13.3Chapter 13: Variation and Natural Selection

Environmental change and natural selection — Alhussan Biology - Stage 9 Revision Notes & Topical Questions

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📚 Alhussan Biology - Stage 9 Hub / Topical Revision

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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 9Environmental change

Adaptation

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

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

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

Survival living organisms must adapt or they will not survive, and natural selection changes populations to fit the environment.

Section 2 of 9Drought-adapted plants

Original environment

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

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

Result as dry conditions continue, natural selection acts until most of the population is the drought-adapted variation.

Section 3 of 9Interdependence and extreme events

Life cycles

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

Linked species if one species changes by natural selection, other interdependent species must also adapt or die out.

Kestrels

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

Speed of change natural selection has always allowed adaptation, but climate change is now happening very fast.

Section 4 of 9Antibiotics and bacteria

Antibiotics

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

Fast reproduction bacteria sometimes divide every 20 minutes, so a population can evolve rapidly.

Section 5 of 9How 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.

1Selection pressure

Selection pressure this is natural selection with the antibiotic as the selection pressure.

2Plasmids

Plasmids bacteria can pass resistance genes to other bacteria, even of different species, in small rings of DNA.

Section 6 of 9Superbugs

Superbugs

MRSA (methicillin-resistant Staphylococcus aureus)

MRSA (methicillin-resistant Staphylococcus aureus) a well-known resistant bacterium spread in hospitals.

Tuberculosis

Tuberculosis multidrug-resistant forms are a global concern.

Danger

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 9Reducing 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

Section 8 of 9Key terms

Term	Meaning
Antibiotic	A medicine that kills bacteria or stops them growing.
Resistance	The ability of bacteria to survive an antibiotic.
Mutation	A random change in a gene.
Selection pressure	An environmental factor that affects survival, such as an antibiotic.
Plasmid	A small ring of DNA that bacteria can pass to each other.
MRSA	A hospital-spread bacterium resistant to methicillin.