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Waec 2025 Biology Question And Answer

Friday, 23rd May 2025
Biology 2 (Essay), 9:30am – 11:10am
Biology 1 (Objective), 11:10am – 12:00pm

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*NOTE: YOU ARE TO TRACE THIS ANSWERS FROM YOUR BOOKLET TO GET ACCURATE RESULTS*

COMPLETED…
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(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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(2a)
[TABULATE]

=Photosynthetic nutrition=
(i) Uses sunlight as an energy source to produce food
(ii) Occurs in plants, algae, and some bacteria

=Chemosynthetic nutrition=
(i) Uses chemical energy from inorganic compounds to produce food
(ii) Occurs in certain bacteria and archaea

(2bi)
Saprophytes are organisms that obtain their nutrients by decomposing dead and decaying organic matter, commonly found among fungi and certain bacteria.

(2bii)
(i) Yeast
(ii) Mushroom

(2biii)
Saprophytes feed by external digestion. They secrete enzymes onto dead organic material to break it down into simpler soluble substances, which are then absorbed into their cells.

(2biv)
(i) They decompose and recycle organic matter in ecosystems, maintaining ecological balance
(ii) They convert complex organic substances from dead organisms into minerals
(iii) They are used in various industries for the production of bread, beer and cheese.

(2c) (i) They have specialized structures to trap and digest insects or small animals.
(ii) They produce digestive enzymes to break down their prey.
(iii) They usually grow in nitrogen-poor soils and supplement their nutrition through carnivory.

(2d) (i) Adult butterflies feed on nectar from flowers using their specialized tubular mouthpart called a proboscis.

(ii) Mosquito larvae feed on microorganisms and organic matter by filtering water through their mouth brushes.

(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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(3a)
Carbon (IV) oxide (CO₂) and oxygen (O₂) are balanced in nature through the processes of photosynthesis and respiration. During photosynthesis, green plants use CO₂ and release O₂ into the atmosphere. During respiration and decomposition, animals and plants use O₂ and release CO₂ 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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(4a) (PICK ANY TWO)
(i) Genetic recombination resulting in inheritance of two recessive alleles (tt).
(ii) Poor nutrition during the child’s developmental years.
(iii) Hormonal imbalance, especially low levels of growth hormone.
(iv) Genetic mutations affecting height-related genes.
(v) Chronic illnesses or medical conditions during growth.
(vi) Lack of physical activity or inadequate health care.

(4aii) Draw the diagram

(4aiii) Genotype: tt

(4bi) Genotype is the genetic makeup of an organism in terms of the alleles present, e.g, TT, Tt, or tt.

(4bii) (PICK ANY TWO)
(i) Genetic recombination during meiosis.
(ii) Mutations in genes or chromosomes.
(iii) Environmental influences such as diet or climate.
(iv) Random fertilization during sexual reproduction.
(v) Crossing over during meiosis.
(vi) Effects of diseases or infections during development.

(4ci) An allele is an alternative form of a gene found at the same locus on homologous chromosomes.

(4cii) In a Tabular form

-Genotype-
(PICK ANY TWO)
(i) It refers to the genetic makeup of an organism.
(ii) It is determined by the combination of alleles inherited from parents.
(iii) It cannot be observed directly.
(iv) It remains constant throughout the life of the organism.
(v) It can be represented using letters such as TT, Tt, or tt.

-Phenotype-
(PICK ANY TWO)
(i) It refers to the observable characteristics of an organism.
(ii) It is influenced by both genotype and environmental factors.
(iii) It can be seen and measured (e.g., height, skin color).
(iv) It may change due to environmental conditions.
(v) It is the physical expression or outcome of the genotype.
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(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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