D4.1 Natural selection
Practice exam-style IB Biology questions for Natural selection, aligned with the syllabus and grouped by topic.
Question 1
What is the role of natural selection in evolution?
A.
It increases the frequency of heritable traits that improve reproductive success.
B.
It produces new alleles whenever the environment changes.
C.
It makes all members of a population equally adapted to their environment.
D.
It causes individuals to change their genes during their lifetime.
Question 2
What is a gene pool?
A.
Only the dominant alleles found in a species
B.
Only the genes expressed in adult individuals
C.
All genes and alleles present in a population
D.
All genes present in one individual organism
Question 3
What is the main contribution of sexual reproduction to natural selection?
A.
It generates new combinations of alleles in offspring.
B.
It prevents harmful mutations from occurring.
C.
It changes acquired traits into inherited traits.
D.
It makes offspring genetically identical to both parents.
Question 4
A population of seedlings produces many more individuals than can reach maturity under a closed forest canopy. What resource is most likely to limit carrying capacity in this situation?
A.
Carbon dioxide exhaled by animals
B.
Oxygen concentration in air
C.
Light intensity
D.
Number of predators
Question 5
Which factor is density-independent as a selection pressure on a population of lizards?
A.
Competition for basking sites as population density rises
B.
Mortality caused by a sudden freezing night
C.
Spread of parasites more rapidly in crowded habitats
D.
Shortage of insect prey during high lizard abundance
Question 6
Which condition is required for Hardy–Weinberg equilibrium?
A.
A small population with strong chance effects
B.
Frequent immigration into the population
C.
Strong selection against heterozygotes
D.
Random mating with respect to the gene studied
Question 7
Farmers breed only cows with the highest milk yield over many generations. What process is this?
A.
Genetic drift
B.
Artificial selection
C.
Stabilizing selection by predators
D.
Natural selection caused by drought
Question 8
State what is meant by evolution.
[1]
Outline two conditions needed for natural selection to cause evolutionary change.
[1]
Question 9
Define gene pool.
[1]
State why a single organism cannot have a gene pool.
[1]
Question 10
In evolutionary biology, what is meant by fitness?
A.
The ability to survive without competing for resources
B.
The strength and speed of an individual animal
C.
The relative reproductive success of a genotype or phenotype
D.
The number of different species in a habitat
Question 11
A plant grows unusually tall after receiving extra mineral ions and water. Its seeds do not inherit DNA changes for increased height. How should this tallness be classified?
A.
A new allele produced by sexual reproduction
B.
A mutation that must increase in the next generation
C.
An acquired characteristic caused by environmental conditions
D.
A heritable adaptation caused by natural selection
Question 12
Male birds in a population vary in song complexity. Females mate more often with males producing complex songs, and song complexity is heritable. What process is most directly described?
A.
Lamarckism
B.
Sexual selection
C.
Artificial selection
D.
Genetic drift
Question 13
Two populations of the same mammal species are separated by a mountain range and no longer interbreed. What is the most likely long-term effect of this isolation?
A.
Natural selection can no longer act on either population.
B.
All alleles will immediately become fixed in both populations.
C.
Mutation will occur in only one of the populations.
D.
Allele frequencies may diverge because gene flow is reduced.
Question 14
What is distinctive about natural selection as a cause of allele frequency change?
A.
It requires that all genotypes have equal reproductive success.
B.
It prevents alleles from being transmitted through gametes.
C.
It is non-random with respect to fitness differences between phenotypes.
D.
It changes allele frequencies only by chance in small populations.
Question 15
A population of fish experiences selection in which the smallest and largest individuals have higher reproductive success than intermediate-sized individuals. What type of selection is occurring?
A.
Artificial selection
B.
Disruptive selection
C.
Directional selection
D.
Stabilizing selection
Question 16
State how mutation contributes to variation.
[1]
Distinguish the contribution of mutation from that of sexual reproduction in generating variation.
[1]
Question 17
Many marine turtles lay over 100 eggs in a nest, but only a small proportion of hatchlings survive to reproduce.
State the term for producing more offspring than can survive.
[1]
Explain how this can promote natural selection.
[1]
Question 18
A sudden drought kills many shallow-rooted plants in a population, while deeper-rooted plants survive more often.
Identify the abiotic selection pressure.
[1]
Explain how this pressure could change the population over generations.
[1]
Question 19
Define artificial selection.
[1]
Distinguish artificial selection from antibiotic resistance evolving after antibiotic use.
[1]
Question 20
The graph shows survival of a plant population after exposure to different minimum night temperatures.
Describe the relationship between minimum night temperature and survival.
[1]
Identify the abiotic selection pressure.
[1]
Explain why this pressure could cause evolutionary change only if cold tolerance is heritable.
[1]
Question 21
A population of beetle larvae was grown at different larval densities with the same total amount of food in each container.
Describe how mean adult mass changes with larval density.
[1]
Identify the limiting resource in this experiment.
[1]
Explain why this is an example of intraspecific competition.
[1]
Question 22
In an experimental pond with guppies, predatory fish are removed while female mate choice remains. After several generations, mean male spot area increases. What is the best deduction?
A.
Female mate choice had no effect on male colouration.
B.
The environment directly caused males to acquire larger spots.
C.
Predation pressure previously selected against conspicuous males.
D.
Mutation stopped occurring in the pond population.
Question 23
In a population in Hardy–Weinberg equilibrium, the frequency of a recessive phenotype is 0.09. What is the frequency of the recessive allele, q?
A.
0.09
B.
0.91
C.
0.42
D.
0.30
Question 24
An antibiotic is used in a hospital ward. Resistant bacteria survive and reproduce more than susceptible bacteria. Why is this natural selection rather than artificial selection?
A.
Resistance is always acquired during an individual bacterium’s lifetime.
B.
The bacteria are not living organisms.
C.
Allele frequencies cannot change in bacterial populations.
D.
Humans did not deliberately choose resistant bacteria as parents in a breeding programme.
Question 25
Distinguish survival value from reproductive potential.
[1]
Explain why a genotype with high survival value may not have high fitness.
[1]
Question 26
A blacksmith develops stronger arm muscles through work. His children are not born with enlarged arm muscles because of this.
State why the enlarged muscles are not inherited.
[1]
Explain why natural selection cannot cause evolutionary change based only on such acquired characteristics.
[1]
Question 27
In a bird species, females prefer males with longer tail feathers. Longer tails increase mating success but also make escape from predators more difficult.
Identify the type of selection favouring longer tails.
[1]
Explain why the trait may still increase in frequency.
[1]
Question 28
In a geographically isolated island population, 36 of 120 sampled copies of a gene are allele R.
Calculate the frequency of allele R.
[1]
Suggest two reasons why this allele frequency may differ from that in the mainland population.
[1]
Question 29
A beetle population contains green and brown individuals. Birds detect green beetles more easily on dark bark. Brown colour is heritable.
State the phenotype with higher fitness in this environment.
[1]
Explain how natural selection could change allele frequency in the gene pool.
[1]
Question 30
Distinguish directional selection from stabilizing selection.
[1]
State the effect of disruptive selection on intermediate phenotypes.
[1]
Question 31
Observed genotype frequencies for a gene differ from those predicted by the Hardy–Weinberg equation.
State what this indicates about the population.
[1]
Suggest three Hardy–Weinberg conditions that may not be met.
[1]
Question 32
Endler-style experimental streams were set up with male guppies. Predator treatment was controlled and mean male colour spot area was measured after several generations.
Identify the treatment with the greatest mean male spot area.
[1]
Describe the effect of increasing predation pressure on male spot area.
[1]
Suggest why male spot area is higher when predation pressure is weak.
[1]
State one reason why using experimental streams strengthens the conclusion.
[1]
Question 33
Clones of the same aquatic plant genotype were grown in low and high light. Plant height and seedling height of their offspring grown in common conditions were recorded.
| Parent light treatment | Parent height / cm (mean ± SD) | Offspring height / cm (mean ± SD) |
|---|---|---|
| Low light | 18.4 ± 2.1 | 12.7 ± 1.3 |
| High light | 32.8 ± 2.4 | 12.9 ± 1.2 |
State which light treatment produced taller parent plants.
[1]
Compare offspring heights when grown in common conditions.
[1]
Explain what the data suggest about the tallness of parents in high light.
[1]
Suggest one additional measurement that would strengthen the conclusion.
[1]
Question 34
A recessive phenotype was recorded in a large randomly mating population. The population is assumed to be in Hardy–Weinberg equilibrium.
| Category | Number of individuals |
|---|---|
| Total sampled | 2500 |
| Showing recessive phenotype | 400 |
Identify the genotype frequency represented by the recessive phenotype.
[1]
Calculate q from the recessive phenotype frequency.
[1]
Calculate p.
[1]
Calculate the expected heterozygote frequency.
[1]
Question 35
Allele A frequencies for a human alcohol dehydrogenase gene are shown for five geographically separated populations from a public database.
| Population | Region | Sample size / individuals | Allele A frequency |
|---|---|---|---|
| Yoruba (Ibadan) | West Africa | 108 | 0.02 |
| Finnish (Finland) | Northern Europe | 99 | 0.06 |
| Gujarati Indian | South Asia | 103 | 0.28 |
| Peruvian (Lima) | Americas | 85 | 0.39 |
| Han Chinese (Beijing) | East Asia | 103 | 0.71 |
Identify the population with the highest allele A frequency.
[1]
Describe the overall variation among populations.
[1]
Suggest two explanations for differences in allele frequency among geographically separated populations.
[1]
Question 36
A student models natural selection using paper seeds of three shapes placed on a tray. Tweezers are used as predators. Seeds not picked up are copied to make the next generation.
Identify the selection pressure in the model.
[1]
Suggest two variables that should be controlled to make comparisons between generations valid.
[1]
State one limitation of this model.
[1]
Question 37
A recessive phenotype occurs in 4% of a population assumed to be in Hardy–Weinberg equilibrium.
Calculate q.
[1]
Calculate p.
[1]
Calculate the expected frequency of heterozygotes.
[1]
Question 38
The graph shows survival of newborn mammals in relation to birth mass.
Identify the type of selection shown.
[1]
Explain the effect of this type of selection on allele frequencies and variation.
[1]
Question 39
Male display duration and mating success were measured in a bird species. Survival to the next breeding season was also recorded.
Describe the relationship between display duration and mating success.
[1]
Describe the relationship between display duration and survival.
[1]
Explain how the data show a trade-off between sexual selection and natural selection.
[1]
State one condition needed for display duration to evolve.
[1]
Question 40
Graphs show the distribution of beak depth in a finch population before and after a drought. Seed availability changed during the drought.
| Measure | Class | Before drought / % | After drought / % |
|---|---|---|---|
| Finch beak depth | 7.0–7.9 mm | 8 | 2 |
| Finch beak depth | 8.0–8.9 mm | 18 | 6 |
| Finch beak depth | 9.0–9.9 mm | 30 | 17 |
| Finch beak depth | 10.0–10.9 mm | 26 | 29 |
| Finch beak depth | 11.0–11.9 mm | 13 | 31 |
| Finch beak depth | 12.0–12.9 mm | 5 | 15 |
| Available seeds | Small soft | 55 | 18 |
| Available seeds | Medium | 30 | 27 |
| Available seeds | Large hard | 15 | 55 |
Describe the change in the beak-depth distribution after the drought.
[1]
Identify the type of selection shown.
[1]
Explain how the selection pressure could change allele frequencies.
[1]
State why this is not evidence that individual birds changed their inherited beak depth during life.
[1]
Question 41
Observed genotype counts for a two-allele gene were compared with Hardy–Weinberg expected counts in an adult fish population.
| Genotype | Observed / fish | Expected / fish |
|---|---|---|
| AA | 90 | 72 |
| Aa | 60 | 96 |
| aa | 50 | 32 |
| Total | 200 | 200 |
Identify the genotype with the largest difference between observed and expected counts.
[1]
State whether the data support Hardy–Weinberg equilibrium.
[1]
Suggest two Hardy–Weinberg conditions that could have been violated.
[1]
Explain why comparing adults rather than zygotes may reveal selection.
[1]
Question 42
Outline why Darwin’s explanation of evolution by natural selection was a paradigm shift.
[1]
Explain how natural selection can cause evolutionary change in a population.
[1]
Question 43
Distinguish the roles of mutation and sexual reproduction in producing variation.
[1]
Discuss why variation, overproduction and competition are all needed for natural selection to occur.
[1]
Question 44
A crop breeder selected plants with the largest seed mass to breed each generation. Mean seed mass and yield were recorded over six generations.
Describe the change in mean seed mass across generations.
[1]
Identify the selecting agent.
[1]
Explain why this is artificial selection.
[1]
Suggest one possible disadvantage of this breeding programme for the crop population.
[1]
Question 45
In a species of bird of paradise, males with brighter plumage attract more mates but are more visible to predators.
Outline how sexual selection can act as a selection pressure.
[1]
Evaluate how both sexual selection and natural selection by predation could affect the evolution of male plumage.
[1]
Question 46
Outline how a controlled model could be used to investigate natural selection.
[1]
Discuss how Endler’s guppy experiments show interactions between sexual selection and natural selection.
[1]
Question 47
Define gene pool and allele frequency.
[1]
Explain how neo-Darwinism accounts for changes in allele frequency caused by natural selection.
[1]
Question 48
Identify the phenotypes favoured in directional, stabilizing and disruptive selection.
[1]
Compare and contrast the effects of these three patterns of selection on phenotype distributions and allele frequencies.
[1]
Question 49
A biologist studies a two-allele gene in a large animal population.
Outline how p, q, p², 2pq and q² are used in the Hardy–Weinberg model.
[1]
Evaluate how Hardy–Weinberg calculations can be used as a null model for detecting evolutionary change.
[1]
Question 50
Outline how artificial selection changes a crop or domesticated animal population.
[1]
Discuss similarities and differences between artificial selection for a desired trait and natural selection for antibiotic resistance in bacteria.
[1]
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