*1-Characteristics of Living Things

In order to identify living organisms, scientists listed 7 characteristics which all living organisms have:

1. Nutrition:
Taking in nutrients which are organic substances and mineral ions, containing raw materials and energy for
growth and tissue repair, absorbing and assimilating them.

2. Excretion:
Removal from organisms of toxic materials, the waste products of metabolism and substances in excess.

3. Respiration:
Chemical reactions that break down nutrient molecules in living cells to release energy.

4. Sensitivity:
The ability to detect or sense changes in the environment and to make responses.

5. Reproduction:
Progresses that make more of the same kind of organism.

6. Growth:
The permanent increase in size and dry mass by an increase in number of cells, cell size, or both.

7. Movement:
An action by an organism or part of an organism that changes position or place.

The seven characteristics could be memorized by the term “MRS. GREN”:

M- Movement

R- Respiration

S- Sensitivity

G- Growth
R- Reproduction

E- Excretion

N- Nutrition

The Binomial System:

The Binomial System of scientifically naming organisms was developed by Carolus Linnaeus of
Sweden. It consists of the organism’s Genus and species name, and thus it is called as Binomial. It
consists of 7 levels:

 Kingdom
 Phylum
 Class
 Order
 Family
 Genus
 Species
Now, let’s take up a simple example: Humans

 Kingdom- Animal
 Phylum- Vertebrates
 Class- Mammalia
 Order- Primate
 Family- Hominidae
 Genus- Homo
 Species- Sapiens

Rules for writing scientific names:

 The first letter of the genus is ALWAYS capitalised
 The first letter of the species is NEVER capitalised
 Scientific names of organisms are always italicized or underlined
The classification of living organisms

Eukaryotes:
Protoctista: are organisms with a nucleus, and many flexible organelles amongst their species (for
example, some have chloroplasts and cell walls like plants and some like animal cells without these
distinguishing characteristics). Their main characteristics include:

 unicellular or multi-cellular bodies

 cells with or without cell wall and chloroplasts
 some species are autotrophic, rest are heterotrophic
 all species have cells with nucleus
Examples of Protoctista:

 Paramecium
 Chlamydomonas
 Seaweeds
Fungi: are organisms which do not have chlorophyll, thus are heterotrophic and feed on dead
organic matter parasitically. The most common known is the edible mushroom; others include
fungi causing diseases like athlete’s foot, ringworm, panama disease etc.Their characteristics
include:

 Multicellular bodies (very few are unicellular)

 Have nuclei
 Reproduce by spore production
 Are heterotrophic
 Don’t have chloroplasts
 Feed by parasitic or saprophytic means on organic dead matter
Examples include:

 Saccharomyces cerevisiae
 Penicillium
 Mushroom

Animals:
Phylum Arthropoda:
 Hard exoskeleton
 Segmented bodies
 jointed appendages
 exoskeleton composed of protein and chitin
 Open circulatory systems in which heart pumps hemolymph through short arteries into open spaces
(sinuses)
 Aquatic members have gills for gas exchange
 terrestrial members have tracheal system of branched tubes leading from their surface throughout body

Crustaceans:
 More than 4 pairs of jointed legs
 Breathe through gills
 Antennae present
 Mostly marine
Examples of crustaceans: Crabs, lobsters etc.

Arachnids:
 With 4 pairs of jointed legs
 Breathe through gills and book lungs
 Mostly terrestrial
Examples of arachnids: Scorpion,spider etc.

Insects:
 Have 3 pairs of jointed legs
 Have 2 pairs of wings
 Breathe through trachea
 Antennae present
 Mostly terrestrial
Examples of insects: Locust, Moth, House Fly, Grasshopper etc.
Myriapods:

 Body consists of many segments

 Each segment has jointed legs
 They can be both herbivores and carnivores
 Terrestrial
Examples of myriapoda: Centipede, Millipede etc.

Phylum Annelida
 They are worms
 Have bodies made up of ring like segments
 Live in water and moist soil
Example of Annelids: Earthworm

Phylum Mollusca
 Soft bodied animals
 Have unsegmented bodies
 With or without shell
Examples of Molluscs: Octopus, Jellyfish, Squid etc.

Phylum Nematodes
 They are worms
 Bodies are not divided into segments
 Usually white, long and thin bodied
 feed by parasitic means
Examples of Nematodes: Hookworm, Roundworm etc.

Phylum Vertebrates
 Internal skeleton with spine
 Their nervous system has encephalon (brain) and a spinal cord.
 The encephalon is placed inside the skull and spinal cord is placed inside the spine.

Class Fish
 Are cold blooded
 Have streamlined bodies
 Aquatic
 Have scales on their bodies
 May be Herbivores or Carnivores
 Lay eggs in water
 Have fins
 Breathe through gills
Example of Fish: Mackerel, Pomfret, Tuna, Salmon etc.

Class Amphibians
 Give birth to offspring by laying eggs
 Have 4 limbs
 Their habitat is both terrestrial and aquatic
 Have moist skin
 Breathe through gills when young; when mature, breathe through lungs
 Adult often lives on land
Example of Amphibian: Frog, Salamander etc.

Class Reptiles
 Have scales on body
 Are cold blooded
 Terrestrial
 Lay eggs to give birth to offsprings
 Egg shells are rubbery
Examples of Reptiles: Lizard, Snake etc.

Class Birds
 Don’t have teeth, instead have a beak
 Have hollow bones
 Are warm blooded
 Lay hard shelled eggs
 Forelimbs replaced by wings
 Breathe through lungs
Examples of Birds: Flamingo, Eagle, Hawk, Sparrow etc.

Class Mammals
 Warm blooded
 Can maintain a constant body temperature
 Have different types of teeth
 Have skin covered by Hair
 Give birth to live young offsprings
 Have sudoriferous (sweat) glands
 Females have mammary (milk secreting) glands that produce milk to feed young ones.
Example: Human being

The Plant Kingdom

Phylum Angiosperm:
 Have root, stem and leaves
 Have xylem and phloem
 Reproduce by seed production
 Seeds are produced inside the ovary of the flower
 Phloem: Transports sugar
 Xylem: Transports water and minerals

Plant Part Monocot Dicot

Root
System Adventitious root only Adventitious root, Taproot or both

Cotyledons One Two

Stem Vascular bundles scattered Vascular bundles arranged in a ring

Leaves Exhibit parallel venation Exhibit reticulate venation

Either trimerous, tetramerous, seldom Either pentamerous, tetramerous, seldom

Flower pentamerous trimerous

Viruses
 Entirely microscopic
 Consisting of a single nucleic acid surrounded by a protein coat
 Capable of replication only within living cells of bacteria, animals or plants.
Example of Viruses: Human Immunodeficiency Virus, Tuberculosis, etc.

Prokaryotes
Bacteria are prokaryotic and unicellular. they have cell walls and circular DNA called plasmids. They
are Heterotrophs or Autotrophs.

Example: L.bulgaricus
*2-An Overview:
Right from the time when a diploid zygote was formed, till the present, we all are just made up
of 37.2 trillion microscopic and unicellular cells!

The cells cannot be seen by naked eyes; instead microscopes are needed to telescope our view of
these diminutive structures.

In the modern era, there are more than two types of microscopes that are used for viewing the cells
in detail. The most common type of microscope is a light microscope that can magnify the cell
appearance by x1500. Another one is an electron microscope that magnifies cell appearance to
x10,000,000, enabling scientists to see in greater detail.

Cell structure:
Cell membrane:
 Present in all cells
 Also called as plasma membrane or cell surface membrane
 Made up of thin layer of protein and fats
 Partially permeable
 Inside cell membrane lies cytoplasm and other cell organelles.

Cell wall:
 Present in plant and prokaryote cells
 In plants, made up of cellulose
 Cellulose forms fibres in criss-cross patterns over one other
 Cell wall forms very strong covering to cell
 Prevents cell from bursting

Cytoplasm:
 Jelly like substance
 Contains 70% water
 Metabolic reactions of the cell take place over here
 Harmful and useful substances diffuse in and out of cells through the cytoplasm

Nucleus:
 Contains genetic information present in chromosomes
 Chromosomes are made up of Deoxyribonucleic acid or DNA
 Controls the functions of the cells and gives instructions carry them out
 Present in both plant and animal cells and absent in a prokaryotic cell
Vacuole:
 Vacuoles are spaces in cells containing a solution called cell sap
 Large vacuoles are present in plant cells to store the useful products formed in photosynthesis
 In animal cells, small vacuoles or no vacuoles at all can be present as animal cells are heterotrophic
 Small vacuoles in animal cells often store food and water

Chloroplast:
 Is the organelle that distinguishes between an animal and a plant cell
 Contains a green coloured pigment known as chlorophyll
 They are important for plant cells in the process of photosynthesis

Mitochondria:
 Are powerhouses of cells
 Are found in all cells except those of a prokaryote
 In aerobic respiration, oxygen is used to release oxygen from the contents of the mitochondrion (starch in
plants and glycogen in animals)
Cells containing mitochondria are-

1. Muscle cell- to work

2. Sperm cell- to swim in the semen
3. Neurons- to carry electrical nerve impulses

Ribosomes:
 Ribosomes are cell organelles that are the places where a protein is made by the synthesis of amino acids.
 They are arranged in a network known as rough endoplasmic reticulum
 They are found in all kinds of cells ranging from prokaryotic to eukaryotic.

The structure of a plant cell

The structure of an animal cell
A Comparison between a plant and animal
cells:
Plant cells Animal cells

Have a cellulose wall covering the cell membrane Don’t have cell wall

Have a cell membrane Have a cell membrane

Have cytoplasm Have cytoplasm

Have a nucleus Have a nucleus

Often have chloroplasts with chlorophyll in them Chloroplasts absent in animal cells

Often possess large vacuoles containing cell sap Only possess small vacuoles containing food and water

Often have starch grains Only have glycogen granules present sometimes

Often have a regular shape Often irregular in shape

Calculating Magnification:
Top tip!: questions on magnification are quite common in cambridge IGCSE Biology paper 1 and paper 6 so
do learn the formula in advance!
Magnification = Size of Image/Actual Size

Examples of specialized cells:

Ciliated cell : found in the trachea and bronchi, moves the mucus towards the throat.

Memory cell : found in the blood, keep antibodies ready to kill pathogens that have affected you
more than once.

Root hair cell : found at the end of the plant roots are responsible for the absorption of minerals and
water.

Palisade mesophyll cell : found beneath the epidermis of a leaf are specialized at photosynthesis.

Sperm and Egg cell: produced in testes and ovaries, fuse together to produce a zygote.

Nerve cell : found throughout the bodies of all organisms are responsible for the transmission of
electrical nerve impulses.
Red Blood Cell : found throughout in the blood of mammals and specialize at the transport of
oxygen using the red pigment haemoglobin.

What you are made up of:

 Cells : eg: ciliated cells, root hair cells etc.
 Tissues : are are group of cells with the same function and of the same type. eg: epidermis tissue, palisade
tissue, muscle tissue etc.
 Organs: are groups of tissues. eg: heart, lungs, trachea, leaf, fruit, flower, root etc.
 Organ systems: are made from groups of organs. eg: digestive system, respiratory system, circulatory
system, reproductive system, nervous system etc.
 Organism: is what the end result is with several organ systems that make them up! Eg: you, tiger, snake,
scorpion etc.

External Links
1. Plant Cell
2. Eukaryote Cell
3. Cell Organelles
*3-Diffusion
Diffusion is the net movement of molecules and ions from a region of higher concentration, to a
region of lower concentration, as a result of their random movement.

Let’s consider an example:

you are spraying an air freshener in the air and soon you realize that the scent has spread all over
the room. The mixture in the air freshener bottle is the region of higher concentration, and the room
is a region of lower concentration. So the differences in the concentration gradients is what that
causes diffusion.

Diffusion in cells
When a living cell such as a plant or an animal cell is considered, there is an obstacle that can affect
diffusion: A partially permeable cell membrane which controls the movement of substances.

Importance:
Diffusion is needed by living organisms for:

1. Obtaining necessary requirements needed for metabolism

2. Getting rid of waste and toxic substances

Examples:
 Plants need carbon dioxide for photosynthesis; carbon dioxide is just 0.04% in the atmosphere, but still
there is lesser volume of it in the plant cells. So the atmosphere is the region of higher concentration and
the leaves are regions of lower concentration.
 The same example of the leaf can be used with oxygen, which is a waste product for the plant. Oxygen
diffuses from it’s region of production (higher concentration) to the atmosphere where it is scattered (lower
concentration)
 Diffusion is also used by insect pollinated flowering plants to send out the scent of the nectar they produce
to attract insects.
Osmosis
Osmosis is the diffusion of water molecules from a region of high water potential (region which has
more water molecules) to a region of low water potential (region which has less water molecules),
down the concentration gradient, through a partially permeable cell membrane.

Partially permeable membranes

As described previously, partially permeable membranes are those which restrict the passage of
molecules which exceed a particular size.

Cell membranes play a pivotal role in Osmosis as only water molecules are allowed to pass through
the cell membrane.

Visking tubing is an artificial form of the natural cell membrane.

Osmosis in animal cells:
In concentrated solution (Low water potential)
 animal cells shrink as they have a higher water potential than their surroundings

In dilute solution (High water potential)

 Animal cells burst as their surroundings have a higher water potential than them and water enters their cells
up to such an extent that their cell membranes burst

Osmosis in plant cells

In concentrated solution (Low water potential)
 Plant cells become plasmolysed as they have a higher water potential than their surroundings

In dilute solution (High water potential)

 Plant cells become turgid, but do not burst, as they have a supportive cell wall that is tougher than their
cell membrane.
*4-Enzymes
Enzymes are biological catalysts which speed up the reaction rate without getting involved in the
reaction itself.

Examples of enzymes:
1. Salivary amylase
2. Pepsin
3. Renin
4. Lipase
5. Catalase
6. Isomerase
7. Phosphorylase
8. Maltase
9. Lactase
10. Sucrase…etc

Types of Enzymes:
1. Carbohydrase- digests carbohydrates (eg:- Salivary amylase)
2. Protease- digests proteins (eg:- pepsin)
3. Lipase- digests fats (eg:- Enzymes from pancreas)

How an enzyme works:

1. An enzyme has an active site similar to the shape of the substrate.
2. When an enzyme comes in contact with the substrate, it fits like a jigsaw and exerts pressure onto the
substrate at a specific point so that it breaks up into a simpler substance.
Properties of Enzymes:
 All enzymes are proteins
 All enzymes work best at a specific temperature, known as the optimum temperature
 Enzymes get denatured ( lose shape of their active site) if it’s optimum temperature is exceeded
 Enzymes even work the fasted at a specific pH and like temperature, get denatured when the pH exceeds
the optimum
 Enzymes are specific in nature ( they can only break down a specific substrate)

Factors affecting Enzymes:

Temperature:
 As the temperature of a reaction mixture increases, the kinetic energy inside the reacting particles increases
as well
 This leads to a high collision frequency to build up
 This causes the substrate and the enzyme to collide more frequently and thus increase the rate of reaction.
 However, at a certain temperature, the enzyme loses the shape of it’s active site resulting in rate of reaction
to drastically fall.

pH:
 The pH for any enzyme to work depends upon it’s environment of production
 For most enzymes in the human body, the optimum pH is 7 (neutral)
 However, there are a few exceptions such as pepsin the enzyme that works in the stomach where dilute
hydrochloric acid is secreted and pH is as low as 2
 Enzymes can work at pH slightly higher or lower than their optimum pH

Using Enzymes:
Uses in biological washing powders:
 In order to break down organic substances such as carbohydrates,proteins and fats (that chemical detergents
fail to break), such biological catalysts are used
 Organic stains such as blood, oil, egg, butter etc. are broken down to simpler substances in the presence of
proteanases.
 Enzymes need to have an optimum temperature of at least 70 degree celsius and hence are extracted from
thermophilic bacteria or bacteria living near hot springs to remove the other componants of the dirt and so
that other parts of the detergant work well as well.
 The enzymes found in these bacteria are majorly proteases and lipases.
 In order to keep these biological catalysts away from skin contact (as proteases can digest skin cells made
up of protein!), they are packed in microscopic packets that only dissolve in the presence of water.

Uses in the food industry

 Fruits contain a substance known as pectin that is present within the primary and secondary cell walls of
the fruit cell
 In industrial fruit juice extraction, an enzyme called as pectinase is used to break down the pectin present
so that it is more easier to squeeze the juice out
 This relatively increases the volume of juice extracted and thus makes it economical for the company.
 Other than fruit juices, enzymes are also used in baby food production where the food is treated with
proteases and carbohydrases to break it down to simpler substances.
 This helps the baby’s body to easily absorb the food with indigestion prevented.
 Another use of enzymes is in sugar syrup production where amylase is used to break down starch to the
sweet tasting disaccharide- Maltose.

External Links
1. Enzyme
2. Catalysis
*5-An Overview
Wondering what makes you come to life? There are four important chemicals made majorly from
Carbon, Hydrogen, Oxygen that are known as the chemicals of life!

The 4 ‘Chemicals’
Carbohydrates

Carbohydrates are the body’s main source of energy. They contain the elements Carbon, Hydrogen
and Oxygen.

They come in two kinds:

1. Simple sugar (Monosaccharide) are the simplest forms of carbohydrates.

2. Complex sugar (Disaccharide and Polysaccharide)

Simple sugar (Monosaccharide):

Simple sugars can provide a lot of energy for immediate usage. However, they contain no other
useful nutrients. Example : Glucose

Complex sugar (Disaccharide and Polysaccharide):

They are good sources of energy. The body can easily store this form of energy for rapid use in
future.

 Animal cells store complex sugars in the form of glycogen.

 Plant cells store complex sugars in the form of Starch.
Example :
1. Disaccharide: Maltose
2. Polysaccharide: Starch, Glycogen
Foods containing carbohydrates: Bread, Root vegetables, potatoes, pasta, milk
 As mentioned above, energy from carbohydrates is converted into glycogen and is stored in the liver and in
our muscles.
 When energy is needed, the body changes the glycogen into glucose which is used by the body during
aerobic respiration.
 If a lot of carbohydrate is eaten, it will be stored as fat.

Fats:

Fats are used for energy but only when carbohydrate supplies run low.

They contain the elements Carbon, Hydrogen and Oxygen

Their simplest forms are fatty acids and glycerol

There are two types of fat:

 Saturated Fat: These are usually found in foods such as milk, butter, cheese and meat.
 Unsaturated Fat: These usually found in foods such as fish oils, cooking oils and vegetable oils.
Saturated fats are converted to cholesterol by the liver.

There are two types of cholesterol:

1. HDL (High Density Lipids): Must be in greater amounts as it is beneficial and good
2. LDL (Low Density Lipids): Must be in controlled amounts or else the person may get infected with
Coronary Heart Disease.
For this reason, no more than 10% of your energy should come from eating saturated fats.

If the percentage level of saturated fats in your diet increases, fat deposits begin to build up inside
blood arteries, making them stiffer, less elastic, and narrower.

When this particularly happens in the coronary artery that supplies oxygen to the heart, very less
oxygen is supplied to it, decreasing it’s performance and increasing the risk of coronary heart
disease. This usually results in a blood clot and a heart attack.

Eating too much of fat leads to obesity, coronary heart disease and diabetes.

Function of Fats:
 Needed to keep us warm
 Stored in the adipose tissue, which can break the fats if the body’s carbohydrate stores get exhausted
 The Adipose tissue is needed to insulate our body

Proteins

 Proteins are used to generate energy only when the body has exhausted it’s store of fat and carbohydrates.
 Proteins are very important for the body. Our muscles and other tissues, Haemoglobin, fibrin, keratin,
collagen, DNA, enzymes etc. are all made up of proteins.
 The proteins you eat are broken down into amino acids, and are used by the body to build and repair cells
and to make blood cells.
 Proteins are made by the synthesis of amino acids in the ribosomes of cells.
 Carbon, Hydrogen, Oxygen, Nitrogen and a bit of Sulphur is what amino acid molecules contain.
 Food containing proteins are: Eggs, Fish etc.
 Kwashiorkor is characterized by a protruding abdomen due to lack of proteins.

Water:
The body is majorly composed of water. Approximately 60% of adult’s weight is composed of water
(80% of child’s weight). It is vitally important that you drink enough water. Dehydration can seriously
damage performance of body.

Utilization of water:
water is used in our body for a vast number of reasons. Here are some listed below:

1. It is an important solvent
2. It is needed for carrying out metabolic processes
3. It is beneficial in excreting waste body products such as urea
4. It can cool our body down significantly by releasing sweat
5. It is needed for enzymes to dissolve in it
6. It is the major part of blood plasma

The Tests:
This section focuses particularly on the tests to detect the presence of the chemicals of life.

Testing for Carbohydrates

There is a simple test for carbohydrates: Just add benedict’s solution to the food and heat it up!
However, to give you a detailed description, please scroll your eyes below!

1. Cut or grind a piece of the food to be tested.

2. Add some water to the food and try to dissolve it in a test tube.
3. Add some Benedict’s solution to the test tube (which is blue as it contains copper salts).
4. Heat the test tube till 80 degrees celsius.
5. Observe the colour change from blue to brick-red (Blue to Green to Yellow to Orange and ultimately
Brick-red)
Safety precaution: Use a water bath to heat the test tube

Test for Starch

 Put a small piece of food on a white tile (so that colour change can be noticed)
 Add a drop of iodine solution on the food
 Notice the colour to change to blue-black

Testing for Fats

Fats don’t dissolve in water and thus, ethanol needs to be added.
1. Chop and grind small amount of food to be tested
2. Add the food in a clean test tube
3. Pour some pure ethanol on it
4. Shake it to dissolve
5. Take another test tube and add some distilled water in it
6. Pour the liquid part, into the second test tube
7. A milky appearance proves that the food contains fat

Testing for Proteins

1. Put the food into a test tube
2. Add a little water
3. Add some potassium hydroxide solution
4. Add two drops of copper sulfate solution
5. Shake the tube gently
6. An appearance of a purple color proves that protein is present.

Energy Calculations:
 1g of carbohydrates gives 17.1 kJ of energy
 1g of protein gives 18.2 kJ of energy
 1g of fat gives 38.9 kJ of energy
*6-Plant Nutrition
Nutrition
Nutrition is taking in useful substances. You may recall that nutrition is one of the characteristic of a
living thing and therefore it is important that living things take in useful substances ideal for their
growth using nutrition.

Photosynthesis
The process by which plants manufacture carbohydrates from raw materials using energy from light
is called as photosynthesis. Photosynthesis is extremely important in the plant’s nutrition.

Photo: Light

Synthesis: Manufacturing

Chlorophyll- the plant power station

Chlorophyll is a green pigment that is inside a chloroplast molecule.

When the sun shines on a chlorophyll molecule:

 Some of the energy in the light is absorbed by it

 The chlorophyll molecule then releases the trapped energy
 The released energy makes carbon combine with water
 This is done with the help of enzymes in the chloroplast
 This causes glucose to be made
 The glucose contains energy from the light
 Thus the light energy is converted into chemical energy in photosynthesis.
The equation for photosynthesis

Word equation:

Chemical equation:

Leaves- the plant nutritionists

A leaf contains palisade cells, which contains chloroplasts, which contain chlorophyll molecules,
which contain the enzymes that catalyse photosynthesis! Marvellous right?

Let’s learn about the leaf structure now:

The transverse structure of a leaf

Leaf part Function

To protect inner layers of cells

To secrete a waxy substance called the cuticle that
covers the upper epidermis.
The cuticle helps in lowering transpiration rates
Epidermis (upper)
E Don’t contain chloroplasts

To protect inner layers of cells

To help in the gas exchange by using stomata
Epidermis (Lower)
E Contain small openings called stomata

Guard cells Control the movement of substances in and out of the

E Contain chloroplasts stomata

Palisade mesophyll cells

E These cells contain many chloroplasts as
compared to other plant cells To carry out photosynthesis

Spongy mesophyll cells To carry out photosynthesis

Air spaces To help in the diffusion of oxygen and carbon dioxide

Xylem tube To carry water to the mesophyll cells

To take away substances such as sucrose, that the leaf

Phloem tube has made

Adaptation Why is it essential?

To expose most of the leaf to the maximum amount of

Supported by stem and petiole sunlight and air

To expose the cells to the largest amount of sunlight as

Large surface area possible

To allow sunlight reach all cells

To allow CO2 to diffuse in
Thin layered To allow O2 to diffuse out

To keep as few cell walls as possible between sunlight

Palisade cells are arranged end on (vertically) and the chloroplasts

Chloroplasts arranged broadside on

(horizontally) To expose maximum amount of chlorophyll to sunlight

Chlorophyll present in cells in the mesophyll To absorb energy from sunlight

layer So that carbon dioxide combines with water

No chloroplasts in epidermal layer To allow sunlight to reach the cells in the mesophyll layer

To allow CO2 to diffuse in

Stomata in lower epidermis To allow O2 to diffuse out

To allow CO2 and O2 to diffuse in and out of the cells

Air spaces in spongy mesophyll during photosynthesis

Chlorophyll arranged on flat membranes

inside chloroplasts To expose maximum amount of chlorophyll to sunlight

Xylem vessels within short proximity of To supply water to the mesophyll cells for photosynthesis
mesophyll cells and other functions

Phloem vessels within short proximity of To carry away sucrose and other organic products of
mesophyll cells photosynthesis

Uses of glucose in the plant’s nutrition

Use Notes

Energy can be released from glucose using aerobic

Used for energy respiration.

Stored as starch
(and not as glucose as:
 It is reactive
 It is soluble in water
 It is a small molecule
 It might be lost from plant cells when Stored as starch because:
dissolved in water  Is a large molecule
 It may indulge in unwanted chemical  Is unreactive
reactions in the cells  Is not very soluble
 It may increase the glucose concentration  Can be turned into small pieces
in the cell and cause damage)  Can be easily stored inside chloroplasts

Nitrate molecules are mixed with glucose to form strands of

Used to make proteins amino acids which are bound into proteins

Organic substances such as:

 Sucrose
 Cellulose
 Chlorophyll (using nitrogen and magnesium)
 Fats
Used to make organic substances  Oils

Transformed to sucrose for transport Why sucrose is changed for transport:

  Less reactive
 Small molecules
 Soluble in sap in phloem vessels

Mineral ions required by plants

Mineral ion Element Function Deficiency

Nitrates
OR
Weak growth
Ammonium ions Yellow leaves
Nitrogen To build proteins

Magnesium Magnesium ions To make chlorophyll E Yellowing between veins of the leaves

Limiting Factors
A limiting factor is something present in the environment in such short supply that it restricts life
processes. This means that nutrition is restricted at a certain level and the plant is at it’s peak of
growth!

Here is a list of some limiting factors you need to know:

Limiting
factor Notes

As light intensity increases, the rate of photosynthesis will increase as well

But at a certain point, even if the light gets brighter, the rate of photosynthesis will not
increase.
Sunlight

Carbon Similarly, the more the carbon dioxide concentration increases, the more the photosynthesis
dioxide rate, until a maximum is reached.

A plant photosynthesises at a greater rate when temperatures are warmer, than colder
Temperature temperatures

If stomata are closed, then photosynthesis cannot take place

On a warm, sunny day, stomata often close to decrease transpiration rates.

Hence this can lead to low photosynthetic rates.

Stomata
Glasshouses- the tools to maximise nutrition
Plants can be grown in glasshouses where environmental conditions can be controlled and hence
the plant’s nutrition can be enhanced.

These environmental conditions include:

 Light
 Temperature
 Carbon dioxide concentration
 Soil pH
 Moisture (and water)

Light
A range of light intensities can be provided at the correct wavelengths to the plant even in cloudy
and dark conditions.

Temperature
The temperature of the glasshouse can be controlled with heating and cooling equipments, so that
the plant gets an optimum temperature to photosynthesise

Carbon dioxide concentration

As the natural carbon dioxide concentration is very low (0.04%) plants cannot photosynthesise at
greater rates; whereas, in a glasshouse, it is possible to control carbon dioxide concentrations.

Importance of photosynthesis
 Brings the energy of sun into ecosystems
 Essential for maintaining a constant global level of oxygen and carbon dioxide
 Helps to stop level of carbon dioxide to rise too high
*7-Diet
A good diet on its own will not make you skillful or fit as a performer or a sportsperson, but will help
you make the most of your abilities through nutrition; hence, nutrition is very important. Your body is
an endothermic one and has the ability to maintain a constant body temperature and a lot of energy
is needed to do so. Moreover, the electrical impulses that are transmitted by the neurones in your
body as well need energy to do so. Thus it is important that you should have a good balanced diet to
get all the seven nutrients beneficial for nutrition.

Balanced Diet
Everyone, whether involved in sport or not should try to eat a healthy balanced diet. A balanced diet
includes all nutrients that your body needs and is a form of complete nutrition. to achieve this, you
need to eat a range of different types of food in the right proportion.

 Here is a list of the nutrients you require:

1. Carbohydrates
2. Fats
3. Proteins
4. Vitamins
5. Minerals
6. Fibre
7. Water

Carbohydrates

Carbohydrates are the body’s main source of energy. They come in two kinds:

1. Simple sugar (Monosaccharide)

2. Complex sugar (Disaccharide and Polysaccharide)

Simple sugar (Monosaccharide):

Simple sugars can provide a lot of energy for immediate usage. However, they contain no other
useful nutrients. Example : Glucose

Complex sugar (Disaccharide and Polysaccharide):

They are good sources of energy. The body can easily store this form of energy for rapid use in
future.
 Animal cells store complex sugars in the form of glycogen.
 Plant cells store complex sugars in the form of Starch.
Example :
1. Disaccharide: Maltose
2. Polysaccharide: Starch, Glycogen
Foods containing carbohydrates: Bread, Root vegetables, potatoes, pasta, milk
 As mentioned above, energy from carbohydrates is converted into glycogen and is stored in the liver and in
our muscles.
 When energy is needed, the body changes the glycogen into glucose which is used by the body during
aerobic respiration.
 If a lot of carbohydrate is eaten, it will be stored as fat.

Fats:

Fats are used for energy but only when carbohydrate supplies run low.

There are two types of fat:

 Saturated Fat: These are usually found in foods such as milk, butter, cheese and meat.
 Unsaturated Fat: These usually found in foods such as fish oils, cooking oils and vegetable oils.
Saturated fats are converted to cholesterol by the liver.

There are two types of cholesterol:

1. HDL (High Density Lipids): Must be in greater amounts as it is beneficial and good
2. LDL (Low Density Lipids): Must be in controlled amounts or else the person may get infected with
Coronary Heart Disease.
For this reason, no more than 10% of your energy should come from eating saturated fats.

If the percentage level of saturated fats in your diet increases, fat deposits begin to build up inside
blood arteries, making them stiffer, less elastic, and narrower.

When this particularly happens in the coronary artery that supplies oxygen to the heart, very less
oxygen is supplied to it, decreasing it’s performance and increasing the risk of coronary heart
disease. This usually results in a blood clot and a heart attack.

Eating too much of fat leads to obesity, coronary heart disease and diabetes.
Proteins

 Proteins are used to generate energy only when the body has exhausted it’s store of fat and carbohydrates.
 Proteins are very important for the body. Our muscles and other tissues, Haemoglobin, fibrin, keratin,
collagen, DNA, enzymes etc. are all made up of proteins.
 The proteins you eat are broken down into amino acids, and are used by the body to build and repair cells
and to make blood cells.
 Proteins are made by the synthesis of amino acids in the ribosomes of cells.
 Food containing proteins are: Eggs, Fish etc.
 Kwashiorkor is characterized by a protruding abdomen due to lack of proteins.

Vitamins:

Your body needs vitamins to help it work normally. they are needed for many functions including:

1. Releasing energy from food

2. Resisting infections and diseases
3. Repair and growth of tissues
4. Regulating chemical reactions in the body
Fruits and vegetables contain a lot of vitamins.

 Fat soluble vitamins: A, D, E, K

 Water soluble vitamins: B,C
The table below gives important information about vitamins:
 Vitamin A: is found in fish,milk, vegetables, eggs and cheese. It is needed for good eyesight and healthy
skin.
 Vitamin C: is found in citrus fruits and vegetables. It is needed for healthy teeth,gums, and to prevent
scurvy.
 Vitamin B1: is found in whole-grain food, nuts and meat. It is needed for breaking down carbohydrates.
 Vitamin D: is found in animal products such as milk and egg. It is also made in the presence of sunlight by
the skin. It is crucial for absorbing calcium and phosphorous and to avoid rickets.

Minerals:

 Minerals are basic elements that are found in the air and in the earth’s crust.
 Our body needs certain minerals in small proportions in order to maintain the nutrient stability.
Below are the names of some minerals needed by our body, where they are found and their
importance:

 Calcium: is present in vegetables, dairy products and dried fish. It is significant for keeping our bones
strong.
 Iron: is found in red meat, liver, beans, lentils and green leafy vegetables. It is crucial for making blood and
for the prevention of anaemia.
 Iodine: is found in seafood and dairy products. It is needed as it maintains the thyroid gland.

Fibre:

Fibres are actually a substance called cellulose. It is found in the cell walls of plants. Fruits,
vegetables, whole grain cereals are good sources of dietary fibre. Fibres cannot be digested, but it is
beneficial for the smooth working of the digestive system. People who eat too little fibre often suffer
from constipation and may acquire high risk of bowel cancer.
Water:

The body is majorly composed of water. Approximately 60% of adult’s weight is composed of water
(80% of child’s weight). It is vitally important that you drink enough water. Dehydration can seriously
damage performance of body.

Energy Calculations:
 1g of carbohydrates gives 17.1 kJ of energy
 1g of protein gives 18.2 kJ of energy
 1g of fat gives 38.9 kJ of energy

Individual energy needs:

The amount of energy required depends from person to person, depending on a number of factors
such as:

 Age
 Size
 Sex
 Lifestyle
 Diet
<chart here>

Making Yoghurt:
 Made with the help of Lactobacillus bulgaricus bacteria.
 Milk (Lactose) » Lactic acid+energy
 Yoghurt is produced when a bacteria called Lactobacillus bulgaricus is added to milk. It uses the sugar
(lactose) from the milk as it’s energy source. It converts the lactose into lactic acid. The presence of lactic
acid lowers the pH of the milk. The proteins in the milk coagulate, forming clumps. The milk separates out
into these clumps called curd and liquid called whey.

The process:
1. The milk is heated to 70 degrees celsius and then cooled.
2. the culture of the bacterium is added to warm milk and is left for a few seconds.
3. The heating is done to kill any other harmful or unwanted bacterium so that it does not ferment the milk
and produces unwanted products.
SCP- Single Celled Protein:
Single celled protein typically refers to sources of mixed protein extracted from mixed or pure
cultures of algae, yeast, fungi or bacteria. They are usually grown on agricultural wastes. They are
used as a substitute for protein rich food in human and in animal feeds.

Mycoprotein:
Mycoprotein has the potential to maintain normal blood cholesterol levels and even lower the
cholesterol levels. It can as well regulate blood glucose levels. It is an excellent source of high
quality protein and contains all the essential amino acids for adults. It is also rich in dietary fibre and
is low in saturated fats and also does not contain trans fats!

Production of mycoprotein:
1. Mycoprotein is manufactured using a bacteria called fusarium.
2. The fusarium is grown in large vats, using carbohydrates as a food source, with other nutrients such as
ammonium nitrate added as well.
3. The carbohydrates often come from waste and leftovers from making flour.
4. Fusarium reproduces and makes a mass of mycelium, which is harvested and treated to remove a lot of the
RNA it contains, and shaped (after drying) into chunks, ready to consume as it is, or for making into other
food products.

Food Additives:
Types of food additives:
1. Flavourings: such as monosodium glutamate, better known by it’s trade name: Ajinomoto, has properties
of enhancing the flavours of savoury food. However, research reveals that msg can damage our nervous
system, introduce joint pain and headache. .
2. Colourings: such as caramel, give an appealing brown colouring. On the other hand, it’s regular
consumption can lead to vomiting, muscular weakness, asthma and cancer!
3. Preservatives: such as ascorbic acid are used as antioxidants as they stop ‘browning’. However, other
preservatives such as Carrageenan has the potential to again, increase the risk of cancer.
4. Emulsifiers: are substances that break fats into simpler substances. It is industrially used for homogenised
milk which comprises of milk fat in water and milk proteins.

The Digestive System

Whatever you eat from your mouth is actually the opening to a 30 feet maze that directly ends at the
anus. Even if you have gobbled up something with unclean hands, the hydrochloric acid in the
stomach and the sodium hydrogen carbonate in your duodenum are definitely going to give any
pathogen a ‘warm’ welcome! So let us begin onto this chapter where we will learn about every single
aspect of your digestive system and for better understanding, give you a free powerpoint
presentation as well!
Here is what will happen when you eat
something:
1. Ingestion
2. Digestion
3. Absorption
4. Excretion

Ingestion
Taking food into the body through the mouth is called as ingestion.

Digestion
The breakdown of large insoluble molecules to small water soluble molecules using mechanical and
chemical digestion is called as digestion.

Absorption
The movement of digestive food molecules through the wall of the small intestine, into the blood or
lymph is defined as absorption.

Excretion
The removal of waste products of metabolism or nutrients in excess is termed as excretion.

Teeth
The structure of teeth:
 The teeth specialize in mechanical digestion of food.
 They can grind,chomp, tear and crush food in order to break it down to smaller and simpler pieces of food,
 The part of the tooth which is embedded into the gum is called the root.
 The part which can be seen is known as the crown.
 The crown is covered by the enamel which is the hardest naturally produced substance amongst animals!
 Beneath the enamel is a large layer of a less hard bone, called the dentine.
 The dentine has channels in it containing living cytoplasm.
 Beneath the dentine is the pulp cavity. it contains nerves and blood vessels.
 The root of the tooth is covered with cement. it has fibres growing out of it. it attaches the tooth to the
jawbone, but allows it to move slightly when chewing.

Types of teeth in mammals:

1. Incisors: are chisel shaped for biting off pieces of food.

2. Canines: are similar to incisors but instead of a chisel shape, they have a sharp pointed crown and are used
to tear off meat.
3. Premolars: are plateau shaped teeth which specialize at grinding food.
4. Molars: are like premolars and are also used to grind food.
Animals have two sets of teeth in their lifetime:

1. Milk teeth: the teeth which form during 5-30 months of your life. there are usually 20-22 milk teeth.
2. Permanent teeth: the teeth that replace milk teeth when you grow towards your teens. there are usually 32
permanent teeth.

Plaque
Some of the bacteria, together with other substances in your mouth, form a sticky film over the teeth,
especially next to the gums and in between the teeth. this substance is known as plaque.

Tartar
Plaque is soft and easy to remove at first. However, if it is left, it hardens to form tartar, which cannot
be removed by brushing.
Gum Disease
If plaque is not removed, the bacteria may infect the gums.

 The gums swell, becoming inflamed.

 They may even bleed when you try brushing your teeth.
 this is normally painless; however, if bacteria are allowed to grow, they may work their way down to the
root of the tooth!
 the tooth will then become loose and will need removing.

Tooth Decay

If sugar is left on the teeth, bacteria in the mouth will feed on it. Soon, due to the metabolic reactions
going in the bacteria’s body, an acidic solution will be produced which lowers the pH of the mouth
and has the potential to dissolve the enamel.

As the bacteria grows, greater volumes of acidic solution is produced. The acid gradually reaches
the dentine which gets dissolved even faster and then worms it’s way down the pulp cavity.

The bacteria can grow up to such an extent that an abscess is created by it at the root of the tooth,
causing excruciating pain!

A person suffering from tooth decay usually is recommended for a root canal treatment.

Dental Care
 Avoid consuming too much of sugar
 Use a fluoride toothpaste regularly as research has revealed that having fluoride ions in the mouth produces
a tough protective layer on top of the enamel and prevents tooth decay.
 Visit a dentist twice a year.
 Don’t use too much of fluoride toothpaste as it may cause blackening of your teeth.
The Alimentary Canal

The alimentary canal runs from the mouth to the anus. It also includes the liver and the pancreas.

Peristalsis is the longitudinal movement of the muscles in the oesophagus that help the food bolus to
travel through the alimentary canal.

Sphincter muscles act as valves and are found throughout the canal. they help regulate the
movement of food through it.

The Mouth
1. The teeth bite and grind the food into smaller pieces.
2. The tongue helps move the food and mixes it evenly with the saliva.
3. This forms a food bolus.
4. Salivary glands produce saliva containing amylase.
5. Amylase breaks down starch containing food such as bread into maltose.
Amylase
Starch —————–> Maltose
The Oesophagus

Originally, when the food moves through the mouth, there are two tubes leading to different
destinations:

1. The trachea
2. The Oesophagus
Food needs to pass into the oesophagus and not through the trachea which leads to the lungs.

 To regulate this passage, the epiglottis is used.

 The epiglottis is a cartilage that stops the food from entering into the trachea.
Note: There are no enzymes in the oesophagus and so the food bolus moves unchanged into the
stomach.

The Stomach

 The stomach is strong and muscular.

 It secretes mucus and other enzymes such as pepsin.
 Another enzyme- renin is only secreted in young mammals and it is used to clot milk.
 Dilute hydrochloric acid is also produced and it acts as a barrier by killing any pathogens that may have
got into the food.
 The mucus is secreted by goblet cells that are present on the walls of the stomach. the mucus prevents the
stomach to get digested by the hydrochloric acid it produces!
Enzymes present:
1.Pepsin: helps the breakdown of proteins to polypeptides

Pepsin
Proteins ——————–> Polypeptides
2. Renin: helps the clotting of milk in young mammals

Renin
Milk ——————–> Coagulate
 The pyloric sphincter opens the stomach and let’s the chyme move into the duodenum.
The Small Intestine

The small intestine is present between the stomach and the colon.

It consists of 3 parts:

1. Duodenum
2. Jejunum
3. Ileum

The Duodenum and the Pancreas

 The duodenum has a duct leading from the pancreas that carries the pancreatic juice to it.
 The Pancreas is a cream coloured gland which is also important for blood glucose concentration control.
 The pancreatic juice contains sodium hydrogen carbonate, which is used to neutralize the acidic chyme so
that the enzymes in it can work efficiently.
Enzymes in pancreatic juice:

1. Amylase: Breaks down starch containing food to maltose

Amylase
Starch —————–> Maltose
2. Trypsin: like pepsin, it breaks down proteins into polypeptides

Pepsin
Proteins ——————–> Polypeptides
3. Lipase: breaks down fats into fatty acids and glycerol

Lipase
Fats ———————> Fatty acids + Glycerol
 Bile is a yellowish-green, watery liquid, which is made in the liver.
 It is stored in the gall bladder.
 It flows to the duodenum along the bile duct.
 There are no enzymes present in bile but it does contain bile salts that emulsify fats.
 Bile also contains bile pigments which are produced when red blood cells are broken down in the spleen.

Villi

 Food is completely digested and absorbed in the parts of the small intestine.
 this happens with the help of the villi which is present on the walls of the stomach.
The villi has special features that makes it efficient in breaking food down. Some include:

1. It has a large surface area

2. It has microvilli on it’s surface that again, amplifies the surface area.
3. It has goblet cells on it’s surface that produce mucus and lubricate the intestine walls.
4. It can secrete a wide range of enzymes in order to break the food in it’s simplest form.
5. It is structured in such a way that the enzymes are recycled and don’t go waste in a single digestion cycle.
6. It has a lacteal that can absorb fats and take it to the hepatic portal vein to the liver.
When the absorbed nutrients reach the hepatic portal vein, the liver:
 produces urea
 transports the absorbed nutrients to the cells
 converts glucose to glycogen
Enzymes present:
1. Maltase: breaks down maltose into glucose

Maltose
Maltose ————-> Glucose
2.Sucrase: Breaks down sucrose into glucose and fructose

Sucrase
Sucrose ————-> Glucose + Fructose
3. Lactase: Breaks down lactose into glucose and galactose

Lactase
Lactose —————-> Glucose + Galactose
4. Peptidase: Breaks down polypeptides into amino acids

Peptidase
Polypeptides——————> Amino acids
5. Lipase: Breaks down fats into fatty acids and glycerol

Lipase
Fats ———————> Fatty acids + Glycerol

Large Intestine
 In the large intestine, caecum and appendix have no functions.
 The Colon specializes in the absorption of water and salt.
 In the rectum, faeces are formed, which is an undigested mixture of undigested food, bacteria, bile
pigments and some dead cells.
 Faeces are disposed out of the body, at the end of the alimentary canal.
*8-Transport in Plants
Transport is all about passing nutrients from one place to another to favour the living organism’s
growth.

Plants need some essential substances such as:

 carbon dioxide
 water
 mineral ions
etc to photosynthesise and grow.

To transport these substances to leaves, plants need to have a network of transport tubes and
tissues. There are two types of plant transport vessels.

These plant transport vessels are:

1. Xylem (pronounced ‘zy-lem’)- Transport water and minerals

2. Phloem (pronounced ‘flo-em’)- Transport sucrose and amino acids
Here is a comparison between the two plant transport vessels: xylem and phloem:

Xylem Phloem

Made of Dead cells Living cells

Cell wall thickness Thick Thin

Cell wall material Lignin and cellulose Cellulose

Permeability Impermeable Permeable

Transports Water and minerals Sucrose and amino acids

Carried to Leaves Growing parts and storage organs

Direction of flow Upwards Upwards and downwards (by translocation)

Cytoplasm None Cytoplasm lining

Tissue also has Fibres Companion cells

Diagram <image for xylem vessel here> <image for phloem Tube here>

Vascular bundles
A group of xylem vessels and phloem tubes are called a vascular bundle.
In IGCSE examinations, questions are often asked about the ‘positions’ of the
xylem vessels and the phloem tubes in a vascular bundle.

Structure of a vascular bundle in the root

Structure of a vascular bundle in the stem

Roots and water uptake
Plants take water from the soil through their roots. Roots have root hairs to absorb water and
minerals from the soil.

Structure of a root:

 At the very tip is a root cap. This is a layer of cells which protects the root as it grows through the soil.
 The rest of the root is covered by a layer of cells called the epidermis.
 The root hairs are a little way up from the root tip. Each root hair is a long epidermal cell.

Function of roots:
 Root hairs provide a large surface area and help significantly in the absorption of water.
 They provide anchorage to the plant
 They also absorb mineral ions through active transport
Water moves through the root hairs through osmosis:
1. The water outside the root is in it’s dilute form (High water potential)
2. The water inside the root is in concentrated form (Low water potential)
3. Thus the water diffuses from a region of high water potential to a region of low water
potential, down their water potential gradients, through a partially permeable cell membrane.
<Image for absorption of water through the root here>

Transpiration
Key definition: Transpiration is the loss of water from plant leaves by evaporation of water at the
surfaces of the mesophyll cells, followed by the loss of water vapour through the stomata.
Transpiration has significant importance in the water cycle and the transport of water in a plant.

The process of transpiration:

1. The mesophyll cells in the plant’s leaves are covered with a thin film of moisture
2. The sun’s heat causes some of this moisture to diffuse out of the stomata and evaporate into the atmosphere
3. Water from the xylem vessels travel to the mesophyll cells by osmosis and replace the water loss

The transpiration stream:

 Water enters root hairs by osmosis
 Water moves up the root and reaches the xylem vessels
 The pressure at the top of the xylem vessels is lower than at the bottom
 This causes the water to move upwards through the xylem vessels till the leaf’s mesophyll cells
 The water is lost through transpiration, in the transpiration stream.

Measuring transpiration rates

 Transpiration rate in a plant can be measured using apparatus called a potometer
 The rate of transpiration is measured by calculating how fast the air-water meniscus travels through the
capillary tube.

Conditions that affect transpiration rates

Environmental
condition How transpiration rates are affected

Transpiration increases as temperature increases due to increased kinetic energy in

Temperature water molecules.

Transpiration decreases as humidity increases

As the difference between the concentration gradients in the leaf and in the
Humidity atmosphere are similar. (Higher the humidity, greater the water molecules in the air)

The wind increases transpiration rates (as water evaporates more quickly on a windy
Wind speed day)

The greater the light intensity, the greater the chance that a plant will open its stomata
to photosynthesise.
Light intensity
Hence the greater transpiration will be.

In short water supply, a plant will conserve water instead of wasting it.
Water supply
The shorter the water supply, the lesser the transpiration.

Translocation
Translocation is the movement of organic food such sucrose and amino acids in phloem; from regions
of production (source), to regions of storage OR regions of utilisation in respiration or growth (sink)
 A source is the part of a plant where sucrose and amino acids are being produced by photosynthesis. For
example: Leaves
 A sink is the part of a plant where sucrose and amino acids are translocated. For example: flowers, roots,
tubers etc.

Uses of sucrose:
 In the Roots: sucrose is changed to starch and may be stored
 In the Flowers: sucrose is converted to sweet tasting nectar (fructose) and is used to attract animals (yum!)
 Developing parts of plant: sucrose and amino acids are translocated to growing parts of the plant for
development.
Translocation during different seasons
 Many plants have a time of year when they become dormant.
 During this stage, they wait out harsh conditions in a state of reduced metabolic
 Dormant plants do not photosynthesise, but survive on their stored starch, oils and other materials.
 When the seasons change, they begin to grow again.
 Now the stored materials are converted to sucrose and transported to the growing region.
For example, potato plants are not able to survive the cold frost of winter. Let’s see what happens!

 Leaves photosynthesise and send sucrose down into underground stems.

Summer  Here, swellings called tubers develop.
 The cells in the root tubers change the sucrose to starch and store it.

Winter  The leaves and stems wear off (die).

 Nothing is left of the potato plant above ground – just the stem tubers beneath the soil.

 They begin to grow new shoots and leaves.

 The starch in the tubers is changed back to the sucrose, and transported in the phloem to the
Spring growing stems and leaves.
 This will continue until the leaves and stems are above ground and start to photosynthesise.

1. So in summer, the leaves are sources and the growing stem tubers are sinks.
2. In spring, the stem tubers are sources and the growing leaves are sinks.
*9-The circulatory system
The main transport system of human is the circulatory system.
The circulatory system consists of:

 Blood vessels– a network of tubes

 The heart– a pump
 Valves– that ensures the flow of blood is in the right direction.
Functions of the circulatory system:

 To transport nutrients and oxygen to the cells

 To remove waste and carbon dioxide from the cells
 To provide for efficient gas exchange

Oxygenated and deoxygenated blood

The blood from the left side of the heart comes from the lungs
The blood capillaries surrounding the alveoli get oxygen that diffuses into the blood
This blood now contains oxygen and thus it is called as oxygenated blood
The oxygenated blood is transported all around the body

The oxygen in the blood is used up by body cells in metabolic reactions

Now, the blood that remains is called as deoxygenated blood

The deoxygenated blood is returned back to the right hand side of the heart, and is sent to the lungs
to get oxygenated once again.

Double circulatory system

The human circulatory system is a double circulatory system.
A double circulatory system is one where blood is transported through the heart twice in one
complete cycle.
Beginning at the lungs, blood flows into the left-hand side of the heart, and then out to the rest of the
body. It is brought back to the right-side of the heart, before going back to the lungs again.

The importance of a double circulatory system

The pressure applied to pump the blood all over the body is not lost; it is returned to the heart to
raise the pressure again.
In a double circulatory system, the oxygenated blood is transported at a faster rate through the
body’s organs.
Transporting blood at a faster rate is particularly important as tissues that are metabolically active
will require oxygen in abundance. A double circulatory system ensures that the oxygenated blood
reaches the tissues on priority.
 The Heart
Is made up of the cardiac muscle which contracts and relaxes throughout life
Is divided into 4 chambers:
Left Atrium Receives oxygenated blood from the lungs and passes it to the left ventricle

Left Ventricle Receives oxygenated blood from the Left Atrium and pumps it all over the body

Right Atrium Receives deoxygenated blood from the body and passes it to the Right Ventricle

Right Receives deoxygenated blood from the right atrium and pumps it over to the lungs to
Ventricle get oxygenated

Has 4 associated blood vessels:

Pulmonary vein Brings oxygenated blood to the left atrium from the lungs

Aorta Receives oxygenated blood from the left ventricle and pumps it all over the body

Vena cava Brings deoxygenated blood to the right atrium from the body

Pulmonary Receives deoxygenated blood from the right ventricle and pumps it over to the lungs to
artery get oxygenated

Important: the reason why the walls of the ventricles are thicker than those of the atria is due to the
fact that the atria just receive the blood; the actual task of pumping it out of the heart is done by
the ventricles.
Important: the reason why the left ventricle’s walls are thicker than those of the right ventricle is due
to the fact that the right ventricle pumps the blood to the lungs, which are in close proximity to the
heart. The left ventricle has the job of transporting the blood all over the body.

The Pacemaker: is a patch of muscle in the right atrium which controls the rate at which the heart
beats according to the needs of the body.
If you are exercising, then the body will need a lot of oxygen; you soon take up an oxygen debt which
causes a drop in the ph of blood (due to the production of lactic acid)
The brain senses the drop in pH and sends electrical impulses to the pacemaker to make the heart
beat faster.
Systole: the stage of a heart beat in which the muscles in the walls of the heart chambers contract
Diastole: the stage of a heart beat in which the muscles in the walls of the heart relax
Atrioventricular valves: are valves between the atria and ventricles in the heart that prevent the
blood from flowing from the ventricles, into the atria.
The valve on the left hand side of the heart is made of 2 parts and thus is called the bicuspid valve
The valve on the right hand side of the heart is made of 3 parts and thus is called the tricuspid valve

Coronary Arteries
The muscles of the heart are so thick that the nutrients and oxygen in the blood inside the heart
would not be able to diffuse to all the muscles quickly enough.

The heart muscles need a constant supply of oxygen and nutrients so that it can keep transporting
and pumping blood. The coronary arteries are responsible for it.
If a coronary artery gets blocked (e.g. by a blood clot), the cardiac muscles run short of oxygen and
they cannot respire to obtain energy to contract causing the heart to stops beating. This is called
a heart attack or cardiac arrest.
Causes of Coronary Heart Disease

Nicotine damages the circulatory system by narrowing and stiffening blood

Smoking vessels

Blood Cholesterol Diets rich in animal fats containing Low Density Lipids (LDL) cause CHD to
levels develop

Age As you grow older, the risk of developing CHD increases

Stress Unmanageable and long term stress leads to the development of CHD

Is caused due to heavy amounts of stress and again leads to the development of
High Blood pressure CHD

Gender CHD often develops in males than in females. (It may be due to sex-linked genes)

Preventing Coronary Heart Disease

Stop smoking

Keep the diet based on saturated fatty food in control

Have a diet based on fish and vegetable oils

Exercise Regularly
Take drugs such as ‘statin’ under the guidance of a physician

Treating Coronary Heart Disease

Help lower blood pressure

Statins
Lower the chances of a blood clot forming

Coronary Bypass A blocked or severely damaged coronary artery is replaced by another length of
Operation blood vessel taken from other parts of the body

A balloon is inserted in the damaged coronary artery and is inflated using water

This pushes the artery open.

Angioplasty

In the rarest and the worst cases of CHD, a heart transplant operation may be
undertaken.

Heart Transplant The patient will have to take immunosuppressants for life if the operation is
successful and if the tissue types don’t match!
Operation

Blood Vessels
Blood vessels are an important part of human transport system.

There are 3 major types of blood vessels in the human transport system:

Blood
vessel: Function Structure of wall Width of lumen

Carry Thick and strong Relatively narrow

blood away from
Arteries the heart Contains muscles and elastic Varies with heart beat due
tissues to recoiling and stretching capacity

Supply all cells with

Extremely narrow
their requirements
Wide enough for red blood cells to
Take away Very thin
pass through
Capillaries their waste
products Only one cell thick
 Quite thin
Carry
blood towards the Contain lesser amounts Wide
Veins heart of muscles and elastic tissues
than arteries Contains valves

Blood
Vessel How structure fits function

Strength and elasticity needed to withstand the pulsing of the blood as it is pumped through
Arteries the heart

No need for strong walls as most of the blood pressure has been lost.
Capillaries
Thin walls and narrow lumen bring blood into close contact with body tissues

No need for strong walls as most of the blood pressure has been lost.

Veins Wide lumen offers less resistance to blood flow

Valves prevent backflow

Components of blood plasma

Component Source Destination

Water Absorbed from small intestine and colon All cells

Fibrinogen Liver Remains in the blood

Antibodies Lymphocytes Remains in the blood

To the liver- for breakdown

To adipose tissue- for storage

Absorbed in the ileum

Derived from fat reserves in the body To respiring cells- as an energy source
Lipids

Carbohydrates Absorbed in the ileum

To all cells for energy release by
 Derived by breakdown of glycogen in the liver respiration

Urea Liver- by deamination Kidneys- for excretion

Mineral ions Absorbed in the ileum and colon To all cells

Hormones Endocrine glands Target hormones

Carbon Released by all cells as a waste product of

dioxide respiration To the lungs for excretion

Oxygen Lungs Whole body

Heat Abdomen and muscles Whole body

Blood cells – structure and functions

There are 3 types of blood cells:

Blood Cell Function

Red blood cells (RBC) Transport oxygen

White blood cells (WBC) Protect the body against disease

Platelets help the blood to clot

1. Red blood cells

 Made in the bone marrow
 Transport oxygen from lungs to all respiring tissues.
 Transport CO2 from all respiring cells to lungs.
 Contain a red pigment- Haemoglobin which contains iron
 Haemoglobin carries oxygen by combining it with iron, to cells that are actively respiring
 Are biconcave disc shaped (this increases the surface area and thus diffusion of oxygen and carbon
dioxide)
 Have no nucleus (hence live up to only 4 months)
 Broken down in the liver, spleen and bone marrow
 Some of the iron from the Haemoglobin is stored, and used for making new haemoglobin; some of it is
turned into bile pigment and excreted.
2. White blood cells
 White blood cells are made in the bone marrow and in the lymph nodes.
 Have a nucleus, often large and lobed.
 Can move around and squeeze out through the walls of blood capillaries.
 They have the function of fighting pathogens
White blood cells are of two major types:

Phagocytes:
 Have lobed nuclei and granular cytoplasm.
 Can move out of capillaries, to the site of an infection.
 Remove any microorganisms that invade the body and might cause infection by engulfing and digesting
Lymphocytes:
 produce antibodies to fight antigens
 Have large nuclei
There are two different types of lymphocytes:

 B-lymphocytes: secrete antibodies in response to contact with their particular antigen, which may be an
invading pathogen or a foreign tissue that has been transplanted.
 T-lymphocytes attack foreign or infected cells and kill them by binding onto their surfaces.

3. Platelets
 Small fragments of cells, with no nucleus.
 Made in the bone marrow.
 Involved in blood clotting: form blood clot, which stop blood loss and the entrance of pathogens.
Substances transported in the blood
Substance Source Destination

Oxygen Lungs Whole body

Carbon dioxide Whole body Lungs

Urea Liver Kidneys

Hormones Endocrine glands Target organs

Digested food Intestine Whole body

Heat Muscles and abdomen Whole body

Blood clotting
Till now, we have learnt that platelets help in the clotting of blood. Let’s see how this happens now!
There is cut in the skin

Blood vessels are damaged

Damaged blood vessels and tissues begin secreting chemicals

This activates blood clotting factors

The soluble plasma protein- fibrinogen changes to an insoluble substance called fibrin.
Fibrin causes fibres to be made in the damaged blood vessel and tissue
Red blood cells and platelets get trapped in the fibres
This forms a blood clot!

Importance of blood clotting

 Prevent excessive blood loss
 Maintain the blood pressure.
 Prevent the entry of pathogens
 Help in healing
Genetic disease where blood does not clot– Haemophilia

The lymphatic system and tissue fluid

Capillaries leak! Their cell walls don’t fit together properly and thus there are small gaps between
them.

Substances that leak out from the capillaries:

 White Blood Cells (WBCs)- can easily change their shape unlike red blood cells.
 Blood Plasma
So the substances that leak out from the blood capillaries are known as tissue fluid.
The tissue fluid simply surrounds the body cells.

Importance and functions of tissue fluid

 Supply cells with all their requirements (such as oxygen and nutrients that diffuse)
 Take away the waste products of metabolism out from the cells
 Immediate environment of every cell in the human body

Lymph
 The tissue fluid surrounding the body cells ought to be eventually returned to the blood.
 To make sure this happens, there are another set of capillaries in our body called as lymphatic capillaries.
 The tissue fluid slowly drains into the lymphatic capillaries.
 It is now called lymph
 The lymphatic capillaries eventually join up to form larger lymphatic vessels which empty themselves
into the subclavian veins.
 Here the lymph enters the blood.

Features of the Lymphatic system and lymph

nodes
 Have valves to ensure the flow of lymph is in one direction
 Run close to the muscles so that muscular contractions squeeze the lymph and for it to move along the
vessels.
 Have structures called lymph nodes where new white blood cells are produced
 The white blood cells help in destroying most toxins in the lymph before entering the blood from
the subclavian vein.
*10-Excretion
Excretion is one of the seven life processess and is the process which means the removal of waste
and toxic products form the body.

 A waste product of metabolic reactions is called as an excretory product.

 For example, Carbon dioxide is an excretory product of respiration.

Egestion
 All food we eat cannot be digested
 For example, cellulose in vegetables (fibre) cannot be digested in the human digestive system as we don’t
have an enzyme called cellulase to digest it.
 So the cellulose simple passes through our digestive system, unchanged.
 Excreting undigested food is known as Egestion.

Urea
 Nitrogenous waste is formed from excess proteins and amino acids.
 Animals are not able to store this waste
 Excess amounts of the waste is broken down to form a nitrogen containing excretory product
 In mammals, this nitrogenous waste is known as urea.

How urea is made

1. Protein in food is taken in to the alimentary canal.
2. Protein molecules are broken down to amino acids during digestion.
3. The amino acids are absorbed into the blood and taken to the liver by the hepatic portal vein.
4. Amino acids that are needed are released into circulation.
5. Amino acids that are not needed are deaminated into carbohydrates and ammonia.
6. The carbohydrate is converted into a polysaccharide called glycogen.
7. The ammonia is converted into urea
8. Urea is excreted by diluting it in water. The solution is now known as urine.

Parts of the human excretory system

 Kidney (nephrons)
 Lungs (alveoli)
 Skin (sweat glands)
 Liver
Types of metabolic wastes
Waste Produced from

Carbon dioxide Aerobic respiration

Water Aerobic respiration

Salts Metabolic activities

Nitrogenous wastes Breakdown of excess amino acids

Types of nitrogenous wastes

Waste Produced from Toxicity

Ammonia Breakdown of excess amino acids Highly toxic

Urea Breakdown of excess amino acids Moderately toxic

Uric acid crystals Breakdown of DNA and RNA Minimally toxic

Creatinine Waste product of muscle action Minimally toxic

Structure of the excretory system:

Kidneys
Functions of the kidney:
 Excrete toxins and nitrogenous wastes
 Regulate chemical levels in the blood
 Maintain water balance
 Help regulate blood pressure
 Filter blood to remove cellular waste

Blood and urine flow:

1. Blood enters the kidney via renal arteries
2. Blood leaves the kidney via renal veins
3. Wastes removed from blood leave kidney by the ureter

Other organs:
1. Ureter: Long narrow tubes with expanded upper end (renal pelvis). Its function is to carry the urine
produced from the kidneys, to the urinary bladder.
2. Urinary bladder: Elastic muscular organ, capable of great expansion. Its function is to store the urine until
it is released.
3. Urethra: Its function is to carry the urine from the bladder to the outside of the body.

Kidney and its parts:

Nephrons
1. The filtering units of kidneys are nephrons.
2. There are approximately 1 million nephrons in each kidney.
3. The nephrons are located within the cortex and medulla of each kidney.
4. The tubes of the nephrons are surrounded by cells and a network of blood vessels spread throughout the
tissue.

The Glomerulus
1. The Glomerulus is a mass of thin walled capillaries.
2. The Bowman’s capsule is a double walled cup shaped structure.
3. The proximal tribule leads from the bowman’s capsule to the loop of Henle
4. The loop of Henle is a long loop which extends into the medulla
5. The distal tribule connects the loop of Henle to the connecting duct

Blood Filtering
1. Blood enters the Bowman’s capsule through a tiny artery (the renal artery).
2. The artery branches to form a Glomerulus.
3. Blood pressure in the artery forces some blood plasma and some small particles into the surrounding
capsule (this is called the nephric filtrate).
4. Large particles such as blood cells and proteins remain in the capillary.
5. The nephric filtrate is pushed out of the capsule and into the proximal tribule
6. This is where reabsorption begins
7. Only materials needed by the body are returned to the blood stream (for example, 99% of the water, all of
the glucose and amino acids, and most of the salts are reabsorbed)
8. The filtrate reaches the end of the proximal tribule
9. Glucose and amino acids have been removed from the filtrate.
10. The filtrate then moves to the loop of henle where water is again reabsorbed through osmosis.

Kidney Dialysis
When a person’s kidney stops functioning, a lot of excretory products start to build up in the person’s
blood. To avoid this, the person can be treated using a kidney transplant operation, but the usual
treatment is using kidney dialysis.

The Process:
1. The person’s blood flows through the machine and back into his/her body.
2. Inside the machine, the person’s blood is separated with a partially permeable membrane (like visking
tubing) containing dialysis fluid.
3. The fluid contains all the necessary components of blood and no urea in it
4. This causes the urea in the person’s blood to diffuse into the partially permeable cell membrane, down their
concentration gradients.
5. This process usually continues till several hours.

Kidney Transplants
Most people under treatment using a dialysis machine would rather prefer treatment using kidney
transplants as, the patient would suffer much less pain and it would enhance their quality of life.

Moreover, surgeons are even quite efficient at successfully conducting kidney transplants.

In a kidney transplant operation, the person donating the kidney is called the donor and the person
receiving the kidney is the recipient.
However, the problem arises when the patient’s immune system recognizes the donor’s organ as
foreign as the DNA in the donor’s organ and the patient’s cells do not match.

This leads to the patient’s WBCs attacking the ‘foreign’ organ and destroying it. This is known as
immune rejection.

Hence it is crucial that the donor’s DNA is a close match with the patient’s cells.

To avoid immune rejection, the patient is prescribed immuno-suppressants in order to stop the
immune system do its usual task. This makes the patient vulnerable to all kinds of diseases and the
worst part is that the immuno-suppressant needs to be taken for life!
*11-Coordination in Animals
Coordination is an important life process for living beings

 Changes in an organism’s environment are called stimuli.

 Stimuli are sensed by specialized cells called receptors (usually our sense organs).
 The organism responds to the stimulus, using effectors (usually muscles and glands).
 There are 2 methods by which information is sent from receptors to effectors:
1. Nerves- the fastest method
2. Hormones- a slower but important method

The nervous system

All mammals have a:

1. CNS ( Central Nervous System)

2. PNS (Peripheral Nervous System)
The CNS is made up of the brain and the spinal cord.

The PNS is made up of nerves and receptors.

Myelin:
Myelin is a layer of protein and fat that is used as insulation for nerves so that the nerve impulses
don’t scatter and increase the time needed to respond to a stimuli.

Types of neurons
 Sensory
 Relay
 Motor

Reflex action/arc
A fast, automatic, involuntary response to a stimulus is known as a reflex action.

Stimulus is detected by receptor --- Sensory neuron --- Spinal cord (relay neuron)

--- Motor neurone

Effector muscle
How does a reflex arc work?
1. Stimulus is detected by receptor
2. An impulse is picked up by a sensory neuron
3. The impulse travels through the axon of the sensory neuron towards the spinal cord
4. In the spinal cord, the impulse is relayed to several other neurons by the relay neuron.
5. The relay neuron passes the nerve impulses to the brain
6. Simultaneously, the impulses are also passed to an effector
7. The effector takes suitable action.

Synapses
A synapse is a junction between two nerve cells, consisting of a minute gap across which impulses
pass by diffusion of a neurotransmitter.

They are also called as one way valves.

How synapses work:

1. There is a small gap between each pair of neurons.
2. These are called synaptic clefts.
3. The vesicles of an axon contain a chemical called neurotransmitter.
4. When an impulse arrives along the axon, it causes these vesicles to move towards the cell membrane and
empty their contents into the synaptic cleft.
5. The neurotransmitter then quickly diffuses across the synaptic cleft.
6. They attach to receptor molecules in the cell membrane of the next neuron.
7. This can happen because the shape of the neurotransmitter molecules is similar to the shape of receptor
molecules (just like an enzyme and its substrate!)
8. The binding of a neurotransmitter with the receptor triggers a nerve impulse in that neuron.
9. The impulse sweeps across the neuron until it reaches the next neuron.
As there is only one neurotransmitter at the end of each synapse, impulses can only pass in one
direction. That’s the reason synapses are called one way valves (like diodes!)

Receptors
In animals, the receptors are often a part of sense organs. For example, the eye is a sense organ
and the cone and rod cells in it are the receptors that are sensitive to light.

Here is a simple list of the 5 sense organs:

1. Eye (Vision)
2. Ear (Hearing, balance)
3. Nose (Smell)
4. Tongue (taste)
5. Skin (touch, temperature, pain)
The eye
The structure of the eye:

1. Retina:
 the part where the receptors are present, which are sensitive to light.
 Consists of the fovea and the blind spot
2. Fovea: the spot where receptor sells are tightly packed
3. Blind spot: the point at which the optic nerve leaves the eve
4. Orbit: a bony socket in the skull that holds the eye.
5. Conjuctiva:
 a thin, transparent membrane, that helps protect the parts behind it.
 Is kept moist by the tear gland
 Contains the enzyme lysozyme that kills bacteria
6. Sclera: A tough coating in the orbit, to protect the parts within.
7. Choroid:
 A part that is rich in blood vessels, situated behind the retina.
 It helps in the absorption of excess light
8. Cone cells:
 Receptor cells that can distinguish between different colours of light.
 Cells that help us to see in bright light and present a sharp image.
 There are three types of cone cells- Red, Green and Blue.
9. Rod cells: Receptor cells that help us to see in dim light and don’t produce a sharp image

Pupil reflex

In bright light:
Circular muscles of the iris contract, Pupil gets smaller

In dim light:
Radial muscles contract, Pupil gets larger

Focusing light:
1. Cornea bends the light (refracts)
2. The lens makes fine adjustments
3. Semi solid vitreous humour is transparent, and nourishes the eye.

Focusing light on distant objects:

 Ciliary muscle relaxes
 Suspensory ligaments are pulled tight
 Lens becomes thin

Focusing light on near-by objects:

 Ciliary muscle contracts
 Suspensory ligaments are slackened (relax)
 Lens is allowed to buldge

Coordination in Plants
 Unlike animals, plants respond to stimuli in a slower manner.
 Plants respond to stimuli in 2 ways:
 Changing their rate of growth
 Changing their direction of growth
 If a plant grows towards a stimulus, it is known as a positive tropism
 If a plant grows away from a stimulus, it is known as a negative tropism
 A tropism is a growth response by a plant.
 Two important stimuli for plant growth are:
 Light
 Gravity
 For example, shoots show positive tropism towards light, whereas roots show negative tropism towards
it.
 For example, shoots show negative tropism towards gravity, whereas roots show positive
tropism towards it.

Importance of tropisms
 It is extremely important that plant parts respond in a correct manner to tropisms.
 For example, it is necessary that shoots respond to phototropism so that they can photosynthesize as they
grow leaves.
 Similarly, for a flower, it is crucial that it only blooms in response to phototropism so that it can attract
insects or the wind to pollinate them.
 Moreover, in roots, it is important that they respond to gravitropism by growing into the soil to absorb
water and anchor the plant.
Key definition:

Gravitropism: A response in which a plant grows towards or away from gravity

Phototropism: A response in which in which a plant grows towards or away from the direction of
light.
*12-The Human Endocrine System
In the previous chapter (Coordination), we have seen one way in which information is sent from a receptor to
an effector (through nerves!). We will be learning the other way – hormones.
In this section, we will be studying about the next way of transmitting information- through hormones.
 Chemicals that transmit information from one part of the body to other are called as hormones
 Hormones are made in endocrine glands
 Endocrine glands release hormones directly into the blood and so they are called as ductless glands (as
they aren’t carried in ducts)
 Hormones only have effect on target organs (specific organs)

Here is a list of some endocrine glands:

 Pituitary gland
 Thyroid gland
 Adrenal gland
 Testes (in males)
 Ovaries (in females)
 Pancreas

Adrenaline
 In our body, there are two adrenal glands, one above each kidney.
 They secrete a hormone called adrenaline.
 Adrenaline is secreted when you are frightened, exited, or keyed up (anxious)
 Importance of adrenaline: Needed for fight and flight response.
What adrenaline does How it helps the body

Makes your heart beat faster (supplying more

oxygen to brain and muscles) Gives more energy for fighting or running away

More oxygen enters the lungs; improved blood

Increases your breathing rate circulation

Gives you butterflies in your stomach (by It ensures that maximum volume of blood is
contracting blood vessels in the skin and digestive transported to your muscles and brain, and you can
system) think faster

Causes the pupils in the eye to widen Helps you to see danger more clearly

Causes the liver to release glucose into the blood It again gives the muscles extra energy to fight or run

To summarise, adrenaline prepares body for vigorous action

Important endocrine glands and their functions:
Gland Hormone secreted Function of hormone

Adrenal Adrenaline E prepares body for vigorous action

Pancreas Insulin E Reduces the concentration of blood glucose

Testis Testosterone E Causes the development of male secondary sexual characteristics

E Causes the development of female secondary sexual characteristics

Ovary Oestrogen
E Helps in the control of the menstrual cycle

The difference between the nervous and endocrine

system:
Nervous system Endocrine system

Made up of neurones Made up of secretory cells (glands)

Information transmitted in form of electrical

impulses Information transmitted in form of hormones

Hormones transmitted along blood plasma (in dissolved

Impulse transmitted along nerve fibres form)

Impulses travel very quickly Hormones travel more slowly

Effect of impulse only lasts for a shorter period Effect of hormone usually lasts for longer duration

Plant hormones
Plants respond to light and gravity with the help of plant hormones.

Plants need to use hormones as they don’t have sense organs.

One kind of plant organ is Auxin

Auxin is being made all the time on the tip of the shoot.

The Auxin then spreads to the rest of the plant by diffusing across cells.

Auxin is responsible for the rate of growth for plants; the more Auxin present, the greater will its
growth be.

How plants respond to phototropism?

Normally, Auxin is equally distributed at the tip of the shoot; however, when light is shined at the
shoot’s tip in one direction, the Auxin gets concentrated at the shady part of the shoot; hence
the growth at the shady part increases and the plant begins to grow in the direction of light.

How plants respond to gravitropism?

If a potted Coleus plant is placed horizontally in the absence of light, Auxin will collect at the lower
part of the shoot and increase the rate of growth in that specific part. This will cause the plant’s shoot
to change direction and give a negative response to gravity.
Similarly, a bean seedling’s root will always show positive response to gravitropism by growing
downwards, irrespective of the position in which it is planted.

Ethiolation
Seedlings grown in the dark tend to be pale and weak. But the reason why they are tall and thin is
Auxin. Auxin gets evenly distributed at the tip of the shoot and grows steadily using the energy from
the food stored in cotyledons of the seed. But once that gets exhausted, it gets ethiolated and will
soon die if it is not given light to photosynthesise.

Weedkillers
Weedkillers are chemicals that are needed to kill unwanted plants that compete with other plants for
minerals, light and water.

Weedkillers are usually selective and kill only specific plants.

They contain a synthetic form of Auxin called 2,4D which causes rapid growth in weeds, so that they
grow faster and die quickly.

This leaves ample space for the other plants, leading to an increase in their growth.
*13-Homeostasis
The term homeostasis is derived from two Greek words:

Words Homeo stasis

Meaning Unchanging Standing

Homeostasis is defined as the maintenance of constant internal environment

It is an organism’s internal environment that needs to stay the same in order to continue metabolic
reactions at the same rate.

Importance of Homeostasis
 Helps your cells work at optimum rate
 Ensures that enzymes work most efficiently
 Ensures that the cells aren’t damaged by absorbing or losing too much water by osmosis
 Ensures that there is enough fuel in reserve for respiration

Controlling body temperature

 Warm blooded animals (Mammals and Birds) keep their body temperature constant, despite of the
fluctuations in environmental conditions.
 They are Homoeothermic or endothermic.
 Endothermic means that the animals get their heat energy within themselves.
 On the other hand, a poikilotherm is an organism whose internal temperature varies rapidly.
Poikilothermic animals include:

1. Fish
2. Amphibians
3. Reptiles
4. Large number of invertebrates
The skin

 Epidermis is on the outside. This has a layer which is always forming new cells through cell division.
 The new cells gradually move towards the surface, become flat, and develop keratin.
 The outermost layer of epidermis is made up of flat dead cells, which are continuously worn away by
friction and are called the cornified layer.
 Epidermis also contains a pigment called melanin, which gives a black colour to the skin and absorbs
harmful UV radiation
 The epidermis folds inwards, forming a hair follicle, surrounded by sebaceous glands which secrete an oily
liquid called sebum.
 Sebum keeps the skin soft and supple.
 The dermis contains sweat glands.
 Sweat travels through the sweat duct and evaporates to regulate the internal body temperature.
 Blood vessels and nerve endings make us aware of pain, pleasure and temperature.
 A layer of fat known as the adipose tissue acts as insulation.
When body temperature drops below 37oC
 Muscles work- heat is generated and distributed all over the body by quick action of muscles
 Metabolism may increase
 Hair stands up and in human erector muscles leads to Goosebumps.
 In hairy animals, thick layer of hair acts as an insulator
When body temperature shoots above 37oC
 Hair lies flat
 erector muscles relax
 Sweat gland secretes sweat (so that sweat evaporates and cools the body down)

Vasodilation
 If the body temperature rises:
 The arteriole supplying sweat gland dilates, bringing more blood, so the gland can make more sweat.
 Arterioles supplying the capillaries dilate, bringing more blood to the capillaries.
 More blood is brought to the surface capillaries where, it can lose heat.

Vasoconstriction
 If the body temperature falls:
 Arterioles and capillaries in the skin constrict, so not much blood flows through them

Negative feedback
A mechanism used in homeostasis, in which a change in a parameter brings about actions that push
it back towards normal.

For example, when the body temperature rises, information about the temperature change is sent to
the hypothalamus which in turn sends signals to the effectors to decrease this change.

It is termed ‘feedback’ as the information about the effects of cooling the body are fed ‘back’ to it and
‘negative’ as it is compelled to ‘stop’ doing these changes in order to stop overcooling.

Control of blood glucose concentration

1. Cells need a steady supply of glucose to allow them to respire. Without this they cannot release energy.
2. Too much glucose in the blood is not good either, as it can cause water to move out of the cell and into the
blood by osmosis.
3. The control of blood glucose concentration is carried out by the pancreas and liver.
4. Islets of Langerhans (Pancreatic cells) make two hormones called insulin and glucagon.
5. These hormones help the liver to control the amount of glucose in the blood.
6. Insulin has the effect of lowering blood sugar
7. Glucagon has the effect of increasing the blood sugar
8. Food with lot of glucose increases the concentration in the blood; insulin is released into the blood.
9. When insulin reaches the liver, it causes the liver to absorb glucose from the blood.
10. Some is used for respiration and some is stored as glycogen
11. If the blood sugar concentration falls too low, the pancreas secrete glucagon
12. Liver cells break down glycogen to glucose and release it into the

Diabetes
When the blood glucose concentration of the body fails to function, the person with such a condition
is said to have diabetes.
Type 1 diabetes is a condition caused when the WBCs destroy our own pancreatic cells that
produce insulin.

This condition leads to a state where the blood glucose concentration does not fall.

If the person has had a high glucose diet, he may suffer from hyperglycaemia.

The symptoms of hyperglycaemia:

1. The person feels unwell
2. The person has a dry mouth
3. Blurred Vision
4. The person feels very thirsty
5. Heart rate increases
6. Breathing rate increases
If the person has a low glucose diet, the blood glucose concentration falls. As not much glycogen
has been built up in the liver due to the absence of insulin, the person suffers from hypoglycaemia.
The cells do not have enough glucose to release through respiration in this condition.

The symptoms of hypoglycaemia:

1. The person feels very tired
2. The person shows confusion
3. The person shows irrational behaviour
4. The person becomes unconscious

Checking Blood Glucose concentration:

Blood glucose concentration can be monitored using:

1. A simple sensor: which needs to be dipped in the person’s blood

2. A urine dipstick: Urine must not contain any glucose in a normal person’s urine. But in a diabetic’s urine,
the kidneys fail to absorb all the glucose and thus glucose is present in it.

Treating Type 1 diabetes

People with type 1 diabetes often need to inject insulin in order to control their blood sugar
concentration
*14-Drugs
A drug is a chemical substance used in treatment, cure, prevention, or diagnosis of diseases, or
otherwise used to enhance physical or mental well being.

Key Definition: Any substance taken into the body that modifies or affects chemical reactions in the
body is called as a drug

Antibiotics
Antibiotics like penicillin are chemicals that kill bacteria by destroying their cell walls. They do not
hurt body cells when doing so.

They are very useful for killing bacteria unless they are used intensively (as intensive use exerts a
selection pressure upon them, causing the bacteria to get resistant to them)

However, they are useless against viruses as viruses don’t have cell walls! So next time you have a
cold or ‘flu they won’t be any use.

Heroin
 Produced from opium
 Opium contains the chemicals morphine and codeine used as medicine for pain relief
 Heroin is addictive and a powerful depressant.
Addictive means that it makes the person dependent on it
Depressant means that it slows down the functions of the brain and the hypothalamus, reduces pain,
and slows down breathing rate.

Symptoms of Heroin Addiction:

 Person loses the ability of being a part of normal society
 Avoiding eye contact
 Avoiding distant field of vision
 Increased time spent in sleeping
 Sudden worsening of performance at school, or work including expulsion or loss of jobs
 Decreasing attention to physical appearance and hygiene
 Loss of motivation
 Apathy towards future goals
 Not able to help and support their family
 Lack of interest in hobbies and favourite activities
 Repeatedly borrowing money from loved ones, or unexplained absence of valuables

Routes of administration
1. Oral
2. Injection – Extremely risky, as it can give rise to HIV transmittion through non-sterile needles
3. Sniffing
The feeling of euphoria
Brain has many neurotransmitters that transfer electrical signals across synapses, from one neurone
to other.
The second neurone that receives the electrical signal has receptors that fit accurately with the
neurotransmitter molecules.
One group of such neurotransmitter molecules is endorphins.
Endorphins help reduce the sensation of pain and it affects our mood, including hunger and thirst.
When a person takes a dose of heroin, it gets broken down to morphine in the brain.
Morphine molecules fit precisely into some endorphin receptors, inducing the feeling of euphoria

Drawbacks of taking heroin:

 Addiction
 Lowers natural endorphin production
 Increases the risk of HIV transmittion
 Increases the demand for the drug to get the same euphoric feeling
 Forces the person to take more doses with unpleasant exposure towards withdrawal symptoms

Alcohol and Alcoholism

Alcohol is a very commonly used drug as people enjoy it’s effect on the body. It helps them get rid of
their woes and worries and boosts their ability to interact socially with people.

However, it has a many drawbacks as well:

1. Alcohol lengthens reaction time: which means that it acts like a depressant and slows down the metabolic
reactions in the body. This can be very risky during situations when people drink and drive.
2. Alcohol can boost aggression in some people: Intake of alcohol can cause a person to succumb to
committing crimes and being violent with family members.
3. Enormous volumes of alcohol consumption can kill: Alcohol is like a poison; it can be life threatening if
a person consumes alcohol in huge volumes, resulting in ecstasy, excitement, confusion, stupor, coma and
even death!

Alcoholism:
Alcoholism is a disease where a person gets addicted to alcohol. Alcoholics drink huge volumes of
alcohol regularly.

Factors leading to alcoholism:

1. Genes
2. Personality
3. Amount of stress

Effects of alcoholism:
 Liver cirrhosis: Alcohol is poisonous to cells and can damage them. One such example is the liver which
has the task of breaking it down. In liver cirrhosis, fibres grow inside the liver. This can be fatal!
 Brain damage: Alcohol consumption can also cause loss of memory and a lot of confusion.
1. Alcohol in the body fluids draws water out of the cells through osmosis
 2. When this happens with the brain cells, they get irreversibly damaged.
3. This damage gets worse when alcohol prohibits the secretion of a hormone that is responsible in the re-
absorption of water.
4. This causes too much of urine to be produced in a dilute form, resulting in low water levels in the
blood.

Anabolic Steroids
Some hormones belong to group called steroids.

Examples of steroids are:

 Testosterone
 Oestrogen
 Progesterone
There are some steroid hormones that stimulate metabolic reactions in the body by the synthesis of
body cells into larger molecules.

Such types of hormones are called anabolic steroids.

Let us consider the example of testosterone, which is a male reproductive hormone that is
responsible for the synthesis of proteins from amino acid molecules in the muscles, so that the
muscles become larger and stronger.

Anabolic steroids have been used in sport by athletes to increase their muscle size and strength.
They help athletes to train harder for longer duration.

However, the usage of anabolic steroids is banned in sport as it can give any athlete unfair
advantage.

Effects of anabolic steroids on health:

 Decreases immune efficiency
 Can causes damage to the liver

Tobacco smoking
The main components of tobacco are:

1. Carbon monoxide
2. Nicotine
3. Tar
4. Carbon particulates

Effects of Carbon monoxide:

 Carbon monoxide is also known as the silent killer as it is a poisonous gas.
 It reduces oxygen carrying capacity of the blood.
 It gets into the alveoli of our lungs and diffuses into the red blood cells.
 In the RBC, it interferes with the haemoglobin and slowly starts to decrease the volume of oxygen each cell
carries.
 This is why smokers experience breathlessness.

Effects of Nicotine
 Nicotine is addictive
 It is also a stimulant (a substance that makes the person feel more alert)
 Nicotine damages the circulatory system
 It makes the smoker’s blood vessels to get narrower
 This can cause an increase in blood pressure
 And finally, cause hypertension
 Nicotine is the substance behind Coronary Heart Disease.

Effects of Tar
 Tar contains many different chemicals such as carcinogens
 Carcinogens are substances that cause cancer
 These substances cause unusual behaviour in the cells inside respiratory passages.
 This can lead to the formation of a tumour.
 If the tumour is malignant, then it can cause cancer by breaking away from the cell and dividing
uncontrollably.
 This causes lung cancer.
 Along with lung cancer, there are many other components in tar that can cause different types of cancers to
the smoker.

Effects of carbon particulates

 Carbon particulates are tiny smoke particles that get into the smoker’s lungs.
 Soon they travel through respiratory passages and reach the alveoli
 The alveolar walls are extremely delicate and when these smoke particles get stuck in them, WBCs try to
eradicate them by secreting chemicals.
 While the chemicals remove the smoke particles, they also damage the delicate alveolar walls.
 This leads to Chronic Obstructive Pulmonary Disease (COPD)
 It causes the surface area of the lungs to decrease and thus decreases the efficiency of obtaining oxygen.
 The person is said to have emphysema.
 A person with emphysema is forced to be less active to such an extent that they may not have the energy to
even walk.

Other effects of smoking

When the chemicals present in cigarette smoke enter the circulatory system, they:

1. Decrease the number of cilia.

2. Decrease the efficiency of the remaining cilia.
3. Increase the production of mucus in goblet cells.
4. Change the direction in which the mucus flows.
5. Encourage the growth of bacteria in the mucus.
6. Cause mucus to get trapped inside lungs.
7. Decrease the efficiency of gas exchange.
8. Decrease the rate of diffusion of oxygen and carbon dioxide.
9. Cause long term infections in the lungs and bronchi.
10. Cause chronic bronchitis.

Smoking and Coronary Heart Disease

 Smoking can cause coronary heart disease by developing a high blood pressure.
 These activities are done by a component in cigarette called nicotine.
 Nicotine damages the circulatory system.
 It also makes blood vessels narrower.
 Moreover, nicotine decreases the elasticity of arteries, disabling them to stretch and recoil much.
 Smoking also increases the probability of a blood clot being formed in the coronary artery.
*15-Reproduction in Plants
Asexual Reproduction
A process resulting in the production of genetically identical offspring from one parent

Sexual Reproduction
A process involving the fusion of the nuclei of two gametes to form a zygote and the production of
offspring that are genetically different from its parents.

The table below shows the difference between asexual and sexual reproduction:

Asexual Reproduction Sexual Reproduction

Involves one parent Involves two parents

Involves mitosis Involves meiosis

Doesn’t involve fusion of gametes involves fusion of gametes

Genetically identical organisms produced Genetically different organisms produced

Sexual Reproduction in flowering plants

In plants, sexual reproduction leads to the production of seeds that may be stored inside its fruit.

Sexual reproduction in flowering plants usually takes place in their flowers. The function of a flower
is to make gametes. Usually, plants are a hermaphrodite, which means that they can produce both-
male and female gametes.

The Structure of a Flower

Parts of the flower Function

Sepal Protect the flower

Petal Attract insects through bright colours

Nectary Contains nectar that insects feed on

Filament Anchors the anther

Anther Contains the male gamete in pollen grains

Stigma Catch pollen

Style Support stigma

Ovary Contains the ovules

Ovule Contains the female gamete

Pollination
Pollination is the transfer of pollen grains, from the male part of the plant (anther of stamen) to the
female part of the plant (stigma)

Methods of pollination
 Insect pollination
 Wind pollination
Insect pollination: involves the medium of transfer of pollen as the insect.
1. An insect such as a bee visits the flower
2. It follows the guidelines towards the nectary
3. And feeds on the nectar.
4. Meanwhile, some pollen gets brushed on its body and remains there.
5. When the insect visits another flower of the same plant or species, it is likely that some pollen sticks onto
the carpel.
Wind pollination: involves the medium of transfer of pollen as the wind.
1. The anther produces large amounts of pollen grains
2. The wind may blow some of these pollen onto the carpel of another flower of the same species.

Types of pollination
 Self pollination
 Cross pollination
Self Pollination
The transfer of pollen grains from the anther of a flower to the stigma of the same flower, or different
flower of the same plant.

Cross Pollination
The transfer of pollen grains from the anther of a flower to the stigma of another flower of the same
species
*16-*Humans undergo sexual reproduction where the sperm from the father fuses with the egg
cell from the mother. This results in an offspring being born…

Male reproductive system

Organ Function

Sperm The male reproductive gamete

Testes Produce sperm and testosterone

Scrotum A sac containing testes (outside body)

Sperm ducts Carry semen from testes to the urethra

Prostrate gland Produces semen; a liquid in which the sperm swim

Urethra Used to pass semen and urine at different times

Penis The male reproductive organ that is inserted into the vagina during sexual intercourse

Female reproductive system

Organ Function

Egg cell Female gamete

Ovaries Produce egg cells once in 4 months

Fallopian tubes
(oviducts) Connect the ovaries to the uterus

Has thick muscular walls that are occupied by the developing baby during
Uterus pregnancy
 Narrow muscular opening at the end of the uterus which is guarded by muscles.

Leads to the vagina

Cervix

Vagina Receives semen from the erect penis during sexual intercourse.

A comparison between Male and

Female reproductive gametes
Sperm Egg cell

Size Smaller than egg cells Larger than sperms

Consists of:

 Head
Structure  Tail (flagellum) Consists of a deep layer of jelly
 Vesicle (containing enzymes)

Ability to move Can swim through the semen; extremely

(Mobility) mobile Can move, but less mobile than sperms

One in 4 weeks, from puberty till

Number(s) produced Millions at a single ejaculation menopause

Puberty
The point in a person’s life where sexual maturity is reached is defined as puberty or
adolescence. Puberty prepares a boy or a girl for adulthood and reproduction.
When a person reaches puberty:

 Sperm production begins in a boy

 Ovulation begins in a girl
Along with these, the secondary sexual characteristics develop as well during this time. These all are
caused by certain sex hormones.
Adolescent Males Adolescent Females
Sex
Hormone Testosterone Oestrogen

 Development of secondary sexual characteristics

Function  Development of secondary  Making the uterus
sexual characteristics lining thick and spongy during menstruation

Secondary Sexual Characteristics

Secondary sexual characteristics in males Secondary sexual characteristics in females

Voice breaks (Becomes harder) Breasts develop and grow bigger

Penis begins to grow Vagina becomes larger and wider

Facial hair, pubic hair, hair in armpits emerge Hairs emerge in armpits and in pubic areas

Body becomes more muscular and stronger The pelvis (hip) widens

Testes begin sperm production Menstruation begins

The Menstrual Cycle

When a girl reaches puberty (adolescence), she begins menstruating. As explained before, this is the
indication that the girl is physically ready for reproduction.
Menstruation is the loss of the uterus lining through the vagina.
The menstrual cycle in women is a continuous process in which the lining of the uterus thickens and
gets prepared for pregnancy; the woman does not get pregnant, the lining is shed at menstruation.
The cycle lasts about 28 days. During this time, the woman (or teenage girl) experience mood
fluctuations due to the hormonal changes in the body.

Hormones in the menstrual cycle

Hormone Site of secretion Function

Follicle Stimulating Hormone Pituitary Gland (in the Stimulate the developing follicle to keep
(FSH) brain) secreting oestrogen

Pituitary Gland (in the Stimulate the developing follicle to keep

Luteinising Hormone (LH) brain) secreting oestrogen
 Makes the uterus lining grow:

Oestrogen Developing Follicle  thick

 spongy

Keeps the uterus lining:

 Thick
Progesterone Corpus Luteum  Spongy
 Well supplied with blood

Common misconception: Oestrogen makes the uterus wall develop into a thick and spongy layer;
progesterone maintains the lining

The process of the menstrual cycle

Ovary Pituitary Gland (In the Brain)

 A follicle develops
 Secretes oestrogen  Secretes LH, FSH
 Oestrogen concentrations in the blood increase  Stimulates follicle to secrete
 Lining of the uterus grows thick and spongy oestrogen.

When the follicle is fully developed, there is a surge in the levels of:

 LH at a greater extent
 FSH at a smaller extent

Ovulation occurs and the follicle releases the egg cell

 Empty follicle stops secreting oestrogen  Levels of LH and FSH fall in the
 It is now called as a Corpus Luteum blood

If the egg cell is not

If the egg cell is fertilized fertilized

 Corpus Luteum doesn’t degenerate quickly Corpus Luteum gradually

 Secretes progesterone until the embryo sinks into uterus wall and disappears
a placenta develops
 Placenta secretes progesterone throughout pregnancy No more progesterone
 Keeps the uterus lining thick and spongy so that menstruation does not secreted
occur during pregnancy Uterus lining breaks down
A new follicle develops

Fertilisation and development

 After ovulation, the egg cell is released out of the follicle.
 It enters the fallopian tube (oviduct) and travels slowly through it.
 If the egg cell is not fertilized within 8-24 hours, it degenerates and the uterus wall lining breaks down.

Sexual Intercourse
 When the man is sexually excited, blood is pumped into his penis. This causes it to become erect.
 Simultaneously, mucus is produced from the woman’s vagina to lubricate the passage of the penis
 The erect penis is inserted into the woman’s vagina.
 At a point, thrusting movements are made which stimulate the tip of the penis with the clitoris.
 This results in a reflex action to take place:
 The walls of the tubes containing the sperm contract rhythmically and sperm is ejaculated into the vagina.
 This biological process is known as sexual intercourse and is the beginning of reproduction.

 Ejaculation deposits the semen at the neck of the vagina (cervix).

 The sperm cells begin the journey towards the egg cell. The journey of life…

Fertilisation
 Once the sperms reach the egg cell, they begin to use enzymes in their vesicles to dissolve their way into
the thick jelly layer.
 Only one sperm cell (in rare cases more than one) is able to do so.
 The head containing the nucleus enters the egg cell; its tail remains outside it.
 The egg cell and the sperm cell fuse together. This is known as fertilisation. A zygote (diploid cell) is
formed.

The formation of an embryo

 The zygote continues to move slowly towards the uterus
 As it proceeds it divides by mitosis
 Soon a ball of cells called the embryo forms

Implantation
 When the embryo reaches the uterus, it sinks into the uterus wall. This is known as
The Placenta
 As the embryo grows, a structure called the placenta also develops.
 It is soft and dark and has finger like projections called the villi
 The villi help connect the placenta to the uterus wall.
 The placenta is the embryo’s life support system.
 It is responsible in the exchange of substances between the embryo and the mother.
 It separates the mother’s and the fetus’s blood and brings them close enough so that substances can diffuse.
 Oxygen and food materials diffuse across the placenta into the fetal blood.
 Carbon dioxide and waste materials diffuse the other way, into the mother’s blood

The formation of a fetus and the umbilical cord

 After implantation, the embryo begins to develop.
 The embryo’s cells begin to take up different functions. Some become skin cells, some muscle cells, some
blood cells and so on.
 6 weeks post fertilization is the time where the major organs begin to emerge.
 It begins to move when the muscles are developed when it is 8 weeks old.
 11 weeks post fertilisation; the organs are in their correct positions.
 the embryo develops into the fetus
 As this happens, an umbilical cord develops as well.
 The umbilical cord consists of 2 arteries and 1 vein.
 The arteries take blood from the fetus into the placenta.
 The vein returns the blood to the fetus.

Ante-natal care
Ante-natal (before birth) care is a routine care for the healthy pregnant woman.

Dietary needs
The mother needs to take care of her diet as everything she will eat will diffuse across the placenta
to her baby.

Some of the nutrients that are necessary for the mother and her baby are:

Nutrient Why needed

amino acids Healthy growth and development of fetus

carbohydrates To give the mother energy to walk around

calcium Development of fetus’s bones

Iron To make Haemoglobin

Exercise
 Gentle exercise (swimming or walking)
 Special exercises (that will prepare the mother when giving birth to the baby)

Things to avoid
Smoking (nicotine and carbon monoxide) Restricts growth of baby

Alcohol consumption May be risky to the baby’s life

Drugs May be risky to the baby’s life

Produces rash and fever

Baby may be born deaf

Illnesses (such as Rubella)

Birth
Giving birth to a child is what brings pleasure to every child’s parents. This is the final stage of
reproduction.

The process of birth

1. Strong muscles in the wall of the uterus begin to contract
2. This is called labour
3. Contractions of the muscles slowly stretches the opening of the cervix
4. Simultaneously, the amniotic sac breaks
5. When the cervix is wide enough for the baby’s head to pass, the muscles of the uterus begin to push the
baby outwards.
6. This stage is excruciatingly painful!
7. When the baby has been pushed out of the uterus, the placenta breaks away and passes out of the vagina.
8. This is called afterbirth
9. The baby is still connected with the umbilical cord, which is removed by cutting it just above the point
where it joins the baby.
10. This leaves a mark at the stomach called the navel
Afterbirth Care
Though a baby develops for 9 months, it is extremely helpless at first. Both parents need to take
special care with their child such as:

 Mammals have a unique feature: lactation; mammary glands in the mother’s breasts begin to produce milk
which is extremely nutritious and beneficial for the child.
 The parents also need to support the child emotionally and physically till its adulthood
 Parental care also includes teaching the child about how to take care of itself in the society

Breast feeding and Bottle feeding (Formula

Milk)
Advantages Disadvantages

 Sterile
 Free of cost
 Improves bond between mother and
baby  Father is unable to bond and spend
 Perfect composition of nutrients time with baby
needed for the baby  Sometimes the mother is unable to
 Composition of nutrients naturally produce sufficient breast milk
changes according to baby’s growth  It can be difficult for mothers to breast
Breast feeding  Contains antibodies feed babies in certain situations
 Gives baby passive immunity  Keeps mother preoccupied

Bottle feeding  Helps father to bond with baby  Expensive

(Formula milk)  Gives mother time to relax and do  Needs extra effort to maintain sterility
other jobs  Probability of getting infected is high

Birth Control
Birth control is important in order to keep families small and limit the increase of the human
population exponentially.

There are many birth control methods practiced by people worldwide. These birth control methods
usually come into 4 categories: Natural, Chemical, Mechanical and Surgical:
Natural methods
Abstinence Woman avoids sexual intercourse completely

Woman keeps track of her body temperature (that rises at ovulation) and
doesn’t have sex during this period

How they Other Woman checks if the mucus produced in her vagina has become slippery
work methods or not

Useful for couples who don’t want to use other measures of birth control for religious or
Advantages other reasons

Disadvantages It is never possible to be 100% certain about ovulation period

Chemical Methods
 Spermicides can be used to kill sperm that enter the vagina
Spermicides  They can be effectively used in combination with another method- a
diaphragm

Contraceptive
Pills  Contraceptive pills containing sex hormones can be taken by the
woman; this stops the production of egg cells in the ovaries

 Sometimes contains copper

IUD (Intra-  A similar device called as an IUS can be used.
How they Uterine-  An IUS
work Device) releases hormones that prevent implantation and development of
any fertilized egg cell.

Advantages  A very effective method only when contraceptive pills are taken at the right time.
 The IUS and IUD lasts till 10 years

 It is important to have regular check ups by a doctor as some women do experience side
effects of contraceptive pills
Disadvantages  Contraceptive pills play a vicious part in river pollution and cause some male fish to
change gender as well!
Mechanical Methods
 A condom is a piece of rubber sheath
Condom  A condom is placed upon the erect penis and acts as a barrier
between the sperm and the vagina.

Femidom
 A femidom is a female version of a condom and is used similarly

How they Diaphragm (or  A diaphragm is a circular and slightly domed piece of rubber
work cap)  Inserted into the vagina on the top of the cervix
 Diaphragms are often used with spermicide for the best results

Condom is a very safe method of contraception only if it is used correctly.

Advantages Condom helps in the prevention of HIV and gonorrhoea

Diaphragm is also a very safe and reliable method IF used with spermicide

Disadvantages Care must be taken when using a condom or a femidom; no sperm should escape through it.

Surgical Methods
 In a man the sperm ducts are cut and tied, thus preventing the passage of
any sperms produced.
How it works Vasectomy  In a woman the oviducts are cut or tied, sopping egg cells from travelling
down the oviduct.

Advantages  Extremely reliable and sure method of contraception.

 Have no side effects.

Disadvantages  The tubes cannot be often opened.

 Not suitable for young couples who may wish to have children later.

Sexually Transmitted Infections (STI)

An infection that is transmitted through body fluids via sexual contact is called as a sexually
transmitted infection (STI)

Till date, the most treacherous STI has been the Human Immunodeficiency Virus (HIV)

HIV reproduces by infecting a particular type of lymphocytes called the T-cells.

Slowly and steadily, it destroys the person’s T-cells and hence, the person’s immune system
becomes more vulnerable to diseases in the environment.

The person may develop cancer as well because one function of the immune system is to destroy
cancerous tumours.

They may also develop AIDS (Acquired Immune Deficiency Syndrome)

Within 10 years if proper treatment is not given

There is no cure for AIDS. Research is being conducted worldwide to produce a vaccine that can kill
the virus without infecting body cells.

But still there is a ray of hope- HIV cannot be cured; it can be prevented.

HIV transmittion methods

 Unprotected sexual intercourse with infected people
 Drug usage involving sharing needle used by infected people
 Transfusion of infected blood
 Infected mother to baby through placenta
 Feeding a baby with breast milk from an infected mother
 Unsterilized surgical instruments

Preventing HIV
 Never have more than one sexual partner
 Use condoms
 Never have unprotected sexual intercourse
 Always sterilise needles before injecting drugs into your blood
 Screen blood for HIV when donating blood
 Always wear protective clothing when dealing with road accidents, if you are a policeman or a paramedic
(I’m sure you aren’t!)
*17-Inheritance
Inheritance is the passing of traits from parents to their offspring, either through asexual reproduction
or sexual reproduction. This is the process by which an offspring cell or organism acquires or
becomes predisposed to the characteristics of its parent cell or organism.

Important Terms:
Term Meaning

Inheritance The transmission of genetic information from generation to generation.

Chromosome A thread of DNA, made up of a string of genes.

Gene A length of DNA that codes for a protein.

A nucleus containing a single set of unpaired chromosomes

Examples:

· Sperm cells

Haploid
· Egg cells
nucleus

A nucleus containing 2 sets of chromosomes

Examples:

· Zygote

· Heart cells

Diploid
· Liver cells
nucleus

Mitosis Nuclear division that gives rise to genetically identical cells

Reduction division in which the chromosome number is halved from diploid to haploid,
Meiosis resulting in genetically different cells
 Any of the alternative versions of a gene

Such as TT, Tt, tt are alternative forms of the gene for height)
Allele

Is the genetic make-up of an organism in terms of the alleles present.

Example: To describe a person with gene for height, ‘T’ can be used.
Genotype

Phenotype Is the feature of an organism (in terms of words)

Means having two identical alleles of a particular gene (such as TT and tt)

· Two identical homozygous individuals that breed together will be pure breeding (for
example if TT breeds with TT, an offspring with TT will be born)
Homozygous

Heterozygous Having two different alleles of a particular gene (such as Tt), not pure breeding.

Dominant
alleles An allele that is expressed if it is present (such as T)

Recessive
alleles An allele that is expressed only if the dominant allele of the gene is absent (such as t)

A condition where both the alleles (dominant and recessive have an effect on the phenotype
of that plant

For example,

· CWCW produces white flowers in a plant.

Codominance · CRCR produces red flowers in a plant.
· CWCR produces pink flowers in a plant (and not white!)

Important:
Dominant and recessive expressions

 TT = Homozygous dominant
 tt = Homozygous recessive
 Tt = Heterozygous
Mitosis
Nuclear division that gives rise to genetically identical cells
<Image for the process of mitosis here>
Meiosis
Reduction division in which the chromosome number is halved from diploid to haploid, resulting in
genetically different cells

<Image for the process of meiosis here>

A comparison between mitosis and meiosis

Mitosis Meiosis

Type of reproduction carried on is asexual Type of reproduction carried on is sexual

Genetically identical chromosomes are formed Genetically different chromosomes are formed

Two diploid cells formed Four haploid cells formed

All cells except sex cells are made by this kind Only sex cells (sperm and egg cells) are made by this kind
of division of division.

Stem cells
When a zygote forms, it begins to divide by mitosis; forming genetically identical cells. This soon
forms an embryo.

After this period, the cells from the embryo (known as embryonic stem cells) begin to take up different
functions; some of them will become skin cells, some liver, some brain, etc.
This is known as differentiation.
Though every cell in our body has the same genes, only some of them specifically, are expressed.

Inherited diseases
Inherited
disease Notes
 In cystic fibrosis, the cells in the lungs make mucus more thicker than usual

It decreases the efficiency of the gas exchange surfaces due to the trapped mucus

The mucus made blocks the pancreatic duct and prevents digestive juices from flowing,
affecting digestion
Cystic fibrosis

In haemophilia, the blood in a person’s body fails to clot when there is a cut or wound.

It is caused by the inheritance of a defective gene that prevents blood clotting

Haemophilia

Sickle cell Is a genetic disease where the red blood cells become sickle shaped in the absence of
anaemia oxygen

Is another genetic disorder where the chromosomes 21s fail to separate during meiosis in a
woman’s ovaries.

This means that an extra chromosome 21 will be in the egg cell; if it gets fertilized, then the
zygote will have 47 chromosomes instead of 46!

Downs Children with downs syndrome are usually extremely friendly people and have heart
diseases when they grow up
syndrome

Genetic diagrams
There is a standard way of writing information such as an organism’s and its parent’s genotypes and
phenotypes. Moreover, these genetic crosses help us to predict the probabilities of an offspring
inheriting a particular characteristic of its parents.

For example, a tall pea plant is bred with a dwarf one. What do you think will its offspring be?

Parental phenotype Tall plant Dwarf plant

Parental genotype TT tt

Gametes T t
‘Tt’ means that all the offsprings born would be tall, and they would be having the ‘hidden’ or non
expressed recessive gene in them. This means that the plant offspring is a ‘carrier’ of the gene for
height.

To get dwarf plants, the offsprings in the above example can be breeded amongst themselves; this
would give rise to half of the offsprings being dwarf.

Sex determination
Similarly, using genetic diagrams can be useful to determine the sex (gender) of an offspring.
Sex linkage
 A sex-linked characteristic is one in which the gene responsible for a particular function is located on a
sex chromosome, which makes it more common in one sex than the other.
 The sex chromosomes X and Y not only determine your gender; they contain other genes as well.
 The X chromosome has a larger chromatid than the Y chromosome. Thus the genes present on the X
chromosome (apart from the gene for your sex) will not be present on the Y chromosome.
 This means that if an X chromosome has a gene for colour blindness, The Y chromosome will not have the
gene; this can lead to a male having colour blindness being born as the X chromosome is dominant and
there is no recessive allele on the Y chromosome.
 Similarly when an X chromosome (from a female) with a gene for colour blindness fuses with another X
chromosome (from a male) with a recessive allele for the same gene, an offspring who is the carrier of
colour blindness is born.
 Hence colour blindness is more common due to these reasons in males rather than in females as:
 There is less chance of a recessive allele being expressed in a female (XX) because the other X
chromosome may carry the dominant form of the allele.
 The male chromosome doesn’t have a recessive allele.
The 5 possible phenotypes and their genotypes for red-green colour blindness are:

1. XBXB : Woman with normal vision

2. XBXb: Woman with normal vision (who is a carrier)
3. XbXb: Woman with red-green colour blindness
4. XBY: Man with normal vision
5. XbY: Man with red-green colour blindness

Inheritance of sex linked characteristics

Let us see a much more simplified genetic diagram that will help explain the inheritance of sex linked
characteristics.

In the following case, a male without red-green colour blindness (XBY) mates with a female with its
carrier gene (XBXb). Let’s see what will happen now!
The genetic diagram predicts that about half of their male children will have red-green colour
blindness; whereas all of their female children will have normal vision.

DNA and Protein synthesis

 A DNA molecule is made up of 2 strands of nucleotides.
 Proteins are made up of long chains of amino acids.
 The sequence of these amino acids in a protein molecule determines the final shape of the molecule.
 This shape affects the way the protein works.
 This can control metabolic reactions in the body.
 This then affects the way the organism’s body works.
DNA and the genetic code
The genetic code is carried by a long and complicated molecule called Deoxyribonucleic acid or DNA.
DNA is responsible in the production of proteins (see protein synthesis)
 The DNA is found in the nucleus of all cells. It is formed into X-shaped structures called In human diploid
cells (except for eggs and sperm), there are 46 chromosomes. These are divided into 23 pairs.
 A chromosome is made up of two chromatids held together in the middle by a centromere.
 This DNA strand looks a bit like a ladder twisted into a double helix structure. The rungs of the ladder are
made up of pairs of base molecules with shapes complimentary to each other.
 It is the order of the bases that carry the actual genetic code.
 There are only 4 different types of bases:
1. Adenine (A),
2. Cytosine (C),
3. Guanine (G)
4. Thymine (T)
 As mentioned above, the pairs of bases have shapes complimentary to each other (like an enzyme and its
substrate!)
 Adenine and Thymine always join together (AT or TA)
 Cytosine and Guanine always join together (CG or GC)
 The genetic code contained in our chromosomes is used to make new cells by making proteins.
Passing on the code
The code is passed on to the new cells using either of two processes, mitosis or meiosis.
(See mitosis and meiosis)

Protein synthesis
Protein synthesis is all about how a protein is made in reality with the ‘synthesis’ (joining) of amino
acid molecules.

Here is the process:

 DNA is found in the nucleus
 Protein synthesis happens on the ribosomes, in the cytoplasm
 An mRNA (Messenger RNA) is used as a mode of transport from the DNA to the ribosomes.
 The DNA in the nucleus unwinds
 This produces a length of mRNA which has bases complementary to the DNA’s length.
 When the mRNA finishes copying the base sequence, it moves out of the nucleus through a nucleus pore.
 It then attaches itself to a ribosome
 As the mRNA molecule passes through the ribosome, a strand of amino acid begins to join simultaneously.
 The ribosome links amino acids exactly in the right order to make the desired protein.
Note: when the mRNA passes through the ribosome, it doesn’t ‘make’ the amino acids but simply
join them to form a protein.

(it is like joining a necklace of fallen beads!)

*18-Variation
Variation is all the difference (in terms of physical characteristics) that exists between the members
of the same species.

There are two types of variation:

1. Continuous variation (affected by genes and the environment)

2. Discontinuous variation (affected only by genes)

Continuous variation:
 Differences in the features of a group of organisms, in which there are no definite categories; each
individual’s characteristics can lie anywhere between two extremes.
Example:

1. Height
2. Weight
3. Finger length
4. Leaf length
5. Heart beat rate

Discontinuous variation:
 Differences in the features of a group of organisms, where each individual fits into one of a few clearly
defined categories.
 For example, blood group. Every person has a specific blood group and there are no exceptions to it; Blood
groups always have specific categories such as A, B, O, and AB.
Genetic variation: where the genes affect an organism’s genotype and thus its phenotype.
Environmental variation: where the environment is responsible in interfering with the organism’s
phenotype; For example, a pine tree has a genotype to grow tall. But it will not realize this until it has
got enough space to grow. It may remain stunted for life!

Causes of variation
Cause Notes

Mutation Mutation is the change in the base sequence in the DNA.

In meiosis, homologous chromosomes exchange genes and separate from one

another.

Thus the genes formed are not exactly the same.

Meiosis
 When two haploid gametes fuse together and form a zygote, an organism that is
completely different from its parents (in terms of genotype) is born.

This is why every person born is genetically unique! (I am sure you are as well
unless you have a twin!)
Fertilization

Adaptation
 Nature has an amazing rule- ‘survival of the fittest’. It means that an organism is much more likely to
survive if it is well adapted.
 The ‘fitness’ of an organism is the probability that it survives in the environment where it is found.
 An adaptive feature is the inherited functional feature that increases an organism’s fitness.
Let us see how organisms are adapted to their environments:

Xerophytes :plants living in habitats where there is water scarcity

Adaptation How it increases the plant’s fitness

Plants loose most water through the stomata by transpiration.

Stomata close when:

It is very hot and arid

Photosynthesis is not possible (at night!)

This helps conserve water by restricting plant growth (as photosynthesis is rarely
possible.
Closing Stomata

The wax makes the leaf waterproof

It cuts down transpiration rates

Waxy cuticle

Some plants have thick growing hair present on their leaves.

These help to trap a layer of moist air next to the leaf.

Hairy leaves

Stomata on underside of
leaves (or less stomata) Lower part of the leaf is usually cooler than the upper part
 Less stoma means less transpiration, hence less growth.

Thus stomata are usually located in deep pits,

Cuts down transpiration rate (with a compromise on photosynthetic rates)

Leaves with lower
Hence conserves water
surface area

Deep roots can access water underground

Have deep or spreading
Spreading roots can access water over a large area
roots

Hydrophytes-Plants that live in very wet places and in water as well!

Adaptation How it increases the plant’s fitness

Roots not attached to

riverbed Help the plant to float freely without the need of anchorage

To help plant float above water

For buoyancy

Leaf stalks and stem

Get plenty of light for photosynthesis as they float above water
have hollow air spaces

Stomata on both
surfaces Helps absorb carbon dioxide for photosynthesis

Thin or no cuticle As there is no need of conserving water, a cuticle is not needed.

*19-Natural Selection
The greater chance of passing genes by the best adapted organisms is known as natural selection.
The term ‘selection’ simply means that nature selects one characteristic of an organism out of
several characteristics as that characteristic is bound to give it a better chance to survive in the wild.
(It’s like a teacher selecting the best student to participate in a competition!)

Darwin’s theory of natural selection

Charles Darwin- the famous naturalist has submitted the following points in his book ‘the origin of
species’

Stage Notes

Variation Organisms in a population vary slightly amongst each other.

Most organisms reproduce to give birth to offsprings that would survive

Over production to adulthood.

There is considerable competition for survival between the organisms in

Struggle for existence non-favourable environmental conditions (such as famine).

Survival of the fittest Organisms who are well adapted to the environment will survive

The organisms who survive reproduce till adulthood. The advantageous

Advantageous characteristics are characteristics that helped them to survive are passed on to their
passed on to the offsprings offsprings

Gradual change over population This continues over generations and soon the well adapted organism has
for a period of time a greater population than the other.

Let’s take an example of the cacti:

Stage Notes

In a population of cacti,

· Some have longer roots.

Variation
 · Some have roots spread over a large area.

In the wet season, they flower and produce large numbers of

Over production offsprings.

Struggle for existence During dry season, there is competition for water.

The cacti with the longest roots are able to go deep and obtain water;
so they survive

The cacti with roots spread over a large area die with dehydration.
Survival of the fittest

Advantageous characteristics are The long rooted cacti reproduce; producing offsprings more likely to
passed on to the offsprings be long rooted themselves!

Gradual change over population for a The population of cacti with long roots increases; the population of
period of time cacti with roots spread over a large area decrease.

For better understanding, here is another example:

Antibiotic resistance in bacteria:

 Penicillin works by stopping bacterial cells from forming cell walls.
 When a person gets affected with a bacterial disease, he/she takes a dose of an antibiotic such as penicillin
to kill the bacteria by stopping bacterial cells from forming cell walls.
 This exerts a selection pressure if the same antibiotic is used again and again.
 The probability that a mutant bacterium will be produced is low; however it is possible.
 When a mutant bacterium (a bacteria with resistance against the antibiotic) forms, it has tremendous
advantage.
 The antibiotic kills all the bacteria except the mutant one.
 The mutant (resistant) one multiplies and forms a population of resistant bacteria just like itself.
 This causes the antibiotic to be ineffective against the resistant bacteria.

Stabilising selection
Many times, natural selection tends to keep the characteristics of organisms the same for
generations to generations.

This is called as stabilising selection.

If

 An organism is well adapted to it’s environment

 The environment around it remains the same
Stabilising selection will begin to show its effects.

Coelacanths for example have remained unchanged for 350 million years. They live in a very stable
environment in the depths of the Indian Ocean.

Sickle cell anaemia

Sickle cell anaemia is a genetic disease.

Some people have mutations in a gene that result in the production of haemoglobin

 People with the normal allele HbA code for the production of haemoglobin
 People with the mutant allele HbS code for the production of a faulty type of haemoglobin
The faulty type of hemoglobin can produce fibers inside RBCs when oxygen concentrations in the
blood drop. These causes the RBC to become sickle shaped and get stuck in blood capillaries.

When this happens, the person is said to be suffering from sickle cell crisis as a blockage in the
capillary forms. This can cause intense pain over hours and weeks! (Ouch!)

Damage caused by sickle cell crisis over a long time:

 Kidneys get damaged

 Liver gets damaged
 Eyes get damaged
 Heart gets damaged
A person having sickle cell anemia will always have breathlessness even when they don’t
experience sickle cell crisis. This is because the faulty hemoglobin decreases the efficiency of the
red blood cells in delivering oxygen to the cells in the body.
*20-Ecology
The study of the interaction between living organisms and their environment is called Ecology.

Words used in Ecology

Ecological
word Meaning Example

Habitat The place where an organism lives A desert

A group of organisms of the same

species, existing at the same time in the
Population same place A population of camels.

All the populations of different species The populations of camels, cactus and scorpion in
Community in an ecosystem the desert, make up a community

An ecological unit containing all biotic The community of all desert animals and plants
and abiotic factors, interacting with along with the sand, the sun, the wind, the water in
Ecosystem each other an oasis, all form the desert ecosystem

The way in which an organism lives its The camel feeds on desert grass, drinks some water
Niche life in an ecosystem from an oasis etc. all form a part of a niche

Food chains and food webs

 A diagram demonstrating the energy flow from one organism to the next, beginning with a producer is
defined as a food chain.
 A network of interconnected food chains is known as a food web.
 In both- a food chain and a food web, the energy comes from the sun and decreases as trophic levels
increase

Producers and consumers

 An organism that makes its own organic nutrients usually using energy from photosynthesis is defined as a
 An organism that obtains its energy by eating producers or other organisms is called as a consumer
 A herbivore is an organism that gets its energy by feeding on plants
 A carnivore is an organism that gets its energy by feeding on other animals

Trophic level
A trophic level is the position of an organism in:

 A food chain
 A food web
 A pyramid of biomass
 A pyramid of numbers

*21-Biotechnology
Biotechnology involves using living organisms to carry out processes that make substances that we
eat.

For example,

 Yeast has been used to make bread and alcohol.

 Lactobacillus bacteria have been used to make yoghurt and cheese
 Microorganisms can also be used to extract some enzymes
 Genetic engineering also uses microorganisms for obtaining substances such as insulin

Why microorganisms?
No ethical issues in using them
 Share the same genetic code of DNA
 Also have little loops of DNA called plasmids that can be used in moving genes from one organism’s cells
into other
 Microscopic structure- easy to store
 Easy to grow in laboratory
 Take up less space
 Able to produce wide range of substances
 Their reproduction rate is high

Yeast
 Yeast is a unicellular fungus.
 It is able to respire anaerobically, and it produces ethanol and carbon dioxide as it does so.

Uses of yeast
 Bread making
 Making bio-fuels
 Making alcohol (brewing)

Bread making
Wheat flour contains lot of starch and a protein called gluten.
To make bread:

1. Flour is mixed in water

2. Yeast is added
3. A dough is prepared
4. In the dough, amylase (enzyme) breaks down starch in the dough to maltose and some glucose.
5. These products are used by the yeast in anaerobic respiration.
6. Yeast produces bubbles of carbon dioxide, that get trapped in the dough
7. Gluten in the flour makes the bread stretchy.
8. Carbon dioxide bubbles help the dough to rise.
9. The dough is baked
10. Baking removes the alcohol and kills the yeast.

Bio-fuels
Bio-fuels are made by yeast and it produces ethanol. They are crucial in order to replace non-
renewable energy sources such as petroleum.

Making bio-fuels:
1. Maize is treated with amylase
2. Addition of amylase breaks down stored starch to glucose.
3. A solution of sugars made by plants is extracted.
4. Yeast is added to the solution.
5. The solution is enclosed in a container with vacuum to support anaerobic respiration in the yeast.
6. An air lock is added so that bacteria cannot enter the solution.
7. At the end of fermentation, ethanol is produced
8. The ethanol is then purified using distillation.
Advantages Disadvantages

Doesn’t contain as much energy per litre, as fossil

Alcohol burns well fuels do

Crops take up land

may harm natural habitats

It is a sustainable source

Growing enormous amounts of such crops increases

its price
Helps to reduce amount of carbon dioxide in the
makes it unaffordable for people to buy food
atmosphere
Making use of enzymes
Enzyme production is one of the most prominent uses of Genetic Engineering (to know more about
enzymes click here)

Lactase
Lactase is an enzyme that breaks down lactose, a sugar found in milk, to glucose and galactose.

Lactose à glucose + galactose

Milk is treated with lactose, so that people of Asian descent can readily digest it and not feel ill.

Reasons of using lactase:

 Babies start secreting lactase in the early months of their life to break down the lactose in the milk to
simple molecules.
 Some people of the Asian descent stop making lactose when they grow older.
 Hence for such people, it is tough to digest milk products. They often feel unwell when they eat food such
as cheese or butter.
 Moreover, glucose and galactose is used commercially to make sweets.

Penicillin
Genetic engineering
Changing the genetic material of an organism by

 Removing
 Changing
 Inserting
…Individual genes is called as genetic engineering.

Where genetic engineering has been used:

 In the production of insulin (for people with type 1 diabetes)

 For crop plants to get resistant towards herbicides and insect pests.
 For rice to produce more vitamin A (so that people with severe vitamin A deficiency can be cured)

The process for genetic engineering

Production of human insulin using bacteria is an important component of biotechnology.

1. Some human cells are liquidized

2. The DNA is made to precipitate by addition of chemicals
3. Restriction enzymes are added to cut the DNA into pieces with specific length.
4. Human DNA with sticky ends are formed
5. Simultaneously, restriction enzyme is used again to cut the plasmid(s) DNA
6. Again DNA with sticky ends forms.
7. Both the sticky ends are complementary (similar) to each other.
8. Using ligase enzyme, the human gene for insulin and the plasmid DNA are joined
9. The plasmid acts as a vector putting the human insulin gene into a bacterium
10. This forms a genetically engineered bacteria
11. The genetically engineered bacteria are grown in a fermenter
12. They reproduce asexually and make human insulin
13. The insulin is filtered and purified and used.

*22-An Overview
The Earth- an exceptional planet isn’t it?

So why do you think life can exist on earth? It’s simple! We’ve got the right distance between the sun
and our planet which leads to an appropriate surface temperature on earth. We have also fortunately
got the right composition of gases in the atmosphere and the unique presence of water. These are
just a few factors from the many!

Earth- Who rules the earth? Mother Nature? Certainly not. The earth is now reined under the
bloodthirsty monarchy of us- the humans!
Food Production
One reason for the increase in our population is food production. Food is produced majorly
by growing crops and breeding livestock.
Factors that led to an increase in food production:
 Advanced agricultural machinery such as tractors and combine harvesters have enabled farmers
to cultivate larger areas of land in shorter time
 Chemical fertilizers containing mineral ions have been used to improve the land’s fertility and hence
it’s yield
 Insecticides have been used to destroy pests that could affect the yield and quality of the produce
 Herbicides (Weedkillers) have been used in order to destroy weeds that compete for minerals, soil, water
and sunlight with the crop plants; this leaves enough space for the crop plant and
thus improves the yield
 Selective breeding has been practiced which has developed new and improved varieties of plants and
animals
 For example, selective breeding has produced crop plants that grow in poor soil and plants that
are resistant to diseases
 Use of satellites to monitor crop development and monitor crop diseases
 Use of antibiotics, hormones and artificial insemination techniques in intensive livestock production.

Monoculture and its negative impacts

A monoculture is the cultivation of a single variety of a crop plant over a large area.

Negative impacts of monocultures

 Reduces species diversity of an ecosystem
 Can lead to an increase in populations of pests as availability of food increases for them
 Insecticides sprayed on the pests may not be selective and may be persistent
 Insecticides can damage other organisms in the environment as well and thus cause harm to the
ecosystem
 Insecticides may even lead to the development of resistance in the insect pests
Solution: Farmers can use mixed cropping. This means that different patches of land will be covered
by different crop plants.

Benefits of mixed cropping:

 Species diversity in the ecosystem may increase
 Pests may find it difficult to spread from one patch to other
 This decreases the number of insect pests
 Thus they need to spray less insecticides
 Hence will benefit species diversity in that ecosystem.

Intensive livestock production

In developed countries, large numbers of livestock are kept in smaller areas. This is known
as intensive farming.
Farmers use:
 High energy food
 A suitable room temperature
 Antibiotic doses
And give them to the livestock so that their growth rates maximise and the farmer yields greater
amounts of meat, milk, wool, etc.

Disadvantages of intensive livestock production:

 Welfare issues between the livestock may emerge
 Diseases can spread easily
 Antibiotic resistance may develop if they are given antibiotics
 Waste from intensive farming units can pollute nearby waterways
 Waste from intensive farming units can cause eutrophication

Factors affecting world food supplies

There is not always enough food available in a country to feed the people living there. A severe food
shortage can lead to famine.
It has been calculated that more than enough food is produced on Earth to provide every single person
with more than enough for their needs. Yet many people do not get enough food.
The fundamental problem is that food is distributed unequally on our planet: while some parts of the
world produce more than enough food for the people that live there, in other part of the world not
enough food is produced.
 Although large amounts of food are transported from one country or area to another, this is still not
sufficient to supply enough food to everybody.
 If food becomes expensive, many people may not be able to afford to buy it.
Famine can occur for many different reasons:
 Climate change and natural disaster such as drought and flooding that prevent crops from growing.
 Increasing population: population may grow so large that the land on which they live can no longer
provide enough food for them.
 Wars may prevent people to grow crops and thus this leads to famine

Habitat Destruction
Deforestation
Deforestation is the removal of large areas of forest.
Reasons why deforestation occurs:

 To clear up land for farming.

 To clear up land for construction and building roads.
 To clear up land for timber for construction, furniture and fuel.
 To clear up land for mining minerals or other natural resources

Effects of deforestation on the environment:

 Deforestation leads to fewer trees, resulting in lesser natural habitats for animals living there
 Deforestation can cause reduction in food resources and breeding grounds of animals and can thus result in
their extinction!
 Deforestation also disrupts food webs and decreases species diversity.
 Removal of trees means there are no roots to hold the soil, which results in the top soil getting washed
away, and causing soil erosion. Desertification can eventually occur as the topmost and most fertile layer
of soil is washed away and the land becomes barren.
 As there are no roots to hold the soil, the top soil may be washed away into nearby waterbodies which can
become silted and can eventually overflow causing flooding.
 Deforestation also causes an increase in the greenhouse effect by increasing the volume of carbon dioxide
in the air (as there are lesser trees to absorb carbon dioxide)
 Deforestation also affects the water cycle; as there are lesser trees, lesser water vapour is produced through
transpiration and thus gradually the air becomes drier leading to less rainfall.

Marine Pollution and Oil spills

 Often, there are massive oil spills in oceans and incidents where undersea oil wells leak.
 Oil is less dense than water and thus the leaked oil accumulates at the top of the ocean, covering a large
area.
 As it covers a large area, it prevents sunlight from reaching the marine plants below, hence restricting
photosynthesis.
 This soon disrupts all food chains and webs as every primary consumer is dependent on these producers
for food.
 Along with that, sea birds also get damaged as they may swallow some oil while hunting for fish. This
can poison and kill them, resulting in a decline in their populations.

Pollution
Eutrophication
Damage by eutrophication can be done in 2 ways:

 By spraying fertilizers or applying too much of manure

 By dumping untreated sewage into water bodies

Eutrophication done by spraying fertilizers or applying too

much of manure:
Farmers often use a lot of fertilizers and manure in order to maximise their crop’s yield. But doing
this can destroy an entire aquatic ecosystem by eutrophication!

1. A farmer sprays a lot of fertilizers and manure on their crops.

2. When it rains, all the sprayed fertilizer is washed out into nearby water bodies, such as a lake.
3. Small populations of algae living on the surface of the lake start to reproduce intensively as they get an
extra source of nutrition from the washed out fertilizers.
4. Soon the algae population is so large that it covers the surface of the lake!
5. This is known as algal bloom.
6. When the algae die, they are decomposed by aerobic bacteria.
7. The aerobic bacteria consume the dissolved oxygen in the lake as they decompose the algae.
8. This leads to the lake having no dissolved oxygen!
9. The fish and other aquatic animals die as a result the entire aquatic food web gets disrupted!
10. This is how spraying fertilizers can cause eutrophication.

Eutrophication done by dumping untreated sewage into

water bodies:
1. A truckload of sewage is dumped into a lake
2. There are many organic compounds in the sewage such as nitrates and phosphates.
3. The sewage is decomposed by aerobic bacteria
4. The aerobic bacteria consume the dissolved oxygen in the lake as they decompose the sewage.
5. This leads to the lake having no dissolved oxygen!
6. The fish and other aquatic animals die as a result the entire aquatic food web gets disrupted!
7. This is how dumping untreated sewage causes eutrophication.

Sewage
Sewage is the untreated organic waste produced, along with household and industrial waste
materials.

Effects of dumping untreated sewage:

 Eutrophication damages the water body
 Aquatic organisms get affected as the untreated waste contains pathogens
 Water borne diseases such as cholera spread rapidly and infect the people who drink the polluted water

Chemical waste
Chemical waste is all the inorganic waste disposed into water bodies. These include:
 Heavy metal compounds such as mercury, lead, nickel and aluminium
 Women contraceptive hormones such as oestrogen
 Crude oil
All these things can cause serious damage to the environment.

When heavy metal compounds are dumped into water bodies, they get accumulated in aquatic
organisms through bioaccumulation and enter food chains and webs.
When humans eat organisms from these polluted water bodies, all the heavy metal compounds get
accumulated in the highest concentrations, causing maximum damage.
These heavy metal compounds are toxic for humans and can damage our Central Nervous
System (CNS)

Contraceptive pills and chemical waste

Females often take women contraceptive hormones as a measure of birth control. One such hormone
is oestrogen. These hormones are excreted out of the body, dissolved in urine. When the urine
containing women contraceptive hormones enter water bodies, they can cause:
 A decrease in the number of sperm produced by male fish
 A change in gender of a male fish
 A decrease in the number of fish born
 A decrease in the number of egg cells produced by female fish

Acid Rain
Causes Sources Damage caused Solutions

Sulphur  Oil refineries.  Using Oil instead of

dioxide gas  Oil and coal powered coal; oil contains
(SO2) power stations. less sulphur.
 Automobiles.  Switching on to
 Causes acid rain more renewable
 Acid rain damages the resources of energy.
cuticles of leaves, eventually  Installing scrubbers
killing the plant. to Power station
 Acid rain acidifies lakes, chimneys and
lowers the pH of the water exhaust vents.
and makes it impossible for  Use catalytic
marine organisms to live. converters to make
 Buildings made up of car exhausts less
limestone are damaged. toxic.
Oxides of  Oxygen and nitrogen in  Stonework is damaged.  Re-design car
nitrogen the air react together at  Aluminium ions are leached engines to burn
(NOx) high temperatures of a car out of the soil and are washed nitrogen at lower
engine. into water bodies. temperatures.
Examiner’s tip: never write the source of nitrogen oxides as ‘form in car engines’; nitrogen and oxygen
in the air simply react together at high temperatures of car engines and are not formed by burning fuel!

The greenhouse effect

There are some gases in the atmosphere which prevent infrared radiation pass through them. These
gases are known as greenhouse gasses. Greenhouse gasses are extremely important in regulating
the surface temperature on earth. Without the greenhouse effect, the surface temperatures would
have been too cold for life to exist..

Greenhouse effect

1. Electromagnetic radiation with short wavelength enters the atmosphere

This radiation strikes the earth’s surface and reflects back in the form of infrared radiation with a shorter
2. wavelength towards the atmosphere.

3. Most infrared radiation with a shorter wavelength is stopped by the greenhouse gases in the atmosphere

4. This causes the heat in the infrared radiation to remain on Earth

Enhanced greenhouse effect

However in the past century, due to the industrial revolution the amount of greenhouse gas
emissions have increased leading to the enhanced greenhouse effect taking place.
The major difference between the greenhouse effect and the enhanced greenhouse effect is that
lesser amount of infrared radiation escapes through the atmosphere due to the increase in
greenhouse gasses in the enhanced greenhouse effect.

Here is a list of some greenhouse gasses:

1. Carbon dioxide
2. Methane
3. CFCs
4. Oxides of Nitrogen
5. Water vapour

Insecticides
Insecticides are chemical compounds used to control populations of insect pests such as
mosquitoes.
Though an insecticide kills the insect pest, it remains in the environment and also kills other
harmless animals. This was the case with a pesticide named DDT (Dichlorodiphenyltrichloroethane)
which was used to kill mosquitoes. DDT remained in the environment and was absorbed into the
food chains. This lead to bioaccumulation and the concentrations of DDT in the organisms increased
as the trophic levels increased. This was lethal and caused a lot of damage to organisms that it was
not supposed to kill.

This means that DDT is a non-specific pesticide as well as a persistent one.

Due to these reasons, DDT is banned in most countries now.

Herbicides
Herbicides are often used by farmers to control the populations of weeds which compete with the
crop plant for nutrients, space, sunlight and water.

However, when herbicides are sprayed onto the crops, they not only kill the weeds, but also can get
washed away into water systems and kill the aquatic plants there. This disrupts the aquatic food
chain as the consumers get affected.

Nuclear fallout
Nuclear fallout can be the result of a leak from a nuclear power station, or from a nuclear
explosion. Radioactive particles are carried by the wind or water and gradually settle in the
environment. If the radiation has a long half-life, it remains in the environment and is absorbed by
living organisms.
The radioactive material bio-accumulates in food chains and can cause cancer in top carnivores.

Plastics and the environment

Most plastics are non-biodegradable; they aren’t broken down by decomposers when dumped in
landfill sites or left as litter. This means they remain in the environment and accumulate, taking up
space or causing visual pollution.

Damage caused by plastics

 Discarded plastic bottles and cans can trap small animals.
 When plastic is burned it can release toxic gases such as hydrogen chloride.
 Plastics gradually deteriorate into smaller pieces; these pieces can be consumed up by fish and birds and
can make them ill.

Conservation
Conservation is the process of looking after the natural environment.
Conservation attempts to maintain or increase the population of different species living in an area,
known as biodiversity.

The need for conservation of species

 Many species of animals and plants are in danger of extinction, due to factors such as habitat destruction,
the introduction of other species, international trade and pollution.
 Loss of a species also means that its genes are lost: these may be important in the future for genetic
engineering (e.g. to improve crops) and the production of useful chemicals such as medicines.
 The presence of rare species can be an important source of money for poor communities, through tourism.
 The species may play an important role in a food chain: its loss could endanger other species.

Ways of conserving species

 Initiating laws to protect them
 Using methods such as captive breeding and re-introduction
 Controlling human activity such as hunting, poaching, deforestation, etc.
 Appointing forest guards to ensure the animals are not poached illegally
 Setting up seed banks where the seeds of millions of plant species are stored

The need for conservation of habitats

 If habitat is lost, so are the species that live in them, so habitat destruction poses the greatest threat to the
survival of species.

Ways of conserving habitats

 Preach sustainable development; sustainable development is development providing for the needs of an
increasing human population without harming the environment.
 Controlling factors, such as water drainage and grazing, That may otherwise contribute to destruction of the
habitat
 Using laws to protect the habitat
 Appointing forest officials to protect the habitat
 Reducing or controlling public access to the habitat
 Monitoring and controlling human activities such as deforestation, air pollution, marine pollution, etc. near
the habitat.

The need for conservation of natural resources

Some natural resources (the material we take from Earth) are not replaceable (non-renewable). For
example, fossil fuels such as coal took millions of years to form. The rate of consumption of fossil
fuels is greater than the rate of formation and so, these natural resources are on a steady rate of
depletion.

Ways of conserving natural resources:

 Increase and promote the use of renewable energy (wind farms, solar power, hydroelectric power,
geothermal power…).
 Improve the efficiency of energy use (better insulation, more efficient car engines, more public
transports…).
 Grow trees specifically for fuel, then replant them as they are cut down. This will maintain the amount of
greenhouse gasses in the atmosphere.