The grey seal, Halichoerus grypus, is an aquatic mammal that lives in the North Atlantic Ocean. It feeds on fish, which it hunts at depths of up to 70 metres. [Figure 10.1] shows a grey seal. Diving to hunt for fish has an effect on the respiration of the grey seal. A study was carried out to measure the blood lactate concentration of a grey seal before, during and after a dive in deep water.

Mark scheme

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

1. [4] (a) any four from: during – increase in lactate concentration 1 (initially) lactate concentration low due to aerobic respiration ; 2 no / less, oxygen available so (increase in) anaerobic respiration ; 3 pyruvate, reduced / converted, to lactate ; after - decrease in lactate concentration 4 (more) oxygen available so aerobic respiration occurs ; 5 lactate, oxidised / converted, to pyruvate ; 6 idea that lactate is processed by liver ; 7 AVP; e.g. ref. to oxygen debt / EPOC
2. [3] (b) any three from: 1 (captive) breeding programs / described / frozen zoos ; 2 marine reserves / protected areas; 3 ban on hunting / trade, (of seals); 4 ref. to education / awareness; 5 research; 6 reduce, ocean / sea, pollution / described ; 7 reduce fishing; 8 reduce climate change;