B6 Synthesis: Required Practicals and Exam Skills

You have now worked through the whole of Topic B6 of OCR Gateway Science A — health and disease, pathogens, the immune system, vaccination and antibiotics, developing medicines, non-communicable disease, feeding the population and protecting the environment. This final lesson pulls it all together as one big idea: applying biology to real-world global challenges. It revisits the B6 required practical (microbiology and the zone of inhibition), drills the calculations and the correlation-versus-cause reasoning that earn reliable marks, and warns you about the misconceptions that catch students out. Treat it as a revision and exam-technique session rather than new content.

By the end you should be able to see how the three strands of B6 connect, recall the required practical and its $\pi r^2$πr2 calculation, reason carefully about correlation and cause, and avoid the most common B6 errors.

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How the B6 Topics Fit Together

Topic B6 is best seen as three strands of a single challenge — keeping people and the planet healthy.

flowchart TD
  A["Global challenges (B6)"] --> B["Human health"]
  A --> C["Feeding the population"]
  A --> D["Protecting the environment"]
  B --> B1["Communicable disease:<br/>pathogens, immunity,<br/>vaccines, antibiotics"]
  B --> B2["Non-communicable disease:<br/>risk factors, lifestyle,<br/>cardiovascular, cancer"]
  C --> C1["Selective breeding + GM crops"]
  C --> C2["Biotechnology + sustainable fishing"]
  D --> D1["Monitoring: indicator species<br/>+ sensors"]
  D --> D2["Maintaining: conservation,<br/>reforestation, less pollution"]

Notice how the strands connect: a virus (communicable) such as HPV can cause cancer (non-communicable); genetic engineering appears in both food (GM crops, GM insulin) and medicine (monoclonal antibodies are a related idea); and sustainable farming and fishing link the food strand to the environment strand. Spotting these links is exactly the kind of synoptic thinking that lifts an answer.

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The B6 Required Practical at a Glance

Practical	What you do / measure	Key technique	Top marks come from
Investigating antimicrobials (microbiology)	Add antibiotic/antiseptic discs to bacteria on agar; measure the zone of inhibition	Aseptic technique; measure the clear-zone diameter	Flaming the loop; incubating at ≤ 25 °C in school; using $\text{area} = \pi r^2$area=πr2 with the radius

The single biggest idea is aseptic technique — keeping unwanted microbes out — and the single biggest calculation is the area of the zone of inhibition.

Exam Tip: Two aseptic details score most often: flame the inoculating loop to sterilise it, and incubate school cultures at no more than 25 °C so that pathogens harmful to humans are unlikely to grow. Always give the reason, not just the action.

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Mastering the B6 Calculation: Zone of Inhibition

The zone of inhibition is a circle, so its area uses:

$\text{area} = \pi r^2$area=πr2

Always halve the diameter to find the radius first. Here is a fresh worked example so you can check your method.

Worked example: An antiseptic produces a clear zone of diameter $16 \text{ mm}$16 mm. Calculate the area of the zone of inhibition. (Use $\pi = 3.14$π=3.14.)

Step 1 — find the radius:

$r = \frac{16 \text{ mm}}{2} = 8 \text{ mm}$r=216 mm​=8 mm

Step 2 — apply the formula:

$\text{area} = \pi r^2 = 3.14 \times 8^2 = 3.14 \times 64 = 200.96 \text{ mm}^2$area=πr2=3.14×82=3.14×64=200.96 mm2

Answer: $200.96 \text{ mm}^2$200.96 mm2 (about $201 \text{ mm}^2$201 mm2). A larger clear zone means a more effective antimicrobial.

Exam Tip: Show three lines — formula, substitution, answer with unit — and use the radius, not the diameter. The unit is $\text{mm}^2$mm2 because it is an area. Method marks are awarded for visible working even if the arithmetic slips.

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Correlation versus Cause: The Key Reasoning Skill

Across B6 — especially for non-communicable disease — you must reason carefully about whether a link proves cause.

• A correlation means two things change together (e.g. more smoking and more lung cancer).
• A correlation alone does not prove cause — there could be a third factor, or coincidence.
• Scientists accept a causal link only when there is a clear correlation, a plausible biological mechanism, and the result is found repeatedly in many studies.

Exam Tip: When a graph shows a risk factor "linked" to a disease and you are asked whether it proves cause, the safe answer is no — correlation does not prove cause; you also need a mechanism and repeated evidence. This phrasing earns marks reliably.

Reading data and graphs in B6

Several B6 ideas are tested through data — risk-factor graphs, zone-of-inhibition results, indicator-species surveys. A reliable routine:

1. Read the axes (or table headings) first — what is plotted against what, and in what units?
2. Describe the trend in words, using comparative language ("the disease rate rises as exposure increases").
3. Quote figures from the data to support what you say.
4. If asked to explain or judge cause, give the biology (a mechanism) and remember that correlation is not proof of cause.

Memory checklist — the facts to know cold

Cover the right-hand column and test yourself.

Prompt	Answer
Definition of health	Physical, mental and social wellbeing, not merely absence of disease
Four types of pathogen	Bacteria, viruses, fungi, protists
How bacteria vs viruses make us ill	Bacteria reproduce fast + release toxins; viruses reproduce inside cells and damage them
Three white-blood-cell roles	Phagocytosis, antibodies (to antigens), antitoxins
What a vaccine contains	Dead/inactivated pathogen or its antigens
Antibiotics work on…	Bacteria only — not viruses
How resistance arises	Mutation → resistant bacteria survive and reproduce (natural selection)
Zone of inhibition area	$\text{area} = \pi r^2$area=πr2 (use the radius)
Drugs from nature	Willow → aspirin; foxglove → digitalis; Penicillium → penicillin (Fleming)
Drug-testing order	Cells/tissues → animals → healthy volunteers → patients
Benign vs malignant	Benign stays put; malignant invades and spreads
Mycoprotein source	The fungus Fusarium (grown in a fermenter)
Air-pollution indicator	Lichens (present = clean air)
Clean vs polluted water indicators	Mayfly larvae = clean; sludgeworms = polluted

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Command Words You Will Meet in B6

Command word	What it asks for
State / Name / Give	A short fact, no explanation
Describe	Say what happens, in order, with no reasons
Explain	Give reasons why — use "because", "so that"
Compare	Give similarities and differences
Calculate	Work out a number — show working and give a unit
Suggest	Apply your knowledge to an unfamiliar context
Evaluate	Weigh advantages and disadvantages and reach a judgement

Exam Tip: B6 has many evaluate questions (e.g. on vaccination, GM crops or treatments). An evaluate answer must give points on both sides and end with a conclusion or judgement.

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Planning and Evaluating: The Skills OCR Tests

Beyond the required practical, OCR expects you to plan and evaluate investigations. The same ideas recur, so learn them as a checklist for any B6 practical:

• Variables. Identify the independent variable (what you change — e.g. the type of antibiotic), the dependent variable (what you measure — e.g. the zone of inhibition), and the control variables (what you keep the same — e.g. the bacterium, the agar, the temperature, the disc size).
• A fair test. Controlling the other variables means any difference in the result is due to the independent variable alone.
• Repeats and a mean. Repeating and taking a mean reduces random error and improves reliability; identify and ignore anomalies.
• Accuracy and resolution. Use equipment of suitable resolution (e.g. a ruler reading to $1 \text{ mm}$1 mm for the zone).
• Safety. Identify hazards and precautions — for microbiology, aseptic technique and incubating at ≤ 25 °C in school.