Page 221 - SUBSEC October 2017_Neat

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02207020/CAPE/SPEC/KMS 2017
BIOLOGY
UNIT 1 – PAPER 02
KEY AND MARK SCHEME

Question 2 cont’d

Adaptations of blood vessels (7-8 marks)

● Arteries have thick walls with large amount of elastic tissue –
allows walls to withstand high pressure of blood from heart
● Small arteries and arterioles have large amount of smooth muscle
in walls – allows constriction, which can divert blood from one
area to another
● Smooth endothelium (inner lining) in blood vessels – allows free
blood flow (lower resistance); reduces the risk of blood clots
● Veins have relatively large lumen (low resistance) and valves (not
present in arteries) – valves allow one-way flow of blood to the
heart – necessary due to the low pressure of blood in veins
● Capillaries have very thin wall (one cell thick and flattened) and
tiny lumen diameter – allows rapid transfer of substances by
diffusion between blood and tissues / tiny lumen brings blood close
to tissues
● All organs have extensive network of capillaries – ensures that
interchange of substances occurs in all tissues.

Any 4 points well discussed – 2 marks each = 8 marks
(incomplete discussion – 1 mark each) 14 marks

Total 30 marks