2015年12月13日 星期日

F4 Biology WS 06 ans

3 Movement of substances across cell membrane II
WS 06
Suggested Answers
Textbook exercise
M.C.       
9
10
11
C
D
C
(3 marks)
Q. 16                                                                                                                                      
(a)    (i)     Glucose and galactose                                                                                                           1
        (ii)    The rates of absorption of these two sugars were reduced in the presence of cyanide.        1
                This is because active transport needs energy.                                                                      1
                Less / no energy is released if cyanide is present.                                                                 1
(b)    All the sugars named in the table can be absorbed when the gut is poisoned by cyanide.           1
        Diffusion does not need an energy supply.                                                                                   1

Q.22
(a)    Molecules have kinetic energy. /
        They are moving randomly. /
        The net movement of the molecules is down the concentration gradient. (any 2)                  1 x 2
(b)    At the beginning there is a concentration gradient. /
        As concentration of substance A outside the membrane decreases, its concentration inside the membrane increases. /
        Substance A moves from the outside to the inside of the membrane. /
        As concentration gradient becomes smaller, the rate of change decreases. /
        When the concentrations of substance A are the same on both sides, there is no change in the concentrations of substance A on both sides. (any 3)                                                                                          1 x 3
(c)    (i)     Active transport requires energy while diffusion does not. /
                Molecules can move against a concentration gradient in active transport, while molecules can only move down the concentration gradient in diffusion. /
                Active transport involves membrane proteins while diffusion may not. (any 2)
                                                                                                                                                         1 x 2
        (ii)    The rate of change would be almost constant. /
                The rate of change would be higher. /

                The movement of molecules would not stop after the concentrations on the two sides become the same. (any 2)                                                                                               1 x 2

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