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MYP Biology Criterion B: Inquiring & Designing FAQ
Answered by RevisionPrep's IB Educators
Criterion B trips up more MYP Biology students than any other criterion — not because the science is hard, but because the writing has to hit specific strands examiners can tick off. Here's what actually earns marks, answered by RevisionPrep's IB Educators.
Understanding Criterion B
How do you score well on Criterion B in MYP Biology?
You score well by writing a testable research question with variables named, a hypothesis justified with real scientific reasoning (not just a guess), and a method detailed enough that a classmate could replicate it exactly. Vague questions and unexplained hypotheses are what cost students the top band.
MYP Biology Criterion B: Inquiring and Designing has four strands, and I mark them separately even though students often blur them together:
- Explain a problem or question — state it clearly, tied to a real-world or scientific context.
- Formulate a testable hypothesis with scientific reasoning — say what you predict AND why, using biology concepts.
- Explain how to manipulate variables and control risks — name IV, DV, at least 3 controlled variables, and any safety/ethical concern.
- Design a logical, complete method — enough detail (equipment, quantities, repeats) for replication.
According to the MYP: From Principles into Practice guide, Criterion B is marked out of 8, in bands of 1–2, 3–4, 5–6, 7–8 against task-specific clarifications your teacher writes for each investigation.
What are the four strands of Criterion B in MYP Biology?
The four strands are: explaining a problem/question, formulating a testable hypothesis with scientific reasoning, explaining how to manipulate variables and address safety/ethical/environmental factors, and designing a logical, complete, replicable method. Each strand is assessed on its own descriptor, so weakness in one drags the whole grade down.
Quick tip: before you submit, go through your write-up strand by strand and highlight where each one is addressed. If you can't point to a sentence for a strand, it isn't there — the marker won't infer it.
What is the maximum mark for Criterion B in MYP Biology?
Criterion B is marked out of 8, the same maximum as Criteria A, C and D in MYP Sciences. Your final subject grade combines all four criteria out of 32 total, then converts to the 1–7 MYP grade using your school's grade boundaries.
| Criterion | Focus | Max marks |
|---|---|---|
| A | Knowing and understanding | 8 |
| B | Inquiring and designing | 8 |
| C | Processing and evaluating | 8 |
| D | Reflecting on impacts of science | 8 |
Writing a strong hypothesis and method
How do you write a good hypothesis for MYP Biology?
A good hypothesis states the predicted relationship between your independent and dependent variables AND explains why, using biology content you've actually studied. "I think enzyme activity will increase" earns almost nothing; "as temperature rises towards 37°C, catalase activity will increase because higher kinetic energy increases enzyme-substrate collisions" earns top marks.
Worked example — investigating light intensity and photosynthesis rate in Elodea:
Weak hypothesis: "More light will make the plant photosynthesise faster."
Strong hypothesis: "As light intensity increases from 0 to 8000 lux, the rate of oxygen bubble production by Elodea will increase, because light-dependent reactions require photons to excite electrons in chlorophyll, and more photons per second means a faster rate of ATP and NADPH production for the Calvin cycle — up to the point where another factor (likely CO₂ concentration) becomes limiting."
Notice the second version names the variables, gives the mechanism, and even anticipates a limiting factor — that last bit is what separates a 7–8 from a 5–6.
How detailed does a method need to be for Criterion B?
Your method needs enough detail that a classmate with no prior knowledge of your experiment could follow it and get comparable results. That means named equipment, exact quantities or concentrations, number of trials/repeats, and the sequence of steps in logical order — not a vague summary of what you did.
Common mistake: students write "measure the temperature and record the results" instead of "use a digital thermometer to record temperature every 60 seconds for 10 minutes, repeating the trial three times per temperature setting." The second version is what earns marks in the top band because it's actually replicable.
What counts as a controlled variable in a Biology experiment?
A controlled variable is anything besides your independent variable that could affect your dependent variable if left unchecked — and that you deliberately keep constant across all trials. In an enzyme investigation, that's substrate concentration, pH, volume of enzyme solution, and reaction time.
Checklist for naming controlled variables well:
- Say what you're controlling (e.g. pH of the buffer solution).
- Say how you're controlling it (e.g. using a pH 7 buffer measured with a pH probe).
- Say why it matters (e.g. pH affects enzyme active site shape).
A list of variables with no "how" or "why" only scrapes the middle bands.
How do you identify independent and dependent variables in Biology?
The independent variable (IV) is the one you deliberately change — temperature, light intensity, concentration. The dependent variable (DV) is what you measure in response — reaction rate, growth rate, number of bubbles. If you're not deliberately changing it and not measuring it as an outcome, it's a controlled variable instead.
Quick tip: ask yourself "what am I changing on purpose?" (IV) and "what am I recording as a result?" (DV). Everything else that could affect the result goes on your controlled variables list.
Common mistakes and how the criterion is assessed
What mistakes do students make on Criterion B?
The most common mistake is writing a hypothesis without scientific reasoning — just predicting an outcome with no "because". Others include vague methods missing quantities, forgetting to mention safety or ethical considerations, and confusing the research question with the hypothesis. Any one of these caps you in a lower band even if the rest is strong.
In fifteen years of marking these investigations, the single biggest mark-loser I see is students copying a method from a textbook or lab manual almost word for word, then wondering why it scored low on originality and detail relevant to their own specific investigation. Markers want YOUR variables, YOUR context, YOUR quantities.
How is Criterion B different from Criterion C in MYP Biology?
Criterion B is about planning your investigation before you run it — the question, hypothesis, variables, and method. Criterion C is about what happens after — processing your actual data, evaluating your method's validity, and suggesting improvements. Think of B as the design phase and C as the analysis phase.
| Criterion | Stage | Key question it answers |
|---|---|---|
| B | Before the experiment | What am I testing, and how? |
| C | After the experiment | What did I find, and how reliable is it? |
Does Criterion B require safety and ethical considerations?
Yes — the strand on manipulating variables also asks you to explain how you'll address safety, ethical, and environmental factors relevant to your investigation. For a Biology practical this might mean handling hot equipment safely, treating living organisms ethically, or disposing of chemicals responsibly.
Even a simple enzyme practical needs at least a line on this — e.g. "hydrogen peroxide is an irritant, so goggles and gloves were worn, and any Elodea used was returned to its aquarium after the investigation rather than discarded." Skipping this entirely is a common reason students don't reach the top band.
Parent & study-support questions
How can I help my child improve their Criterion B marks?
The best thing you can do is ask your child to explain their hypothesis out loud before they write it — if they can't say why they think something will happen, using real biology content, the written version won't score well either. Past task-specific clarifications from their teacher are the clearest guide to what's expected.
Encourage your child to keep a simple log of past investigations and the feedback received — patterns in feedback (e.g. "needs more detail on controlled variables") repeat far more often than students expect, and spotting the pattern is half the fix.
Is MYP Biology Criterion B similar across all IB schools?
The four strands and the descriptors come from the same IB document — the MYP: From Principles into Practice guide — so they're consistent across schools worldwide. What varies is the task-specific clarification each teacher writes to adapt the general descriptor to a particular investigation, so it's worth asking your child's teacher for theirs.
This is why comparing marks between two schools directly can be misleading — the underlying criterion is standard, but the specific task and its clarification aren't identical.
What resources help with MYP Biology Criterion B practice?
Practising with model investigations that show a full worked hypothesis, variable list, and method — then comparing against the criterion strands — is the fastest way to internalise what's expected. RevisionPrep's MYP Biology Revision Notes and Topical Worksheets include exactly this kind of worked practice alongside the wider MYP Sciences criteria.
If your child is preparing for the transition into DP Sciences, strong Criterion B habits — clear variables, justified hypotheses, replicable methods — carry directly into the internal assessment work expected at Diploma level.
Criterion B vs Criterion C in MYP Sciences
| Aspect | Criterion B | Criterion C |
| Stage | Before experiment | After experiment |
| Focus | Question, hypothesis, method | Data, evaluation, improvements |
| Max marks | 8 | 8 |
| Key skill | Designing a testable plan | Analysing and evaluating results |
For worked investigation examples, task-specific clarification breakdowns, and full-mark hypothesis models across all four MYP Sciences criteria, explore the MYP Biology Revision Notes and Topical Worksheets on revisionprep.com.