Drugs
15. Drugs — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 9 parts Lesson 1 of 3 2 quizzes
Lesson summary
15. Drugs — IGCSE BIOLOGY notes: Explain what a drug is, how antibiotics act on bacteria, why they do not treat viral infections, and how resistance develops.Drug = any substance taken into the body that modifies or affects chemical reactions in the body.Medicinal drug — a drug u…
- Metabolism
- Specific targets
- Viruses are not cells
- Reproduction
- Unnecessary use
- Incomplete courses
Part 1 of 7What a drug is
Drug
Drug any substance taken into the body that modifies or affects chemical reactions in the body.
Medicinal drug
- Medicinal drug a drug used to prevent or treat disease or to relieve symptoms.
Metabolism
- Metabolism the liver is the primary site of drug breakdown.
- Breakdown products are removed, often by the kidneys in urine.
Part 2 of 7How antibiotics work
Antibiotics
Antibiotics chemicals, made by certain fungi or bacteria, that affect the working of bacterial cells.
- They kill bacteria or stop them reproducing.
- Examples of action are blocking cell wall production or protein synthesis.
Specific targets
- Specific targets they act on structures and processes found only in bacterial (prokaryotic) cells, so they do not generally harm animal cells.
Stopping bacterial growth gives the immune system time to clear the infection.
Part 3 of 7Antibiotics and viruses
Viruses are not cells
- Viruses are not cells they have no cell wall and no metabolism of their own.
Reproduction
- Reproduction viruses reproduce inside host cells using the host machinery.
Result
- Result antibiotics have no target in a virus, so they do not treat colds or flu.
Unnecessary use
- Unnecessary use harms useful bacteria and can select resistant strains.
Part 4 of 7How resistance develops
1
A random mutation makes a bacterium resistant to an antibiotic.
2
When the antibiotic is used, susceptible bacteria die.
3
Resistant bacteria survive and reproduce.
4
They pass the resistance allele to their offspring.
5
The resistant proportion of the population rises.
- This is an example of natural selection, with the antibiotic as the selection pressure.
Part 5 of 7Causes of increasing resistance
Overuse
- Overuse antibiotics prescribed when not necessary, including for viral infections.
Incomplete courses
- Incomplete courses patients stop before finishing the prescribed course.
Farming
- Farming large-scale use to prevent disease in livestock kept in close quarters, even when animals are not sick.
Superbugs
- Superbugs resistant bacteria such as MRSA are harder to treat.
Part 6 of 7Reducing resistance
1
Use antibiotics only when essential and prescribed.
2
Complete the whole course even if feeling better after a few days.
3
Do not share or save leftover antibiotics.
4
Use good hygiene and infection control to limit spread.
Part 7 of 7More from the specification
- Incidence
- Number of new cases in a period per population.
Key terms
| Term | Meaning |
|---|---|
| Drug | A substance taken into the body that modifies or affects chemical reactions in the body. |
| Antibiotic | A chemical made by fungi or bacteria that kills bacteria or stops them reproducing. |
| Resistance | The ability of bacteria to survive an antibiotic that would normally kill them. |
| MRSA | A resistant bacterium known as a superbug. |
| Natural selection | The survival and reproduction of the best-adapted individuals. |
| Selection pressure | A factor, such as an antibiotic, that favours some individuals over others. |
Avoid these mistakes
1
Saying antibiotics cure viral infections — they act only on bacteria.
2
Saying the patient becomes resistant — the bacteria become resistant.
3
Saying antibiotics cause the mutation — the mutation is random and the antibiotic selects.
4
Stopping a course when symptoms disappear — the full course must be completed.
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