(a) What is growth? (b) State two differences each between; (i) growth in plants and animals (ii) metamorphosis in housefly and toad. (c) Name two hormones ...

Answer Details

(a) Growth is the permanent (irreversible) increase in size, mass and volume of an organism resulting from cell division, cell enlargement and the addition of new living material.

(b)(i) Two differences between growth in plants and in animals

(b)(ii) Two differences between metamorphosis in housefly and in toad

(c) & (d) Hormones and their effects

(i) Plant growth hormones

• Auxin: promotes cell elongation of shoots, controls phototropism and geotropism, and promotes root formation in cuttings.
• Gibberellin: promotes stem elongation, breaks seed dormancy and stimulates germination and flowering.

(ii) Animal growth hormones

• Growth hormone (somatotrophin, from the pituitary): stimulates general body growth, especially of bones and muscles; excess causes gigantism and deficiency causes dwarfism.
• Thyroxine (from the thyroid gland): controls the rate of metabolism and is necessary for normal growth and development (in amphibians it brings about metamorphosis).

(e) Type of germination

• (i) Monocotyledonous plants (for example maize): hypogeal germination.
• (ii) Dicotyledonous plants (for example bean/cowpea): epigeal germination.

(f) Differences between epigeal and hypogeal germination