The movement of leaves in a sensitive plant (Mimosa pudica) is a rapid, involuntary response to touch, known as thigmonasty, causing the leaves to fold inward quickly. In contrast, the movement of a shoot towards light, known as phototropism, is a slow, directional growth response where the plant grows towards a light source for optimal light absorption, a process driven by growth hormones.

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Rapid Response of Sensitive Plant Leaves

The sensitive plant, Mimosa pudica, exhibits a unique movement known as thigmonasty or seismonasty. This movement is a rapid, involuntary response to physical stimuli such as touch, shaking, or thermal stress. When touched, the leaves of the sensitive plant quickly fold inward and droop. This response is thought to deter herbivores or protect the plant from damage.

Mechanism behind Thigmonastic Movements

The mechanism of thigmonasty in Mimosa pudica involves a rapid change in cell turgor pressure. When the plant is stimulated, cells at the base of the leaflets lose water rapidly, leading to a loss of turgor pressure. This causes the leaves to fold and the petioles to droop. The movement is quick, often occurring within seconds of stimulation.

Phototropism in Shoots

On the other hand, the movement of a shoot towards light, known as phototropism, is a growth-oriented response. This slow, directional movement allows the plant to optimize its exposure to sunlight, which is crucial for photosynthesis. Phototropism is most commonly observed in young shoots, which bend towards the light source.

Role of Plant Hormones in Phototropism

Phototropism is primarily driven by the uneven distribution of plant hormones called auxins. When a shoot is exposed to light, auxins accumulate on the shaded side of the plant. This higher concentration of auxins on the darker side stimulates cells to elongate more than those on the light-exposed side, causing the shoot to bend towards the light.

Distinct Nature of Movements

In summary, the movement of leaves in the sensitive plant is a rapid, protective response to physical stimuli, involving changes in cell turgor pressure, while the movement of a shoot towards light is a slow, growth-driven process regulated by hormonal gradients. These distinct movements reflect the plant’s adaptation to environmental interactions – one being a defensive mechanism and the other a growth optimization strategy.

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List of Questions of Class 10 Science Chapter 6

What is the difference between a reflex action and walking?
What happens at the synapse between two neurons?
Which part of the brain maintains posture and equilibrium of the body?
How do we detect the smell of an Agarbatti (Incense Stick)?
What is the role of the brain in reflex action?
What are plant hormones?
How is the movement of leaves of the sensitive plant different from the movement of a shoot towards light?
Give an example of a plant hormone that promotes growth.
How do auxins promote the growth of a tendril around a support?
Design an experiment to demonstrate hydrotropism.
How does chemical coordination take place in animals?
Why is the use of iodised salt advisable?
How does our body respond when adrenaline is secreted into the blood?
Why are some patients of diabetes treated by giving injections of insulin?
What is the function of receptors in our body?
Draw the structure of a neuron and explain its function.
How does phototropism occur in plants?
Which signals will get disrupted in case of a spinal cord injury?
How does chemical coordination occur in plants?
What is the need for a system of control and coordination in an organism?
How are involuntary actions and reflex actions different from each other?
Compare and contrast nervous and hormonal mechanisms for control and coordination in animals.
What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?