WAEC Biology 2013 Theory Past Questions

Model answer

(a)(i) Respiration is the process by which glucose is broken down to release energy. Respiration is said to be aerobic if it involves oxygen and anaerobic if it does not involve oxygen. (ii) Differences between gaseous exchange and aerobic respiration: Gaseous exchange: energy is not released; it occurs outside the body cells; it does not involve enzymatic reactions; it is a physical process. Aerobic respiration: energy is released; it occurs within the body cells; it involves enzymatic reactions; it is a chemical process. (b)(i) The air that is left in the lungs (not expelled during normal breathing out) is known as the residual air. (ii) Residual air is mainly there to prevent the lungs from collapsing. (c) Characteristics of respiratory structures: they are moist; they are sufficiently vascularised; they have thin membranes; they have a wide surface area. (d)(i) Oxygen debt refers to the amount of oxygen that is required to get rid of the lactic acid that has accumulated as a result of anaerobic respiration. (ii) Oxygen debt occurs as a result of strenuous exercises. Activities that can result in oxygen debt include: running, jumping, boxing.

Model answer

(a) Photosynthesis refers to the process by which green plants manufacture their food using CO₂ and H₂O in the presence of sunlight and with the release of oxygen as a by-product. (b)(i) External factors affecting the rate of photosynthesis include: light intensity, carbon dioxide, water and temperature. (ii) Internal factors affecting the rate of photosynthesis include chlorophyll and enzymes. (c)(i) The major products of the light-dependent stage of photosynthesis include hydrogen ion (H⁺), hydroxyl ion (OH⁻), nicotinamide adenine dinucleotide phosphate hydrogen (NADPH₂), and oxygen gas. (ii) H⁺ generates H₂O and oxygen gas: 4OH⁻ → 2H₂O + O₂ + 4e⁻. NADPH₂ releases hydrogen which is eventually fixed on to form carbohydrate. Oxygen gas is harnessed by living things for respiration. (d)(i) There are no green plants at the lower depths of some lakes due to the fact that the light intensity decreases as we go down an aquatic body. At a level where the amount of light is minimal, the rate of photosynthesis will be so low that the plant can barely survive. (ii) Decomposers break down dead organic matter to release nutrients back to the soil for plant uptake.

Model answer

(a)(i) Ecological succession refers to a long-term, gradual or progressive series of changes occurring in the structure, composition, variety and number of species in an area until a stable/climax community is established. (ii) The first set of organisms to inhabit a plot of land are known as the pioneers. As the pioneers die, they are broken down and nutrients are added to the soil. Higher plants and animals are now found there as the soil is more fertile. When these species die, they are also broken down to release more nutrients to the soil, and more advanced species emerge. Eventually, a stable community known as the climax community is established. (b)(i) The biosphere refers to the part of the environment where life exists. The biosphere is divided into the atmosphere, lithosphere and hydrosphere. (ii) Population refers to the total number of organisms of the same species living in a particular place at a particular time. (iii) A community is a group of organisms of different species living and interacting in a given habitat. (iv) Ecosystem refers to living organisms and their non-living environment interacting together. (c)(i) The instrument used for measuring relative humidity is the hygrometer. (ii) The instrument used for measuring the speed of wind is the anemometer. (Note: while the anemometer measures the speed of the wind, the wind vane measures the direction of the wind.)

Model answer

(a)(i) Conservation refers to the controlled use of natural resources to ensure their continuous availability and to protect the environment. (ii) Factors responsible for the decline in abundance and variety of wildlife include: deforestation, urbanization, uncontrolled hunting, environmental pollution, bush burning, and some industrial activities. (b) Ways government can improve the situation include: The foremost way is to educate people about the need for conservation of wildlife. Laws should be enacted to govern some practices. Environmental Protection Agencies should be established. Game reserves and parks should be created. Zoological gardens should be established. Campaigns should be made against bush burning. (c)(i) Eutrophication refers to the excessive growth of algae in a body of water due to an increase in minerals and nutrients. (ii) Causes of eutrophication: release of sewage into water bodies; inordinate/excessive use of fertilizers (which run off into water bodies).

Model answer

(a) The aerobic respiration of living organisms leads to the release of carbon(IV) oxide into the atmosphere. Combustion and decay are other processes that release carbon(IV) oxide into the atmosphere. This explains how carbon is released into the environment. Carbon is also removed from the atmosphere by photosynthesis, which uses up carbon(IV) oxide to build carbohydrates in green plants; these carbon compounds pass along the food chain to animals, and are also released back through respiration, decay and combustion, completing the cycle. (b)(i) Nitrogen-fixing bacteria convert nitrogen gas into ammonium compounds for plants' use. An example is Rhizobium leguminosarium (found in root nodules of leguminous plants). (ii) Nitrifying bacteria (such as Nitrobacter and Nitrosomonas) convert ammonium compounds into nitrite and then into nitrate, making nitrogen available to plants in a usable form. (iii) Denitrifying bacteria are those bacteria that break down ammonium compounds to release nitrogen back into the atmosphere as nitrogen gas.

Model answer

(a)(i) Excretion is the removal of waste products of metabolism from the body of an organism. (ii) Excretory organ — waste excreted: Skin — water, salt and urea. Liver — bile salt, water and urea. Lungs — carbon dioxide and water vapour. Kidneys — urea, water and salt. (b) Functioning of the kidney as excretory: blood from the renal artery enters the Bowman's capsule; through the afferent arteriole; ultrafiltration occurs in the Bowman's capsule; high pressure in the glomerulus causes the filtration of small molecules/amino acids/glucose/mineral salts/water/urea out of the blood plasma into the cavity of the capsule; the filtrate/glomerular filtrate passes through the nephron, where selective reabsorption of useful metabolites/glucose/amino acids takes place in the descending/first proximal convoluted tubule; the reabsorption of salts and water is regulated in the loop of Henle, and the ascending/second distal convoluted tubule; large waste molecules like creatine are secreted at the loop of Henle; depending on blood concentration, the filtrate continues into the main collecting duct/tube where further reabsorption of water and salt takes place; the remaining fluid in the duct becomes urine. (c)(i) The excretory organ in insects is the malpighian tubule. (ii) The excretory organ in earthworms is the nephridium (plural: nephridia).

Model answer

(a) Living organisms respire aerobically and release carbon(IV) oxide into the atmosphere. Combustion (of fuels) and decay (of dead organisms) are other processes that release carbon(IV) oxide into the atmosphere. Carbon is removed from the atmosphere by photosynthesis, in which green plants use carbon(IV) oxide, together with water and sunlight, to build carbohydrates. These carbon compounds are passed along the food chain from plants to herbivores to carnivores, and are eventually returned to the atmosphere or soil through respiration, excretion, death and decay, and combustion, thereby completing the cycle. (b)(i) Nitrogen-fixing bacteria convert nitrogen into ammonium compounds plants can use. An example is Rhizobium leguminosarium. (ii) Nitrifying bacteria (such as Nitrobacter and Nitrosomonas) convert ammonium compounds into nitrite and then into nitrate. Denitrifying bacteria are those bacteria that break down ammonium compounds to release nitrogen back into the atmosphere.