Theory question 106
Reproduction in Animals(a) Explain briefly the following types of fertilization in animals: (i) external fertilization; (ii) internal fertilization. (b) Name two groups of animals each that exhibit the types of fertilization in 6(a): (i) external fertilization; (ii) internal fertilization. (c)(i) If the placenta in a pregnant woman is detached from uterine wall, give three effects this would have on the foetus. (ii) Name three other features in the uterus of pregnant woman that are useful for the development of the foetus. (d) Explain briefly how the activities of organisms bring about dynamic equilibrium in the habitat. (e) State four problems that organisms in the intertidal zone of a marine habitat could encounter. (f) Explain briefly the reason that following factors are necessary for germination: (i) moisture; (ii) viable seed. (g) Explain briefly the reason light energy is considered a limiting factor in the production of food by autotrophs.
Show the model answer
(a)(i) External fertilisation: the male and female gametes are released into water and fuse outside the female's body.
(ii) Internal fertilisation: the male places sperm inside the female's body and the gametes fuse inside her reproductive tract.
(b)(i) External, any two: fishes (bony fish such as tilapia), amphibians (toads, frogs).
(ii) Internal, any two: mammals, birds, reptiles, insects.
(c)(i) Any three: the foetus will not get oxygen; it will not get food (nutrients); its wastes (CO2, urea) will not be removed; it will lose protection by maternal antibodies; it may die (miscarriage/stillbirth); bleeding.
(ii) Any three: umbilical cord; amnion (amniotic sac) with amniotic fluid; chorion; thick, blood-rich uterine wall (endometrium); muscular uterine wall.
(d) Producers make food, consumers eat producers and other consumers, and decomposers return nutrients to the soil; predators keep prey numbers in check and prey numbers limit predators; materials such as carbon, nitrogen and water are cycled. These feeding relationships and cycles keep population sizes and materials fairly steady over time, which is dynamic equilibrium.
(e) Any four: drying out (desiccation) when the tide goes out; changes in temperature; changes in salinity; strong wave action that can wash them away; predators from land and sea at different tides; changes in oxygen supply; strong sunlight.
(f)(i) Moisture: water activates the enzymes in the seed, softens the seed coat and dissolves stored food so it can move to the growing embryo.
(ii) Viable seed: only a seed with a living embryo can respire and grow; a dead (non-viable) seed cannot germinate whatever the conditions.
(g) Light supplies the energy for photosynthesis. When light is weak (or absent), the rate of photosynthesis is held back even if CO2, water and temperature are favourable, so the factor in shortest supply (light) limits how much food autotrophs can make.
Section C (candidates in Nigeria only). Answer every lettered part briefly.