A-LevelBiologyEnergy and respiration9700/42 · Feb/Mar 2021 · Q816 Marks

Fig. 8.1 shows a transmission electron micrograph of a mitochondrion. [Figure 8.1]

(a)(i)On Fig. 8.1, use the letter A with a label line to show a location where the Krebs cycle occurs.[1]
(a)(ii)Name the structure labelled B on Fig. 8.1 that forms part of the inner mitochondrial membrane.[1]
(a)(iii)The inner mitochondrial membrane is the site of oxidative phosphorylation. Explain how the structure of the inner mitochondrial membrane is linked to its function.[5]
(b)The activity of succinate dehydrogenase, an enzyme in the Krebs cycle, is used as a measure of the rate of respiration in the mitochondria. The redox reaction catalysed by succinate dehydrogenase is shown in Fig. 8.2. [Figure 8.2] The activity of succinate dehydrogenase can be measured using a redox indicator. Name a redox indicator and explain why this indicator can be used to measure the activity of succinate dehydrogenase.[2]
(c)(i)Describe the trends shown in Fig. 8.4.[3]
(c)(ii)Explain the difference in the rates of respiration between liver at 37°C and muscle at 37°C.[3]
(c)(iii)During torpor in ground squirrels, muscle tissue uses more energy than liver tissue. Suggest one reason for this difference.[1]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2021). The mark or mark type is shown in brackets.

[1] A – label line pointing to mitochondrial matrix ;
[1] crista(e);
[1] folded (inner) membrane / many cristae ;
[1] forms large surface area ;
[1] (for) electron carriers / electron transport chain / ETC / cytochromes ;
[1] ref. to ATP synth(et)ase / ATP synthesis ;
[1] impermeable to, protons / hydrogen ions ;
[1] (so) allows, formation of proton gradient / high concentration of protons in intermembrane space;
[1] proton pumps ;
[1] DCPIP / methylene blue ;
[1] changes, colour / blue to colourless, when, reduced / accepts electrons (from succinate);
[1] rate of respiration increases (as succinate concentration increases) up to 1.0 mmol dm-3 or maximum rate at 1.0 mmol dm-³;
[1] rate of respiration higher at 37 °C than at 10 °C (in liver and muscle);
[1] rate of respiration higher in muscle than in liver (at both temperatures);
[1] comparative data quote to support mp2 or mp3;
[1] muscles have higher rate of respiration because:
[1] respiration produces ATP ;
[1] muscle has higher need for, ATP / energy ; ora
[1] for muscle contraction or muscle is more metabolically active / AW ;
[1] AVP; e.g. shivering to maintain body temperature ;
[1] muscle, is contracted / generates heat / is more metabolically active / AW ; ora

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