# Explain how countercurrent heat exchange in the flippers of marine mammals such as dolphins reduces heat loss to the surrounding water.

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

> Marine mammals maintain a constant core body temperature despite living in cold ocean water. Their flippers, which lack significant insulating blubber, contain a specialised arrangement of blood vessels that helps conserve body heat.

## Mark scheme (4 marks)

1. Arteries carrying warm blood from the core run alongside veins returning cold blood from the flipper surface
2. Heat transfers from the warmer arterial blood to the cooler venous blood across the vessel walls, down a temperature gradient
3. Because blood flows in opposite directions, a temperature gradient is maintained along the entire length of the exchanger, maximising heat transfer
4. Venous blood is pre-warmed before returning to the core, so less metabolic energy is needed to maintain core temperature, reducing overall heat loss

## Key terms

- [countercurrent heat exchange](https://www.gradenine.co.uk/glossary/countercurrent-heat-exchange)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-countercurrent-heat-exchange-in-ed5acf74) · Published by Druglandscape Ltd.