WAEC Biology 2012 Theory Past Questions

Model answer

(a) Factors affecting diffusion: Temperature — the higher the temperature the higher the rate of diffusion and vice-versa. Surface area — the larger the surface area of the exposed fluid, the faster the diffusion and vice-versa. Size of particles — small particle tends to diffuse faster than big ones. State of matter — diffusion occurs the fastest in gases, intermediate in liquids and slowest in solids. (b)(i) Active transport is simply defined as the movement of molecules against the concentration gradient. (ii) Transpiration is the loss of water in the form of water vapour from the stomata, lenticels or cuticle of a plant. (c) Ways by which plants can reduce the rate of transpiration include: closing of stomata, development of thick cuticle, reduction of leaf size, and the presence of hair on leaves. (d) The disc-like shape of red blood cells (erythrocytes) makes it able to house sufficient amount of oxygen. The haemoglobin in erythrocytes aids the attachment of oxygen.

Model answer

(a) The role of the stomach in digestion is mainly as a result of the presence of the gastric juice. The gastric juice contains pepsin, rennin and HCl. Pepsin converts protein to peptones. Rennin curdles/coagulates milk — it does this by converting soluble caseinogens to insoluble casein. HCl helps to neutralize the base in the saliva and also activates pepsin (it converts inactive pepsinogen to active pepsin). (b)(i)/(ii) Roots: cassava and sweet potatoes. Stems: sugarcane and ginger. Leaves: onions and garlic. (c) The regulation of blood sugar is done by the liver, using the hormones (insulin and glucagon) secreted by the pancreas. When the blood sugar level is high, the pancreas stimulates the... conversion of glucose into glycogen. When the blood sugar level is low, the pancreas secretes glucagon which stimulates the conversion of glycogen back to glucose.

Model answer

(a)(i) Conservation refers to the judicious use of natural resources to ensure their continuous availability. (ii) Endangered species are organisms that are very few in number due to man-made or natural causes. These organisms, if care is not taken, stand the chance of becoming extinct. (b)(i) Reasons for conservation of forests: Forests serve as a source of tourism. It prevents the extinction of some species. Forests serve as natural habitat for some organisms. Forests provide timber for many constructions. Forests play an important role in the maintenance of oxygen and carbon dioxide balance. (ii) Ways of conserving forest: Controlled deforestation. Ensuring afforestation. Establishment of forest reserves. Enactment of sustainable forest laws. (c)(i) Decomposers help to release nutrients from plants and animals remains for plants' uptake. (ii) Earthworm is a good example of an animal decomposer, while mushroom (a fungus) is an example of a plant decomposer.

Model answer

(a)(i) A gene is defined as a unit of inheritance. (ii) Genotype refers to the genetic constitution of an organism while phenotype refers to the observable features of an organism. The phenotype of an organism depends on the genotype and the environment. (b)(i) Hybrid refers to the progeny of a cross between organisms with contrasting characters. (ii) Pure breeding occurs when a particular trait is retained in subsequent generations. (iii) A nucleotide is a unit of DNA. Each nucleotide contains a five-carbon sugar, phosphate group and an organic nitrogen-containing base (adenine, guanine, cytosine or thymine). (c) Note: since smooth is dominant over rough, if a smooth seed coat is dominant over rough seed coat, the said parent could only be rough coated if they have no gene for smooth seed coat at all; consequently, there is no way such parents could produce an offspring that would be smooth coated. (i.e. the cross of homozygous recessive rough (rr) with a plant that is itself rough-coated, having rough-coated parents — meaning it too is homozygous recessive rr — produces only rough-coated offspring, all rr.)

Model answer

(a)(i) Disease is a state of infirmity or lack of wellbeing. (ii) Symptoms of a disease are those observable manifestations of the disease, for instance, painful urination is a symptom of gonorrhea. (b)(i) Physical barriers that prevent pathogens from penetrating the body of an organism include the skin and mucus membranes. Chemical barriers include sebum and mucus, which are chemical examples of such. (ii) Vaccination works basically by stimulating the immune system to recognize and combat pathogens, by introducing molecules from the pathogen into the body. (c) Antibodies are produced in response to the presence of a foreign substance (i.e. antigen) and are proteinous in nature. Antigens are substances which invoke immune responses; they are proteins but may also be lipids, polysaccharides or even nucleic acids, and cause disease or allergic reaction. Antibodies protect the body by lysis of antigenic materials. (Lysis means the breakdown or rupture of the membrane of a cell.) (d)(i) The causative agent of malaria is Plasmodium spp. (ii) The causative agent of cholera is Vibrio cholerae. (iii) The causative agent of AIDS is Human Immuno-deficiency Virus (HIV).

Model answer

(a)(i) Epigeal germination is a type of germination in which the cotyledons are carried above the soil. The hypocotyl elongates rapidly and arches upwards, moving the cotyledon above the soil. (ii) Differences — Hypogeal germination: the cotyledon remains under the soil; the epicotyl elongates faster; the cotyledon cannot photosynthesize. Epigeal germination: the cotyledon is carried above the soil; the hypocotyl elongates faster; the cotyledon photosynthesizes. (b)(i) Seed dormancy refers to the slowing down or seizure of the growth of a seed. (ii) Ways dormancy can be broken include addition of water, treatment with some enzymes, and exposure to alternating low and high temperature. (c) Advantages of using contraceptives in human populations: It prevents over-population. It controls birth rate. It prevents unwanted pregnancies. Some of them (barrier contraceptives) prevent sexually transmitted diseases. It promotes standard of living. It helps to control the size of a family.