(a) What is sexual reproduction? (b) State five functions of the placenta and four functions of the umbilical cord of a mammal. (c) List four types of place...

Answer Details

(a) Sexual reproduction is the production of new offspring by the fusion (fertilisation) of two haploid sex cells (gametes), a male gamete and a female gamete, to form a diploid zygote which develops into a new individual.

(b) Five functions of the placenta

• Allows diffusion of oxygen from the mother's blood to the foetus.
• Allows dissolved food (glucose, amino acids, minerals, vitamins) to pass from mother to foetus.
• Removes excretory wastes (carbon dioxide, urea) from the foetus into the mother's blood.
• Secretes hormones (progesterone and oestrogen) that maintain pregnancy.
• Acts as a barrier that prevents the mixing of maternal and foetal blood and keeps out some harmful microbes.

Four functions of the umbilical cord

• Connects the foetus to the placenta.
• Contains the umbilical vein that carries oxygenated, food-laden blood from placenta to foetus.
• Contains umbilical arteries that carry deoxygenated, waste-laden blood from foetus to placenta.
• Provides some support and allows the foetus to move freely in the amniotic fluid.

(c) Four types of placentation in flowering plants

• Marginal placentation
• Axile placentation
• Parietal placentation
• Basal placentation (free-central is also acceptable)

(d) Four conditions necessary for seed germination

• Water (moisture)
• Suitable (warm) temperature
• Oxygen (air)
• Viable, living embryo (with adequate stored food)