MODEL ANSWERS FOR AQA BIOLOGY UNIT 1- BIOLOGY AND DISEASE
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
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…