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Subject: Biology
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WAEC Biology OBJ 2025
01-10: CACDBCADDB
11-20: ABBDAABDAC
21-30: BABCCCABBA
31-40: BBBAACCBAA
41-50: DBCCCDBCAC
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WAEC Biology Essay 2025
Number 1
(1a)
Excretion is the biological process by which living organisms remove metabolic waste products and toxic substances produced from their body to maintain internal balance and prevent harm.
(1bi)
(i) Urea
(ii) Carbon dioxide
(1bii)
(i) Oxygen
(ii) Water.
(1c)
[TABULATE]
=Organism=
(i) Paramecium
(ii) Planaria
(iii) Leaf of plant
(iv) Earthworm
=Excretory structure=
(i) Contractile vacuole
(ii) Flame cells
(iii) Stomata
(iv) Nephridia
=Mechanism involved in excretion=
(i) Osmoregulation
(ii) Diffusion and filtration
(iii) Transpiration
(iv) Filtration and diffusion
=Adaptation of the structure for excretion=
(i) Thin semi-permeable membrane
(ii) Highly branched tubules for efficient removal
(iii) Guard cells regulate opening and closing of stomata
(iv) Extensive network increases surface area for excretion.
(1d)
(i) Removes metabolic waste products from the blood.
(ii) Regulates water and salt balance.
(iii) Maintains acid-base balance and regulates blood pH.
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Number 2
(2a)
[TABULATE]
=Photosynthetic Nutrition=
(i) Energy is obtained from sunlight.
(ii) It occurs in green plants and some bacteria.
=Chemosynthetic Nutrition=
(i) Energy is obtained from chemical reactions involving inorganic substances.
(ii) It occurs in certain bacteria like nitrifying bacteria.
(2bi)
Saprophytes are organisms that feed on dead and decaying organic matter for their nutrition.
(2bii)
(i) Rhizopus
(ii) Mucor
(2biii)
Saprophytes secrete digestive enzymes onto dead organic material to break it down into simpler substances, which are then absorbed into their bodies.
(2biv)
(i) They decompose organic waste, helping in nutrient recycling.
(ii) They are used in the production of antibiotics.
(iii) Some are used in food production processes like fermentation.
(2c)
(i) They trap and digest small animals or insects.
(ii) They have specialized structures like sticky leaves or pitfall traps.
(iii) They often grow in nutrient-poor soils, hence the need for alternative nitrogen sources.
(2d)
(i) Butterflies feed by sucking nectar from flowers using a proboscis.
(ii) Mosquito larvae are filter feeders, feeding on microorganisms and organic matter in water.
(iii) Mucor feeds saprophytically by breaking down dead organic matter with enzymes and absorbing the nutrients.
(iv) Housefly feeds by sucking up liquid or semi-liquid food, often after regurgitating digestive enzymes to liquefy solid food.
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Number 3
(3a)
Carbon (IV) oxide (COâ‚‚) and oxygen (Oâ‚‚) are balanced in nature through the processes of photosynthesis and respiration. During photosynthesis, green plants use COâ‚‚ and release Oâ‚‚ into the atmosphere. During respiration and decomposition, animals and plants use Oâ‚‚ and release COâ‚‚ back into the atmosphere. This continuous cycle maintains a balance between the two gases in nature.
(3b)
(i) Amount of sunlight
(ii) Soil type and fertility
(iii) Availability of water
(iv) Temperature
(v) Presence of pests and diseases
(3ci)
Overcrowding in an ecosystem is a situation where the number of organisms exceeds the carrying capacity of the environment, leading to competition for limited resources such as food, space, and water.
(3cii)
(i) Increased competition for food and other resources
(ii) Spread of diseases and parasites
(iii) Higher mortality rate
(iv) Reduced growth and reproduction
(v) Migration or displacement of some organisms
(3di)
Density-dependent factors are factors whose effects on the population increase or decrease depending on the population density while density-independent factors are factors that affect populations regardless of their density.
(3dii)
(i) Competition for food
(ii) Spread of diseases
(3diii)
Density-dependent factors like competition and disease affect populations more as their size increases, helping regulate their numbers. Density-independent factors such as floods or temperature changes affect populations regardless of size. Both influence the balance of organisms in an ecosystem.
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Number 4
(4ai)
(i) Genetic factors
(ii) Environmental factors
(4aii)
Diagram
(4aiii)
Genotype: tt
(4bi)
Genotype is the genetic makeup or set of alleles possessed by an organism, usually with respect to a specific characteristic.
(4bii)
(i) Genetic recombination/mutation
(ii) Environmental influences
(4ci)
Allele is an alternative form of a gene found at the same locus (position) on homologous chromosomes, controlling the same characteristic.
(4cii)
[TABULATE]
=GENOTYPE=
(i) The genetic constitution or makeup of an organism.
(ii) Determined by inherited genes
=PHENOTYPE=
(i) The observable physical characteristics of an organism
(ii) Determined by genotype and environmental factors
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Number 5
(5a)
(i) Increased rate of evaporation leading to water loss and dehydration in organisms.
(ii) Denaturation of enzymes affecting metabolic processes.
(iii) Reduced reproductive success due to stress or death of gametes.
(iv) Migration or death of heat-sensitive species.
(v) Altered behavior such as seeking shade or burrowing to escape heat.
(5b)
(i) Destruction of vegetation and loss of plant cover.
(ii) Death of animals and destruction of habitats.
(iii) Soil erosion due to loss of protective plant cover.
(iv) Reduction in soil fertility as nutrients are lost through burning.
(v) Air pollution from smoke and release of greenhouse gases.
(5c)
(i) Coordination of international response to disease outbreaks.
(ii) Provision of guidelines and information on disease prevention and control.
(iii) Distribution of vaccines and medical supplies to affected areas.
(iv) Monitoring and surveillance of disease spread globally.
(5di)
Countershading in Tilapia is a camouflage adaptation where the back is dark and the belly is light. It helps the fish blend with its surroundings, protecting it from predators.
(5dii)
Seasonal migration in birds is the regular movement of birds from one region to another in response to changes in seasons. Birds often migrate to warmer areas to find food, breed, or escape harsh weather.
(5ei)
(i) Bacteria
(ii) Viruses
(iii) Fungi
(iv) Protozoa
(v) Algae
(5eii)
(i) Bacteria
(ii) Viruses
(5fi)
(i) Blood group A
(ii) Blood group B
(5fii)
(i) Agglutination (clumping) of red blood cells, which can block blood vessels and cause organ damage.
(ii) Hemolytic reaction, where the immune system destroys the transfused blood cells, leading to fever, chills, kidney failure, or even death
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NUMBER FIVE
(5a)
(PICK ANY FIVE)
(I) It Increases water loss and dehydration in plants and animals.
(ii) It Reduces dissolved oxygen levels in water bodies, there by affecting aquatic life.
(iii) It increases the risk of heat-related illnesses and mortality in animals.
(iv) organisms tend to move to cooler areas.
(v) It reduces the growth and development in some organisms.
(vi) It affects the reproductive cycles of orgamism
(b)
(i) It reduces soil fertility
(ii) It leads to soil erosion
(iii) It causes air pollution which leads to greenhouse effect
(iv) It leads to death of organisms.
(v) It polutes the water reduce it’s quality.
(C)
(PICK ANY FOUR)
(I) They help in providing guidance and recommendations for disease prevention and control.
(ii)They help in providing technical and medical support to affected countries.
(iii) They help in monitoring and reporting on the global spread of diseases and emerging health threats.
(iv) They help in disseminating accurate information and guidelines to the public and governments.
(v) They help to coordinate international efforts for research, data sharing, and resource allocation.
(d)
Countershading is an adaptive feature in Tilapia where the coloration of their upper body is darker than their lower body. This helps them blend in with the water when viewed from above, making it difficult for predators to spot them. However, when viewed from below, their lighter lower body matches the lighter water surface, providing camouflage. This adaptation enhances their survival by reducing the likelihood of predation in their natural freshwater habitats.
