Correct Option
The correct option is 2 only.
Explanation
The rapid leaf-folding observed in sensitive plants like Mimosa pudica (Touch-me-not) is a classic example of thigmonasty (or seismonasty). These are non-directional movements that occur in response to touch or vibration. Unlike tropic movements, which are based on growth, these rapid movements are physiological responses driven by fluid mechanics within the plant cells.
Statement-wise Analysis
- Statement 1 is Incorrect. Rapid leaf-folding is not dependent on growth. Growth-related movements (tropisms) are typically slow and directional. The folding of a sensitive plant is a turgor-based movement (nastic movement) that is rapid, reversible, and independent of the direction of the stimulus.
- Statement 2 is Correct. Plants lack a specialized nervous system. While animals have specialized tissues (nerves) for conducting information, plants do not have specific tissue dedicated solely to this function. Instead, they utilize electrical-chemical signals that travel from cell to cell to transmit information about the stimulus.
- Statement 3 is Incorrect. This statement describes the mechanism of movement in animal muscle cells, which contract by rearranging specialized proteins. In contrast, plant cells change their shape by altering the amount of water inside them. The movement is caused by a sudden change in turgor pressure (swelling or shrinking) in the cells of the pulvinus (the swollen base of the leaf stalk), not by altering protein structure.
Key Takeaway
Key Takeaway: Rapid movements in plants (nastic movements) are driven by changes in turgor pressure and are independent of growth. Unlike animals, plants do not use specialized proteins for movement or specialized nervous tissue for signal conduction.