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1. 1990/I/2b
The diagram below shows a germinating seed placed horizontally inside a glass box containing moist soil.
The radicle of the seed was marked with ink lines at 2 mm intervals. The whole set-up was put in darkness.
(i) What is the purpose of marking the radicle of the seed with lines at equal intervals ? (2 marks)
(ii) (1) Draw a diagram to show the changes in the appearance of the radicle after a few days.
(2 marks)
(2) Explain the importance of such changes to the plant. (3 marks)
(iii) If this experiment were to be carried out inside a space shuttle flying in space, what would be the
appearance of the radicle after a few days ? Give a reason for your answer. (2 marks)
2. 1992/I/4b
In a growth response experiment, a bean seedling was inserted into a transparent plastic vial. The whole
set-up (A) was held horizontally and placed in a well-illuminated area. It took 4 hours for the seedling to
curve upwards as shown below :
Another similar set-up (B) was placed inside a light-proof box. It took 2 hours for the seedling to curve
upwards. The seedling, however, is longer and more slender than that grown in light.
HKCEE BIOLOGY | 5.4 Growth responses of plants | P.1
115
(i) Explain the curvature of the seedling observed in set-up B on a horizontal basis. (4 marks)
(ii) Suggest a reason why it took a longer time for the seedling in set-up A to curve upwards. (2 marks)
(iii) What other evidence can be obtained from the experimental results to support your answer in (ii) ?
(1 mark)
(iv) Draw a diagram to show how set-up B could be modified to demonstrate the relative effects of
gravity and light on the growth response of the seedling. (2 marks)
3. 1999/I/3b
The diagram below shows a bean seedling with developing roots. In an experiment to study the effect of
auxins on the growth of roots, 10 mm sections of region A were obtained from a number of seedlings. Auxin
solutions of different concentrations were prepared, and one root section was put into each solution for two
days.
The results are shown in the table below :
Auxin concentration
(ppm)
Length of the root section
after 2 days (mm)
% change in length of the
root section
0
10
5
10
4
10
3
10
2
10
1
12.0
12.3
12.8
12.4
11.2
10.6
20
23
28
24
x
6
HKCEE BIOLOGY | 5.4 Growth responses of plants | P.2
116
(i) Calculate value x. (1 mark)
(ii) When compared with water, list all auxin concentrations
(1) that have a stimulatory effect on the growth of the root section,
(2) that have an inhibitory effect on the growth of the root section. (2 marks)
(iii) (1) Why should the root sections used in this experiment be taken from region A rather than from
region B ? (1 mark)
(2) Suggest a method to test whether your explanation in (iii) (1) is correct or not. (3 marks)
(iv) A bean seedling, with its root tip removed, was left hanging free in a moist and dark chamber. A
paste of cream containing 10
2
ppm auxins was smeared on one side of region A of the seedling as
indicated in the diagram below :
Based on the conclusion obtained in (ii), explain what would happen to the root after two days.
(3 marks)
HKCEE BIOLOGY | 5.4 Growth responses of plants | P.3
