BIOLOGY UNIT `1 MODEL ANSWERS AS

MODEL ANSWERS FOR AQA BIOLOGY UNIT 1- BIOLOGY AND DISEASE

June 2014

9 a. Explain why Maltase only breaks down Maltose, How does enzymes allow reactions to occur at body temperature? (5 marks)

·         Active site Specific to substrate-Complementary (Enzyme and Substrate)

·         Enzyme Substrate complex

·         Specific Amino Acid structure/ Primary Structure

·         Specific Tertiary Structure

·         Lowers activation energy

·         Reaction requires less energy for hydrolysis

·         Idea Biological catalyst/Not used up in reaction/Remains the same at the end of Reaction

b. Explain in terms of the effect on enzymes how Competitive and Non-competitive inhibitors effect the enzymes (5 mark)

·         Competitive inhibitor similar shape to substrate

·         Blocks/Bound to Active site / Substrate can't bind

·         Enzyme substrate complex

·         Fewer Enzyme substrate complexes formed / Reduced products formed- example accepted e.g. Maltose --->2* Glucose / Reduced rate of reaction (Hydrolysis)

·         Non Competitive binds to site other than active site

·         Conformational change in shape of active site

·         Bonding breaks/ change shape / rearrange e.g. H-bond, Disulphide bridge, Ionic bond

·         Change in proteins Tertiary structure

·         Reduced/No Enzyme substrate complexes formed

·         Substrate no longer complementary to active site/ Active site not specific to substrate

June 13

8 (a) Describe how a heartbeat is initiated and coordinated. (5 marks)

§  A wave of electrical activity spreads form SAN to both atria- making them contract.

§  A layer of non-conductive tissue stops this passing to the ventricles.

§  The wave of electrical activity is passed to the AVN which delays the response.

§  This delay allows the atria to fully empty and allow A-V valves to close to prevent the backflow of blood.

§  After the short delay the AVN then sends a wave of electrical activity to the bundle of his

§  This makes the ventricles to contract forcing the blood out of the heart (apex>upwards and out of the aorta)

8 (b) Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta. (5 marks)

·         Atrium has higher pressure than ventricle (due to filling/contraction)

·         Atrioventricular valve opens

·         Ventricle has higher pressure than atrium (due to filling/contraction).

·         Atrioventricular valve closes

·         Ventricle has higher pressure than aorta

·         Semilunar valve opens

·         Higher pressure in…