The big idea: Whales, dolphins and seals are mammals that returned to the sea. Their bodies are adapted to swim fast while still breathing air.
The points to remember
- Streamlined: a smooth, torpedo-shaped body; no hind limbs, ear flaps or fur: less drag.
- Flippers: front limbs flattened into paddles, with hand bones inside, for steering.
- Fluke: a flat, horizontal tail beaten up and down by back muscles to drive forward.
- Blowhole: the nostril on top of the head, so breathing needs only a brief surfacing.
- Periodic breathing: a flap seals the blowhole on a dive; at the surface a quick breath out and in.
| Dolphin (mammal) | Shark (fish) | |
|---|---|---|
| Tail | Horizontal fluke, beaten up and down | Vertical fin, swept side to side |
| Breathing | Air, through a blowhole, at the surface | Water, over gills, all the time |
| Front limbs | Flippers containing hand bones | Fins supported by rays |
Remember it as: Smooth body, paddle arms, up-down tail, nose on top.
Real example: the sperm whale. It can stay under water for over an hour on one breath while it hunts squid in the deep ocean, then surfaces to breathe through its blowhole.
Trap: A whale's tail moves up and down, a fish's tail side to side. And whales breathe air: they have lungs, not gills.
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How it is asked: Expect 'outline the adaptations of a named marine mammal for swimming', or a comparison of its tail with a fish's.
IB-style questionOutline[3 marks]
Outline how a humpback whale is adapted for swimming.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.