Time and Displacement
New Senior Secondary Mastering Biology Chapter 3
Suggested answers to Exercise and Reading to learn p.2/5
Suggested answers to Exercise and Reading to learn
(Note: The overseas examination boards bear no responsibility for the suggested answers contained in this publication. Answers for HKCEE and HKALE questions are not available due to copyright restrictions.)
Ch 3 Movement of substances across cell membrane
Exercise
Multiple-choice questions (p. 3-25)
1 D / 2 D / 3 B / 4 B5 D / 6 B / 7 B / 8 A
9 C / 10 A / 11 C
Short questions (p. 3-27)
12 HKALE Biology 2006 I Q9
13 a Passive / do not require energy or ATP 1m
Movement down a concentration gradient / by diffusion 1m
b Active transport 1m
It occurs only when oxygen is present because energy / respiration is required. 0.5m
There is no uptake in curve Z. 0.5m
c The concentration inside cells is higher than surrounding solution. 1m
d Diffusion is proportional to the concentration gradient. 1m
14 Water has a higher water potential than the cell contents. It moves across the differentially permeable membrane into the cells by osmosis. 1m
As the cell membranes of red blood cells are thin and not surrounded by cell walls, the cells burst when more and more water enters. Therefore no blood cells can be observed under the microscope. 2m
15 a Distilled water has a higher water potential than potato. 0.5m
Therefore in distilled water, water moves into potato by osmosis. 1m
Concentrated sugar solution has a lower water potential than potato. 0.5m
Therefore in concentrated sugar solution, water moves out of potato. 1m
Potato in distilled water becomes heavier than the one in concentrated sugar solution. 1m
b Any two from: 1m x 2
The vacuoles of the cells in distilled water are bigger than the ones in sugar solution.
1m
The cell membranes are pulled away from the cell walls in the cells in sugar solution / cells in sugar become flaccid / cells become plasmolysed. 1m
Contents of the cells push against the cell walls in the cells in distilled water / cells in distilled water become turgid. 1m
16 HKALE Biology 1998 I Q4
17 a III should show two arms of membrane surrounding particle and meeting / almost meeting. 1m
IV should show restored membrane surface and vesicle enclosed in cell. 1m
Label ‘vesicle’ vacuole OR cell membrane 1m
b Surface area is reduced. 1m
c Phagocytosis 1m
Structured questions (p. 3-29)
18 a i A — glycoprotein 1m
B — phospholipid 1m
ii Cell recognition / cell attachment / receptor / antigen 1m
iii Fatty acids / tails are water-repelling / non-polar 0.5m
Fatty acids are in the middle of the bilayer 0.5m
Phosphate / heads are water-loving / polar 0.5m
Phosphate groups are on the outside of the bilayer 0.5m
Cytoplasm / tissue fluid are polar in nature 1m
b The membrane is fluid in nature. 0.5m
Phospholipids / B are able to move (within membrane). 0.5m
Proteins can move (within membrane / phospholipid bilayer). 0.5m
Therefore the proteins will have a new rearrangement in the fused cell. 0.5m
19 HKCEE Biology 2003 I Q1b
20 a 8.2 - 12.0 1m
= –3.8 1m
b concentrated sugar solution beaker C
dilute sugar solution beaker A
water beaker B (2m for all 3 correct, 1m for 2 correct)
c The water potential of the water in beaker is higher than that of the dilute sugar solution inside the bag. 0.5m
Water moves into the bag 0.5m
by osmosis 0.5m
through the differentially permeable membrane of the Visking tubing bag. 0.5m
d The water potential inside the bag and in the beaker is the same. 0.5m
No net water movement into or out of the tubing. 0.5m
e Differentially permeable 1m
Osmosis took place. 1m
21 a In test tube A, distilled water had a higher water potential than the red blood cells.
1m
Water entered red blood cells by osmosis. 1m
All red blood cells burst and haemoglobin was released into the water. 1m
In test tube C, concentrated saline had a lower water potential than the red blood cells. 1m
Water did not enter the cells and they did not burst. 1m
b Dilute saline had a higher water potential than some of the red blood cells. 0.5m
Water entered these red blood cells by osmosis. 0.5m
Since only some red blood cells burst, a smaller amount of haemoglobin was released. 1m
c I would take some fluid from tube A and some solid matter from the bottom of tube B and observe them under a microscope. 1m
The fluid from tube A should contain no intact cells while the solid matter from tube B should contain some. 1m
d Sea water has a lower water potential than that of the cytoplasm. 1m
Too much water may leave the cells and the animals die. 1m
22 a i Axes labelled plus units 1m
Suitable scale 1m
Points plotted accurately 1m
Line drawn without extrapolation 1m
(Deduct 2m if axes are wrongly used)
ii 0.3 M 1m
iii Water potential outside the cells is the same as inside / no water potential gradient / isotonic 1m
No net movement of water into and out of the cells 1m
by osmosis. 1m
b i Active transport requires energy 0.5m
produced from respiration. 0.5m
The activity of enzymes involved in respiration is affected by temperature.
0.5m
Cyanide also stops respiration / inhibits enzyme activity. 0.5m
The graph shows that the rate of potassium ion uptake decreases when temperature is lowered or cyanide is added. This shows that the root hairs take up the ions most likely by active transport. 1m
ii Diffusion continues / not affected by cyanide / not an active process 1m
Essays (p. 3-31)
23 a The structure of the cell membrane can be explained by the fluid mosaic model.
0.5m
The cell membrane is mainly made up of phospholipids and proteins. 1m
The phospholipid molecules are arranged in a bilayer. 0.5m
Their water-loving heads face the water based environment inside and outside of the cell. 0.5m
Some protein molecules embed half-way through the phospholipid bilayer, 0.5m
while some penetrate through the bilayer. 0.5m
Some proteins have carbohydrates molecules attached to their surface for recognition purposes. 0.5m
b Lipid-soluble molecules can pass through the phospholipid bilayer by diffusion.
1m
Small molecules like oxygen and carbon dioxide can also diffuse through the bilayer freely. 1m
Water molecules enter the cell by osmosis through channel protein. 1m
Proteins can also act as carriers, 1m
which pick up molecules on one side of the membrane and release them on the other side. 1m
This happens during active transport that requires energy. 1m
24 Osmosis is the net movement of water molecules 2m
from a region of high water potential to a region of low water potential 1m
across a differentially membrane. 1m
It is important to living organisms in many ways. For example,
it gives turgidity and support to plant cells;
it plays an important role in the relationship between plasma and tissue fluid;
it is important in the process of reabsorption taken place in the kidney;
it takes place in the absorption in gut;
it is important for the movement of water from soil to leaves in plants.
(any 3 importance; 2m each)
Reading to learn (p. 3-32)
1 The water potential of distilled water is higher than that of normal cells or the contact lens. 0.5m
When it is in contact with the cells or the contact lens, water enters the cells or the contact lens by osmosis which may cause damage to them. 0.5m
Since normal saline is isotonic to the cells or the contact lens, 0.5m
no osmosis occurs and the cells or the contact lens would not be damaged. 0.5m
2 Patients who cannot take fluids orally and have developed or are in danger of developing dehydration. 1m
This helps to maintain the normal blood circulation of the patients. 1m
3 If the normal saline is hypotonic or hypertonic to the body cells, water will enter or leave the cells by osmosis when it is in contact with the cells. 2m
As a result, the cells burst or shrink. This highly affects the normal functioning of the cells. 1m
ã Oxford University Press 2009