2016年4月3日 星期日

F4 Biology 2nd Term WS 05 ans: 8 Transport in humans I

8    Transport in humans I
2nd Term WS 05

1     
(a)     P: blood platelet                                                                                                                      1m
It is involved in blood clotting.                                                                                                        1m
Q: red blood cell                                                                                                                      1m
It contains haemoglobin to carry oxygen.                                                                                        1m
R: white blood cell                                                                                                                   1m
It protects our body against diseases.                                                                                               1m

(b)    Plasma                                                                                                                                    1m

(c)    Red blood cells                                                                                                                                1m

2     
(a)     X: phagocyte                                                                                                                           1m
Y: red blood cell                                                                                                                      1m
Z: lymphocyte                                                                                                                         1m

(b)    Cell Y has a biconcave disc shape.                                                                                                 1m
There is less cytoplasm at the centre and thus fewer haemoglobin molecules.                                1m

(c)     Its biconcave disc shape increases the surface area to volume ratio.                                              1m
This allows oxygen to diffuse in and out of the cells more efficiently.                                           
/ This provides a short distance for oxygen to reach and leave the haemoglobin in the cell rapidly. 1m
OR
It has no nucleus when mature.                                                                                                       1m
This provides more room for holding haemoglobin.                                                                       
/ It is fully packed with haemoglobin which is an excellent oxygen carrier.                                    1m

(d)   

X
Z
Shape of the nucleus
Lobed
Round
Role in body defence       
It engulfs germs by phagocytosis.
It produces antibodies to kill germs.

                                                                                                                                        1m x 4

3
(a)   (i)      Vein                                                                                                                                 1m
       (ii)     Artery                                                                                                                              1m

(b)   The blood pressure in Y is higher than that in X.                                                                              1m
The blood pressure in Y is high due to the pumping action of the heart.                                         1m
The blood pressure in X is low as the blood has overcome great resistance
of the blood vessel walls after travelling for a long distance.                                                           1m

(c)   X has a larger lumen                                                                                                                 1m
to reduce the resistance to blood flow.                                                                                             1m
Y has a thicker wall,                                                                                                                        1m

which allows it to withstand high blood pressure.                                                                   1m


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