All 27 questions from the West African Examinations Council (WAEC) Biology 2011 Theory paper, with the correct answer and a full explanation for each. Free, no signup needed.
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PART I (Answer two questions only from this part) 1(a)(i) What is the effect of gravity on plant growth?
Model answer
The root grows towards gravity (i.e. exhibits positive geotropism) while the shoot grows away from gravity (i.e. exhibits negative geotropism).
1(a)(ii) Describe an experiment to demonstrate the effect of gravity on the roots of plants.
Model answer
Demonstration of the effect of gravity on the roots of plants using a potted plant and Klinostat: Seeds of cowpea are sown in small pots (one seed per pot). After the appearance of the first foliage leaves, the pots are placed in the dark with the seedlings in a horizontal position. A klinostat with a seedling is also kept working in a horizontal position to serve as a control. The whole set-up is left for about 24 hours. After 24 hours, the shoot of the seedling in the pot curves and grows vertically upwards (away from gravity). If the soil is carefully washed off, it will be observed that the root has curved downwards (towards gravity). The shoot of the working klinostat remains in a horizontal position and does not curve.
1(b) How is bitter taste detected in humans?
Model answer
The substance first dissolves in the saliva. As the taste buds that detect bitter taste are located at the back of the tongue, the sensory cells at the back of the tongue are stimulated and the impulse is passed to the brain for interpretation.
1(c) Copy and complete the table below on endocrine glands and their functions (Thyroid; Insulin/Pancreas; and a third gland producing development of secondary sexual characters of females).
Model answer
Thyroid gland produces Thyroxine, which controls the rate of metabolism. Pancreas produces Insulin (converts glucose to glycogen) and Glucagon (converts glycogen to glucose). Ovary produces Oestrogen, responsible for development of secondary sexual characteristics of females.
2(a) Make a diagram 8-10cm long to show the relative position of the following organs in the mammalian gut: (i) stomach (ii) pancreas (iii) liver (iv) gall bladder (v) duodenum and label fully.
Model answer
See labelled diagram: Oesophagus (gullet) leads to the Stomach; the Liver produces bile which passes through the Bile duct from the Gall bladder; the Pancreas releases pancreatic juice through the Pancreatic duct; the Duodenum receives secretions from the bile duct and pancreatic duct.
2(b)(i) List two diseases of the liver.
Model answer
Liver diseases include liver cancer, hepatitis, liver abscess and liver cirrhosis (any two).
2(b)(ii) State five effects of the diseases in 2(b)(i) on the human body.
Model answer
Liver diseases cause: fatigue/tiredness; painful sensations; jaundice; loss of appetite; loss of weight (any five).
2(c) State the deficiency symptoms of the following vitamins: (i) vitamin A (ii) vitamin C (iii) Vitamin K
Model answer
(i) Deficiency of vitamin A causes night blindness. (ii) Deficiency of vitamin C causes scurvy. (iii) Deficiency of vitamin K causes haemophilia (poor blood clotting).
3(a)(i) State the second law of thermodynamics.
Model answer
The second law of thermodynamics, as it applies to biological systems, states that when energy is transferred, there will be less energy available at the end of the transfer process than at the beginning.
3(a)(ii) Use the second law of thermodynamics to explain the flow of energy across different trophic levels in a food chain.
Model answer
The highest amount of energy is found in the producers. When the primary consumers feed on the producers, energy is transferred to the primary consumers. However, according to the second law of thermodynamics, this energy transfer is never 100% efficient, so the primary consumers only acquire a fraction of the initial total energy. This loss of energy continues as we move across the trophic levels.
3(b)(i) State three factors that can likely limit the size of human populations.
Model answer
Factors that can limit the size of human populations include: diseases, low birth rate, high death rate, wars, and emigration (any three).
3(b)(ii) Outline two ways each by which humans can overcome the factors named in 3(b)(i).
Model answer
Ways to overcome disease: immunization and good sanitation. Ways to overcome low birth rate: provision of basic amenities and encouragement of polygamy. Ways to curb emigration: provision of adequate food and shelter. Ways to control war: prohibition of illegal firearms and good governance. Ways to reduce high death rate: provision of adequate security and good medical care.
4(a)(i) What is the difference between the genotype and phenotype of an individual?
Model answer
The genotype of an organism is its genetic make-up, while the phenotype refers to its observable features. The phenotype depends on both the genotype and the environment.
4(a)(ii) State two factors each which determine each of the terms in 4(a)(i).
Model answer
Factors affecting genotype: the genotype of the parents and mutation. Factors affecting phenotype: genes and environment.
4(b) In a breeding experiment a homozygous dog (BB) was crossed with a homozygous white dog (bb) to produce black puppies in the first filial generation (F1). The second filial generation produced a total of two hundred and forty (240) black and white puppies. With the aid of a genetic diagram, determine: (i) the number of white puppies (ii) the number of black puppies in the second filial generation.
Model answer
Since the original parents are BB and bb, all of the F1 will be Bb (black). Crossing F1 x F1 (Bb x Bb) gives F2 ratio BB:Bb:Bb:bb = 1 black : 2 black : 1 white, i.e. 3 black : 1 white. (i) Number of white puppies = 1/4 x 240 = 60. (ii) Number of black puppies = 3/4 x 240 = 180.
PART II (Answer one question only from this part) 5(a)(i) What is putrefaction?
Model answer
Putrefaction is the process by which dead organic matter is broken down/decomposed by some organisms (known as agents of putrefaction).
5(a)(ii) What is nitrogen fixation?
Model answer
Nitrogen fixation is the process by which some organisms (such as rhizobium leguminosarium) convert atmospheric nitrogen to soil nitrates.
5(a)(iii) What is nitrification?
Model answer
Nitrification is the process by which some bacteria (the nitrifying bacteria - nitrobacter and nitrosomonas) convert ammonium compounds to nitrites and then nitrates.
5(a)(iv) What is denitrification?
Model answer
Denitrification is the process by which soil nitrate is converted to atmospheric nitrogen by some bacteria known as denitrifying bacteria.
5(b) State three differences between nitrogen fixation and denitrification.
Model answer
During nitrogen fixation, nitrogen is converted to nitrate; during denitrification, nitrate is converted to atmospheric nitrogen. Nitrogen fixation involves nitrogen-fixing bacteria while denitrification involves denitrifying bacteria. Nitrogen fixation requires moderate soil temperature while denitrification requires high soil temperature.
5(c) Explain how nitrogen from urine gets to the roots of plants in solution form.
Model answer
When urine is released onto the soil, urea (an ammonium compound) is converted into nitrite by nitrosomonas. Eventually, the nitrite is converted into nitrate by nitrobacter. The nitrate is then transported through the root in solution form.
6(a)(i) What is immunity?
Model answer
Immunity is the ability of the body to resist or fight off infection or diseases.
6(a)(ii) Explain two ways by which a person becomes immune to yellow fever.
Model answer
The immune system enjoys immunity against yellow fever either naturally or artificially acquired. Naturally Acquired Immunity: this is through the production of antibodies by the body which help combat the disease. Artificially Acquired Immunity: this is through the production of antibodies by vaccination.
6(a)(iii) Name four diseases for which babies are immunized.
Model answer
Diseases against which babies are immunized include poliomyelitis, measles, tuberculosis and tetanus.
6(b) What is translocation?
Model answer
Translocation is the process by which manufactured food substances are moved from the site of production to where they are either used or stored.
6(c)(i) State three differences between the transport system in flowering plants and mammals.
Model answer
The medium of transport in mammals is blood (and lymph) while in flowering plants it is water. Transport in mammals is by pumping action of the heart, while transport in flowering plants results from biophysical processes such as transpiration and osmosis. Transport in mammals does not depend on environmental factors, while transport in flowering plants depends on environmental factors.
6(c)(ii) State three similarities between the transport system in flowering plants and mammals.
Model answer
Both require a fluid medium; both employ vessels; both supply nutrients.
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