Theory question 108
Growth and Development(For candidates in Nigeria only)
(a)(i) Describe epigeal germination of a seed.
(ii) In a tabular form, state three differences between epigeal germination and hypogeal germination.
(b)(i) What is seed dormancy? (ii) State three ways by which dormancy in seeds can be broken.
(c) State six advantages of using contraceptives in human populations.
Show the model answer
(a)(i) The seed absorbs water through the micropyle and swells; enzymes become active and food in the cotyledons is broken down; the radicle emerges first and grows down to form the root; the hypocotyl grows rapidly, forming a hook that pulls the cotyledons above the soil; the hypocotyl straightens, the cotyledons open, turn green and photosynthesise for a while; the plumule grows up to form the first foliage leaves; e.g. bean.
(ii) Table — Epigeal: cotyledons brought above the soil / Hypogeal: cotyledons remain below the soil; Epigeal: hypocotyl elongates / Hypogeal: epicotyl elongates; Epigeal: cotyledons become green and photosynthesise / Hypogeal: cotyledons do not; e.g. bean / e.g. maize.
(b)(i) Seed dormancy is the state in which a viable seed does not germinate even when conditions (water, oxygen, warmth) are suitable.
(ii) Any three: scarification (scratching/cracking the testa); soaking in water to leach out inhibitors; treatment with gibberellin; exposure to light or to low temperature (stratification); heat/fire; passage through an animal's gut; ageing/after-ripening.
(c) Any six: prevents unwanted pregnancy; allows spacing of births; helps control population growth; improves health of mother and child; some (condoms) prevent sexually transmitted infections including HIV; allows parents to plan family size they can support; reduces unsafe abortions; lets women continue education/careers.
Use a ruled table in (a)(ii).