JAMB UTME - Biology - 2025

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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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In Nigeria, rainfall is the most significant climatic factor influencing the distribution of organisms. Nigeria's vegetation zones - from the mangrove swamps in the south to the Sahel savanna in the north - are primarily determined by the amount and pattern of annual rainfall rather than by any other single climatic variable.

The southern regions receive heavy rainfall (over 2,000 mm annually) and support dense tropical rainforests, while the northern regions receive progressively less rainfall (as low as 500 mm in the far north) and support savanna grasslands and semi-arid vegetation. This rainfall gradient directly controls which plant species can grow in each zone, and the plant communities in turn determine which animal species inhabit the area.

While temperature, humidity, and light also affect organisms, they do not vary as dramatically across Nigeria as rainfall does. Nigeria lies entirely within the tropics, so temperature remains relatively warm throughout the country year-round. Humidity and light intensity are themselves partly consequences of rainfall patterns. It is the marked north-south rainfall gradient, driven by the movement of the Inter-Tropical Convergence Zone (ITCZ), that creates the distinct ecological zones across the country.

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Sickle cell anaemia is the heritable disease characterised by distorted (sickle or crescent-shaped) red blood cells. It is caused by a point mutation in the gene encoding the beta-globin subunit of haemoglobin, where the amino acid glutamic acid is replaced by valine at position 6. This produces an abnormal form of haemoglobin called haemoglobin S (HbS). Under low oxygen conditions, HbS molecules polymerise and cause the red blood cells to become rigid and sickle-shaped, rather than their normal biconcave disc shape.

These distorted cells are inflexible and tend to clump together, blocking small blood vessels and hindering the free flow of blood. This leads to painful crises, tissue damage from oxygen deprivation, and chronic anaemia because the sickle cells are fragile and break down more rapidly than normal red blood cells.

Haemophilia is a heritable bleeding disorder caused by deficiency of clotting factors, not by distortion of red blood cells. Albinism is the lack of melanin pigment production. Colour blindness is the inability to distinguish certain colours due to defective cone cells in the retina. None of these involves abnormal red blood cell shape.

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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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Germination is classified based on the fate of the cotyledons (seed leaves) relative to the soil surface. In epigeal germination, the hypocotyl elongates rapidly and arches upward, pulling the cotyledons above the soil. Once above ground, the cotyledons may photosynthesize briefly before the true leaves take over. Examples include beans (Phaseolus) and castor oil plant.

In hypogeal germination, the epicotyl elongates instead, pushing the plumule (young shoot) above the soil while the cotyledons remain buried underground. Maize and mango are common examples of hypogeal germination.

The prefix epi- means "above" and hypo- means "below," while -geal relates to the earth. This makes the terminology self-explanatory: epigeal means the cotyledons come above the earth, and hypogeal means they stay below.

Note that epicotyl and hypocotyl are parts of the embryonic axis, not types of germination. The epicotyl is the region above the cotyledon attachment point, and the hypocotyl is the region below it. The question asks about the type of germination, not a plant structure, so the correct answer is epigeal germination.

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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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Buccal respiration is a mode of breathing in which an animal pumps air into and out of its lungs by raising and lowering the floor of its mouth (the buccal cavity). The toad, an amphibian, uses this method. During buccal respiration, the toad lowers the floor of its mouth with the nostrils open, drawing air into the buccal cavity. The nostrils then close, and the floor of the mouth is raised, forcing air into the lungs. This buccal pumping mechanism supplements cutaneous (skin) respiration, which is also important in amphibians.

Tilapia (a bony fish) respires using gills, not buccal pumping. Birds use a highly efficient system of air sacs and parabronchi in their lungs, powered by movements of the ribcage and sternum. Grasshoppers and other insects respire through a tracheal system, a network of tubes (tracheae and tracheoles) that deliver air directly to body tissues through openings called spiracles.

Buccal respiration is a characteristic feature of amphibians, and it is commonly tested alongside cutaneous respiration as a defining amphibian trait.

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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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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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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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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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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.

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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 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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Plants are classified according to the type of habitat in which they grow and their water requirements. Xerophytes are plants adapted to survive in dry, arid conditions such as deserts. They possess structural and physiological adaptations to minimise water loss, including thick, waxy cuticles, reduced or modified leaves (often as spines), deep or extensive root systems, sunken stomata, and the ability to store water in succulent stems or leaves. Examples include cacti, euphorbia, and agave.

The other categories describe different habitat preferences. Mesophytes grow in environments with moderate water availability. Hydrophytes are aquatic plants adapted to waterlogged or submerged habitats. Sporophytes refer to the diploid, spore-producing generation in a plant's life cycle and are not a habitat-based classification.

When distinguishing plant habitat types in an exam, focus on the prefix: xero- (dry), hydro- (water), meso- (moderate).

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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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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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Obudu Game Reserve (also known as Obudu Cattle Ranch or Obudu Mountain Resort) is located in Cross River State, in the south-eastern part of Nigeria. It sits on the Obudu Plateau in the Sankwala Mountains, near the border with Cameroon.

Cross River State is known for its rich biodiversity and is home to several important conservation areas, including the Cross River National Park. The cool highland climate of the Obudu Plateau, at an elevation of about 1,576 metres above sea level, supports unique montane grassland and forest ecosystems that are distinct from the surrounding tropical lowlands.

The other states listed do not contain Obudu Game Reserve. Anambra State is in the south-east but lacks this highland reserve. Akwa Ibom State is a coastal state in the Niger Delta region. Rivers State, also in the Niger Delta, is distinct from Cross River State despite the similarity in names.

Exam tip: Do not confuse Rivers State with Cross River State. They are separate states with different geographical features and conservation areas.

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An estuary is a partially enclosed coastal body of water where freshwater from rivers meets and mixes with saltwater from the sea. Estuarine habitats have fluctuating salinity, tidal influence, and waterlogged, often muddy substrates. Only specially adapted plants can thrive in these conditions.

Mangrove trees and shrubs are the characteristic vegetation of estuarine and coastal swamp habitats in tropical regions. They possess several key adaptations for this environment:

• Prop roots (stilt roots): Provide anchorage in soft, unstable mud and raise the plant above tidal water.
• Pneumatophores (breathing roots): Aerial roots that project above the waterlogged soil to obtain oxygen, since the anaerobic mud lacks sufficient dissolved oxygen for root respiration.
• Salt-excreting glands: Allow the plant to tolerate the high salt concentration of brackish water.
• Viviparous seeds: Seeds germinate while still attached to the parent plant, producing seedlings that can establish quickly once they drop into the water or mud.

Plantain, Gmelina, and Iroko are all terrestrial plants that grow in well-drained, non-saline soils. They lack the specialised adaptations required for survival in a saline, waterlogged estuarine environment.

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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 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.

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Vestigial structures are anatomical features that have lost most or all of their original function through the course of evolution. The tiny, non-functional hind leg bones (pelvic bones) found inside a whale's body are a classic example of vestigial structures. These bones have no role in locomotion or swimming, yet they persist in the whale's skeleton.

The presence of these remnant bones is powerful evidence that whales descended from four-legged terrestrial mammals. Over millions of years, as whale ancestors transitioned from land to a fully aquatic lifestyle, natural selection favoured a streamlined body for efficient swimming. The hind limbs gradually reduced in size across generations because they were no longer needed for walking and eventually became a hindrance in water. The bones that remain today are evolutionary leftovers from those ancestral limbs.

The claim that whales are not related to land animals contradicts the fossil record, which shows a clear lineage of transitional forms (such as Pakicetus and Ambulocetus) connecting modern whales to land-dwelling ancestors. Saying whales have never had legs ignores the very evidence the question presents. And describing these tiny bones as serving a major swimming function is incorrect, since they are internal, reduced, and disconnected from the main skeleton in a way that provides no mechanical advantage for swimming.

Exam tip: Vestigial structures (e.g. the human appendix, whale pelvic bones, python hind limb remnants) are always cited as evidence of evolution from ancestors in which those structures were fully functional.

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The diagram shows a bird's head with two labelled structures. Structure I is the upper mandible (upper beak), which is long, slender, and curved. Structure II is the lower mandible.

This beak shape is characteristic of nectar-feeding birds such as sunbirds and hummingbirds. The long, thin, curved beak is adapted for reaching deep into tubular flowers to extract nectar by sucking.

Other feeding adaptations in birds produce distinctly different beak shapes:

• Tearing beaks are short, strongly hooked, and powerful, as seen in raptors like eagles and hawks.
• Sieving beaks are broad and flat with comb-like lamellae along the edges, as seen in ducks and flamingos.
• Boring beaks are strong, straight, and chisel-shaped, as seen in woodpeckers.

The slender, curved beak labelled I is therefore adapted for sucking nectar from flowers.

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The rumen is the first compartment of the stomach in ruminant animals such as cattle. It houses a dense community of microorganisms, including bacteria and protozoa, that help break down cellulose and other complex plant materials that the cow cannot digest on its own.

This relationship is symbiosis (specifically mutualism), because both parties benefit. The bacteria and protozoa gain a warm, moist, anaerobic environment with a constant supply of food from the plant material the cow ingests. In return, they produce enzymes such as cellulase that digest cellulose into simpler compounds like volatile fatty acids, which the cow absorbs and uses as a major energy source. The microorganisms also synthesise vitamins (such as B-vitamins) and microbial protein that the cow digests further along the alimentary canal.

This is not commensalism, because commensalism involves one organism benefiting while the other is neither helped nor harmed. Here, both parties clearly benefit. It is not parasitism, because neither organism is harmed. It is not predation, because neither organism kills and consumes the other as prey.

Exam tip: Whenever a question describes two different organisms living together with mutual benefit, the correct ecological term is symbiosis (mutualism). The rumen of cattle is the classic JAMB example of this association.

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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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The question asks which feature is unique to photosynthesis and not shared with respiration. To answer this, compare the two processes:

Now examine each option:

• "Food is usually broken down" describes respiration, not photosynthesis. It does not differentiate photosynthesis from respiration; it describes respiration itself.
• "Oxygen is usually liberated" is characteristic of photosynthesis only. In photosynthesis, water molecules are split and oxygen is released as a by-product. Respiration does the opposite: it consumes oxygen. This is a clear differentiating feature.
• "It occurs both during the day and night" describes respiration, which is continuous. Photosynthesis requires light and occurs mainly during the day.
• "It occurs in both plants and animals" again describes respiration. Photosynthesis occurs only in organisms with chlorophyll, not in animals.

The liberation of oxygen is the feature that belongs to photosynthesis and sets it apart from respiration.

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Population replacement among species in a given habitat under competition is a core outcome of natural selection. Natural selection is the process where organisms better adapted to their environment (including competition for limited resources) are more likely to survive, reproduce, and pass on their advantageous traits to the next generation, eventually leading to the replacement of less-adapted species or populations over time. The concept of "survival of the fittest" is often associated with natural selection, but natural selection is the formal, broader mechanism of evolution that explains this phenomenon. 

A. survival of the fittest: While related, "survival of the fittest" is a phrase used to describe the result (the fittest survive), but natural selection is the actual mechanism or law that causes this differential survival and reproduction, leading to population changes.

B. climax community: is the stable, final stage of ecological succession in an area, where the species composition remains relatively constant over time because they are well-adapted to the local conditions, not the cause of population replacement during the competitive process itself.

D. dominant population: is one that outcompetes others, but this dominance is a result of the underlying process (natural selection), not the fundamental mechanism explaining the replacement across species generally

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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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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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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 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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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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Mating colouration is a temporary, vivid change in body colour that certain animals display during the breeding season to attract mates. It is a form of courtship behaviour driven by hormonal changes.

The male agama lizard is a well-known example. Outside the breeding season, the male is typically dull brown or grey. During the mating period, however, the male develops a bright orange-red head and a deep blue body. This dramatic colour change signals reproductive fitness and attracts females while also warning rival males.

The variegated grasshopper displays warning (aposematic) colouration year-round to deter predators; this is not a seasonal mating change. The chameleon changes colour primarily for camouflage, thermoregulation, and social signalling rather than specifically for mating display. The leopard has a permanent spotted coat pattern (rosettes) used for camouflage; it does not change colour during breeding.

When revising courtship behaviour, remember to distinguish mating colouration (temporary, seasonal, for attracting mates) from camouflage, warning colouration, and permanent pigmentation patterns.

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A cypsela is a type of dry, one-seeded indehiscent fruit characteristic of plants in the family Asteraceae (Compositae), such as the dandelion and sunflower. In many species, the cypsela bears a feathery structure called a pappus, which acts like a parachute and enables the fruit to be carried long distances by wind. This is a classic example of wind dispersal (anemochory).

A schizocarp is a dry fruit that splits into single-seeded segments at maturity and may be dispersed by various means depending on the species. A caryopsis is the fruit type of grasses, where the seed coat is fused to the fruit wall; grasses are typically wind-pollinated, but the caryopsis itself may be dispersed by wind, animals, or water depending on the species. A capsule is a dry dehiscent fruit that splits open to release seeds and can be dispersed by several mechanisms (wind, shaking, explosive).

The cypsela with its pappus is the most specifically and consistently associated with wind dispersal among these options.

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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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In a herbaceous (dicotyledonous) root, the tissues are arranged in concentric layers from the outside to the centre. Understanding this arrangement is essential for plant anatomy questions.

Moving inward from the surface:

1. Piliferous layer (epidermis): The outermost layer, bearing root hairs that absorb water and mineral salts from the soil.
2. Cortex: A broad region of parenchyma cells just beneath the epidermis. It stores food and allows lateral movement of water.
3. Endodermis: A single layer of cells at the inner boundary of the cortex (sometimes grouped with cortex in simplified descriptions).
4. Pericycle: A thin layer of meristematic cells just inside the endodermis. It gives rise to lateral roots.
5. Vascular tissue: The xylem and phloem, arranged in an alternating pattern within the stele.
6. Pith: The central core of parenchyma cells at the very centre of the root (in dicots, the pith may be small or absent, but in herbaceous roots it is typically present).

The correct sequence from circumference to centre is therefore: piliferous layer, cortex, pericycle, vascular tissue, and pith.

Exam tip: The pericycle always lies between the cortex (specifically the endodermis) and the vascular tissue. Any option that places vascular tissue before pericycle, or pith before vascular tissue, is incorrect.

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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 cell sap is the aqueous solution found within plant cells, particularly in the vacuole, and it serves as the medium in which dissolved substances (mineral salts, sugars, amino acids, and other metabolites) are transported within and between plant cells. The question specifically asks about the medium of transportation, meaning the liquid substance that carries materials, rather than the structural tissues or channels through which transport occurs.

Xylem and phloem are vascular tissues (the channels or pathways) through which materials are transported, not the medium itself. The xylem conducts water and dissolved minerals upward, while the phloem translocates organic solutes such as sucrose. Cytoplasm is the general cellular matrix that fills the cell, but it is not the term used to describe the transport medium in the context of whole-plant material movement.

When a question distinguishes between the transport medium and the transport tissue, remember: the medium is the solution (cell sap), while the tissues are the conduits (xylem and phloem).

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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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Each kidney receives blood through a renal artery. Inside the kidney, the renal artery branches into smaller and smaller arterioles. Within each nephron (the functional unit of the kidney), an afferent arteriole enters the cup-shaped structure called the Bowman's capsule (or Bowman's capsule / renal capsule) and splits into a dense, tangled ball of capillaries. This capillary tuft is called the glomerulus.

The glomerulus is the site of ultrafiltration: the high blood pressure inside these capillaries forces water, salts, glucose, urea, and other small molecules out of the blood and into the cavity of the Bowman's capsule, forming the glomerular filtrate. Large molecules such as proteins and blood cells are too big to pass through the capillary walls and remain in the blood.

The other structures named in the question serve different roles. The tubule (renal tubule) is the long tube leading away from the Bowman's capsule where selective reabsorption occurs. The pelvis (renal pelvis) is the funnel-shaped cavity that collects urine before it drains into the ureter. The nephron is the entire functional unit comprising the Bowman's capsule, glomerulus, and tubule together, not the capillary mass alone.

Remember: the glomerulus is specifically the knot of capillaries inside the Bowman's capsule where filtration begins.