Plant Hormones and Growth Responses

Plant hormones like auxins, gibberellins, and ethene regulate various aspects of plant growth and development. Auxins in plant growth regulation play a key role in phototropism and gravitropism.

Auxins are sensitive to light and accumulate on the shaded side of plant stems. This causes faster growth on that side, making the stem bend towards light in a process called phototropism. For gravitropism, auxins gather on the lower side of horizontal stems and roots due to gravity. In shoots, this stimulates growth on the lower side, causing upward bending. In roots, auxins inhibit growth, causing downward bending.

Definition: Phototropism is the growth response of plants to light, while gravitropism is the growth response to gravity.

Gibberellins stimulate seed germination and promote flowering and fruit growth. Ethene controls cell division and fruit ripening.

Example: Auxins are used in weed killers, rooting powders, and tissue culture. Gibberellins are used to end seed dormancy and increase fruit size.

Phototropism and gravitropism practical steps involve setting up experiments to observe plant responses:

1. Use a petri dish with cotton wool and water
2. Place seeds in different light conditions
3. Measure growth and record results daily
4. For gravitropism, turn the dish on its edge

Highlight: Results typically show taller growth in darker conditions as plants grow rapidly to reach sunlight.