Cambridge Biology for the IB Diploma
Extension worksheet – Chapter 9
1
Consider the information given below and answer the questions that follow.
Two sets of plants, labelled Set A and Set B, were grown in different light/dark regimes.
Set A flowered in the first experiment but not the second.
Set B flowered in the second experiment but not the first.
In a third experiment, the light conditions used for experiment 2 were repeated but a burst of
light was given halfway through the period of darkness.
Set A flowered but Set B did not.
a
From these observations, what is the most important factor controlling flowering in the
plants in:
i
Set A
(1)
ii
Set B?
(1)
b
Give one biological advantage that plants gain from flowering in response to light.
(1)
c
It has been said that ‘Short-day plants are best described as being long-night plants’.
Do you agree?
(1)
Dandelions and roses are day-neutral plants. When would you expect to see them
flowering?
(1)
d
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Cambridge Biology for the IB Diploma
2
3
Phototropism is a plant’s response to the direction of light. In the diagram below, a
plant has been exposed to directional sunlight and turned to grow towards the light.
a
What is the plant growth substance (hormone) that controls this response?
(1)
b
How have the cells at points A and B responded to this hormone?
(2)
c
Would the hormone be at a higher concentration at point A or point B?
(1)
a
Compare the processes of transpiration and translocation.
(4)
b
What causes movement of:
c
4
i
water through the xylem
(1)
ii
sugars through the phloem?
(1)
List three ways in which mineral ions enter a plant root.
(3)
Researchers have shown that there has been a decrease in the density of stomata in some plants
in the last 75 years.
a
Suggest a possible reason for this observation.
(1)
b
What is the importance of each of the following to the opening and closing of stomata?
i
thickened inner walls of guard cells
(1)
ii
K+ ions
(1)
iii
abscisic acid
(1)
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