Question 33:
(a) What is meant by ‘tropisms’ (or tropic movements) ? Explain with an example.
(b) What are the different types of tropisms ? Define each type of tropism. Write the name of stimulus in each case.
(c) How do tropisms differ from nasties (or nastic movements) ?
Lakhmir Singh Biology Class 10
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a) A growth movement of a plant part in response to an external stimulus in which the direction of stimulus determines the direction of response is called tropism .
Example :- The bending of plant stem towards light is an example of positive phototropism .
b ) 1) Phototropism :- The movement of a plant part in response to light is called phototropism . It's stimulus is light .
2) Geotropism :- The movement of a plant part in response to gravity is called geotropism . Its stimulus is gravity .
3) Chemotropism :- The movement of a plant part in response to a chemical stimulus is called Chemotropism . Its stimulus is chemical .
4) Hydrotropism :- The movement of a plant part in response to a water stimulus is called Hydrotropism . Its stimulus is water .
5) Thigmotropism :- The movement of a plant part in response to a touch stimulus is called Thigmotropism . Its stimulus is touch .
c ) TROPISMS
1) These movements are always in the direction of the stimulus .
2) These movements are slow .
3) These movements are exhibited by all parts of a plant . For example , movement of shoot towards the light and not towards .
NASTIES :
1) These movements are neither away nor towards the stimulus .
2) These movements are fast .
3) These movements are exhibited by the flat organs ( like leaves and petals of flowers ) of a plant .
For example , the bending and dropping of leaves in ' Touch-me-not ' plant .
Example :- The bending of plant stem towards light is an example of positive phototropism .
b ) 1) Phototropism :- The movement of a plant part in response to light is called phototropism . It's stimulus is light .
2) Geotropism :- The movement of a plant part in response to gravity is called geotropism . Its stimulus is gravity .
3) Chemotropism :- The movement of a plant part in response to a chemical stimulus is called Chemotropism . Its stimulus is chemical .
4) Hydrotropism :- The movement of a plant part in response to a water stimulus is called Hydrotropism . Its stimulus is water .
5) Thigmotropism :- The movement of a plant part in response to a touch stimulus is called Thigmotropism . Its stimulus is touch .
c ) TROPISMS
1) These movements are always in the direction of the stimulus .
2) These movements are slow .
3) These movements are exhibited by all parts of a plant . For example , movement of shoot towards the light and not towards .
NASTIES :
1) These movements are neither away nor towards the stimulus .
2) These movements are fast .
3) These movements are exhibited by the flat organs ( like leaves and petals of flowers ) of a plant .
For example , the bending and dropping of leaves in ' Touch-me-not ' plant .
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Answer:
Question 33:
(a) What is meant by ‘tropisms’ (or tropic movements) ? Explain with an example.
(b) What are the different types of tropisms ? Define each type of tropism. Write the name of stimulus in each case.
(c) How do tropisms differ from nasties (or nastic movements) ?
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