A-LevelBiologyEnergy and respiration9700/43 · May/June 2024 · Q89 Marks

(a) Fig. 8.1 is a diagram of a mitochondrion. [Figure 8.1]

(a)Outline the roles played by the mitochondrial membranes in respiration.[4]
(b)(i)The shapes and numbers of mitochondria are continually changing due to fission. Fission occurs when one mitochondrion splits to form two mitochondria. Suggest reasons why mitochondria carry out fission.[2]
(b)(ii)Guanosine triphosphate (GTP) is a molecule that is used as a source of energy in some reactions, instead of ATP. Guanosine is composed of a purine, similar to adenine, and ribose. Suggest why GTP can be a suitable source of energy in some reactions.[1]
(c)Old or damaged mitochondria reduce the ability of a cell to carry out aerobic respiration and produce the ATP needed for the metabolic processes of the cell. Suggest what occurs to these mitochondria to allow the cell to maintain the same overall rate of respiration and ATP production.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[4] any four from:
[4] outer/inner membranes 1 allow entry of, oxygen for oxidative phosphorylation / pyruvate for link reaction; I Krebs cycle
[4] 2 allow exit of carbon dioxide from, Krebs cycle / link reaction ;
[4] 3 compartmentalisation / described ;
[4] inner membrane 4 (location of) ETC to release energy to pump protons into intermembrane space ;
[4] 5 (location of) ATP synthase for production of ATP ;
[4] 6 cristae / infoldings, to increase surface area for many, ETCs / ATP synthases ;
[4] 7 impermeable to, hydrogen ions / protons, to maintain proton gradient or impermeable to, hydrogen ions / protons, to maintain, high H+ concentration in intermembrane space ;
[4] 8 site of, oxidative phosphorylation / chemiosmosis ;
[2] any two from:
[2] 1 ref. to cells, metabolic rate / energy needs;
[2] 2 in cells about to undergo, mitosis / cell division ;
[2] 3 AVP; e.g. to replace damaged mitochondria
[1] hydrolysed / bond broken, (to release energy) or G proteins bind to GTP rather than to ATP ;
[2] 1 degraded / broken down by, lysosomes / hydrolytic enzymes ;
[2] 2 components of breakdown / AW, used to produce new mitochondria ;

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.