WAEC SSCE - Biology - 1999

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The term "biotic" refers to living organisms, so the answer to this question is "Pressure," which is a non-living or abiotic factor. Biotic factors are all living things that affect an ecosystem, such as plants, animals, fungi, and bacteria. Parasites, predators, and grazers are all examples of biotic factors because they are living organisms that interact with other living organisms in an ecosystem.

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Among the options given, the trait that may not be important in marriage counseling is the color of skin. This is because skin color is not a genetic trait that can be passed down from parents to their children. Therefore, it does not have any direct impact on the health of the offspring. On the other hand, the other options, such as sex-determination, sickle-cell anaemia, and rhesus factor, are genetic traits that can affect the health of the offspring, and therefore may be important to consider in marriage counseling.

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Volvox is the organism that does not exist as a single cell. Unlike Amoeba, Euglena, and Chlamydomonas, which are unicellular organisms, Volvox is a colonial organism made up of thousands of individual cells that work together to form a larger sphere-shaped organism. These individual cells are specialized to perform specific functions, such as reproduction and movement, and work in coordination with one another to sustain the entire organism.

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Desert plants are usually called xerophytes. Xerophytes are plants adapted to survive in dry environments such as deserts. They have evolved various mechanisms to conserve water, such as reduced leaf surface area, thick cuticles, and water-storing tissues. These adaptations allow them to survive in environments where water is scarce and temperatures can be extreme.

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In water-culture experiments, protecting the culture solutions from sunlight is done in order to prevent algae from growing in the solution. Algae require sunlight for photosynthesis, and in a water-culture experiment, algae growing in the solution can interfere with the growth of the plant being studied. Therefore, shading or covering the culture solutions is a common practice in water-culture experiments to prevent the growth of unwanted organisms and ensure accurate results.

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Iodine is needed by a patient suffering from a malfunctioning of the thyroid gland. The thyroid gland uses iodine to produce hormones that help regulate the body's metabolism, growth, and development. Without enough iodine, the thyroid gland can't produce enough hormones, which can lead to a condition called hypothyroidism. Symptoms of hypothyroidism include fatigue, weight gain, and sensitivity to cold. Therefore, iodine supplementation is recommended for patients with thyroid disorders, especially those with iodine deficiency.

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Humidity may not affect living organisms in an aquatic habitat. Humidity refers to the amount of moisture in the air, which is not relevant in an aquatic habitat where the organisms are surrounded by water. Turbidity, temperature, and light are all important factors that can affect living organisms in an aquatic habitat. Turbidity refers to the clarity of the water, which can affect the penetration of light and the ability of organisms to find food. Temperature is important because it can affect the metabolic rates of organisms and their ability to survive. Light is important for photosynthetic organisms and for visual communication and orientation in many species.

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A balanced diet is important to provide good health for an individual. This is because a balanced diet contains all the necessary nutrients such as carbohydrates, proteins, fats, vitamins, and minerals in the right proportions that the body needs to function properly. These nutrients help in the growth, maintenance, and repair of body tissues and organs, as well as provide energy for daily activities. A balanced diet also helps to prevent malnutrition, obesity, and other diet-related diseases. Therefore, it is important to have a balanced diet to ensure good health and well-being.

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The medulla oblongata is a part of the brainstem that is responsible for regulating many vital autonomic functions of the body such as heart rate, breathing rate, blood pressure, and digestion. However, it does not control balance and posture. These functions are controlled by the cerebellum, a separate part of the brain. Therefore, the correct answer is "balance and posture."

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The option that is not a function of the liver in mammals is "Filtration of urea from the blood". The liver is a vital organ that performs many functions, including the ones listed in the options. However, the liver does not filter urea from the blood. Instead, the liver is responsible for converting toxic ammonia, which is produced when amino acids are metabolized, into less toxic urea, which is then transported to the kidneys and excreted in the urine.

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During prolonged exercises, glucose in the muscle is converted to lactic acid. When muscles are engaged in intense exercise, they require energy to function, and this energy is derived from glucose. The glucose is broken down in a process called glycolysis to produce pyruvic acid, which is then converted to lactic acid. The accumulation of lactic acid in the muscles can cause muscle fatigue and cramps. However, once the exercise stops, the lactic acid can be converted back to pyruvic acid and then used to produce energy for the body.

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The correct statement about variation is that "offsprings differ from their ancestors and from each other". This means that due to the process of genetic recombination and mutation, offspring inherit a unique combination of genes from their parents, which can result in differences between siblings and differences from their ancestors. While siblings may share some similarities due to inheriting some of the same genes from their parents, they are not identical and will exhibit variations in traits such as height, eye color, and hair color. These variations allow for diversity within a species and can be important for adaptation to changing environments.

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Spirogyra and pond skater can be found in a fresh water habitat. Spirogyra is a type of green algae commonly found in freshwater environments such as ponds and streams. It forms long, unbranched, filamentous strands that can be seen floating on the surface of the water. Pond skaters, also known as water striders, are insects that are adapted to life on the surface of the water. They are able to walk on water due to their specialized legs and are commonly found in calm freshwater habitats such as ponds and lakes. On the other hand, Sargassum and red mangrove are typically found in saltwater or marine environments, while dog fish is a type of shark that is also found in marine environments.

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The brooders in fishes return to their parent's mouth for protection. Some fish species, such as cichlids, have a behavior called mouthbrooding, in which the female fish carries the eggs in her mouth until they hatch and the young fish continue to stay in the parent's mouth for protection until they are able to swim independently. During this period, the parent fish provide protection against predators and ensure that the young fish have enough food and oxygen to survive. Therefore, the correct answer is protection.

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Hypermetropia, also known as farsightedness, is a refractive error of the eye in which light entering the eye focuses behind the retina instead of directly on it, resulting in blurred vision. To correct hypermetropia, a person needs a lens that can converge the light rays and focus them onto the retina. This is achieved by using a convex lens, which is thicker at the center than at the edges. The convex lens helps to refract the light rays in such a way that they converge and focus correctly on the retina, allowing a person with hypermetropia to see more clearly. Therefore, convex lenses are used to correct hypermetropia.

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Blood groups of patients is an example of discontinuous variation. Discontinuous variation refers to traits that can only be expressed in certain discrete categories, with no intermediate forms between categories. Blood groups are a good example of this because they can only fall into certain categories (A, B, AB, or O) and there are no intermediate forms. Height, complexion, and weight can all vary continuously and can fall anywhere along a spectrum.

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The correct answer is: "Reducing oxygen carrying capacity of blood." Carbon monoxide is a poisonous gas that can be emitted from incomplete combustion of fuels such as coal, wood, and gasoline. When inhaled, it binds to the hemoglobin in red blood cells, forming carboxyhemoglobin, which reduces the amount of oxygen that can be transported in the blood. This can lead to oxygen deprivation in various organs and tissues, which can have serious health consequences, including headache, dizziness, weakness, nausea, and even death.

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The statement that is correct about sex determination is "the probability of male to female offspring is 1/2". Sex determination is the process by which an individual develops into a male or female. In humans, it is determined by the combination of sex chromosomes received from the parents during fertilization. An egg from the mother always contains an X chromosome, while a sperm from the father may contain either an X or a Y chromosome. If the sperm carrying an X chromosome fertilizes the egg, the resulting offspring will be female (XX), and if the sperm carrying a Y chromosome fertilizes the egg, the resulting offspring will be male (XY). Therefore, the probability of having a male or female offspring is equal, and it is not influenced by the Y chromosome of the father or the XX chromosome of the mother. The vigour of either parent also does not determine the sex of the offspring.

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Carbon is added to the atmosphere by respiration, burning, and volcanic eruption. Carbon is removed from the atmosphere through photosynthesis, a process where plants take in carbon dioxide and convert it into oxygen and glucose. Therefore, the correct answer is "photosynthesis".

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The genotypic ratio of 1:2:1 in the offspring of a hybrid cross illustrates the law of segregation. This law states that two alleles for a trait separate during the formation of gametes, so that each gamete receives only one allele. In other words, each parent contributes one of their two alleles to their offspring, and the alleles segregate during the formation of the gametes. The resulting genotypic ratio in the offspring is 1:2:1 for the three possible genotypes, which correspond to the homozygous dominant, heterozygous, and homozygous recessive individuals. This ratio is a predictable outcome of the random segregation of alleles during gamete formation.

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The means of measuring primary production is the harvested plants in a unit area. Primary production refers to the amount of organic matter produced by photosynthesis in an ecosystem, and one way to measure this is to quantify the amount of plant material produced in a given area over a given time period. The harvested plant method involves clipping or cutting all the above-ground plant material in a defined area, drying and weighing it, and then calculating the total amount of plant biomass produced per unit area. This method provides an estimate of the amount of energy available to support other trophic levels in the ecosystem, including herbivores and carnivores. The other options listed in the question are not measures of primary production, but rather different ecological parameters such as reproductive rate, lifespan, and predator-prey relationships.

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Soil factors in an ecosystem are referred to as "edaphic". This refers to the physical and chemical properties of the soil such as pH, texture, nutrient content, and structure that influence the growth and survival of plants and other organisms living in the ecosystem. Soil factors are an important component of the ecosystem and can have a significant impact on the types of plants and animals that are able to survive in a particular area.

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The scientist involved with organic evolution is Lamarck. Lamarck was a French naturalist who proposed the theory of inheritance of acquired characteristics, which suggests that organisms can pass on traits acquired during their lifetime to their offspring. This theory was later rejected, but Lamarck's work is considered a precursor to the theory of evolution proposed by Charles Darwin. Therefore, the correct answer is Lamarck.

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During photosynthesis, light energy is absorbed by the pigment called chlorophyll. Chlorophyll is a green pigment found in the chloroplasts of plant cells and is responsible for the absorption of light energy from the sun. The energy absorbed by chlorophyll is then used to power the chemical reactions that take place during photosynthesis, ultimately converting light energy into chemical energy in the form of glucose.

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The secchi disc is used to measure the turbidity of water. It is a simple device consisting of a circular disk, typically white and black on opposite sides, that is lowered into the water until it disappears from view. The depth at which the disk disappears from view, known as the Secchi depth, is used as a measure of the water's clarity or turbidity. Turbidity refers to the degree to which the water is cloudy or hazy due to suspended particles such as sediment or plankton.

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The teeth used for tearing and cutting are canine and incisors. Canines are the long and pointed teeth located next to the incisors, and they are used for biting and tearing tough foods. Incisors are the front teeth used for biting and cutting food into smaller pieces. Together, the canines and incisors make up the front teeth of mammals and are important for the initial stages of food processing.

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The resource that is competed for by organisms in the desert is water. In the desert, water is a scarce resource, and organisms have to compete for the limited water available. Many desert plants have evolved adaptations to survive in low water conditions, such as deep root systems to access underground water and waxy coatings on their leaves to reduce water loss through transpiration. Animals in the desert have also developed various adaptations to conserve water, such as producing concentrated urine and reducing water loss through respiration. Therefore, water is a critical resource that organisms in the desert must compete for to survive.

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Schistosoma is a flatworm. Plasmodium is a protozoan parasite that causes malaria, Trypanosoma is also a protozoan parasite that causes sleeping sickness, and Ascaris is a roundworm.

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The statement that is true is: "Pepsin acts on proteins to give peptide." Pepsin is a digestive enzyme produced in the stomach that breaks down proteins into smaller peptide fragments. It is one of the main enzymes responsible for protein digestion in the human body. The other options are incorrect. Ptyalin is an enzyme found in saliva that breaks down starch into maltose and other simple sugars, lactase is an enzyme that breaks down lactose into glucose and galactose, and amylase is an enzyme that breaks down starch into maltose and other simple sugars.

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One of the similarities between algae and mosses is their possession of chlorophyll. Chlorophyll is the pigment responsible for capturing light energy from the sun and converting it into chemical energy through the process of photosynthesis. Algae and mosses both use chlorophyll to carry out photosynthesis, which allows them to produce their own food and grow. While they may differ in their physical characteristics such as the presence or absence of stems, leaves, and roots, both algae and mosses are photosynthetic organisms that rely on chlorophyll for their survival.

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Spirogyra exhibits the stages listed above during conjugation. During conjugation, Spirogyra forms a protuberance on the vegetative cell, which develops into a conjugation tube. The contents of one cell are transferred to the adjacent cell through the conjugation tube. The zygospore then secretes a thick wall and undergoes meiosis to produce four haploid cells. Finally, one of the haploid cells germinates to form a new filament.

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Root hairs absorb water from the soil by osmosis. Root hairs are slender, elongated, and tubular outgrowths that arise from the outermost layer of cells in a root known as the epidermis. They increase the surface area of the root, allowing for more efficient absorption of water and minerals from the soil. Osmosis is the movement of water molecules from a region of higher water concentration to a region of lower water concentration across a semi-permeable membrane. In the case of root hairs, the soil water has a higher concentration of water molecules compared to the cytoplasm of the root hair cell, so water moves from the soil into the root hair by osmosis.

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Well-cultivated land cannot be used for the study of succession because it lacks the natural process of vegetation establishment and development that occurs in less disturbed environments. Well-cultivated land is typically managed by humans to maintain specific crops, and the natural successional process is often interrupted by frequent disturbance, tillage, and the use of pesticides and fertilizers. Therefore, the successional stages that occur in other habitats, such as savanna grassland, abandoned farmland, and a pond, are more suitable for studying succession.

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The situation whereby some mammals remain inactive throughout dry and hot seasons is known as aestivation. Aestivation is a survival mechanism that enables some animals to conserve energy and water during periods of extreme heat and drought. During aestivation, the animals become dormant and reduce their metabolic rate to a minimum, allowing them to survive without food and water for extended periods of time. This is different from dormancy, which is a state of reduced metabolic activity in response to low temperatures or other adverse environmental conditions.

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The disease that results from the deficiency of insulin is diabetes. Insulin is a hormone produced by the pancreas that helps regulate glucose levels in the blood. In individuals with diabetes, the body either does not produce enough insulin or cannot effectively use the insulin that is produced. This leads to high blood glucose levels, which can cause a range of health problems if left untreated.

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According to Charles Darwin's Theory of Evolution, natural selection involves the survival of the fittest. This means that individuals who are best adapted to their environment are more likely to survive and reproduce, passing on their advantageous traits to their offspring. Those who are less fit are less likely to survive and reproduce, so their traits are less likely to be passed on to future generations. Over time, this can result in significant changes in a population, as the traits that confer an advantage become more common while those that are disadvantageous become less common.

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The correct option is "There are valves in veins but not in arteries." This is because veins and arteries have different structures and functions. Arteries are blood vessels that carry oxygenated blood away from the heart to the body, while veins are blood vessels that carry deoxygenated blood from the body back to the heart. The transverse section of a vein is different from that of an artery in that it has valves to prevent backflow of blood, which are absent in arteries. The lumen, or the central opening of a vein, may or may not be wider than that of an artery, depending on the specific veins and arteries being compared. The endothelium, or the inner lining of the blood vessel, may also vary in thickness between veins and arteries, but it is not necessarily always thinner in veins. The presence or absence of smooth muscles also varies depending on the specific veins and arteries being compared.

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(a)(i) Metamorphosis

Metamorphosis is the series of changes in body form and structure that an animal undergoes from the egg (or young stage) to the adult stage.

(a)(ii) Two types of metamorphosis with organisms

• Complete metamorphosis (egg → larva → pupa → adult): butterfly and housefly (also mosquito, beetle, moth).
• Incomplete (partial) metamorphosis (egg → nymph → adult): cockroach and grasshopper (also termite, locust, dragonfly).

(b)(i) Four economic importances of insects (with examples)

• Pollination of flowers: honey bee – helps in fertilisation and fruit/seed formation.
• Production of useful products: honey bee – produces honey and wax; silkworm (moth larva) – produces silk.
• Serve as food: termites and locusts – eaten by humans and animals (source of protein).
• Destruction of crops (pests): grasshopper/locust – destroys farm crops, causing loss.
• Transmission of diseases (vectors): mosquito – transmits malaria; housefly – transmits typhoid and cholera; tsetse fly – transmits sleeping sickness.
• Decomposition: some beetles help to break down dung and dead matter.

(Any four, each with an example.)

(b)(ii) Four peculiar features of social insects

• They live together in large numbers in a colony (community).
• There is division of labour, with different castes performing different duties.
• They show polymorphism, that is, different body forms for different castes (queen, workers, soldiers, drones).
• They cooperate and communicate to build and defend the nest and to care for the young.
• Only certain members (the queen/king) are fertile and carry out reproduction.

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(a)(i) Law of independent assortment

Mendel's law of independent assortment states that when two or more pairs of contrasting characters (alleles) are considered together, each pair separates and is inherited independently of the other during the formation of gametes.

(a)(ii) Findings from the red-flowered and white-flowered pea cross

When a pure-breeding red-flowered pea plant was crossed with a pure-breeding white-flowered pea plant, all the offspring of the first filial generation (F₁) were red-flowered. When these F₁ plants were self-crossed, the second generation (F₂) contained both red-flowered and white-flowered plants in the ratio of about 3 red : 1 white. This showed that red is dominant to white, and that the white character had only been hidden (masked) in the F₁, reappearing in the F₂.

(a)(iii) Illustration by diagrams

Let R = allele for red flower (dominant), r = allele for white flower (recessive).

Parents: RR (red) × rr (white)

Gametes: R and r

F₁: all Rr (red-flowered)

F₁ cross: Rr × Rr

F₂ ratio: 3 red : 1 white.

(b) Why A and B can be heterozygous or homozygous but O only homozygous

Blood groups in man are controlled by three alleles: IA and Ib, which are both dominant, and io, which is recessive. Because IA and Ib are dominant over io, group A can be produced by either IAIA (homozygous) or IAio (heterozygous), and group B can be produced by either IbIb (homozygous) or Ibio (heterozygous); in the heterozygous forms the dominant allele still expresses A or B and masks the recessive io. Group O, on the other hand, is caused only by the recessive allele io, which is expressed only when no dominant allele is present. Therefore group O can arise only from the homozygous recessive genotype ioio and cannot exist in a heterozygous state.

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(a)(i) Four similarities in plant and animal cells

• Both possess a cell membrane (plasma membrane).
• Both have cytoplasm.
• Both have a nucleus.
• Both have mitochondria.
• Both have ribosomes and an endoplasmic reticulum.

(Any four.)

(a)(ii) Four cells found in man and their functions

(Any four.)

(b)(i) Two types of cell division

Mitosis and meiosis.

(b)(ii) Two examples of life processes involving each

• Mitosis: growth (increase in body size); repair of damaged tissues / healing of wounds; asexual reproduction.
• Meiosis: formation of gametes (sperms and eggs / pollen grains and ovules); sexual reproduction (ensuring the constant chromosome number is restored at fertilization).

(c) Two types of reproduction in organisms

Asexual reproduction and sexual reproduction.

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(a) Principles of food preservation methods

• (i) Salting: salt draws water out of the food and out of any microorganisms by osmosis, creating a dry, high-salt condition in which bacteria and fungi cannot grow or multiply.
• (ii) Refrigeration: low temperature slows down (inactivates) the enzymes and the growth and multiplication of the microorganisms that cause food to spoil, so decay is delayed.
• (iii) Drying: removal of water (moisture) from the food deprives spoilage microorganisms of the water they need to grow and reproduce, and slows enzyme activity, so the food does not decay.
• (iv) Smoking: heat and smoke dry the food and coat it with chemicals (such as creosote and other antiseptic substances in wood smoke) that kill or check the growth of microorganisms.
• (v) Chemicals (chemical preservatives): added chemicals such as sodium benzoate, sugar or vinegar kill microorganisms or create conditions (acidity, high sugar concentration) in which they cannot grow.

(b) Four problems caused by human overpopulation

• Shortage of food, leading to malnutrition and hunger.
• Shortage of housing / overcrowding and growth of slums.
• Unemployment and poverty.
• Pressure on and inadequacy of social amenities (schools, hospitals, water, roads).
• Increased pollution and destruction of the environment.
• Increased spread of diseases and rise in crime rate.

(c) Three ways the Government may increase food production

• Providing loans, subsidies and farm inputs (improved seeds, fertilisers, pesticides) to farmers at cheaper rates.
• Encouraging mechanised farming and providing modern farm machinery and irrigation facilities so that larger areas can be cultivated all year round.
• Establishing agricultural research institutes to produce improved (high-yielding, disease-resistant) crop varieties and livestock breeds, and training farmers through extension services.
• Building good storage and processing facilities and good roads to reduce post-harvest losses and encourage farmers.

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(a)(i) Pollution

Pollution is the release of harmful or unwanted substances (pollutants) into the environment (air, water or soil), which makes it unclean, unsafe or unfit for living things.

(a)(ii) Two pollutants each

• Air pollutants: carbon monoxide and sulphur dioxide (also carbon dioxide, smoke/soot, oxides of nitrogen).
• Water pollutants: crude oil (petroleum) and sewage (also industrial chemicals, detergents, fertilisers, refuse).

(b)(i) Four effects of water pollution

• It kills fish and other aquatic organisms.
• It causes water-borne diseases such as cholera and typhoid in humans.
• It makes water unfit for drinking, domestic and industrial use.
• It reduces the dissolved oxygen in water (leading to death of aquatic life).
• It destroys the beauty of water bodies and can cause the growth of harmful algae (eutrophication).

(b)(ii) Four ways of preventing water pollution

• Treating sewage and industrial waste before discharging it into water bodies.
• Preventing the dumping of refuse and chemicals into rivers, streams and drains.
• Preventing oil spillage and cleaning up spills promptly.
• Enforcing laws (legislation) against polluting water bodies and educating the public.

(c)(i) Three sources of noise pollution

Vehicles and aeroplanes (traffic), industries and factory machines, and loud music/loudspeakers (also generators, blasting/explosions, market noise).

(c)(ii) Three effects of noise pollution on man

• It causes deafness or partial loss of hearing.
• It causes headache, high blood pressure and stress.
• It disturbs sleep, concentration and communication, and can cause nervousness or irritability.

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(a)(i) Hydrosphere

The hydrosphere is the part of the earth that is made up of all the water bodies; that is, the total mass of water that covers the surface of the earth in liquid, solid or vapour form.

(a)(ii) Three examples of the hydrosphere

Oceans and seas, rivers and streams, and lakes (also ponds, springs, ground water, and ice caps/glaciers).

(b) The two laws of thermodynamics

• First law (law of conservation of energy): energy can neither be created nor destroyed but can only be transformed (changed) from one form to another. In a food chain, light energy is converted into chemical energy and then into other forms.
• Second law: whenever energy is transformed from one form to another, some of the energy is lost (usually as heat) to the surroundings, so no energy transfer is 100 per cent efficient. This is why the amount of usable energy decreases from one trophic level to the next.

(c)(i) Two local biotic communities in Nigeria (with a State)

• Mangrove swamp / rainforest community – Rivers or Delta State (Niger Delta area).
• Guinea/Sudan savanna (grassland) community – Kano or Sokoto State (northern Nigeria).

(Other acceptable pairs: freshwater swamp – Bayelsa; derived savanna – Oyo.)

(c)(ii) Three factors affecting organisms in the marine habitat

• Salinity (high salt concentration of the water).
• Light penetration (which decreases with depth).
• Temperature of the water.
• Water pressure and wave/tidal action (also acceptable).

(c)(iii) Three adaptive features of seaweeds

• They have holdfasts (root-like structures) for firm attachment to rocks against wave action.
• They have flexible, slippery (mucilage-covered) bodies that bend with the waves and resist drying.
• They possess air bladders that keep the fronds afloat near the surface for adequate light for photosynthesis.
• Their whole surface can absorb water and dissolved mineral salts.