JAMB UTME - Biology - 2025

Bayanin Amsa

This question refers to the classic Mendelian monohybrid cross. In the standard cross studied at this level, a homozygous tall plant (TT) is crossed with a homozygous short plant (tt). Every offspring in the \(F_1\) generation receives one dominant allele (T) from the tall parent and one recessive allele (t) from the short parent, giving them all the genotype Tt - that is, they are heterozygous.

Since tallness (T) is dominant over shortness (t), all \(F_1\) offspring express the tall phenotype despite carrying one recessive allele. The correct description is therefore heterozygous tall.

It is important to note that the question asks for the phenotype of the \(F_1\) offspring. While "homozygous" and "heterozygous" are genotype terms, the options combine genotype and phenotype descriptions. The \(F_1\) offspring are heterozygous (Tt) in genotype and tall in phenotype, making "heterozygous tall" the complete and accurate answer.

They cannot be homozygous tall (TT) because each offspring inherits a t allele from the short parent. They cannot be short (whether homozygous or heterozygous) because the dominant T allele masks the recessive t allele.

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The Sahel savanna is a semi-arid belt stretching across West Africa just south of the Sahara Desert. It is characterised by low, erratic rainfall (typically 250-500 mm per year), sandy soils, and high temperatures. Plants that thrive here must be drought-resistant and adapted to hot, dry conditions.

The date palm (Phoenix dactylifera) is one such plant. It is well adapted to arid and semi-arid climates, with deep root systems that reach underground water and the ability to tolerate extreme heat. In Nigeria, the Sahel zone covers the northernmost states, including Borno, Yobe, Sokoto, Zamfara, and Katsina.

Borno State sits squarely within the Sahel belt, bordering the Lake Chad Basin. Its climate is characteristically Sahelian, making it the most representative location for date palm cultivation among the options given. Katsina also lies partly in the Sahel, but Borno is the classic example used in Nigerian biology curricula for Sahel vegetation, including the date palm.

Plateau State has a cooler, highland climate unsuitable for date palm cultivation, and Taraba State lies in the Guinea savanna zone with higher rainfall, neither of which matches the arid conditions the date palm requires.

Exam tip: Associate the date palm with the driest vegetation zones in Nigeria (Sahel savanna) and the states in the far northeast, particularly Borno.

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The segregation of genes occurs during gamete formation, which is the process of meiosis. This principle is known as Mendel's Law of Segregation, which states that during the formation of gametes, the two alleles for each gene separate (segregate) so that each gamete carries only one allele for each trait.

Specifically, segregation occurs during anaphase I of meiosis, when homologous chromosomes (each carrying one allele of a gene pair) are pulled to opposite poles of the cell. This ensures that each resulting gamete receives only one allele from each pair.

Mitosis produces genetically identical daughter cells and does not involve the separation of allele pairs into different cells. Fertilization is the fusion of gametes, which combines alleles from two parents rather than segregating them. Transmission of characters describes the passing of traits from parents to offspring and is a consequence of segregation, not the event during which it occurs.

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The biosphere is the zone of the Earth that provides habitat for all living organisms. It encompasses all ecosystems on the planet and includes the parts of the atmosphere, lithosphere (land), and hydrosphere (water) where life exists. The biosphere extends from the deepest ocean trenches to several kilometres into the atmosphere, wherever conditions permit organisms to survive.

The atmosphere is the layer of gases surrounding the Earth; while some organisms live in the lower atmosphere, it is not itself a habitat zone for all life. The lithosphere is the solid outer layer of the Earth (the crust and upper mantle); it provides the physical surface on which terrestrial life exists but does not include aquatic or atmospheric habitats. "Environment" is a broader, more general term that refers to the surroundings of an organism and includes both biotic and abiotic factors; it is not the specific ecological term for the life-supporting zone.

The biosphere is the correct ecological term because it specifically denotes the global sum of all ecosystems, integrating land, water, and air wherever life is found.

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In ecology, the carrying capacity of a habitat is the maximum number of individuals of a particular species that the available resources (food, water, shelter, space) can sustain indefinitely without degrading the environment. When a population exceeds its carrying capacity, resources become insufficient, leading to increased competition, starvation, disease, or emigration, which brings the population back down.

The other options do not accurately describe this concept. "Maximum population" sounds plausible but is not a standard ecological term for this idea. "Working potential" and "operating capacity" are not recognised biological terms in this context. The precise, universally accepted term in ecology is carrying capacity, often symbolised as K in population growth equations.

For examinations, remember that carrying capacity is determined by limiting factors in the environment and can change if environmental conditions change.

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A vestigial structure is an anatomical feature that has lost most or all of its original function through the course of evolution. These structures were functional in ancestral species but have become reduced or purposeless in the descendant organism.

The human appendix is a classic example of a vestigial structure. In herbivorous ancestors, the caecum (to which the appendix is attached) was large and played an important role in digesting cellulose from plant material. In modern humans, the appendix is a small, narrow tube attached to the caecum that no longer serves a significant digestive function. While recent research suggests it may have a minor role in immune function and gut flora, it is dramatically reduced compared to its ancestral form and can be surgically removed without noticeable consequences.

The other structures listed are all fully functional in their respective organisms. The elephant trunk is a highly developed, multi-purpose organ used for breathing, drinking, grasping, and communication. Bird wings are essential for flight (or, in flightless birds, have been repurposed for balance or swimming). Fish gills are the primary respiratory organs, extracting dissolved oxygen from water. None of these has lost its original function.

Exam tip: Vestigial structures provide evidence for evolution because they indicate common ancestry with organisms in which the same structure is fully functional.

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The question asks specifically about a medium of transportation within animal cells (intracellular transport), not between cells or organs.

The cytoplasm is the gel-like fluid that fills the interior of every animal cell. It serves as the medium through which molecules, ions, organelles, and vesicles are transported from one part of the cell to another. Processes such as cytoplasmic streaming (cyclosis) and vesicular transport all take place within the cytoplasm.

The other options do not fit:

• Blood is a medium of transportation between cells and organs in a multicellular animal, but it is not an intracellular transport medium.
• Latex is a milky fluid found in certain plants (e.g. rubber trees). It is not present in animal cells.
• Cell sap is the fluid found inside the large central vacuole of plant cells. Animal cells typically lack a large central vacuole and do not contain cell sap.

The correct answer is cytoplasm, because it is the internal medium through which materials move within an animal cell.

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The haemocoel is a structure specifically associated with an open circulatory system. In an open circulatory system, found in arthropods (insects, crustaceans, spiders) and most molluscs, blood (called haemolymph) is not confined to blood vessels throughout its entire circuit. Instead, the heart pumps haemolymph through short arteries into open body cavities called haemocoels, where the fluid directly bathes the tissues and organs, allowing exchange of nutrients, gases, and waste products. The haemolymph then drains back into the heart through openings called ostia.

Veins, arteries, and arterioles are all components of a closed circulatory system, in which blood is always contained within a continuous network of vessels (as in vertebrates, annelids, and cephalopods). In a closed system, exchange between blood and tissues occurs across capillary walls, not by direct bathing of organs.

The presence of a haemocoel is one of the defining features that distinguishes an open circulatory system from a closed one.

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The savanna biome is characterised by distinct wet and dry seasons, with prolonged dry periods that bring drought and frequent bush fires. Plants that thrive in this habitat must possess adaptations that help them survive water scarcity and fire damage.

The baobab tree (Adansonia digitata) has a thick bark that serves as a critical adaptation to the savanna. The thick, fire-resistant bark insulates the living cambium tissue beneath it from the intense heat of bush fires, allowing the tree to survive fires that would kill thinner-barked species. The bark also helps reduce water loss from the trunk, which is important during the long dry season.

While the baobab does shed its leaves during the dry season (deciduous habit) and has a deep root system, among the options given, the presence of thick bark is the most distinctive and widely recognised savanna adaptation for this species. Broad leaves would actually be a disadvantage in the savanna because they increase the surface area for water loss through transpiration. Tap roots help access deep water but are common to many trees in various biomes and are not unique to the baobab's savanna adaptation in the way thick bark is.

Exam tip: Savanna plant adaptations centre on surviving fire and drought. Thick bark (fire resistance), water-storing trunks, deep roots, and deciduous leaves are all relevant, but thick bark is the hallmark adaptation most frequently tested.

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The levels of organization in living things, from simplest to most complex, are: cell, tissue, organ, organ system, and organism. An organ is a structure made up of two or more different types of tissues working together to perform a specific function.

An onion bulb is an organ. It is a modified underground stem composed of several tissue types: the fleshy scale leaves (which store food), the outer dry protective scales, the basal plate (a compressed stem), and the growing point. These different tissues work together to store nutrients and enable vegetative reproduction, which is the hallmark of organ-level organization.

Euglena and Paramecium are unicellular (single-celled) organisms. They exist at the cell level of organization because all their life processes are carried out within a single cell. They do not have tissues or organs.

Hydra is a simple multicellular organism that exists at the tissue level of organization. It has two cell layers (ectoderm and endoderm) that form simple tissues, but these tissues are not organized into distinct organs.

Exam tip: To identify the level of organization, ask whether the structure contains multiple tissue types working together. If yes, it is at least at the organ level.

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Seaweeds are large, multicellular marine algae that grow attached to rocks, coral, and other hard substrates in saltwater environments. They require sunlight for photosynthesis and are typically found in the intertidal and shallow subtidal zones of the ocean. Barnacles are sessile marine crustaceans that attach permanently to hard surfaces such as rocks, ship hulls, and piers in saltwater. Both organisms are characteristically associated with the marine habitat.

Terrestrial habitats are land-based environments where neither seaweeds nor barnacles can survive, as both require saltwater. Estuarine habitats are brackish zones where rivers meet the sea; while some salt-tolerant organisms are found there, seaweeds and barnacles are more accurately described as marine organisms. Freshwater habitats (lakes, rivers, ponds) lack the salinity that seaweeds and barnacles depend on.

Exam tip: When a question pairs an alga (flora) with a sessile saltwater invertebrate (fauna), the habitat is marine. Remember that seaweeds are not found in freshwater, and barnacles are exclusively marine crustaceans.

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Osmosis is the movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) across a semi-permeable membrane. This is the primary process by which plant roots absorb water from the soil.

Soil water is a dilute solution with a higher water potential than the cell sap inside root hair cells, which contains dissolved mineral salts and sugars and therefore has a lower water potential. The cell membrane of the root hair cell acts as a semi-permeable membrane, allowing water molecules to pass through but restricting larger solute molecules. Because of this water potential gradient, water moves by osmosis from the soil into the root hair cells.

Diffusion is the movement of molecules from a region of higher concentration to one of lower concentration, but it applies to solute particles or gases moving down their own concentration gradient, not specifically to the net movement of water across a membrane. Transpiration is the loss of water vapour from the aerial parts of the plant (mainly through stomata) and, while it helps create the pull that draws water upward, it is not the mechanism of absorption at the roots. Photosynthesis is the process of converting light energy into chemical energy in the form of glucose and is unrelated to water uptake from the soil.

The correct process is osmosis, because it specifically describes the movement of water across the semi-permeable membrane of root cells driven by a water potential difference.

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Loamy soil is the most suitable soil for crop cultivation in Nigeria and in agriculture generally. Loam is a mixture of sand, silt, and clay in roughly balanced proportions, which gives it a combination of properties ideal for plant growth:

• Good water retention and drainage: It holds enough moisture for roots to absorb but drains excess water, preventing waterlogging.
• Good aeration: The presence of sand particles creates air spaces, allowing root respiration and the activity of beneficial soil organisms.
• High nutrient content: The clay and silt fractions hold mineral ions through cation exchange, while organic matter (humus) further enriches the soil.
• Easy to work: Loam is neither too heavy nor too light, making it easy to plough and cultivate.

Laterite soil is highly weathered and leached, with poor fertility and a hard, iron-rich crust that limits root penetration. Sandy soil drains too quickly and has very low nutrient-holding capacity. Clayey soil holds too much water, has poor drainage and aeration, and becomes very hard when dry, making it difficult for roots to penetrate.

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Paternity determination is a practical application of biological variation. Genetic variation between individuals produces unique patterns of DNA, blood groups, fingerprints, and other heritable traits. These differences can be used to determine whether a particular man is the biological father of a child by comparing the child's genetic markers with those of the alleged father and the mother. Techniques such as DNA profiling (genetic fingerprinting) and blood group analysis exploit the fact that no two unrelated individuals (except identical twins) share the same combination of genetic markers.

Sex determination is governed by sex chromosomes (XX or XY in humans) and is a fixed genetic mechanism, not an application of variation across a population. Population control involves managing population size through birth control, family planning, or policy measures and is not directly an application of biological variation. Survival of the fittest (natural selection) is a mechanism of evolution driven by variation, but it is a natural process rather than a deliberate human application of variation.

Other recognised applications of variation include crime detection (forensic fingerprinting), blood transfusion compatibility, and selective breeding in agriculture.

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Genetically Modified Organisms (GMOs) are organisms whose DNA has been altered using genetic engineering techniques to introduce desirable traits that do not occur naturally in the species. In agriculture, one of the primary goals of genetic modification is to produce resistant crop varieties.

GMO crops can be engineered to resist specific pests, diseases, herbicides, or environmental stresses such as drought and salinity. For example, Bt cotton contains a gene from the bacterium Bacillus thuringiensis that produces a protein toxic to certain insect pests, reducing the need for chemical pesticides. Herbicide-resistant crops allow farmers to control weeds without damaging the crop itself.

These resistant varieties benefit farmers by reducing crop losses, lowering input costs (fewer pesticides and herbicides needed), and improving yield reliability. The entire purpose of developing GMO food products is to improve crop performance, not to make crops more susceptible to diseases, lower in quality, or lower in yield. Those outcomes would represent failures of crop development, not benefits.

Exam tip: GMO technology in agriculture is primarily associated with introducing resistance (to pests, diseases, herbicides, or environmental stress) and improving nutritional content or shelf life. When a question frames GMOs as beneficial to farmers, look for traits that increase productivity and reduce losses.

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The femur (thigh bone) is the longest and strongest single bone in the human body. It extends from the hip joint to the knee joint and typically measures about one quarter of a person's total height.

The femur supports the weight of the body during standing, walking, and running, which is why it is both long and robust. Its length reflects the need for a large stride length in bipedal locomotion.

The other options are shorter bones with different functions:

• The humerus is the bone of the upper arm, extending from the shoulder to the elbow. It is the longest bone in the upper limb but is shorter than the femur.
• The scapula (shoulder blade) is a flat, triangular bone at the back of the shoulder. It is not a long bone at all.
• The sternum (breastbone) is a flat bone in the centre of the chest that connects to the ribs. It is relatively short compared to the femur.

For examination purposes, remember: femur = longest bone, and it is located in the thigh.

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Pests and diseases that affect plants and animals in a habitat are biotic factors. Biotic factors are the living components of an ecosystem that influence other organisms. Pests (such as insects, rodents, and parasitic organisms) and disease-causing agents (bacteria, viruses, fungi, protists) are all living organisms or products of living organisms, making their prevalence a biotic factor.

Abiotic factors are the non-living physical and chemical components of the environment, such as temperature, light, water, pH, and wind. Edaphic factors are a subset of abiotic factors relating specifically to soil properties (texture, pH, mineral content, water-holding capacity, humus content). Climatic factors are another subset of abiotic factors related to weather and climate (temperature, rainfall, humidity, wind).

When classifying ecological factors, ask whether the factor involves a living organism or its activity (biotic) or a non-living physical/chemical condition (abiotic). Pests and diseases are always biotic because they involve living agents.

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A flower is borne on a stalk called the pedicel. At the tip of the pedicel, the stalk expands into a slightly swollen or flattened structure known as the receptacle (also called the torus or thalamus). The receptacle is the region where all the floral parts are attached.

The four main whorls of a flower - the calyx (sepals), corolla (petals), androecium (stamens), and gynoecium (carpels/pistil) - all arise from the receptacle. It provides the structural base that holds every part of the flower in position.

Understanding the distinction between the pedicel and the receptacle is important:

• The pedicel is the stalk itself that connects the flower to the main stem or peduncle.
• The receptacle is the enlarged end of the pedicel where the floral organs are inserted.

The corolla refers to the collective term for all petals, and the calyx is the collective term for all sepals. Neither of these is a region of the flower stalk.

Exam tip: Remember that the receptacle is the attachment point for all floral parts, while the pedicel is the stalk that carries the entire flower.

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A chameleon's ability to change the colour of its skin to match its surroundings is a well-known example of camouflage, which is a form of defensive adaptation. By blending into the background, the chameleon becomes difficult for predators such as birds and snakes to detect. This dramatically increases its chances of survival.

The colour change is achieved through specialised pigment-containing cells called chromatophores in the skin. Different layers of chromatophores contain different pigments, and the chameleon can expand or contract these cells to produce a wide range of colours and patterns that match the surrounding vegetation, bark, or soil.

While colour change in some contexts can play a role in communication or thermoregulation, the primary biological advantage tested at this level is defence against predation. The other options do not accurately describe the main survival purpose of this adaptation: it is not primarily for attracting mates, inviting other organisms, or launching attacks on prey.

Exam tip: Camouflage, mimicry, and warning colouration are all classified as defensive adaptations. When a question asks about an organism blending with its environment, the answer points to protection from predators.

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Cross fertilization (also called cross-pollination in plants or outbreeding in animals) involves the fusion of gametes from two genetically different individuals of the same species. Its primary advantage is that it increases genetic variation in the offspring, which leads to the production of healthier, more vigorous individuals.

This occurs because cross fertilization brings together different alleles from two parents, increasing heterozygosity. Heterozygous individuals are less likely to express harmful recessive traits, a phenomenon known as hybrid vigour (heterosis). The resulting offspring tend to be more resistant to diseases, better adapted to environmental changes, and generally more robust.

The other options describe disadvantages or consequences of self-fertilization (inbreeding), not cross fertilization:

• Inbreeding depression is a reduction in fitness caused by repeated self-fertilization, which increases homozygosity and the expression of deleterious recessive alleles.
• Production of weak offspring is likewise a consequence of inbreeding, not outbreeding.
• While cross-fertilized offspring may occasionally be less adapted to a very specific local environment (because they carry new allele combinations), this is a potential trade-off, not an advantage.

For examinations, remember: cross fertilization promotes genetic diversity, hybrid vigour, and healthier offspring, while self-fertilization risks inbreeding depression.

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This is a monohybrid cross between a heterozygous red-flowered plant (Rr) and a homozygous white-flowered plant (rr), where R (red) is dominant over r (white).

To find the probability of Rr offspring, set up a Punnett square:

The possible offspring genotypes are:

• Rr (heterozygous red) - 2 out of 4 offspring
• rr (homozygous white) - 2 out of 4 offspring

The probability of an offspring being Rr is therefore:

\[ \frac{2}{4} = \frac{1}{2} \]

This means there is a 50% chance that any given offspring from this cross will have the genotype Rr (heterozygous red). This type of cross is called a test cross, commonly used to determine the genotype of an organism showing a dominant phenotype. In a test cross of a heterozygous individual with a homozygous recessive individual, the offspring always appear in a 1:1 ratio of heterozygous dominant to homozygous recessive.

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When resources such as food, water, space, or light are limited in a community, organisms must compete for those resources. This is known as competition, and it is one of the key ecological interactions that shapes community structure.

In such situations, species that are better adapted to exploit the available resources - those that are more vigorous, reproduce faster, or use resources more efficiently - tend to survive and increase in population. Less vigorous species, which are less competitive, gradually decline and may eventually be eliminated from the community. This outcome is consistent with the competitive exclusion principle (Gause's principle), which states that two species competing for exactly the same limited resource cannot coexist indefinitely; the inferior competitor will be outcompeted.

Disease, while it can reduce populations, is not specifically triggered by limited resources in the way competition is. Drought is a specific environmental event, not a general ecological process of elimination. Natality refers to the birth rate in a population and describes population growth, not the elimination of species.

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Ferns are vascular plants (pteridophytes) that possess true roots, stems, and leaves. Their roots are the structures responsible for absorbing water and dissolved mineral nutrients from the soil, just as in flowering plants. The roots of ferns are adventitious, arising from the rhizome (underground stem), and they have root hairs that increase the surface area for absorption.

Hyphae are the thread-like filaments that make up the body of fungi and are used by fungi for absorption, not by ferns. Rhizoids are simple, root-like structures found in bryophytes (mosses and liverworts) and some algae; they anchor the plant and assist with absorption in organisms that lack true roots. A rhizome is the horizontal underground stem of a fern that functions in anchorage and vegetative reproduction, not directly in nutrient absorption.

The key distinction is that ferns, unlike simpler plants such as mosses, have evolved true roots with vascular tissue (xylem and phloem) for efficient absorption and transport.

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A reflex action is a rapid, involuntary, and automatic response to a stimulus that does not require conscious thought or decision-making from the brain. Reflex actions are mediated by a reflex arc: a stimulus is detected by a receptor, a sensory neuron carries the impulse to the spinal cord (or brainstem), a relay neuron processes it, and a motor neuron sends a response to the effector (muscle or gland), all without the cerebral cortex making a deliberate decision.

Coughing is a reflex action. When an irritant enters the airways, receptors in the throat and bronchi are stimulated, and a rapid, involuntary cough is triggered to expel the irritant. This happens automatically and does not require a conscious decision, although it can sometimes be voluntarily suppressed or initiated.

Writing, talking, and walking are all voluntary actions that require conscious thought and coordination by the cerebral cortex of the brain. Although walking can become somewhat automatic with practice, it is initiated and controlled voluntarily and involves complex motor planning, making it a learned voluntary action rather than a true reflex.

Exam tip: True reflex actions are involuntary and immediate. Common examples include coughing, sneezing, blinking, knee-jerk response, and withdrawal of the hand from a hot object.

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Chemical digestion is the process by which large, insoluble food molecules are broken down into smaller, soluble molecules through the action of enzymes. This occurs primarily in the duodenum, the first section of the small intestine.

The duodenum receives partially digested food (chyme) from the stomach. Here, three key secretions contribute to chemical digestion:

• Bile from the liver and gallbladder emulsifies fats, breaking them into smaller droplets to increase the surface area for enzyme action.
• Pancreatic juice from the pancreas contains enzymes such as trypsin (for protein digestion), pancreatic lipase (for fat digestion), and pancreatic amylase (for starch digestion).
• Intestinal juice (succus entericus) from the duodenal wall contains enzymes that complete the breakdown of peptides, disaccharides, and lipids into their simplest absorbable forms.

The other parts of the alimentary canal listed serve different primary functions. The large intestine reabsorbs water and mineral salts from indigestible food residue and does not perform significant chemical digestion. The rectum is a short terminal segment that stores faeces before defecation. The ileum, the longest part of the small intestine, is primarily responsible for absorption of already-digested nutrients into the bloodstream through its villi and microvilli, not for further chemical breakdown.

The duodenum is therefore the principal site of chemical digestion because it is where the greatest concentration and variety of digestive enzymes act together on food.

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DNA (deoxyribonucleic acid) is a polymer, meaning it is built from many repeating smaller units linked together in a long chain. The repeating unit of DNA is called a nucleotide.

Each nucleotide consists of three components:

• A phosphate group
• A five-carbon sugar called deoxyribose
• A nitrogenous base (adenine, thymine, guanine, or cytosine)

While a phosphate group, a nitrogenous base, and deoxyribose sugar are each individual components of a nucleotide, none of them alone constitutes the repeating unit of DNA. The repeating unit is the complete nucleotide, which contains all three components bonded together. Nucleotides are joined by phosphodiester bonds between the phosphate group of one nucleotide and the sugar of the next, forming the sugar-phosphate backbone of the DNA strand.

When revising this topic, remember to distinguish between the monomer (nucleotide) and its individual parts. The question asks for the repeating unit - that is always the complete monomer, not one of its sub-components.

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The bright colouration of flowers is an adaptation for reproduction. Flowering plants that depend on animal pollinators (insects, birds, bats) need to attract these agents to their flowers so that pollen can be transferred from the anther of one flower to the stigma of another, enabling fertilisation and seed production.

Brightly coloured petals serve as visual signals that make the flower conspicuous to pollinators. Different colours attract different pollinators: bees are drawn to blue and violet flowers, butterflies to red and orange, and hummingbirds to bright red. Once a pollinator visits the flower, pollen grains attach to its body and are carried to the next flower it visits, completing cross-pollination.

Growth refers to an irreversible increase in size and dry mass and has no connection to petal colour. Excretion is the removal of metabolic waste products from the body, and respiration is the biochemical process of releasing energy from food. None of these life processes are aided by having brightly coloured petals.

Bright flower colour is therefore directly linked to attracting pollinators, which is a step in the reproductive process of the plant.

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The genotype of an organism is the complete set of genes (alleles) it carries in its DNA. It represents the organism's genetic constitution, whether or not those genes are visibly expressed. Two organisms can share the same outward appearance yet differ in genotype if one carries a hidden recessive allele.

It is important to distinguish the genotype from related but different terms:

• A nucleotide is the basic building block of nucleic acids (DNA and RNA). Each nucleotide consists of a phosphate group, a five-carbon sugar, and a nitrogenous base. It is a molecular unit, not a description of an organism's overall genetic makeup.
• A karyotype is the organised visual profile of an organism's chromosomes, arranged by size and shape. It shows chromosome number and structure but does not describe the specific allele composition at each gene locus.
• The phenotype is the set of observable physical and biochemical characteristics of an organism (e.g. eye colour, height, blood group). Phenotype results from the interaction of genotype with the environment, but it is not the genetic makeup itself.

Exam tip: Remember the pair: genotype = genes you carry; phenotype = traits you display. Questions often test whether students can distinguish between the two.

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The diagram shows a monohybrid cross between two heterozygous parents, both with the genotype Rr. Each parent produces two types of gametes: R and r.

When these gametes combine during fertilisation, the F₂ offspring are:

• RR (homozygous dominant)
• Rr (heterozygous)
• Rr (heterozygous)
• rr (homozygous recessive)

Counting the genotypes gives 1 RR : 2 Rr : 1 rr, which simplifies to a genotypic ratio of 1 : 2 : 1. This is the classic Mendelian ratio for a cross between two heterozygotes at a single gene locus with complete dominance.

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The diagram shows an animal cell with four labelled parts. Label I points to the large, dark, roughly spherical structure located centrally within the cell. This is the nucleus, the membrane-bound organelle that contains the cell's genetic material (DNA) and controls cell activities such as growth, metabolism, and reproduction.

The other labelled structures can be identified as follows: Label II points to the cell membrane (the outer boundary), Label III indicates the cytoplasm (the gel-like substance filling the cell), and Label IV points to small, elongated organelles which are the mitochondria (responsible for cellular respiration and energy production).

The nucleus is distinguishable by its large size relative to other organelles, its dark staining (due to dense chromatin material), and its roughly circular shape. It is often the most prominent structure visible in a cell diagram.

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Competition is an ecological interaction in which organisms struggle for the same limited resources, such as food, water, or space. It is classified into two types based on whether the competing organisms belong to the same or different species.

Interspecific competition occurs between organisms of different species that require the same resources. A cow (species Bos taurus) and a goat (species Capra aegagrus hircus) are two distinct species. When they both graze on scarce grasses during the dry season, they compete for the same limited food resource across species boundaries. This is therefore interspecific competition.

Intraspecific competition occurs between members of the same species - for example, two cows competing for the same grass. Since the question involves a cow and a goat (different species), it is not intraspecific. Predation involves one organism killing and eating another, which is not the case here. Commensalism is an association in which one organism benefits and the other is unaffected, which does not apply to a struggle for scarce resources.

Exam tip: The prefix inter- means "between" (different species), while intra- means "within" (same species). Always check whether the competing organisms belong to the same or different species before choosing.

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Chlamydomonas is a unicellular, microscopic, photosynthetic organism found in freshwater habitats. It possesses a cell wall, a cup-shaped chloroplast, an eyespot (stigma), and two flagella for locomotion. Because it is a simple, unicellular organism that can both photosynthesise and move, it is classified among the most primitive plant-like organisms.

In the traditional classification system used at WAEC/JAMB level, such simple, unicellular, plant-like organisms are placed in the phylum Protophyta (meaning "first plants"). This phylum includes algae and other simple photosynthetic organisms that do not have true roots, stems, or leaves.

The other phyla listed contain more complex organisms:

• Bryophyta includes mosses and liverworts, which are small, non-vascular land plants.
• Pteridophyta includes ferns and horsetails, which are vascular plants that reproduce by spores.
• Tracheophyta refers to all vascular plants (those with xylem and phloem), encompassing ferns, gymnosperms, and angiosperms.

Chlamydomonas lacks all of these complex features. Its unicellular, flagellated, photosynthetic nature places it firmly in Protophyta.

Bayanin Amsa

Plants have two main vascular tissues: xylem and phloem. Xylem is responsible for transporting water and dissolved mineral salts from the roots upward to the leaves. Phloem, on the other hand, is the tissue responsible for translocation, which is the movement of manufactured food (mainly sucrose and amino acids) from the sites of production (typically leaves, where photosynthesis occurs) to sites of use or storage throughout the plant.

Phloem cells, specifically sieve tube elements and their companion cells, form a continuous pathway that carries dissolved organic nutrients bidirectionally: from leaves downward to roots, and from storage organs upward to growing tips, flowers, and fruits. This process is driven largely by pressure differences created by the active loading and unloading of sugars into and out of the sieve tubes.

The pericycle is a layer of cells in the root that gives rise to lateral roots. The endodermis is a single cell layer in the root that regulates which substances enter the vascular cylinder. Neither of these tissues is involved in the long-distance transport of food. Xylem vessels transport water, not manufactured food.

Exam tip: Remember the distinction: xylem moves water up, phloem moves food (sugars) to where the plant needs it.

Bayanin Amsa

Pepsin is a proteolytic enzyme (protease) that is active in an acidic medium. It is secreted as its inactive precursor, pepsinogen, by the chief cells of the gastric glands in the stomach lining. Hydrochloric acid (HCl), produced by the parietal (oxyntic) cells of the stomach, converts pepsinogen into active pepsin and maintains the stomach contents at a pH of approximately 1.5 to 2.5. Pepsin functions optimally within this strongly acidic pH range, where it breaks down proteins into shorter polypeptide chains.

In an alkaline medium, pepsin is denatured and loses its catalytic activity. It does not function in a neutral medium either. The statement that pepsin works in both alkaline and acidic media is incorrect because the enzyme's three-dimensional structure, which is essential for substrate binding, is disrupted outside its narrow acidic pH range.

Each digestive enzyme has a specific optimum pH: pepsin requires acid (stomach), while enzymes like trypsin and pancreatic lipase require an alkaline environment (small intestine, pH approximately 7.5 to 8.5).

Bayanin Amsa

The relationship between a fungus and an alga in a lichen is an example of mutualism. In this association, both organisms benefit. The alga (or cyanobacterium) is photosynthetic and produces organic food (sugars) through photosynthesis, which nourishes both itself and the fungus. The fungus, in return, provides a protective structure, retains moisture, and anchors the lichen to substrates such as rocks, tree bark, or soil, creating a stable microenvironment for the alga.

Parasitism involves one organism benefiting at the expense of the other (the host is harmed). Commensalism is a relationship in which one organism benefits while the other is neither helped nor harmed. Predation involves one organism (the predator) killing and consuming another (the prey). None of these accurately describes the lichen relationship, where both partners derive a clear benefit.

Lichen is one of the most commonly cited examples of mutualism in biology examinations. It is also a pioneer organism in ecological succession, colonising bare rock surfaces.

Bayanin Amsa

The nervous system is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS consists of the brain and spinal cord. The PNS consists of all the nerves and neurones that connect the CNS to the rest of the body.

The components of the peripheral nervous system include:

• Sensory neurones (afferent neurones), which carry impulses from receptors (such as those in the skin, eyes, and ears) to the CNS.
• Motor neurones (efferent neurones), which carry impulses from the CNS to effectors (muscles and glands).
• Cranial nerves (12 pairs emerging directly from the brain) and spinal nerves (31 pairs emerging from the spinal cord).
• Ganglia (clusters of nerve cell bodies located outside the CNS).

The cerebellum is a part of the brain responsible for coordinating movement and balance, so it belongs to the CNS. The brain itself is the main organ of the CNS, and the spinal cord is the other major CNS structure. None of these three are components of the PNS.

Of the options given, sensory neurones are a component of the peripheral nervous system, as they form the pathways that carry information from the body's receptors to the central nervous system.

Bayanin Amsa

The stamen is the male reproductive organ of a flower, and it consists of two parts: the filament and the anther. The filament is a slender stalk that supports the anther, holding it in a position where pollen can be effectively released or accessed by pollinators. The anther is the expanded, often bilobed structure at the tip of the filament that contains pollen sacs (microsporangia), where pollen grains (containing male gametes) are produced through meiosis and subsequently released.

The ovary and stigma are parts of the carpel (pistil), which is the female reproductive organ. The ovary contains the ovules, and the stigma is the receptive surface that captures pollen. "Filament and ovary" incorrectly combines a male part with a female part. "Sepals and petals" are accessory floral parts: sepals protect the flower bud, and petals attract pollinators. Neither is part of the stamen.

For examination purposes, remember the complete structure: a stamen = filament + anther (male), and a carpel = stigma + style + ovary (female).

Bayanin Amsa

In ecology, organisms in a habitat are connected through feeding relationships. A food chain is a simple, linear sequence showing how energy passes from one organism to the next, for example: grass to grasshopper to frog to snake to hawk. Each organism feeds on the one before it.

However, most ecosystems are far more complicated than a single chain. A grasshopper may be eaten by both frogs and birds; a frog may eat insects other than grasshoppers; a hawk may eat snakes, mice, and birds. When multiple food chains in a habitat overlap and interconnect, the result is a food web. A food web captures the complex feeding relationships among all the organisms in the habitat, showing how energy in the form of food is transferred through many interlinked pathways.

A pyramid of numbers shows how many organisms exist at each trophic level, while a pyramid of energy shows the amount of energy available at each trophic level. Neither of these describes a feeding relationship between organisms. They are graphical representations of quantity, not of who eats whom.

The key phrase in the question is "complex feeding relationship ... that involves transfer of energy in form of food." Only a food web fits this description, because it is the model that represents the full network of interconnected feeding relationships within a habitat.

Bayanin Amsa

Agglutination is the clumping together of red blood cells, which can block blood vessels and be fatal. It occurs during a blood transfusion when the antigens on the donor's red blood cells react with the antibodies in the recipient's plasma. In other words, agglutination happens when the antigen-antibody combination between donor and recipient is incompatible.

In the ABO blood group system, each blood group carries specific antigens (agglutinogens) on the surface of its red blood cells and specific antibodies (agglutinins) in its plasma:

When a donor's antigen meets a matching antibody in the recipient (for example, antigen A meets anti-A antibody), the antibodies bind to the red blood cells and cause them to clump. This is agglutination.

Race has no bearing on blood compatibility. Same antibodies do not fuse with each other to cause a problem. Being in the same blood group actually ensures compatibility, not agglutination.

The key principle: always match donor antigens against recipient antibodies. Incompatibility between them is what triggers agglutination.

Bayanin Amsa

An auxanometer is a specialised instrument designed to measure the rate of growth in plants, particularly elongation growth. It works by magnifying small increments of growth using a lever, pulley, or rotating drum system connected to the tip of a growing plant. As the plant grows, even tiny increases in height are amplified and recorded, making it possible to measure growth that would be too small to detect by direct observation alone.

The other instruments listed measure entirely different environmental quantities:

• A hygrometer measures the relative humidity (moisture content) of the air.
• A barometer measures atmospheric pressure.
• A thermometer measures temperature.

None of these three instruments is designed to detect or quantify changes in plant size or growth rate.

Exam tip: The prefix auxano- comes from the Greek word for "growth" (the same root as the plant hormone auxin). Linking "auxanometer" to "auxin" is a reliable way to remember that both relate to plant growth.