Download Answers for extension worksheet – Chapter 6

Cambridge Biology for the IB Diploma
Answers for extension worksheet – Chapter 6
1
a
(6)
Function
2
3
Stomach
Small intestine
Large intestine
physical digestion –
mixing with protease
and hydrochloric acid
digestion and
absorption
reabsorption of water
and storage of faeces
b
any two points from:
capillaries absorb nutrients from the villi;
the blood flowing through the capillaries maintains a concentration gradient so nutrients
can be absorbed by diffusion;
the thin walls of capillaries reduce the diffusion distance to a minimum
(2)
a
Tendons must be strong and non-elastic to withstand the pressure of blood, which might
otherwise ‘invert’ the valve and allow blood to flow in the wrong direction.
(2)
b
Blood pressure in the atria increases during atrial systole.
(1)
c
It prevents blood flowing backwards into the veins.
(1)
d
i
Blood pressure is affected by gravity. Pressure in lower parts of the body increases
and pressure in higher parts decreases when a person stands up.
(2)
ii
Blood that flows to the head and feet is affected by friction in the blood vessels,
which causes a reduction in its pressure.
(2)
iii
Membranes enclose the chemicals and ensure they are present at a sufficiently
high concentration. Reactants are kept in close proximity to the enzymes that
catalyse reactions.
(2)
a
New drugs are expensive and may be unaffordable in less-developed countries. There are
fewer medical facilities to administer drugs in less-developed countries (or similar
statements).
(2)
b
either of the following:
T-cells form an important part of the immune response – as numbers of T-cells decline, a
person cannot fight off opportunistic infections;
T-cells activate B-cells, which produce antibodies – without antibodies it is not possible
to resist infections adequately.
(2)
c
any four points from:
antibiotics interfere with metabolic processes in prokaryotic cells;
some work at specific times in the lifecycle of a bacterium;
symptoms may disappear as the numbers of live bacteria fall;
if antibiotics are not completed, these live organisms can reproduce again;
the last bacteria to be killed may be more resistant to the antibiotic so not completing the
course may lead to a build-up of antibiotic-resistant organisms
(4)
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Cambridge Biology for the IB Diploma
4
5
a
Atmospheric air contains about 20% oxygen. In the alveoli, oxygen is removed
and exchanged for carbon dioxide so the percentage falls to 13.5%. However, as
this air is exhaled it mixes with some air in the bronchi and trachea which is
higher in oxygen, and so the final percentage in expired air increases to 14.9%.
(3)
b
Water vapour is a product of respiration and the alveoli are lined with aqueous surfactant
so the percentage in expired air is greater than in inspired air.
(2)
c
Expired air will be warmer than inspired air as heat lost from the pulmonary circulation
raises the temperature of the air in the alveoli.
(2)
a
Ca2+ ions enter the synaptic knob
→ neurotransmitter diffuses across the synaptic cleft
→ neurotransmitter binds to receptors on post-synaptic membrane
→ ion channels open
→ action potential is generated
→ neurotransmitter is deactivated and reabsorbed
b
i
(5)
Myelinated neurons conduct impulses faster than non-myelinated neurons of the
same diameter.
(1)
Thicker unmyelinated neurons conduct impulses faster than thinner ones.
(1)
Mammalian axons that are myelinated conduct impulses faster than those of squid
or frogs.
(1)
ii
6
Mammals have a fast metabolic rate and have more energy to conduct impulses
more quickly.
Resistance to the flow of an impulse is lower in a thicker axon.
Myelinated neurons enable impulses to ‘jump’ between sections of myelin,
making transmission faster.
(3)
a
Ovulation follows a peak in the level of estrogen and of FSH.
(2)
b
ovary, oviduct, uterus, cervix, vagina
(2)
c
LH and FSH stimulate the development of follicles in the ovary. LH stimulates the
oocyte to resume meiosis and the growth of the follicle, and also stimulates the
formation of the corpus luteum, which produces progesterone to sustain a pregnancy.
Higher levels of LH and FSH stimulate the ovaries to produce several oocytes, which
can be collected.
(3)
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