Question

Give one example, of following plants :
(a) Which is (i) positively phototropic and (ii) negatively geotropic.
(b) Which is positively hydrotropic as well as positively geotrophic ?
(c) Which synthesises auxin ?


CBSE Class X Science SA 2 (3 Marks)

Answer 1

a) (i) Positively phototropic - Shoot

Reason :

Stem of plant or shoot responds to light and bend towards it.

Thus stem, leaves of plant are positively phototropic

(ii) Negatively geotropic - Shoot

Reason:

the movement of plant roots towards the earth and that of stem away from

earth are Geo-tropism

Since the roots grow down the downward growth of root is positive

Geo-tropism.

the stem or shoot grows upwards away from pull  

of gravity so upward movement of stem or shoot is negative Geo-tropism.

(b) root

(c) Shoot tip

Answer 2

Positively phototropic plant= sunflowers; negatively geotropic plant= pneumatophores or respiring roots one finds in mangrove vegetation; Which is positively hydrotropic as well as positively geotropic= A tap root. (c ) The natural auxin found in plants is called Indole Acetic Acid (IAA) and it is the first of the phyto-hormones discovered with Indole acetic acid, which is predominantly synthesized in the stem apexes.