(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 placentation in flowering plants.
(d) State four conditions necessary for seed germination.
Explanation
(a) Sexual reproduction is the fusion or joining of male and female gametes or nuclei from different individual to form a zygote which later develops into an embryo or organism.
(b) Functions of the placenta:
(i) The placenta attaches the foetus to the uterine wall of the mother.
(ii) It filters out urea or nitrogenous waste of baby's blood and transfers it to the.mother's blood and kidneys.
(iii) It absorbs digested food from the mother's blood and passes it on to foetus by diffusion.
(iv) The placenta allows passage of ingredients or antibodies that protect the developing foetus against infection.
(v) It exchanges CO from the foetus' blood for oxygen from the mother's blood.
(vi) It prevents the mixing of foetal-and mother's blood.
(vii) The placenta produces the hormones that prevent ovulation and menstruation during pregnancy.
(viii) It prevents passage of some pathogens from mother to foetus.
(ix) It converts glucose to fructose.
(x) It allows the passage of drugs or vaccines and alcohol from mother to foetus.
Functions of the umbilical cord:
(i) The umbilical cord attaches the foetus to the placenta.
(ii) The vein in the umbilical cord transports digested food and oxygenated blood from the placenta to the foetus.
(iii) The artery transports waste metabolic products or excretory products and deoxygenated blood from the foetus to the placenta
(vii) It suspends foetus in the amniotic cavity.
(c) Types of placentation in flowering plants:
(i) Axile (tomato)
(ii) Marginal (legumes)
(iii) Parietal (pawpaw)
(iv) Free-central (orange)
(v) Basal
(vi) Central
(vii) Pendulous
(viii) Superficial
(d) The conditions necessary for seed germination include;
(i) viability of seed
(ii) adequate supply cif moisture or water
(iii) suitable temperature i.e warmth
(iv) adequate supply of air e.g. oxygen
(v) suitable soil pH.