(a) In a tabular form distinguish between tropic movement and nastic movement (b) Explain how light brings about tropic movement in the stem and root of a f...

Answer Details

(a) Tropic movement versus nastic movement

(b) How light brings about tropic movement in the stem and root

Light coming from one side causes the growth hormone auxin to move to the shaded (dark) side of the shoot tip. In the stem, the extra auxin on the dark side makes those cells elongate faster than the lit side, so the stem bends and grows towards the light: the stem is positively phototropic. In the root, the same higher concentration of auxin on the dark side slows down growth there (roots are inhibited by high auxin), so the lit side grows faster and the root bends away from the light: the root is negatively phototropic.

(c) Observation when a growing seedling is placed horizontally

Under the influence of gravity, auxin gathers on the lower side of both stem and root. The stem tip bends and grows upward (away from gravity, negatively geotropic) because the lower side grows faster, while the root tip bends and grows downward (towards gravity, positively geotropic) because the extra auxin slows the lower side of the root. The seedling therefore turns so the shoot points up and the root points down.

(d) Five functions of the pituitary gland

1. Secretes growth hormone that controls growth of the body.
2. Secretes hormones that control the thyroid gland (TSH).
3. Secretes hormones that control the adrenal cortex (ACTH).
4. Secretes hormones (FSH and LH) that control the gonads and reproduction.
5. Secretes anti-diuretic hormone (ADH) that controls water reabsorption in the kidney, and prolactin/oxytocin for milk production and birth.

(e) Two differences between growth in plants and in animals