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Question
The bending of the stem of a plant towards a source of light is caused by the action of a phytohormone known as :
(a) abscisic acid
(b) auxin
(c) gibberellins
(d) cytokinin
Solution
(b) auxin
Auxin causes phototropism, i.e., bending of plant stems towards the source of light.
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RELATED QUESTIONS
Why is the folding up of the leaves of a sensitive plant on touching with a finger not a tropism?
What is meant by 'tropisms' (or tropic movements)? Explain with an example.
What is meant by positive tropism and negative tropism? Explain with examples.
Which of the following are not tropisms?
(i) growing of pollen tube in response to a sugary substance
(ii) folding up of leaves of sensitive plant in response to touch
(iii) winding of tendril around a support in response to touch
(iv) opening up of the leaves of a daisy flower in response to light
(a) (i) and (ii) (b) (ii) and (iii) (c) (i) and (iv) (d) (ii) and (iv)
There are three plants A, B and C. The flowers of plant A open their petals in bright light during the day but close them when it gets dark at night. On the other hand, the flowers of plant B open their petals at night but close them during the day when there is bright light. The leaves of plant C fold up and droop when touched with fingers or any other solid object.
- Name the phenomenon shown by the flowers of (i) plant A and (ii) plant B.
- Name one flower each which behaves like the flower of (i) plant A and (ii) plant B.
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- Name a plant whose leaves behave like those of plant C.
- Which plant/plants exhibit the phenomenon based on growth movements?
Match column A with column B.
| Column A | Column B |
| Roots growing downwards into soil. | Positive phototropism |
| Shoots growing towards the light. | Negative geotropism |
| Shoots growing upward. | Negative phototropism |
| Roots growing downwards away from light. | Positive geotropism |
Differentiate phototropism from photonasty.
The leaves of Mimosa are sensitive to ____________.
Write the scientific terms used to represent the following:
Growing of roots towards the gravity.
Study the diagrams given below and answer the following questions:
- Name the structures shown as X and Y in the figures (A) and (B), respectively.
- Write the functions performed by the structures X and Y.
- Name the phenomenon depicted and define it.
- How do the structures X and Y differ from each other?
- Give examples of the plants which show the said phenomenon.
