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Respiration exam questions AQA A2 BIOLOGY 2023 with 100% correct answers

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Respiration exam questions AQA A2 BIOLOGY 2023 Describe how acetylcoenzyme A is formed in the link reaction. (2) - ANSWER-1. Oxidation of / hydrogen removed from pyruvate and carbon dioxide released; 2. Addition of coenzyme A. In the Krebs cycle, acetylcoenzyme A combines with four-carbo...

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  • March 5, 2023
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Respiration exam questions AQA A2
BIOLOGY 2023

Describe how acetylcoenzyme A is formed in the link reaction. (2) - ANSWER-1. Oxidation of / hydrogen
removed from pyruvate and carbon dioxide released;



2. Addition of coenzyme A.



In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form six-carbon citrate



This reaction is catalysed by the enzyme citrate synthase.



(i) Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This induces a change in
the enzyme, which enables the acetylcoenzyme A to bind. Explain how oxaloacetate enables the
acetylcoenzyme A to then bind to the

enzyme. (2) - ANSWER-1. Change (in shape) of active site / active site moulds around the substrate;



2. (Substrate / active site) now complementary.



(ii) Another substance in the Krebs cycle is called succinyl coenzyme A. This substance has a very similar
shape to acetylcoenzyme A.



Suggest how production of succinyl coenzyme A could control the rate of the reaction catalysed by
citrate synthase. (2) - ANSWER-1. Is a competitive inhibitor / attaches to active site;



2. Reduces / prevents enzyme-substrate / E-S complex forming.



(c) In muscles, pyruvate is converted to lactate during anaerobic respiration.

, (i) Explain why converting pyruvate to lactate allows the continued production of ATP during anaerobic
respiration. (2) - ANSWER-1. Regenerates / produces NAD / oxidises reduced NAD;



2. (NAD used) in glycolysis.



(ii) In muscles, some of the lactate is converted back to pyruvate when they are well supplied with
oxygen. Suggest one advantage of this. (1) - ANSWER-(Pyruvate used) in aerobic respiration / (lactate /
lactic acid) is toxic / harmful / causes cramp / (muscle) fatigue.



Carbon dioxide in the breath contained the radioactive form of carbon, 14C. Explain how 14C in carbon
dioxide came from 14C in glucose in the blood. - ANSWER-Respiration ( produce CO2);

By cells / tissues;



What measurements should the student have taken to calculate the rate of

aerobic respiration in mm3 of oxygen g-1 h-1? - ANSWER-1. Distance (drop moves) and time;

2. Mass;

3. Diameter / radius / bore of tubing / lumen / cross-sectional area;



The student closed the tap. After thirty minutes the drop of coloured liquid had moved to the left.
Explain why the drop of coloured liquid moved to the left. (3) - ANSWER-1. Oxygen taken up / used

2. Carbon dioxide (given out) is absorbed by solution / potassium

hydroxide;

3. Decrease / change in pressure;



DNP inhibits respiration by preventing a proton gradient being maintained across

membranes. When DNP was added to isolated mitochondria the following changes

were observed

• less ATP was produced

• more heat was produced

• the uptake of oxygen remained constant.

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