Biology

Notes
Form one
“It is not what I do for you but what I will teach
you to do for and by yourselves that will eventually
make you successful beings in the society”

INTRODUCTION TO BIOLOGY
By the end of the topic, the learner should be able to:
(a) Define biology (b) List branches of biology

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(c) Explain the importance of biology (e) State the main differences between plants
(d) State the characteristics of living and animals.
organisms
Practical Activities
Collecting, observing and recording external features of plants and animals
Biology is a branch of science that deals study of living things.
Branches of Biology
Biology is such a broad field of knowledge. It is divided into two broad branches
1. Zoology- This is a branch of biology that deals with the study of animal life.
2. Botany- This is a branch of biology that deals with the study of plant life.
Within the two branches, there exist even smaller branches because the branches (botany and
zoology) are very wide and complex.
The smaller branches of biology include:
a) Ecology- This is the study of the interrelationships between living organisms and
their environment.
b) Genetics- This is the study of inheritance and variation.
c) Entomology- This is the study of insects.
d) Parasitology- This is the study of parasites.
e) Physiology- This deals with the study of the functions of various structures of an
organism.
f) Anatomy- The study of the internal structure of organisms
g) Microbiology- This is the study of microorganisms
h) Bacteriology- The study of bacteria
i) Ornithology- This is the study of birds
j) Ichthyology -This is the study of fishes
Importance of biology
1. The knowledge is helpful in solving environmental problems such as food shortage,
poor health services, pollution and environmental degradation.
2. Entry into various careers such as medicine, veterinary medicine, animal husbandry,
horticulture and dentistry.
3. Development of scientific skills which are very useful in life. E.g. observing, identifying,
recording, classifying, measuring, analyzing and evaluating.

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 4. Enhancing international cooperation. Some biology related international conventions
include:
 Joint development of HIV/AIDS vaccine by Kenyan and British scientists.
 The coordinated fight against Severe Acute Respiratory Syndrome involving scientist
all over the world.
 The fight to save the ozone layer from depletion through various international
agreements such as the Kyoto protocol.
 Management of resources through international treaties such as the CITES
(Convention against International Trade on Endangered Species).

CHARACTERISTICS OF LIVING THINGS
Living things share a lot of characteristics in common. These characteristics are discussed below.
a) Nutrition
Nutrition is the process by which living things obtain and assimilate (utilize) nutrients.
Living things require nutrients for various physiological purposes; growth, repair of worn out
tissues and for provision of energy. Plants manufacture their own food using light energy, carbon
(IV) oxide, water and mineral salts through the process of photosynthesis. Conversely, animals
feed on already manufactured foods from plants and other animals.
b) Respiration
Respiration is the process by which food substances are chemically broken down to release
energy. The energy produced in living things is very useful as it enables the living things carry
out some of their physiological processes. E.g. Growth and development, movement and repair
of worn out tissues
c) Gaseous Exchange
The process by which living things exchange oxygen and carbon (IV) oxide across the
respiratory surface. Animals require oxygen for aerobic respiration. Gaseous exchange,
therefore, enables animals obtain oxygen for respiration and get rid of carbon (IV) oxide, a waste
product.
Plants, however, require carbon (IV) oxide for photosynthesis during the day. They give away
oxygen as a by-product. The plants equally require oxygen for respiration and give away carbon
(IV) oxide.

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 d) Excretion
This is the process by which living things separate and eliminate the waste or harmful materials
from their cells. These harmful waste products of metabolism are toxic to the body if they are left
to accumulate in the cells of the living things.
e) Growth and Development
Growth refers to an irreversible/ permanent increase in size and mass
Development refers to the irreversible/permanent change in complexity of the structure of living
things. Growth and development is essential as it enables the living things to attain maximum
size and can enable them to perform their functions and roles.
f) Reproduction
This is the process by which mature living things give rise to new individuals of the same kind.
All living things reproduce. Reproduction is essential as it leads to perpetuation of species and it
avoids extinction of certain animals and plants.
g) Irritability
This is the ability of living things to perceive (detect) changes in their environment and respond
to them appropriately.
These changes are crucial as it enables them to escape from harmful stimuli.
Also obtain resources in their environment.
h) Movement/Locomotion
Movement refers to change is position (displacement) of a part or parts of an organism.
Movement in plants includes folding of leaves, closing of flowers and growing of shoots towards
light. The change of position of an entire organism from one position to another is locomotion.
Living thing; is any organism/life form that possesses or shows characteristics of life.
Study questions
a) Motor vehicles move, use energy and produce carbon dioxide and water. Similar
characteristics occur in living organisms yet motor vehicles are not classified as living.
List the other characteristics of living things that do NOT occur in motor vehicles.

Characteristic Plants Animal

Movement Localized growth movement Generalized and locomotory movements

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Nutrition Autotrophic Heterotrophic
Irritability Slow response Rapid response
Excretion Lack specialized system Have complex system
Growth Indeterminate/occur at root, shoot Determinate/ occur equally in all parts
tips
Cell Have cellulose cell wall/chloroplast No cell walls and no chloroplast

Main differences between plants and animals

Plants Animals
Have chlorophyll hence carry out Lack chlorophyll hence feed on already made
photosynthesis(Autotroph) food (heterotroph)
Only move Move and locomote
Respond slowly to stimuli Respond rapidly to stimuli
Lack specialized excretory system Have a complex excretory system
Their cells have cellulose cell wall Their cells lack cellulose cell wall
Store carbohydrates as starch and oils Store carbohydrates as glycogen and fats

Collection of Specimen
Specimen; living things or some parts of living things for observation and analysis.
A laboratory is a building or a room that is designed and equipped for scientific studies.
Some of the animals are not easy to catch while some are quite dangerous. Knowledge on proper
specimen collection and handling of is very important.
a) Sweep net- This is used for catching flying insects.

b) Fish net- This is used for trapping small fish and other small water animals.

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c) Pooter- This is used for sucking small animals from rock surfaces or barks of trees.

d) Bait trap- This is used for attracting and trapping small animals including rats.
e) Pit fall trap- This is used for catching crawling animals.

f) Pair of forceps- an apparatus used for picking up small crawling stinging insects.
g) Specimen bottles- These are bottles used for keeping collected specimen.
h) Magnifying lens/hand lens- used to enlarge the image small objects being viewed
The magnifying power of the hand lenses is always indicated on the lens e.g. X10, X5,
X8. The magnifying power of a lens shows how many times the image will be enlarged
compared to the object.

How to use a magnifying lens

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To use a magnifying lens, place the object to be enlarged on the bench. Hold the magnifying lens
on one hand and while closing one eye, move the lens towards the object until the image comes
into clear focus.If a magnifying lens is used to make a drawing of a specimen, the magnification
of the drawing will have no relation with the size of the drawing.
The magnification of the drawing can be calculated using the formula shown below.

Drawing magnification=

The sign of “times” must come before the magnification value e.g. X10, X5, X 15 etc.
Handle for holding hand lens and focusing
Biconvex lens for magnifying the image of the specimen
Frame hold biconvex lens in position
Precautions During Collection and Observation of Specimen
 Collect only the number of specimen you need; (do not collect more than you need.)
 Do not harm the specimen during the capture/collection exercise.
 Do not destroy the natural habitat of the specimens.
 Handle dangerous/injurious specimens with care(stinging plants or insects). Forceps and
hand gloves should be used in such cases.

CHAPTER TWO: CLASSIFICATION I

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By the end of the topic, the learner should be able to:
(a) Use the magnifying lens to observe the external features of plants and animals
(b) Record observations of the main external characteristics of living organisms,
Preserved specimens and photographs
(c) State the necessity and significance of classification
(d) Name the major units of classification
(e) State the application of binomial nomenclature in naming organisms.
Introduction
 Classification refers to the grouping of living organisms according to their similarities and
differences in structure.
 Taxonomy The scientific study of classification.
 Taxonomist A biologist who specializes in classification.
 Taxon is a unit/rank/level of classification. (plural – taxa)
 In classifying organisms taxonomists to a great extent rely on the use of external observable
features of organisms.
External features of plants used in classification
 The rhizoids as in moss plant  Presence or absence of flowers
 Fronds in ferns  Type of leaves; simple or compound;
 The type of root; tap root, leaf venation- parallel or net work
adventitious, fibrous, prop, buttress veined.
roots.  Presence and types of fruits and
 Stem presence and type. cones.
External features of animals used in classification
 Tentacles in hydra  Proglotids in tapeworms
 Body covering- feathers, scales, fur  Mammary glands in mammals
 Shells in snails  Locomotory structures
 Wings in birds  Body pigmentation
Importance of Classification
 Enable identify similarities and differences among organism
 Organize scientific information in an orderly manner to avoid confusion
 Monitor the emergence, presence & disappearance of organisms into & out of the earth
 Know the evolutionary trends among the organisms
 Help group organisms in specific Taxa
Taxonomic Units of Classification

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  Taxonomic units of classification refer to the groups or taxa into which organisms are
placed as a matter of convenience.
 In a classification scheme, a hierarchy of groups is recognized and it proceeds from the
first largest and highest group, the kingdom to the smallest and lowest unit, the species.
There are seven taxonomic units of classification.

Kingdom, Phylum (animals)/Division (plants), Class, Order, Family, Genus, Species

All living organisms are classified into five major kingdoms:

a) Monera- unicellular organisms mainly bacteria e.g amoeba.

b) Protoctista- are microscopic. Members of this kingdom include algae and protozoa.
c) Fungi- e.g. the mushrooms, toadstools, moulds and yeast.
d) Plantae- e.g. moss plant, ferns, maize plants, hibiscus, meru oak
e) Animalia – e.g. tapeworms, hydra, fishes, human beings, lizards, earthworms etc.
In hierarchy of classification, a kingdom is further divided into several phyla (plural of
phylum) or divisions (in plants). Within the phyla or divisions, organisms are further sorted out
into groups known as classes based on their similarities and mode of life. Each class is further
subdivided into small groups called orders based on structural similarities. Orders subdivide into
families which subdivide into genera (plural for genus).Genera are then subdivided into smaller
units of classification called the species.
Species is the unit of classification whose members freely/naturally interbreed to give
rise to fertile /viable offspring
Members of a particular species can, however, exhibit various differences e.g. differences in skin
colour or body forms. Within the species, organisms can further be classified based on the
differences in colour or forms. In humans, this gives the races, in animals the term used is breed
while in plants, variety is preferred. In bacteria, the term strain is used to describe the variant
forms.
Members of different but very closely related species can breed but the resulting
offspring will be sterile (infertile). In particular, a mule is a sterile offspring between a horse and
a donkey. Moving from kingdom to species, it is important to note that the number of organisms
in each taxon decreases. The similarities, however, increase as one move from kingdom to
species.
Binomial Nomenclature

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Scientific system of naming organisms using genus and species names
Reasons for binomial nomenclature
1. To avoid confusion while describing organism in local languages
2. To enable scientists to communicate internationally
3. To predict occurrence of new organisms
4. Enable scientists to understand the evolutionary relationships between two organisms
Rules of Binomial Nomenclature
a) The first name is the genus name which should begin with a capital letter. The second
name is that of species written in small letters e.g.
a) Maize- Zea mays c) Leopard- Panthera pardus
b) Lion- Panthera leo d) Human being- Homo sapiens
b) When printed in books and other printed works, the scientific names should be printed in
italics. However, in handwritten manuscripts and typed works, the genus and species
names should be lined separately.
Printed work- Homo sapiens
c) The specific name is frequently written with the name of the scientist who first
adequately described and named the organism e.g. Balanus balanoides (Linneaus.)
d) Scientists must give a latinised name for a newly described animal or plant species where
a Latin name is missing e,g.
Aloe kilifiensis- A type of aloe found in kilifi
Meladogyne kikuyuensis- A nematode found in kikuyu.

CHAPTER THREE: THE CELL

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By the end of the topic, the learner should be able to:
(a) Define the cell
(b) State the purpose of a light microscope
(c) Identify the parts of a light microscope and state their functions
(d) Use and care of the light microscope and calculate the magnification
(e) Identify the components of a cell as seen under the light and electron microscopes and relate
the structures to functions
(f) Compare plant and animal cells
(g) Mount and stain temporary slides of plant cells
(h) Describe animal cells as observed from permanent slides
(i) Estimate cell size
(j) State the differences between cells, tissues, organs and organ systems.
Introduction
 Cell is the basic unit of life/ basic structural and functional unit of life.
 The bodies of living organisms are made up of small microscopic units called cells.
 The cells make up the structures of the living organisms and are responsible for carrying
out various biological processes in the bodies of the living organisms.
 Unicellular organisms are made up of a single cell only e.g. amoeba and other bacteria.
 Multicellular organisms are composed of many cells e.g. most plants and animals.
 Being very small, the cell cannot be seen with a naked eye. A powerful magnifying
instrument is required. The microscope is used to view the cells.
The Light Microscope
 The light microscope uses a beam of light to illuminate the specimen being studied.
 Functions of microscope are resolution and magnification
Resolution Magnification
Ability of a microscope to show two enlarges the image of the object / specimen
objects/structures that lie together as
separate entities.
 Magnification= Eyepiece lens magnification X Objective lens magnification
 In particular, if the eyepiece lens magnification is X10 and objective lens magnification
power is X8, then the total magnification of the specimen would be:
Magnification=Eyepiece magnification X Objective lens magnification
= 10 X8 =X80.

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Part of the Microscope Function of the Part
Limb. Supports the body tube and stage
Holding the microscope in transit
Base Provides firm and steady support to the microscope
Body Tube Holds the eyepiece and the revolving nose piece in position
Coarse adjustment knob Raises or lowers the body tube for longer distances to bring the image
into focus
Fine adjustment knob Raises or lowers the body tube through smaller distances to bring the
image into sharper focus.
Diaphragm An aperture that regulates the amount of light passing through the
condenser to illuminate the specimen
Eye-piece Contains a lens which contributes to the magnification of the
specimen under review.
Objective lens Magnifies the image of the spacemen.
Mirror Reflects light through the condenser to the object on the stage
Revolving nose-piece Holds the objective lenses in place and enables the change from one

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 objective lens to the other
Condenser Concentrates light on the object on the stage
Stage Flat platform where specimen on the slide is placed.
It has two clips to hold the slide into position.
Clips Holds the specimen on the slide in position
Field of view a circular space on the stage where the image of the specimen is
viewed through the light microscope
Micrograph image of the specimen printed on the screen by the electron
microscope

Handling and Care of the Microscope

1. Always use both hands when carrying a microscope , one hand to hold the base and the other
to hold the limb
2. Place the microscope away from the edge of the working bench / table
3. Do not touch the mirror and the lenses with your fingers
4. Dirty lenses should be cleaned using a special soft lens tissue paper / tissue paper moistened
with ethanol
5. Do not wet any part of the microscope
6. Make sure the lower power objective lens clicks into position in line with the eyepiece before
and after use
7. After use always clean and store the microscope in a safe place free from moisture and dust
8. When focusing always move the lenses upwards to avoid breaking the microscope slide and
the cover slip
How to use the Microscope
 Place the microscope on the bench with the stage facing away from you.
 Turn the low power objective lens until it clicks into position.
 Ensure that the diaphragm is fully open.
 Look through the eye-piece with one eye; meanwhile adjust the mirror under the stage to
ensure that maximum light can pass through. The circular area seen is referred to as the
field of view.

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 Again look through the eyepiece while adjusting the mirror under the stage to ensure that
sufficient light is passing through the specimen.
 Use the coarse adjustment knob to bring the low power objective lens to the lowest point.
Viewing through the eye-piece, turn the coarse adjustment knob gently until the specimen
comes into focus.
 Use the fine adjustment knob to bring the image into sharp focus. Make a drawing of
what you observe.
 For higher magnifications, turn the medium power objective lens into position and adjust
the focus using the coarse adjustment knob. For sharper images, use the fine adjustment
knob.
 If finer details are required, turn the high power objective lens into position; now use only
the fine adjustment knob to bring the details into sharper focus.
The electron microscope
 Uses a beam of electrons to illuminate the object /object being viewed.
 Has higher resolving and magnification power

Structural differences between light and electron microscope

Electron Light
Uses beam of electrons to illuminate the Uses beam of light rays to illuminate the
specimen specimen
Uses electromagnetic lens Uses lens made of glass quartz
Image is viewed on the screen Image vied directly on the stage
Fixed permanently in a place Portable
Specimen put in copper vacuum plate Specimen put on glass slides on the stage
Functional difference

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 Electron Light
Higher resolution power Lower resolution power
Higher magnification power lower magnification power
View dead specimen View live and dead specimen
Cell Structures as seen under the Light Microscope
 Cell organelles are structures within the cell that carry out specific functions.
 Cell inclusion dissolved ions/nutrients found in the cytoplasm.
 Some of the cell organelles that can be observed under the light microscope include the
cell wall, cell membrane, cytoplasm, nucleus, vacuole and chloroplasts.

The cell as seen under the Electron Microscope

 The electron microscope is more powerful than the light microscope. It uses a beam of
electrons to illuminate the specimen instead of light as in the case of light microscope.
 Electron microscope can magnify an object up to 500, 000 times.
 It also has a very high resolving power. Resolving power is the ability to distinguish
between separate things which are close to each other.
 The high resolving power makes the electron microscope a very important research tool
in microbiology.
 Through the electron microscope, very fine details of the cell can be observed.

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 Structure and Functions of the Cell Organelles
Cell wall
 Found only in plant cells where it forms the outer boundary of the cell
 Is composed of cellulose fibres
 Is fully permeable to water and mineral salts
Functions
1. Gives the plant cell a definite / fixed shape
2. Provides mechanical support to the cell
3. Provides protection against mechanical injury
4. Allows gases, water and other substances to pass through it due to permeability to water and
mineral salts.
Cell membrane / plasma membrane
 Found in both animal and plant cells where it encloses the entire cell
 Its structure consists of 3 layer: A phospholipid layer sandwiched between 2 protein
layers
 Is flexible and has fibres

Functions
1. Encloses the cell contents.
2. The pores allow selective movement of substances into and out of the cell

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  The cell membrane therefore only allows small molecules like water and glucose to pass
through but not large molecules
The membrane in this case is said to be semi-permeable

b. Cytoplasm
 Cytoplasm consists of a fluid medium in which chemical reactions take place. It contains
organelles and other inclusions such as starch, glycogen, fat droplets and many other
dissolved substances.
 Cytoplasm is not static; it undergoes a movement known as cytoplasmic streaming.
 It provides a suitable medium for cellular reactions to take place.
Mitochondrion
 Are sausage-shaped cylindrical structures in the cytoplasm
 They are the sites for respiratory activities that yield energy for the cell
 Is bound by two membranes, the inner membrane is greatly folded into cristae to increase
the surface area for respiration, the outer membrane is smooth.
 It has a fluid-filled cavity called the matrix where the respiratory reactions take place
 The matrix contains respiratory enzymes which catalyze the respiratory reactions
 Some cells have higher numbers of mitochondria, cells include muscle cell, sperm cell,
apical meristem cells, and kidney cell.
 Mitochondria are self replicative that is they can divide to form new ones.

Endoplasmic Reticulum
Rough Endoplasmic Reticulum
 Appear as a series of interconnected channels which run throughout the cytoplasm
 Is continuous with the outer membrane of the nuclear membrane
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 They have granules called ribosomes on their surfaces therefore appear rough on their
surface hence the name rough
Function: Transport of proteins
Smooth Endoplasmic Reticulum
 Appear as a series of interconnected channels running throughout the cytoplasm
 They do not have ribosomes
Function
Transport of lipids and steroids
Breakdown of foreign material e.g. chemical drugs
N/B found in large numbers in the liver where detoxification takes place.
Ribosomes
 These are spherical in shape. While some are bound to the endoplasmic reticula, some
ribosomes are scattered within the cytoplasm (free ribosomes).
 They are synthesized by the nucleolus.
 They form sites for protein synthesis.
Lysosomes
 These are spherical sac-like organelles bound by a single membrane. They contain lytic
enzymes which break down large molecules, destroy worn out organelles or even the
entire cells.
 Lysosomes also play crucial role in digestion in unicellular organisms.
 The lysosomes are also vital in breakdown of bacteria and other harmful microbes that
might have been ingested in food. This explains their high relative abundance in injured
or infected cells.
 The membrane of the lysosomes is intact. This is important because if the enzymes leak
out, they may destroy the whole cell.
a) Golgi bodies/Golgi apparatus
 These are stacks of membrane bound tube like sacs. They are found close to the cell
membrane.
 Golgi bodies perform the following functions:
1) They package and transport glycoproteins.
2) They are involved in secretion of synthesized proteins and carbohydrates.
3) They manufacture lysosomes.

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Note: Golgi bodies are abundant in cells that are active in secretion.
For instance pancreatic cells which secrete enzymes and the nerve cells which secrete
neurotransmitter substances
Centrioles
 These are rod shaped structures located just outside the nuclear membrane.
 They take part in cell division by formation of spindle fibers
 In the formation of cilia and flagella in lower organisms.
 Plant cells lack centrioles.
Chloroplasts
 Are Spherical structures surrounded by two membranes
 Consist of numerous plate-like bodies called grana which contain chlorophyll
 The chlorophyll traps light energy used during photosynthesis
 Contain a gel-like stroma with photosynthetic enzymes.
 In between the grana is the intergrana
Function
Is the organelle in which photosynthesis occurs
b) Vacuoles
Plant / Sap vacuole
 Are seen as spherical spaces in the cytoplasm
 Are filled with a fluid called cell sap in plants
 The plant vacuole is therefore also known as sap vacuole
 Sap vacuoles store sugars and salts therefore contribute to the osmotic properties of the
cell
Food vacuole
 Some unicellular organisms have food vacuoles which store and digest food
 E.g. in paramecium and amoeba

Contractile vacuole
 The unicellular organisms have contractile vacuoles used to expel excess water and
wastes from the organism
 The membrane that surrounds the vacuole is called the tonoplast

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 In plant cells the vacuole is large and centrally placed
 In animal cells the vacuoles are lacking;
 If present they are small in size and scattered within the cytoplasm
c) Nucleus
 Is surrounded by a membrane called nuclear membrane
 The membrane has nuclear pores which allow the passage of materials in and out of the
nucleus
 The nucleus has a viscous fluid known as nucleoplasm
 Nucleolus and chromatin materials are suspended in nucleoplasm
Functions
 It controls all the cell activities and
 it contains chromatin which contains the hereditary materials
Nucleolus
 Is a small spherical structure found within the nucleus
 Is responsible for the manufacture of ribosomes and DNA/hereditary material
Comparison between Plant Cells and Animal Cells
Plant cell Animal cell
Usually large Smaller in size
Regular in shape Irregular in shape rj shapeless
Has a cell wall Has no cell wall
Usually has a large central vacuole Usually has no vacuoles but when present, they
are often temporary and small structures within
the cytoplasm
Cytoplasm and nucleus are usually Cytoplasm occupies most space in the cell with
located towards the periphery of the cell the nucleus usually centrally placed
Some have chloroplasts Has no chloroplasts
Usually more store oils, starch and Store glycogen and fats
Has no centriole Has centrioles

 Two types of slides can be prepared in order to observe a specimen under the microscope
1. Temporary slides : Are prepared for immediate use during a laboratory experiment

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 2. Permanent slide : Can be preserved for re-use
Estimation of Cell Size
 The light microscope can be used to estimate the size of a cell. Most cells have diameters
smaller than a millimeter. Due to this, cell sizes are always measures in smaller units.
These are micrometres and nanometers. These units of measurements are related as
shown below.
I millimeter (mm) = 1000 micrometres (µm).
I micrometer (µm) = 1000 nanometres (nm).
Procedure in cell size estimation
 One requires a microscope, transparent ruler marked in millimeters and a prepared slide
of cells.
 With the low power objective lens in place, keep a transparent ruler on the stage of the
microscope.
 Focus so that the millimeters marks on the ruler are seen as thick dark lines.
 Estimate the diameter of the field of view by counting the one millimeter spaces between
the first mark and the last one across the field of view. Count only the spaces between
two thick dark lines.
 Convert the diameter of the field of view from millimeters to micrometres.
 Remove the ruler and place the prepared slide of cells.
 Count the number of cells along the diameter of the field of view.
 Calculate the diameter of one cell using the formula:

Cell Diameter=

Types of sections
Cross / transverse section; its cut a cross the structure of the specimen
Longitudinal section; cut along the length of the specimen
Procedure followed during preparation of slides in the laboratory
Use sharp razor; to make thin sections and avoid distortion of cells
Make thin sections; allow light to pass through the specimen making the components visible.
Adding a drop of water; to make the cell turgid/maintain shape and prevent cell from drying
Staining (iodine/methyl blue/Bromothymol blue); make the parts of specimen clearer/ distinct

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 Cell Specialization, Tissues, Organs and Organ Systems
Cell Specialization/Cell Differentiation
 This refers to structurally modified to perform specific functions
 They become differentiated to perform specific functions.
Examples of plant cell
a. Root hair cell; Has extended surface to increase surface area for water and mineral salts
absorption
b. Epidermal cell; Have a layer of wax on their outer surface to minimize excessive loss of
water by evaporation
c. Meristematic cell; Small, thin wall, dense cytoplasm that divides continuously giving
rise to new cells
d. Parenchyma cell; Thin walled, large and cylindrical that take in water and nutrients to
maintain shape & firmness
e. Collenchymas cell; Wall are thickened by cellulose to offer mechanical strength
f. Sclerenchyma cell; Walls are thickened by lignin to provide support
g. Xylem; The cells are dead and lignified to provide support
h. Palisade cell; Have numerous chloroplast that contain chlorophyll which trap light
energy used in photosynthesis
i. Guard cell; Has chloroplast site for photosynthesis, and thicker in elastic inner walls and
thin elastic outer wall that stretches faster leading to opening and closing of stomata
Animal cells
a. Sperm cell; has motile tail that enables it swim towards the ovum
b. Nerve cell; has long axon with dendrites effective for nerve conduction
c. Muscle cell; have long myofibril that contract and relax to bring about movement
d. Epithelial cell; have cilia on their surface to bring about movement in the canals
Tissues
 A tissue is a group of cells of a particular type that are grouped together to perform the
same function.
a) Tissue types in animals

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 1. Epithelial tissue- This is a thin continuous layer of cells for lining and protection of
internal and external surfaces.
2. Skeletal muscle- This is a bundle or sheets of elongated cells with fibres that can
contract. Its contraction and relaxation brings about movement.
3. Blood tissue- This is a fluid containing red blood cells, white blood cells and platelets.
The main functions of blood tissue are transportation of nutrients and gases as well as
protection of the body against infections.
4. Connective tissue- This tissue consists of strong fibres that connects other tissues and
organs thereby holding them in position.
b) Tissue types in plants
1. Epidermal tissue- This is a single thin layer of cells covering the outer surfaces. It
protects inner tissues of plants from mechanical damage and infection.
2. Palisade tissue- This is a group of cells rich in chloroplasts containing chlorophyll. It has
a site for the absorption of light energy and manufacture of food by photosynthesis.
3. Parenchyma tissue- This tissue consists of special thin walled irregularly shaped cells.
They form packaging and storage cells.
4. Conducting tissue/Vascular bundle- This tissue consists of xylem and phloem. Xylem
conducts water and dissolved mineral salts in a plant while phloem conducts food
substances in solution.
Organs
 An organ is a group of specialized tissues that are grouped together to perform a common
function.
 Organs in animals include:
a) Heart- composed of connective, muscle, epithelial and blood tissues.
b) Kidney- Composed of connective, epithelial and muscle tissues
c) Brain- Composed of epithelial, connective tissues
d) Lungs- Composed of epithelial, connective tissues.
 Organs in plants include:
a) Roots- composed of epidermal, conducting and parenchyma tissues.
b) Flowers- This is composed of epidermal, conducting tissues.

23
 c) Stem- Composed of conducting, parenchyma, and epidermal tissues and palisade
tissues in some cases
d) Leaves- Composed of palisade, conducting and epidermal tissues.
Organ system
 This is a group of organs whose functions are coordinated and synchronized to perform
the same function.
 Organ systems are more pronounced in animals than in plants
 Organ systems in animals include
a) Digestive system composed of organs such as oesophagus, stomach, intestines and
their associated glands.
b) Circulatory system composed of the heart, blood vessels (arteries, veins, capillaries).
c) Excretory this is composed of kidney, liver, and blood vessels.
d) Respiratory system composed of trachea, bronchus, and lungs.
e) Reproductive system composed of the reproductive organs and associated glands.
f) Nervous systems composed of the brain, spinal cord, eye, ear organs.

24
 CHAPTER FOUR: CELL PHYSIOLOGY
Introduction
By the end of the topic, the learner should be able to:
(a) Define cell physiology
(b) Correlate the membrane structure with cell physiology in relation to permeability
(c) Differentiate between diffusion, osmosis and active transport
(d) State and describe factors affecting diffusion, osmosis and active transport
(e) Carry out experiments on diffusion and osmosis
(f) Explain the roles of diffusion, osmosis and active transport in living organisms
(g) Explain turgor and plasmolysis in terms of osmotic pressure
 Cell physiology refers to the study of functions of the cell structures.
 For photosynthesis to occur, carbon (IV) oxide, mineral salts and water have to be taken
into the chloroplasts.
 For respiration (energy production) to take place, food substrate such as glucose and
oxygen have to be taken into the mitochondrion. Energy, carbon (IV) oxide, water and
alcohol (in plants) are some of the end products of respiration.

Structure of the membrane

 Is the structure that encloses the cell and cell organelles?
 Examples cell membrane, tonoplast, nuclei membrane, mitochondrial membrane and
chloroplast membrane.
 The membranes have a common basic structure which regulates the movement of materials
in and out of the cells.
 The cell membrane is made up of a phospholipid layer sandwiched by two protein layer has
small pores that allow the passage of substances in and out of the cells.
Properties of the cell membrane
a) Semi permeable- The pores allow selective passage of the small size molecules but do not
allow the passage of the large sized molecules. In particular, when a cell is surrounded by a
dilute sugar solution, the small sized water molecules will enter the cell but the larger sugar
molecules will not pass through the cell membrane.

25
b) Sensitive to changes in temperature and pH- Cell membranes are made up of protein.
Proteins are adversely affected by extreme changes in temperature and pH. Changes in
temperature and pH will alter the structure of the cell membrane thereby hindering the
normal functioning of the cell membrane. High temperature denatures (destroys) the proteins
thereby impairing the functions of the cell membrane.
c) The cell membrane possesses electric charges- The cell membrane has both positive and
negative charges. These charges affect the manner in which substances move in and out of
the ells. The charges also enable the cell to detect changes in the environment.
Physiological Processes of the Cell membrane
 Various physiological processes by which materials move in and out of the cells across
the cell membrane.
a) Diffusion c) Active transport
b) Osmosis
Diffusion
 The process by which particles move from their region of high concentration to their
region of low concentration.
 In particular, the scent of a flower or perfume particles moves from a region of high
concentration to low concentration.
 Diffusion occurs until the regions have an even concentration of the liquid or gas
particles.

Demonstration of the process of diffusion using potassium manganate (VII)

Requirements: potassium manganate (VII) crystals, glass tubing, 100 cm3 beaker and water.
Procedure
a) Hold the glass tubing vertically in a beaker so that one end of the tubing rests on the
bottom of the beaker.
b) Cautiously and quickly drop a crystal of potassium manganate (VII) through the upper
opening of the glass tubing.
26
 c) Close the upper hand of the glass tubing with the thumb.
d) Half fill the beaker with water.
e) Carefully withdraw vertically the glass tubing so that the crystal is left undisturbed at the
bottom of the beaker.
f) Record your observations for the first 15 minutes.
g) Explain your observations.
Expected observations
 After some time, the purple colour of the potassium manganate (VII) spread throughout
the water and eventually all the water turned purple.
Explanation
 The crystals of potassium manganate (VII) are highly concentrated with the potassium
manganate (VII) particles. The potassium manganate (VII) particles break away from the
crystals, dissolve in water and then diffuse through the water until they are evenly
distributed.

The Role of Diffusion in Living Organisms

a) In Plants
 Absorption of mineral salts from the soil to the plant. For those salts whose concentration
in soil water is higher that their concentration in the cell sap of root hair cells, they move
into the root hair cells by diffusion
 Diffusion plays a role in gaseous exchange in plants. The respiratory gases (oxygen and
carbon (IV) oxide) diffuse across the stomata and lenticels of plants.
 Transportation of dissolved manufactured food materials from the leaves to other parts of
the plant/ translocation.
b) In Animals
 Absorption of digested food materials/nutrients in the alimentary canal.
 Gaseous exchange in animals. In animals, gaseous exchange occurs across the respiratory
surfaces.

27
 Excretion of nitrogenous wastes especially in unicellular animals.

Factors affecting the rate of Diffusion

a) Diffusion gradient/ concentration gradient
 A greater diffusion gradient between two points increases the rate of diffusion. Increasing
the concentration of diffusing molecules also increases diffusion gradient with
corresponding regions hence increases the rate of diffusion.
b) Surface area to volume ratio

 The greater the surface area to volume ratio, the greater the rate of diffusion will be.
Conversely, low surface area to volume ratio results in a low diffusion rate.
 Diffusion rate is greater in small organisms than the large organisms. This is because the
small organisms have a large surface area to volume ratio. As a result, most of their body
parts are closer to the external surrounding leading to faster diffusion.

c) Thickness of membranes and tissues

 The thicker the membrane or tissue, the lower the rate of diffusion. This is because the
distance covered by the diffusing molecules is greater through the thicker membranes.
 The rate of diffusion is higher in thinner membranes.
d) Size of molecules
 Small and light molecules diffuse much faster than the heavy and large sized particles.
e) Temperature
 An increase in temperature increases the kinetic energy of the diffusing particles; thereby
causing them to move faster, this implies that the rate of diffusion increases with increase
in temperature and vice versa
Ksce 2004
What is diffusion (2mks),

28
 How do the following factors affect diffusion (3mks)
Diffusion gradient, surface area to volume ratio, temperature
What is the significance of diffusion to plant pollination? (2mks)
Enable pollinators to move from a region of low concentration to a
region of high concentration in scented flowers; to enhance cross
pollination;
Is diffusion an energy driven process? Explain (2mks)
No; molecules move along their concentration gradient;
Osmosis
 Osmosis is a process by which water molecules move from their region of high
concentration to their region of low concentration across a semi permeable membrane
/movement of water molecules from a hypotonic solution to hypertonic solution across a
semi permeable membrane.
Kcse 2007 distinguish between diffusion and osmosis.

Ksce 2006
An experiment was set up as shown below for 30 min

Observation
Visking tubing will become turgid/ increase in volume
Explanation

29
Sucrose solution is hypertonic to distilled water; water molecules moved
from the beaker to the visking tubing; by osmosis; across a semi permeable
membrane

 Other than visking tubing, dialysis tubing or cellophane as semi permeable membranes
Terminologies explained
Hypotonic solution; solution with lower solute concentration
Hypertonic solution; solution with higher solute concentration
Isotonic solution; solution with equal concentration of solute and solvent concentration
Osmotic pressure
 Pressure developed by a hypertonic solution across a semi permeable membrane to draw
water from hypotonic solution.
 An osmometer is an instrument used to measure the osmotic pressure.
Osmotic potential
 This is a measure of the pressure a solution would develop to withdraw water molecules
from pure water when separated by a semi permeable membrane.
 For osmosis to occur there must be;
1. a semi permeable membrane
2. Hypertonic solution
3. Hypotonic solution
4. Water molecules move along a concentration gradient

Water Relations in Animals

a) Red blood cell in hypotonic solution e.g. distilled water
 When a red blood cell is placed in a hypotonic solution, water molecules will move into
the cell by osmosis; swell and burst. Haemolysis is bursting of animal cell when placed
in hypotonic solution.
b) Red blood cell in hypertonic solution
 When placed in hypertonic solution water molecule are drawn out of the cell into the
hypertonic solution . The cell will shrink and become crenated. The process by which

30
 animal cells shrink and become smaller when placed in hypertonic solutions is referred to
as crenation.
c) Red blood cell in isotonic solution
 T he cell remains unchanged. This is because there will be no net inflow or outflow of
water molecules between the cell and the solution.

Note:
 When the cell becomes haemolysed or crenated, its functioning is impaired. This implies
that the body fluids and blood plasma surrounding the cells must be kept at the same
concentration as the animal cells. This will prevent bursting or shrinking of the cells that
would otherwise impair their physiology.

The figure below shows results when red blood cells were paced in different solutions
during an experiment?

iii. Name the processes represented by letters A and B (2mks)

………………………………………………………………………………………………
iv. Explain what happens to the cell in process A (2mks)
………………………………………………………………………………………………
v. What name is given to process B in plant cells? (1mk)
………………………………………………………………………………………………
vi. Give the reason why the plant cell won’t burst when placed in distilled water (1mk)
………………………………………………………………………………………………

Water Relations in Plants

 A plant cell has both a cellulose cell wall and cell membrane. The centre of the cell
contains vacuole with sap. That stores salts and sugars which contribute to the osmotic
property of the cell.

31
 The cell membrane and tonoplast are semi permeable while the cellulose cell wall is fully
permeable.
a) Plant cell in hypotonic solution e.g. distilled water
 The cell sap is hypertonic to distilled water; absorbs water by osmosis becoming turgid
 The cellulose cell wall is rigid and does not allow plant cells to burst as in the case of
animal cells.
 As the cell gains more water, the vacuole enlarges and exerts an outward pressure on the
cell wall.
 Turgor pressure is the outward pressure that the cell cytoplasm exerts on the cell wall as
it gains more water through osmosis.
 When wall pressure is equal to turgor pressure the cell is said to be turgid
b) A plant cell in a hypertonic solution
 The cell sap is hypotonic to the solution hence it loses water by osmosis (the cell starts to
shrink, becomes less rigid or flabby and is said to be) flaccid.
 It the cell loses more water, its contents reduce in size and the plasma membrane pulls
away from the cell wall towards the centre.
 The process through which plant cells lose water, shrink and become flaccid is called
plasmolysis.
 Deplasmolysis when a flaccid cell is placed in hypotonic solution it absorbs water by
osmosis and becomes turgid

 The plant cells below were placed in two different solutions they underwent processes I
& II

i) Name the nature of solutions the cells were placed (2mks)

A …………………………………… B ……………………………………..

32
 ii) Name the process I and process II (2mks)
Process I……………………………… Process II ……………………………………….
iii) State three importance of this process in Plants (3mks)
Wilting
 Drooping of plant parts (young) as a result of increased rate of water lose than rate of
absorption.
 Water lose in plants to the atmosphere is through transpiration and evaporation.
 At night, plants always recover from wilting since stomata are closed and water loss
through evapotranspiration is significantly reduced.
Role of Osmosis in Organisms
 Absorption of water from the soil-The root hair cell of plants absorbs water from the soil
by osmosis. Osmosis also helps in distribution and movement of water from the roots to
other parts of the plant.
 Support in herbaceous plants and young seedlings. When the cells of these plants take in
water through osmosis, the cells become firm or turgid and thus gain support.
 Opening and closing of stomata in plants The guard cells surrounding the stomata
synthesize glucose through photosynthesis in the presence of light. As glucose
accumulates in the guard cells, the osmotic pressure of the guard cells increase making
them to draw water from adjacent cells through osmosis. When the guard cells become
turgid, they bulge outwards leading to opening of the stomata. Opening of the stomata is
crucial as it allows for gaseous exchange in plants. At night, there is no glucose synthesis.
The glucose available in the guard cells is respired on leading to reduction of glucose and
consequently reduction in osmotic pressure. The guard cells lose turgidity and close the
stomata.
 Feeding in insectivorous plants These plants live on nitrogen deficient soils and trap
insects from whence they obtain the nutrients. These plants possess special structures that
suddenly change their turgor pressure when disturbed. The change in turgor pressure
enables the special structures to rapidly close thereby trapping the insects.
 Osmoregulation in animals; In kidney tubules of animals, water is withdrawn from the
tubules into the body cells through osmosis through the tubular walls. This enables
animals to maintain the osmotic pressure of the body fluids.

33
 Factors Affecting the Rate of Osmosis
 Concentration gradient, the greater the concentration gradient, the faster the rate of
osmosis and vice versa.
 Temperature-An increase in temperature would increase the rate of osmosis as it
increases the kinetic energy of the water molecules.
 Thickness of the membranes-The thicker the membrane the slower the rate of osmosis
while the rate of osmosis is greater through thinner membranes.
Q. pawpaw strips were cut and placed in different liquids. The diagram below shows how the
strips looked like after an hour.

Active Transport
 Process by which particles/molecules are moved across the cell membrane and against a
concentration gradient with the use of energy.
For active transport to occur there must be;
Energy – ATP, Enzymes (carrier molecules), a living cell/cell membrane

Role of active transport in living organisms

 Re-absorption of sugars and some salts by the kidney to the bloodstream.
 Absorption of dissolved mineral salts from the soil by plant roots.
 Absorption of digested food from alimentary canal of animals into the bloodstream.
 Accumulation of substances into the body to offset osmotic imbalance in arid and saline
environments
 Excretion of waste products from body cells.
 Used in nerve impulse transmission.
 Used in muscle contraction
Factors affecting the rate of Active Transport
a) Oxygen concentration
Oxygen is required for aerobic respiration process that yields energy for active transport.
Under low oxygen concentration, the rate of respiration will be low hence there will be
production of little energy leading to low rate of active transport. Increase in oxygen

34
 concentration translates into a higher energy production leading to high rate of active
transport.
b) Change in pH
Change in pH affects the respiratory process which is enzyme controlled. Respiratory
enzymes require optimum pH for their efficient activity. Extreme pH conditions lower the
rate of active transport since the enzymes controlling respiration will be denatured.
c) Glucose concentration
Glucose is the chief respiratory substrate. At low glucose concentration, there will be less
production of energy leading to decreased rate of active transport. Rate of active transport
increases with increase in glucose concentration due to increase in the rate of energy
production
d) Temperature
At low temperatures, the enzymes are inactive hence the rate of respiration will be slow be
less production of energy resulting into slow rate of active transport. An increase in
temperature up to optimum activates respiration enzymes thus increases the rate of active
transport. At temperatures beyond optimum / 40 0C, the enzymes become denatured,
respiration stops and so does active transport.
e) Presence of metabolic inhibitors e.g. cyanide.
These are metabolic poisons. They stop the rate of respiration leading to production of no
energy. Active transport is, thus, stopped.
The diagram below illustrates a certain physiological process in cells

Q. Name the physiological process above, give a reason for your answer (1mks)
Active transport; energy is spent for the food molecule to pass across the
cell membrane;

35
 NUTRITION PLANTS AND ANIMALS
Introduction
By the end of the topic, the learner should be able to:
(a) Define nutrition and state its importance in living organisms
(b) Differentiate various modes of feeding
(c) Describe photosynthesis and show its importance in nature
(d) Explain how the leaf is adapted to photosynthesis
(e) Explain the factors affecting photosynthesis
(f) Distinguish between carbohydrates, proteins and lipids
(g) State the importance of various chemical compounds in plants and animals
(h) Relate various types of teeth in mammals to their feeding habits
(i) Describe internal structure of mammalian (human) teeth
(j) Differentiate between omnivorous, carnivorous and herbivorous modes of feeding
(k) Relate the structures of the mammalian (human) alimentary canal to their functions
(1) Explain the role of enzymes in digestion in a mammal (human)
(m) Explain the properties and functions of enzymes
(n) Explain the factors that determine energy requirements in humans.

 Nutrition refers to the process by which living organisms obtain and assimilate (utilize)
nutrients.
 The nutrients obtained are useful to the living organisms in many ways:
a) Growth and development of the living organisms.
b) Energy provision as they are broken down to release energy.
c) Repair of worn out tissues
d) Synthesis of very vital macromolecules in the body such as hormones and enzymes.

36
Modes of nutrition
There are two main nutrition modes:
a) Autotrophism: mode of nutrition through which living organisms manufacture their own
food from simple inorganic substances in the environment such as carbon (IV) oxide,
water and mineral ions.
Organisms that make their own food through this mode are autotrophs.
b) Heterotrophism: mode of nutrition in which living organisms depend on already
manufactured food materials from other living organisms.
Heterotrophs are the organisms that feed on already manufactured food materials.

TYPES OF AUTOTROPHISM
a) Chemosynthesis
 This is the process whereby some organisms utilize energy derived from chemical
reactions in their bodies to manufacture food from simple substances in the environment.
 Common in non green plants and some bacteria which lack the sun trapping chlorophyll
molecule.
b) Photosynthesis
 This is the process by which organisms make their own food from simple substances such
as carbon (IV) oxide and water in presence of chlorophyll and sunlight energy.
 Such organisms often have chlorophyll which traps the required sunlight energy.
Importance of Photosynthesis
1. Helps in regulation of carbon (IV) oxide in the environment.
2. Release oxygen in the atmosphere used for aerobic respiration.
3. Photosynthesis enables organisms get food.
To understand the process of photosynthesis, it is important to understand the leaf structure.
Internal leaf structure.

37
 a) Cuticle
 This is the outermost layer of the leaf.
 It is a thin non-cellular, waxy, transparent and waterproof layers that coats the upper and
lower leaf surfaces.

Functions of the cuticle

a) Being waterproof, it minimizes water loss from the leaf cells to the environment through
transpiration and evaporation.
b) It protects the inner leaf tissues from mechanical damage.
c) It prevents entry of pathogenic microorganisms into the leaf.
b) Epidermis
 This is the outermost one cell thick layer covering upper and lower leaf surfaces. Its cells
are flattened and lack chloroplasts.
Functions of the epidermis:
a) It protects the leaf from mechanical damage.
b) It also protects the leaf from entry of disease-causing microorganisms.
c) It secretes the cuticle.
 There are many small pores on the epidermis known as stomata (singular-stoma) through
which exchange of materials occur. The opening and closing of the stomata is controlled
by the guard cells. Each stoma is controlled by two guard cells.
 The guard cells have chloroplasts and are bean shaped. They have thicker inner cell wall
and thinner outer cell wall.
Adaptations of the guard cells
 They have differentially thicker walls to enable them bulge as they draw water through
osmosis from the neighboring cells making them to open the stomata.

38
  They contain chloroplasts that manufacture sugars which increase osmotic pressure of the
guard cells. As they draw water through osmosis, they bulge making the stomata to open.
c) Palisade mesophyll
 This is the chief photosynthetic tissue in plants. Its cells are regular in shape.
 Its cells contain numerous chloroplasts for photosynthesis.
 Their close packing and location just below the epidermis enables them to trap maximum
sunlight for photosynthesis.
 Location of palisade layer on the upper surface explains why upper leaf surfaces are
greener than the lower surfaces.

d) Spongy mesophyll layer

 This layer contains loosely arranged irregular cells. This leaves large airspaces between the
cells which permits free circulation of gases carbon (IV) oxide and oxygen into the
photosynthetic cells. Spongy mesophyll cells contain fewer chloroplasts compared to
palisade cells.
e) Vascular bundle/tissue
 This is found in the midrib and leaf veins. Vascular bundle is made of phloem and xylem
tissues. Xylem tissues conduct water and some dissolved mineral salts from the roots to other
plant parts while phloem translocates manufactured food materials from photosynthetic areas
to other plant parts.
f) Chloroplast
 This is the organelle in which photosynthesis takes place. It is an oval shaped double
membrane bound organelle.
 Internally, it is made up of membranes called lamellae suspended in a fluid filled matrix
called stroma.
 Lamellae forms stacks at intervals called grana (singular-granum). Chlorophyll molecules are
contained in the grana.
 Within the stroma, fat droplets, lipid droplets and starch grains are found.
 The stroma contains enzymes and forms the site where light independent reactions take
place.

39
Adaptations of the leaf to photosynthesis
 Flat and broad lamina to increase surface area for trapping sunlight energy and for gaseous
exchange.
 Numerous stomata through which carbon iv oxide diffuse in the photosynthetic cells.
 Some leaves is thin to reduce the distance through which carbon (IV) oxide has to diffuse to
the photosynthetic cells.
 The palisade mesophyll cells contain numerous chloroplasts which contain chlorophyll
molecules which trap sunlight energy for photosynthesis.
 Mesophyll cells are loosely packed to allow free circulation of gases.
 The leaf has an extensive network of veins composed of xylem which conducts water and
mineral salts to the photosynthetic cells and phloem to translocate manufactured food
materials to other plant parts.
 The epidermis and cuticle are transparent to allow light to penetrate to the photosynthetic
cells.
 Leaf mosaic minimizes overlapping and overshadowing of leaves.
Raw materials for photosynthesis
 Water
 Carbon (IV) oxide
Conditions for photosynthesis
 Light energy
 Chlorophyll
PHOTOSYNTHESIS PROCESS
 It can be summarized into two main reactions.

a) Light reaction/Light stage

 This is the first stage of photosynthesis. It occurs in the presence of light energy.

40
  Occurs in the grana of the chloroplasts.
 During light stage, two fundamental processes occur:
i. Photolysis of water
 This refers to the splitting of water molecules using sunlight energy to give hydrogen ions
and oxygen gas.
 The grana contain chlorophyll molecules that trap sunlight energy for photolysis.
 The oxygen gas produced is released into the atmosphere or be utilized by the plant for
respiration.
Water Hydrogen atoms + Oxygen gas
ii. Formation of adenosine triphosphate (ATP)
 Some of the sun light energy is used to combine Adenosine Diphospate molecule in the
plant tissues with a phosphate molecule to form Adenosine Triphosphate (ATP).
 ATP is an energy rich molecule that stores energy for use in the dark stage when sunlight
energy could be unavailable.
ADP + P  ATP
 The hydrogen ions and ATP formed during light stage are later used in dark stage.
b) Dark stage/ carbon (IV) oxide fixation
 These reactions are light independent. Dark reactions take place in the stroma.
 The energy that propels these reactions is derived from the ATP formed during light
stage.
 Also known as carbon (IV) oxide fixation, dark stage involves combination of carbon
(IV) oxide molecule with hydrogen ions to form a simple carbohydrate and a water
molecule.
6CO2 +12 H+ C6H12O6
 Other food materials are then synthesized from the simple sugars through complex
synthesis reactions.
 The simple sugar formed in dark stage is quickly converted to starch which is osmotically
inactive. Fatty acids, protein and vitamins are formed after combination with elements.
 To test whether photosynthesis has taken place in a leaf, therefore, a test for presence of
starch and not simple sugars is carried out.
Testing for starch in a leaf

41
Procedure

Put the plant in the sun for about six hours. This duration ensures that the leaf has
photosynthesized.
Put the leaf in boiling water for 10 minutes. This kills the protoplasm, denatures the
enzymes and /burst starch grains
Put it in a boiling tube containing methylated spirit or alcohol and boil in a water bath. To
decolorize the leaf (removes the chlorophyll).
Remove the leaf and wash off in hot water to remove excess methylated spirit and to
soften the leaf/ make the leaf soft.
Spread the leaf on a white tile and add drops of iodine solution onto the leaf and observe.
Observations
If there is formation of blue black patches on the leaf then starch is present
If the yellow/brown colour of iodine persists on the leaf then starch is absent in the leaf.

Factors affecting the rate of photosynthesis

a) Carbon (IV) oxide concentration
 While the concentration of carbon (IV) oxide in the atmosphere is fairly constant at
0.03%, an increase in carbon (IV) oxide concentration translates into an increase in the
rate of photosynthesis up to a certain point when the rate of photosynthesis becomes
constant. carbon (IV) oxide concentration of 5% is toxic to plant cells.At this point, other
factors such as light intensity, water and temperature become limiting factors.

42
Q. the potted plant below was kept in the dark for 48 hours before leaf A was fitted with the
conical flask and then put in sunlight for 3 hours

a. What was the aim of the experiment? Carbon IV oxide is necessary for
photosynthesis.
b. What was the role of leaf B? control experiment;
c. Name the reagent that was used to test the leaf? iodine solution;
d. Account for the results on leaf A and B? leaf A brown color persists coz sodium
hydroxide absorbed all the carbon Iv oxide needed for photosynthesis;
leaf B blue black colour seen , starch present coz all conditions for
photosynthesis were present;
Light intensity
 The rate at of photosynthesis increases with an increase in light intensity up to a certain
level. Beyond the optimum light intensity the rate of photosynthesis becomes constant.
To this effect, plants photosynthesize faster on bright and sunny days than on dull cloudy
days.
 Light quality/wavelength also affects the rate of photosynthesis. Most plants require red
and blue wavelengths of light for photosynthesis. Light duration also affects
photosynthesis rate.

Q. kcse 1998.
43
In an experiment to investigate a factor affecting photosynthesis, a leaf of a potted plant
which had been kept in the dark overnight was covered with aluminum foil as shown in the
diagram below

The set up was kept in sunlight for three hours after which a food test was carried out on the
leaf.

(a) Which factor was being investigated in the experiment?.Light ;

(b)Why was the plant put in the sun; for the plant to carry out photosynthesis;
(c) What food test was carried out? Starch test.
(d)(i) State the results of the food test the ;brown/ yellow color of iodine solution
persists
(ii) Account for the results in c (i) above; alluminium reflected away light from
reaching the photosynthetic cell thus no photosynthesis didn’t occur

(e)Why was it necessary to keep the plant in darkness; before the experiment? Destarch
the leaves /make sure all the starch is used up;

(f) Give the products of the light stage of photosynthesis; oxygen gas; hydrogen
atoms and ATP;

(g) Name three photosynthetic cells ? Palisade cell; Guard cell; spongy mesophyll
cell;

b) Temperature
 Photosynthesis is an enzyme controlled process. At very low temperatures the rate of
photosynthesis is slow because the enzymes are inactive. As temperature increases, the
rate of photosynthesis increases because the enzymes become more active. Rate of
photosynthesis is optimum at (35-40) °C. Beyond 40°C the rate of photosynthesis
decreases and eventually stops since the enzymes become denatured.

44
 c) Water
 Water is a raw material for photosynthesis. At extreme level of water shortage, rate of
photosynthesis will be severely affected.

e) Mineral salts
 Nitrogen and magnesium are constituents of chlorophyll. Iron is needed for chlorophyll
synthesis.
 Deficiency of iron, nitrogen and magnesium in plants leads to leaf chlorosis (yellowing of
leaves) thus no photosynthesis
Experiment to investigate the gas produced during photosynthesis
Requirements
 Water plant e.g. elodea, spirogyra, Nymphea (water lily), glass funnels, beakers, small
wooden blocks, test tubes, wooden splints and sodium hydrogen carbonate.
Procedure
a) Set up the apparatus as shown in the figure below

45
 b) Place the set up in the sunlight to allow photosynthesis to take place.
c) Leave the set up in the sun until sufficient gas has collected in the test tube.
d) Test the gas collected with a glowing splint.
e) Record your observations.
Note:
 In this experiment, sodium hydrogen carbonate is added to the water to boost the amount
of carbon (IV) oxide in the water since water has a low concentration of carbon (IV)
oxide.
 A water plant is also selected because water plants are adapted to photosynthesis under
the low light intensity in water where terrestrial plants cannot easily photosynthesize.
 This experiment can also be used to investigate the factors affecting the rate of
photosynthesis:
1) Carbon (IV) oxide concentration: Carry out the experiment using different amounts of
dissolved sodium hydrogen carbonate e.g 5g, 10g, 15g, 20g and examine the rate at
which the gas collects.
2) Light intensity: An artificial light source can be used. Illuminate the plant and vary the
distance between the set up and the light source while recording the time it takes for the
gas jar to fill or counting the number of bubbles peer unit time.
3) Temperature: carry out the experiment at varying temperatures and record the rate at
which the gas collects.
Experiments on factors necessary for photosynthesis
Light
Requirements
 Methylated spirit, iodine solution, water, white tile, droppers, beaker, source of heat,
boiling tube, light proof material e.g. aluminium foil, potted plant and clips.
Procedure

46
  Cover two or more leaves of a potted plant with a light proof material.
 Place the plant in a dark place for 48 hours (keeping the plant in the dark for 48 hours is
to ensure that all the starch in it is used up. This makes the leaves ideal for investigating
whether starch would form in the experimental period. This is called destarching).
 Transfer the potted plant to light for 5 hours.
 Detach and uncover the leaves and immediately test for starch in one of the covered
leaves and one that was not covered.
Carbon (IV) oxide
Requirements
 Sodium hydroxide pellets, flask, jelly
Procedure
 Destarch the plant for 48 hours
 Place a few pellets of sodium hydroxide in the flask
 Bore a hole in the cork of the same size as the petiole of the leaf being used
 Cut the cork lengthwise.

Chlorophyll
 For this experiment, a variegated leaf is required. This is a leaf in which some patches
lack chlorophyll.
 These patches could be yellow. They lack chlorophyll hence photosynthesis does not take
place in them.
Procedure
 Detarch or remove variegated leaf that has been exposed to light for at least three hours.
 Draw a large diagram of the leaf to show the distribution of the chlorophyll
 Test the leaf for starch and record observations.

CHEMICALS OF LIFE
 Biochemistry is the branch of science that deals with the study of the chemical
compounds that constitute the living organisms.
 Chemicals of life include carbohydrates, proteins, lipids, vitamins and enzymes.

47
 Carbohydrates
 Are compounds of carbon, hydrogen and oxygen in the ratio of 1:2:1
 They have a general formula (CH2O)n where ‘n’ represents the number of carbon atoms.
 Carbohydrates are grouped into three categories:
Monosaccharides
 These are the simplest carbohydrates.
 Their general formula is C6H12O6
 They include glucose, fructose, galactose.
Properties of Monosaccharide
1. They are sweet tasting 4. They are reducing sugars; reduce
2. They readily dissolve in water blue copper (II) sulphate in
3. They are crystalline Benedict’s solution to red brown
copper (I) oxide when heated.
Note:
 Most fruits are sweet tasting because they contain a lot of monosaccharides.
Functions
 They are the chief respiratory substrate. (Broken down to release energy in the body.
 They are condensed to form disaccharides and water.
Reactions of monosaccharide
Molecules of monosaccharide link together to form complex carbohydrate molecules in a
process called condensation
 During condensation water molecules are also formed e.g. two glucose molecules can be
condensed and linked together to form one molecule of disaccharide.
Test for monosaccharide
1. Put 2cm3 of test solution in a test tube
2. Add an equal amount of Benedict’s solution into the test tube
3. Heat the mixture to boil
4. Note the colour of the mixture(color change from blue to green to yellow to brown)
Observation/ and conclusion
 Green : Very little reducing sugar is present in the solution
 Yellow : Average amount of reducing sugar is present

48
  Red, orange, brown, brick red: a lot of reducing sugar is present
Disaccharides
 These are complex sugars formed by linking two monosaccharide units through
condensation.
 They have a general formula C12H22O11. The bond that holds two monosaccharide units is
called glycosidic bond.
 Examples of disaccharides include: Maltose, Sucrose, Sucrose
Glucose + Glucose Maltose + water
 Glucose + Fructose Sucrose + water
 Glucose + Galactose Lactose + water
Properties of Disaccharides
1. They are sweet tasting 3. They are water soluble
2. They are crystallizable
4. While they are non reducing sugars, some such as maltose is sugar reducing and is known
as a complex reducing sugar.
They can be broken down into their constituent monosaccharide units through hydrolysis.
Hydrolysis is the process through which complex molecules are broken down in the
presence of water molecules.
In living systems, hydrolysis is carried out by enzymes. However, in the laboratory,
hydrolysis can be carried out by boiling the disaccharide in dilute aid such as
hydrochloric acid.
Functions
They are hydrolyzed into monosaccharides and respired on to yield energy
They are the form in which carbohydrates are transported in plants due to their soluble
and inert nature.
Test for non reducing sugars
1. Put 2cm3 of sucrose solution into a test tube
2. Add a few drops of dilute hydrochloric acid
3. Place the test tube into a hot water bath for 3 minutes
4. Remove the test tube and cool it in cold water
5. Add sodium hydrogen carbonate solution drop by drop until fizzing stops

49
 6. Add 2cm3 of Benedict’s solution to the mixture
7. Heat the mixture to boil and record the colour change of the solution
Explanation
 dilute HCL is to hydrolyse / Break down non-reducing sugars of reducing sugars
 Sodium hydrogen carbonate neutralize the unreacted hydrochloric acid in the solution
 The final colour ranges from green, yellow, orange, brown, or brick red which indicates
the presence of reducing sugars after hydrolysis
Polysaccharides
 These are formed through linking of numerous monosacchride units through
condensation.
 Their general formula is (C6H10O5)n where n is a very large number.
Properties of polysaccharides
 They are non sweet  They are non crystalline
 They do not dissolve in water  They are non-reducing sugars

Examples of polysaccharides
a) Starch- Made by linking numerous glucose molecules. It is a form in which
carbohydrates are stored in plants.
b) Glycogen- Is a storage carbohydrate in liver and muscles of animals. It is broken down to
glucose in animals when blood glucose falls.
c) Cellulose- This is a structural polysaccharide in plants. It is a component of the cell wall
d) Chitin- A structural carbohydrate found in cell wall of fungi and arthropod exoskeletons

Functions of polysaccharides
 They are storage carbohydrates; their insolubility and inertness makes them ideal for
storing carbohydrates.
 They are structural carbohydrates e.g. cellulose forms the plant cell walls
 They can be hydrolyzed into monosacharides and be broken down to release energy
Test for starch
1. Add 3-4 drops of iodine solution to the test solution using a dropper and shake
2. Observe the colour changes and record your observation

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 Conclusion
 A colour change to blue black indicates the presence of starch
 If brown / yellow colour of iodine is retained, starch is absent
Lipids
 These are compounds of carbon, hydrogen and oxygen. However, they contain lesser
oxygen but higher hydrogen compared to carbohydrates.
 Building units for lipids are fatty acids and glycerol. To synthesize a molecule of lipid,
three fatty acids and a glycerol molecule are linked through a condensation reaction.
Two types
Oils- are found in plants and are liquid at room temperature.
Fats-found in animal and are solid at room temperature
Properties of lipids
 Fats easily change to oil when heated while oils easily solidify when cooled.
 They are insoluble in water but readily dissolve in organic solvents such as chloroform to
form emulsions
 They are inert hence can be stored in tissues of organisms.

Functions
a) They are a source of energy when oxidized. They yield more energy compared to
carbohydrates when oxidized per unit weight. However, they are less preferred as source
of energy because they require a lot of oxygen to oxidize. In addition, they are insoluble
in water hence not easy to transport to respiratory sites.
b) They are a source of metabolic water. When oxidized, they yield a lot of metabolic water.
This explains why some desert animals such as camels store large quantities of fat in their
bodies.
c) Lipids offer protection to internal organs as they are deposited around them to act as
shock absorbers.
d) Lipids provide heat insulation when stored underneath the skin as they are poor
conductors of heat hence do not conduct heat away from the body. Organisms in cold
areas tend to have fatter fat adipose.

51
 e) Lipids form structural compounds for instance phospholipids in cell membrane.
f) Complex lipids such as waxes in leaves help minimize water loss through transpiration.
g) Some lipids mediate communication between cells
Test for lipids
Grease spot test
1. Rub a little test substance on a filter paper
2. Remove any excess from the paper
3. Hold the paper above the flame taking care not to burn it
4. Hold the paper against light, observe and record what happens to the spot on which
the fat was rubbed
5. Repeat this procedure with a drop of water and note the difference between the fat
and the water spot (This acts as a control experiment)
Observation
 Presence of lipids is indicated by formation a permanent translucent spot
Emulsion test
1. Put a little oil or melted fat in a test tube
2. Add 4cm3 of ethanol into the melted fat or oil and shake thoroughly
3. Add to the mixture 2-3cm of water
Observation and conclusion
 Formation of a white emulsion confirms the presence of lipids
Proteins
 These are compounds of carbon, hydrogen and oxygen. In addition, they also contain
nitrogen and sometimes phosphorous or sulphur or both.
 Some proteins molecules contain other elements. In particular, haemoglobin contains iron.
 Proteins are made up of amino acids. There are about twenty known amino acids. Amino
acids are of two kinds:
a) Essential- These are those amino acids that cannot be synthesized by the body
systems hence have to be supplied in the diet.
b) Non essential- These are amino acids that can be synthesized by the body
mechanisms hence do not need to be supplied in the diet.

52
  An amino acid has an amino group, carboxyl group, hydrogen atom and an alkyl, R
group. Amino acids differ from each other by the alkyl group.
 Proteins are of two kinds:
a) First class proteins- Contain all essential amino acids
b) Second class proteins- Proteins lack one or more essential amino acids
Protein synthesis
 Two amino acids combine through a condensation process to form a dipeptide molecule.
Several amino acids link up to form a polypeptide chain. Proteins are made up of long
chain polypeptides.
 Properties of a protein depend on the type of amino acids present in its chain and the
sequence in which the amino acids link up in the polypeptide chain.
Properties of Proteins
They dissolve in water to form colloidal suspensions in which the particles remain
suspended in water.
They are denatured at temperatures beyond 40°C. Strong acids, bases, detergents and
organic solvents also denature proteins.
They are amphoteric- possess both basic and basic properties.
This property enables them to combine with other non protein substances to form
conjugated proteins such as:
 Mucus- Protein plus carbohydrate
 Haemoglobin- Protein plus iron
Functions of proteins
a) They are structural compounds of the body. Cell membrane is protein in nature. Hair,
nails and hooves are made up of protein keratin.
b) Proteins are broken down to release energy during starvation when all carbohydrate and
lipid reserves are depleted.
c) Functional proteins play vital roles in metabolic regulation. Hormones are chemical
messengers while enzymes regulate the speed of metabolic reactions.
d) Proteins such as antibodies provide protection to the body against infections
e) Some protein molecules are transport molecules. Haemoglobin molecule plays a crucial
role in transportation of respiratory gases.

53
 f) Proteins play a vital role in blood clotting e.g. fibrinogen.
g) Contractile proteins such as actin and myosin bring about movement.
Test of proteins
1. Put 2cm3 test solution into a test tube
2. Into the test tube add an equal amount of the 10% sodium hydroxide solution and shake
3. Into the mixture, add a few drops of 1% copper 11 sulphate solution drop by drop
shaking well after each addition
4. Observe and record the colour change
Observation/ conclusion
 Purple colour indicates the presence of protein
ENZYMES
What are enzymes?
Are organic catalysts that are protein in nature and regulate the rate of metabolic reactions.
They speed up or slow down the rate of metabolic reactions but to not get used up in the process.
Types of enzymes
a) Extracellular: Are produced within the cells but used outside the cells e.g. digestive
enzymes.
b) Intracellular: Are enzymes produced and used within the cells e.g. respiratory enzymes.
Properties of Enzymes
1. They are protein in nature; hence affected by temperature and pH.
2. They are substrate specific e.g. maltase cannot digest sucrose.
3. They are efficient in small amounts since they are re-used in the reactions.
4. They mostly take part in reversible reactions.
5. They regulate the rate of metabolic activities but are not used up.
Q. Study the equation below and use it to answer questions below
Food substance A + enzyme B product C + enzyme B
State two properties of enzyme exhibited
They do not get used up in the reaction;
Enzyme catalyzed reactions are reversible;
Importance of Enzymes
 They speed up the rate of chemical reactions that would otherwise be too slow to support life.
 Some enzymes take part in synthesis/building of useful complex substances such as DNA.

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 Digestive enzymes breakdown complex food substances into simple foods that can be
utilized by the cells.
 Some metabolic enzymes such as catalase play a vital role in detoxification (making
poisonous substances less harmful.
Enzyme nomenclature
 Two systems of naming enzymes have been adopted.
a). Trivial naming
 This is where an enzyme is named by the scientist who discovered it.
 In trivial naming all enzyme names end in prefix –in.
 Examples
 Pepsin  Ptyalin  Trypsin.
b). Use of suffix –ase
Enzymes are assigned names by adding suffix –ase to the food substrate acted by the enzyme
or by adding the suffix to the reaction being catalyzed by the enzyme.
Substrates Lactose……………………...lactase
Amylose (starch)……… .amylase. Processes/Reactions
Lipids……………………. lipase. Hydrolysis……………….hydrolase
Protein………………… .protease. Reduction………………..reductase
Carbohydrate………carbohydrase. Oxidation…………………...oxidase
Mechanism of action of Enzymes
 Enzymes are not used up during metabolic reactions. They do have “active sites” through
which the substrate molecules bind to the enzymes. The reaction is then catalyzed and the
end products released. The enzyme is free to bind with another substrate molecule. The
enzymes can be used again and again.

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Factors affecting enzyme activity
 Temperature.  Enzyme co-factors and co-enzymes;
 pH. Fe, Mg, Zn, Cu ions.
 Substrate Concentration.  Specificity.
 Enzyme Concentration.  Enzyme inhibitors.
a) Temperature
At low temperatures, the enzymes are inactive hence the rate of enzyme reaction will be
slow. An increase in temperature up to optimum activates enzymes increases the rate of
enzymatic reaction. At optimum temperature the rate of enzymatic activity is at its highest/
maximum. At temperatures beyond optimum /40 degrees Celsius, the enzymes become
denatured, enzyme reaction stops.
b) pH
 an Enzymes work best at a narrow range of pH conditions.
 Some enzymes work best under alkaline conditions e.g amylase, trypsin while some
work better under acidic conditions e.g. pepsin. However, most intracellular enzymes
work better under neutral conditions.
 Altering the pH conditions would affect enzyme activity.

c) Enzyme Specificity
 A particular enzyme will only act on a particular substrate or will only catalyze a
particular reaction.
 For instance, sucrase enzymes can only breakdown sucrose.
d) Substrate Concentration
 Assuming all other factors are constant, at low substrate concentration, the rate of
enzyme activity is slow.
 Increase in substrate concentration increases the rate of enzyme activity since more active
sites of the enzymes will be occupied and there will also be an increase in enzyme-
substrate collisions leading to increased reaction.

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 The reaction increases up to a point at which it becomes constant. At this point, all active
sites are utilized. The enzymes become the limiting factor of reaction. Increasing enzyme
concentration would increase the rate of enzyme activity.
e) Enzyme Concentration
 An increase in enzyme concentration increases the rate of enzyme reaction up to a level
beyond which the rate of reaction becomes constant.
 At low enzyme concentration, rate of enzyme activity is low because there are fewer sites
and also fewer enzyme-substrate collisions that would lead to reactions.
 Increasing enzyme concentration increases rate of enzyme activity since there will be an
increase in number of active sites and enzyme-substrate collisions.
 At optimum enzyme concentration, substrate concentration is the limiting factor.
Increasing substrate concentration increases the rate of reaction.
f) Enzyme co-factors
 These are inorganic substances which activate enzymes.
 Without them, most enzymes would not function properly.
 Co- factors include mineral ions like iron, magnesium, copper, manganese, zinc
 They are used again and again since like enzymes, they do not get used up during the
reactions.

g) Co-enzymes
 These are organic molecules that are required by some enzymes for their efficient
functioning. Some enzymes will not function without them.
 Most co-enzymes are derivatives of vitamins.
 Examples;
Vitamins, NAD- Nicotine Adenine Dinucleotide.
FAD- Flavine Adenine Dinucleotide., NADP- Nicotine Adenine Dinucleotide Phosphate.
h) Enzyme inhibitors
 These are chemical substances which slow down or eventually stops enzyme activity.
 They are of two types:

57
 1. Competitive 2. Non- competitive
Competitive inhibitors
 These are chemical substances which resemble the substrate molecules i.e. they take up
the shape of the substrates and compete for the active sites of the enzymes.
 They bind with the enzymes and do not disentangle easily (they stay in the enzyme active
site for a long time) thereby slowing down the rate of enzyme activity.
Non competitive inhibitors
 These are inhibitors that do not resemble the substrate molecules but they combine and
alter the structure of the active site of the enzyme.
 The enzymes are destroyed permanently hence the effect cannot be reversed.
 Note that these substances do not compete for the active sites of the enzymes.
Examples of non competitive inhibitors
Heavy metals (such as lead, mercury, silver), Cyanide, organophosphates such as malathion.

HETEROTROPHISM
 This is a mode of nutrition in which organisms take in already manufactured complex
food substances such as carbohydrates, proteins and lipids.
 Heterotrophs are organisms that feed on already manufactured food substances.
 These substances are broken down in the bodies of the Heterotrophs into simple soluble
food substances that can be absorbed and be utilized by the cells.
Modes of Heterotrophism
 There are four main heterotrophic modes on nutrition:
Holozoic- Where organisms ingest, digest and assimilate solid complex food substances.
Saprophytism – Where organisms feed on dead decaying matter causing decomposition.
Parasitism- a feeding association in which one organism (parasite) feeds on or obtain
nutrients on another organism, the host.
Symbiosis/Mutualism- An association where two organisms live together and mutually
benefit from each other.
a) Parasitism
 There are two main types of parasites:

58
 Endo parasites- Live inside the host
 Ecto-parasites- Found on the external surface of the host.
 The parasite benefits but the host does not. Some of the parasites cause diseases to the
hosts and damage their tissues thereby weakening them.
b) Symbiosis
 In symbiosm, both organisms benefit: e.g
› Rhizobium and leguminous plants: rhizobium fixes nitrogen for the legume while
the bacteria obtain manufactured food from the legumes.
› Lichen: association of fungi (absorbing water and nutrients) and algae
(manufacturing food for the association.
› Catalase digesting bacteria and ruminants.
DENTITION
 Dentition refers to the description of types of teeth, their arrangement and specialization.
 Large animals depend on complex manufactured food substances.
 These food substances once ingested must be broken down to simpler forms that can be
utilized by the cells. The breakdown is both physical and chemical.
Types of Dentition
 Homodont dentition: An organism has teeth of the same size and shape. E.g Fishes and
birds have homodont dentition.

 Heterodont dentition: where an organism has teeth of different sizes and shapes ; that is
(incisors, canines, premolars and molars). E.g is common with mammals and reptiles.
a) Incisors
 Are flat and chisel shaped with sharp ridged edges for cutting and biting food.
 They have one root.

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b) Canines
 Are conical teeth with sharp pointed edges modified for seizing and tearing prey among
carnivores.
 They have one root
c) Premolar and molar
 They have cusps on their surface to suit their grinding action.
 Premolars have two roots.
 Molars have either two or three roots.
Structure of a tooth
External structure
Externally the tooth is made up of 3 regions:
1. Root: the part embedded in the jaw
2. Neck: region between the crown and root
3. Crown: Projects above the gum
 hard non-living layer made of calcium phosphorous and carbonate

 forms a surface for biting and grinding food

 forms a protective covering of the tooth
Internal structure of the tooth
Internally it is composed of enamel, dentine, Pulp cavity and cement
1. Enamel
 Is the hardest outer part of the tooth, Is made up of calcium phosphate and carbonate salts
 Forms a surface for biting and grinding food also provides a protective covering for the
tooth.

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 2. Dentine
Is the living part of the tooth, gives rise to enamel
 Within the dentine is the pulp cavity containing nerves and blood vessels
3. Pulp cavity
 Has blood vessels provide nutrients to the tooth and remove the waste products
 Has nerves ending that detect heat, pain and cold
4. Cement
 Is a spongy calcareous substance that fixes the tooth to the socket in the jaw
5. Periodontal membrane
 Found between the cement and the jaw bone, has collagen fibres which hold the tooth
securely in the socket
Dental Diseases

a) Dental Carries/ Teeth decay

Caused by;

1. lack of hard food, 4. lack of vitamin D,

2. too much sweet or sugary food, 5. Lack of cleaning teeth and general
3. lack of calcium in diet, ill-health.

 The bacteria in the mouth break down the sugars to form energy and organic acids which
corrode the enamel.
b) Periodontal Diseases
 Caused by
1. lack of vitamins A and C,
2. Lack of massage of the gums and imperfect cleaning of gums.
 The gums become flabby and soft so they do not support the teeth. Common in adults
than children.
 Are of two types:
a) Gingivitis- Characterized by reddening of gums, bleeding and pus in the gums.
b) Pyorrhea- The teeth become loose due to infection of the fibres holding the teeth in
the sockets.

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Dental Hygiene

 Proper teeth care requires:

 Regular cleaning or brushing teeth after every meal
 Avoid eating too much sugary foods.
 Eating hard foods e.g. raw carrots, cassava, yams, sugar cane.
 Eating diet rich in calcium, phosphate and vitamins A, C and D.
 Teeth should be used for their correct purpose.
 Regularly visit the dentist if necessary.

Classes of Holozoic Heterotrophs

 Holozoic heterotrophs are classified according to the type of food they consume.
 These are:
a) Herbivorous: heterotrophs that exclusively feed on vegetation.
b) Carnivorous: heterotrophs that exclusively feed on flesh.
c) Omnivorous: heterotrophs that feed on both flesh and vegetation.
 Dentition of heterotrophs is based on the kind of food they consume.
Dental Formula
 This is the description of the number, type and position of teeth in the jaws of animals.
 Number of teeth recorded represents half the total teeth in the upper and lower jaws.
 The teeth names are abbreviated as
i-incisors. c-canines. pm-premolars. m-molars.
 An animal was found to have no incisors and canines on the upper jaw. It had six
premolars and four molars on the upper jaw. On the lower jaw, it had eight incisors, no
canines, six premolars and six molars.
a) Write down its dental formula.
b) State its mode of feeding.
c) Give a reason.
Herbivorous
Are animals that feed exclusively on vegetation.
Are grouped into grazers and browsers
Grazers: Feed on grass e.g. cow, donkey, zebra, sheep

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Browsers: Feed on shrubs and herbs e.g. giraffe, goat, antelope
The teeth of herbivores have several adaptations that suit them to the kind of food they take in:
 Most do not have the upper incisor but instead have a horny pad against which the grass
is pressed and cut by the lower incisors
 They have a gap in the lower jaw called a diastema, separating the canines from
premolars; It provides a space for the tongue to turn the food
 Have a long tongue for cutting, turning of grass, and moving the food during grinding
 The teeth have an open enamel in the crown, which allows continuous growth to replace
worn-out surfaces caused by grinding
 The presence of loose jaws of the jaw bone jaws that move side by side to enable
premolars and molars to grind the food.
 The molars and premolars are worn out unevenly resulting in the formation of ridges
called cusps which help in crushing and grinding vegetation

I 0/4 c0/0 pm 3/3 m 2/3 = 30

Carnivores
 Their incisors are chisel shaped and closely fitting to seize the prey.
 Their canines are long, conical and curved to hold, kill and tear the prey.
 Some of their premolars in the lower and upper jaw are modified into specialized
carnassial teeth which have smooth sides and sharp edges to slice through flesh and crush
bones
 Premolars and molars are broad with cusps for crushing bones.
 Their jaws are attached to powerful muscles that move the jaws up and down
 Carnivores are adapted to fast running by possessing well developed leg muscles.

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 i 3/3 c 1/1 pm4/4 m2/3 = 42

Omnivores

 Are animals that feed on both vegetation and flesh

 Example: Human being

 Mammals produce teeth in two sets:

1. Milk teeth: Are the first set of teeth to be produced and are lost between 6-12 years of age

Are 20 in human beings

2. Permanent teeth: They replace the milk teeth, Are 32 in an adult human being

DIGESTION IN MAMMALS
 The process through which complex food substances is broken down physically and
chemically into simpler food substances that can be absorbed by body cells.
 However, small molecules like those of vitamins, mineral salts and water are directly
absorbed into the bloodstream without undergoing digestion.
 Digestion occurs along the alimentary canal i.e. mouth, stomach, duodenum and ileum.
 There are glands also associated i.e the pancreas, gall bladder, salivary glands.
 Five Stages of digestion in Human Nutrition
 Ingestion, Digestion, Absorption, Assimilation, Egestion
1. Ingestion: introduction/placement of food into the alimentary canal
2. Digestion: Is the physical/ mechanical and chemical breakdown of complex food into
their simple soluble absorbable subunits.

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 3. Absorption: the products of digestion enter into the blood or lymph, occurs in the villi on
the ileum
4. Assimilation: Is the in cooperation /utilization of the absorbed nutrients by the cells.
5. Egestion: Is the removal of undigested and indigestible food material from the alimentary
canal through the anus.
The main functions of the digestive tract are digestion and absorption of food
Main functions of muscles inthe digestive tract are
 Contract and relax to enhance peristalsis,
 Secrete digestive enzymes ,
 Contract and relax to enhance churning of food

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Relate the structures of the alimentary canal to their function;
Digestion in the mouth
 At the mouth both physical and chemical digestion takes place.
 Sharp teeth broke down large food particles by grinding and chewing (mastication).
 Small size to increase the surface area for enzymatic action and for easy swallowing.
 The tongue mixes the food with the saliva, has taste buds to detect the quality of food,
rolls food into boluses for easy swallowing.
 The salivary glands are:
a) Sublingual salivary gland; beneath the tongue
b) Sub mandibular gland: under the jaw

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 c) Parotid gland: Found in the cheeks in front of the ears.
 Components of saliva
Water; dissolve food, enhance hydrolysis , moisten food, medium of enzymatic reaction.
Mucus; lubricate food during chewing
Salivary amylase/ ptyalin; breaks down/digests/hydrolyses starch to maltose.
Bicarbonate salt; provide alkaline medium for action of ptyalin
 The tongue also rolls the food into small round masses called boluses. The boluses are
then pushed to the back of the mouth to initiate the swallowing process.
 Movement is facilitated by a wave of muscular contractions of longitudinal and circular
muscles of the oesophagus known as peristalsis.
 There is a flap of cartilage, epiglottis which closes the wind pipe (trachea) during
swallowing.
Q.The diagram below shows how food moves along the human esophagus and intestines

Identify the process illustrated in the diagram peristalsis

Explain the movement of the bolus; achieved by wave like contraction and
relaxation of circular and longitudinal muscles of the alimentary canal;

Digestion in the stomach

 The boluses enter the stomach via the cardiac sphincter (a muscular valve).
 The stomach has thick circular and longitudinal muscle layers which contract and relax to
produce movements that mix the contents of the stomach.(churning) results in formation
of a fluid called chyme
 Arrival of food in the stomach stimulates secretion of the hormone gastrin which
stimulates the gastric glands in the stomach walls to secrete gastric juice which contains:
a) Pepsinogen-This is activated to pepsin which breaks down proteins to peptides.
b) Rennin- Digests caseinogens protein in milk to casein (curd).
c) Hydrochloric acid- This:
Activates pepsinogen to pepsin
Provides a favorable medium for action of the enzymes rennin and pepsin

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 Kills some bacteria ingested with food.
d) Mucus- Forms a protective barrier to the stomach wall against corrosion by the
HCl. Also prevent auto digestion.
Mucus is secreted by goblet cells in the epithelial membrane of the alimentary
canal. Pepsin is secreted in the inactive form(pepsinogen) to prevent digestion of
the cells that secrete it/(Chief peptic cells)

Duodenum
 The chyme then passes down to the duodenum through the pyloric sphincter in small
quantities in to the Duodenum (first section of the small intestine)
 Arrival of food in the duodenum stimulates secretion of
i. Secretin hormone from the pancreas: stimulates secretion of pancreatic juice into
the duodenum
ii. Cholecystokinin from the duodenal wall: stimulates the gall bladder to secrete
bile.
 Pancreatic juice contains:
a) Pancreatic amylase- This facilitates breakdown of the remaining starch into maltose
b) Trypsinogen- activated by (enterokinase) to trypsin to digest proteins into peptides.
c) Pancreatic lipase-Digests lipids into fatty acids and glycerol
d) Sodium hydrogen carbonate- This:
Provides alkaline medium for activity of the duodenum enzymes.
It also neutralizes the acidic chyme.
 The bile juice contains bile salts that include sodium glycocholate and sodium
taurocholate. These salts:

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 i. Aid in emulsification (breakdown of fat molecules into tiny fat droplets to
increase surface area for digestion).
ii. The salts also provide a suitable alkaline medium for action of the duodenal
enzymes.
iii. In addition they neutralize the acidic chyme.

Digestion in the ileum

 Ileum is the final part of the small intestine. The arrival of chyme in ileum stimulates
secretion of intestinal juice
 Brunner’s glands secrete mucus that protect and lubricate the ilium from digestive
enzymes
 Crypts of Lieberkuhn an alkaline fluid known as succus entericus (intestinal juice).
which contains:
a) Maltase: speeds up breakdown of maltose to glucose
b) Sucrase: speeds breakdown of sucrose to glucose and fructose
c) Peptidase: speeds breakdown of peptides to amino acids
d) Lipase: speeds breakdown of lipids to fatty acids and glycerol.
e) Lactase: speeds breakdown of lactose to glucose and galactose.
f) Polypeptidase: speeds breakdown of plypeptides into amino acids
Note:
 The mucus secreted by the goblet cells lubricates food along the alimentary canal and
also protect the canal from being digested by enzymes.

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  At the end of digestion in the ileum, the resulting watery emulsion is called chyle; it
contains soluble end products of digestion/ nutrients ready to be absorbed.
ABSORPTION
The soluble end products of digestion diffuse into the cellular lining of the villi.
Micronutrients such as water soluble vitamins, mineral salts and alcohol are absorbed at
the stomach. Alcohol is equally absorbed here without undergoing digestion.
Molecules of amino acids and glucose are absorbed in blood capillary by active transport.
The capillaries drain into the hepatic portal vein where the absorbed products are
transported to the liver before they are circulated to other body parts.
The fatty acids are absorbed into the lacteals of the villi which drain into the lymphatic
vessels.
The ileum is adapted to absorption in many ways
a) It is long to provide a large surface area for absorption
b) It has a narrow lumen so as to bring the digested food into close contact with the walls of
the ileum for easier absorption
c) It is highly coiled to slow down movement of food thus allowing more time for digestion and
absorption of food.
d) The inner surfaces have numerous villi and microvilli to increase surface area for
absorption of end products of digestion.
e) The epithelial lining is one cell thick to reduce the distance through which digested food
diffuses.
f) Has a dense network of blood capillaries into which digested food materials diffuse to
increase transport and thus maintain a steep concentration gradient.
g) Have lacteal vessels in the villi for absorption of fatty acids and glycerol.

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The Colon
 It absorbs water and vitamins from the remaining food that has passed through the
alimentary canal.
 The waste then becomes semi-solid called faeces. Faeces are stored in the rectum and
then egested through the anus
Caecum and Appendix
 Have no roles in man, in the ruminant animals / herbivores. They contain some bacteria
which secrete cellulose enzyme that digest cellulose to maltose.
 The bacteria and the herbivores are in a symbiotic relationship.
Assimilation
 Utilization/ incorporation of the end products of digestion into the cell metabolism. It
a) Glucose
 Oxidized to release energy
 Excess glucose is converted to glycogen stored in liver/ stored under the skin to provide
heat insulation
 Some is maintained in the blood stream circulation to maintain normal osmotic pressure
of blood.
b) Fatty acids and glycerol
 oxidized to release energy
 Combine to form neutral fats stored under the skin to provide heat insulation
 Used to build structures (membanes)
c) Amino acids
 Used to synthesize proteins for general body growth
 Oxidized during starvation to release energy.
 Excess is deaminated
Vitamins

 They play vital roles in metabolic reactions. Some act as co-enzymes while some
influence the intake of certain substances. In particular, vitamin C influences uptake of
iron while vitamin D influences absorption of calcium ions in the gut.
 There are two classes of vitamins owing to their solubility:

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 a) Fat soluble vitamins- They dissolve in fats and are often stored in the liver. Include
Vitamins A, D, E, K.
b) Water soluble vitamins- Dissolve in water. Include vitamins B1, B2, B5, B12 and C.

A balanced diet must have required proportions seven components:

Carbohydrates, Proteins, Lipids, Vitamins, Minerals salts, Fibre and Water

Vitamin Main food source Uses in the body Deficiency disease symptoms
Vitamin A Liver, milk, eggs, cod liver For vision especially Poor night vision, sore eyes, dry
(Retinol) oil, carrots, fresh green at night, protects skin scaly skin and cornea. Reduced
vegetables and cornea from resistance to diseases
drying or becoming
scaly
Vitamin B1 Ground nuts, beans, Cell respiration, General weakness, retarded
(Thiamine) unpolished cereals, egg-yolk, proper growth in growth in children, Beriberi-
milk, liver, and kidney. children. wasting of muscles and swelling
of feet and legs
Vitamin B2 Green veg., yeast extract, Cell respiration Pellagra-Skin disorders, sores
(Riboflavin and ground nuts, unpolished Normal skin health and bleeding in mouth and gum.
nicotinic acid) cereals, egg-yolk, milk, liver, and function
kidney.
Vitamin B5 Like B1 and B2 but more in Cell respiration Malfunctioning of nervous
(Pantothenic acid) eggs. Proper functioning of system and digestive system
nervous system and
alimentary canal
Vitamin B12 Liver, beef and kidney Formation of blood Pernicious anemia- low blood
(Cobalamine) cells. cell count.
Vitamin C Fresh citrus fruits, green Protection against Scurvy- bleeding of mouth and
(Ascorbic acid) vegetables, mangoes, paw infection gum, anaemia, swellings on skin,
paws and tomatoes poor healing of wounds, reduced
resistance to infection.
Vitamin D Milk, fish, liver, egg-yolk, Formation and Rickets-An abnormal bone
(Calciferol) formed in skin in the presence hardening of bones formation in children, soft and
of sunlight. and strong teeth brittle bones in adults.
Absorption of calcium
and phosphorous.
Vitamin E Milk, egg-yolk, green Necessary for normal Sterility in some animals
(Tocopherol) vegetables and vegetable oils fertility in some
animals.
Cell metabolism
Vitamin K Liver, egg-yolk, green Necessary for blood Excessive bleeding
(Quinone) vegetables, unpolished cereals clotting
Mineral salts

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  These are important inorganic compounds containing elements required for essential
body functioning. Depending on body requirements, mineral salts are of two classes:
a) Macro-nutrients: Nutrients required in large quantities. These include nitrogen,
sulphur, phosphorous, calcium, sodium, iron and magnesium.
b) Micro-nutrients: Nutrients required in small quantities. Include copper, manganese,
boron, iodine and cobalt.
Element Source Functions in the body Deficiency Symptoms

Nitrogen Meat, milk, eggs, Synthesis of proteins, formation of cell,

fish, other tissues and structures
proteins

Phosphorous Protein foods Protein synthesis, bone and teeth Rickets-Poorly developed
formation, ATP formation.
bones
Calcium Green Blood clotting and muscle contraction, Muscle cramps and rickets.
vegetables, milk, formation of bone and teeth
cheese
Iodine Iodized table Formation of thyroxin hormone, Goiter- swelling of thyroid
salt, cheese, sea regulates rate of energy production
glands in the neck region
fish such as cod
and salmon
Potassium Liver, beef, Transmission of nerve impulses, proper Muscular cramps, twitching
vegetables, milk heart functioning, growth and
and weakness, irregular
and eggs maintenance
heartbeat.
Iron Liver, eggs, Formation of haemoglobin in red blood Anaemia
green vegetables. cells, role in respiration.
Sodium Table salt, green Maintaining osmotic balance of the
vegetables, fish body fluids, transmission of nerve
milk. impulses, regulation of blood pressure.
Chlorine Table salt Maintain osmotic balance of body
fluids, transmission of nerve impulses.
Sulphur Protein foods Protein synthesis, formation of body
tissues.
Magnesium Almost present Bone and teeth formation, activates Muscle tremors and
in all foods enzymatic activities in the body, proper
convulsions, fatigue,
functioning of the nerves and muscles,
activating B vitamins, insulin secretion nervousness.
and functioning, energy production,
making of new cells
Roughages

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  This is the indigestible material in food. Mainly composed of cellulose from plant cell
walls.
 They are found in full cereals, fresh fruit fibres like lemons, oranges, mangoes and
vegetables.
Importance of roughage
a) Roughage enhance peristalsis since as they rub against the walls of the alimentary canal,
they stimulate contraction and relaxation of the muscles.
b) Adds bulk in food easily propelled by peristaltic movements. This prevents constipation.
Factors affecting energy requirements in humans
Discuss how the following factors affect energy requirements in humans:
› Occupation › Sex
› Health of an individual › Body size
› Age › Environmental temperature

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