8 Transport in humans II
2nd Term WS 06
(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.
This makes the blood flow faster despite its low pressure.
(c) The slow blood flow allows more time for exchange of materials between blood and body cells.
(a) X: right atrium
Z: pulmonary artery
(b) The left ventricle has to provide a greater force
to create a higher pressure
to pump blood to all parts of the body (except the lungs).
(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
(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
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