(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 ...
Question 1 Report
(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 each involved in:
(i) plant growth
(ii) animal growth.
(d) State the effects of the hormones named in (c) above.
(e) Name the type of germination which takes place in:
(i) monocotyledonous plants
(ii) dicotyledonous plants.
(f) In a tabular form state four differences between the forms of germination named in (e) above.
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
| Growth in plants | Growth in animals |
|---|---|
| Continues throughout life (indefinite) | Stops when a certain adult size is reached (definite) |
| Localised at growing regions (meristems) at root and shoot tips | Takes place all over the body (diffuse) |
(b)(ii) Two differences between metamorphosis in housefly and in toad
| Housefly | Toad |
|---|---|
| Complete metamorphosis: egg \( \rightarrow \) larva (maggot) \( \rightarrow \) pupa \( \rightarrow \) adult | Incomplete (has no pupa): egg \( \rightarrow \) tadpole \( \rightarrow \) adult |
| Development takes place on land/in decaying matter | Early development (tadpole) takes place in water |
(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
| Epigeal germination | Hypogeal germination |
|---|---|
| Cotyledons are carried above the soil surface | Cotyledons remain below the soil surface |
| The hypocotyl elongates and lifts the cotyledons up | The epicotyl elongates while the hypocotyl stays short |
| Cotyledons usually become green and may photosynthesise | Cotyledons remain within the seed coat and do not turn green |
| Common in dicots (bean, groundnut) | Common in monocots (maize) and some dicots |
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