Natural Sciences is not one subject and has no pack of its own. One cross-disciplinary question worked end to end below, then a plain map from your Part IA choices to the pack that holds questions of that shape.
Cambridge Natural Sciences interviewers care less about how much biology, chemistry or physics you have memorised than whether you can reason across all three at once. The material behind this page draws on the site's Biological Sciences pack: ten questions running from warning colouration and mimicry to the Meselson-Stahl DNA-replication experiment, each one argued through rather than simply answered. Most NatSci candidates sit two or three science subjects, of which this is one.
The Biological Sciences pack — £180
Ten questions across 47 pages. Every question appears once on its own, once with the hints to reach for when you stall, and once worked through to a finished answer. One PDF, one payment, instant download.
Get the Biological Sciences pack — £180Cambridge Natural Sciences interviews rarely start with a definition. More often they start with a graph you have not seen before, a short data set, a specimen, or a scenario — and the immediate expectation that you begin reasoning out loud. Natural Sciences (NatSci) is the broadest course Cambridge offers: first-year students study three experimental subjects and one mathematics course before specialising from the third year, so interviewers are not testing depth in a single field so much as your ability to think like a scientist across disciplines — noticing a pattern, proposing a mechanism, and revising it the moment new evidence contradicts you. That is also why Natural Sciences has no pack of its own on the resource hub: the thirty packs there are organised by discipline, and a Natural Sciences candidate is interviewed across two or three of them. Below, one cross-disciplinary question is answered from its first line to its last - the question, the nudges an interviewer would release, a step of my own that a check on the units destroys, and the arithmetic that replaces it - and after it, a map from the eight Part IA subjects to the packs that do and do not exist for them.
Most Natural Sciences applicants have two interviews at their college of application, each lasting 20–30 minutes and conducted by two academics. Colleges typically pair interviews to your intended subject choices — a candidate applying with Biology and Chemistry in mind might have one interview weighted towards biological sciences and a second towards physical sciences or mathematics, though the exact split varies by college. A small number of candidates are called for a third interview if their college is considering pooling them to another college. The interview itself is not an exam. It is closest in feel to a supervision, the small-group teaching format Cambridge uses throughout the degree — you will be handed a problem, given time to think, and expected to talk through your reasoning while the interviewer probes, redirects, or extends your answer.
Since October 2024 (for 2025 entry), all Natural Sciences applicants have been required to sit the Engineering and Science Admissions Test (ESAT), which replaced the previous Natural Sciences Admissions Assessment (NSAA). The ESAT is a computer-based test delivered at Pearson VUE centres worldwide, made up of five 40-minute modules of 27 questions each. Mathematics 1 is compulsory for every candidate, and you choose two further modules from Biology, Chemistry, Physics and Mathematics 2 depending on your intended subjects. ESAT performance directly affects whether you receive an interview invitation, so preparation for the test and preparation for the interview should run in parallel rather than as separate projects — see our dedicated ESAT preparation page for module-by-module guidance.
Natural Sciences is Cambridge's largest Tripos by student numbers, taught across 14 departments spanning the Schools of Biological Sciences and Physical Sciences, plus the Department of History and Philosophy of Science. In the most recent year for which Cambridge has published full admissions figures, 2,594 students applied to Natural Sciences and 577 were admitted — an acceptance rate of approximately 22%, though competition varies by intended subject combination and college. Roughly half of NatSci students go on to specialise in biological sciences and half in physical sciences from Part II onwards. Typical offers are A*A*A at A-level, or 41–42 points in the IB with 776 at Higher Level, with Mathematics required alongside two further subjects from Biology, Chemistry, Physics or Further Mathematics. Full course and entry details are published on the official Cambridge Natural Sciences course page.
| Factor | Cambridge Natural Sciences |
|---|---|
| Annual applicants (latest published year) | ~2,594 |
| Annual admissions (latest published year) | ~577 |
| Acceptance rate | ~22% |
| Typical A-level offer | A*A*A |
| Typical IB offer | 41–42 points (776 at HL) |
| Required subjects | Maths + 2 of Biology / Chemistry / Physics / Further Maths |
| Pre-interview test | ESAT (from 2024 entry; replaced NSAA) |
| Interview format | 2 interviews, 20–30 min each, 2 academics |
| Departments delivering the course | 14 |
| Part IA (Year 1) subject choice | 3 of 8 experimental subjects + 1 of 2 maths routes |
The most common misconception is that Natural Sciences interviewers want candidates who already know the answer. They do not — most questions are deliberately built around material you have not encountered before. What they are assessing is the quality of your scientific thinking under pressure. Specifically, interviewers at Cambridge Natural Sciences look for five things:
1. Cross-disciplinary reasoning. Can you connect a concept from chemistry to a question that is framed biologically, or use a physical principle to explain a pattern in a data set? NatSci interviewers reward candidates who reach across subject boundaries without being told to.
2. Comfort with quantitative reasoning. Even biology-heavy interviews frequently involve a calculation, an estimation, or a graph. Candidates who freeze when numbers appear in a biological context are at a real disadvantage — Natural Sciences assumes fluency with mathematics across every specialisation.
3. Willingness to revise a hypothesis. Interviewers often give you a piece of new information partway through a question specifically to see whether you update your reasoning or defend your first answer. Revising your position when the evidence changes is a scientific virtue, not a sign of weakness.
4. Precise scientific language. "The rate goes up" is not the same as "the rate increases exponentially with temperature, consistent with the Arrhenius relationship." Precision in how you describe a pattern signals precision in how you are actually thinking about it.
5. Genuine curiosity. The strongest interviews end with the interviewer extending the question — "now what would happen if the pressure doubled?" — and the candidate engaging with real interest rather than relief that the original question is over. Interviewers who conduct these interviews every year remember the candidates who seemed excited by the science.
Because Natural Sciences spans four disciplines in the first year, the topics tested at interview are correspondingly broad. There is no single pack to map them onto, because questions of each shape sit in the pack for the discipline they belong to. The areas that come up most often are:
Cellular and molecular biology. Osmosis and membrane transport, enzyme kinetics, and questions that ask you to interpret an unfamiliar diagram of a cell process are common starting points. A typical question gives you an observation — a cell shrinking in a particular solution, or an enzyme's activity plateauing at high substrate concentration — and asks you to propose and test a mechanism.
Physical and organic chemistry. Reaction rates, equilibrium, and the shapes of titration or reaction-progress curves appear regularly, often via a graph you are asked to interpret cold. Interviewers are less interested in whether you recall the named law and more interested in whether you can reason from first principles about why a curve has the shape it does.
Mechanics and physical reasoning. Classic Cambridge physical-reasoning questions — why a spinning object resists falling, how the mean free path of a gas changes with pressure, how to estimate a physical quantity using dimensional analysis alone — test your ability to build a model from basic principles rather than recall a formula.
Quantitative and mathematical reasoning. Order-of-magnitude estimation, exponential growth and decay, and simple calculus applied to a scientific context (finding a rate of change, or a maximum) are woven through interviews regardless of your intended biological or physical specialisation.
Cross-disciplinary synthesis. The strongest Natural Sciences questions deliberately sit between subjects — for example, connecting enzyme kinetics to the mathematics of reaction rates, or using a physical principle to explain a biological structure. These questions specifically reward candidates who do not mentally partition biology, chemistry, physics and maths into separate boxes.
Everything above describes the interview. What follows is one question answered in full, in the three sections a paid pack uses — Questions, then Prompts, then Suggested answers — the guidance meant to be read only after your own attempt. Cover the last two before reading them.
A single-celled organism is a sphere of radius r. It takes in oxygen through its surface and consumes it throughout its volume.
(a) How does the oxygen supply available to each unit of cytoplasm depend on r?
(b) One species has cells ten times the radius of another’s. What has happened to that quantity?
(c) A molecule diffuses a distance x in a time of order x2/D. Take D = 2 × 10−9 m2 s−1. How long does oxygen take to reach the centre of a cell of radius 10 µm? Of one of radius 1 mm? What does the comparison say about why a large organism is not simply a large cell?
These are the nudges an interviewer releases one at a time, and only once you have stalled. In a pack they sit on their own page between the questions and the answers.
I will start with the geometry, because both halves of part (a) are geometric. The surface of a sphere is 4πr2 and its volume is (4/3)πr3. Oxygen arrives through the surface and is consumed through the volume, so the quantity I want is the ratio of the two: 4πr2 divided by (4/3)πr3, which is 3/r. Supply per unit of cytoplasm therefore falls as the cell grows, and it falls in proportion to 1/r.
I nearly said something weaker first: a bigger cell has more surface, so it takes in more oxygen, so bigger is better — true and useless, because that compares a supply with a supply rather than with the demand it has to meet. The ratio is the object, not either term inside it.
Part (b) then costs nothing. Multiply the radius by ten and 3/r divides by ten: every unit of cytoplasm has a tenth of the oxygen supply it had before.
Part (c) is where I went wrong in a way worth showing. Ten microns is 1 × 10−5 m, so x2 is 1 × 10−10 m2, and dividing by 2 × 10−9 m2 s−1 gives 0.05 s. Then I reached for the millimetre case by saying a millimetre is a hundred times ten microns, so the time is a hundred times 0.05 s, or 5 s — and I said it out loud before checking it.
It does not survive the units. D is measured in metres squared per second, so the only quantity you can build from x and D that comes out in seconds is x2/D: the distance enters squared, not linearly, which is what the expression I had been handed already said. A millimetre is 1 × 10−3 m, so x2 is 1 × 10−6 m2, and 1 × 10−6 divided by 2 × 10−9 is 500 s. Against 0.05 s that is a factor of ten thousand — the hundredfold change in radius, squared. Five hundred seconds is more than eight minutes.
That answers the last part on its own. A cell of that size would spend more than eight minutes getting oxygen to a centre that had been consuming it throughout. So a large organism cannot be a large cell — and there are three ways out rather than one. It can stop being a sphere, since a flattened or branched shape buys surface area at fixed volume and cheats 3/r rather than obeying it. It can move the fluid instead of relying on diffusion, which is what a circulation is for. Or it can stay small and be many cells at once. I would offer all three and say which one I thought the question pointed at.
Very little of that was knowledge. The geometry is GCSE, the arithmetic is two divisions, and the diffusion relation was handed over inside the question. What is being watched is whether you reach for a ratio when you are asked about supply against demand, whether you check a scaling against its units before you trust it, and whether you say so out loud when the check fails. It is also three subjects at once: the biology sets the problem, the physics supplies the constraint, and the mathematics decides the answer goes as the square. A candidate who keeps those in separate boxes answers part (a) and stops.
Four of the nine free samples are Natural Sciences disciplines.
The resource hub carries nine free sample PDFs between its thirty packs, and Biology, Chemistry, Physics and Maths — four first-year Natural Sciences disciplines — are four of the nine. That is the useful accident of applying for a Tripos rather than for a subject: you can read finished questions and finished answers on both sides of your own first year without paying for anything. The Biology sample works the giraffe cardiovascular question through in full; the Physics sample runs to eight pages carrying two questions, their hints and their solutions.
Read one from each side of your subject combination before deciding whether a paid pack at £180 is worth it to you.
Read the free samples ↓The packs are organised by discipline and your interview is not, so the decision is made from your Part IA choices rather than from the course name. Read the table with those choices in front of you, not your UCAS subject line.
| If your Part IA choices lean | The pack holding questions of that shape | Free sample to read first |
|---|---|---|
| Biomolecules and Cells; Biodiversity, Evolution and Ecology; Biomedical Sciences | Biological Sciences, with Evolution & Behaviour and Physiology beside it | Biology sample |
| Chemistry | Inorganic Chemistry, where most Chemistry candidates start, with Organic Chemistry and the two Biochemistry sets beside it | Chemistry sample |
| Physics | Dynamics and Fields, the Physics pack | Physics sample |
| Either mathematics course | Maths I, the one to open first of the five Maths sets | Maths sample |
| Earth Sciences; Introduction to Experimental Psychology; Materials Science | Nothing on the hub is written for these three | — |
The last row is the limitation worth stating before you spend rather than after: three of the eight Part IA experimental subjects have no pack, so a candidate whose interview is likely to sit on Earth Sciences or Materials Science is buying for part of their timetable and not the whole of it. Everybody else is buying two, because the interview crosses disciplines and the packs do not.
Match your Part IA subjects to a pack — £180 each →Thinking aloud is a skill every Oxbridge interview rewards, but Natural Sciences adds a second layer: you also need to narrate which discipline you are reasoning from, and when you are switching. The technique is this: name the principle you are reaching for as you reach for it. "I'm going to think about this using conservation of energy first, since that's the physical constraint." "This looks like it could be a diffusion-limited process, so let me check whether the rate depends on concentration the way Fick's law predicts." Each of these statements costs nothing and gives the interviewer a clear window into your reasoning, which is exactly what they are trying to assess.
When a question sits between two disciplines — as many of the best NatSci questions deliberately do — say so explicitly. "This feels like it needs both a biological explanation and a physical one — let me start with the physical constraint and then see what it implies biologically." Interviewers respond well to candidates who recognise cross-disciplinary structure without being told, because that recognition is precisely what the first two years of the Tripos are designed to build.
That habit is the whole of what the packs drill. Each question arrives bare, the prompts arrive one at a time only if you stall, and the answer is written as somebody reasoning rather than as somebody concluding — at the length of the walkthrough above, not a paragraph.
Effective preparation for Natural Sciences has to cover more ground than a single-subject interview, so structure matters. Here is a realistic six-to-eight week plan.
Weeks 1–2: Diagnosis and foundation. Identify which of your intended Part IA subjects is weakest at interview-style reasoning rather than exam recall — for most candidates this is whichever science they are not planning to specialise in early. Read the free sample for that discipline before anything else: it is the cheapest way to see the standard an answer is expected to reach, and it costs neither money nor a week of the plan.
Weeks 3–4: ESAT and unseen-problem practice. Work through ESAT-style questions across Mathematics 1 and your chosen modules under timed conditions, alongside unseen interview-style problems. The two reinforce each other: both are testing whether you can apply first-principles reasoning to material you have not seen before.
Weeks 5–6: Cross-disciplinary mock interviews. Find someone who can ask questions that deliberately sit between two of your intended disciplines, and practise narrating your reasoning aloud while they push back. A teacher of either science will do, provided they are willing to change the discipline on you mid-answer instead of waiting politely for the end. Written questions will not change discipline on you halfway through an answer. A person will, and that is the half of the rehearsal you cannot run alone.
Weeks 7–8: Consolidation and review. Revisit the questions you found hardest and re-work them from scratch without the model answer in front of you. In the final days before your interview, return to problems you can solve fluently so you walk in confident rather than anxious.
The strongest Natural Sciences performances are rarely the ones with the fewest errors. Interviewers describe the same pattern year after year: the candidate who reaches the right answer silently in two minutes is less memorable than the candidate who takes seven minutes, tries an approach that does not work, says so, tries a second approach, and narrates the reasoning throughout. The interview is a preview of a supervision — the one-to-one and small-group teaching format Cambridge uses for the entire degree — and what tutors are really asking is whether they could spend the next three or four years teaching you.
Twenty-five minutes is enough to settle it, provided the right things are visible: structured thinking, comfort moving between disciplines, willingness to revise a position mid-sentence, and real interest in the science rather than in the offer. It is why the answers in the packs are written as somebody thinking rather than as somebody concluding, and why the walkthrough above keeps the line that failed instead of quietly deleting it: the version of an answer that shows its own wrong turn is the version that teaches the habit.
"I had no idea what to expect from my interview at Magdalen — A-level gives you no preparation for the style of question they ask. Working through the pack beforehand meant I'd practised thinking through problems I'd never seen before and talking through my reasoning out loud. When I got stuck in the actual interview, I knew how to keep going rather than freeze. I got my offer in January."— James H., Mathematics, Magdalen College Oxford, 2024 entry
“My panel at Gonville & Caius handed me a short article about a clinical trial and asked what I thought the key limitation was. I’d never seen the paper before. The pack was the only preparation I found that actually trains you for that — reading through the model answers showed me how to reason about evidence out loud, identifying what is missing or uncertain rather than just summarising what is there. By the time I got into the room I knew how to think, not just what to say.”— Priya S., Medicine, Gonville & Caius Cambridge, 2024 entry
Most Natural Sciences candidates have two interviews at their college of application, each lasting 20–30 minutes and conducted by two academics. Interviews are usually paired to your intended subjects — for example, one interview weighted towards biological sciences and one towards physical sciences or mathematics — though the exact split depends on your college and subject choices. A small number of candidates are called for a third interview if their college is considering pooling them to another college.
The Engineering and Science Admissions Test (ESAT) has been required for all Cambridge Natural Sciences applicants since October 2024 (for 2025 entry), when it replaced the previous Natural Sciences Admissions Assessment (NSAA). The ESAT is a computer-based test made up of five 40-minute modules of 27 questions each, sat at Pearson VUE centres worldwide. Mathematics 1 is compulsory for every candidate, and you choose two further modules from Biology, Chemistry, Physics and Mathematics 2. ESAT performance directly affects whether you are invited to interview.
In your first year (Part IA) at Cambridge, Natural Sciences students choose three experimental subjects from eight options — Biodiversity, Evolution and Ecology; Biomedical Sciences; Biomolecules and Cells; Chemistry; Earth Sciences; Introduction to Experimental Psychology; Materials Science; and Physics — plus one of two mathematics courses. Your interview will typically focus on the subjects you have indicated as your intended choices, so a candidate leaning towards Chemistry and Physics should expect quantitative, physical-science-led questions, while a candidate leaning towards the biological sciences should expect more questions rooted in cellular and organismal biology.
Natural Sciences is Cambridge's largest Tripos by student numbers. In the most recent year for which Cambridge has published full admissions figures, 2,594 students applied and 577 were admitted — an acceptance rate of around 22%. The course is taught across 14 departments spanning the Schools of Biological Sciences and Physical Sciences, plus the Department of History and Philosophy of Science, and roughly half of admitted students go on to specialise in biological sciences and half in physical sciences from Part II onwards.
The typical offer is A*A*A at A-level, or 41–42 points in the International Baccalaureate with 776 at Higher Level. You need Mathematics plus two further subjects from Biology, Chemistry, Physics or Further Mathematics, and the specific combination should align with the Part IA subjects you intend to take. Strong grades are a baseline requirement, not a differentiating factor — ESAT performance and the interview itself are what ultimately decide the offer.
There is no Natural Sciences pack. The thirty packs on the resource hub are organised by discipline and a Natural Sciences interview is not, so the pack follows from your intended Part IA subjects rather than from the course name: Biological Sciences for a candidate leaning to Biomolecules and Cells or to Biodiversity, Evolution and Ecology, and it is the first of the three Biology sets, the other two being Evolution & Behaviour and Physiology; Inorganic Chemistry for a Chemistry lean, which is where most Chemistry candidates start; Dynamics and Fields for Physics; and Maths I for either mathematics course. They are £180 each. Three of the eight Part IA experimental subjects — Earth Sciences, Introduction to Experimental Psychology and Materials Science — have no pack written for them at all, which is worth knowing before you pay rather than after. Two packs is the ordinary case here rather than the exception, so it is worth knowing that the hub prices two together at 10% less and three or more at 20% less, with nothing to type in at checkout.
None of the nine free sample PDFs is badged Natural Sciences, but four of the nine are first-year Natural Sciences disciplines: Biology, Chemistry, Physics and Maths. The Biology sample works the giraffe cardiovascular question through in full; the Physics sample runs to eight pages carrying two questions, their hints and their solutions. Chemistry and Maths are there as well. Take one from each side of your subject combination first: between them they show the writing across both halves of the Tripos, which no single sample on the hub can.
A printed answer has already chosen which discipline to solve the problem in. The move that decides most Natural Sciences interviews is the one where an interviewer takes a question you have started answering biologically and asks for a physical argument instead, or hands you the number you were about to estimate and asks what it does to your conclusion. A page can show you that a route was chosen and why it was chosen. Committing to one under time pressure, and having it taken away from you mid-sentence, needs somebody in the room. Work the questions on paper for the reasoning, then give the same question to somebody reading over your shoulder with instructions to switch the discipline on you halfway through.
Further Reading: For a free collection of real Cambridge Natural Sciences interview questions with full worked solutions and technique notes, see our companion blog guide: Cambridge Natural Sciences Interview Questions 2026 — With Model Answers. For the full picture on interview format, admissions tests, and college-by-college preparation, see our Cambridge Natural Sciences interview guide. If your subject combination leans towards a single science, the Biology, Chemistry and Physics pages go deeper on each discipline and name every pack that covers it.
Buying for a Tripos, not for a subject
The diffusion question above is one shape of Natural Sciences problem and it is answered here in full, for nothing. A paid pack is where the rest of that shape lives, discipline by discipline: ten questions, each one worked under the same three headings you have just read above — Questions, Prompts, Suggested answers — with the answer taken to the length of the diffusion walkthrough rather than compressed into a paragraph. Written by specialist subject tutors; a printable PDF, bought once.
There is still no pack with Natural Sciences on the cover. There is one for each discipline you will be interviewed in, and the table above says which of them are yours.
Open the pack grid and pick your disciplines — £180 each →