Question

Name the movement which causes 'X' and 'Y' to grow downwards and upwards respectively.

Answer 1

The movement which causes 'X' (roots) to grow downwards is known as geotropism (or gravitropism), which is the growth of plant parts in response to gravity. In this case, the roots grow downwards due to gravity. The movement which causes 'Y' (stem) to grow upwards is known as phototropism, which is the growth of plant parts in response to light. In this case, the stem grows upwards towards the light source.

Answer 2

The following plant hormones are involved in the processes mentioned: 1. Falling of leaves (abscission): The hormone responsible for the falling of leaves is Abscisic acid (ABA). It plays a significant role in promoting leaf senescence and abscission, which leads to the leaves falling from the plant. 2. Rapid cell division: The hormone responsible for rapid cell division, particularly during growth phases, is Cytokinin. Cytokinins promote cell division and play a role in delaying leaf senescence.

Answer 3

The sensitive plant, Mimosa pudica, exhibits rapid movement of its leaves in response to touch. This movement is known as thigmotropism, which is the plant's response to mechanical stimuli. \flushleft Communication of the Touch Stimulus:
1. When the plant's leaves are touched, it triggers a change in turgor pressure in the cells of the leaf. This is caused by the movement of water out of the vacuoles in certain cells of the leaf. 2. The change in turgor pressure leads to the folding of the leaflets. The rapid movement occurs because the plant cells respond to the mechanical stimulus through changes in ion concentration and water movement. 3. This response is an adaptation to protect the plant from herbivores. The quick movement of leaves makes the plant appear less palatable to herbivores or insects.

Answer 4

The plant hormone that is synthesized at the shoot tip is Auxin. Role of Auxin in Bending Towards Light:
- Auxin is a growth hormone that is responsible for phototropism (growth in response to light). When light shines on one side of a plant, auxin accumulates on the shaded side of the plant.
- The increased concentration of auxin on the shaded side promotes cell elongation, causing the cells on that side to grow longer than those on the lighted side.
- This differential growth results in the bending of the plant towards the light source.