The shape of the lesson
By the end of the lesson, learners can
- What counts as a drug: In biology the word drug is wider than the medicines in a pharmacy.
- Antibiotics cure bacterial infections only: The dish holds a bacterial infection of 300 bacteria: most are sensitive (blue) and 4 are resistant (red).
- How resistance spreads, and how to slow it: Extended.
- Drug: any substance taken into the body that modifies or affects chemical reactions in the body.
- Antibiotics: treat bacterial infections; they kill bacteria but do not affect viruses.
- Resistance: some bacteria are resistant, which reduces the effectiveness of antibiotics. The mutation is random; the antibiotic selects it.
- Extended: use antibiotics only when essential (never for viruses, full course) to limit resistant strains such as MRSA.
One picture every idea returns to
A drug is any substance taken into the body that modifies or affects chemical reactions in the body. Antibiotics are drugs used to treat bacterial infections: they kill bacteria (or stop them growing) but they do not affect viruses. Some bacteria are resistant to antibiotics, which reduces how effective antibiotics are. Extended: using antibiotics only when they are essential limits the development of resistant bacteria such as MRSA.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Kill the bacteria, not the patient.. A drug is any substance that changes the chemical reactions in your body. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: What counts as a drug | In biology the word drug is wider than the medicines in a pharmacy. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Antibiotics cure bacterial infections only | The dish holds a bacterial infection of 300 bacteria: most are sensitive (blue) and 4 are resistant (red). Project tab 7 of the lab (Antibiotics and resistance) and let a student drive it while the class predicts. | Pairs |
| 21 to 30 min | Teach and check: How resistance spreads, and how to slow it | Extended. Project tab 6 of the lab (Antibiotic resistance in a bacterial colony) and let a student drive it while the class predicts. | Corners |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 18 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in How resistance spreads, and how to slow it, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Corners
Put one answer or viewpoint in each corner of the room. Students move to the corner they agree with, justify the choice to a partner there, then hear one voice from each corner before the reveal.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Do not define a drug as "a medicine" or "an illegal substance". | The syllabus definition is about effect: any substance taken into the body that modifies or affects chemical reactions in the body. |
| Antibiotics kill bacteria, not viruses, and they do not "kill germs" in general. | Taking an antibiotic for a cold does nothing to the virus but still gives resistant bacteria in the body an advantage. |
| The antibiotic does not cause the mutation, and bacteria do not "get used to" or become immune to the drug. | The resistance mutation arises at random; the antibiotic only kills the bacteria without it, so the resistant ones are left to multiply. |
Drugs and antibiotics: worksheet
6 questions, 18 marks. Written in the style of the papers; no past paper question is reproduced.
Define the term drug and name one drug that is used to treat bacterial infections.
A student has a sore throat caused by a virus. Explain why a doctor would not prescribe an antibiotic.
State what is meant by a resistant bacterium and explain why resistant bacteria are a problem for medicine.
A hospital recorded the percentage of Staphylococcus aureus infections that were resistant to the antibiotic methicillin (MRSA).
| Year | 2000 | 2004 | 2008 | 2012 | 2016 |
|---|---|---|---|---|---|
| Infections that were MRSA / % | 12 | 26 | 38 | 30 | 21 |
(a) Describe the trend in the data. (b) After 2008 the hospital began prescribing antibiotics only when essential. Suggest how this explains the change after 2008.
Extended. Explain how resistant bacteria such as MRSA become common in a population, and how using antibiotics only when essential limits this.
A patient stops taking a course of antibiotics after three days because they feel better. One week later the infection returns and the same antibiotic no longer works. Suggest an explanation.
Answer key and marking notes
- Any substance taken into the body that modifies or affects chemical reactions in the body.
- An antibiotic, for example penicillin.
- Antibiotics kill bacteria (or stop them growing) but do not affect viruses.
- So the antibiotic would not cure the infection or shorten it.
- Unnecessary use of antibiotics favours resistant bacteria / increases antibiotic resistance.
- A resistant bacterium is not killed (or not stopped from growing) by an antibiotic.
- Infections caused by resistant bacteria are hard to treat, because the antibiotic is less effective or does not work.
- (a) The percentage rose from 12% in 2000 to a peak of 38% in 2008, then fell to 21% by 2016.
- (b) Before 2008, frequent use of antibiotics killed sensitive bacteria and let resistant MRSA survive and multiply.
- After 2008 antibiotics were used less often, so there was less selection pressure favouring MRSA.
- Sensitive strains were no longer killed so often, so MRSA made up a smaller proportion of infections.
- A random mutation makes a few bacteria resistant to the antibiotic.
- When the antibiotic is used, sensitive bacteria are killed but the resistant ones survive.
- The survivors reproduce and pass on resistance, so the proportion of resistant bacteria increases with each use.
- Using antibiotics only when essential (not for viral infections, completing the course) means fewer occasions on which resistant bacteria are selected, so resistance develops more slowly.
- After three days the antibiotic had killed most of the sensitive bacteria, so the patient felt better, but some bacteria survived.
- The survivors included the resistant bacteria, which were not killed by the antibiotic.
- These multiplied, so the returning infection was mostly resistant bacteria and the same antibiotic was not effective.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which substance is a drug, using the biological definition?
- ACaffeine in a cup of coffee
- BAmylase made by the salivary glands
- CGlucose made by photosynthesis
- DOxygen diffusing into a leaf cell
Which disease could be treated with an antibiotic?
- ATuberculosis, caused by a bacterium
- BInfluenza, caused by a virus
- CThe common cold, caused by a virus
- DMeasles, caused by a virus
Which statement about antibiotics is correct?
- AThey kill bacteria but do not affect viruses
- BThey kill viruses but do not affect bacteria
- CThey kill both bacteria and viruses equally
- DThey make the body produce more antibodies
Some bacteria in an infection are resistant to penicillin. What is the most likely effect when the patient is given penicillin?
- AThe infection may not be cured, as resistant bacteria survive
- BThe infection is cured faster, as resistant bacteria die first
- CThe penicillin turns the resistant bacteria back into sensitive ones
- DThe patient becomes resistant to penicillin and it stops working
A culture of bacteria was grown and an antibiotic was added on day 2 and kept present. Which explains the change in numbers between day 5 and day 8?
- AResistant bacteria survived and multiplied
- BThe antibiotic began to kill the bacteria
- CThe bacteria used up the antibiotic as food
- DViruses replaced the bacteria in the culture
(Extended) What does the abbreviation MRSA describe?
- AA strain of bacterium resistant to several antibiotics
- BA virus that cannot be treated with any vaccine
- CAn antibiotic used to treat resistant infections
- DA fungus that produces the antibiotic penicillin
(Extended) A doctor is asked for antibiotics by four patients. Which decision best limits the development of resistant bacteria?
- APrescribe only for the patient with a serious bacterial infection
- BPrescribe for all four, as a precaution against any infection
- CPrescribe for the patient with a cold, to stop it turning bacterial
- DPrescribe a short course for each, so less antibiotic is used
(Extended) Why does using an antibiotic often make a population of bacteria more resistant over time?
- AIt kills the sensitive bacteria, so the resistant ones multiply
- BIt causes mutations that make the bacteria resistant
- CThe bacteria learn to avoid it after their first contact
- DIt strengthens the bacteria the more often they meet it
Quiz key
Caffeine is taken into the body and modifies chemical reactions in it, so it is a drug even though it is not a medicine. Amylase is an enzyme made inside the body, not taken in. Glucose made by photosynthesis is a product of the plant's own reactions. Oxygen is a normal raw material for respiration, not a substance that modifies the body's reactions.
Antibiotics are used to treat bacterial infections, and tuberculosis is caused by a bacterium. Influenza, the common cold and measles are all caused by viruses, and antibiotics do not affect viruses, so they would not cure any of these.
Antibiotics kill bacteria (or stop them growing) but do not affect viruses. The reverse statement is wrong, and so is the idea that they work equally on both. Antibodies are made by lymphocytes in response to antigens; antibiotics are drugs that act on the bacteria directly, not on antibody production.
Resistant bacteria are not killed by penicillin, so they survive and may keep the infection going: resistance reduces the effectiveness of the antibiotic. Resistant bacteria do not die first, the drug cannot reverse resistance, and it is the bacteria, not the patient, that are resistant.
After the sensitive bacteria were killed (days 2 to 4), the few resistant bacteria survived and multiplied, so the number rose again from day 5 even with the antibiotic present. The antibiotic killing bacteria explains the fall, not the rise. Bacteria do not grow because they feed on the antibiotic, and viruses do not replace bacteria in a culture.
MRSA is methicillin-resistant Staphylococcus aureus, a strain of bacterium resistant to many antibiotics, which makes its infections hard to treat. It is not a virus (antibiotics do not affect viruses anyway), not an antibiotic, and not the mould that produces penicillin.
Using antibiotics only when essential, for a serious bacterial infection, gives resistant bacteria the fewest chances to be selected. Prescribing for everyone or for a viral cold is unnecessary use that favours resistant strains. A short course leaves surviving bacteria, including resistant ones, which then multiply.
Resistance arises by random mutation; the antibiotic kills the sensitive bacteria and leaves the resistant ones to survive, reproduce and pass resistance on, so their proportion rises with each use. The antibiotic does not cause the mutation, bacteria cannot learn, and contact with the drug does not make individual bacteria stronger.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.