# Explain how the physiology of a diving mammal, such as a Weddell seal, allows it to sustain aerobic respiration in the muscles during a prolonged dive.

> IB DP Biology Higher Level (2023 syllabus) — B4.1 Adaptation to environment · Explain · 4 marks

> Weddell seals (Leptonychotes weddellii) can dive to depths of over 600 m and remain submerged for more than 80 minutes without surfacing to breathe.

## Mark scheme (4 marks)

1. Diving mammals have a greatly elevated myoglobin concentration in skeletal muscle, which stores oxygen bound to myoglobin for use during the dive.
2. Myoglobin has a higher affinity for oxygen than haemoglobin, so it retains oxygen at the low partial pressures found in respiring muscle, only releasing it when oxygen tension is very low.
3. Diving mammals have a higher blood volume and/or elevated haemoglobin concentration / higher haematocrit compared with non-diving mammals, increasing the total oxygen carried in the blood.
4. Cardiovascular adjustments during diving (diving reflex) include bradycardia and peripheral vasoconstriction, which reduces oxygen delivery to non-essential organs and conserves the oxygen supply for the heart and brain, extending the time aerobic metabolism can be sustained in active muscles.

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