Activity Book

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Activity Book
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Practical 10.1 Demonstration of the occurrence of
transpiration Practical 10.2 Design an
investigation of the distribution of stomata on
both sides of a leaf Practical 10.3 Measurement
of the rate of transpiration using a bubble
potometer Practical 10.4 Measurement of the
amount of water absorbed and lost by a plant
using a weight potometer
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Practical 10.5 Design an investigation of the
effects of environmental factors on the rate of
transpiration Practical 10.6 Examination of the
structure of roots Practical 10.7 Examination of
the vascular tissues in a young dicotyledonous
stem Practical 10.8 Investigation of the plant
tissue responsible for water transport
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Activity 10.1 Water sucking competition Exercise
10
5
10.1
Demonstration of the occurrence of transpiration
Questions
1 Why are the pots enclosed in plastic bags?
To prevent the respiration of soil organisms and
the evaporation of soil water from affecting the
results.
ANS ?
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10.1
Demonstration of the occurrence of transpiration
2 What does dry cobalt (II) chloride paper test
for?
Water. (Water turns dry cobalt (II) chloride
paper from blue to pink.)
ANS ?
3 Identify any liquid present on the wall of the
bell jar.
Water.
ANS ?
7
10.1
Demonstration of the occurrence of transpiration
4 Do you think the same results will be obtained
if plant A is placed in the dark rather than in
bright light? Explain.
No. Little or no transpiration will take place in
plant A because the stomata are only slightly
open or are even closed in the dark.
ANS ?
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10.1
Demonstration of the occurrence of transpiration
Conclusion
What conclusion can you draw from this practical?
Water vapour is released from plant A but not
from plant B. Therefore, transpiration takes
place in the aerial parts of the plant.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Propose a hypothesis
1 According to the above observation, which side
of the leaf loses water at a slower rate?
The upper side of the leaf.
ANS ?
2a Try to propose some hypotheses.
The upper side of the leaf has a lower stomatal
density.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
2b Which hypothesis in a is the most
appropriate? State your reasons.
The upper side of the leaf has a lower stomatal
density. It is because the upper side of the leaf
is directly illuminated by sunlight. The smaller
number of stomata helps reduce water loss by
transpiration.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Design an perform an experiment
1 How are you going to record and present the
results?
(Answer varies with the design.)
ANS ?
2 How can you make sure that the results are
reliable?
(Answer varies with Ss.)
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
3 What precautions should be taken?
(Answer varies with the design.)
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Write an experimental report
Objective
To compare the stomatal densities of both sides
of a leaf.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Apparatus and materials
Method 1 1 microscope 1 pair of forceps 1 cover
clip 1 microscope slide
1 microscope slide with a transparent grid 1
green leaf (e.g. Zebrina) distilled water
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Method 2 1 pair of forceps 1 beaker of hot
water 1 freshly-picked leaf from a terrestrial
plant
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Procedure (Method 1)
1. Use a pair of forceps to peel off the lower
epidermis of a leaf. Put it on a slide. 2. Mount
the epidermis with a drop of distilled
water. 3. Find a portion of the epidermis which
fills the microscopes field of vision at X100
magnification.
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
4. Count the number of stomata in the field of
vision. 5. Repeat 4 for 3 times and take the
average value. 6. Repeat 1 to 5 for the upper
epidermis
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
7. Use a slide with a transparent grid of a
stated grid size to estimate the dimension of the
field of vision. 8. Calculate the stomatal
densities of the upper and lower epidermis of the
leaf.
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Procedure (Method 2)
1. Immerse a leaf from a terrestrial plant
quickly into a beaker of hot water. 2. Observe
carefully and compare the amount of bubbles
coming out from each side of the leaf.
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Results
Method 1
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Method 2
More bubbles come out from the underside of the
leaf.
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Analysis and discussion
1 Which side of the leaf has fewer stomata?
Suggest reason(s) for such distribution of
stomata.
ANS ?
The upper side of the leaf has fewer stomata. The
upper side is directly illuminated by sunlight.
Fewer stomata on the upper side can reduce water
loss by transpiration.
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
2 Based on your reason(s) in 1, deduce and
explain the stomatal densities of both sides of a
monocotyledonous leaf which usually grows in an
upright position.
Stomatal densities of both sides of a
monocotyledonous leaf are about the same because
both sides are exposed to more or less the same
amount of sunlight.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
3 In submerged plants, diffusion of gases takes
place all over the leaf surface because they have
thin or no cuticle. What do you think about the
distribution of stomata in these plants?
Stomata are absent as they are not necessary.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
4 What do you think about the distribution of
stomata in floating plants?
Stomata are present only on the upper side which
is in contact with the air.
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
5 What are the possible sources of errors in this
experiment? Suggest ways for improvement.
(Answer varies with the design.)
ANS ?
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10.2
Design an investigation of the distribution of
stomata on both sides of a leaf
Conclusion
The upper side of the leaf has fewer stomata than
the underside.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
Questions
1 Why is it necessary to cut the leafy shoot and
fit it into the potometer under water?
To prevent air bubbles from entering the xylem
vessels of the plant and blocking water uptake.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
2 Explain the movement of the air bubble in the
capillary tube.
When the plant transpires and absorbs water,
water is drawn from the capillary tube. The air
bubble therefore moves towards the shoot along
the tube.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
3 Is the rate of movement of the air bubble a
direct measurement of the rate of transpiration?
If not, what does it indicate?
No. The rate of movement of the air bubble
indicates the rate of water uptake.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
4 What assumption is made in using the bubble
potometer to measure the rate of transpiration?
The water absorbed is to replace an equal amount
of water lost by transpiration.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
5 State the limitations of the bubble potometer
for measuring the rate of transpiration in a
whole plant.
It measures the rate of water uptake, rather than
the rate of transpiration. It is too small to
include the whole root system of a plant.
ANS ?
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10.3
Measurement of the rate of transpiration using a
bubble potometer
6 What is the possible source of error in this
experiment?
The movement of the air bubble may be affected by
the friction between the air bubble and the wall
of the capillary tube.
ANS ?
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
Questions
1 Why is a layer of oil added to the water
surface in the burette?
To prevent evaporation of water in the burette
which will affect the results.
ANS ?
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
2 Calculate the amount of water absorbed and the
rate of water uptake by the plant.
(Answer varies with Ss. The amount of water
absorbed is the difference between the water
levels in the burette before and after the
practical.)
ANS ?
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
3 Calculate the amount of water lost and the rate
of water loss by the plant.
(Answer varies with Ss. The amount of water lost
is the difference between the weights of the
whole set-up before and after the practical.)
ANS ?
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
4 Assume 1 cm3 of water weighs 1 g, compare the
amount of water absorbed and lost by the plant.
Give an explanation for any difference between
the two parameters.
ANS ?
The amount of water lost is slightly less than
the amount of water absorbed. It is because some
of the absorbed water is used in photosynthesis
and other metabolic activities.
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
5 Based on your answer in 4, does the rate of
water uptake equal to the rate of transpiration?
No. As some water remains in the plant, the rate
of water uptake is slightly higher than the rate
of transpiration.
ANS ?
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10.4
Measurement of the amount of water absorbed and
lost by a plant using a weight potometer
Conclusion
What conclusion about the amount of water
absorbed and lost by the plant can you draw from
this practical?
The amount of water lost is slightly less than
the amount of water absorbed by the plant.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Design and perform an experiment
1 Which environmental factor are you going to
investigate?
Light intensity, temperature, humidity or air
movement, etc.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
2 How are you going to provide the environmental
condition in 1?
Light intensity use a bench lamp. / Temperature
use a heater. / Humidity put the potometer in a
room without air-conditioning. / Air movement
use a blowing fan.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
3 What are the controlled variables in this
experiment?
The parameters and conditions other than the one
being investigated.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
4 What is the independent variable in this
experiment?
The environmental factor being investigated.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
5 What is the dependent variable in this
experiment?
The weight of water lost as shown in the weight
potometer, the distance travelled by the air
bubble in a given time in the bubble potometer,
etc.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
6 What is the control in this experiment?
The potometer that is put in a laboratory with
normal conditions.
ANS ?
7 How are you going to record and present the
results?
(Answer varies with Ss.)
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
8 How can you obtain faster results?
Blot dry the leaves if they are wet. Use a shoot
with more leaves. Use a capillary tube with a
narrower bore in the bubble potometer.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
9 How can you make sure that the results are
reliable?
Allow a few minutes for the shoot to equilibrate
before taking any readings or ignore the first
few readings.Take the average of several readings
under the same condition.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
10 What precautions should be taken?
ANS ?
Cut the leafy shoot and fit it into the potometer
under water to prevent air bubbles from entering
the xylem vessels of the plant and blocking water
uptake. (To be continued.)
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
continued from previous page
Seal off all connections of the potometer with
vaseline to ensure no leakage of water.Do not
allow the air bubble in the bubble potometer to
reach the end of the shoot.
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Write an experimental report
Objective
(Answer varies with Ss.).
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Apparatus and materials
2 pipettes (1cm3) 2 glass tubings 2 rubber
tubings 2 restort stands
4 clamps 1 wash bottle with water 1 scalpel 1
plant with leafy shoots
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Procedure
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
2. Put the U-shaped potometer in one of the
following places, depending on the environment
factor being investigated Light intensity
near a bench lamp Temperature near a
heater Humidity in a room without air
conditioning Air movement near a blowing fan
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
3. Put another U-shaped potometer in a laboratory
with normal conditions to act as the
control. 4. Allow 5 minutes for
equilibration. 5. Adjust the water levels in the
glass tubing and the pipette to the same level by
raising or lowering the 2 arms of the U-shaped
potometer.
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
6. Record the initial water level in the
pipette. 7. Record the water level again after a
certain time (e.g. 15minutes). 8. Readjust the
water levels and repeat with 2 more readings.
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Result
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Analysis and discussion
1a Higher light intensity
Stomata open wider at higher light intensity,
therefore the rate of transpiration increases.
Higher light intensity also increases the
temperature which in turn increases the rate of
transpiration.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
1b Higher temperature
Higher temperature increases the rate of
evaporation from the water film on the cell
surfaces and the diffusion rate of water vapour
out of the stomata. It also lowers the relative
humidity of the air. Hence, the rate of
transpiration increases.
ANS ?
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
1c Higher relative humidity
Higher relative humidity in the surrounding air
decreases the concentration gradient of water
vapour between the air spaces in the leaves and
the atmosphere. Hence, water vapour diffuses out
of the leaves slower and the rate of
transpiration decreases.
ANS ?
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60
10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
1d Greater air movement
Greater air movement helps remove water vapour
that has diffused out of the stomata. This
increases the concentration gradient of water
vapour between the air spaces in the leaves and
the atmosphere. (To be continued.)
ANS ?
61
10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
continued from previous page
Hence, water vapour diffuses out of the leaves
faster and the rate of transpiration increases.
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
2 What are the possible sources of errors in this
experiment? Suggest ways for improvement.
Changing of one environmental condition may have
changed another, (To be continued.)
ANS ?
63
10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
continued from previous page
e.g. the use of the heater to increase the
temperature may also have lowered the relative
humidity in the surrounding air. Fluctuation in
environmental conditions, e.g. temperature.
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10.5
Design an investigation of the effects of
environmental factors on the rate of transpiration
Conclusion
The rate of transpiration increases at higher
light intensity / higher temperature / lower
relative humidity/ when there is greater air
movement.
ANS ?
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10.6
Examination of the structure of roots
Questions
1 Which structure of the root is responsible for
the absorption of water and minerals?
Root hair.
ANS ?
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10.6
Examination of the structure of roots
2 Explain how the structure of the root is
adapted to the absorption of water and minerals.
The epidermal cells are not covered by cuticle
and thus water can easily pass into
them. Numerous root branches and root hairs
provide a large surface area for absorption. (To
be continued.)
ANS ?
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10.6
Examination of the structure of roots
continued from previous page
The root hairs are very small structures and can
easily grow between the soil particles and absorb
the water and minerals around them. Xylem
transports the water and minerals away and
maintains a steep water potential gradient
between the root and the soil.
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10.7
Examination of the vascular tissues in a young
dicotyledonous stem
Questions
1 What are the functions of the xylem and the
phloem?
Xylem transports water and minerals in the
plant. Phloem transports organic nutrients in the
plant.
ANS ?
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10.7
Examination of the vascular tissues in a young
dicotyledonous stem
2 How does the distribution of the vascular
tissues in the young dicotyledonous stem differ
from that in the root and the leaf?
The vascular tissues in the stem, the root and
the leaf are found on the periphery, at the
centre and in the mid-rib vein respectively.
ANS ?
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10.8
Investigation of the plant tissue responsible for
water transport
Questions
1 Are the tissues stained red in the root, stem
and leaf the same? What are these tissues?
Yes. The xylem.
ANS ?
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10.8
Investigation of the plant tissue responsible for
water transport
2 Suggest ways to speed up the absorption and
transport of the eosin solution in the plant.
Put the plant near a blowing fan. Put the plant
in bright light or near a bench lamp.Put the
plant near a heater. Put the plant in a
desiccator. Blot dry the leaves.
ANS ?
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10.8
Investigation of the plant tissue responsible for
water transport
Conclusion
What conclusion can you draw from this practical?
The xylem is the main tissue responsible for
water transport in the herbaceous plant.
ANS ?
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10.1
Activity
Water sucking competition
Questions
1 How does water go from the glass to your mouth?
ANS ?
By the suctional force produced by the mouth, the
water moves up from the glass to the mouth
through the long drinking straw.
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10.1
Activity
Water sucking competition
2 Is it easier to drink with a long drinking
straw or a short one?
A short drinking straw
ANS ?
3 What will happen if there is a break in the
drinking straws?
ANS ?
Water will not reach the mouth.
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10.1
Activity
Water sucking competition
4 Some structures in flowering plants are similar
to the drinking straws in this activity. What are
they?
The xylem vessels.
ANS ?
76
Exercise 10
Multiple-choice questions
D
A
D
B
A
D
D
B
B
C
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Exercise 10
Structured questions
1a Name parts A to D.
ANS ?
A Root hair cell (1m) B Xylem vessel (1m) C
Spongy mesophyll (1m) D Guard cell (1m)
78
Exercise 10
1b Explain how water enters cell A.
ANS ?
As the water potential of the soil water is
usually higher than that of the cytoplasm of cell
A (1m), water enters cell A by osmosis through
the differentially permeable membrane (1m).
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Exercise 10
1c i What is transpiration?
ANS ?
Transpiration is the loss of water vapour from
the plant surface due to evaporation. (1m)
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Exercise 10
1c ii What are the importance of transpiration
to plants?
Transpiration provides a cooling effect to the
plants (1m). It also helps in the absorption and
transport of water and minerals (1m).
ANS ?
81
Exercise 10
2a How can the air bubble be adjusted to position
0?
Open the tap of the reservoir slowly to let the
water push the air bubble to the right hand side
(1m). Close the tap when the air bubble reaches
the position 0 (1m).
ANS ?
82
Exercise 10
2b What precaution should be taken in this
investigation?
Seal off all connections with vaseline to ensure
no leakage of water. (1m)
ANS ?
83
Exercise 10
2c i Calculate the transpiration rates, in units
of mm h-1, under different temperatures in the
table below.
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Exercise 10
2c ii Plot the results in ci as a graph.

• Correct title (1m)
• Correct labelling of axes (1m1m)
• Correct scale of axes (0.5m0.5m)
• Correct curve (1m)

85
Exercise 10
2d What can you conclude from the experiment?
ANS ?
The transpiration rate increases with
temperature. (1m)
86
Exercise 10
2e A student claims that this experimental set-up
cannot truly measure the transpiration rate of a
plant. Is he / she right? Give your reasons.
ANS ?
He / she is right (1m). It is because this
experiment can only measure the volume of water
that absorbed by the plant (1m). However, some
water absorbed is used in photosynthesis and
growth (1m).
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Exercise 10
2f i Design an investigation that can measure
the transpiration rate of a plant more
accurately.
ANS ?
Prepare a weight potometer as follows cut a
leafy shoot from a plant and fit it into a
conical flask with a rubber stopper (1m). Open up
the rubber stopper a little bit and remove small
amount of water from the flask (1m). (To be
continued.)
88
Exercise 10
continued from previous page
Add a thin layer of oil on the water surface in
the flask (1m). Put the apparatus on a weight
balance and record the loss of weight over a
period of time (1m).
89
Exercise 10
2f ii State any precautions needed in your
investigation.
Cut the leafy shoot under water (1m) and seal
off all connections with vaseline to ensure no
leakage of water (1m).
ANS ?
90
Exercise 10
3a What will happen to the part of stem just
above the steamed part after a week? Explain your
answer.
This part will become swollen (1m). It is
because the hot steam kills the phloem (1m) and
make the organic nutrients accumulate in the
upper part of the stem (1m).
ANS ?
91
Exercise 10
3b What will happen to the plant finally?
ANS ?
Since the organic nutrients cannot be passed
down to the lower part of the plant (1m), the
root cells will die first (1m). As the roots can
no longer absorb water, the whole plant dies
eventually (1m).
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Exercise 10
3c Suggest another method that can produce the
same result in a.
Remove a ring of bark containing phloem (1m),
leaving the xylem vessels intact with the stem
(1m).
ANS ?
93
Exercise 10
3d i What is the transported form of sugar in
plants?
Sucrose (1m)
ANS ?
3d ii Explain its significance.
ANS ?
Sucrose is soluble in water for easy transport.
(1m) Sucrose will not be consumed when travelling
along phloem.(1m)