Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
7 The electron micrograph shows parts of some myofibrils in a striated muscle that is in a relaxed state.
K
L
M
360
a i Name the parts labelled K, L and M. [3]
ii How many myofibrils are visible in the electron micrograph? Explain your answer. [2]
b i There are many glycogen granules and mitochondria visible in the electron micrograph. Explain why
they are both there. [2]
ii Describe how you can tell that this electron micrograph is from relaxed muscle and not
contracted muscle. [3]
c The electron micrograph is magnified 20 000 times. Calculate the actual length of the sarcomere
which includes the region labelled K. Give your answer in micrometres (μm). [2]
[Total: 12]
8 The diagrams show a sarcomere in different states of contraction.
A
C
P
B
Q
D
R
a Name the parts labelled P, Q and R. [3]
b Explain why there are no actin–myosin cross-bridges visible in diagram A. [2]
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. [4]
d Explain why the muscle shown in diagram D would not be able to contract any further. [1]
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. [2]
ii Suggest how the muscle in diagram D could be returned to the state shown in diagram A. [2]
[Total: 14]