Theory question 108
Growth and Development(For candidates in Nigeria only)
(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 8(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 8(e) above.
Show the model answer
(a) A permanent (irreversible) increase in size or dry mass of an organism due to the addition of new protoplasm.
(b)(i) Plants: growth restricted to meristems (tips) / animals: growth occurs all over the body; plants grow throughout life / animals stop growing at maturity; plants have an indefinite number of parts / animals a definite number.
(ii) Housefly: complete metamorphosis with a pupa (egg-larva-pupa-adult) / toad: no pupa (egg-tadpole-adult); housefly develops on land / toad's young develop in water; housefly is quicker.
(c)(i) Any two: auxin (IAA), gibberellin, cytokinin. (ii) Any two: growth hormone (somatotrophin), thyroxine, testosterone/oestrogen.
(d) Auxin: cell elongation, tropisms, root formation; gibberellin: stem elongation, breaks seed dormancy, larger fruits; cytokinin: cell division, growth of lateral buds. Growth hormone: growth of bones and muscles (too little causes dwarfism, too much gigantism); thyroxine: controls metabolic rate, growth and development (lack causes cretinism); sex hormones: development of secondary sexual features.
(e)(i) Hypogeal germination. (ii) Epigeal germination (most dicots, e.g. bean).
(f) Table — Hypogeal: cotyledons stay below ground / Epigeal: cotyledons are carried above ground; Hypogeal: epicotyl elongates / Epigeal: hypocotyl elongates; Hypogeal: cotyledons do not become green or photosynthesise / Epigeal: cotyledons turn green and photosynthesise; Hypogeal: plumule emerges first, protected by coleoptile (maize) / Epigeal: hypocotyl hooks out of the soil first; e.g. maize / e.g. bean.
Note some dicots (e.g. pea) germinate hypogeally; give the common case for each group.