GCSE · Biology · Edexcel · Spec 1BI0

Antibiotics and bacterial infections

Your friend has a streaming cold and says, "Just take an antibiotic." Why is that a bad idea, and what happens to bacteria when antibiotics get used when they shouldn't?

Biology · Infection and medicine

Could an antibiotic treat it?

Place each infection. Commit first — the reason appears after you do. Then switch the rule and sort the same five again.

Could an antibiotic cure this infection?

Still to sort

Yes — an antibiotic can treat it (0)

A bacterial infection: antibiotics kill the bacteria, or slow down or stop their growth.

Where the line is: The line is the type of pathogen, nothing to do with how bad the infection feels.

No — an antibiotic can't treat it (0)

Viruses, and also other pathogens such as protozoa and fungi: antibiotics don't work against them.

Where the line is: Antibiotics only work on bacterial infections.

5 of 5 still to sort.

Antibiotics are picky about what they work on. Have a guess for each infection, then read the reason.

Watch out: Antibiotics are only taken when a doctor prescribes them. This sort is about understanding what they can and can't do, not about choosing medicine for yourself.

Antibiotic or painkiller?

AntibioticsvsPainkillers (e.g. paracetamol, ibuprofen)

Both are medicines. They don't do the same job.

Focus

What it does

Antibiotics

Kills bacteria, or slows down or stops their growth

Painkillers (e.g. paracetamol, ibuprofen)

Relieves symptoms, such as the pain of a headache

The insight

One goes after the bacteria themselves. The other just turns down how you feel.

Effect on the pathogen

Antibiotics

Kills the bacteria (or slows or stops their growth)

Painkillers (e.g. paracetamol, ibuprofen)

Doesn't kill the pathogen

Effect on the disease

Antibiotics

Cures the disease itself

Painkillers (e.g. paracetamol, ibuprofen)

Treats the symptoms only

How one antibiotic does its job

?

Reason it through

Why can an antibiotic that stops cell-wall production kill bacteria but not work on your own cells?

Link 1 of 3

First link · your turn

Antibiotics work by inhibiting the cellular processes of bacteria. What do some of them stop bacteria doing?

2
Locked — reveal the link above first
3
Locked — reveal the link above first

How resistance gets going

Click through the stages, from one bacterium to a whole population.

  2. The antibiotic stops working on itThe antibiotic no longer works effectively to kill that resistant bacterium.
  5. Resistant bacteria multiplySo the number of resistant bacteria can increase very quickly.

Stop halfway? Predict first

A patient is prescribed a course of antibiotics for a bacterial infection. Halfway through, they feel better and stop.

What's most likely to be left behind in their body?

Biology · Antibiotic resistance

Write your own answer, then mark it

Describe four ways to reduce the spread of antibiotic resistance. [4 marks]

0 words · your answer stays on this page and is not sent anywhere.

Exam line: Each measure earns its own mark, so give four different measures rather than rewording one.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

What antibiotics can fix, what they can't, and how resistance gets going.

What you need to know

  • Antibiotics kill bacteria, or slow down or stop their growth, and that cures the disease.
  • They only work on bacterial infections: not on viruses, and not on other pathogens such as protozoa and fungi.
  • Have a goPriya announces, "Antibiotics kill every germ, so I'll take one for my virus." Confident. What's wrong with her plan?

    Antibiotics only work on bacterial infections, not viruses.

    Antibiotics don't work against viruses, so "every germ" is wrong: they're for bacterial infections only.

  • Painkillers like paracetamol or ibuprofen only relieve symptoms, such as a headache; they don't kill the pathogen.
  • Some antibiotics stop bacteria making their murein cell wall, so without it the cell dies.
  • Human and other animal cells have no cell wall, so these antibiotics don't work on animal cells.
  • Have a goA scientist adds an antibiotic that stops cell-wall production to a dish of human cells. Will the antibiotic work on them?

    No.

    Human and other animal cells have no cell wall, so antibiotics that stop cell-wall production do not work on animal cells.

  • Different antibiotics work on different types of bacteria, and they're only taken when a doctor prescribes them.
  • A random mutation in a bacterium's DNA can make it resistant, and it passes the mutation on when it reproduces.
  • Many bacteria can double every 20 minutes, so resistant bacteria can increase very quickly.
  • Have a goStart with one resistant bacterium that keeps doubling every 20 minutes. How many are there after one hour?

    8 resistant bacteria.

    One hour is three 20-minute doublings: 1 → 2 → 4 → 8. Keep going and the number climbs faster and faster.

  • If a course isn't completed, the least resistant bacteria die first and the resistant ones are left to divide.
  • To cut resistance: use antibiotics only when necessary, finish the course, never take leftovers, and reduce the need with vaccination and good hygiene.

The big picture

Antibiotics kill bacteria, or slow down or stop their growth, so they cure bacterial infections and only those. They don't work against viruses, and unlike painkillers they go after the pathogen rather than just the symptoms. Resistance starts with a random mutation and spreads when antibiotics aren't used correctly, which is why they're only used when necessary and why a prescribed course is always completed.

Key points

1Antibiotics treat bacterial infections only; they do not work against viruses or other pathogens such as protozoa and fungi.
2Antibiotics kill bacteria (or slow or stop their growth) and cure the disease; painkillers only relieve symptoms.
3Resistance begins with a random mutation, is passed on when bacteria reproduce, and can spread quickly because many bacteria can double every 20 minutes.
4Not completing a course leaves the resistant bacteria to divide, so resistance spreads and the infection is much harder to treat.

Worked example

Problem

A friend has a streaming cold. They've got some antibiotics left over from an infection last month and say, "These will sort it." Explain why they shouldn't take them.

⚠ Watch out

Thinking an antibiotic helps with any infection, even a cold, or that you can stop the course once you feel better. Antibiotics only work on bacterial infections, and stopping early leaves the resistant bacteria alive to divide.

🧠

Memory hook

Antibiotics are for bacteria only. Finish the course, or the toughest bacteria get a head start.

✓

Check yourself

Look away and talk yourself through how resistance gets going, from one mutated bacterium to a large resistant population. Can you get every stage in order without peeking?

Flashcards

(15)
What do antibiotics do to bacteria?
They kill them, or slow down or stop their growth, and so cure the disease.
Which pathogens do antibiotics work against?
Only bacteria. They don't work against viruses or other pathogens such as protozoa and fungi.
Paracetamol or ibuprofen: what do they do for a headache?
They relieve the symptoms but do not kill the pathogen.
What is the bacterial cell wall made of, and what does it do?
Murein. It gives the bacterial cell structure and protection.
How do some antibiotics kill bacteria?
They stop bacteria producing their cell wall, so the cell dies.
Why don't cell-wall antibiotics work on human cells?
Human and other animal cells have no cell wall.
Why must the right antibiotic be used for an infection?
Different antibiotics work on different types of bacteria.
When should antibiotics be taken?
Only when prescribed by a doctor.
Which can antibiotics treat: tuberculosis or HIV?
Tuberculosis, which is caused by bacteria. HIV is viral, so antibiotics cannot treat it.
How does a bacterium become resistant to an antibiotic?
A random mutation in its DNA means the antibiotic no longer works effectively to kill it.
How is resistance passed on?
When the resistant bacteria reproduce, they pass the mutation on.
Why can resistant bacteria increase so quickly?
Many bacteria can double every 20 minutes.
What happens if a course of antibiotics isn't completed?
The least resistant bacteria are killed first and the resistant ones are left to divide, so resistance spreads and the infection becomes much harder to treat.
Name three things individuals can do to reduce antibiotic resistance.
Only use antibiotics when necessary, always complete the prescribed course, and never take antibiotics left over from another infection.
How can hospitals and farms help reduce antibiotic resistance?
Hospitals isolate patients who have antibiotic-resistant infections; farms avoid the routine use of antibiotics on farm animals.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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