Page 23 - Biology_Form_3

Biology for Secondary Schools
6. Cytokinins are hormones that
primarily promote cell division
and plant growth, especially in the
shoots and roots. They regulate the
development of new tissues and
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organs by stimulating cytokinesis (the
division of cells).
7. Ethylene promotes growth of shoots
and roots. It also accelerates fruit
ripening, colouring and sweetness.
8. Normally plants remain fixed on the
ground and they are incapable of
moving from one place to another.
However, parts of plants such as
leaves, stems and roots show some
growth responses away from or
towards to stimuli such as water, light
and gravity.
9. There are two common types of
movements in plants, namely nastic
movement and tropic movement.
Tropisms are growth responses of
plants that result in curvatures of plant
organs toward or away from specific
stimuli.
10. Important tropisms shown by plants
include phototropism, geotropism,
hydrotropism and chemotropism.
11. Nastic movements are non-directional
movements of a part of stationary
plant in response to external stimuli.
Based on the nature of stimuli, nastic
movements can be divided into the
following groups; thigmonasty,
chemonasty, thermonasty and
photonasty.
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BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 16 KAMISHNA
BIOLOGY FORM 3 FINAL EDITED 16.09.2025.indd 16
Revision exercise 1
Choose the most correct answer to each
of the following questions.
1. Which of the following is primarily
responsible for coordinating the
growth and development of plants?
(a) Phytochromes
(b) Auxins
(c) Chlorophyll
(d) Glucose
2. How do plants detect and respond to
gravity?
(a) Using photoreceptors
(b) By changing the shape of their
leaves
(c) Through the movement of auxins
(d) By altering the rate of
photosynthesis
3. Which of the following mechanisms
are used by plants to coordinate their
response to environmental stress?
(a) Hormonal signaling
(b) Leaf colour change
(c) Temperature regulation
(d) Photosynthesis enhancement
4. What is the primary function of
cytokinins in plant coordination?
(a) Stimulate leaf abscission
(b) Inhibit root growth
(c) Promote cell division
(d) Promote seed dormancy
Student’s Book - Form Three
23/10/2025 11:52:31
23/10/2025 11:52:31 KAMISHNA