Part (A):
The movement of sensitive plant leaves (e.g., Mimosa pudica) differs from the downward root movement in the following aspects:
Sensitive Plant Leaf Movement:
- Characterized as seismonastic movement, a rapid response to touch or shaking.
- Caused by turgor pressure changes in leaflet cells, leading to folding or drooping upon disturbance. This response is quick and reversible, occurring within seconds.
- Serves as a protective mechanism against herbivores, wind, or other environmental damage.
Root Movement:
- Exhibits positive geotropism, growing towards gravity.
- A slow process regulated by the plant hormone auxin, which stimulates cell growth on the lower root side, causing downward bending.
- Essential for anchoring the plant and seeking water and nutrients.
In essence, sensitive plant leaf movement is rapid and triggered by physical stimuli, while root movement is slow, directed by gravity, and supports plant anchorage and nutrient acquisition.
Part (B):
The hormone governing carbohydrate, protein, and fat metabolism is insulin, secreted by the pancreas (specifically beta cells of the islets of Langerhans).
Significance of Iodised Salt:
Iodised salt is crucial as iodine is vital for producing thyroid hormones, thyroxine (T4) and triiodothyronine (T3), which regulate metabolism, growth, and development.
- Iodine deficiency can result in thyroid issues like goitre and hypothyroidism, impacting physical and mental development, especially in children.
- Iodised salt prevents these conditions and ensures optimal thyroid function.