biology- igcse revision (not topical)

State the name given to a length of DNA that codes for a protein.

gene

State features of all prokaryotes.

1. unicellular

2. asexual reproduction

3. ribosomes

4. cell wall

5. cytoplasm

6. circular DNA (free in cell)

Describe what is meant by the term decomposer.

organisms that get energy from dead organism or waste organic material

state the function of mitochondrion.

aerobic respiration

Enzymes are involved in chemical digestion which produces small ................................................ molecules that can be absorbed into the blood.

soluble

Two examples of protease enzymes are pepsin and trypsin. Pepsin is produced by the ................................................ and requires acidic conditions. These conditions are created by the release of ................................................ , which provides the optimum pH for pepsin activity and also kills harmful ................................................ .

• stomach

• hydrochloric acid

• pathogens

The ................................................ produces trypsin which breaks down protein in ................................................ pH conditions. These conditions are created by a substance called ................................................ , which neutralizes the gastric juices and also has an important role in the ................................................ of fats and oils.

• pancreas / small intestine

• alkaline

• bile / bile salts

• emulsification

State the name and function of the cell structure labelled A in Fig. 5.1

• mitochondrion

• (aerobic) respiration

features of incisors

Rectangular shape, sharp for cutting and biting

Explain the reasons for changes in pressure seen in arteries

• caused by contraction of muscles (of the heart/ventricle)

• pressure increases when the heart/ ventricles contract/pump

• pressure decreases when the heart/ventricles relax

describe the structure of capillaries

• One cell thick wall for easy diffusion

• Highly branched; large surface area

• Capillary beds constantly supplied with fresh blood, so diffusion occurs

equation for anaerobic respiration in yeast

• Glucose → Ethanol + Carbon Dioxide

• C6H12O6 → 2C2H5OH + 2CO2

what is a synapse

a junction between two neurones, consisting of a gap across which impulses pass by diffusion of a neurotransmitter

describe the carbon cycle

• Carbon is taken from the atmosphere by photosynthesis (plants)

• It is passed on to animals and decomposers by feeding. It is returned by respiration in plants and animals and decomposed by microorganisms.

state the features of arachnids

• Two body segments – cephalothorax and abdomen

• Four pairs of legs (8 legs)