Question

Movement stimulated by external factor is
a. Spontaneous movement
b. Autoimmune movement
c. Physical movement
d. Paratonic movement

Answer 1

Hint: Plant movements include the opening and closing of flowers, growth of developing roots in search of water and nutrients, movements toward the light, etc. The higher plant movement is in the form of bending, twisting, and elongation of parts and organs of certain plants. It involves two types of movement: Spontaneous and Induced movements.

Complete answer:
Plants show movements in response to various types of stimuli. The reaction of the plant to any stimulus is called a response. The ability of a plant to respond to a stimulus is called sensitivity or reactivity. The perceptive region is the area that perceives a stimulus, while the plants part showing the response is known as the responsive region. Presentation time is the minimum duration of time required for a stimulus to be applied continuously in the perceptive region to produce a visible response.

The duration between the application of a stimulus and the production of visible response is called latent time or reaction time. Hence spontaneous movements are defined as movement caused by an internal stimulus, and if the movements are produced in response to an external stimulus, they are known as paratonic or induced movements.

- Spontaneous: These take place without any external stimuli and take place spontaneously. Also called autonomous movements.
- Induced movements (paratonic): Plant movements in response to certain external stimuli.

The plant movements that are in response to certain stimuli is called paratonic movement and are said to be induced or move without any irritability or sensitivity of the protoplasm. They are of three types - Tropic, Tactic, and Nastic movements. Growth movements in response to unidirectional external stimuli and results in positioning in the direction of the stimulus are called trophic movements. They are divided as phototropism, geotropism, hydrotropism, chemotropism.

- Spontaneous movements take place without any external stimuli and take place spontaneously.
- Autoimmune is not a movement but a disorder that retards the growth of plants.
- Physical movement is found in dead parts of plants that are not related to protoplasm.

Hence, the correct answer is option (D).

Note: Paratonic movement is a movement that is stimulated by external stimuli that include trophic, tactic, and nastic movements. They include light, chemical, and heat stimulus to induce movements. Various examples include curling of leaves, swimming of algae. Plant movements are in response to unidirectional stimuli.