Name: Reflex Action
Uploaded: 2019-07-19
Duration: 2 min 28 s
Description: When you experience a powerful emotion like fear or pleasure, does that leave you with goosebumps? That's a reflex action! Watch this video and learn more.

Question

What is (i) phototropism and (ii) geotropism with labelled diagrams describing an activity to show that light and gravity change the direction that plant parts grow in.

Accepted Answer

(i) Phototropism:- The directional movement of a plant in response to light is called phototropism. The shoot responds by bending towards light and roots respond by bending away from light.

This happens as follows:

When sunlight falls straight on the plant, the auxin hormone synthesized at the tip of the stem spreads uniformly down the stem and due to equal concentration of auxin, the stem grows straight.

When a plant is kept in a dark room near the window, the light intensity of light falling on the plant is less, as a result, the production of auxin increases which get accumulated on the darker/shaded side of the plant. Under the effect of auxin, the cells undergo elongation and subsequent increase in weight. As a result of which the dark side bent down and the plant part towards light is projected up. This kind of movement is called a curvature movement.

(ii) Geotropism :

Geotropism is the growth movement by a plant due to gravity. It is also known as Gravitropism. Roots usually show positive geotropism and stems show negative geotropism.

In an experiment, a kidney bean was placed on a rotating turntable, known as a Clinostat, and the roots which grow over a period of time was observed. The root growth was found to be affected by the rotation of the Clinostat. Instead of growing towards the ground, roots grew towards the centre of the Clinostat.

What is (i) phototropism and (ii) geotropism with labelled diagrams describing an activity to show that light and gravity change the direction that plant parts grow in.

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