Biology Revision

All biology needed for pre- gcses. i.e. year 9


Inherited Variation

The Features of Organisms are called their characteristics for example, Blue Eyes.

Offspring normally share some characteristics with their parents and brothers or sisters.

Offspring often inherit characteristics from their parents

Characteristics can be different, this is known as variation.

Variation occurs in plants and animals

1 of 15

An organism's characteristics are controlled by genetic information which is found inside the nucleus of nearly all it's cells.

Genetic information is passed from parents to offspring during reproduction.

In sexual reproduction, a male sex cell (gamete) and a female gamete fuse.

This fusing produces a fertilised egg cell which grows into the new organism.

Each gamete contains half the amount of genetic information that a normal body cell has.

The fertilised egg gets half it's information from each parent.

Non-identical twins are formed from two egg cells and two sperm cells.

Identical twins are formed from one egg cell which splits into two.

2 of 15

Species, breeds and varieties

A species is a group of organisms that are able to produce offspring that are also able to reproduce.

Members of the same species have very similar characteristics but there is some variation.

A group of animals may have special differences from the rest of the species, this is called a breed.

There are also breeds of plants and these are called varieties.

3 of 15

Selective Breeding

Farmers and plant breeders can select an animal or plant with certain characteristics to breed from. Their offspring are then bred again. This is selective breeding.

Many new breeds and varieties can be created by selective breeding.

Cross-breeding is when two different breeds or varieties are bred together to produce offspring with characteristics from both breeds or varieties.

4 of 15

Plant Breeding

Pollen grains are carried by the wind or insects to the stigma of another flower, this is called pollination.

Plant breeders transfer the pollen that they want to the stigma using a paintbrush.

A pollen grain grows a tube down through the style until it meets an ovule. It grows into the ovule and meets an egg cell.

The nucleus from the pollen grain goes into the egg cell and fuses with the nucleus. This is fertilisation.

5 of 15

Variation caused by the environment

Some characteristics vary due to the organism's environment.

Plants growing in different areas of a field may be different heights due to amount of light, water and mineral salts they get.

These things are all physical environmental factors.

6 of 15

Fit and Healthy

Heart disease is when heart muscle cells start to die.

Muscle cells need more energy during exercise. This is obtained from glucose by the process of AEROBIC RESPIRATION. The word equation is:


The RESPIRATORY system supplies the oxygen and removes the carbon dioxide.

The DIGESTIVE system provides the glucose.

The CIRCULATORY system carries the glucose and oxygen to the muscle cells and carries the carbon dioxide away to the lungs.

Breathing is carried out by the DIAPHRAGM and the RIB MUSCLES. These change the volume of the chest. Breathing ventilates the lungs. (moves air in and out of)

7 of 15

Breathing In:

  • Diaphragm contracts and moves downwards
  • Rib muscles contract and lift ribs up and outwards
  • The volume of the chest increases
  • Air flows into the lungs

Breathing Out:

  • Diaphragm relaxes and moves upwards
  • Rib muscles relax and move ribs down and inwards
  • The volume of the chest decreases
  • Air flows out of the lungs
8 of 15

Drugs and Health

Drugs are chemicals that affect how the body works.

Nicotine makes arteries narrower, causes heart disease.

Tar clogs up the lungs and stops the cilia working, causes cancer andbronchitis.

Carbon Monoxide stops red blood cells carrying so much oxygen.

Recreational drugs are legal eg caffeine and alcohol.

Drugs that slow down the nervous system are called depressants.

Drugs that speed up the nervous system are stimulants.

Misuse of drugs can be harmful to the liver especially.

9 of 15

A balanced diet is made up of seven food substances:


A shortage of a particular substance can cause a deficiency disease.

Eating too much fat can cause obesity and heart disease.

10 of 15


Muscles move bones at joints. They cannot push so they work in antagonistic pairs to pull in opposite directions.

One muscle contracts and gets shorter and fatter to pull a bone.

At the same time the other muscle in the pair relaxes and gets longer and thinner.

Exercise strengthens bones and muscles but too much can damage muscles and joints.

Triceps pull the lower arm down

Biceps pull the lower arm up

Muscles are attached to bones by tendons.

11 of 15

Plants and Photosynthesis

The chemical reaction for Photosynthesis is:

water + carbon dioxide (+light energy) ----> glucose + oxygen

Light energy and chlorophyll are needed for photosynthesis to happen. The light energy is changed into chemical energy which is stored in the glucose that is made

Water is taken out of the soil by the roots of a plant. Roots are branched and spread out to absorb water from a large volume of soil.

Root hair cells are adapted to their function by having a large surface area to absorb water quickly. The water flows up the xylem tubes (hollow cells) to the leaf.

Water is also needed because mineral salts are dissolved in it which are needed to keep plants healthy. Water also stops plants wilting and keeps their leaves cool.

12 of 15

Air containing carbon dioxide diffuses into leaves through small holes called stomata. Leaves are thin so that the carbon dioxide does not need to go very far before reaching the cells that need it.

Photosynthesis can often be speeded up by increasing the amount of carbon dioxide around a plant.

Many leaves are wide so that they have a big surface area to trap as much sunlight as possible.

Most photosynthesis happens in the palisade cells which are found near the upper surface of leaves.

Palisade cells are packed with chloroplasts which contain chlorophyll to absorb light energy.

Photosynthesis can often be speeded up by increasing the amount of light.

13 of 15

Respiration in Plants

Plant cells release the energy stored in glucose using aerobic respiration.

glucose + oxygen -----> carbon dioxide + water (+ energy)

All living things need energy and so all living cells respire. Respiration happens all the time but photosynthesis only happens when there is light.

14 of 15

Uses of glucose

Glucose is a type of sugar that can be used for three things: respiration, making other substances that act as stores of energy, (eg starch), and making new materials for growth.

Glucose is turned into cellulose (for cell walls), fats and proteins. To make proteins, mineral salts called nitrates are needed.

New substances made by a plant are carried around the plant in phloem tubes.

New substances help to build up a plant's biomass, (the mass of all the materials in the plant except water).

15 of 15


No comments have yet been made

Similar Biology resources:

See all Biology resources »