JAMB UTME - Biology - 2025

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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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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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Cells produce various metabolic waste products that must be stored or removed. The organelle primarily responsible for storing waste products within the cell is the vacuole.

Vacuoles are membrane-bound sacs found in cells. In plant cells, there is typically one large central vacuole that can occupy up to 90% of the cell volume. In animal cells, vacuoles tend to be smaller and more numerous. Vacuoles store a variety of substances including water, nutrients, pigments, and importantly, metabolic waste products. By sequestering waste inside the vacuole, the cell prevents these potentially harmful substances from interfering with cytoplasmic reactions.

The other options serve different functions:

• The Golgi apparatus packages, modifies, and sorts proteins and lipids for transport to their final destinations. It does not function as a waste storage site.
• The cell wall (found in plant cells) provides structural support and rigidity. It is not an organelle involved in storage.
• Lysosomes contain digestive enzymes that break down worn-out organelles, food particles, and foreign material. They destroy waste rather than store it.

Exam tip: Distinguish between lysosomes (which digest and break down waste) and vacuoles (which store waste and other substances). Storage and digestion are different functions.

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

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

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

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

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The 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 DNA, the two strands of the double helix are held together by complementary base pairing through hydrogen bonds. The pairing follows strict rules discovered by Erwin Chargaff and confirmed by Watson and Crick's model of DNA structure.

The two base-pairing rules are:

• Adenine (A) always pairs with thymine (T) via two hydrogen bonds.
• Guanine (G) always pairs with cytosine (C) via three hydrogen bonds.

These pairings occur because of the molecular shapes and hydrogen-bonding capacity of the bases. Adenine and thymine are complementary in size and bonding sites, as are guanine and cytosine. A purine (adenine or guanine, which are larger, double-ringed bases) always pairs with a pyrimidine (thymine or cytosine, which are smaller, single-ringed bases), maintaining a uniform width of the DNA double helix.

Adenine - thymine is therefore one of the two correct base pairs in a DNA molecule. The other options listed (cytosine - adenine, cytosine - thymine, guanine - adenine) violate Chargaff's rules and would result in mismatched hydrogen bonding and irregular helix geometry.

Exam tip: Remember the pairing rule with the mnemonic: A-T (Apple-Tree) and G-C (Good-Cat). In RNA, thymine is replaced by uracil, so adenine pairs with uracil instead.

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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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The mosquito possesses a piercing and sucking type of mouthpart. Its mouthparts are modified into a long, needle-like proboscis composed of six stylets enclosed within the labium (lower lip). The stylets include the mandibles and maxillae, which pierce the skin of the host, and the labrum-epipharynx, which forms a channel through which blood is sucked up. The hypopharynx delivers saliva containing anticoagulants into the wound. This arrangement allows the mosquito to penetrate skin and feed on blood.

The cockroach has biting and chewing mouthparts, adapted for cutting and grinding solid food. The butterfly and moth both have siphoning (sucking only) mouthparts: a long, coiled proboscis used to sip nectar from flowers. Their mouthparts are not designed for piercing; they can only access liquid that is already exposed.

In examinations, distinguish carefully between "piercing and sucking" (penetrates tissue, e.g. mosquito, tsetse fly, aphid) and "siphoning/sucking" (draws exposed liquid, e.g. butterfly, moth).

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

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

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

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A burrow is an underground tunnel or hole dug by an animal to serve as a shelter, nesting site, or place to store food. Among the options given, the bush rat is the animal that creates its natural habitat in burrows.

Bush rats, like many other rodents, are well adapted for digging. They use their strong claws and compact bodies to excavate burrows in soil, where they live, breed, and shelter from predators and extreme weather. These burrows may have multiple entrances and chambers for different purposes.

The other options do not create burrows. Doves build nests in trees, on ledges, or on the ground surface using twigs and other materials. Chameleons are arboreal reptiles that live on tree branches, relying on camouflage rather than burrowing for protection. Snails carry their own protective shells on their backs and shelter under rocks, leaves, or in moist crevices rather than digging into the ground.

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

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

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

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

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

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

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

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

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

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The cooling effect on the body of mammals is brought about by sweat excretion. When the body temperature rises, sweat glands in the skin produce sweat, which is secreted onto the surface of the skin. As this sweat evaporates, it absorbs latent heat of vaporisation from the skin, thereby lowering the body temperature.

This process is a key thermoregulatory mechanism in mammals. It is controlled by the hypothalamus, which detects a rise in blood temperature and triggers increased sweat production alongside vasodilation (widening of blood vessels near the skin surface) to dissipate heat.

The other processes listed do not produce a cooling effect:

• Digestion is the breakdown of food in the alimentary canal to release nutrients - it actually generates metabolic heat rather than removing it.
• Urine formation (occurring in the kidneys) is an excretory process that removes nitrogenous waste and regulates water and ion balance, but does not function as a cooling mechanism.
• Respiration is the metabolic process of releasing energy from food (glucose). It is exothermic and produces heat, which is the opposite of cooling.

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Poliomyelitis (polio) is a highly infectious disease caused by the poliovirus, which attacks the motor neurons of the spinal cord and brainstem. In severe cases, the destruction of these nerve cells leads to irreversible paralysis of the limbs, particularly the legs. This is why the statement that polio is capable of paralysing the limbs is correct.

Evaluating the other statements:

• Polio is a viral disease, not a bacterial one. It is caused by the poliovirus, a member of the enterovirus group.
• Effective vaccines exist against polio. The oral polio vaccine (OPV, Sabin) and the inactivated polio vaccine (IPV, Salk) have been used worldwide and have nearly eradicated the disease through mass immunisation programmes.
• While polio can technically infect people of any age, it predominantly affects children under five years old. The claim that it affects both young and old equally is misleading; it is primarily a disease of early childhood, which is why it was historically called "infantile paralysis."

Remember: polio is viral, vaccine-preventable, and primarily causes paralysis by destroying motor neurons in the spinal cord.

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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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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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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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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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The stick insect's slender, elongated, twig-like body shape is a classic example of cryptic coloration and form (camouflage). This structural adaptation serves the purpose of protection and defence against predators.

By closely resembling twigs or branches in both shape and colour, stick insects become extremely difficult for predators such as birds, lizards, and spiders to detect among vegetation. This form of passive defence does not require the insect to fight or flee; instead, the insect avoids detection altogether by blending into its surroundings. This strategy is a type of protective mimicry known as crypsis.

The stick-like shape has nothing to do with water conservation, which typically involves physiological or behavioural adaptations such as waxy cuticles or burrowing. It is also unrelated to securing a mate, which involves courtship displays or pheromone signalling. While escaping predators is related to defence, the term "escaping adaptation" does not accurately describe what the body shape achieves. The insect's shape is primarily about avoiding detection rather than facilitating escape once spotted.

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UNICEF (the United Nations Children's Fund) is the United Nations agency specifically mandated to provide emergency assistance and long-term developmental support to children and mothers worldwide. Originally established in 1946 as the United Nations International Children's Emergency Fund, UNICEF works in over 190 countries to deliver healthcare, nutrition, clean water, education, and emergency relief to children affected by crises such as conflicts, natural disasters, and disease outbreaks.

WHO (the World Health Organization) focuses on international public health for all populations, not specifically children. It coordinates global health responses, sets health standards, and monitors disease outbreaks, but its mandate covers all age groups rather than targeting children's emergency needs.

NMA (the Nigerian Medical Association) is a national professional body for medical practitioners in Nigeria. It is neither a global organization nor one specifically focused on children's emergency needs.

UNIDO (the United Nations Industrial Development Organization) promotes industrial development in developing countries. Its focus is on economic and industrial growth, not on children's welfare or emergency relief.

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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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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 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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The question describes cells that are constantly dividing and are found at the apex (tip) of roots and stems. These are meristematic cells, which form the meristematic tissue (meristem).

Meristematic cells are undifferentiated cells that retain the ability to divide continuously by mitosis. They are responsible for primary growth in plants, adding length to roots and shoots. The key characteristic that defines meristematic tissue is its capacity for active and continuous cell division, which is exactly what the question describes.

The other options describe types or locations of meristems rather than the fundamental nature of the cells:

• Apical refers to the location of the meristem (at the apex/tip), not the type of cells themselves. Apical meristem is made up of meristematic cells, but "apical" describes where the meristem is, not what the constantly dividing cells are called.
• Intercalary meristems are found at the base of internodes (e.g., in grasses), not at the apex of roots and stems.
• Lateral meristems (such as the cambium) are responsible for secondary growth (increase in girth), not primary growth at the tips.

The question asks what type of cells these are. The answer is meristematic, because the defining property of these cells is their ability to divide indefinitely.

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

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

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

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

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Rhizopus (commonly known as bread mould) is a saprophytic fungus. Saprophytes are organisms that obtain their nutrition by secreting digestive enzymes onto dead or decaying organic matter and then absorbing the resulting soluble products. Rhizopus grows on stale bread, decaying fruits, and other dead organic substrates, breaking them down extracellularly and absorbing the nutrients.

The other organisms listed obtain nutrition by different means. Bladderwort (Utricularia) and sundew (Drosera) are both carnivorous (insectivorous) plants that trap and digest small insects to supplement the mineral nutrients they cannot obtain from their nutrient-poor habitats. Mistletoe (Viscum) is a parasitic plant that grows on host trees and extracts water and nutrients from the host's vascular tissue using specialised structures called haustoria.

To distinguish modes of nutrition in exams, remember: saprophytes feed on dead matter, parasites feed on living hosts, and carnivorous plants trap living prey.

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A long beak with saw-like edges (also described as having tooth-like serrations or denticles) is a specific adaptation found in pelicans. This feature serves several vital functions such as grip, water drainage (the "saw-like" structures allow the bird to drain excess water from its beak while keeping the prey trapped inside before swallowing), tearing prey(in some species, these structures act like sharp shears to help tear through tougher prey). 

A. wood pecker: Woodpeckers have strong, chisel-shaped beaks adapted for drilling into wood and excavating insects. They do not have saw-like edges.

B. kingfisher: Kingfishers possess long, straight, dagger-like beaks. This shape is streamlined to allow them to dive into water with minimal splash and resistance, but the edges are not saw-like.

D. duck: Most ducks have broad, flat beaks with comb-like structures called lamellae for filtering food from water. While some specialized ducks like mergansers are nicknamed "sawbills" because of their serrated beaks, the term "saw-like edges" in standard biological questions of this type most frequently refers to the pelican's adaptation for managing large quantities of water and slippery fish. 

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Spermatophytes are seed-bearing plants. They are divided into two major groups: gymnosperms (seeds not enclosed in a fruit) and angiosperms (seeds enclosed within a fruit, formed from the ovary wall).

Angiosperms are considered the most advanced spermatophytes because they possess several evolutionary innovations:

• Double fertilisation, which produces both an embryo and a nutrient-rich endosperm.
• Flowers, which allow efficient pollination by wind, water, insects, and other animals.
• Fruits, which aid in seed dispersal.
• Highly efficient vascular tissue, including vessel elements in the xylem.

Angiosperms also form the largest group in the plant kingdom, with over 300,000 known species, far exceeding the roughly 1,000 species of gymnosperms.

Ferns are not spermatophytes at all; they reproduce by spores, not seeds. Cones are reproductive structures of gymnosperms, not a plant group. Gymnosperms are spermatophytes but are less advanced and far fewer in number than angiosperms.

The correct answer is therefore angiosperm.

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

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

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

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

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

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The cortex is the region of a plant stem located between the epidermis and the vascular bundles. In a herbaceous (non-woody) stem, the cortex is composed of two main tissue types:

• Collenchyma occupies the outer part of the cortex, just beneath the epidermis. It consists of living cells with unevenly thickened cell walls that provide flexible mechanical support, allowing the young stem to bend without breaking.
• Parenchyma makes up the bulk of the inner cortex. These are thin-walled, living cells with large vacuoles. They function in storage of food, water, and waste products, and they also carry out photosynthesis when chloroplasts are present (chlorenchyma).

Xylem is a vascular tissue found in the stele (vascular cylinder), not in the cortex. Sclerenchyma, which consists of dead cells with uniformly thickened lignified walls, is characteristic of woody stems and mature tissues rather than the cortex of a typical herbaceous stem.

The correct combination is therefore parenchyma and collenchyma, as these are the ground tissues that together constitute the cortex of a herbaceous stem.

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

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

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

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

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

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

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

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