14 End-of-chapter test
1
The growing shoot of a cereal plant is covered by a sheath known as a coleoptile. An experiment
was carried out to find the effects of light on the growth of oat coleoptiles. The coleoptiles of one
batch of seedlings were covered with opaque caps of aluminium foil. The second batch were left
uncovered. Both sets were illuminated with a directional light source. The results are shown in
Figure 14.3.
Figure 14.3
a
b
c
d
e
2
Describe the growth shown by the seedlings in Figures 14.3 (a) and 14.3 (b).
What is the name given to the growth response to the light shown by the seedlings in
Figure 14.3 (b)?
A growth response of this kind is known to be mediated by a plant hormone called auxin.
Explain how the light is detected by the plant, and how auxin is involved in the response.
Explain the response shown by the coleoptiles in Figure 14.3 (a).
Describe two ways in which auxins are used commercially.
[2]
[2]
[5]
[2]
[4]
Plant growth substances are important in controlling the life cycles of flowering plants.
Changes in the concentration of plant substances in cells can regulate the expression of
specific genes. One such substance is abscisic acid (ABA).
The concentration of ABA was
measured during the development
of cotton fruits. Figure 14.4 shows
the change in concentration of
ABA as cotton fruits develop.
Figure 14.4
a
With reference to Figure 14.4, describe the relationship between the fruit development
and ABA concentration.
b Suggest a way in which ABA acts within plant cells to bring about changes.
c ABA concentrations have also been measured in the leaves of broad bean seedlings
grown in outdoor experimental plots. It has been observed that the concentration of
ABA increases on hot, dry and breezy days.
Explain:
i why these environmental conditions led to an increase in the concentration of ABA
ii the effect of raised ABA concentrations on the leaf.
[3]
[2]
[2]
[2]
OCR Biology A (2804) January 2003
COAS Biology 2 Teacher Resources
Original material © Cambridge University Press 2009
1
14 End-of-chapter test
3
An investigation was carried out into the effects of two plant growth substances, gibberellins and
auxins, on apical dominance. The terminal (apical) buds of a number of pea plants were removed
and discarded. The tops of each of the remaining shoots were given one of the following
treatments:
• coated with a paste containing gibberellin
• coated with a paste containing auxin (IAA)
• coated with a paste without any plant hormone
In addition, a control group of plants did not have their terminal buds removed and were not
coated with paste.
The growth of the side shoots was measured at regular time intervals and a mean value calculated.
The results are shown in Figure 14.5 below.
Figure 14.5
a
b
c
Explain why the side shoots grow when the terminal buds are removed.
Side shoots show greater growth when paste containing gibberellin is applied than
when paste without any plant hormone is applied.
Calculate the percentage increase in growth due to gibberellin in 8-day-old seedlings
compared with seedlings with paste only. Show your working.
Using data from Figure 14.5, describe and explain the effect of auxin (IAA) on the
growth of side shoots.
[3]
[2]
[3]
OCR Biology A (2804) June 2004
Total:
32
Score:
%
Grade boundaries: 80% A, 70% B, 60% C, 50% D, 40% E
COAS Biology 2 Teacher Resources
Original material © Cambridge University Press 2009
2