3 Movement of substances across cell membrane II
WS 06
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Answers
Textbook exercise
M.C.
9
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10
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11
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C
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D
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C
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(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
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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