BIOLOGY · Stage 9 · Chapter 13: Variation and Natural Selection
Biology 13.3 Environmental change and natural selection — Antibiotic Resistance
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Lesson summary
13.3 Environmental change and natural selection — Antibiotic Resistance — Alhussan International Academy — Biology (Stages 7–9) notes: Explain how environmental change drives natural selection and how bacteria evolve resistance to antibiotics.Adaptation — natural selection produc…
- Climate change
- Variation helps
- Original environment
- After the change
- Life cycles
- Linked species
Section 1 of 7Environmental change
- Adaptation
- natural selection produces populations that survive in their environment, and changes in that environment affect the organisms living there.
- Date palms and olive trees may survive in low temperatures but will not bear fruit.
- Climate change
- many environments are getting hotter and drier, some are getting wetter, winters may be colder or end sooner, and rains are failing.
- Variation helps
- every population contains variation, and individuals that were different may have characteristics suited to the new conditions,
- so the population can survive.
- Survival
- living organisms must adapt or they will not survive, and natural selection changes populations to fit the environment.
Section 2 of 7Drought-adapted plants
- Original environment
- with 25 mm of rain in the growing season most plants produce 7 flowers and an average of 28 seeds,
- but some produce 5 flowers or 3 flowers with fewer seeds.
- After the change
- when global warming cuts rainfall to 15 mm many plants die or fail to set seed.
- The variants with fewer flowers and seeds cope better with less water and reproduce successfully.
- Result
- as dry conditions continue, natural selection acts until most of the population is the drought-adapted variation.
Section 3 of 7Interdependence and extreme events
- Life cycles
- plant and animal life cycles are often linked through feeding relationships,
- so patterns of reproduction change and food supply can fail if the environment changes.
- Many organisms in hot, dry regions depend on rains to reproduce, so delayed or failed rains threaten whole populations.
- Linked species
- if one species changes by natural selection, other interdependent species must also adapt or die out.
- Kestrels
- they are small birds of prey widespread in Africa, Asia and Europe, with a diet that varies with where they live.
- They reproduce successfully when average temperature rises, because those best able to cope breed successfully.
- Extreme droughts damage kestrel populations, because there are no adaptations for severe, unpredictable drought.
- Speed of change
- natural selection has always allowed adaptation, but climate change is now happening very fast.
Section 4 of 7Antibiotics and bacteria
- Antibiotics = medicines that kill bacteria or stop them growing, without harming human cells.
- They treat bacterial infections such as pneumonia but do not work on viruses, so they are no use against colds or flu.
- Fast reproduction
- bacteria sometimes divide every 20 minutes, so a population can evolve rapidly.
Section 5 of 7How resistance develops
- Variation caused by mutation occurs in a population,
- and a random mutation produces a resistant bacterium, for example by changing the target of the drug.
- The antibiotic kills most non-resistant bacteria, but the resistant one survives.
- The survivor reproduces with little competition and passes on the resistance allele.
- The population of resistant bacteria increases, so the antibiotic no longer works well.
- Selection pressure
- this is natural selection with the antibiotic as the selection pressure.
- Plasmids
- bacteria can pass resistance genes to other bacteria, even of different species, in small rings of DNA.
Section 6 of 7Superbugs
- MRSA (methicillin-resistant Staphylococcus aureus)
- a well-known resistant bacterium spread in hospitals.
- Tuberculosis
- multidrug-resistant forms are a global concern.
- Danger
- infections by resistant bacteria are harder, more expensive and sometimes impossible to treat.
- The World Health Organization regards antibiotic resistance as a major threat.
- Routine operations and cancer treatments depend on effective antibiotics.
Section 7 of 7Reducing resistance
- Doctors should prescribe antibiotics only when necessary and not for viral infections.
- Patients must complete the whole course so that all the bacteria are killed.
- Farmers should reduce routine use of antibiotics in animal feed.
- Hospitals should use strict hygiene, such as hand washing and isolating infected patients.
- Scientists develop new antibiotics and drug combinations, though this is difficult and costly.
| Normal evolution | Antibiotic resistance |
|---|---|
| Takes thousands of years in large animals | Occurs in years because bacteria reproduce quickly |
| Selection by climate, predators | Selection by the antibiotic |
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