Page 21 - Biology_Form_3

Biology for Secondary Schools

Importance of chemonasty Thigmonasty
Chemonasty is important in various Refers to response of a plant or part of plant
plant survival strategies, such as trapping to stimulus of touch. The best example of
insects and digest them to obtain nitrogen, nastic movement is folding of leaves of
phosphorus and sulphur nutrients. It also the sensitive plant or shy plant (Mimosa
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plays a role in plant defence. Insectivorous pudica) plant when its leaves are touched
plants such as the Venus flytrap. with fingers or any object as shown in
Figure 1.13 (a) and (b). The leaves also

(a)
(b)

Figure 1.13: Nastic movement in the leaflets of Mimosa plant (a) unfolded leaves
(b) folded leaves
fold even when swayed by wind. Also Thermonasty
the specialised touch-sensitive tendrils of This is a movement of plant parts in
many vining plants such as peas, will bend response to temperature. For example, sun
towards the side receiving a touch stimulus. flowers close when the temperature drops,
or some leaves fold when the temperature
Importance of thigmonasty raises above normal. Also tulip and crocus
It help plants in defence against external flowers open with warmth and close when
stimuli and survival of the plant. cooler, optimising reproductive success.

Exercise 1.2

1. Match each statement in part A with the correct response from the options
provided in part B by writing a letter of the correct response from part B against
the statement in part A.

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