Lesson overview
Antibiotics: Why won’t antibiotics cure a cold?
Place paper discs of three antibiotics and a sterile-water control on a plate spread with bacteria, incubate it and measure the clear zones with a ruler; then look at a cold virus beside a bacterium and test a plate of bacteria that resist one antibiotic. For the Supplement, follow a population of bacteria through repeated courses of an antibiotic.
Suggested sequence
- Lesson 1 · Antibiotics against bacteria. Drugs; antibiotics treat bacterial infections; testing antibiotic discs on a plate of bacteria and measuring the clear zones. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- Lesson 2 · Viruses and resistant bacteria. Antibiotics do not affect viruses; resistant bacteria make antibiotics less effective; (Supplement) using antibiotics only when essential. Read together (10–15 min), show or explore the experiment (10 min), practise with self-checking (15–20 min).
- End of module · final check. 4 new questions, 20–30 min, without hints or notes; pupils check their answers once they have answered them all.
- One to two weeks later · return questions. 5 questions, 15 min, lesson closed.
Learning goals
Part 1: Antibiotics against bacteria
- Describe a drug as any substance taken into the body that modifies or affects chemical reactions in the body (15.1.1)
- Describe the use of antibiotics for the treatment of bacterial infections (15.1.2)
Part 2: Viruses and resistant bacteria
- State that antibiotics kill bacteria but do not affect viruses (15.1.4)
- State that some bacteria are resistant to antibiotics which reduces the effectiveness of antibiotics (15.1.3)
- Supplement: explain how using antibiotics only when essential can limit the development of resistant bacteria such as MRSA (S15.1.5)
Misconceptions to listen for
- “Any substance that kills microorganisms, inside or outside the body.” — A disinfectant kills microorganisms on a surface but is never taken into the body, so it is not a drug. A drug is defined by what it does to the reactions in the body.
- “Any medicine that a doctor prescribes to treat an illness.” — Prescribed medicines are drugs, but so are substances nobody prescribes, such as the alcohol in a drink. The definition covers every substance taken in that changes the body's reactions.
- “Any illegal substance that people can become addicted to.” — Being illegal has nothing to do with it. Many drugs are legal, from cough medicines to the alcohol in a drink.
- “Bleach poured into a sink to kill bacteria.” — Bleach kills bacteria, but in the sink, not in the body. A drug must be taken into the body.
- “A plaster stuck over a cut.” — A plaster protects the cut from outside. It is not a substance taken into the body that changes its chemical reactions.
- “Not the alcohol, because it is not a medicine.” — A drug does not have to be a medicine. Alcohol is taken into the body and changes the reactions in nerve cells, so it is a drug.
- “It makes the patient's white blood cells stronger, so they can fight any germ.” — An antibiotic acts on the bacteria themselves, not on the patient's cells.
- “It kills the throat cells that the bacteria have infected.” — An antibiotic acts on something bacteria have and human cells do not, such as the cell wall, so it leaves the patient's cells alone.
- “It numbs the throat so that the pain stops while the infection clears.” — That is what some throat sprays do. An antibiotic acts on the cause, the bacteria.
- “Subtract the disc's 6 mm.” — The zone's diameter includes the disc. Every zone is measured the same way, so nothing is subtracted.
Scope
Drugs (15.1.1–15.1.5): a drug as any substance taken into the body that modifies or affects chemical reactions in the body; antibiotics in the treatment of bacterial infections; some bacteria becoming resistant to antibiotics, which reduces their effectiveness; antibiotics not affecting viruses; and, for the Supplement, how using antibiotics only when essential limits the development of resistant bacteria such as MRSA. How bacteria cause disease and how the body defends itself are left to the disease and immunity modules.