IGCSE Biology Topic 18: Variation and Selection MCQs – 30 Practice Questions with Answers (Cambridge 0610)
Free practice for Cambridge IGCSE Biology 0610 on variation and selection, covering types and causes of variation, mutation, adaptive features, natural selection and selective breeding. Every question comes with a worked explanation to help you revise with confidence.
Types and Causes of Variation
Q1. What is meant by variation?
- (A) Differences between individuals of the same species
- (B) Differences between two different species
- (C) Changes in an individual during its lifetime only, without any genetic basis.
- (D) The number of offspring produced by one parent
Show Answer
Answer: A – Variation describes how members of one species differ from each other, for example in height or blood group.
Q2. Which example shows continuous variation?
- (A) Blood group, which falls into four clear groups
- (B) Seed shape in peas, which is either round or wrinkled with no intermediates.
- (C) Body mass, which shows a range of values between two extremes
- (D) Seed colour in peas, which is either yellow or green
Show Answer
Answer: C – Continuous variation gives a smooth range of phenotypes, while blood group and pea seed traits fall into distinct categories.
Q3. Which example shows discontinuous variation?
- (A) Body length in a population of fish
- (B) ABO blood group in humans
- (C) Height in a class of students
- (D) Leaf length on a single tree
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Answer: B – Discontinuous variation produces a limited number of phenotypes with no intermediates, such as groups A, B, AB and O.
Q4. How do the causes of continuous and discontinuous variation differ?
- (A) Both are caused by the environment only.
- (B) Continuous variation is caused by genes only, while discontinuous variation is caused by the environment only.
- (C) Both are caused by genes only.
- (D) Discontinuous variation is usually caused by genes only; continuous variation by genes and environment.
Show Answer
Answer: D – A trait like height is shaped by many genes plus factors such as nutrition, whereas blood group is set by genes alone.
Q5. Two plants of the same species grow to different heights, one in rich soil and one in poor soil. What does this best illustrate?
- (A) The environment can affect a continuously varying trait such as height.
- (B) The plants must belong to different species.
- (C) Height is a discontinuous trait with no intermediates between short and tall.
- (D) The shorter plant has lost the genes for growth.
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Answer: A – Continuous traits respond to both genes and surroundings, so identical genotypes can still grow differently.
Q6. Identical twins share the same genes but may differ slightly in body mass as adults. What best explains the difference?
- (A) Their blood groups changed as they grew older.
- (B) One twin lost chromosomes during growth.
- (C) Diet and lifestyle differences affected their mass.
- (D) Their genes for body mass stopped working entirely as adults.
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Answer: C – Because body mass is continuous variation, environment acts alongside genes to shape the final phenotype.
Q7. What is a mutation?
- (A) The fusion of two gamete nuclei during fertilisation
- (B) A random change in the base sequence of DNA
- (C) The sorting of chromosomes during mitosis
- (D) The transfer of pollen from one flower to another
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Answer: B – Mutation is a genetic change, and it is the way in which new alleles are formed.
Q8. How do new alleles first arise in a population?
- (A) Through selective breeding by farmers
- (B) Through the sorting of existing alleles in meiosis
- (C) Through competition between individuals
- (D) Through mutation changing the base sequence of DNA
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Answer: D – Meiosis and random fertilisation shuffle existing alleles, but only mutation creates a genuinely new allele.
Q9. Which list gives sources of genetic variation within a population?
- (A) Mitosis, growth and repair of tissues
- (B) Photosynthesis, respiration and digestion in individual organisms.
- (C) Mutation, meiosis, random mating and random fertilisation
- (D) Pollination, germination and seed dispersal
Show Answer
Answer: C – Together these four processes produce new allele combinations in every generation of a sexually reproducing population.
Q10. What effect do ionising radiation and some chemicals have on mutation?
- (A) They increase the rate of mutation.
- (B) They prevent mutation from ever happening.
- (C) They repair all mutated DNA immediately.
- (D) They change discontinuous variation into continuous variation.
Show Answer
Answer: A – Exposure to ionising radiation or certain chemicals raises the chance that a random genetic change occurs.
Mutation and Adaptive Features
Q11. Most mutations are harmful or neutral, and only a few are useful. In what sense can a mutation be described as useful?
- (A) It always makes the organism larger and stronger.
- (B) It can give an advantage in a particular environment.
- (C) It removes all other harmful alleles from the population in a single generation.
- (D) It stops the organism from reproducing.
Show Answer
Answer: B – Whether an allele helps depends on the surroundings, so the same change can be useful in one habitat and harmful in another.
Q12. A new allele spreads through a population over many generations. What must have happened for this to occur?
- (A) Every individual in the population chose to carry the allele.
- (B) The allele was passed from parent to offspring by inheritance.
- (C) The allele changed back into its original form each generation, losing its effect entirely.
- (D) Individuals carrying the allele survived and reproduced more successfully than others.
Show Answer
Answer: D – An allele becomes more common only when its carriers leave more offspring, the core of natural selection.
Q13. What is an adaptive feature?
- (A) A feature an individual learns during its lifetime
- (B) A feature that appears only when the environment changes suddenly during a lifetime for the individual.
- (C) An inherited feature that helps an organism survive and reproduce in its environment
- (D) A feature produced by selective breeding in a laboratory
Show Answer
Answer: C – Adaptive features are inherited, so they can be passed on and become more common through natural selection.
Q14. Which feature of a xerophyte helps it survive in a dry habitat?
- (A) A thick, waxy cuticle that reduces water loss from its leaves
- (B) Large, thin leaves that lose water rapidly
- (C) Roots that stay only at the soil surface
- (D) Air spaces that keep the plant floating on water in a pond or lake.
Show Answer
Answer: A – Xerophytes are adapted to dry conditions, for example by cutting water loss and storing water in fleshy tissues.
Q15. Which feature of a hydrophyte helps it live in water?
- (A) A thick, waxy cuticle to prevent drying out in hot, dry conditions.
- (B) Large air spaces in its tissues that provide buoyancy.
- (C) Deep roots that reach water far underground
- (D) Small, rolled leaves that trap moist air
Show Answer
Answer: B – Hydrophytes live in or on water, so floating leaves and air-filled tissues suit their habitat rather than drought defences.
Natural Selection and Adaptation
Q16. Which sequence correctly describes natural selection?
- (A) Struggle for survival → variation appears → all offspring survive equally → alleles stay unchanged
- (B) Best-adapted individuals reproduce least → their alleles disappear → the population becomes less suited
- (C) Many offspring are produced → variation disappears → no competition occurs → the population stays the same
- (D) Variation exists, many offspring are produced, competition occurs, and better-adapted individuals pass on their alleles.
Show Answer
Answer: D – Natural selection works through variation, overproduction, a struggle for survival, and differential reproduction.
Q17. What is meant by the struggle for survival in natural selection?
- (A) Organisms fighting each other deliberately to choose the strongest
- (B) Organisms deciding which features to pass to their offspring
- (C) Competition for limited resources such as food, water and space
- (D) Organisms migrating to a new habitat every generation
Show Answer
Answer: C – Because more offspring are born than the environment can support, individuals compete and not all survive to breed.
Q18. What is adaptation?
- (A) The process by which populations become better suited to their environment over many generations.
- (B) A change a single organism makes to its own body during its lifetime in response to its surroundings alone.
- (C) The movement of a population to a warmer climate
- (D) The loss of all variation from a population
Show Answer
Answer: A – Adaptation happens to populations over generations, not to individuals within one lifetime.
Q19. How does natural selection explain the rise of antibiotic-resistant bacteria?
- (A) Antibiotics teach bacteria to change their genes on purpose.
- (B) Resistant bacteria survive treatment and reproduce, passing on resistance alleles.
- (C) Antibiotics create resistant bacteria from non-living material.
- (D) All bacteria become resistant at the same rate, regardless of their genes or environment.
Show Answer
Answer: B – Variation already exists in the bacterial population, and the antibiotic acts as a selection pressure favouring resistant cells.
Q20. After a course of antibiotics, why might an infection return with bacteria that are harder to treat?
- (A) The antibiotic changed the patient’s own genes.
- (B) The antibiotic killed the patient’s immune cells.
- (C) The antibiotic only killed bacteria on the skin surface, leaving deeper infections untouched.
- (D) The antibiotic killed non-resistant bacteria, leaving resistant ones to multiply.
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Answer: D – Removing the susceptible competitors lets the resistant survivors increase, so the resistant strain becomes dominant.
Q21. How does natural selection differ from artificial selection?
- (A) Natural selection acts over one generation only.
- (B) Artificial selection produces no variation at all.
- (C) Natural selection is driven by the environment; artificial selection by human choice.
- (D) Natural selection only affects plants, while artificial selection only affects animals in captivity.
Show Answer
Answer: C – In nature the environment favours the best-adapted individuals, whereas in artificial selection humans pick the parents.
Q22. A species of moth becomes better camouflaged against tree bark over many generations. Which statement best explains this?
- (A) Individual moths changed their own colour during their lifetimes to match the bark exactly as adults.
- (B) Moths that were better camouflaged survived predation more often and passed their alleles on.
- (C) The tree bark changed colour to match the moths.
- (D) All moths in the population changed colour at the same time.
Show Answer
Answer: B – Better-camouflaged moths survive predation more often and pass their alleles on, so the population shifts over generations.
Q23. Which statement about natural selection is correct?
- (A) Organisms choose which useful features to develop during their own lifetimes.
- (B) Better-adapted individuals are more likely to survive and reproduce.
- (C) The strongest individual in a population always survives.
- (D) Natural selection creates variation from nothing.
Show Answer
Answer: B – Selection is not a choice: it is the greater reproductive success of better-adapted individuals that shifts allele frequencies.
Selective Breeding
Q24. What is the first step in selective breeding?
- (A) Crossing two different species to create a hybrid
- (B) Waiting for a useful mutation to appear on its own in the population.
- (C) Releasing the organisms into the wild
- (D) Selecting individuals that show the desirable features
Show Answer
Answer: D – Humans choose parents with wanted traits, cross them, then select offspring showing those traits again.
Q25. A farmer wants wheat plants that give a higher grain yield. How is selective breeding carried out over many generations?
- (A) The highest-yielding plants are crossed, and the best offspring are selected again.
- (B) The lowest-yielding plants are crossed every generation.
- (C) One high-yielding plant is cloned once and never crossed again with other plants in later generations.
- (D) The wheat is grown without any human choice of parent plants.
Show Answer
Answer: A – Repeated selection of the best offspring each generation gradually improves the crop.
Q26. Which example is an outcome of selective breeding in domesticated animals?
- (A) Dairy cattle that produce a higher milk yield than their wild ancestors
- (B) Bacteria that survive treatment with antibiotics in a hospital ward over time.
- (C) Moths whose colour matches tree bark more closely
- (D) Fish that develop resistance to a new predator
Show Answer
Answer: A – Farm animals and crop plants have been improved over many generations by repeatedly breeding the best performers.
Q27. What is a risk of selective breeding carried out over many generations?
- (A) The population gains new alleles through mutation every generation, increasing variation.
- (B) The selected feature disappears in a single generation.
- (C) Offspring stop inheriting genes from their parents.
- (D) Genetic variation is reduced, so the population may be more vulnerable to disease.
Show Answer
Answer: D – Repeatedly breeding from a narrow set of parents concentrates wanted alleles but also narrows the gene pool.
Q28. Which of these is artificial selection rather than natural selection?
- (A) Drought killing all but the most drought-tolerant wild plants in a dry season alone.
- (B) Predators catching the slowest members of a prey population
- (C) A grower crossing only the sweetest strawberry plants to produce the next crop
- (D) Disease removing the least resistant wild animals
Show Answer
Answer: C – The grower, not the environment, decides which individuals breed, which is the mark of artificial selection.
Q29. Why can selective breeding change a crop more quickly than natural selection usually changes a wild population?
- (A) Humans control which individuals breed in every generation.
- (B) Humans introduce completely new species each generation to replace the old crop.
- (C) Crops do not carry genes for the selected features.
- (D) Natural selection never changes wild populations.
Show Answer
Answer: A – Human control of mating each generation applies selection pressure consistently towards one goal.
Q30. A grower breeds maize plants that survive well in dry soil by crossing the most drought-tolerant plants each year. What is this process called?
- (A) Natural selection in the wild, without any human choice of parents.
- (B) Selective breeding by artificial selection
- (C) Asexual reproduction
- (D) Random fertilisation
Show Answer
Answer: B – Choosing parents with a desirable feature and crossing them over generations is selective breeding.
Revisit any questions you missed, especially the natural selection sequence and the difference from selective breeding, and try the set again until the ideas feel secure.