A-LevelBiologyEnergy and respiration9700/42 · Feb/Mar 2023 · Q69 Marks

(a) Fig. 6.1 is a diagram of a section through a mitochondrion. [Figure 6.1]

(a)(i)The four arrows, A, B, C and D, show the movement of molecules and ions. Use the letters to identify all the arrows (one or more) that show: active transport of protons[1]
(a)(ii)diffusion of carbon dioxide.[1]
(b)Outline the role of the mitochondrial matrix in respiration.[3]
(c)Explain how a lack of oxygen affects oxidative phosphorylation.[4]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

[1] (a)(i) D ;
[1] (a)(ii) D and C ;
[3] (b) any three from:
[3] (b) 1 site of, link reaction / Krebs cycle;
[3] (b) 2 DNA / ribosomes, for production of proteins (used in respiration);
[3] (b) 3 named example ; e.g. enzymes / coenzymes / electron carriers ;
[3] (b) 4 production of, reduced FAD / reduced NAD, for oxidative phosphorylation ;
[3] (b) 5 substrate-linked phosphorylation ;
[4] (c) any four from:
[4] (c) process, stops/decreases, because:
[4] (c) 1 no/fewer, electrons accepted by oxygen or oxygen is the final electron acceptor;
[4] (c) 2 no/fewer, electrons, enter / move along, electron transport chain / ETC or ETC stops;
[4] (c) 3 no /fewer, H+ pumped into intermembrane space or no/less steep, proton gradient ;
[4] (c) 4 no/less, chemiosmosis ;
[4] (c) 5 reduced NAD / reduced FAD, not oxidised / or NAD/FAD, not recycled;
[4] (c) 6 no/less, ATP produced ;
[4] (c) 7 AVP; e.g. no/less, pyruvate enters mitochondrion.

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