The diagrams show a sarcomere in different states of contraction.

a. Name the parts labelled P, Q and R.

b. Explain why there are no actin–myosin cross-bridges visible in diagram A.

c. Muscle fibres are able to contract with more force in some states of contraction than others. Suggest which of the diagrams shows the state that can develop the greatest force, and explain the reasons for your answer.

d. Explain why the muscle shown in diagram D would not be able to contract any further.

e. A muscle can contract with force, but it cannot pull itself back to its original relaxed length.

i. With reference to the mechanism of muscle contraction, explain why this is so.

ii. Suggest how the muscle in diagram D could be returned to the state shown in diagram A.

Transcribed Image Text:

A B D