8 Transport in humans II
2nd Term WS 06
1
(a) The blood flow rate decreases
with a decrease in blood pressure. 1m
(b) The contraction of skeletal muscles
lying next to the veins gives additional force
to drive the blood to flow. 1m
This makes the blood flow faster despite
its low pressure. 1m
(c) The
slow blood flow allows more time for exchange of materials between blood and
body cells. 1m
2
(a) X: right atrium 1m
Y: aorta 1m
Z: pulmonary artery 1m
(b) The left ventricle has to
provide a greater force 1m
to create a higher pressure 1m
to pump blood to all parts of the body
(except the lungs). 1m
(c) When the left ventricle
contracts, pressure in the ventricle becomes higher than that of atrium. 1m
The pressure difference pushes the valve to
shut. 1m
3
(a) W 1m
The muscles contract and relax to change
the size of the lumen, 1m
so that the amount of blood flow to
different parts of the body can be regulated. 1m
(b) X is highly branched. 1m
This provides a large surface area for
diffusion of materials. 1m
OR
X has a large total cross-sectional area. 1m
This allows blood to flow slowly and hence
more time for exchange of materials. 1m
(c) (i) Tissue fluid 1m
(ii) The pressure of blood in X near W
is higher than the pressure of the fluid
surrounding the body cells. 1m
This forces some
components of the plasma out of the capillary walls to form tissue fluid. 1m
(iii) Y / lymph
capillary → lymph vessel → (anterior) vena cava → heart 2m
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