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New Senior Secondary Mastering Biology
Suggested answers to Exercise and Reading to learn
Chapter 9
p.1/3
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 9 Nutrition and gas exchange in plants
Exercise
Multiple-choice questions (p. 9-23)
1
5
9
C
D
A
2
6
10
B
C
A
3
7
C
C
4
8
D
D
Short questions (p. 9-25)
11
a
photosynthesis, autotrophs
0.5m x 2
b
Minerals, deficiency diseases
0.5m x 2
c
photosynthesis, respiration
0.5m x 2
d
Oxygen, carbon dioxide
0.5m x 2
e
compensation point, respiration
0.5m x 2
12
HKCEE Biology 2005 I Q8b
13
a
Any one from:
1m
Long
Thin cell wall
Lack of waterproof layer / cuticle
Large surface area
Present in large numbers
Membrane proteins / carriers / channels
Many mitochondria
b
Active transport / diffusion
c
The water potential of soil water is usually higher than that of the root cells.
1m
0.5m
Water moves down the water potential gradient into the root cells by osmosis 0.5m
through the channel proteins / differentially permeable cell membranes and
0.5m
the freely permeable cell walls.
0.5m
 Oxford University Press 2009
New Senior Secondary Mastering Biology
Suggested answers to Exercise and Reading to learn
14
a
D (mesophyll cell), E (air space) and F (guard cell)
Chapter 9
p.2/3
0.5m x 3
There are many air spaces to allow diffusion of gases on the moist surfaces
of mesophyll cells.
Guard cells control the opening of stomata, which allow diffusion of gases.
b
A (cuticle) and F (guard cell)
Cuticle is impermeable to water.
1m
0.5m
0.5m x 2
0.5m
Guard cells control the opening of stomata, which allow diffusion of
water vapour.
15
a
0.5m
Area of the field of view
= 0.1 mm (height)  (5.7 cm / 3.4 cm  0.1 mm) (length)
= 0.0168 mm2
1m
Stomatal density
= 4 stomata / 0.0168 mm2
b
16
a
 238 stomata per mm2 of the leaf surface
Sorghum grows in dry conditions.
1m
1m
It loses water through the stomata rapidly.
1m
Having few stomata can reduce water loss and hence conserve more water.
1m
To carry out photosynthesis.
1m
The cells locate near the top of the leaf so that they can trap the maximum amount of
light for photosynthesis.
1m
The cells are densely packed and contain many chloroplasts.
b
1m
Buoyancy
Storage of oxygen / carbon dioxide / gases
Allows rapid diffusion of gases
(any 2)
c
1m x 2
To enable exchange of gases.
1m
It would let in water if stomata are in lower epidermis.
1m
Structured questions (p. 9-26)
17
HKALE Biology 1998 I Q9a
18
HKCEE Biology 2004 I Q4c
19
HKCEE Biology 2005 I Q9
 Oxford University Press 2009
New Senior Secondary Mastering Biology
Suggested answers to Exercise and Reading to learn
Chapter 9
p.3/3
Essay (p. 9-27)
20
Plants need to obtain oxygen and carbon dioxide from the atmosphere for respiration and
photosynthesis respectively.
They also need to obtain water and minerals from the soil for the production of different
substances they need.
1m
Carbon dioxide and oxygen:
Plants exchange gases with the environment by diffusion. In terrestrial plants, gas exchange
takes place through leaves, stems and roots.
In leaves, gases from the environment diffuse into the air space through the stomata. Gases
dissolve in the moist surface of the mesophyll cells. They then diffuse to the neighbouring
cells.
1m
Gases diffuse from the leaves to the environment in the reverse way.
In woody stems, gas exchange takes place through the lenticels.
1m
In roots, gas exchange takes place all over their surfaces.
1m
Water and minerals:
The water potential of the soil water is usually higher than that of the cytoplasm of the root
hairs, water moves into the root hairs by osmosis.
1m
Water passes across the cortex from cell to cell by osmosis or moves along the cell walls.
1m
Water is drawn up the xylem vessels by transpiration pull.
1m
Most minerals are absorbed into the root cells by active transport. They are taken up against
a concentration gradient using energy from respiration.
1m
Some dissolved minerals are absorbed along water.
Communication
1m
max 3m
Reading to learn (p. 9-28)
1
Certain plants can make use of toxic substances as their nutrients.
1m
2
It is cost-effective.
1m
3
The toxic substances absorbed by the plants may escape from the leaves and pollute the air.
The plants containing the toxic substances may affect the environment if they are not
properly disposed of.
The clean-up process is slow because the plants take months to grow.
(any 2)
4
1m x 2
When the plants decay, the toxic substances absorbed by the plants may return to the soil.
Animals living in soil may be harmed by the toxic substances.
1m
 Oxford University Press 2009