Q29 of 231 Page 93

Name the plant hormones which are responsible for the following effects:

(a) falling of leaves


(b) opening of stomata


(c) bending of stem towards light


(d) closing of stomata

(a) Abscisic acid is responsible for abscission of falling of leaves.

(b) Cytokinin is responsible for opening of stomata.


(c) Auxin is responsible for bending of stem towards light.


(d) Abscisic acid is responsible for closing of stomata.


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27

What is the difference between photonasty and thigmonasty?

 28

A potted plant is kept horizontally for a considerable time. The three positions of the parts A and B of the potted plant are shown in the following figures:


(a) Which figure shows the correct position taken by the parts A and B of the plant?


(b) What type of phenomenon is exhibited by the figure chosen in (a) above?

 30

Name the plant organs which are:

(a) positively phototropic


(b) positively geotropic


(c) negatively geotropic


(d) positively hydrotropic

 31

Why is the folding up of the leaves of a sensitive plant on touching with a finger not a tropism?