WAEC SSCE - Biology - 1996

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The phenomenon whereby some organisms get established in an environment after struggling for existence by taking advantage of some special features possessed by the organism is called natural selection. Natural selection is the process by which organisms with advantageous traits or characteristics are more likely to survive and reproduce in a given environment compared to those with less advantageous traits. As a result, the advantageous traits become more common in the population over time, leading to the evolution of new species. This process is driven by competition for resources and other environmental pressures, such as predators or disease, that favor certain traits over others.

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The culture solution turned green due to the growth of algae. Algae can grow in water culture experiments when there is sufficient light and nutrients present in the solution. To prevent the culture solution from turning green, the beaker should have been covered with a dark material or placed in a dark environment to limit the amount of light reaching the solution. This will reduce the amount of light available for the growth of algae. Alternatively, the experiment could have been carried out in a growth chamber where the light intensity and duration can be controlled to prevent excessive growth of algae.

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The movement of water across a semi-permeable membrane from a weaker solution to a stronger solution is known as osmosis. In osmosis, water moves across a membrane from a region of high water concentration (weaker solution) to a region of low water concentration (stronger solution) in an attempt to equalize the concentration of solutes on both sides of the membrane. This process continues until the concentration of solutes on both sides of the membrane is the same or until the pressure on the stronger side is too high for water to move.

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Plasmodium is a parasitic organism that lives inside the red blood cells of its host. Therefore, the pathway of energy that will reach Plasmodium in the red blood cells is pathway II only, which is "Energy passes to decomposers and parasites". In this pathway, energy is transferred from one organism to another in a food chain, and in the case of Plasmodium, it gets its energy from the red blood cells it infects. Pathways I, III, and IV are not relevant to the energy transfer to Plasmodium as they do not involve the transfer of energy to parasites.

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The material that is not required for insect collection in an ecological field-trip is the Secchi disc. A Secchi disc is a device used to measure the transparency of water bodies and is not related to insect collection. The other options are commonly used materials for insect collection during ecological field-trips. - Pooter: A small device used for aspirating small insects and other invertebrates. - Spreading board: A flat surface used for spreading and mounting insects for study and preservation. - Jar containing alcohol: Used for killing and preserving insects collected in the field. - Sweep net: A net used to sweep through vegetation and collect insects.

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Continuous tillage can have a negative impact on an ecological system, which is a decrease in productivity. This is because continuous tillage causes soil erosion, which leads to a decrease in soil fertility and loss of important nutrients. As a result, the yield of crops will decrease over time. Additionally, continuous tillage also leads to the destruction of soil structure, which is an important aspect of soil health.

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Cells undergoing meiosis are seen in the ovary of a flower. Meiosis is a type of cell division that leads to the formation of sex cells (gametes) such as sperm and egg cells. In flowering plants, the ovary is the female reproductive organ that contains the ovules which eventually develop into seeds. During meiosis, the diploid cells in the ovary divide to form haploid cells that become the egg cells. Therefore, meiosis occurs in the ovary of a flower, where the reproductive cells are formed.

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The Tulgren’s funnel is used to extract minute soil organisms. The funnel consists of a glass funnel with a stem and a collecting jar. The soil sample is placed in the upper part of the funnel, and a light source is placed above it to drive the organisms downwards. As the organisms move through the soil, they fall into the collection jar below. This is a useful tool for studying the biodiversity and abundance of microorganisms in the soil.

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Option II - Thoracic vertebrae articulate with the ribs. The thoracic vertebrae are the twelve vertebrae of the upper back, between the cervical (neck) vertebrae and the lumbar vertebrae. Each thoracic vertebrae has a pair of ribs attached to it on either side. The rib bone curves around and attaches to the vertebra, forming a joint that allows for movement during breathing. Therefore, the correct answer is II.

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The non-renewable resource among the options provided is minerals. Minerals are naturally occurring substances that are extracted from the earth for human use, such as for building materials, electronics, and fuel. Unlike renewable resources such as forests and livestock, minerals are finite and their reserves can be depleted over time with extraction and use. Therefore, they are considered non-renewable resources.

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Fat droplets are not cell organelles. They are storage structures that are found within cells, especially adipose cells. These droplets are made up of triglycerides, which are fats that have been stored for future use. Cell organelles, on the other hand, are specialized structures within cells that perform specific functions. Examples of cell organelles include the nucleus, ribosomes, Golgi body, endoplasmic reticulum, mitochondria, and chloroplasts (in plant cells).

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Cross-breeding is a way of applying the principles of heredity in agriculture to develop superior varieties of plants and animals. It involves the deliberate breeding of two different varieties or breeds of the same species in order to obtain offspring with desirable traits from both parents. The process of cross-breeding can result in offspring that are stronger, more disease-resistant, or have other desirable traits, depending on the specific goals of the breeding program. Cross-breeding is a common practice in modern agriculture and has been used to produce a wide variety of crops and livestock with improved traits.

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The correct answer is IV, cervical vertebrae. The cervical vertebrae are located closest to the skull and form the neck region of the vertebral column. The thoracic vertebrae are located in the chest region, lumbar vertebrae in the lower back, sacral vertebrae in the pelvic region and caudal vertebrae in the tail region.

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The ecological condition which favours the spread of malaria is the presence of stagnant water in ponds. Stagnant water provides a suitable breeding environment for mosquitoes, which are the vectors responsible for transmitting the malaria parasite to humans. The mosquitoes lay their eggs on the surface of stagnant water, and the larvae develop in the water. If the water is not disturbed, it can serve as a breeding ground for many generations of mosquitoes, increasing the risk of malaria transmission in the area. Therefore, the proper management of stagnant water in ponds is necessary to control the spread of malaria.

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Ecology may not yield strong evidence of evolution. Ecology is the study of how organisms interact with their environment, their behavior, and their distribution. While it can provide indirect evidence of evolution, such as changes in species distribution over time, it does not directly study the genetic changes that drive evolution. In contrast, fields like genetics, cytology, and histology can provide direct evidence of evolutionary changes at the genetic and cellular levels, and fossils provide direct evidence of changes in the physical structures of organisms over time.

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Encouraging poaching is not a way of conserving natural resources. Poaching refers to the illegal hunting, killing or capturing of wild animals, which can lead to the depletion of animal populations and loss of biodiversity. Conservation, on the other hand, involves the protection and management of natural resources to ensure their sustainable use for present and future generations. Therefore, encouraging poaching would not be a way of conserving natural resources, but rather, it would lead to their destruction.

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The nucleus is labelled structure II. The nucleus is a membrane-bound organelle that contains genetic material (DNA) and regulates the activities of the cell by controlling gene expression. It is usually the largest organelle in eukaryotic cells and is responsible for the cell's growth, metabolism, and reproduction. In the given options, structure II is the only one that resembles the typical appearance of a nucleus with a round shape, distinct boundary, and a dense, central region called the nucleolus.

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Gametes are reproductive cells that fuse during sexual reproduction to form a zygote. Out of the given options, the pair of gametes is "Ova and spermatozoa". Ova, also known as eggs, are female gametes produced in the ovary, while spermatozoa are male gametes produced in the testes. When they unite during fertilization, they form a zygote, which develops into a new individual.

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The statement "The lymph vessels are always larger in size than the arteries" is not correct. Arteries are blood vessels that carry oxygenated blood away from the heart to different parts of the body, while lymph vessels are part of the lymphatic system and carry lymph, a fluid that contains immune cells and waste products, from the body tissues back to the bloodstream. Lymph vessels are generally smaller in size than arteries. The other statements are correct. The flow of lymph is assisted by general muscular movement, lymph flows only in one direction due to the presence of valves, lymph is emptied into the blood circulatory system through a vein, and lymph nodes become swollen during serious infections as a result of increased immune activity.

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The most sensitive part of the retina is called the fovea centralis. It is located at the center of the macula lutea, which is a small yellowish spot in the retina responsible for central vision. The fovea contains a high concentration of cone cells, which are responsible for color vision and visual acuity (sharpness of vision). The fovea is important because it allows us to see fine details and perceive colors with greater clarity than other parts of the retina.

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The part labelled I in A represents the "hypocotyl". The hypocotyl is the part of the embryonic stem of a plant that is located between the cotyledons (seed leaves) and the radicle (embryonic root). It is responsible for the elongation of the stem during germination and emergence of the seedling from the soil. The hypocotyl also helps to support the cotyledons and protects the developing shoot apical meristem.

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The yellow color in this case can be said to be recessive to red. This is because when the red variety of pepper was crossed with the yellow variety, all the offspring produced were red, indicating that the red trait was dominant. When these red offspring were self-pollinated, they produced both red and yellow peppers, indicating that the yellow trait was present but hidden in the previous generation. This suggests that the yellow trait is recessive to the red trait. In genetics, dominant traits mask recessive traits, and recessive traits only express themselves in the presence of two copies of the same gene (homozygous recessive) or in combination with a dominant allele (heterozygous). Therefore, the yellow pepper in this case is homozygous or heterozygous for the recessive trait.

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Nitrifying bacteria are responsible for the conversion of nitrites to nitrates in the nitrogen cycle. This process is known as nitrification and involves two separate steps. First, nitrosomonas bacteria convert ammonia (NH3) to nitrite (NO2-), and then nitrobacter bacteria convert nitrite (NO2-) to nitrate (NO3-). Nitrates are an important form of nitrogen that plants can use to grow. Without nitrifying bacteria, the nitrogen cycle would be incomplete and plants would not have access to the nitrogen they need to survive.

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The statement "Members of a population may be of the same species but do not interbreed" is not true of a population. A population is defined as a group of individuals of the same species that live in the same area and can interbreed. If members of the same species do not interbreed, they belong to different populations. Therefore, this statement is not true of a population.

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Homologous chromosomes do not occur in pairs naturally is not a true statement about chromosomes. Homologous chromosomes are chromosome pairs (one from each parent) that are similar in size, shape, and carry the same genes but can have different alleles. They occur naturally in diploid cells, which have two sets of chromosomes, one from each parent. The other statements are true about chromosomes. Each chromosome is made up of two chromatids that are held together by a centromere. Body cells have diploid numbers of chromosomes, meaning they have two sets of chromosomes. The sex cells have haploid number of chromosomes, meaning they have only one set of chromosomes. Finally, chromosomes have many transverse bands that help to distinguish one chromosome from another and aid in their identification.

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The statement(s) related to Darwin's theory of evolution are II and IV only. Darwin's theory of evolution states that organisms produce many offspring and members of a species vary. This variation leads to differences in phenotype, which can be selected for by the environment. The changes in the phenotype are not brought about by the individual itself, but rather by natural selection acting on the variation present in the population. Therefore, statement III, which refers to the inheritance of acquired characters, is not related to Darwin's theory of evolution.

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Infant paralysis is not a hereditary variation. Infant paralysis, also known as poliomyelitis, is a viral disease that affects the nervous system and is transmitted through contaminated food and water. It is not a genetic trait that is passed down from parents to offspring. The other options listed are all examples of hereditary variations: blood group, sickle cell trait, shape of face and nose, and colour of hair are all determined by genes that are inherited from parents.

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The correct answer is "Water, carbon dioxide and energy." During aerobic respiration, glucose is broken down in the presence of oxygen to produce water, carbon dioxide and energy. The process occurs in the mitochondria of the cell and involves several steps, including glycolysis, the Krebs cycle, and the electron transport chain. The energy produced is in the form of ATP (adenosine triphosphate), which is used by the cell for various metabolic activities.

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The structure that articulates with the pelvic girdle in mammals is the sacral vertebrae, which is represented by option V in the given list. The sacral vertebrae are located at the base of the vertebral column, just above the caudal vertebrae. They are fused together to form the sacrum, which is a bony structure that articulates with the pelvic girdle. The sacrum helps to provide stability and support to the pelvic girdle, and it also plays a role in transferring weight and force from the upper body to the lower limbs during locomotion.

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Producers are the organisms responsible for capturing energy for the biotic community. They are typically plants or algae that can convert energy from the sun through photosynthesis into a form that can be used by other organisms. This energy is then passed on to other organisms in the food chain. Consumers, omnivores, detritus feeders and decomposers all rely on producers to obtain energy for survival.

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The term for the maintenance of a constant internal environment of an organism is called "homeostasis". It refers to the process of regulating the internal conditions of an organism despite changes in the external environment. This allows the organism to maintain a stable and functional state, which is necessary for survival and proper physiological functioning. Homeostasis is achieved through various biological processes, such as feedback mechanisms, hormonal regulation, and physiological responses to environmental stimuli.

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The social insects are those insects that live in colonies or groups and exhibit cooperative behaviors. Of the options listed, the honey bee is a social insect because they live in colonies with a queen bee, worker bees, and drones. They have a complex social organization and division of labor, with each individual having a specific role to play in the colony. In contrast, mosquitoes, butterflies, grasshoppers, and cockroaches are not social insects and generally live solitary lives.

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Biotic components refer to living things, while abiotic components refer to non-living things. The interaction between the biotic and abiotic components is what makes up an ecosystem. Out of the options given, "osmosis" is not due to interaction between the biotic and abiotic components of an ecosystem. Osmosis is the movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. It is a physical process that occurs due to differences in water concentration and does not involve living organisms or the environment. The other options - soil nutrient depletion, condensation, decomposition, and photosynthesis - all involve interactions between living organisms and the environment. Soil nutrient depletion occurs when living organisms consume nutrients from the soil, leading to a decrease in the availability of nutrients for other organisms. Condensation is a process that occurs when water vapor in the atmosphere interacts with cooler air, leading to the formation of clouds and precipitation. Decomposition is the breakdown of organic matter by microorganisms, which releases nutrients back into the soil. Photosynthesis is a process in which plants use energy from the sun to convert carbon dioxide and water into glucose and oxygen. Therefore, the correct answer is "osmosis."

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The need for conservation aims to protect natural resources for the benefit of current and future generations. It involves preserving them for scientific and recreational purposes, ensuring that everybody benefits from them, and keeping them sustainable for continued use. However, the option that does not fit in with these objectives is to maximize the use of natural resources. Conservation focuses on using natural resources sustainably, which means using them in a way that balances their benefits with their impact on the environment. Therefore, maximizing the use of natural resources could lead to their depletion and ultimately undermine the goals of conservation.

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The instrument that can be used to perform an experiment on geotropism is the klinostat. A klinostat is a device that is used to study geotropism, which is the growth of a plant in response to gravity. It is designed to rotate a plant at a constant speed, which cancels out the effect of gravity, and allows the experimenter to study the effects of other stimuli, such as light, on the growth and orientation of the plant. Therefore, the correct answer is the third option, klinostat. The other options are instruments used for different experiments in biology, such as measuring water uptake in plants (potometer), wind speed (cup anemometer), recording muscle movements (kymograph), and blood pressure (sphygmomanometer).

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The correct sequence, starting from the most complex to the simplest level of organization in living things, is: System → Organ → Tissue → Cell. Explanation: A system is made up of different organs that work together to perform specific functions, such as the digestive system or the circulatory system. Organs are composed of different tissues that work together, for example, the heart is made up of muscle tissue, connective tissue, and nervous tissue. Tissues are made up of similar cells that work together to perform a specific function. Cells are the smallest unit of life, and they are the building blocks of tissues. Therefore, the correct sequence, starting from the most complex to the simplest level of organization, is System → Organ → Tissue → Cell.

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Temperature is an abiotic factor that affects a population. Abiotic factors are non-living components of an ecosystem, and they can have a significant impact on the growth and survival of organisms. Temperature affects the metabolism, reproduction, and behavior of organisms, and it can also influence the distribution and abundance of species in an ecosystem. For example, some species are adapted to specific temperature ranges and may struggle to survive or reproduce outside of those ranges. Therefore, changes in temperature can have profound effects on populations and communities of organisms.

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In grasshopper/cockroach digestion starts from the mouth. When they eat, their mouthparts cut and grind the food. Saliva is added to the food to help moisten and digest it. The food then passes through the oesophagus, crop, gizzard and midgut where further digestion and absorption of nutrients occurs.

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The option that is not an aquatic habitat is "Rainforest". Rainforest is a terrestrial habitat found in areas with high rainfall and biodiversity. It is characterized by tall trees, dense vegetation, and high humidity. On the other hand, aquatic habitats are those that are in or near water. These habitats can be freshwater or saltwater, and may include ponds, estuaries, swamps, and salt lakes.

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Urea is more concentrated in the blood within the renal artery than the blood within the renal vein. The renal artery carries blood from the heart to the kidneys, while the renal vein carries blood from the kidneys back to the heart. The kidneys filter waste products from the blood, and urea is one of the primary waste products of protein metabolism. As blood flows through the kidneys, urea is removed from the blood and excreted in the urine. Therefore, the blood within the renal vein has a lower concentration of urea compared to the blood within the renal artery, as the renal vein has already undergone filtration and removal of waste products.

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Hydra captures small crustaceans by means of tentacles. Hydra is a freshwater cnidarian that feeds on small aquatic organisms, such as crustaceans, by using its tentacles. These tentacles are armed with specialized stinging cells called nematocysts, which can immobilize and capture prey. Once the prey is immobilized, the tentacles bring it to the mouth of the Hydra, where it is engulfed and digested.

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The entire habits and habitat of an organism can be described as its ecological niche. An ecological niche includes all the physical, chemical, and biological factors that an organism needs to survive and reproduce in its environment. This includes its food sources, shelter, temperature, humidity, and other abiotic factors, as well as its interactions with other organisms in the community, such as predators, competitors, and symbiotic partners. The ecological niche is a fundamental concept in ecology and helps us understand how different species interact and coexist in their environment.

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The type of relationship that exists in the large intestine of sheep between bacteria and the sheep is symbiosis. Symbiosis refers to a close and long-term interaction between two different species, where both benefit from the relationship. In the large intestine of sheep, bacteria break down the cellulose and other complex substances in the plant material consumed by the sheep, producing simpler compounds that the sheep can digest and utilize for energy. The bacteria, in turn, obtain a stable habitat and a constant supply of nutrients from the sheep's intestine. This mutualistic relationship benefits both the bacteria and the sheep, and is an example of symbiosis.

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Nephridium is a type of excretory organ found in annelids, which are segmented worms. Therefore, the group in which nephridium is found is "Annelids".

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The characteristic that is not true of tropical rainforest is "Annual rainfall is less than 100 cm". This statement is incorrect because the tropical rainforest is known to have high annual rainfall, typically ranging from 1750 to 2000 mm (or 175-200 cm) per year. The other characteristics mentioned are true of tropical rainforests. Tropical rainforests are characterized by tall trees with thick canopies, epiphytes and climbers, low light intensity, high humidity, and damp floors. The fruits of trees are often large-sized and adapted for dispersal by animals rather than wind.

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(a) Two advantages of complex structural organisation in higher organisms

• Division of labour through cellular differentiation: similar cells become grouped and specialised into tissues, organs and systems, so that each part carries out one particular function efficiently (for example, muscle cells for movement and nerve cells for coordination). This mutual interdependence between cells increases overall efficiency.
• Greater adaptation and independence from the environment: the specialised systems (circulatory, respiratory, excretory) allow the organism to maintain a stable internal environment, grow larger in size and survive in varied or changing external conditions.

(b)(i) Two differences between colonial organisms and filamentous organisms

Colonial organism	Filamentous organism
Identical cells form a loose ball or mass with no true intercellular cross wall between them.	Identical cells are joined end to end by intercellular cross walls to form a thread-like, linear structure.
Cells are linked by cytoplasmic bridges and are physiologically dependent on one another.	Each cell is physiologically independent and can carry out its life processes on its own.

(b)(ii) Examples

• Colonial organism: Volvox (or Pandorina).
• Filamentous organism: Spirogyra (a filamentous alga).

(c) Labelled diagram of the structure of a named filamentous alga (Spirogyra)

The diagram below (drawn 10 to 12 cm long) shows part of a Spirogyra filament: a chain of long, cylindrical cells joined end to end by cross walls, each cell containing one or more spiral (ribbon-like) chloroplasts bearing pyrenoids, with the nucleus suspended in the centre by cytoplasmic strands.

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(a) Transmittable (heritable) characters

(i) In human beings:

• Colour of the eyes (eye colour)
• Colour of the skin
• Blood group (A, B, AB, O)

(ii) In plants:

• Height of the plant (tallness or shortness)
• Colour of the flower
• Shape or colour of the seed

(b) Three ways genetics has contributed to the improvement of agriculture

• Production of improved (high-yielding) varieties: selective breeding and hybridisation have produced crops and animals that give higher yields of grain, milk, meat or eggs.
• Development of disease- and pest-resistant varieties: genetics is used to breed crops and livestock that resist diseases and pests, reducing losses.
• Breeding for desirable qualities and adaptation: production of varieties that are early maturing, drought resistant, or tolerant of poor soils, and animals with better feed conversion (also improved food quality).

(c) Cross between a homozygous tall parent and a homozygous short parent

Let the allele for tallness be T (dominant) and for shortness be t (recessive).

Parental genotypes: tall = TT; short = tt.

Gametes: T from the tall parent; t from the short parent.

First filial (F₁) generation: all offspring are Tt (heterozygous) and are therefore all tall, since T is dominant. Ratio: 100% tall.

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(a) Competition is the struggle or interaction between organisms for the same limited resources (such as food, water, light, space, mates or shelter) when the supply of the resource is not enough for all of them.

(b)(i) Interspecific (interspecies) competition is competition that takes place between organisms of different species for a common resource, for example a lion and a hyena competing for the same prey, or maize and weeds competing for soil nutrients and light.

(b)(ii) Intraspecific (intraspecies) competition is competition that takes place between organisms of the same species for the same resource, for example two cocks competing for the same hen, or maize plants in a crowded field competing for light and nutrients. It is usually more intense because the needs are identical.

(c) Structural adaptations of the toad/frog

(i) For obtaining food

• A long, sticky, protrusible tongue attached at the front of the mouth which can be shot out rapidly to trap insects.
• A wide gape (large mouth) and backwardly directed teeth (in the frog) that hold the prey and prevent its escape; large bulging eyes that help detect moving prey.

(ii) For protection

• Camouflage (cryptic) colouration of the skin (greenish/brown) that blends with the surroundings and hides it from enemies.
• Poison (mucous) glands in the skin (especially the parotid glands of the toad) that secrete an irritating/toxic fluid to discourage predators.

(iii) For movement

• Long, muscular hind limbs that are folded and act like springs to leap on land.
• Webbed hind feet that increase surface area and push against water for efficient swimming.

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(a) Osmoregulation is the control of the water and solute (salt) balance of an organism so that its internal osmotic pressure is kept steady.

(i) In a named unicellular organism (Amoeba / Paramecium)

Amoeba lives in fresh water. The surrounding water is more dilute (hypotonic) than the cell contents, so water continuously enters the cell by osmosis across the cell membrane. To avoid bursting, the excess water collects in a contractile vacuole. The vacuole gradually fills, moves to the surface and discharges the water to the outside (osmoregulation by active removal of water). This is repeated continually, using energy (ATP).

(ii) In man

Osmoregulation is carried out mainly by the kidneys under the control of antidiuretic hormone (ADH) from the pituitary gland.

• When the blood is too concentrated (little water), the pituitary releases more ADH, which makes the kidney tubules (nephrons) reabsorb more water back into the blood, so a small volume of concentrated urine is produced and water is conserved.
• When the blood is too dilute (excess water), less ADH is released, less water is reabsorbed, and a large volume of dilute urine is produced.
• Water is also lost through sweating and in expired air, and gained by drinking and from food; the kidney adjusts urine output to keep the balance.

(b) How mammalian skin regulates body temperature in a hot room

In a hot environment the skin acts to lose heat and cool the body:

• Vasodilation: the blood vessels (arterioles) supplying the skin surface widen, so more warm blood flows near the surface and heat is lost by radiation and convection, giving the skin a flushed appearance.
• Sweating: the sweat glands become active and pour out sweat onto the skin surface; as the sweat evaporates it takes latent heat from the body, cooling it.
• Hair lies flat: the erector (hair) muscles relax so the hairs lie flat, trapping less air, allowing heat to escape.
• Reduced metabolic heat: the rate of metabolism (heat production) is lowered.