Question

(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)?

Answer 1

(a) The growth movement of plant parts in which the direction of the stimulus determines the direction of the response is known as tropisms.
Example: Phototropism, where the stems of plants grow upwards in response to sunlight.

(b) The different types of tropisms are:
(i) Phototropism: The movement of plant parts in response to light is known as phototropism. The stimulus is light.
(ii) Geotropism: The movement of plant parts in response to gravity is known as geotropism. The stimulus is gravity.
(iii) Hydrotropism: The movement of plant parts in response to water is known as hydrotropism. The stimulus is water.
(iv) Chemotropism: The movement of plant parts in response to chemicals is known as chemotropism. The stimulus is chemicals.
(v) Thigmotropism: The movement of plant parts in response to touch is known as thigmotropism. The stimulus is touch.

(c)

Tropism	Nasties
Tropisms are the directional movement of plant parts in response to an external stimulus.	Nasties are the non-directional movements of plant parts in response to an external stimulus.