JAMB UTME - Biology - 2025
Question 1 Report
Use the illustration above to answer the question that follows
What is the genotypic ratio of the F\(_2\) generation?
Answer Details
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.
Question 2 Report
Which of the following statements is correct about sedimentation of a given soil?
Answer Details
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.
Question 3 Report
An example of a reflex action is
Answer Details
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.
Question 4 Report
The ability of chameleon to change its colour to that of the environment is for
Answer Details
A chameleon's ability to change the colour of its skin to match its surroundings is a well-known example of camouflage, which is a form of defensive adaptation. By blending into the background, the chameleon becomes difficult for predators such as birds and snakes to detect. This dramatically increases its chances of survival.
The colour change is achieved through specialised pigment-containing cells called chromatophores in the skin. Different layers of chromatophores contain different pigments, and the chameleon can expand or contract these cells to produce a wide range of colours and patterns that match the surrounding vegetation, bark, or soil.
While colour change in some contexts can play a role in communication or thermoregulation, the primary biological advantage tested at this level is defence against predation. The other options do not accurately describe the main survival purpose of this adaptation: it is not primarily for attracting mates, inviting other organisms, or launching attacks on prey.
Exam tip: Camouflage, mimicry, and warning colouration are all classified as defensive adaptations. When a question asks about an organism blending with its environment, the answer points to protection from predators.
Question 5 Report
Agglutination occurs in blood transfusion when the
Answer Details
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:
| Blood Group | Antigen on RBC | Antibody in Plasma |
|---|---|---|
| A | A | anti-B |
| B | B | anti-A |
| AB | A and B | None |
| O | None | anti-A and anti-B |
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.
Question 6 Report
A form of adaptive colouration that helps animals to remain unnoticed is
Answer Details
Countershading is a form of adaptive colouration in which an animal's dorsal (upper) surface is darker and its ventral (lower) surface is lighter. This colour gradient counteracts the natural shadowing effect caused by overhead light, making the animal appear flatter and less three-dimensional. The result is that the animal blends more effectively into its background and becomes harder for predators (or prey) to detect.
Countershading is widespread in nature. Many fish are dark on top and light on the belly, so they blend with the dark water below when viewed from above and with the bright sky when viewed from below. Deer, sharks, penguins, and many birds also display countershading.
The other options are not forms of colouration at all:
- Hibernation is a behavioural adaptation in which an animal enters a prolonged state of dormancy during cold seasons to conserve energy.
- Aestivation is a similar dormancy response to hot, dry conditions (e.g. lungfish burying in mud during drought).
- Migration is the seasonal movement of animals from one region to another in search of favourable conditions.
None of these three involves body colouration. The question specifically asks about adaptive colouration that helps animals remain unnoticed, which directly describes countershading.
Question 7 Report
One characteristic which differentiates bats from birds is that bats
Answer Details
Bats are mammals, while birds belong to class Aves. Although both can fly and share certain features, the question asks for a characteristic that differentiates bats from birds - something bats have that birds do not.
The distinguishing feature is that bats possess mammary glands. Mammary glands are the defining characteristic of all mammals (class Mammalia). Female bats produce milk to suckle their young, which is something no bird does. Birds instead feed their young by regurgitation or by bringing food to the nest.
The other options describe features that both bats and birds share, so they cannot differentiate the two:
- Both bats and birds possess a four-chambered heart (two atria and two ventricles), so this is not a distinguishing feature.
- While many bat species are nocturnal (active at night), some birds are also nocturnal (e.g., owls, nightjars), so nocturnal activity is not a reliable differentiating characteristic.
- Both bats and birds are warm-blooded (endothermic), maintaining a constant body temperature regardless of the environment, so this does not differentiate them.
When comparing animal groups in examinations, focus on features that are exclusive to one group. Mammary glands are exclusive to mammals and are never found in birds.
Question 8 Report
The correct base pair in DNA molecule is
Answer Details
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.
Question 9 Report
Which of these animals uses buccal respiration?
Answer Details
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.
Question 10 Report
The maximum number of organisms that the resources in the habitat can support is referred to as
Answer Details
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.
Question 11 Report
The most suitable soil for crops cultivation in Nigeria is
Answer Details
Loamy soil is the most suitable soil for crop cultivation in Nigeria and in agriculture generally. Loam is a mixture of sand, silt, and clay in roughly balanced proportions, which gives it a combination of properties ideal for plant growth:
- Good water retention and drainage: It holds enough moisture for roots to absorb but drains excess water, preventing waterlogging.
- Good aeration: The presence of sand particles creates air spaces, allowing root respiration and the activity of beneficial soil organisms.
- High nutrient content: The clay and silt fractions hold mineral ions through cation exchange, while organic matter (humus) further enriches the soil.
- Easy to work: Loam is neither too heavy nor too light, making it easy to plough and cultivate.
Laterite soil is highly weathered and leached, with poor fertility and a hard, iron-rich crust that limits root penetration. Sandy soil drains too quickly and has very low nutrient-holding capacity. Clayey soil holds too much water, has poor drainage and aeration, and becomes very hard when dry, making it difficult for roots to penetrate.
Question 12 Report
The prevalence of pests and diseases which affect plants and animals in a terrestrial habitat is
Answer Details
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.
Question 13 Report
The genetic make up of an organism is referred to as the
Answer Details
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.
Question 14 Report
An instrument used in measuring plants growth is
Answer Details
An auxanometer is a specialised instrument designed to measure the rate of growth in plants, particularly elongation growth. It works by magnifying small increments of growth using a lever, pulley, or rotating drum system connected to the tip of a growing plant. As the plant grows, even tiny increases in height are amplified and recorded, making it possible to measure growth that would be too small to detect by direct observation alone.
The other instruments listed measure entirely different environmental quantities:
- A hygrometer measures the relative humidity (moisture content) of the air.
- A barometer measures atmospheric pressure.
- A thermometer measures temperature.
None of these three instruments is designed to detect or quantify changes in plant size or growth rate.
Exam tip: The prefix auxano- comes from the Greek word for "growth" (the same root as the plant hormone auxin). Linking "auxanometer" to "auxin" is a reliable way to remember that both relate to plant growth.
Question 15 Report
The variation that can be applied in crime detection is
Answer Details
Fingerprints are the variation most applicable to crime detection. Every individual (including identical twins) has a unique set of ridge patterns on their fingertips. These patterns - classified as loops, whorls, and arches - are formed during foetal development and remain unchanged throughout life. This uniqueness and permanence make fingerprints an extremely reliable tool for identifying individuals.
In forensic science, fingerprints left at a crime scene (latent prints) can be lifted, analysed, and matched against databases of known prints to identify suspects or confirm the presence of a particular person. This technique, known as dactyloscopy, has been used in criminal investigations worldwide for over a century.
The other variations listed are not suitable for crime detection:
- Tongue rolling is a genetic trait (the ability to roll the tongue into a tube shape), but it is shared by a large proportion of the population and cannot distinguish one individual from another.
- Height is a continuous variation influenced by both genetics and environment. Many people share similar heights, making it useless as a unique identifier.
- Colour (skin, eye, or hair colour) is also shared among large groups and provides no individual-level identification.
Exam tip: Fingerprints are an example of discontinuous variation - each person's pattern is qualitatively distinct, not just a point on a continuous scale. This uniqueness is what makes them forensically useful.
Question 16 Report
Which of the following differentiates photosynthesis from respiration?
Answer Details
The question asks which feature is unique to photosynthesis and not shared with respiration. To answer this, compare the two processes:
| Feature | Photosynthesis | Respiration |
|---|---|---|
| Raw materials | CO2 and H2O | Glucose and O2 |
| Products | Glucose and O2 | CO2 and H2O (+ energy) |
| Oxygen | Released (liberated) | Consumed (used up) |
| Food | Built up (synthesised) | Broken down |
| When it occurs | Only in light (daytime) | Continuously (day and night) |
| Organisms | Green plants and some bacteria | All living organisms |
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.
Question 17 Report
One of the following is a reflex action
Answer Details
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.
Question 18 Report
The date palm is commonly planted in Sahel zone of
Answer Details
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.
Question 19 Report
Example of animal exhibiting mating colouration is
Answer Details
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.
Question 20 Report
Chlamydomonas belongs to the phylum
Answer Details
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.
Question 21 Report
Competition between cow and goat for scarce grasses during dry season can be described as
Answer Details
Competition is an ecological interaction in which organisms struggle for the same limited resources, such as food, water, or space. It is classified into two types based on whether the competing organisms belong to the same or different species.
Interspecific competition occurs between organisms of different species that require the same resources. A cow (species Bos taurus) and a goat (species Capra aegagrus hircus) are two distinct species. When they both graze on scarce grasses during the dry season, they compete for the same limited food resource across species boundaries. This is therefore interspecific competition.
Intraspecific competition occurs between members of the same species - for example, two cows competing for the same grass. Since the question involves a cow and a goat (different species), it is not intraspecific. Predation involves one organism killing and eating another, which is not the case here. Commensalism is an association in which one organism benefits and the other is unaffected, which does not apply to a struggle for scarce resources.
Exam tip: The prefix inter- means "between" (different species), while intra- means "within" (same species). Always check whether the competing organisms belong to the same or different species before choosing.
Question 22 Report
Transparency of water is measured using a
Answer Details
The transparency (or clarity) of water is measured using a Secchi disc. A Secchi disc is a circular disc, typically 20 cm in diameter, divided into alternating black and white quadrants. It is lowered into the water on a calibrated rope or chain until it is no longer visible from the surface. The depth at which the disc disappears from view is called the Secchi depth, and it provides a simple, standardised measure of water transparency.
Water transparency is an important ecological parameter because it indicates how far light can penetrate, which directly affects photosynthesis by aquatic plants and phytoplankton. Low transparency (shallow Secchi depth) may indicate high levels of suspended sediment, algal blooms, or dissolved organic matter.
The other instruments measure entirely different environmental factors:
- A hygrometer measures the humidity (moisture content) of the atmosphere.
- A barometer measures atmospheric pressure.
- An anemometer measures wind speed.
Exam tip: Ecological measurement instruments are commonly tested. Remember that the Secchi disc measures water clarity, while a hydrometer (not hygrometer) measures the relative density of liquids.
Question 23 Report
Which of the following is a behavioural adaptation of animals for avoiding adverse weather conditions?
Answer Details
Hibernation is a behavioural adaptation in which an animal enters a prolonged state of dormancy during adverse weather conditions, particularly cold winters. During hibernation, the animal's metabolic rate, body temperature, heart rate, and breathing rate drop significantly, allowing it to conserve energy when food is scarce and temperatures are too low for normal activity. Examples include bears, hedgehogs, bats, and some rodents.
The key word in the question is "adverse weather conditions." Hiding is a behavioural response primarily used to escape predators, not specifically to cope with weather. Remaining motionless (freezing) is a defence mechanism against predators. Swelling up (puffing up the body) is a defensive display used by some animals to appear larger and deter predators, such as the puffer fish or the toad.
Hibernation (for cold weather) and its warm-weather counterpart, aestivation (for hot, dry conditions), are the two main behavioural adaptations specifically for surviving adverse weather.
Question 24 Report
Long beak with saw-like edges is an adaptation in
Answer Details
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.
Question 25 Report
Part of the littoral zone of the marine habitat above the high tide mark, wetted by spray of water from breaking of waves is referred to as the
Answer Details
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.
Question 26 Report
Albinism is a disorder caused by
Answer Details
Albinism is a genetic condition in which the body cannot produce normal amounts of the pigment melanin. Melanin is responsible for giving colour to the skin, hair, and eyes. The disorder is caused by inheriting two copies of a recessive gene that codes for a defective or non-functional form of the enzyme tyrosinase, which is needed for melanin synthesis.
Since albinism follows an autosomal recessive inheritance pattern, an individual must receive the defective allele from both parents (homozygous recessive, aa) to express the condition. A person who carries only one copy of the recessive allele (heterozygous, Aa) is a carrier but does not show symptoms because the dominant allele produces enough functional enzyme.
The other options are incorrect. Sebum is an oily substance produced by sebaceous glands in the skin that lubricates the skin and hair; it plays no role in pigmentation. Over-production of melanin would result in hyperpigmentation (darker skin), not albinism. The root cause is genetic, not a simple over- or under-production of a glandular secretion.
Exam tip: Albinism is a classic example of a condition caused by homozygous recessive alleles. Remember that the underlying mechanism involves a faulty enzyme (tyrosinase) leading to absence or severe reduction of melanin.
Question 27 Report
In Nigeria, the major climatic factor that determines the distribution of organisms is
Answer Details
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.
Question 28 Report
A repeating unit of a very large DNA molecule is made up of
Answer Details
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.
Question 29 Report
Which of the following blood groups will clump when mixed with anti-a antibody serum?
Answer Details
In the ABO blood group system, each blood group is defined by the antigens present on the surface of red blood cells. Blood group A carries the A antigen, blood group B carries the B antigen, blood group AB carries both A and B antigens, and blood group O carries neither.
Anti-A antibody serum contains antibodies that specifically bind to the A antigen. When anti-A serum is added to a blood sample, agglutination (clumping) occurs if the red blood cells carry the A antigen on their surface.
Blood group A has the A antigen, so it will clump with anti-A serum. Blood group AB also has the A antigen (along with B), so it too will clump with anti-A serum. Blood group B has only the B antigen and blood group O has no antigens, so neither of these will clump with anti-A serum.
Therefore, both A and AB blood groups will clump when mixed with anti-A antibody serum.
Exam tip: Remember that anti-A serum reacts with any blood group that carries the A antigen. AB carries both antigens, so it reacts with both anti-A and anti-B sera.
Question 30 Report
The relationship between fungus and alga in lichen is an example of
Answer Details
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.
Question 31 Report
The segregation of genes occurs during
Answer Details
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.
Question 32 Report
The slender and stick-like shapes of the stick insect is a structural adaptation for
Answer Details
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.
Question 33 Report
In a community with limited resources, the less vigorous species are eliminated due to
Answer Details
When resources such as food, water, space, or light are limited in a community, organisms must compete for those resources. This is known as competition, and it is one of the key ecological interactions that shapes community structure.
In such situations, species that are better adapted to exploit the available resources - those that are more vigorous, reproduce faster, or use resources more efficiently - tend to survive and increase in population. Less vigorous species, which are less competitive, gradually decline and may eventually be eliminated from the community. This outcome is consistent with the competitive exclusion principle (Gause's principle), which states that two species competing for exactly the same limited resource cannot coexist indefinitely; the inferior competitor will be outcompeted.
Disease, while it can reduce populations, is not specifically triggered by limited resources in the way competition is. Drought is a specific environmental event, not a general ecological process of elimination. Natality refers to the birth rate in a population and describes population growth, not the elimination of species.
Question 34 Report
Which of the following is an example of vestigial structure?
Answer Details
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.
Question 35 Report
Macronutrients required by plants include
Answer Details
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.
Question 36 Report
The two - hoofed toes of camels allow easy walking on desert because of
Answer Details
Camels have broad, two-hoofed toes connected by a thick, leathery pad. When the camel steps on sand, the toes spread apart, creating an enlarged foot surface area. This increased surface area distributes the camel's body weight over a wider area, reducing the pressure exerted on the sand and preventing the animal from sinking into the loose desert substrate.
This principle follows the physics of pressure: \( P = \frac{F}{A} \), where P is pressure, F is force (body weight), and A is the contact area. By increasing the area, the pressure per unit area decreases, making it easier for the camel to walk on soft sand.
A narrow foot surface would cause the animal to sink deeper into the sand. "Elongated" and "long" foot surfaces do not accurately describe the adaptation; the critical feature is the widening or enlargement of the foot's contact area, not its length.
Question 37 Report
Which of the following controls protein and enzyme syntheses in the cytoplasm of the cell?
Answer Details
DNA (deoxyribonucleic acid) is the molecule that controls protein and enzyme synthesis in the cytoplasm. DNA carries the genetic code - a specific sequence of nucleotide bases (adenine, thymine, guanine, cytosine) that determines which proteins and enzymes are produced.
The process works in two main stages:
- Transcription: In the nucleus, the relevant section of DNA unwinds and one strand serves as a template for the synthesis of messenger RNA (mRNA). The mRNA carries a complementary copy of the genetic instructions.
- Translation: The mRNA moves out of the nucleus into the cytoplasm, where it attaches to ribosomes. Transfer RNA (tRNA) molecules bring specific amino acids to the ribosome, matching them to the codons on the mRNA. The amino acids are joined together in the correct sequence to form the protein or enzyme.
While the nucleus houses the DNA and chromosomes are the structures that DNA is packaged into, the question asks specifically what controls protein synthesis. That controlling agent is the DNA molecule itself, because it is the sequence of bases in DNA that determines which proteins are made. Chromosomes are the physical packaging of DNA, not the controlling molecule. Mitochondria have their own DNA and carry out cellular respiration, but they do not control the synthesis of proteins and enzymes in the cytoplasm of the cell.
Question 38 Report
In a cross involving a heterozygous red flower plant (Rr) and a white flowered plant (rr), what is the probability that the offspring will be Rr?
Answer Details
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:
| r | r | |
|---|---|---|
| R | Rr | Rr |
| r | rr | rr |
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.
Question 39 Report
What is the phenotype of the offspring produced in F\(_1\)?
Answer Details
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.
Question 40 Report
Seaweeds and Barnacles are common flora and fauna found in which of these habitats?
Answer Details
Seaweeds are large, multicellular marine algae that grow attached to rocks, coral, and other hard substrates in saltwater environments. They require sunlight for photosynthesis and are typically found in the intertidal and shallow subtidal zones of the ocean. Barnacles are sessile marine crustaceans that attach permanently to hard surfaces such as rocks, ship hulls, and piers in saltwater. Both organisms are characteristically associated with the marine habitat.
Terrestrial habitats are land-based environments where neither seaweeds nor barnacles can survive, as both require saltwater. Estuarine habitats are brackish zones where rivers meet the sea; while some salt-tolerant organisms are found there, seaweeds and barnacles are more accurately described as marine organisms. Freshwater habitats (lakes, rivers, ponds) lack the salinity that seaweeds and barnacles depend on.
Exam tip: When a question pairs an alga (flora) with a sessile saltwater invertebrate (fauna), the habitat is marine. Remember that seaweeds are not found in freshwater, and barnacles are exclusively marine crustaceans.
