Marking Scheme
Section A (Multiple Choice) (30 marks)
1
2
3
4
5
1-10
B
A
D
B
D
11-20 D
B
D
C
B
21-30 B
D
B
A
A
6
C
A
B
7
C
C
C
8
A
B
A
9
C
C
D
10
D
B
B
Section B (Structured Questions) (60 marks)
1.
(a) The cell wall is drawn inside the cell membrane but the cell wall should be the outermost
layer of a plant cell. (1)
Mitochondria cannot be seen under a light microscope. (1)
Too many nuclei are drawn but there should be one only. (1)
Plant cells do not have glycogen granules but starch granules. (1)
(b) Cell membrane (1)
Controls the movement of materials into and out of the cells / encloses the cytoplasm (1)
Cytoplasm (1)
Holds small organelles / provides a medium for cellular chemical reactions to take place (1)
(c) Cell wall, large vacuole, chloroplast (any 2) @1 (1) x2 = (2)
Total: 10 marks
2.
(a)
(i) Q (1)
(ii) T (1)
(b) Fluid: The phospholipid molecules and some protein molecules can move laterally. (1)
Mosaic: Different kinds of protein molecules are interspersed among the phospholipid
molecules in a mosaic pattern. (1)
(c) The curve rises slowly at the beginning. (1)
Then it rises sharply and later levels off. (1)
The rate of diffusion increases as the molecules move faster at higher temperatures. (1)
At about 45oC, the sharp rise of the curve is due to the breakdown of the cell membrane. (1)
The curve levels off when the concentration of chloride ions inside the cell is the same as that
outside. (1)
Total: 9 marks
3.
(a) There is a net movement of water into the cells (1)
from a salt solution of higher water potential (1)
through the differentially permeable membrane (1)
by osmosis. (1)
(b)
(i) Differentially permeable membrane / cell membrane (1)
(ii) The solution in boiling tube / salt solution Q (1)
(c)
(i) There is no net water movement into and out of the membrane. / water level remain
unchanged (1)
(ii) The level would move up. (1)
(d) They would lose water by osmosis. (1)
Total: 9 marks
4.
(a)
(i) 12 cm3 O2 min-1 (1)
(ii) Increase of 11.75 cm3 O2 min-1 or 48 times (1)
(b)
(i) Concentration of enzyme (1)
(ii) Concentration of substrate (1)
(c)
(i) A new curve is drawn roughly lower than the original curve and is of the similar shape as
the original curve. (1)
(d)
(e)
(f)
(g)
(ii) Inhibitor of low concentration alters the shape of some of the enzyme molecules,
rendering them non-functional / lowers the number of active sites. (1)
(iii) Non-competitive because inhibitor molecules do not compete with the substrate for active
site. (1)
The inhibitor attaches elsewhere on the enzyme, distorting the active site. (1)
To break tissue / cell walls to release the enzyme. / To increase the surface area for substrate
contact. (1)
The pH changes may otherwise occur during the experiment. (1)
The pH changes alter the shape of the protein and affect the efficiency of the active sites. (1)
Reaction may take up or produce heat, causing changes in rate. / To avoid fluctuations in
external temperature. (1)
Denaturation / breakdown of active site. (1)
Total: 13 marks
5.
(a) X: cane; Y: milk; Z: rice @(1) x3 = (3)
(b) Test for proteins:
Dip the test end of Albustix paper into the sample and observe any colour changes. (1)
The test end changes from yellow to green if proteins are present. (1)
Test for starch:
Put the sample into a test tube and add a few drops of iodine solution to the sample. (1)
It changes from brown to blue-black if starch is present. (1)
(c) Sample Y / milk (1)
It is rich in calcium. Calcium is important for healthy bones and teeth. (1)
Total: 9 marks
6. Water is essential to life, though it carries no energy value. It has the following important
functions.
Water acts as a solvent (1) in our body. It dissolves many chemical substances (1) which are
important in basic body activities. For example, the cytoplasm (1) contains many dissolved
chemicals. Many secretions such as digestive juices (1) consist of substances dissolved in water
too.
Water also provides the medium for chemical reactions (1) to take place. All reactions occur in
an aqueous medium: the molecules must interact with water to some extent and collide in the
water medium (1) for reactions to take place, such as various chemical reactions in cytoplasm.
In addition, water is a transport medium. (1) It transports substances such as glucose, amino acids,
minerals and hormones in blood. (1)
Water is also a cooling agent (1) which helps to regulate body temperature. For example,
sweating (1) brings cooling effect through evaporation of water. (1)
Besides, water can be a reactant itself. (1) It is a raw material in some metabolic reactions. For
example, it is used to hydrolyse polymers of macromolecules into their respective monomers, such
as the hydrolysis of starch into glucose. (1)
Water is also used to provide turgidity for support purpose, (1) such as the aqueous and vitreous
humours of the eye. (1)
As water is so important to our body, we need about eight glasses of water daily to keep ourselves
healthy.
content : (7)
style : (3)
This Question: 10 marks