A-LevelBiologyEnergy and respiration9700/42 · Oct/Nov 2023 · Q19 Marks

Some organisms carry out respiration in anaerobic conditions when oxygen is not available or when there is a low concentration of oxygen. In yeast and some plants, this is called ethanol fermentation. In mammals, it is called lactate fermentation. Fig. 1.1 outlines ethanol fermentation and lactate fermentation. [Figure 1.1]

(a)Identify substances A–D.[3]
(b)Explain how processes such as ethanol fermentation and lactate fermentation allow cells to continue to function in the absence of oxygen.[3]
(c)The cereal crop rice, Oryza sativa, grows in fields that are flooded with water. The roots of the rice plants are submerged in water that contains very little oxygen. Describe and explain how rice plants are adapted to grow in flooded fields.[3]

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 (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] (a) A: carbon dioxide / CO2;
[1] (a) B: reduced NAD / NADH and C: NAD/NAD+;
[1] (a) D: ethanal;
[1] (b) (recycles / produces) NAD ; I ref. to reduced NAD produced ;
[1] (b) ref. to glycolysis ;
[1] (b) ref. to ATP (produced);
[1] (b) by substrate-linked phosphorylation ;
[1] (c) aerenchyma provides oxygen for aerobic respiration;
[1] (c) high concentration of ethanol dehydrogenase / high tolerance for ethanol, allows (higher rate of), ethanol fermentation / anaerobic respiration;
[1] (c) fast growth / grow tall, so leaves, out of water / exposed to air;
[1] (c) AVP; e.g. ridges in submerged leaves to trap air

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.