WAEC SSCE - Biology - 2013

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Ecology is the study of the interrelationship between organisms and their environment. It focuses on how living things interact with each other and with their physical surroundings. Ecologists study the relationships between organisms and their habitats, how energy and nutrients flow through ecosystems, and how human activities impact the natural world. By understanding ecology, we can better protect and manage our environment for the benefit of both humans and other living organisms.

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The bacteria that reduce nitrates in the soil into gaseous nitrogen are referred to as "denitrifying bacteria". Denitrifying bacteria convert nitrates, which are important nutrients for plants, into gaseous nitrogen, which cannot be used by plants. This process is part of the nitrogen cycle and helps to maintain a balance of nitrogen in the soil.

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The structure that is only formed during cell division in animal cells is the centrosome. The centrosome is responsible for organizing microtubules which are necessary for cell division. During interphase, which is the period between cell divisions, centrosomes are not present. However, during cell division, the centrosomes duplicate and move to opposite poles of the cell, forming the spindle apparatus which is crucial for proper chromosomal segregation. Therefore, the correct answer is option (C) centrosome.

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Haemophilia is a genetic disorder that is passed down from parent to child through their genes. It is a recessive disorder, which means that an individual must inherit two copies of the defective gene (one from each parent) in order to have the disorder. In this case, the man has haemophilia, which means he has two copies of the defective gene. The woman is a carrier, which means she has one normal gene and one defective gene. When they have children, each child has a 50% chance of inheriting the defective gene from their mother and a 50% chance of inheriting the defective gene from their father. Therefore, the probability of their children having haemophilia is 50%.

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Glucose is not a complex carbohydrate. Glucose is a simple sugar, also known as a monosaccharide, and it is the primary source of energy for many organisms. Complex carbohydrates are made up of long chains of simple sugars and include substances like glycogen, cellulose, and starch.

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The structure that is not essential in a wind-pollinated flower is the petal. Wind-pollinated flowers do not need to attract pollinators with bright colors and scents, so they often have inconspicuous petals. Instead, they rely on the wind to carry pollen from the male reproductive structures (anthers) to the female reproductive structures (stigmas). The ovary is also essential for wind-pollinated flowers to produce seeds, while the anther and stigma are important for the transfer of pollen.

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Darwin noticed that organisms in similar habitats across the world looked alike, which illustrates convergent evolution. Convergent evolution occurs when different species that are not closely related evolve similar traits in response to similar environmental pressures. In this case, the similar habitats across the world created similar environmental pressures on different species, resulting in the development of similar traits.

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The correct arrangement of food classes of the same quantity in the order of magnitude of energy value in animals in descending order is "Fats and oils, carbohydrates, protein, water". This is because fats and oils have the highest energy value per unit mass compared to other food classes. Carbohydrates have an intermediate energy value, while proteins have the lowest energy value. Water does not provide any energy value as it is not a source of energy but an essential component for life processes.

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Insects breathe through small openings on their body surface called spiracles. These spiracles lead to a system of internal tubes called tracheae, which transport oxygen to the cells for respiration. Therefore, the correct option is Spiracles.

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Glomerular filtrate is a liquid that is formed in the glomerulus of the mammalian kidney. It is formed by filtering blood from the renal artery. One substance that can be found in the glomerular filtrate is glucose. Glucose is a simple sugar that serves as a major source of energy for the body.

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In genetics, linkages refer to the linking of genes of the same chromosome. Chromosomes contain genes, and each chromosome carries a large number of genes that determine different traits. Genes located on the same chromosome tend to be inherited together, rather than being independently assorted. This is because during meiosis, homologous chromosomes pair up and exchange genetic material through a process called recombination. The closer two genes are on a chromosome, the less likely they are to be separated by recombination events, and the more likely they are to be inherited together, which is called linkage. The degree of linkage between two genes can be measured by the frequency of recombination events between them.

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The main reason for immunizing children is to stimulate the production of antibodies. Immunization, also known as vaccination, is a process that involves introducing a weakened or dead pathogen or a part of it into the body of an individual, usually through injection. The body then responds by producing specific antibodies to fight the pathogen. The antibodies are produced in large numbers, providing immunity to the individual against that particular disease. Immunization helps to prevent the spread of infectious diseases and protects individuals, especially children, from serious and life-threatening illnesses.

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The producers in a food chain in an aquatic environment are phytoplankton. Phytoplankton are microscopic organisms that live in water and convert sunlight, carbon dioxide, and nutrients into organic matter through the process of photosynthesis. They are the primary producers in aquatic environments and serve as the base of the food chain, providing food for zooplankton, small fishes, and other aquatic organisms. Without phytoplankton, the food chain in aquatic environments would collapse, leading to a loss of biodiversity and a disruption of ecosystem services.

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Ascaris lumbricoides is a parasitic roundworm. It is one of the most common intestinal parasites found in humans, and it can cause a disease called ascariasis. The adult worms live in the intestines and feed on the contents of the digestive system. The eggs are passed out of the body in the feces and can contaminate the soil. When the eggs are ingested by another host, they hatch into larvae, which migrate to the intestines and develop into adult worms, continuing the life cycle.

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Anaerobic respiration is the process of producing energy in the absence of oxygen. Unlike aerobic respiration, it produces less energy. The end products of anaerobic respiration in animals are lactic acid or ethanol and carbon dioxide. In plants, the end product is ethanol and carbon dioxide. Therefore, the correct option is "less energy than aerobic respiration".

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The function of the drone in a colony of bees is to mate with the queen. Drones are male bees that are reared solely for the purpose of reproduction. Their main task is to mate with the queen bee and ensure the survival of the colony. After mating, the drones die. Therefore, they do not engage in other activities such as cleaning cells, protecting the colony or laying eggs, which are the responsibilities of female bees.

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The absence of alimentary canal in the parasitic flatworm can be attributed to the fact that its body absorbs digested food. Parasitic flatworms are adapted to a parasitic lifestyle and obtain their nutrients by absorbing digested food directly from the host's body. They do not need a digestive system to break down food, and therefore, they lack an alimentary canal. The nutrients obtained from the host's body are absorbed directly through their body wall. This adaptation helps the flatworms to remain inside the host's body for a longer period, increasing their chances of survival and reproduction.

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The statement "blood passes from of blood into the right ventricle to the left auricle through the aorta" is not correct about the mammalian heart. This statement is incorrect because the aorta is a large artery that carries oxygenated blood from the left ventricle of the heart to the rest of the body, while the blood passes from the right ventricle to the left atrium through the pulmonary vein. The tricuspid valve prevents the backflow of blood into the right atrium, not the left atrium. The walls of the ventricles are thicker than those of the atria because they have to pump blood to the rest of the body.

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An increase in leaf surface area to volume ratio is likely to increase the rate of transpiration in plants. This is because transpiration occurs when water evaporates from the surface of leaves into the atmosphere through small pores called stomata. The larger the leaf surface area, the greater the number of stomata available for water to evaporate from, and the faster the rate of transpiration. Additionally, a smaller leaf volume relative to its surface area means that the water has to travel a shorter distance from the innermost cells to the stomata, which can also increase the rate of transpiration. Therefore, an increase in leaf surface area to volume ratio will result in an increase in the rate of transpiration in plants.

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The enzyme that catalyses the conversion of glucose to glucose-6-phosphate at the beginning of glycolysis is hexokinase. This enzyme transfers a phosphate group from ATP to the 6-carbon of glucose, producing glucose-6-phosphate. This phosphorylation step helps to trap glucose inside the cell and prepares the molecule for further processing in glycolysis.

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The correct arrangement of tissues in the anatomy of a young dicotyledonous stem from the inside to the outside is: - pith, xylem, cambium, phloem, cortex, collenchyma, and epidermis. Explanation: - Pith is a central region of parenchyma cells in the stem. - Xylem is located just outside the pith, and it transports water and minerals from roots to leaves. - Cambium is a layer of meristematic cells between xylem and phloem, which can differentiate into both types of tissues. - Phloem is located on the outer side of cambium, and it transports sugars from leaves to other parts of the plant. - Cortex is a layer of ground tissue located outside the phloem. - Collenchyma is a type of ground tissue located just below the epidermis and helps provide support to the plant. - Epidermis is the outermost layer of cells that protects the plant and helps in the exchange of gases and water vapor. Therefore, the correct option is: pith, xylem, cambium, phloem, cortex, collenchyma, and epidermis.

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The correct answer is "homeostasis." Homeostasis refers to the process by which the body of a mammal maintains a stable internal environment, despite changes in the external environment. This is achieved through a variety of mechanisms, including the regulation of body temperature, the balance of fluids and electrolytes, and the control of hormone levels. The body constantly monitors and adjusts these factors in order to maintain a stable, healthy internal environment.

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If the boy has blood type O, that means he received an O allele from his father, as O is recessive and masks the expression of A and B alleles. Since his mother has blood type A, she could have either genotype AA or AO, with either of them possessing an A allele. Therefore, the father must have genotype AO or OO to pass on an O allele to the son. So, the possible genotypes of the father are AO or OO.

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Chameleons are known for their remarkable ability to change the color of their skin to match their surroundings, which is called adaptive coloration. They use this feature as a survival mechanism to escape predation. By blending in with their environment, chameleons can avoid detection by predators, making it easier for them to hide or flee. Therefore, adaptive coloration is the feature used by chameleons to escape predation.

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The gene that is only located on X-chromosome is said to be sex-linked. Sex-linked genes are those genes that are located on the sex chromosomes (X or Y) and are typically associated with traits that are more commonly expressed in one sex than the other. In humans, sex-linked genes on the X chromosome are particularly important because males only have one X chromosome while females have two, which means that mutations on X-linked genes can lead to different genetic disorders or diseases that are expressed differently in males and females.

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If the shoot tip of a plant is cut off and replaced by an agar block containing auxin, the plant will grow rapidly. This is because auxin is a plant hormone that promotes cell elongation and division. When the shoot tip is cut off, the plant loses its source of auxin, which normally inhibits the growth of lateral buds. By replacing the shoot tip with an agar block containing auxin, the plant is provided with a source of the hormone that stimulates the growth of the lateral buds, leading to the rapid growth of the plant. Therefore, is the correct answer.

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A man with blood group AB has two different alleles (A and B) and no allele for O. For the man to pass on blood group O to his child, he must contribute an O allele. However, since he does not have an O allele, he cannot pass it on to his child. Therefore, the probability of the man giving birth to a child with blood group O is 0%.

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Ultra-filtration is the process of filtering blood in the kidneys to form urine. This process occurs in the nephron, which is the functional unit of the kidney. Bowman's capsule is the part of the nephron that is associated with ultra-filtration. It is a cup-shaped structure that surrounds the glomerulus, which is a network of tiny blood vessels. As blood flows through the glomerulus, Bowman's capsule filters out water, ions, and small molecules such as glucose and amino acids, while preventing the passage of larger molecules such as proteins and blood cells. The filtered fluid then moves through the nephron, where additional processes take place to form urine. Therefore, the correct answer is Bowman's capsule.

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Rhizobium is an example of mutualism. Mutualism is a type of symbiotic relationship between two organisms where both organisms benefit from each other's presence. In this case, Rhizobium lives in the root nodules of leguminous plants and fixes atmospheric nitrogen into a form that can be used by the plant. In return, the plant provides the bacteria with nutrients and a suitable environment to live in. This association is mutually beneficial to both the plant and the bacteria, making it an example of mutualism.

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The statement that the diaphragm is made of epithelial cells is not correct. The diaphragm is a sheet of muscle that separates the thorax from the abdomen in mammals, including humans. It is an important muscle for respiration, contracting and flattening when the lungs inhale and relaxing back into a dome shape when the lungs exhale. The diaphragm is not made of epithelial cells, which are a type of tissue that line organs and body cavities, but rather it is made up of muscle fibers.

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The process by which plants manufacture food from carbon dioxide and water using energy from the sun is called photosynthesis. In simple terms, it is the way plants produce their food. During photosynthesis, plants take in carbon dioxide from the air, water from the soil, and sunlight, and use these raw materials to produce glucose (sugar) and oxygen. This process is critical to the survival of plants, as well as to the well-being of the entire planet, as it produces the oxygen that we and other organisms need to breathe.

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The scientist who was involved in the development of evolution theory is Lamarck. He proposed the theory of inheritance of acquired characteristics, which suggested that traits acquired during an organism's lifetime could be passed down to its offspring. He also proposed that organisms adapt to their environment over time, which is now known as the principle of use and disuse. Lamarck's ideas were later built upon by Charles Darwin, who is considered the father of the theory of evolution by natural selection.

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The maximum size of a population that a given area can support is known as carrying capacity. Carrying capacity refers to the number of individuals of a species that can be sustained by the available resources, such as food, water, and shelter, in a particular environment. Once a population reaches its carrying capacity, it means that the environment can no longer support additional individuals of that species. At this point, the population growth rate slows down and may eventually stabilize. Understanding the carrying capacity of a particular ecosystem is important in managing and conserving natural resources.

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The members are most similar in the species level of classification. The species is the basic unit of classification in the biological classification system, and it refers to a group of organisms that share similar characteristics and are capable of interbreeding to produce viable offspring. Members of the same species have the highest level of similarity because they share many common traits, such as physical appearance, behavior, and genetic makeup. On the other hand, organisms in higher levels of classification such as phylum or order have fewer similarities, as they encompass a wider range of organisms with varying characteristics. Therefore, the correct answer is species.

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The animal which possesses scales, nares, and a backbone is likely to be a lizard. Lizards are reptiles and possess scales which provide protection and help in reducing water loss. They also have nares or nostrils which are openings for the nasal passage. Lizards have a backbone or vertebral column which is part of their skeletal system, and it supports and protects their spinal cord. Toads are amphibians and do not possess scales, while rats and bats are mammals and do not have scales or nares.

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The statement "increasing the amount of rainfall" is not a reason for conserving wildlife. While wildlife can play a role in maintaining ecosystem balance and contributing to environmental health, it does not directly impact rainfall. The other statements, on the other hand, are valid reasons for conserving wildlife. For example, conserving wildlife can attract tourists who are interested in viewing and experiencing the natural beauty and diversity of a region. It can also serve as a source of food for local communities and as a source of income for those involved in activities such as ecotourism, wildlife conservation, and scientific research.

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Plasma is not a skeletal tissue. Plasma is a component of blood and is mainly composed of water, electrolytes, proteins, and other nutrients that are essential for maintaining bodily functions. Skeletal tissues include bone, cartilage, and chitin, which provide support and protection to the body.

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The opening of the guard cells of the epidermis in plants is by the process of **osmosis**. Guard cells are specialized cells that control the opening and closing of stomata on the surface of leaves. When water is absorbed by the guard cells, they become turgid and swell, causing the stomata to open. This process is due to the movement of water through the cell membrane from an area of low solute concentration (outside the cell) to an area of high solute concentration (inside the cell), which is called osmosis. The opening and closing of stomata are important for gas exchange and regulating water loss in plants.

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(a)(i) Respiration

Respiration is the process by which food substances (mainly glucose) are oxidised within living cells to release energy (stored as ATP) needed for the activities of the organism, usually with the uptake of oxygen and release of carbon dioxide and water.

(a)(ii) Four differences between gaseous exchange and aerobic respiration

(b)(i) Residual air

Residual air is the volume of air that remains in the lungs and cannot be breathed out even after the most forceful expiration.

(b)(ii) Importance of residual air

It keeps the alveoli (air sacs) inflated so they do not collapse, and it allows continuous gaseous exchange between breaths, so oxygen is still absorbed into the blood even during expiration.

(c) Four characteristic features of respiratory structures

1. They have a large surface area for maximum gaseous exchange.
2. They are thin (one or few cells thick) for rapid diffusion of gases.
3. They are moist so that gases dissolve before diffusing.
4. They are well supplied with blood vessels (highly vascular) to maintain a steep diffusion gradient.

(d)(i) Oxygen debt

Oxygen debt is the extra amount of oxygen that the body needs to take in after vigorous exercise, to oxidise the lactic acid that accumulated in the muscles during anaerobic respiration.

(d)(ii) Three activities that can result in oxygen debt

• Sprinting / fast running (a race).
• Weight lifting / heavy physical work.
• Vigorous swimming or fast cycling.

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(a) Photosynthesis

Photosynthesis is the process by which green plants manufacture their own food (glucose) from carbon dioxide and water, using light energy trapped by chlorophyll, and releasing oxygen as a by-product. It is summarised as:

(b) Factors affecting the rate of photosynthesis

• (i) Four external factors: light intensity, concentration of carbon dioxide, temperature, and availability of water.
• (ii) Two internal factors: amount of chlorophyll present, and the number/distribution of stomata (also acceptable: accumulation of end products, leaf structure).

(c)(i) Major products of the light-dependent stage

• Oxygen.
• ATP (energy).
• Reduced hydrogen carrier (NADPH₂), formed from the splitting of water (photolysis).

(c)(ii) Importance of each product

• Oxygen: released to the atmosphere and used by living organisms for respiration.
• ATP: supplies the energy used in the light-independent (dark) stage to fix carbon dioxide into glucose.
• Reduced NADP (NADPH₂): supplies the hydrogen used to reduce carbon dioxide to carbohydrate in the dark stage.

(d)(i) Why there are no green plants at the lower depths of some lakes

Light does not penetrate to the great depths of the water; without light the green plants cannot carry out photosynthesis to make food, so they cannot survive there.

(d)(ii) Why decomposers are important to flowering plants

Decomposers break down dead organisms and wastes, releasing mineral nutrients (for example nitrates, phosphates, carbon dioxide) back into the soil and air, which the flowering plants absorb and use for growth and photosynthesis.

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(a)(i) Excretion

Excretion is the process by which living organisms remove the waste products of metabolism (for example carbon dioxide, urea, excess water and mineral salts) from their bodies. If these wastes were allowed to accumulate they would be poisonous to the organism.

(a)(ii) Excretory organs in humans and the waste product excreted by each

(b) Excretory organs in other animals

• (i) Insects: Malpighian tubules (they excrete uric acid).
• (ii) Earthworms: nephridia.

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(a) The carbon cycle

The carbon cycle is the continuous circulation of carbon between the atmosphere, living organisms and the non-living environment.

• Carbon exists in the air as carbon dioxide. Green plants take in this carbon dioxide and, by photosynthesis, fix it into organic food (carbohydrates), so carbon becomes part of the plant body.
• Animals feed on the plants (and on other animals), so the carbon passes along food chains into animal bodies (feeding/nutrition).
• Plants and animals return carbon dioxide to the air through respiration.
• When plants and animals die, decomposers (bacteria and fungi) break down their bodies, releasing carbon dioxide back into the air during decay.
• Combustion (burning) of wood and of fossil fuels (coal, petroleum, natural gas), which were formed from the buried remains of organisms, also returns carbon dioxide to the atmosphere.

In this way the amount of carbon in circulation is kept roughly in balance.

(b) Functions of bacteria in nature

• (i) Nitrogen-fixing bacteria: convert free atmospheric nitrogen into nitrogen compounds (ammonia/nitrates) that plants can absorb and use; for example Rhizobium in the root nodules of legumes and free-living Azotobacter.
• (ii) Nitrifying bacteria: convert ammonium compounds to nitrites (Nitrosomonas) and nitrites to nitrates (Nitrobacter), making nitrate available to plants (nitrification).
• (iii) Denitrifying bacteria: break down nitrates in the soil into free gaseous nitrogen, which is released back into the atmosphere (denitrification).

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(a)(i) Ecological succession

Ecological succession is the gradual and orderly replacement of one community of organisms by another in an area over time, until a stable climax community in equilibrium with its environment is established.

(a)(ii) Ecological succession on a bare plot of land

The succession may be represented as follows. The rising curve shows the gradual increase in vegetation biomass, soil depth and complexity of the community from the pioneer stage to the climax stage.

1. A bare plot is first colonised by pioneer organisms such as algae, lichens and mosses which can tolerate harsh conditions.
2. As the pioneers grow and die, their remains decay and add humus and mineral nutrients to the surface. Their activities also help to break down the surface and form a thin soil layer.
3. The improved soil retains more water and supports grasses, herbs, ferns and small animals such as insects and worms.
4. Continued death and decay of organisms make the soil deeper and more fertile. Perennial grasses are then replaced by shrubs and small trees.
5. Eventually, large trees and a greater variety of animals, including birds and mammals, become established.
6. A stable climax community, such as a forest where climatic conditions permit, is finally formed. It remains in dynamic equilibrium with the environment.

(b) Explanation of terms

(i) Biosphere: the parts of the earth, including land, water and air, in which life exists.

(ii) Population: all the organisms of the same species living in a particular area at a given time.

(iii) Community: all the populations of different species living and interacting in the same habitat.

(iv) Ecosystem: a functional natural unit made up of living organisms and their non-living environment interacting with one another.

(c) Instruments

Quantity measured	Instrument
(i) Relative humidity	Hygrometer, or wet-and-dry bulb thermometer
(ii) Wind speed	Anemometer

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(a)(i) Conservation

Conservation is the wise use, protection and careful management of natural resources (wildlife, forests, soil, water) so that they are not destroyed or wasted but are preserved and made available for present and future generations.

(a)(ii) Six factors responsible for the decline in abundance and variety of wildlife

1. Indiscriminate hunting and poaching of wild animals.
2. Destruction of habitats through deforestation and clearing of land for farming and settlement.
3. Bush burning, which destroys animals and their habitats.
4. Pollution of air, water and soil.
5. Overgrazing and overexploitation of resources.
6. Introduction of pests, diseases and predators; and use of pesticides.

(b) Six ways the government can improve the situation

1. Establish and protect game reserves, national parks and forest reserves.
2. Enact and enforce laws against poaching, indiscriminate hunting and bush burning.
3. Ban or license the hunting of endangered species and set closed seasons.
4. Practise afforestation and reforestation to restore habitats.
5. Educate the public on the importance of wildlife conservation.
6. Control pollution and the misuse of pesticides; and set up breeding/restocking programmes.

(c)(i) Eutrophication

Eutrophication is the excessive enrichment of a body of water with mineral nutrients (especially nitrates and phosphates), which causes a rapid overgrowth of algae and water plants; when these die and decay, the dissolved oxygen is used up and aquatic animals die.

(c)(ii) Two causes of eutrophication

• Run-off of nitrate and phosphate fertilizers from farmland into water.
• Discharge of sewage and detergents (phosphates) into water bodies.