Biology • Year 11 • Module 3 • Lesson 16
Modern Examples of Evolutionary Change
Lock in the core vocabulary, the four modern examples (antibiotic resistance, cane toad, peppered moth, radiometric dating), and the natural-selection mechanism 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
Modern evolution is observable when the _______________ is short, so that many generations pass quickly. When an antibiotic is applied, it acts as a _______________ that kills susceptible bacteria but spares the rare individuals carrying _______________ resistance mutations. Because these survivors reproduce, the _______________ of the resistance gene rises in the population, this is the mechanism of _______________. To confirm the long timescales seen in the fossil record, scientists use _______________, which relies on the constant _______________ of a radioactive isotope. The rise of dark peppered moths during the Industrial Revolution is called _______________.
2. Term–definition match
Write the matching term from this list in the right-hand column: antibiotic resistance • selection pressure • radiometric dating • half-life • industrial melanism • allele frequency • heritable variation • relative dating. 8 marks
| # | Definition | Matching term |
|---|---|---|
| 2.1 | The ability of bacteria to survive and reproduce in the presence of an antibiotic that would normally kill them. | |
| 2.2 | An environmental factor that affects an organism's chance of surviving and reproducing. | |
| 2.3 | A technique that uses the known decay rate of radioactive isotopes to determine the age of fossils or rocks. | |
| 2.4 | The time it takes for half of a radioactive isotope's atoms to decay into the daughter product. | |
| 2.5 | The increase in frequency of dark-coloured forms of a species in response to pollution darkening the environment. | |
| 2.6 | The proportion of a particular version of a gene within a population. | |
| 2.7 | Inherited differences between individuals that can be passed to offspring and acted on by selection. | |
| 2.8 | Dating that uses rock-layer position to say a fossil is older or younger, without giving an actual age in years. |
3. Identify the modern example
For each statement below, write the matching modern example in the Example column: write AR (antibiotic resistance), CT (cane toad), PM (peppered moth) or RD (radiometric dating). 8 marks
| Example (AR/CT/PM/RD) | Statement |
|---|---|
| The dark allele frequency rose to roughly 90% as soot blackened tree trunks, then fell after the Clean Air Act. | |
| Bacteria reproducing every 20 minutes allow measurable change within months when treated. | |
| Invasion-front individuals have longer legs than those in established populations. | |
| Carbon-14, with a half-life of about 5,730 years, is used to date samples up to roughly 50,000 years old. | |
| MRSA rose from under 0.2% to around 12% of hospital infections in Australia between 1990 and 2020. | |
| Some freshwater crocodiles and snakes in high-exposure areas show reduced sensitivity to bufotoxin. | |
| Potassium-Argon dating was used to date the volcanic ash surrounding hominin fossils such as Lucy. | |
| Before industrialisation the dark form was rare (~1%) because it stood out on lichen-covered pale trees. |
4. True or false, with correction
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 Antibiotics cause bacteria to mutate and become resistant. T / F
4.2 The cane toad invasion shows evolution in the toads and in their native predators at the same time. T / F
4.3 Carbon-14 dating is the best method for dating a 2-billion-year-old zircon crystal. T / F
4.4 In the peppered moth, the dark allele only existed after industrial soot first appeared. T / F
5. Put the steps in order
The five steps below describe how antibiotic resistance becomes common in a bacterial population, but they are out of order. Write the numbers 1 to 5 in the boxes to show the correct sequence. 5 marks
| Order (1–5) | Step |
|---|---|
| Resistant bacteria reproduce and pass the resistance gene to their offspring. | |
| A mixed population contains many susceptible bacteria and a few resistant ones from random pre-existing mutations. | |
| Over many generations the frequency of the resistance gene in the population increases. | |
| An antibiotic is applied to the population, acting as a selection pressure. | |
| Susceptible bacteria die while resistant bacteria survive (differential survival). |
Q1, Cloze paragraph
In order: generation time • selection pressure • pre-existing • allele frequency • antibiotic resistance • radiometric dating • half-life • industrial melanism.
Q2, Term–definition matches
2.1 antibiotic resistance • 2.2 selection pressure • 2.3 radiometric dating • 2.4 half-life • 2.5 industrial melanism • 2.6 allele frequency • 2.7 heritable variation • 2.8 relative dating.
Q3, Identify the modern example
PM Dark allele rose to ~90% then fell • AR Bacteria reproduce every 20 minutes • CT Invasion-front longer legs • RD Carbon-14 up to ~50,000 years • AR MRSA 0.2% to 12% • CT Crocodiles/snakes reduced bufotoxin sensitivity • RD Potassium-Argon dating of Lucy's ash • PM Dark form rare (~1%) on pale lichen trees.
Q4, True/False with correction
4.1 False. Correction: Antibiotics do not cause resistance mutations. Resistance mutations arise randomly and pre-exist in the population. The antibiotic is a selection pressure that removes susceptible bacteria, leaving resistant ones to reproduce.
4.2 True.
4.3 False. Correction: Carbon-14 is effective only up to about 50,000 years. A 2-billion-year-old zircon crystal would be dated with Uranium-Lead (U-Pb), which suits the oldest geological specimens.
4.4 False. Correction: Both light and dark forms existed before industrialisation. The dark (melanic) allele was simply rare (~1%) because dark moths were visible on pale lichen-covered trees and eaten by birds.
Q5, Sequence the mechanism
Correct order:
- 1 A mixed population contains many susceptible bacteria and a few resistant ones from random pre-existing mutations.
- 2 An antibiotic is applied to the population, acting as a selection pressure.
- 3 Susceptible bacteria die while resistant bacteria survive (differential survival).
- 4 Resistant bacteria reproduce and pass the resistance gene to their offspring.
- 5 Over many generations the frequency of the resistance gene in the population increases.
Award 1 mark per correctly ordered step. Maximum 5 marks.