• Stage 1: the origin of biological monomers
• Stage 2: the origin of biological polymers
• Stage 3: the evolution from molecules to cell
 Bernal suggested that evolution may have commenced at some time between stages 1 and 2.
 The first two stages have been demonstrated as being possible in the conditions of the
primitive Earth, and research on stage 3 is well advanced.
Other ideas on the biochemical theory
 Professor William Martin Dusseldorf and Dr. Michael Russell Glasgow claim that cells
came before the complex organic molecules.
 Not living cells but inorganic ones made of iron sulphide, formed not at the Earth‘s surface
but at the bottom of the oceans.
 In their theory, a fluid rich in compounds such as cyanide, sulphides and carbon monoxide
emerged from the Earth‘s crust at the ocean floor.
 It then reacted inside the tiny metal sulphide cavities.
 They provided the right microenvironment for chemical reactions to take place. That kept
the building blocks of life concentrated at the site where they were formed rather than diffusing
away into the ocean. The iron sulphide cells are where life began

188
  All forms of the biochemical theory (abiogenesis) suggest that: life evolved from non-
biological molecules which reacted together and eventually formed pre-cells
Summary of main steps in the origin of life according to Modern theory of Origin of life
1. Free Atoms: - Hydrogen, Carbon, Nitrogen, Oxygen etc.
2. Formation of inorganic molecules: - H2, H2O, NH3, CO2
3. Formation of simple organic molecules:- CH4, HCN, simple sugars, fatty acids, glycerol, amino
acids, nitrogen bases ( purines and pyrimidine)
4. Formation of complex organic molecules: - Polysaccharides, fats, proteins, nucleotides, nucleic acids
5. Formation of protocell or protobiont: - Coacervates and microspheres
6. Heterotrophic prokaryotes: - Non photosynthetic and without organized nucleus
7. Autotrophic prokaryotes: - Photosynthetic and without organized nucleus
8. Eukaryotes: - With well-organized nucleus
How did autotrophs evolve on Earth?
 However the first organisms appeared – about 4 billion years ago – they were prokaryotes.
 They had no true nucleus.
 It seems likely also that they had RNA rather than DNA as their genetic material.
 It seems likely that they gave rise to three distinct lines of evolution leading to:
• Archaebacteria – prokaryotes including thermophilic sulphobacteria, methanobacteria and
halophilic bacteria
• Eubacteria – prokaryotes; ordinary bacteria and cyanobacteria (blue-green bacteria and
sometimes known as blue-green algae)
• Eukaryotes – eventually evolving into protoctistans, fungi, plants, animals (nearly all are
aerobic)
 One great change affected the evolution of early life forms was shift from the reducing
atmosphere to an atmosphere containing oxygen.
 This took place about 2.4 billion years ago. Where did this oxygen come from?
 The fossil record shows that cyanobacteria had been producing oxygen by photosynthesis
from about 3.5 billion years ago but that for almost 1 billion years the levels in the
atmosphere did not rise because the oxygen was absorbed by the vast amount of iron in the
Earth – it rusted!
 But, by 2.4 billion years ago, the concentration began to rise and the rate of increase
accelerated from 2.1 billion years ago.
 Cyanobacteria are photo-autotrophs; they use light as a source of energy, and CO2 as a
source of carbon (photosynthesis).
 They are among the earliest of autotrophs, using, not chlorophyll, but another pigment,
phycocyanin (which gives them their blue-green appearance), to capture light energy.
 Other primitive autotrophs used not light as a source of energy but chemical reactions and
are called chemo-autotrophs.
 Chemo-autotrophs use the energy from chemical reactions to synthesize all necessary
organic compounds, starting from carbon dioxide, only use inorganic energy sources.
 Most are bacteria or archae that live in hostile environments such as deep sea vents and are
the primary producers in ecosystems on the sea beds.
 Scientists believe that some of first organisms to inhabit Earth were chemo-autotrophs.
 The primitive sulphobacteria use hydrogen sulphide as the energy source.
 Hydrothermalism, particularly in deep sea vents, maintains the bacterial life of
sulphobacteria and/or methanobacteria.

189
 Bacteria are the only life forms found in the rocks for a long time, 3.5 to 2.1 billion years
ago. Eukaryotes became numerous 1.9 to 2.1 billion years ago fungi-like organisms
appeared about 0.9 billion years ago.
 The O2 produced by the photo-autotrophs had made it possible for aerobic respiration to evolve
as an energy-releasing pathway.
4.2 Theories of Evolution
1. Lamarck’s theory of evolution
 Lamarckism:
i. use and disuse
ii. Inheritance of acquired traits
Use and disuse:
- The continual use of structure or process develops or enlarges the structure or the process. Conversely if
not used the structure will be reduced.
E.g. use: 1. the neck of the giraffe and
2. The toes of water birds
According to Lamarck giraffes stretched their necks to reach higher branches and eventually become long
necked. Water birds strained their toes to swim and finally became webbed toes.
- Disuse – e.g. the wing of penguin
Inheritance of acquired characteristics:
The traits changed or acquired during the life time of an individual‘s could pass on to its offspring.
Accordingly, Giraffe‘s that had acquired long necks would have long necked offspring rather than short
necked of their parents.
These views of Lamarck were disproved after discoveries of genetics.
However, Lamarck believed that evolutionary change takes place gradually and constantly and this is
accepted.
2. Darwin’s theory of evolution
- Published his famous paper natural selection
- He observed different species finches in different Islands of Galapagos.
- He noticed by different finches occupied these islands and became adapted in different ways because
they faced different selection pressures.
e.g.: - Some of them with pointed beaks adapted to eat insects.
- Some of them with strong and short beaks adapted to crush seeds.
- He explained this as descent with modification. We now call this adaptive radiation.
- He summarized his observations in two main ideas:-
1. All species tend to produce more offspring than can possibly survive.
2. There is variation among the offspring.
From these observations he deduced that:
There will be a struggle for existence between members of a species (because of high reproduction and
resources are limited). Some members of a species Will be better adapted than others to their environment
(because there is variation combining these two deductions:
Those members of a species which are best adapted to their environment will survive and reproduce in
greater numbers than others less well adapted.
Therefore, the main ideas in his theories are:
- Fecundity
- Variation
- Competition leads to ‘Natural selection theory’
- Adaptation
Comparison of Lamarck’s theory of use and disuse with Darwin’s theory of natural
selection
190
Aspect of theory Lamarck’s theory of use and Darwin’s theory of natural
disuse selection
Variation Environment changes,There is a natural variation in
creating a need for the features and the variations are
organism to change heritable
Survival Development of new features Environment selects in favor
(e.g. longer neck of giraffe) in
of those traits that adapt the
order to survive organism to the environment
and against those that do not
Inheritance new features acquired during individuals with advantageous
lifetime of an individual are variations of traits survive in
passed to the offspring greater numbers and pass on
these advantageous variations
to their offspring
Evolution new species over time new species over time

3. Neo- Darwinism
 This incorporates the science of genetics.
Darwin didn‘t know the driving force behind variation and hence evolution.
Gene pool: - all the alleles of the all genes in a population.
Suppose an allele determines a feature (advantageous) to an organism in its environment.
The following will happen:
 Those with the advantageous allele of the gene will survive to reproduce than others
 They will pass these advantageous alleles to their offspring
 The frequency of the advantageous allele in the gene pool of the population will be higher in
the next generation.
 This process repeats over generations and their frequencies in the gene pool increase over
time.
- Mutations are important in introducing variation in to populations.
- Any mutation could produce an allele which:
 Confers selective advantage - the frequency increases
 Is neutral in its overall effect - the frequency may increase slowly, remain stable or decrease
 Is disadvantageous - the frequency of the allele will be low and could disappear from the
population.
 Neo - Darwinism take in to account the genetics and animal behavior (Ethology)
 Behavior can also be advantageous or not
Behavior patterns that confers a survival advantage will be selected for whilst those that do not will be
selected against.
e.g.: Imprinting in geese.
Darwinism Neo Darwinism

- Proposed by Darwin and Alfred - It is the modified Darwinism in the light of

Wallace genetics and ethnology

- Causes of variation are not included - It includes causes of variations like

recombination the theory of genes, hybridization and etc.

- Only small useful and continuous - Genetic variations especially mutation help

191
Variations help in evolution in evolution

- Unit of evolution is individual - Unit of evolution is population

4.3. The Evidence for Evolution

A. Evidence from fossil study (paleontology}
B, Evidence from Comparative anatomy (body structure)
C, Evidence from comparative embryology
D, Evidence from comparative biochemistry
E, Evidence from plant and animal breeding
A. Paleontology (Fossil record):-
 The word ‘paleontology’ refers to the study of ancient life and comes from the Greek words
palaios (ancient) and logos (study). Fossils form the basis of this science as they are the main
direct evidence about past life.
- Displays that living things have different age of fossils as they appeared on earth at different times. The
most direct evidence for evolution comes from the discovery, identification, and interpretation of fossils,
which are the remains or traces typically left in sedimentary rock by previously existing organisms.
 We can group fossils into two categories:
Category 1: the remains of the dead animal or plant or the imprint left from the remains, including:bones,
teeth, skin impressions, hair, the hardened shell of an ancient invertebrate such as a trilobite or an
ammonite, an impression of an animal or plant, even if the actual parts are missing.
Category 2: something that was made by the animal while it was living that has since hardened into stone;
these are called trace fossils and include: footprints, burrows, coprolite (animal faeces)
How Fossils form?
1. Death without decomposition
 The organism must die near water
 The dead is covered with water.
 This prevents higher decomposition by bacteria but soft parts could decompose.
2. Sedimentation
 Tiny particles (solid) settle out of the water and bury parts of an organism.
 Sedimentation further insulates the dead from decomposition.
 The nature of the sediment also determines the quality of fossil.
 Sediments like clay form more detailed fossil.
 The chemical content of the sediment determine the nature of the fossil. E.g.: Iron rich
Sediment makes a reddish color, whereas phosphate rich will give a grey or black color.
3. Permineralisation
 As time passes, the sediments change into rock.
 As water seeps through it, the minerals in the water glue the sediment together more (these
minerals are different from the original).
 Over millions of years, these minerals dissolve the original hard parts of an organism replacing
exoskeleton with molecules of Calcium carbonate or another.
 This takes the shape of an organism (now rock).
 Now, this rock is differently visible (appear) from other nearby rocks.
4, Uplift
 As the continental plates move around the earth, colliding with each other, mountains form
 Therefore, what were sea floors are lifted up and become dry land.
192
  The fossil becomes exposed.
How can we date fossils?
1. Stratigraphy
- Uses a strata of sediment rocks
- The lowest layers become the oldest strata and also the oldest fossil.
- The upper strata is the recent strata and also be the recent fossil
 Used to date fossils over 10 million years old
2. Radioactive dating method.
i. Radioactive Carbon dating or
ii. Potassium argon dating
These methods rely on the principle that radioactive atoms decay into other atoms overtime.
Half-life time (1/2t)
 During this period (1/ 2t), half of the radioactive element (50%) decay and 50% remains.
For example: The half-life of C14 is 5730 years.
 By 5730 years, half (50%) of the original C14 is decay into N and 50% remains radioactive.
 By the 2nd half-life (11460 years), 25% remains radioactive. Therefore, 75% already decayed.
 By 3rd half-life (17190 years) 12.5% of Carbon 14 is still radioactive and etc.
 Potassium–argon dating works in the same way, but the half-life in this case is 1.3 million years.
This makes potassium–argon dating suitable for dating rocks millions of years old, whereas
radiocarbon dating is really only accurate with rocks up to 60 000 years old.

B. Comparative anatomy: shows that organisms may have either homologous structure or analogous
structure.
Homologous structure: structures which have the same origin (common ancestor) but may or may not
have the same function.
- Anatomically similar structures inherited from a common ancestor and have a
common evolutionary origin; but may have different functions.
- have different functions because of their adaptation for different habitat (divergent evolution)
Examples: - wings of birds and forelimbs of mammals

Analogous structure: structures those have different origin (have no common origin) but have
the same function (same adaptation for similar habitat) what it is called convergent evolution.
Examples: - wings of birds and wings of insects -
C. Comparative embryology: similar origin and development of embryos show common origin of
vertebrates.
- This shows similarities which supports common ancestry.
 Comparative embryology provides evidence of evolution because: very different embryos show
similarities in their early development
Example: All vertebrates embryo have gill slits and tails.
- Gill slits - connect throat to outside in next development in some. But in others it will be closed.
- In fishes it develops into gills.
- In humans, the tail is reduced to coccyx (tail bone).
D. Comparative biochemistry: ancestrally related species show similar biochemistry and physiology
because of common origin.
- rely on DNA and proteins.
DNA:
- The base sequences of d/t organisms compared.
Isolating DNA from two species (Species A and Species B)
193
- Heating both DNAs to form single stranded DNA (ssDNA)
- Mixing the ssDNA of two species and cooling.
- Looking the hybridization of two ssDNA from two species
- There are also sites of mismatching (not pairing).
- This helps to calculate the percentage of similarities.
Proteins
Ex: - Cytochrome C (in ETC of respiration)
- Hemoglobin
Haemoglobin is similar in all organisms that possess it, but there are differences.
Example: In lamprey (fish like animal) is only one polypeptide chain of hemoglobin not 4.
- Most animals have 4 chains but the chains do vary.
Example: Lampreys 125 amino acid difference to humans.
- Frogs 67 amino acid differences in chain.
- Dogs 32 amino acid sequence in chain.
- Macaque 8 amino acid sequences only in the hemoglobin.
This indicates that, macaques are the close relative to humans.
E. Breeding of plants and animals: selective breeding of domestic plants and animals shows
that the characteristics of species are modifiable and changeable
- This is artificial selection (selective breeding).
- These were done to obtain:
 High yield (like milk, seed, beef)
 Desired traits.
 If new verities can be produced by selective breeding, then natural selection should also
able to produce new verities, and eventually, new species.
 Plant and animal breeding provide evidence of evolution because they show that selective
breeding can produce new varieties
4.4 The Processes of Evolution
Natural selection:-
- is the differential survival and reproduction of individuals due to difference in phenotype.
- favors the survival and reproduction of individuals with the best fitted and adapted genotypes
while it perishes the unfavorable genotypes in a population
It is constantly changing due to mutations, and gene recombination that introduces new genes into the
population.
Types:-
A. Directional selection: favors the phenotypes at one extreme over the others.
- reduces variation
Individual at one extreme could have a disadvantage whereas those at the other extreme have an
advantage.
Ex: Thicker fur (longer fur) in cold climate (in foxes) is an advantage.
B. Stabilizing selection:
- Favors individuals of a population with average values (traits).
- Favors an intermediate phenotype and acts against extreme variants.
- reduces variation and improves adaptation of population to aspect of the
environment that remains relatively constant.

194
Ex: Birth mass in human. Both over weight and under weight babies shows a higher neo natal mortality
rate than those of medium mass.
C. Disruptive selection:
- favors individuals of a population with the extreme value (trait)
- Intermediate phenotypes can be eliminated from the population
- May even split a population into two sub- populations
Example; Darwin Finches, The medium sized beak finches neither crush the seeds unlike those with
powerful and short beaked nor look for insects from cracks unlike those with very longer beaks.
Therefore, overtime, both with shorter and powerful beaks and longer beaks increase in number and those
with medium sized beaks number decreased in number.
Formation of new species
 This is called speciation.
Species: A group of similar, interbreeding organisms that produce fertile offspring.
There are two forms how different species form. These are:
a. Allopatric speciation
b. Sympatric speciation
a. Allopatric Speciation
- Some physical barriers must isolate the population.
E.g.: - river changing course
- Mountains
- Land mass separating two bodies of water
 This is type of geographical isolation
 There is no interbreeding between the population and speciation could result.
e.g.: Isthmus of Panama separating the Caribbean Sea and North Pacific ocean which were joined 3
million years ago. Two populations of shrimps formed as a result. Now, they will not reproduce even if
they come together, rather they show an aggressive behavior.
b. Sympatric speciation
- No physical barrier.
The population inhabits the same area but prevented from breeding in different ways.
i Seasonal isolation - reproducing at different seasons.
ii. Temporal isolation - reproducing at different times of a day.
iii. Behavioral isolation - with different courtship patterns.
e.g.: palm trees growing on one island of Australia. The islands soil is partly acidic and partly alkaline.
 The palm trees growing on these soils reproduce at different seasons of a year.
 This is also an example of disruptive selection as the palms must grow on acidic or alkaline soil
types.
Divergent evolution: a pattern of evolution in which species that was once the same diverges or
become increasingly distinct.
- occurs when populations change as they adapt to different environmental conditions. The
pattern of speciation and adaptive radiation are examples of divergent evolution. Adaptive
radiation was noticed by Charles Darwin in different species of finches found in Galapagos Islands
- finches have adapted to feeding on different kinds of food.
Convergent evolution:
- Two completely unrelated species share similar traits. Similarity arises because each species
has independently adapted to similar environmental conditions.
- In which different species appear similar due to similar adaptations (analogous structures).
- Example pectoral fins of fish and flipper-like forelimbs in dolphin.
What are Divergent evolution and convergent evolution?

195
Divergent evolution(adaptive radiation) Convergent evolution
- Development of different characteristics - Tendency of different species to develop
by organisms derived from the same ancestor similar characteristics
- Occurs when similar organisms occupy - Occurs when different organisms
different niches occupy similar niches
- Evolution of different adaptations - Evolution of similar adaptations
E.g. - the evolution of the different species of E.g. -evolution of the giant armadillo, giant
finches on the Galapagos Islands pangolin, giant anteater, and spiny
- the evolution of the different forms of the anteater.
pentadactyl limb
 Convergent evolution is also responsible for the wings of a bird, a bat, and the extinct
pterodactyl.
Co- evolution: when two or more species depend heavily on each other for their survival and
propagation that they constantly evolve together.
A population is a group of individuals of one species that live in the same geographic area at the
same time.
4.5 The evolution of humans
 Human evolution shows the gradual changes of genetic make ups, physical appearance,
sizes, physiology, morphology and other aspects due to different causes.
 Human evolution is caused by different factors.
 Cause of human evolution can be manmade and natural cause of human evolution
without human input (effect) are natural causes of evolution like genetic disorders, natural
mutation, evolution due to ultraviolet etc.
 Same are induced causes of evolution like genetic engineering (biotechnology) different
therapy, medicine, processed food, food preservatives etc.

Who are we and where have come from?

The evolution of homo sapiens is still debated a lot and remains to be studied.

- Human beings can be described as:

Homo-erectus - up righted man

Homo habilus - hand users to hold tools

In general we modern humans: Homo sapiens.

are the latest of several human to live on the planet
have two unique features that distinguish from other human races. These are:
1. Very huge brain

2. Bipedalism to walk truly on two legs

Evolution has its own evolutionary lines represented by evolutionary tree.

Evolutionary tree shows the relationship among different primates.
Hominine: represents any member of genus Homo.
196
 Hominid: represent groups of species that includes all species that belong to genus homo.
What is significant about Lucy & Ardi?

Lucy and Ardi are important fossils found in Ethiopia.

Modern human and chimpanzee came from common ancestor.
Lucy was discovered by Donald Johansson and Tom Gray in 1974 at Hadar in Ethiopia.
Lucy is a fossil dated about 3.2 million years ago with following characters:
Species Australopithecus Afarensis
she was female adult.
she was 25 years old.
her skeleton was 40% completed.
She was bipedal.
She was partly arboreal /tree dwellers/
Has 107cm tall.
She was 28kg by mass.
She was the oldest fossil Hominines.
Size is between modern human & Chimpanzee.
She had brain its size is like chimpanzee.
Bipedalism came before large brain.
Ardi Fossil: was first discovered in 1992 in the afar desert in Ethiopia.
Research papers show Ardi’s unique character position in human evolution.
It was 1.2 million years older than Lucy.
It was female.
The fossil is 4.2 million years older.
It belongs to Ardipithecus -Ramidus.
She was bipedal.
Her ancestor is nearest to humans & chimpanzee.
Ancestors of chimpanzee & humans are not exactly resembled because chimpanzee
is not truly bipedal (two legs).

 According to evolutionary lines human brain size increases from time to time.

Large brain size helps people to: Run faster

Have more upright posture
Plan in advance to avoid attack
Develop & use tools as well as weapons
Are we still evolving?
Homosapines originated from East Africa and distributed into different environments
throughout the world.
Due to different biological & physical factors we are still evolving throughout the
world.
Based on this evolutionary effect there are three human races.
1. African (Negroid) includes 100 million peoples from Africa & Melanesians of the South pacific.
197
2. Eurasian (Caucasoid) 1000 million people ranging from white to dark brown.
 Nordic - often tall, blonde and narrow-headed; includes people from Scandinavian and Baltic
countries, Germany, France, Britain
 Mediterranean - usually lighter in body build, dark and narrow-headed; includes people from
Southern France, Spain, Italy, Wales, Egypt, Jews, Arabs, Afghanistan, Pakistan, India
 Alpine includes usually broad headed, square jaws, olive skin, brown hair, includes peoples
from Mediterranean to Asia.
3. East Asian (Mongoloid)- are most numerous of the present day populations and split into three groups:
a. East Serbians, Eskimos, North American Indians.
b. Japanese, Koreans & Chinese.
c. Indonesians & Malays
We may still evolve into diverse species, but, at the moment, the mechanisms that usually drive
speciation have been modified by our large brains.

UNIT 5
BEHAVIOUR
5.1. What is behavior?
Behavior has many definitions as follows. Behavior:-
- is behaving bad or good.
- is observable response to any situation
- is manner of acting or conducting
- Way of behaving towards others
- Action or reaction of a person with stimuli
- The movement of organisms to some stimulus or away from the stimulus
However the better definition of behavior is coordinated response to internal or external stimuli.
- Any behavior has the following components.
 Receptor - detect stimuli
 Effector - produce response
 Coordinators - influenced by receptor and influence effector
- This is represented by the following flowchart
Stimulus Receptor Coordinating system Effector Response.
 Neuroscience the branch of science concerned with the brain and the nervous system
 neuroethology the study of how behavior is linked to neural pathways
 neural pathway a sequence of nerve cells involved in bringing about a specific behavior
 The study of animal behavior is often called ethology and the biologists are known as
ethnologists
How do plants respond to unidirectional stimuli?
 The process of elongating plant shoots towards light intensity is known as phototropism.
 Plant shoots are positively phototropic because they grow towards light.
 Plant growth towards light is maintained by plant growth hormone called auxin.
 Plants can response in the following pattern
1. Phototropism- Provide response to light
2. Thigmotrpism - Provide response to touch.
3. Gravitropism - Provide response to gravity
4. Hydrotropism -Provide response to water and etc.
How do simple animals respond to stimuli?
 Plants respond to stimuli by growing towards or away from stimuli but animals move away or
towards stimulus.

198
Taxis (pl. taxes): is movement of small animals towards (positive taxis), or away from (negative taxis) a
stimulus.
Positive taxis: - Move towards Intensity of Stimuli
e.g. euglena Towards Light
Negative taxis: - move away from intensity of stimulus
e.g. some animals move away from light
Kinesis (pl. kineses): is change in rate of movement due to change in stimulus intensity. It
does not involve change in direction.
 Intensity of stimulus change threats of movement. But not directional
e.g woodlice
Importance of studying behavior

 Studying animal behavior is important because we can gain information that can be used in:-
- Neuroscience: - in collecting behavioral data, determining neural pathways and
displaying influences on physiology and cellular process.
- the environment and resource management:- in providing early clues of environmental
damage
- Animal welfare: - to ensure effective standards for the care and wellbeing of research
animals.
- science education:- to intensify studies and students interest at higher education
- Human behavior:- as basis for interpreting human society and understanding possible
causes of problems in society

Types of behavior
Innate behavior(inborn) Learned behavior(acquired)
- is natural potential (software) - gained by experience
- Programmed by nature - easily gained and lost
- hard to lose or modify - can be modified
- has fixed action pattern - may not have fixed pattern
5.2 Innate behavior (inborn)
Instinctive behaviors have the following characteristics:
• They are common to all members of a species
• They are fully functional the first time they are performed (they require no learning)
• There is a key stimulus that triggers the behavior
• There is an innate releasing mechanism that links the stimulus to the response (this may be
nervous or hormonal)
• There is a fixed action pattern in response to the key stimulus that is always the same, and
• Instinctive behaviors are adaptive – they have been retained in the species by natural selection
because they confer a survival advantage.
Structure of Nervous System (NS)

199
5.2.1. Types of innate behavior
1. Reflex actions
- are simplest forms of behavior
- out of human control
e.g - with draw hand
- sneezing
- Knee jerk
- Blinking
- vomiting
2. Orientational
eg - taxis and kinesis
- More complex behavior
- Process of moving from unfavorable to favorable conditions
3. Instinctive behavior
- Most complex behavior
- Hard to modify
- has fixed action pattern
- has key stimulus
e.g - nest building
- weaving a web
- imprinting
How human reflex action brought about?
 Somatic reflex
Controlled by skeletal muscles
e.g Knee jerk, withdraw hand from heat

 Autonomic reflex
- Controlled by internal organs
eg heart beat
Biological clock

A biological clock is an internal regulatory mechanism that controls a cyclical process in an

organism; it may be:-

- circadian (controls a daily cycle)

- lunar (controls a monthly cycle)
- circannual (controls a yearly cycle)

200
 Biological clock
A biological clock is an internal regulatory mechanism that controls a cyclical process in an
organism; it may be:-

- circadian (controls a daily cycle)

- lunar (controls a monthly cycle)
- circannual (controls a yearly cycle)

 It can be entrained.

Imprinting is another kind of instinctive (inborn) behavior in newly born (hatched)

organisms. It is the process by which animals acquire their first forms of behavior,
particularly their attachment to their mother. Fixed action pattern (FAP) is for newly
born/hatched/ organisms to imprint on or become attached to the first thing they see that has
certain general features
E.g. In humans, Strong emotional bond (attachment) between an infant and its primary care
giver (often the mother) occurs in three stages:
• Pre-attachment (0-2 months):- the infant prefers people to objects without discrimination.
• Indiscriminate attachment (2-7 months):- the infant begins to show a preference for
familiar people
• True emotional attachment to one person initially (from7th months onwards):- but soon
multiple attachments form.
5.3. Learned behavior
It is known as acquired behavior.

 Is gained after birth.

 Gained by experience.
 Is not common to all members of the group.
 Trial and error improves their effectiveness
There are different kinds of learned behavior. These are:
- Habituation - associative learning
- Sensitization - classical conditioning
- Insight learning - latent learning
Habituation: is a type of learned behavior in which organisms being sensitive to the stimulus and then
decrease their sensitivity due to repeated response.
e.g deodorant smell into new room through time our sense of smell adapts & loses response.
Sensitization: is the opposite of habituation
- increasing sensitivity of the organism to particular stimulus
- increase response to harmless stimulus
 In higher animals, peripheral sensitization refers to the sensitization those results from changes in
neurons of the peripheral nervous system.
 Central sensitization refers to the same process occurring in neurons of the central nervous system.
e.g. A person becomes more sensitive to snake sight during his adulthood proceeded by a snake
bite during childhood.
201
Classical conditioning: Is the process of associating naturally occurring stimulus with different stimuli
example Pavlov’s experiment on dogs.
It has - Unconditioned stimulus (US) - natural e.g. Food
- Unconditioned response (UR) - e.g. hunger (salivation)
- Conditioned stimulus (CS) - bell attached with food.
- Conditioned response (CR) - salivation for bell.
What is operant conditioning?
Operant conditioning can modify more complex, voluntary behaviors by animals,
person learning to associate the behavior with certain specific consequences.
Skinner identified three types of responses that he called operant that can follow behavior:
1. Neutral operant:-Neither increase nor decrease the probability of behavior being repeated.
2. Reinforcer:-Increase the probability of the behavior being repeated.
3. Punishers:- decrease the probability of behavior being repeated.
Example parents offering praise when their children do something positive and beating by stick when
they do something negative.
Specific examples of where shaping is used include:
• Training guide dogs for the blind
• Training horses
• Training dolphins and killer whales at marine parks
• Training zoo animals
 Both classical and operant conditioning are sometimes referred to as associative learning because
the animals learn to modify their behavior as a result of either associating two different stimuli or
associating particular behavior patterns with operant responses
What is latent learning?
 It is the process of using hidden knowledge to provide response or repeated behavior
 Using the previous experience to repeat the behavior
 Latent learning happens when the brain acquires knowledge at certain time, without
reinforcement, but does not use it until later, at a time when that knowledge is needed.
Example: a student studying very hard but not sure of his knowledge until he/she answers exam
questions correctly.
What is insight learning?
This one is different from trial and error in classical conditioning.
Insight learning is the process of finding solutions for particular problems without
actual experience.
Insight learning is finding solutions to problems without experience (trial and error), it involves mental
―trial and error‖ and often the solution is learned suddenly.
Example: Wolfgang Kohler worked (experimented) with chimpanzees to demonstrate insight knowledge.
A chimpanzee was placed in an enclosed room where a bunch of bananas was hanging from the ceiling
out of reach of the chimpanzee. Empty boxes were also placed in the room. The chimpanzee piled up the
boxes and climbed up to reach the fruits.
5.4. Examples of behavioral pattern
 Different organisms have different behavioral patterns.
What is courtship behavior?
Courtship behavior is the interaction of couple animals for the mating and reproduction purposes.
Animals have different communication styles for their courtship behavior.
Example: some use pheromones /chemicals /
- Some Use Sound /songs/
202
 - Some Use Physical activity and other communication style.
• Generally courtship behavior may involve:-
−secretion of sex pheromones
−courtship vocalizations
−touch
−complex displays involving a series of fixed action patterns
Pheromones:
This is yet another term derived in part from a Greek word and translates as ‗hormone bearer‘. It is a
chemical secreted by one animal, usually the female, to produce a behavioral response in another. There
are many different pheromones, including:
• Alarm pheromones that are secreted by animals when attacked and produce the response of flight or
aggression by others of the same species

• Releaser pheromones that are highly volatile and can attract a mate from a distance of two miles or more

• Territorial pheromones that are used to mark the boundaries of a territory by the owner; dog urine
contains a powerful territorial pheromone

• Sex pheromones that signal the availability of a female for mating

What is territorial behavior?

Territory: is any space that an animal defends against intruders of the same species.
- Territorial behavior is found in nearly every species of animal‘s even humans.
- Possessing territory gives the holder‘s areas to forage for food and
increase the chance of attracting for mating.
Territorial behavior can involve:
−marking the area
−threatening vocalizations
−threat displays (exaggerating size or displaying weapons)
−ritual fighting
- Territorial animals usually defend areas for:-
 nest
 Den or mating
 Sufficient food for themselves & their young.
Examples Ethiopian wolves defend territory by urination.
Some animals are fighting for defending their territory.
Ritual fighting: is the behavior in which the acts of fighting are displayed without physical contact.
What is social behavior?
- Social behavior is the interaction between or among individuals of some species.
- It is common in social animals like honey bee.
- There are three castes of honey bees.
These are:-
1. Queen: reproductive female
2. Workers: non-reproductive female
3. Drones: reproductive male.
 Only 1 queen is found in one hive.
 Workers from 10,000 - 50,000 are in one colony.
 Drones are from 100 - 500 in one colony.
 Honey bees have complete metamorphosis.

203
 Egg →Larva→ Pupa→ Adult
 Many duties are left for workers bees.
 Worker bees have different communication styles to show:-
 Food source.
 Distance from their hive
 Angle & direction too.
 Honey bee make wag - dance to show food source and distance.
 Angle of dance shows angle of nectar from the sun.
 The length of the straight run is part of dance that shows proportional distance from the nest.
 Social insects have division of labor among themselves.
Benefit s of social behavior

- form stable groups and reduce intra-specific aggression

- improve the effectiveness of reproduction and/or parenting
- forage more efficiently – especially if sources of food are localized
- protect themselves against attack more effectively
- increase the chance of surviving migration
- increase the chance of surviving extreme conditions
- Communicate across long distances.

204