Moving is expensive. Every step costs ATP, and every animal on the move is one that could be resting instead. So there has to be a payoff — and the shape of an animal’s body usually tells you what that payoff is.
📘 What you need to know
Locomotion is the ability to move from one place to another.
Animals move for four main reasons: finding food, escaping danger, finding a mate, and migration.
You should be able to give a named animal for each reason.
Marine mammals are the example of adaptation for swimming.
Their key adaptations are a streamlined body, flippers for steering, no rear limbs, a tail fluke for propulsion, and a blowhole for breathing.
These animals evolved from land mammals, so their flippers are modified front limbs.
Why bother moving?
Locomotion matters to a huge range of organisms, and it is especially important in the animal kingdom. Almost every reason for it comes down to one of four things.
Reason
Named example
What is going on
Finding food
Guinea pig
Spends most of its waking hours on the move, searching out and grazing on plants.
Escaping danger
Jumping spider
Uses its legs to leap clear of a predator in a fraction of a second.
Finding a mate
Salmon
Adults swim from the open ocean back up freshwater rivers to breed.
Migration
Caribou
Travels thousands of kilometres a year between winter feeding grounds and the place it gives birth.
Pick one animal per reason and memorise those four. In the exam you will not have time to think of a good example from scratch, and a vague “some animals migrate” will not score.
Adaptations for swimming
Water is roughly 800 times denser than air. Push a hand through air and you barely feel it; push it through water and you feel every bit of the resistance. That resistance is drag, and for a swimming animal it is the main thing standing between it and its dinner.
So the biggest adaptation is about shape. A streamlined body lets water slide past instead of piling up and swirling, which means far less energy is wasted for the same speed.
Same water, same speed, completely different cost. This is why fast swimmers all end up roughly the same shape.
The marine mammal package
Dolphins and whales are mammals that evolved from ancestors living on land. Every one of the features below is a change from that land-living body plan.
Streamlined body — lets the animal move through dense water easily and at speed.
Front limbs became flippers — used mainly for steering, not for power.
Rear limbs lost altogether — anything sticking out would add drag, so losing them improves streamlining.
Tail became a fluke — it beats up and down and provides the propulsion.
Nostrils moved to a blowhole on top of the head — the animal can breathe between dives without lifting its whole head clear, and the blowhole seals shut underwater so water cannot get into the airways.
Flippers steer, the fluke powers. Mixing those two up is the easiest mark to lose on this diagram.
A detail worth having. A whale’s tail beats up and down, while a fish’s tail beats side to side. That is because the whale’s spine bends the same way a running land mammal’s does — the swimming stroke is a leftover from its ancestors.
Worked examples
WORKED EXAMPLE
State two reasons why animals move from place to place, giving a named example for each. [4]
Reason 1 with its exampleTo escape danger — a jumping spider leaps away from a predator.Reason 2 with its exampleTo find a mate — salmon swim from the ocean up rivers to breed.Two reasons, two named animals, two marks each“an animal” is not a named example. Say the species or the group.
WORKED EXAMPLE
Explain three ways a dolphin is adapted for swimming. [3]
Give the feature, then what it doesStreamlined body — reduces drag, so less energy is needed to move through dense water.Tail fluke — beats up and down to provide propulsion.Front limbs modified into flippers — used to steer and control direction.Each mark needs a feature plus its functiona list of body parts with no functions scores one mark at best.
WORKED EXAMPLE
Suggest why the loss of rear limbs is an advantage in a marine mammal. [2]
Think about what limbs would do in water
Rear legs would stick out into the flow and break up the smooth shape.
Now say the consequenceLosing them makes the body more streamlined, so drag is reduced.Less drag means less energy used for the same swimming speedfinish on the energy point — that is usually the second mark.
💡 Exam tip
Learn four reasons and four named animals. That covers almost any version of the question.
For adaptation questions, always pair a structure with its function. Never just list parts.
Use the word drag when you talk about streamlining. It shows you know why the shape matters.
Remember flippers steer and the fluke propels. They are not the same job.
Mention that marine mammals evolved from land mammals if a question asks about their limbs.
Locomotion is whole-body movement. Do not use the word for a wagging tail or a beating heart.
⚠ Common mix-up
Saying the flippers push the animal along. The fluke does the pushing; the flippers steer.
Calling a whale a fish. They are mammals — they breathe air, which is exactly why the blowhole exists.
Forgetting the blowhole seals. That is the point of it, and it is often the marking detail.
Naming a reason with no example. The question almost always wants both.
Treating streamlining as being about being slim. It is about the shape of the flow, not thinness.
Mixing up locomotion and movement. All locomotion is movement; not all movement is locomotion.
That is the full Muscle & Motility chain. Up next: Habitats — we leave the body behind and look at how organisms fit the places they live in.
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