Vaccines, antibiotics and drugs
By the end of this chapter you will be able to
- Explain how a vaccine works and calculate the percentage vaccinated
- Explain why antibiotics work on bacteria but not on viruses
- Explain how antibiotic resistance develops and why overuse speeds it up
- Interpret the agar-plate results and the zones of inhibition
- [H] Describe the stages of drug development, and the purpose of a double-blind trial
You should already know
- Immune response and memory cells (Chapter 13)
- Pathogens: bacteria and viruses (Chapter 13)
- Percentage calculations (Chapter 1)
Where this leads
- Mutation and natural selection (Chapter 16)
- Monoclonal antibodies and cancer (Chapter 4)
- Ecology of infection (Chapter 18)
GCSE Biology. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Explain how vaccination gives artificial immunity, and what herd immunity means, Explain how antibiotics work, and why they do not kill viruses, Describe antibiotic resistance and how it spreads, Investigate the effect of an antiseptic or antibiotic on bacterial growth, as a teacher demonstration, Describe painkillers, antiseptics and the stages of drug development, [H] Explain the mechanism of antibiotic resistance by natural selection, double-blind trials and monoclonal antibodies.
Exercise P Do you remember?
Method. Find one quarter of 400.
- Divide. 400 / 4 = 100.400 / 4 = 100
- Write the answer. 100
Check. 100 is 25% of 400. ✓
Method. Recall the antibody producers.
- Recall. Lymphocytes make antibodies.make antibodies
- Write the answer. lymphocytes
Check. Phagocytes engulf pathogens. ✓
Method. Recall the cells.
- Recall. Memory cells remain after an infection.remain after an infection
- Write the answer. memory cells
Check. They make the second response faster. ✓
Method. Recall what antibiotics target.
- Recall. Antibiotics target bacteria, not viruses.target bacteria
- Write the answer. no
Check. Viruses are not cells. ✓
Method. Recall the cause of measles.
- Recall. Measles is caused by a virus.caused by a virus
- Write the answer. virus
Check. Viruses reproduce inside host cells. ✓
Vaccination and herd immunity
A vaccine contains a weakened or dead pathogen, or part of it, which carries the antigen. It is injected, and it triggers lymphocytes to make antibodies and memory cells. The person is protected against the disease without catching it. This is artificial immunity, because the immunity comes from a vaccine rather than from an infection.
When a large proportion of the population is vaccinated, the pathogen cannot spread easily, so people who cannot be vaccinated are also protected. This is herd immunity.
| Group in the town (invented) | Number | Percentage |
|---|---|---|
| vaccinated | 375 | 75% |
| not vaccinated | 125 | 25% |
| total | 500 | 100% |
Key ideas
- A vaccine contains an antigen, without causing the full disease.
- It triggers lymphocytes to make memory cells and antibodies.
- This is artificial immunity: it does not come from catching the disease.
- Herd immunity protects people who cannot be vaccinated.
Method. Recall the immunity from a vaccine.
- Recall. A vaccine gives immunity without the disease, so it is not from an infection.without the disease
- Name it. So the type is artificial immunity.artificial immunity
- Write the answer. artificial immunity
Check. Natural immunity comes from catching the disease. ✓
Method. Divide the vaccinated number by the total, then multiply by 100.
- Divide. 375 / 500 = 0.75.375 / 500 = 0.75
- Multiply. Multiply by 100 to give 75%.75%
- Write the answer. 75%
Check. 75% of 500 is 375. ✓
Method. Think about how many people are protected.
- Think. When most people are immune, the pathogen cannot spread easily.cannot spread easily
- Conclude. So people who cannot be vaccinated are also protected.also protected
- Write the answer. When enough people are immune, the pathogen cannot spread easily, so those who cannot be vaccinated are also protected.
Check. Herd immunity depends on a high proportion. ✓
Watch out
Watch out: a vaccine does not give immunity by giving the disease. It contains a harmless form of the antigen, so the body makes memory cells.
Exam tip
Exam tip. When you describe a vaccine, say that it contains an antigen and triggers memory cells, and that it does not cause the illness.
Try it (with your teacher). With your teacher, use a calculator-free method to work out the percentage of your class who have had a particular vaccine, using the numbers your teacher gives. Do not ask pupils about their medical records.
Exercise 14A Vaccination and herd immunity
Method. Recall what a vaccine carries.
- Recall. A vaccine contains a weakened or dead pathogen, or part of it, carrying the antigen.carrying the antigen
- Write the answer. antigen
Check. The antigen triggers memory cells. ✓
Method. Recall the cells.
- Recall. A vaccine triggers lymphocytes, which make antibodies and memory cells.make antibodies and memory cells
- Write the answer. lymphocytes
Check. Phagocytes do not make memory cells. ✓
Method. Recall the type.
- Recall. Immunity from a vaccine is artificial, because it does not come from catching the disease.artificial
- Write the answer. artificial immunity
Check. Natural immunity comes from infection. ✓
Method. Recall the protection.
- Recall. When most people are immune, the spread is limited, which protects others.the spread is limited
- Write the answer. herd immunity
Check. Herd immunity needs a high proportion vaccinated. ✓
Method. Recall the vaccine content.
- Recall. A vaccine contains a weakened or dead pathogen, or part of it, so it does not cause the full disease.does not cause
- Write the answer. So no.no
- Write the answer. no
Check. The body is primed without illness. ✓
Method. Divide the vaccinated by the total, then multiply by 100.
- Divide. 150 / 200 = 0.75.150 / 200 = 0.75
- Multiply. Multiply by 100.75%
- Write the answer. 75%
Check. 75% of 200 is 150. ✓
Method. Subtract the vaccinated from the total.
- Subtract. 500 - 375 = 125.500 - 375 = 125
- Write the answer. 125
Check. 375 + 125 = 500. ✓
Method. Find 80% of 1000.
- Divide. Divide 1000 by 100 to find 1%, which is 10 people.1000 / 100 = 10
- Multiply. Multiply by 80 for 80%: 10 x 80 = 800.10 x 80 = 800
- Write the answer. 800
Check. 800 out of 1000 is 80%. ✓
Method. Think about the risk.
- Think. Young children are at high risk from some diseases.high risk
- Conclude. A vaccine protects them before they are exposed to the disease.before they are exposed
- Write the answer. Accept any sentence that says it protects them before they are at high risk of catching the disease.
Check. Early protection reduces risk. ✓
Method. Think about herd immunity.
- Think. If most people are immune, the pathogen spreads less.spreads less
- Conclude. So a person who cannot be vaccinated is still protected.still protected
- Write the answer. Accept any sentence that says herd immunity limits the spread, so the allergic person is still protected.
Check. Herd immunity is a community benefit. ✓
Method. Link memory cells to timing.
- Memory. Memory cells must already be present to respond quickly.already be present
- Timing. If the vaccine comes after exposure, the disease may already be established.already established
- Write the answer. Accept any answer that says memory cells must already exist, so the response is fast when the pathogen arrives.
Check. Timing decides whether the response is fast enough. ✓
Antibiotics and viruses
Antibiotics are medicines that kill or slow the growth of bacteria. They work by interfering with processes that are particular to bacteria, such as the making of their cell wall. Antibiotics do not work on viruses, because a virus is not a cell and reproduces inside the host cells, using the host’s own processes. An antibiotic cannot target these processes without harming the host.
Antibiotics are not painkillers, and they do not give immunity. They are used only for bacterial infections, and they must be used as the doctor advises.
Key ideas
- Antibiotics kill or slow the growth of bacteria.
- They do not work on viruses, which are not cells.
- Antibiotics do not give immunity.
- Antibiotics must be used only for bacterial infections, as directed.
Method. Recall what antibiotics target.
- Recall. Antibiotics kill or slow the growth of bacteria.kill or slow
- Name it. So the pathogen is a bacterium.bacterium
- Write the answer. bacteria
Check. Antibiotics do not kill viruses. ✓
Method. Think about what a virus is.
- Think. A virus is not a cell and uses the host cell’s processes to reproduce.not a cell
- Conclude. Antibiotics cannot target these without harming the host.without harming
- Write the answer. A virus is not a cell and reproduces inside the host cells, so antibiotics that target bacteria do not affect it.
Check. The target of the drug must match the pathogen. ✓
Method. Recall the cause of a cold.
- Recall. The common cold is usually caused by a virus.caused by a virus
- Name it. So the group is viruses.viruses
- Write the answer. viruses
Check. Antibiotics will not help a cold. ✓
Watch out
Watch out: antibiotics do not give immunity. Taking them does not protect you from the same infection in future.
Exam tip
Exam tip. When you explain why an antibiotic does not work, say that the pathogen is a virus, not a bacterium, and that the target is missing.
Try it (with your teacher). With your teacher, sort a list of infections into bacterial and viral. Explain for each one whether an antibiotic would be a suitable treatment. Do not handle any pathogens.
Exercise 14B Antibiotics and viruses
Method. Recall what antibiotics do.
- Recall. Antibiotics kill or slow the growth of bacteria.kill or slow
- Write the answer. yes
Check. Viruses are not killed. ✓
Method. Recall what antibiotics target.
- Recall. Antibiotics target bacteria, and viruses are not affected.not affected
- Write the answer. no
Check. Viruses are not cells. ✓
Method. Recall the structure of a virus.
- Recall. A virus is not made of cells, and it reproduces only inside a host cell.not made of cells
- Write the answer. Accept any sentence that says viruses are not made of cells and cannot reproduce on their own.
Check. Viruses rely on the host. ✓
Method. Recall what antibiotics do.
- Recall. Antibiotics kill bacteria, but they do not give immunity.do not give immunity
- Write the answer. So no.no
- Write the answer. no
Check. Immunity comes from memory cells. ✓
Method. Recall the medicine.
- Recall. An antibiotic kills bacteria, and it is used for bacterial infections.bacterial infections
- Write the answer. antibiotic
Check. A painkiller relieves pain but does not kill pathogens. ✓
Method. Recall the medicine.
- Recall. A painkiller relieves symptoms, but it does not kill pathogens.relieves symptoms
- Write the answer. painkiller
Check. Painkillers are not antibiotics. ✓
Method. Recall the target.
- Recall. Antibiotics interfere with processes particular to bacteria, such as making the cell wall.cell wall
- Choose one. Either answer is correct.either
- Write the answer. Accept any one: making the cell wall, or other processes particular to bacteria.
Check. Viruses do not have a cell wall to target. ✓
Method. Think about the bacteria left behind.
- Think. Stopping early may leave some bacteria alive.leave some bacteria alive
- Conclude. Those bacteria may be resistant and harder to treat later.resistant
- Write the answer. Accept any sentence that says stopping early can leave some bacteria alive, which may become resistant.
Check. The full course kills the infection fully. ✓
Method. Think about the target.
- Think. The infection is viral, so antibiotics have no target in it.no target
- Conclude. So the infection would continue, and the antibiotics would only add risk.add risk
- Write the answer. Accept any sentence that says antibiotics do not act on viruses, so the infection would continue.
Check. Unnecessary antibiotics add risk of resistance. ✓
Method. Give the lack of effect and the risk.
- Effect. The antibiotic will not act on the virus causing the sore throat.will not act
- Risk. Unnecessary use of antibiotics encourages resistant bacteria to develop.encourages resistant bacteria
- Write the answer. Accept any answer that says the antibiotic will not kill the virus, and using it unnecessarily encourages antibiotic resistance.
Check. Responsible prescribing protects everyone. ✓
Antibiotic resistance
In any bacterial population, a few bacteria may have a random mutation that makes them resistant to an antibiotic. When the antibiotic is used, most bacteria are killed, but the resistant ones survive and reproduce. Their resistance is passed on, so the population becomes mostly resistant over time. Overuse and incomplete courses of antibiotics increase this selection pressure.
| Step | What happens |
|---|---|
| 1 | a bacterial population contains a few individuals with a random mutation |
| 2 | the antibiotic kills most bacteria, but the resistant ones survive |
| 3 | the survivors reproduce and pass the resistance gene on |
| 4 | the population is now mostly resistant |
Key ideas
- Resistance comes from random mutations that already exist in a population.
- The antibiotic is a selection pressure: resistant bacteria survive.
- Resistant bacteria reproduce, so the resistance spreads.
- Overuse and incomplete courses speed up resistance.
Method. Recall the process.
- Recall. Resistant bacteria survive and reproduce while others are killed.survive and reproduce
- Name it. This process is natural selection.natural selection
- Write the answer. natural selection
Check. Natural selection acts on existing variation. ✓
Method. Recall the source of variation.
- Recall. A random change in DNA is a mutation.random change
- Name it. So the change is a mutation.mutation
- Write the answer. mutation
Check. Most mutations are neither helpful nor harmful. ✓
Method. Think about the bacteria left behind.
- Think. An incomplete course leaves some bacteria alive.leaves some alive
- Conclude. These survivors may be the resistant ones, and they reproduce.resistant ones
- Write the answer. An incomplete course leaves some bacteria alive, and the survivors may be resistant and reproduce.
Check. Selection pressure is kept up by incomplete courses. ✓
Watch out
Watch out: antibiotics do not cause the mutation. The mutation happens at random; the antibiotic selects the resistant bacteria that are already there.
Exam tip
Exam tip. [H] When you explain resistance, say that the mutation is random, and that the antibiotic acts as the selection pressure.
Try it (with your teacher). With your teacher, use a simple model: beads of two colours, with some beads of one colour being harder to pick up. Show how the surviving beads change the make-up of the next generation.
Exercise 14C Antibiotic resistance
Method. Recall the process.
- Recall. Resistant bacteria survive and reproduce, so they become more common.survive and reproduce
- Write the answer. natural selection
Check. The antibiotic is the selection pressure. ✓
Method. Recall the source of resistance.
- Recall. A random mutation in the DNA can make a bacterium resistant.random mutation
- Write the answer. mutation
Check. Mutations happen at random. ✓
Method. Recall the cause of mutations.
- Recall. Mutations happen at random; the antibiotic only selects the resistant bacteria.happen at random
- Write the answer. So no.no
- Write the answer. no
Check. The antibiotic is a selection pressure. ✓
Method. Recall which bacteria survive.
- Recall. The antibiotic kills the non-resistant bacteria, so the resistant survive.the resistant survive
- Write the answer. resistant
Check. The survivors reproduce. ✓
Method. Recall the factors.
- Recall. Overuse and incomplete courses increase the selection pressure.selection pressure
- Choose one. Either factor is a correct answer.either
- Write the answer. Accept any one: overuse of antibiotics, or incomplete courses.
Check. Both keep resistant bacteria surviving. ✓
Method. Recall how resistance spreads.
- Recall. When resistant bacteria reproduce, they pass the resistance on to their offspring.reproduce
- Write the answer. reproduce
Check. Offspring inherit the resistance gene. ✓
Method. Subtract the killed bacteria from the total.
- Count. The antibiotic kills 98 of the 100 bacteria.98
- Remaining. The 2 resistant bacteria survive, so 2 remain.2
- Write the answer. 2
Check. 100 - 98 = 2, all resistant. ✓
Method. Compare the resistant number with the total.
- Total. If the total is 20 and all 20 are resistant, the proportion is 20 / 20.20 / 20
- Percentage. 20 / 20 = 1, so 100%.100%
- Write the answer. 100%
Check. All the survivors are resistant. ✓
Method. Think about the advantage.
- Think. The antibiotic kills the non-resistant bacteria.kills the non-resistant
- Conclude. The resistant one survives and has more offspring, so it has the advantage.more offspring
- Write the answer. Accept any sentence that says the resistance lets it survive the antibiotic that kills the others.
Check. The advantage is selective, only in the presence of the antibiotic. ✓
Method. Consider the random mutations.
- Mutation. Random mutations occur in every population, and some are resistant.occur in every population
- Selection. Even correct use kills the susceptible bacteria, so the resistant ones survive.the resistant ones survive
- Write the answer. Accept any answer that says random mutations already exist, and the antibiotic still selects the resistant ones.
Check. Correct use still selects. ✓
Required practical: antiseptics and bacterial growth (teacher demonstration)
This practical is a teacher demonstration only. A school-approved, non-pathogenic culture is used in sealed dishes, and the school’s microbiology rules apply. Pupils do not open the dishes or handle any microorganisms. The independent variable is the concentration of the antiseptic. The dependent variable is the diameter of the clear zone (the zone of inhibition). The radius is half the diameter.
| Concentration (invented) | Clear zone diameter (mm) |
|---|---|
| 1% | 4 |
| 2% | 8 |
| 4% | 12 |
| 8% | 16 |
Key ideas
- Independent variable: antiseptic concentration. Dependent variable: clear zone diameter.
- A larger clear zone means the antiseptic was more effective in that test.
- Radius = diameter / 2.
- Pupils never open the sealed dishes; the teacher handles all microbiology.
Method. Radius is half the diameter.
- Halve. Radius = 16 / 2.16 / 2
- Calculate. The radius is 8 mm.8 mm
- Write the answer. 8
Check. 8 x 2 = 16. ✓
Method. Find the largest diameter.
- Compare. The diameters are 4, 8, 12 and 16 mm.4, 8, 12, 16
- Choose. The largest is 16 mm, at 8%.8%
- Write the answer. 8%
Check. The largest zone is at the highest concentration. ✓
Method. Think about what is missing in the zone.
- Think. There are no bacteria growing in the zone around the disc.no bacteria
- Conclude. So the antiseptic has stopped their growth there.stopped their growth
- Write the answer. A clear zone shows that the antiseptic has stopped the bacteria growing in that area.
Check. The zone size compares the effectiveness. ✓
Watch out
Watch out: the diameter is across the whole clear zone, not from the centre of the disc. The radius is half the diameter.
Exam tip
Safety. This is a teacher demonstration only, under the school’s microbiology rules. Pupils do not open the dishes, and they wash their hands after any lesson with cultures. Do not use real pathogens.
Try it (with your teacher). Watch the teacher demonstration. Write down the four concentrations, and the diameter of each clear zone. Calculate the radius of each zone, and describe the pattern.
Exercise 14D Required practical: antiseptics and bacterial growth
Method. Find what is measured.
- Find it. The diameter of the clear zone is measured.diameter of the clear zone
- Write the answer. diameter of the clear zone
Check. The concentration is the independent variable. ✓
Method. Find what is changed on purpose.
- Find it. The concentration of the antiseptic is changed on purpose.changed on purpose
- Write the answer. antiseptic concentration
Check. The clear zone is measured. ✓
Method. Halve the diameter.
- Halve. Radius = 12 / 2.12 / 2
- Calculate. The radius is 6 mm.6
- Write the answer. 6
Check. 6 x 2 = 12. ✓
Method. Halve the diameter.
- Halve. Radius = 4 / 2.4 / 2
- Calculate. The radius is 2 mm.2
- Write the answer. 2
Check. 2 x 2 = 4. ✓
Method. Read the table.
- Read. The 8 mm diameter is at 2%.2%
- Write the answer. 2%
Check. Each concentration has a different zone. ✓
Method. Recall the meaning.
- Recall. A clear zone shows where bacteria cannot grow near the disc.cannot grow
- Write the answer. where bacteria cannot grow
Check. The antiseptic stops their growth. ✓
Method. Subtract the two diameters.
- Read. The 8% zone is 16 mm and the 1% zone is 4 mm.16 and 4
- Subtract. The difference is 16 - 4 = 12 mm.16 - 4 = 12
- Write the answer. 12
Check. 4 + 12 = 16. ✓
Method. Think about the risk of the culture.
- Think. Microorganisms can spread from an open dish.spread from an open dish
- Conclude. Sealing the dishes stops them escaping into the room.escaping into the room
- Write the answer. Accept any sentence that says it stops microorganisms escaping into the room.
Check. Safe practice protects everyone. ✓
Method. Find a weakness and its fix.
- Weakness. Only one disc was used at each concentration.one disc
- Fix. Repeating each concentration and taking a mean makes the zone size more reliable.more reliable
- Write the answer. Accept any sensible improvement, such as testing more concentrations, or repeating each concentration.
Check. A specific fix matches a named weakness. ✓
Method. Link the zone to the effect.
- Zone. The clear zone is the area where bacterial growth is stopped.area where growth is stopped
- Measure. A larger zone shows a stronger effect, if the other conditions are the same.stronger effect
- Conclude. So the zone diameter is a fair measure of the antiseptic’s effect.fair measure
- Write the answer. Accept any answer that says the clear zone is the area where growth is stopped, so a larger zone shows a stronger effect, as long as the other conditions are kept the same.
Check. Control the other factors. ✓
Painkillers, antiseptics and drug development [H]
Painkillers relieve pain and symptoms, but they do not kill pathogens. Antiseptics kill microorganisms on the skin or on surfaces, and they are not used inside the body.
[H] New drugs go through stages: preclinical testing in cells and animals, then clinical trials in people. Phase 1 checks safety in healthy volunteers, phase 2 finds a suitable dose in patients, and phase 3 compares the drug with an existing treatment or a placebo. In a double-blind trial, neither the patient nor the doctor knows who is given the drug and who is given the placebo, which reduces bias.
[H] Monoclonal antibodies are identical antibodies made from a single clone of lymphocytes. They bind to one specific molecule, so they can be used to target a treatment, for example to a cancer cell.
| Stage | What happens | Who is involved |
|---|---|---|
| preclinical testing | in cells and in animals, to check safety and effect | laboratory |
| clinical trial phase 1 | a small group of healthy volunteers, to check safety | volunteers |
| clinical trial phase 2 | a small group of patients, to find a suitable dose | patients |
| clinical trial phase 3 | a larger group, compared with an existing treatment or a placebo | many patients |
Key ideas
- Painkillers relieve pain; antiseptics kill microorganisms on surfaces.
- [H] Drugs are tested in cells and animals before people.
- [H] Clinical trials have phases, and a double-blind trial reduces bias.
- [H] Monoclonal antibodies are identical antibodies that bind to one target.
Method. Recall the medicine type.
- Recall. Painkillers relieve pain and symptoms.relieve pain
- Name it. So the medicine is a painkiller.painkiller
- Write the answer. painkiller
Check. Antiseptics are for skin and surfaces. ✓
Method. Recall the stage before people.
- Recall. Drugs are first tested in cells and animals, which is preclinical testing.cells and animals
- Name it. So the stage is preclinical testing.preclinical testing
- Write the answer. preclinical testing
Check. Clinical trials come after this stage. ✓
Method. Think about bias.
- Think. If the patient or doctor knew who had the drug, their expectations could bias the result.expectations
- Conclude. Keeping both unaware reduces bias, so the result is more reliable.reduces bias
- Write the answer. Neither the patient nor the doctor knows who has the drug, so their expectations cannot bias the result.
Check. A placebo is a dummy treatment. ✓
Watch out
Watch out: an antiseptic is for the skin and surfaces, not for use inside the body. A painkiller is not an antibiotic, and it does not kill bacteria.
Exam tip
Exam tip. [H] When you describe a trial, name the phase, the group of people and what the drug is compared with.
Try it (with your teacher). With your teacher, sketch the stages of drug development as a flow chart, from preclinical testing to phase 3. Add one question you would ask at each stage.
Exercise 14E Painkillers, antiseptics and drug development [H]
Method. Recall the job.
- Recall. A painkiller relieves pain and symptoms.relieves pain
- Write the answer. relieves pain
Check. A painkiller does not kill pathogens. ✓
Method. Recall the job.
- Recall. An antiseptic kills microorganisms on the skin or on surfaces.on the skin or on surfaces
- Write the answer. kills microorganisms on skin or surfaces
Check. Antiseptics are not used inside the body. ✓
Method. Recall the phase for safety.
- Recall. Phase 1 checks safety in healthy volunteers.healthy volunteers
- Write the answer. phase 1
Check. Phase 2 finds the dose in patients. ✓
Method. Recall the comparison phase.
- Recall. Phase 3 compares the drug with an existing treatment or a placebo.compares
- Write the answer. phase 3
Check. Phase 3 uses a larger group of patients. ✓
Method. Recall the trial type.
- Recall. In a double-blind trial neither the patient nor the doctor knows who has the drug.neither
- Write the answer. double-blind trial
Check. A single-blind trial hides it from only one. ✓
Method. Recall the term.
- Recall. A placebo is a dummy treatment that looks like the real drug but has no active ingredient.dummy treatment
- Write the answer. a dummy treatment with no active drug
Check. It allows comparison with the real drug. ✓
Method. Recall the source.
- Recall. Monoclonal antibodies come from a single clone of lymphocytes.single clone
- Write the answer. clone
Check. Identical antibodies bind to one target. ✓
Method. Recall the stage.
- Recall. Testing in cells and animals comes before clinical trials in people.cells and animals
- Write the answer. preclinical testing
Check. Clinical trials are the next stage. ✓
Method. Think about the comparison.
- Think. A placebo group shows the effect of taking something without the active drug.without the active drug
- Conclude. So any difference can be attributed to the drug itself.attributed to the drug
- Write the answer. Accept any sentence that says it allows the drug to be compared with a treatment that has no active ingredient.
Check. Comparison isolates the drug’s effect. ✓
Method. Think about their specificity.
- Think. Monoclonal antibodies are all identical, so they bind to one target.bind to one target
- Conclude. This allows a treatment to be aimed at a particular cell.aimed at a particular cell
- Write the answer. Accept any sentence that says they bind to one specific target, so they can be aimed at a particular cell.
Check. Targeting reduces harm to other cells. ✓
Method. Link the complexity of the body to the trial.
- Complex. A whole body has many interacting systems that cells alone do not show.interacting systems
- Fail. So the drug may be unsafe or ineffective in people, and this is only found in trials.only found in trials
- Write the answer. Accept any answer that says the body is more complex than cells, so the drug may be unsafe or not effective in people.
Check. This is why each phase is needed. ✓
Chapter summary
| Skill | Method |
|---|---|
| Vaccination | Antigen without the full disease triggers memory cells: artificial immunity; herd immunity protects others. |
| Percentage vaccinated | Vaccinated / total x 100. |
| Antibiotics | Kill or slow bacteria; do not affect viruses; do not give immunity. |
| Resistance | Random mutation, then antibiotic kills the others, resistant survive and reproduce (natural selection). |
| Agar practical | Teacher demonstration: clear zone diameter; radius = diameter / 2. |
| Painkillers and antiseptics | Painkillers relieve pain; antiseptics kill microorganisms on skin and surfaces. |
| [H] Drug development | Preclinical, then phases 1 to 3; double-blind trials reduce bias; monoclonal antibodies are identical and target one molecule. |
Can you…?
- I can explain how a vaccine gives immunity and what herd immunity means
- I can explain how antibiotics work and why they do not kill viruses
- I can describe how antibiotic resistance develops by natural selection
- I can interpret the agar-plate results and calculate a radius from a diameter
- [H] I can describe drug development, double-blind trials and monoclonal antibodies
Key terms
- vaccine
- a preparation containing an antigen that triggers immunity without the full disease
- artificial immunity
- immunity that comes from a vaccine rather than from an infection
- herd immunity
- protection of a population that results when most people are immune
- antibiotic
- a medicine that kills or slows the growth of bacteria
- antibiotic resistance
- the ability of bacteria to survive an antibiotic
- painkiller
- a medicine that relieves pain without killing pathogens
- antiseptic
- a substance that kills microorganisms on the skin or surfaces
- [H] placebo
- a dummy treatment with no active ingredient
- [H] double-blind trial
- a trial in which neither the patient nor the doctor knows who has the drug
- [H] monoclonal antibody
- an identical antibody made from a single clone of lymphocytes
Exercise 14Z Check-up
Method. Recall the type.
- Recall. Immunity from a vaccine is artificial.artificial
- Write the answer. artificial immunity
Check. It does not come from infection. ✓
Method. Recall the content.
- Recall. A vaccine contains an antigen, without the full disease.contains an antigen
- Write the answer. antigen
Check. Memory cells are triggered. ✓
Method. Recall the term.
- Recall. Herd immunity protects those who cannot be vaccinated.cannot be vaccinated
- Write the answer. herd immunity
Check. It needs a high level of vaccination. ✓
Method. Recall what antibiotics target.
- Recall. Antibiotics target bacteria, not viruses.target bacteria
- Write the answer. no
Check. Viruses are not cells. ✓
Method. Recall the process.
- Recall. Resistant bacteria survive and reproduce, so natural selection makes them common.survive and reproduce
- Write the answer. natural selection
Check. Antibiotics are the selection pressure. ✓
Method. Recall the change.
- Recall. A random change in DNA is a mutation.random change
- Write the answer. mutation
Check. Mutations occur at random. ✓
Method. Halve the diameter.
- Halve. Radius = 8 / 2 = 4.8 / 2 = 4
- Write the answer. 4
Check. 4 x 2 = 8. ✓
Method. Divide the vaccinated by the total, then multiply by 100.
- Divide. 100 / 200 = 0.5.100 / 200 = 0.5
- Multiply. Multiply by 100 to give 50%.50%
- Write the answer. 50%
Check. 50% of 200 is 100. ✓
Method. Recall the medicine.
- Recall. A painkiller relieves pain and does not kill pathogens.does not kill pathogens
- Write the answer. painkiller
Check. Antibiotics kill bacteria. ✓
Method. Think about the survivors.
- Think. An incomplete course leaves some bacteria alive.leaves some alive
- Conclude. Those survivors may be resistant and reproduce, spreading resistance.spreading resistance
- Write the answer. Accept any sentence that says some bacteria survive and may be resistant, and they reproduce.
Check. Survival and reproduction spread the resistance. ✓
Total 25 marks. Allow about 25 minutes.
Exercise 14X Exam-style questions
Method. Recall the medicine.
- Recall. Antibiotics kill bacteria.kill bacteria
- Write the answer. antibiotic
Check. Antibiotics do not kill viruses. ✓
Method. Recall the type.
- Recall. Immunity from a vaccine is artificial.artificial
- Write the answer. artificial immunity
Check. Natural immunity comes from infection. ✓
Method. Recall the process.
- Recall. Resistant bacteria survive and reproduce, so they become common.become common
- Write the answer. natural selection
Check. Antibiotics are the selection pressure. ✓
Method. Give the difference and the consequence.
- Virus. A virus is not a cell and reproduces inside host cells.not a cell
- Antibiotic. Antibiotics target bacteria, so they do not kill the virus.do not kill
- Write the answer. Accept any answer that says viruses are not cells and antibiotics target bacteria, so they would not kill the virus.
Check. The target must match the pathogen. ✓
Method. Follow the vaccine through the body.
- Antigen. The vaccine contains an antigen without the full disease.contains an antigen
- Response. Lymphocytes make antibodies and memory cells.memory cells
- Protection. On later exposure, the memory cells respond quickly, so the person is protected.protected
- Write the answer. Accept any three of: the vaccine contains an antigen; lymphocytes make memory cells; antibodies are made; the person is protected on later exposure.
Check. Memory cells provide the protection. ✓
Method. Describe the spread and the protection.
- Immune. When most people are immune, the pathogen has few people to infect.few people to infect
- Spread. So the pathogen cannot spread easily through the population.cannot spread easily
- Protection. People who cannot be vaccinated are therefore less likely to meet the pathogen.less likely to meet
- Write the answer. Accept any answer that says most people are immune, the pathogen cannot spread easily, so those who cannot be vaccinated are protected.
Check. Herd immunity is a community effect. ✓
Method. Calculate the radius, then describe the trend.
- Radius. The radius at 4% is 12 / 2 = 6 mm.12 / 2 = 6
- Pattern. The clear zone gets larger as the concentration of the antiseptic rises.gets larger
- Write the answer. Accept 6 mm, and a sentence that says the clear zone gets larger as the concentration rises.
Check. The diameters rise from 4 to 16 mm. ✓
Method. Follow the population through the treatment.
- Mutation. A random mutation gives a few bacteria resistance.random mutation
- Antibiotic. The antibiotic kills the non-resistant bacteria.kills the non-resistant
- Survive. The resistant bacteria survive and reproduce.survive and reproduce
- Result. So the population becomes mostly resistant over time.mostly resistant
- Write the answer. Accept any four of: a random mutation gives resistance; the antibiotic kills the non-resistant bacteria; resistant bacteria survive and reproduce; the population becomes mostly resistant.
Check. Natural selection is the mechanism. ✓
Method. Follow the drug from the laboratory into patients.
- Preclinical. The drug is first tested in cells and animals.cells and animals
- Phase 1. Phase 1 checks safety in a small group of healthy volunteers.healthy volunteers
- Phase 2. Phase 2 finds a suitable dose in a small group of patients.suitable dose
- Phase 3. Phase 3 compares the drug with an existing treatment or a placebo, in many patients.compares
- Write the answer. Accept any four of: preclinical testing in cells and animals; phase 1 safety in healthy volunteers; phase 2 dose in patients; phase 3 comparison with an existing treatment or placebo.
Check. Each phase answers a different question. ✓
Method. Describe the blinding and the placebo.
- Blind. In a double-blind trial neither the patient nor the doctor knows who has the drug.neither
- Bias. This reduces bias from expectations, so the result is more reliable.reduces bias
- Placebo. A placebo is a dummy treatment with no active ingredient.dummy treatment
- Write the answer. Accept any answer that says neither patient nor doctor knows who has the drug, which reduces bias, and that a placebo is a dummy treatment with no active ingredient.
Check. The placebo is the control for the drug. ✓