Question

The closure of the lid of the pitcher in the pitcher plant is
A. A paratonic movement
B. A tropic movement
C. A turgor movement
D. An autonomous movement

Answer 1

Hint: The closure of the lid of the pitcher in the pitcher plant happens only when an insect sits on it which acts as an external stimulus for the pitcher plant.

Complete answer:
To solve this question, we must first know about the anatomy of pitcher plants. Pitcher plant or Nepenthes is an insectivorous plant which feeds on insects. It fulfills its nitrogen deficiency by engulfing insects.
This plant is a very good example of leaf modification. Here, the leaves are modified into a pitcher-like structure. The leaf apex forms the lid of the pitcher. The petiole forms a thin tendril that keeps the pitcher vertical and in position. As the insect gets attracted to this plant, it is trapped inside the slippery pitcher and is digested by the various digestive juices present inside it.
The closure of the lid takes place as soon as the insect enters the pitcher. And so it is unable to escape from there. The movement of this lid is an example of paratonic movement. Paratonic movements are those movements where an external stimulus is required. Here, the insects act as a stimulus and the lid closes.
Tropic movement refers to the growth or the turning of a particular plant part in the direction of the environmental stimuli. Here the environment of the plant acts as the stimulus.
Autonomous movement does not require any external stimuli and occurs due to the internal stimuli.
Turgor movement is the movement which occurs due to the fully extended or turgid cells.

Note: The paratonic movement discussed above should not be confused with the tropic movement. The paratonic movements are non-directional whereas the tropic movements occur in a particular direction, i.e. either away from the stimulus or towards the stimulus.