Cambridge International A Level Biology Revision Guide

Cambridge International A Level Biology
Answers to end-of-chapter questions
calcium ions bind to troponin;
stimulates movement of tropomyosin;
myosin binding sites on thin filaments exposed;
cross-bridges form;
when no action potential calcium ions
pumped back into sarcoplasmic reticulum;
[max. 6]
[Total: 13]
10
Hormone
FSH
LH
oestrogen
progesterone
Site of
secretion
anterior
pituitary
gland;
anterior
pituitary
gland;
ovarian
follicle
cells;
corpus
luteum in
ovary;
Effect(s) of hormone
ovary
stimulates
secretion of
oestrogen from
follicle cells;
stimulates
ovulation /
stimulates
secretion of
progesterone
from corpus
luteum;
none
none
endometrium
none
none
thickens
endometrium
/ develops
blood vessels in
endometrium;
maintains
thickness of
endometrium
/ stimulates
development
of glands in
endometrium;
[Total: 8]
11a ref to generator / receptor potential;
pressure / stimulus, causes deformation / AW
(of Pacinian corpuscle);
increased permeability to sodium ions /
sodium channels open;
sodium (ions) move into, receptor / axon;
causes depolarisation / AW (e.g. potential
difference changes from –ve to +ve; [max. 4]
b No action potential recorded with low and
medium pressure / action potential recorded
only with high pressure;
(no action potential at B because)
depolarisation of, receptor / unmyelinated
part of axon, did not reach threshold;
threshold is between medium and high
pressure;
threshold is between –40 mV to –30 mV;
more depolarisation at higher pressure
because more sodium ion voltage-gated
channels open;
sensory neurone either conducts impulses or
it does not / ref to all-or-none principle;
[max. 4]
c myelinated neurones transmit impulses
much faster than unmyelinated neurones;
any suitable figures, e.g. up to 100 m s −1 for
myelinated and 0.5 m s −1 for unmyelinated;
stimulation of Pacinian corpuscle might
indicate damage to the skin;
may need to remove the part of the body
from danger very quickly;
ref to a reflex arc in which Pacinian corpuscle
provides the sensory input; [max. 3]
[Total: 11]
12a gibberellin secreted by embryo;
stimulates cells in the aleurone layer;
stimulates protein synthesis;
to make amylase;
to break down starch in the endosperm;
mobilises glucose;
for respiration;
to provide energy for germination; [max. 5]
b gibberellin increases the mean length of the
stem in the short-stemmed varieties of all
species;
figures for any one species;
increase is significant in all but one species;
gibberellin increases the mean length of the
stem in the long-stemmed varieties of four of
the species;
not tomato;
increases are not significant; [max. 5]
c short-stemmed plants do not make (much)
gibberellin;
(because) they do not have the allele for the
enzyme that makes gibberellin;
long-stemmed variety has dominant allele
for gibberellin synthesis;
Cambridge International AS and A Level Biology © Cambridge University Press 2014