Given below is an experimental setup to demonstrate a particular tropic movement in germinating seeds (seeds fixed to a perforated trough of moist sawdust). Study the diagram and answer the questions that follow: Given below is an experimental setup to demonstrate a particular tropic movement in germinating seeds (seeds fixed to a perforated trough of moist sawdust). Study the diagram and answer the questions that follow:
What is Thigmotropism? Give one example.
Topic: Thigmotropism
Answer
THIGMOTROPISM is the directional growth movement of a plant part in response to the stimulus of TOUCH or contact with a solid object.
Example: the TENDRIL of a pea plant or a grapevine coiling around a support.
THIGMO- means touch, -TROPISM means directional growth. The definition must contain both ideas, and an example secures the mark.
HOW IT WORKS: where the tendril touches the support, the cells on the side AWAY from the contact grow faster than those touching it. That unequal growth curls the tendril around.
A CAUTION: Mimosa pudica (touch-me-not) is often offered as an example and is NOT one. Its leaf-drooping is a NASTIC movement — non-directional (the same whichever side is touched) and caused by a change of TURGOR rather than growth. A tendril is the safe example.