SKEMA JAWAPAN
MARKING SCHEME MODUL 2MOVEMENT OF SUBSTANCES ACROSS THE PLASMA
MEMBRANESECTION A:Objective Question:
1B
2D
3B
4A
5D
6C
7B
8D
9B
10B
11C
12B
13C14C15A16D17A18D19B20A
SECTION B: Structured questions
1(a)
(b) (i) 0.25 M
(ii) Isotonic solution(c) More than 6%
(d) (i) Plasmolysis//osmosis(ii) 0.5 M sucrose solution is
hypertonic compared to the cell sap of a potato.
Due to this, the water molecules from the potato cell diffuse
out by osmosis.
(e)(i) turgid
(ii) 0.1 M sucrose solution is hypotonic compared with the cell
sap of a potato.
Due to this, the water molecules diffuse into the potato cell
and cause it to
become turgid.
2. (a) P: hydrophilic head Q: hydrophobic tail
R: pore protein
S: carrier protein
(b) A semi-permeable plasma membrane allows only certain
substances to move freely across it while others cannot do so.
(c)
StructureMoleculeHow the molecule moves across
QLipid-soluble molecule such as glycerolSimple diffusion
RIonFacilitated diffusion
SGlucoseFacilitated diffusion
(d) -The glucose molecule moves towards the binding site of the
specific carrier protein
-The molecule binds to a specific site on the carrier
protein
-The carrier protein changes its shape to transport the molecule
across the plasma membrane
-The carrier protein assumes its original shape and is free to
assist the passage of other glucose molecules into the cell.
(e) -The addition of preservatives such as concentrated sugar
solution makes the surrounding solution hypertonic.
-The hypertonic solution causes water to leave the food by
osmosis and the preservatives to enter the food.
-The dehydrated condition of the food as well the presence of
preservatives prevent the grouth of bacteria and fungi.
3 (a) Mixture of starch suspension and glucose solution
(b) Iodine molecules diffuse into the Visking tubing and react
with the starch in
solution X to give a blue black colour.
(c) (i) A brick-red precipitate is formed
(ii) The brick-red precipitated shows that glucose molecules are
present in the
beaker. The glucose molecules are small enough to diffuse
through the
membrane of the Visking tubing to the surrounding distilled
water.
(d) (i) The Visking tubing swells and become firm.
(ii) Since the concentration of solution X inside the Visking
tubing is higher, water
enters the Visking tubing by osmosis and caused the tubing to
swell and
become firm.SECTION C:Essay question
1(a)- Distilled water is hypotonic to the cytoplasm of red blood
cells and the cell sap
of the onion cells.(1m)
- Osmosis occurs, resulting in a net flow of water from the
surrounding into the
cell.(1m)
- The red blood cells will swell and eventually burst (1m) - The
vacuoles in the onion cells expand, and the plant cells become
turgid (1m)
- However, the cell wall prevents the onion cells from bursting
because it is tough
and rigid (1m)
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5m
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(b)(i) -Vegetables which are soaked too long in a salt solution
will become soft because
the salt solution is more hypertonic than the cytoplasm of the
vegetable cells
(1m)
-Water flow out of the cells, causing the cytoplasm and the
vacuoles to shrink
(1m).
-The plasma membranes pull away from the cell walls (1m)
-In this condition, the cells are said to be plasmolysed
(1m)
(ii) To make the vegetables crisp again, housewives can soak the
vegetables in
water (1m) ------
5m
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(c) (i) Transport of amino acids across the plasma membrane:
-Amino acids move across the plasma membrane through
facilitated diffusion.(1m)
-Amino acids are transported from a region of higher
concentration to a region of
lower concentration with the help of carrier proteins(1m) -One
of the amino acids moves towards the active site of a specific
carrier
protein and binds to it (1m)
-The carrier protein changes its shape to transport the amino
acids across the
plasma membrane (1m).
-The carrier protein assumes its original shape and is free to
assist the passage
of other amino acids molecules into the cell (1m)
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5m
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(ii) Transport of sodium ions across the plasma membrane :
-The transport of sodium ions across the plasma membrane is by
meant of active
transport (1m)
-The concentration of sodium ions is higher outside the cell.
Sodium ions are
transported against a concentration gradient, from a region of
lower
concentration to a region of higher concentration (1m) -In
active transport, sodium ions approach the carrier protein. Each
carrier
protein has a site for binding of three sodium ions at one time
and another site
for ATP (1m)
-The ATP molecules is split into ADP (Adenosine diphosphate) and
P
(phosphate). The phosphate group (P) attaches itself to the
carrier protein. The
spliting of ATP releases energy to the carrier protein (1m)
-Energy from the ATP changes the shape of the carrier protein
and this causes
the carrier protein to release the three sodium ions ooutside
the cell (1m).
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5m
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