A-LevelBiologyEnergy and respiration9700/43 · May/June 2025 · Q110 Marks

Fig. 1.1 is a diagram of part of a liver cell. [Figure 1.1]

(a)With reference to Fig. 1.1, name: the type of membrane transport protein represented by A.. process B area C..[3]
(b)The mitochondrial pyruvate carrier (MPC), shown in Fig. 1.1, allows the passage of pyruvate into the mitochondrial matrix. When pyruvate enters the mitochondrial matrix, it takes part in the link reaction. Describe the link reaction.[4]
(c)Some tumour cells have a greatly reduced ability to transport pyruvate into the matrix of the mitochondrion. Suggest how a reduction in pyruvate transport could affect respiration in these tumour cells.[3]

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Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[3] 1(a) A - GLUT/carrier; I channel B - glycolysis; C - intermembrane space; A intermembranal R inner membrane
[4] 1(b) any four from: 1 (pyruvate) decarboxylation / decarboxylase / carbon dioxide released ; 2 (pyruvate) dehydrogenation / dehydrogenase / oxidation ; 3 formation of, acetyl group / acetate; 4 reduced NAD produced / described; 5 acetyl group / acetate, combines with coenzyme A or formation of acetyl CoA;
[3] 1(c) any three from: 1 little / no, link reaction / Krebs cycle / oxidative phosphorylation ; 2 ATP, mostly / only, produced by, glycolysis / process B / substrate-linked phosphorylation ; 3 (so) less ATP produced; 4 anaerobic respiration / production of lactate ;

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