JAMB UTME - Biology - 2025

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DNA (deoxyribonucleic acid) is the molecule that controls protein and enzyme synthesis in the cytoplasm. DNA carries the genetic code - a specific sequence of nucleotide bases (adenine, thymine, guanine, cytosine) that determines which proteins and enzymes are produced.

The process works in two main stages:

1. Transcription: In the nucleus, the relevant section of DNA unwinds and one strand serves as a template for the synthesis of messenger RNA (mRNA). The mRNA carries a complementary copy of the genetic instructions.
2. Translation: The mRNA moves out of the nucleus into the cytoplasm, where it attaches to ribosomes. Transfer RNA (tRNA) molecules bring specific amino acids to the ribosome, matching them to the codons on the mRNA. The amino acids are joined together in the correct sequence to form the protein or enzyme.

While the nucleus houses the DNA and chromosomes are the structures that DNA is packaged into, the question asks specifically what controls protein synthesis. That controlling agent is the DNA molecule itself, because it is the sequence of bases in DNA that determines which proteins are made. Chromosomes are the physical packaging of DNA, not the controlling molecule. Mitochondria have their own DNA and carry out cellular respiration, but they do not control the synthesis of proteins and enzymes in the cytoplasm of the cell.

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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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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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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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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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The diagram shows the arrangement of teeth in the human jaw, with four distinct types labelled I through IV. Label I indicates the incisors, which are flat, chisel-shaped teeth at the front used for cutting and biting. Label II indicates the canines, the pointed, conical teeth located just behind the incisors. Label III indicates the premolars, which have two cusps and are used for crushing. Label IV indicates the molars, the broad, multi-cusped teeth at the back used for grinding.

The teeth used for tearing in humans are the canines. Canines have a single, sharp, pointed cusp that is well-suited for gripping and tearing food, particularly meat. They are the longest teeth in the human dentition and are homologous to the prominent fangs seen in carnivorous mammals. In the diagram, the canines are labelled II.

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An onion bulb represents the organ level of biological organisation. An organ is a structure made up of two or more different types of tissues working together to perform a specific function. The onion bulb consists of several tissue types: the fleshy scale leaves (modified leaves that store food), a short compressed stem (the basal plate), adventitious roots, and a protective outer covering of dry, papery scales. These different tissues are integrated into a single functional unit, making the bulb an organ.

A cell is the basic structural and functional unit of life, representing the simplest level. A tissue is a group of similar cells performing a single function (e.g. parenchyma tissue). A system is a group of organs working together to carry out a broad body function (e.g. the digestive system). The onion bulb is more complex than a single tissue but is not a system of multiple organs, so it falls at the organ level.

The hierarchy of biological organisation is: cell, tissue, organ, organ system, organism. Identifying the correct level requires asking how many types of tissues are present and whether they function as a coordinated unit.

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The shoreline of a marine habitat is divided into distinct zones based on their relationship to the tides. The area described in the question - above the high tide mark, not submerged by normal tides but regularly wetted by the spray from breaking waves - is the splash zone (also called the supralittoral zone or spray zone).

The key zones from shore to deep water are:

• Splash zone (supralittoral) - above the high tide mark; only reached by wave spray, not by normal tides. Organisms here (such as lichens, periwinkles, and some crabs) must tolerate long periods of dryness and only occasional wetting.
• Intertidal zone (littoral) - the area between the high tide mark and the low tide mark. It is alternately submerged and exposed as tides rise and fall. Barnacles, mussels, and seaweeds are common here.
• Subtidal zone (sublittoral) - permanently submerged below the low tide mark.
• Benthic zone - the bottom of a body of water, not a shoreline zone defined by tides.

The question specifically states "above the high tide mark" and "wetted by spray," which precisely matches the definition of the splash zone.

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The coronary artery is the artery that carries blood to the heart. Specifically, the coronary arteries branch off from the base of the aorta and supply oxygenated blood to the heart muscle (myocardium) itself. Without this blood supply, the cardiac muscle cells would not receive the oxygen and nutrients they need to function, which is why blockage of the coronary arteries leads to a heart attack (myocardial infarction).

The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs for gas exchange. The renal artery carries blood from the aorta to the kidneys. The aorta is the largest artery in the body and carries oxygenated blood away from the left ventricle to the rest of the body.

A common source of confusion is thinking that "carries blood to the heart" means veins (since veins generally return blood to the heart). However, the coronary arteries specifically deliver arterial blood to nourish the heart tissue itself.

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Cilia and flagella are hair-like projections from the cell surface that are involved in locomotion (in unicellular organisms and sperm cells) or in moving substances across cell surfaces (such as mucus in the respiratory tract). Their formation depends on a specific organelle: the centriole.

Centrioles are cylindrical structures made of microtubules arranged in a characteristic 9+0 pattern (nine triplets of microtubules with no central pair). They are found in the centrosome of animal cells. During the formation of cilia and flagella, a centriole migrates to the cell surface and becomes the basal body, which serves as the organising centre from which the microtubules of the cilium or flagellum grow outward. The internal structure of cilia and flagella (the axoneme) has a 9+2 arrangement of microtubules, templated by the basal body.

The other options serve different functions:

• Plastids are organelles found in plant cells (e.g., chloroplasts for photosynthesis); they play no role in cilia or flagella formation.
• Golgi bodies (Golgi apparatus) are involved in modifying, packaging, and transporting proteins and lipids.
• Lysosomes contain hydrolytic enzymes for intracellular digestion and recycling of cellular components.

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The carbon cycle describes how carbon moves between the atmosphere, living organisms, the oceans, and the earth's crust. The key processes in the carbon cycle include photosynthesis, respiration, decomposition, combustion, and fossilisation.

Combustion (burning) releases carbon dioxide into the atmosphere when fossil fuels (coal, oil, natural gas) or organic matter (wood, biomass) are burned. This is a major pathway by which stored carbon re-enters the atmospheric pool as CO₂. It is therefore a direct component of the carbon cycle.

The other options belong to different nutrient cycles or involve water, not carbon:

• Nitrification is a process in the nitrogen cycle, in which nitrifying bacteria convert ammonium ions (NH₄⁺) to nitrites and then nitrates in the soil.
• Evaporation is a phase of the water cycle (hydrological cycle), where liquid water changes to water vapour.
• Transpiration is also part of the water cycle. It involves the loss of water vapour from the aerial parts of plants, mainly through stomata.

Exam tip: When asked about processes in a specific nutrient cycle, focus on the element being cycled. Carbon cycle processes involve movement of carbon-containing compounds: photosynthesis, respiration, decomposition, combustion, and fossilisation.

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When a soil sample is mixed with water, shaken vigorously, and allowed to stand, the particles separate into distinct layers based on their size and density. This process is called sedimentation.

During sedimentation, the heaviest and largest particles (gravel and coarse sand) settle first and form the bottom layer. Medium-sized particles (fine sand and silt) settle above them, and the finest particles (clay) settle on top of the mineral layers because they are the lightest solid particles. Decaying organic matter (humus) has a lower density than the mineral particles and water, so it floats on the surface of the water rather than sinking.

The correct statement is that decaying organic matter remains afloat. This is because humus particles are light and often contain trapped air, giving them a density lower than that of water.

The statement that the largest and medium-sized particles settle at the bottom is partially true (the largest do settle at the bottom), but it is imprecise because it groups two different size classes without noting that they form separate layers. The claim that decaying organic matter settles at the bottom contradicts what actually happens - humus floats. The claim that the largest soil particles remain suspended in water is incorrect because large particles are the first to settle due to their greater weight.

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The diagram shows a longitudinal section of a flower with four labelled parts. Label I points to the anther at the tip of the stamen, label II points to the stigma at the top of the style, label III points to the petals (the broad, conspicuous structures surrounding the reproductive organs), and label IV points to the sepal at the base of the flower.

The part of a flower that is brightly coloured to attract pollinating agents such as insects, birds and butterflies is the petal (collectively called the corolla). Petals produce pigments such as anthocyanins and carotenoids that give them vivid colours, and in some species they also produce nectar guides visible under ultraviolet light. These visual signals help pollinators locate the flower and its nectar or pollen rewards, facilitating cross-pollination.

In the diagram, the petals correspond to the structures labelled III.

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The theory that characters acquired during an organism's lifetime through the use or disuse of organs can be inherited by offspring is known as the theory of inheritance of acquired characteristics, proposed by Jean-Baptiste Lamarck (spelled "Larmark" in the question).

Lamarck's theory rests on two main principles:

1. Use and disuse: Organs that are used extensively become larger and stronger, while those that are not used deteriorate and may eventually disappear.
2. Inheritance of acquired characteristics: Changes that an organism acquires during its lifetime are passed on to its offspring.

A classic example Lamarck used is the giraffe: he proposed that giraffes stretched their necks to reach high leaves, and this elongated neck was inherited by the next generation. Modern genetics has shown this mechanism to be incorrect - acquired physical changes do not alter the DNA passed to offspring.

Darwin proposed evolution by natural selection, not inheritance of acquired traits. Mendel established the laws of heredity through his work on pea plants. Morgan demonstrated the chromosomal theory of inheritance using fruit flies. None of these scientists supported the idea that use or disuse of organs produces heritable changes.

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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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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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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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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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Countershading is a form of adaptive colouration in which an animal's dorsal (upper) surface is darker and its ventral (lower) surface is lighter. This colour gradient counteracts the natural shadowing effect caused by overhead light, making the animal appear flatter and less three-dimensional. The result is that the animal blends more effectively into its background and becomes harder for predators (or prey) to detect.

Countershading is widespread in nature. Many fish are dark on top and light on the belly, so they blend with the dark water below when viewed from above and with the bright sky when viewed from below. Deer, sharks, penguins, and many birds also display countershading.

The other options are not forms of colouration at all:

• Hibernation is a behavioural adaptation in which an animal enters a prolonged state of dormancy during cold seasons to conserve energy.
• Aestivation is a similar dormancy response to hot, dry conditions (e.g. lungfish burying in mud during drought).
• Migration is the seasonal movement of animals from one region to another in search of favourable conditions.

None of these three involves body colouration. The question specifically asks about adaptive colouration that helps animals remain unnoticed, which directly describes countershading.

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Ecological succession is the gradual, sequential process by which the species composition and community structure of an ecosystem change over time. It begins with colonisation of a bare or disturbed habitat by hardy organisms called pioneer species and progresses through a series of intermediate stages called seral stages (or seral communities).

The final, stable, self-sustaining community that develops at the end of the successional process is called the climax community. A climax community is in dynamic equilibrium with the prevailing environmental conditions (climate, soil type, topography). It remains relatively stable over long periods because:

• The dominant species are well adapted to the local environment.
• Birth and death rates are roughly balanced.
• Energy input and output are approximately equal.
• Species composition does not change significantly unless disturbed.

A pioneer community is the first to colonise a new habitat. A secondary community relates to secondary succession (which occurs after a disturbance that does not destroy the soil seed bank). A seral community (sometimes written "serial" in this context) is any intermediate stage, not the final one.

The term to remember: the endpoint of succession is always the climax community.

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The calyx is the outermost whorl of a flower, made up of individual units called sepals. When the sepals of the calyx are fused (joined together), the condition is described as gamosepalous.

The prefix gamo- means "united" or "fused," while sepal- refers to the sepals. So gamosepalous literally means "united sepals."

To distinguish the other terms:

• Polysepalous describes a calyx in which the sepals are free (separate from each other). The prefix poly- here indicates "many separate" units.
• Gamopetalous refers to fused petals (the corolla), not sepals. An example is the trumpet-shaped corolla of Datura.
• Polypetalous describes a corolla in which the petals are free and separate.

A helpful memory aid: terms beginning with gamo- always indicate fusion, while those beginning with poly- indicate separate parts. The second half of the word tells you which floral part is involved: -sepalous for sepals, -petalous for petals.

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Canine teeth are the sharp, pointed teeth located between the incisors and premolars. Their primary function is to grip, pierce, and tear flesh. This makes them essential for animals that hunt and consume other animals as their primary food source.

Carnivores have the most prominent and well-developed canine teeth because their diet consists mainly of meat. Animals such as lions, tigers, wolves, and dogs possess large, elongated canines that allow them to seize prey and tear through tough muscle and connective tissue. The strength and sharpness of these teeth are directly related to the demands of a predatory lifestyle.

Herbivores generally have reduced or absent canine teeth because they feed on plant material and rely instead on broad, flat molars and premolars for grinding. Omnivores do possess canines, but these are moderately developed compared to those of carnivores, since omnivores eat both plant and animal material and do not depend solely on tearing flesh. Parasites are organisms that live on or in a host and obtain nutrients from it; the term does not describe a dentition group at all.

Exam tip: When asked about tooth types and animal groups, remember that the degree of development of each tooth type reflects the animal's diet: incisors for cutting, canines for tearing, and premolars/molars for grinding.

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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 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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Holozoic nutrition is a mode of nutrition in which organisms ingest solid or liquid organic food, digest it internally, absorb the useful nutrients, and egest the undigested waste. This is the typical mode of feeding in most animals.

Within holozoic nutrition, organisms are classified according to the type of food they consume:

• Omnivorous organisms feed on both plant and animal material. Humans, pigs, bears, and domestic fowl are common examples. Omnivores typically possess a mixed dentition - incisors for cutting, canines for tearing, and molars for grinding - reflecting their varied diet.
• Herbivorous organisms feed exclusively on plant material. Examples include cattle, rabbits, and grasshoppers. They often have broad molars for grinding tough plant fibres and longer digestive tracts to process cellulose.
• Carnivorous organisms feed exclusively on other animals. Lions, hawks, and sharks are examples. They have sharp teeth or beaks for tearing flesh and shorter guts suited to a protein-rich diet.

Saprophytic nutrition is fundamentally different from the three categories above. Saprophytes, such as many fungi and certain bacteria, feed on dead and decaying organic matter by secreting enzymes externally onto the substrate and then absorbing the digested products. This is extracellular digestion without ingestion, so saprophytic nutrition does not fall under holozoic nutrition at all.

Since the question asks specifically about holozoic nutrition involving both plant and animal food sources, the correct classification is omnivorous.

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The diagram shows a longitudinal section of a typical animal cell (or protozoan such as Amoeba) with four organelles labelled I through IV. Label II points to the nucleus, the large, membrane-bound organelle located centrally within the cell.

The nucleus is the control centre of the cell. It contains the cell's genetic material (DNA) organised into chromosomes, which carry instructions for protein synthesis and all cellular activities. Through gene expression, the nucleus directs metabolism, growth, reproduction, and responses to stimuli.

The other options describe functions of different organelles: mitochondria produce energy for the cell through aerobic respiration, the endoplasmic reticulum transports materials within the cell, and secretory vesicles or the cell membrane transport materials outside the cell. Since the structure labelled II is the nucleus, its primary function is to coordinate the activities of the cell.

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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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The diagram shows the female reproductive system with four labelled parts. Label I points to the fallopian tube (oviduct), label II points to the uterus, label III points to the cervix, and label IV points to the vagina.

The part labelled II is the uterus. It is the large, hollow, pear-shaped muscular organ located in the centre of the diagram. The uterus is where a fertilised egg implants and develops during pregnancy. Its thick muscular walls (myometrium) contract during labour to push the baby out, while its inner lining (endometrium) thickens each menstrual cycle in preparation for possible implantation. If fertilisation does not occur, this lining is shed during menstruation.

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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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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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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.

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Flowering plants that rely on insects for pollination have evolved specific adaptations to attract insect visitors. These adaptations include brightly coloured petals, the presence of nectar (a sugary reward), sticky or spiky pollen grains that attach to insect bodies, and scented flowers that release fragrances to draw insects from a distance.

Large anthers are characteristic of wind-pollinated flowers, not insect-pollinated ones. Wind-pollinated flowers produce enormous quantities of light, smooth pollen and hang their large anthers freely so the wind can carry the pollen away. They typically lack bright colours, scent, and nectar because they do not need to attract animal visitors.

The absence of nectar and scentless flowers would both be disadvantages for insect-pollinated plants, since insects are guided to flowers largely by scent and the promise of a nectar reward.

Of the options provided, scented flowers is the feature specifically associated with insect pollination. The scent acts as a chemical signal that helps insects locate the flower, ensuring effective pollen transfer.

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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.

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Comparative anatomy is the study of similarities and differences in the body structures of different species. When most vertebrates share a common basic structural plan consisting of a skull, a vertebral column, and a pair of limb girdles (pectoral and pelvic), this provides strong evidence that they descended from a common ancestor. These shared structures are called homologous structures.

Homologous structures have the same fundamental design and embryonic origin but may be modified for different functions in different species. For example, the forelimb of a human (arm), a whale (flipper), a bat (wing), and a horse (leg) all contain the same set of bones - humerus, radius, ulna, carpals, metacarpals, and phalanges - arranged in the same basic pattern, even though they serve very different purposes. This shared blueprint points to a common evolutionary ancestor.

The other options represent different lines of evolutionary evidence:

• Fossil records provide evidence of organisms that lived in the past, showing how body forms have changed over geological time.
• Molecular records compare DNA, RNA, or protein sequences across species to determine evolutionary relatedness.
• Embryology examines similarities in the early developmental stages of different organisms (e.g., pharyngeal pouches in vertebrate embryos).

The question specifically describes structural similarities in adult body plans across living vertebrates, which falls squarely under comparative anatomy.

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Proteins are large biological macromolecules (polymers) built from smaller repeating units called amino acids. Each amino acid has a central carbon atom bonded to an amino group (\(-\text{NH}_2\)), a carboxyl group (\(-\text{COOH}\)), a hydrogen atom, and a variable side chain (R group) that gives each amino acid its unique chemical properties.

Amino acids are linked together by peptide bonds, formed through condensation reactions between the amino group of one amino acid and the carboxyl group of the next, releasing a molecule of water. A chain of two amino acids is a dipeptide; a long chain is a polypeptide. One or more polypeptide chains fold into a specific three-dimensional shape to form a functional protein.

There are about 20 different amino acids used in biological systems. The specific sequence, number, and types of amino acids in a polypeptide chain determine the protein's structure and function.

The other options are not the monomers of proteins:

• Glycerol is a three-carbon alcohol that forms part of lipids (fats and oils) along with fatty acids.
• Fatty acids are long hydrocarbon chains with a carboxyl group; they are components of lipids, not proteins.
• Carboxylic acid is a broad chemical class characterised by the \(-\text{COOH}\) group. While amino acids do contain a carboxyl group, the term "carboxylic acid" alone does not specifically describe the building blocks of proteins.

Exam tip: Match each macromolecule to its monomer: proteins to amino acids, carbohydrates to monosaccharides (simple sugars), lipids to glycerol and fatty acids, and nucleic acids to nucleotides.

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A reflex action is a rapid, automatic, involuntary response to a stimulus that does not require conscious thought or decision-making from the brain. Reflex actions are coordinated by the spinal cord (or brainstem) through a pathway called a reflex arc, which consists of a receptor, sensory neurone, relay neurone (in the spinal cord), motor neurone, and effector.

Sneezing is a classic reflex action. When irritants such as dust, pollen, or strong odours stimulate nerve endings in the nasal mucosa, sensory signals travel to the sneeze centre in the brainstem, which triggers an involuntary, explosive expulsion of air through the nose and mouth. A person cannot consciously decide to sneeze or easily prevent a sneeze once it is triggered.

The other options are not reflex actions:

• Walking is a voluntary, coordinated motor activity that requires conscious initiation and control from the cerebrum, even though some aspects become semi-automatic with practice.
• Dancing is a deliberate, learned motor activity involving planning and coordination by the brain.
• Crying is an emotional response that involves higher brain centres; it is not an immediate, involuntary response to a physical stimulus in the way a true reflex is.

Exam tip: Other common reflex actions include blinking, knee-jerk response, coughing, and withdrawal of the hand from a hot surface. They are all rapid, involuntary, and protective.

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Plant nutrients are classified into two groups based on the quantities required:

• Macronutrients (needed in large amounts): nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulphur (S).
• Micronutrients (needed in trace amounts): iron (Fe), boron (B), zinc (Zn), manganese (Mn), copper (Cu), molybdenum (Mo), and chlorine (Cl).

Calcium is a macronutrient. It is required in relatively large quantities by plants and plays essential roles in cell wall structure (as calcium pectate in the middle lamella), membrane stability, cell signalling, and root development.

Boron, iron, and zinc are all micronutrients (trace elements). Although they are essential for plant health, they are needed only in very small quantities. A common examination mistake is to confuse macro- and micronutrients. Remember: macronutrients include the six elements listed above (N, P, K, Ca, Mg, S), and most other mineral elements fall into the micronutrient category.

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Hypogeal germination is the type of seed germination in which the cotyledons remain below the soil surface. During hypogeal germination, the epicotyl (the part of the embryonic axis above the cotyledon attachment point) elongates and pushes the plumule (young shoot) upward through the soil, while the hypocotyl (the part below the cotyledon attachment) does not elongate significantly. As a result, the cotyledons stay underground, where they continue to supply stored food to the developing seedling until it becomes self-sufficient through photosynthesis. Examples include maize, rice, mango, and most monocots.

In epigeal germination, the hypocotyl elongates rapidly, pulling the cotyledons above the soil surface, where they may turn green and photosynthesise temporarily. Examples include beans and groundnuts.

The plumule is the embryonic shoot, not a type of germination. The micropyle is the tiny pore in the seed coat through which water enters during imbibition, not a germination type.

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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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In the ABO blood group system, each blood group is defined by the antigens present on the surface of red blood cells. Blood group A carries the A antigen, blood group B carries the B antigen, blood group AB carries both A and B antigens, and blood group O carries neither.

Anti-A antibody serum contains antibodies that specifically bind to the A antigen. When anti-A serum is added to a blood sample, agglutination (clumping) occurs if the red blood cells carry the A antigen on their surface.

Blood group A has the A antigen, so it will clump with anti-A serum. Blood group AB also has the A antigen (along with B), so it too will clump with anti-A serum. Blood group B has only the B antigen and blood group O has no antigens, so neither of these will clump with anti-A serum.

Therefore, both A and AB blood groups will clump when mixed with anti-A antibody serum.

Exam tip: Remember that anti-A serum reacts with any blood group that carries the A antigen. AB carries both antigens, so it reacts with both anti-A and anti-B sera.