Biology • Year 11 • Module 3 • Lesson 5
Darwin, Wallace and Natural Selection
Lock in the core vocabulary, the four conditions of natural selection, and the difference between Darwin and Lamarck before moving to application tasks.
1. Complete the paragraph
Fill each blank with the correct term from the word bank. Use each term once only. 8 marks
_______________ is the mechanism by which _______________ evolve over generations. For it to occur, four conditions must be met. First, individuals in a population must differ in their traits — this is called _______________. Second, some of that variation must be inherited by offspring, which is called _______________. Third, some individuals must leave more offspring than others, known as _______________. Fourth, an environmental factor must make that difference matter by favouring some traits — this is the _______________. Over generations, favoured _______________ increase in the population, improving the average _______________ of surviving individuals.
2. Term–definition match
Write the matching term from this list in the right-hand column: natural selection • variation • overproduction • struggle for existence • differential reproduction • fitness • heritability • selection pressure. 8 marks
| # | Definition | Matching term |
|---|---|---|
| 2.1 | The reproductive success of an individual relative to others in the population. | |
| 2.2 | Differences in traits among individuals in a population. | |
| 2.3 | Producing more offspring than can survive to adulthood. | |
| 2.4 | Competition for limited resources in a population. | |
| 2.5 | Some individuals leaving more offspring than others. | |
| 2.6 | An environmental factor that affects survival or reproduction. | |
| 2.7 | The degree to which differences in traits are passed from parent to offspring. | |
| 2.8 | The process by which favoured alleles become more common in a population over generations. |
3. Complete the four conditions table
Fill in the missing information for each condition of natural selection. 8 marks — 1 per completed cell
| Condition | What it means | Why it is necessary |
|---|---|---|
| Variation | Selection cannot act if all individuals are identical. | |
| Heritability | Differences must be passed to offspring. | |
| Differential survival/reproduction | ||
| Selection pressure | The environment favours some variants over others. |
4. Lamarck vs Darwin — true or false
Circle T or F. If the statement is false, write the corrected version on the line below. 8 marks — 1 for T/F, 1 for correction where needed
4.1 Lamarck proposed that organisms could pass on characteristics acquired during their lifetime. T / F
4.2 Darwinian natural selection acts on changes that individual organisms make during their own lifetimes. T / F
4.3 Darwin and Wallace independently developed the idea of natural selection and presented it jointly in 1858. T / F
4.4 Bacteria become resistant to antibiotics because exposure to the antibiotic causes them to mutate and develop resistance. T / F
5. Sequence the MRSA antibiotic-resistance example
The following steps explain how antibiotic resistance increases in a bacterial population. Number them 1–4 in the correct order. 4 marks
| Order (1–4) | Step |
|---|---|
| Resistant bacteria survive, reproduce, and pass the resistance allele to their offspring. | |
| Some bacteria in the population already carry a mutation that confers resistance, due to random variation. | |
| The frequency of the resistance allele increases across generations and resistance becomes more common. | |
| Antibiotics are applied; they kill most susceptible bacteria but resistant bacteria survive more often. |
Q1 — Cloze paragraph
In order: Natural selection • populations • variation • heritability • differential reproduction • selection pressure • allele frequencies • fitness.
Q2 — Term–definition matches
2.1 fitness • 2.2 variation • 2.3 overproduction • 2.4 struggle for existence • 2.5 differential reproduction • 2.6 selection pressure • 2.7 heritability • 2.8 natural selection.
Q3 — Four conditions table
- Variation: Individuals differ in their traits / traits differ among individuals. — Necessary because selection cannot act if all individuals are identical.
- Heritability: Differences must be passed to offspring. — Necessary because if variation is not inherited, favourable traits cannot accumulate across generations.
- Differential survival/reproduction: Some individuals survive or reproduce more successfully than others. — Necessary because this is the mechanism that shifts allele frequencies.
- Selection pressure: The environment favours some variants over others. — Necessary because without an environmental filter, no variant has a consistent advantage.
Award 1 mark per correctly completed cell. Accept paraphrasing.
Q4 — True/False with correction
4.1 True. Lamarck did propose that acquired characteristics could be inherited by offspring.
4.2 False. Correction: Darwinian natural selection acts on existing heritable variation already present in a population — not on changes individuals make during their own lifetimes.
4.3 True.
4.4 False. Correction: Resistant variants already existed in the population due to random mutation before antibiotic exposure. The antibiotic acts as a selection pressure by killing more susceptible bacteria, allowing resistant bacteria to survive and reproduce more — it does not cause bacteria to mutate on purpose.
Q5 — MRSA sequence
Correct order: 2 (resistant variants pre-exist) → 4 (antibiotic applied) → 1 (resistant bacteria reproduce) → 3 (resistance frequency increases).