Cambridge International A Level Biology Revision Guide

Chapter 15: Coordination
9 A biopsy was taken from a leg muscle of a healthy racehorse. The muscle fibres were teased apart and
cross-sections were taken from one of the muscle fibres. These cross-sections were examined with a transmission
electron microscope. The figure shows drawings made from three different cross-sections of a myofibril from
the muscle fibre.
X Y Z
a Explain the differences between the sections X, Y and Z. You may draw a labelled diagram to illustrate your answer. [4]
b The sections were taken from a relaxed muscle fibre. Suggest how the sections would appear if taken from a fibre
that had contracted to its maximum extent. Explain your answer. [3]
c Muscle weakness in racehorses may sometimes be related to a deficiency of calcium.
Outline the roles of calcium ions in the coordination of muscle contraction. [6]
[Total: 13]
10 Copy and complete the table to show, for each hormone, the precise site of its secretion, and its effects on the ovary or
on the endometrium of the uterus.
Hormone
FSH
LH
oestrogen
progesterone
Site of secretion
Effect(s) of hormone
ovary
endometrium
none
none
none
none
[8]
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11 The Pacinian corpuscle is a type of receptor found in the dermis of the skin. Pacinian corpuscles contain an ending of a
sensory neurone, surrounded by several layers of connective tissue called a capsule. The activity of a Pacinian corpuscle
was investigated by inserting microelectrodes into the axon at the positions shown in the diagram below.
microelectrode A
microelectrode B
pressure
(stimulus)
capsule containing
many collagen fibres
endings of sensory
neurone
unmyelinated
axon