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Questions
on transpiration
Monacia
Williams, Contributor
Welcome
to another lesson in our series. Last
week, we looked at transpiration and
the factors that affected it. At the
end of the lesson, I promised that
we would be looking at some questions
on transpiration and, today, I will
honour my promise and do just that.
Most
of the questions on transpiration
are centred on the experiments so,
as I told you previously, it is important
that you spend some time reading these
experiments in your text as well understanding
the principles behind them. Let us
now look at the first question.
Question
1
A
student conducted an experiment to
estimate the transpiration rate of
a plant. Measurements of the water
absorbed were taken every two hours,
from 4:00 a.m. to 8:00 p.m. The results
are shown in the following table:
TABLE
SHOWING WATER ABSORPTION RATE BY A
TRANSPIRING PLANT
| Time |
Water
Absorption rate cm3
hr-1 |
| 4.00
a.m. |
2 |
| 6.00
a.m. |
4 |
| 8.00
a.m. |
8 |
| 10.00
a.m. |
14 |
| noon |
30 |
| 2:00
p.m. |
29 |
| 4:00
p.m. |
24 |
| 6:00
p.m. |
12 |
| 8:00
p.m. |
8 |
a)
i. Describe fully the rate of
water absorption over the 16-hour
period. 2 marks
Answer:
In order to answer the question and
earn the full two marks, you need
to look carefully at the information
in the table. What do you notice?
You notice that:
In
the early part of the day, between
4:00 a.m. and 8:00 a.m., the water
absorption rate is slow. Between the
hours of 8:00 a.m. and noon, the rate
increases rapidly. After 12 p.m.,
the rate begins to decrease, dropping
sharply after 4:00 p.m., getting back
by 8:00 p.m. to the level it was at
8:00 a.m.
ii.
What environmental factor is likely
to be responsible for the water absorption
rate shown in the table between 6:00
a.m. and 6:00 p.m.? Give ONE reason
for your response. 2 marks
Answer:
You will need to draw on your knowledge
to answer this one. What process in
the plant is water absorption connected
to? Did you answer, transpiration?
If you did, you are correct! This
means then that the question can now
be connected to knowledge that you
already have! What are the environmental
factors influencing transpiration?
These are light, temperature, wind
and humidity. Which of these would
affect the water absorption most in
this period? Your best answer would
be:
Light,
because the times given in the table
show the transition from dawn until
dusk, the times when the stomata would
be partially open to being fully open
and back again to being partially
open in order to facilitate photosynthesis.
iii.
Describe how you would use the pieces
of apparatus and materials shown below
to collect data similar to that shown
in the table. 4 marks
Let
us look at what you have been given
and what they would be used for:
- Water
serves two purposes - the cutting
of the twig and the filling of the
measuring cylinder.
- The
measuring cylinder - to measure
the volume of water lost over time.
- The
oil - to cover the surface of the
water in the measuring cylinder.
Let
us now put these together to arrive
at an answer.
Answer:
- Fill
the measuring cylinder to a level
where the meniscus can be read.
- Cut
the twig under water and place it
in the measuring cylinder.
- Pour
the oil on top of the water.
- Read
and record the level of the water
in the measuring cylinder every
two hours.
iv.
If the twig had roots, what difference
would you expect in the results? Give
ONE reason for your answer. 2 marks
Answer:
The
rate of water absorption would be
greater because the presence of the
roots increases the surface area over
which absorption can take place.
The
questions given above are a part of
a compulsory question from a past
biology paper. I certainly hope that
they were of some assistance to you.
Next week, we will look at the rest.
Monacia
Williams teaches at Glenmuir High
School. Send questions and comments
to kerry-ann.hepburn@gleanerjm.com
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