Question

Plants exhibit movements in response to various environmental stimuli to adopt and survive in their surroundings. These movements, influenced by external factors such as light, gravity, water and chemicals are regulated by specific plant hormones. For example, the differential growth of plant parts allows them to bend, grow or orient themselves in particular directions. Roots and shoots often show contrasting response to the same stimulus, highlighting the complex mechanisms involved in plant growth and development.

(a) Why is hydrotropism essential for plants?

(b) What role does auxin play in the growth of plants?

(c) Differentiate between movement shown by the sensitive plant and tropic movement by plants (Two points).

OR

(c) How does movement of roots differ from that of shoots in response to gravity and light?

Answer 1

(a) Hydrotropism is the growth response of plant roots towards water. It is essential because:

1. It enables efficient water absorption from the soil, which is essential for various physiological processes.
2. It promotes the growth of roots towards areas with higher moisture, so the plant receives adequate water for survival.

(b) The role of auxin in the growth of plants is:

1. Auxin is a plant hormone that regulates growth by promoting cell elongation.
2. It facilitates phototropism (growth towards light) and gravitropism (growth in reaction to gravity) through uneven distribution, resulting in differential growth.
3. Auxin also affects root and shoot development, apical dominance, and the formation of new roots.

(c)

Aspect	Movement in Sensitive Plant (Nastic Movement)	Tropic Movement
Direction of movement:	It is independent of stimulus direction.	It is dependent on the stimulus direction.
Cause:	It is due to changes in turgor pressure.	It is due to differential growth influenced by hormones.

OR

(c) 

Stimulus	Response of roots	Response of shoots
Gravity:	Roots show positive gravitropism, i.e., they grow downwards.	shoots show negative gravitropism, i.e., they grow upwards.
Light:	Usually show negative phototropism (grow away from light)	They show positive phototropism (grow towards light).