WAEC Biology 2020 Theory — Question 5

Model answer

(c)(i) Effects on the foetus if the placenta is detached: It will cause the foetus to stop receiving food. It will stop the removal of waste products from the foetal blood. It may lead to still birth. (ii) Other features present in the uterus of a pregnant woman useful for foetal development: Chorion; Allantois; Amnion; Amniotic fluid. (d) The activities of organisms are a driving tool for the dynamic equilibrium in a habitat. For instance, the activities of decomposers (such as bacteria, fungi and some protists) help to release nutrients into the soil; the CO2 released during respiration is harnessed during photosynthesis, and the O2 released during photosynthesis is used for respiration. (e) Problems that organisms in the intertidal zone of a marine habitat could encounter: Desiccation/drying up; Oxygen deficiency; Reduced visibility; Varied osmotic balance; Fluctuation of water temperature. (f)(i) Moisture is necessary for germination to soften the testa or seed coat so that the plumule and radicle can easily come out. It is also required to activate the cell. (ii) For a seed to germinate, it must be alive or viable. Seeds that are already damaged by insects, birds etc cannot germinate as they are not viable. (g) Sunlight is needed to split water into hydrogen ions and hydroxyl ions (in a process known as photolysis). Photolysis is an important step in photosynthesis, and light energy provides the energy needed for this process; hence it is a limiting factor in food production by autotrophs.