IGCSE · Practice questions · Natural selection

Variation, struggle, survival.

Six original Cambridge-style questions on natural selection: describing the steps, applying them to new examples, moth data, and (Extended) antibiotic resistance and adaptation.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.

Keep these straight

Five steps, every time.

Variation: genetic variation within the population (from mutation).
Overproduction and struggle: many offspring; competition, predation, disease.
Selection: better adapted individuals are more likely to survive and reproduce, and pass on their alleles.
Never say the environment causes the useful mutation or that individuals change to adapt.

Recall

[5 marks]

Describe the process of natural selection.

There is genetic variation within a population. ✓
Organisms produce many offspring, more than can survive. ✓
There is a struggle for survival, including competition for resources such as food. ✓
Individuals that are better adapted to the environment are more likely to survive and reproduce. ✓
They pass on their alleles to the next generation, so these alleles become more common. ✓

Data

[4 marks]

Scientists counted peppered moths in a polluted woodland, where the bark was dark with soot, over several years after clean-air laws.

Year	1970	1980	1990	2000
Dark moths / %	90	70	35	10

(a) Describe the trend. (b) Use natural selection to explain it.

(a) The percentage of dark moths fell from 90% to 10% over 30 years. ✓
(b) Clean air let lichens grow back, so the bark became paler. ✓
Dark moths were now more visible to birds and more were eaten; pale moths were camouflaged and more survived to reproduce. ✓
Pale moths passed on their alleles, so the pale form became more common each generation. ✓

Explain

[4 marks]

Giraffes with longer necks can reach leaves high in trees. Use natural selection to explain how the average neck length in a giraffe population could increase over many generations.

Neck length varies in the population because of genetic variation. ✓
When food is short there is competition; giraffes with longer necks reach more leaves. ✓
They are more likely to survive and reproduce. ✓
They pass on the alleles for long necks, so the average neck length increases over many generations. ✓

Explain

[5 marks]

Extended. Describe how a strain of bacteria resistant to an antibiotic develops.

A random mutation gives one bacterium an allele for resistance to the antibiotic. ✓
When the antibiotic is used, non-resistant bacteria are killed. ✓
The resistant bacteria survive; this is natural selection. ✓
They reproduce rapidly with less competition and pass on the resistance allele. ✓
Over many generations most of the population is resistant: a resistant strain. ✓

Analysis

[3 marks]

Extended. Suggest three ways in which doctors and patients can reduce the spread of antibiotic resistant bacteria.

Only prescribe or use antibiotics when they are really needed (not for viral infections such as colds). ✓
Patients should complete the full course, so that all the bacteria are killed. ✓
Good hygiene in hospitals, such as hand washing, stops resistant bacteria spreading between patients. (Also accept: avoid routine use in farm animals.) ✓

Recall

[3 marks]

Extended. Distinguish between an adaptive feature and adaptation.

An adaptive feature is an inherited feature of an individual that helps it survive and reproduce in its environment. ✓
Adaptation is a process, resulting from natural selection, ✓
by which a population becomes more suited to its environment over many generations. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.