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Movement on Land

The diagram shows the muscles in one of the joints in the leg of a crab. Study the diagram and answer the questions which follow.

Crab limb

Questions	Answers
(a) What is the label M pointing to?
(b) Which of the muscles N and O is contracted and which is relaxed?
(c) What happens to the muscles when the leg is straightened?
(d) Give one advantage to the crab of having an external skeleton.
(e) (i) Give one disadvantage of having an external skeleton. (ii) How do animals such as the crab overcome this disadvantage.

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