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Question
What is phototropism ? How does occur in plants? Describe an activity to demonstrate phototropism.
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Solution
Growth movement of the shoot in plants in response to a light stimulus is called phototropism. this movement is caused due to more growth of cells towards the shaded side of the shoot as compared to the side of shoot towards the light. This happens as follows:(i) 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 an equal concentration of auxin, shoot grows straight.(ii) When sunlight falls on only one side of the plant, the auxin diffuses toward the shady side of the shoot. The concentration of auxin stimulates the cells to grow longer. Therefore, the stem appears to bend towards the source of light.
To demonstrate it we will place a potted plant in a box in which light. comes from only one direction. in a few days, we will observe that the shoot has moved towards the side from which light came in the box.
This happens as follows:
(i) 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 an equal concentration of auxin, shoot grows straight.
(ii) When sunlight falls on only one side of the plant, the auxin diffuses toward the shady side of the shoot. The concentration of auxin stimulates the cells to grow longer. Therefore, the stem appears to bend towards the source of light.
To demonstrate it we will place a potted plant in a box in which light. comes from only one direction. in a few days, we will observe that the shoot has moved towards the side from which light came in the box.
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