What the Grading Data Really Shows

Biology is also the most popular of the three, with more than 65,000 entries in 2025 — a larger, broader cohort, which matters for the next question. Before you read the table as "Biology is just harder", look at who is sitting each paper.

If chemistry grades are higher, why do examiners call it more severely graded?

Because Chemistry's higher grades come from a stronger starting cohort, not from easier marking. When you compare students of equal prior attainment, Ofqual's inter-subject comparability research finds Chemistry is graded more harshly than most subjects — meaning a student of given ability is less likely to earn a top grade in Chemistry than in many other A-levels.

This is the piece almost every comparison article misses. Chemistry, Physics and the sciences attract students with high GCSE scores, so a larger share of them naturally land top grades. Strip that selection effect out and the subject looks tough: the foundational Durham CEM study by Coe and colleagues in 2008, which the Ofqual work builds on, found the sciences, mathematics and languages were graded up to a whole grade more severely than other subjects. In 2018 Ofqual reviewed whether to adjust science grading and decided not to, while acknowledging the perceived severity and committing to stop these subjects becoming statistically harder still.

A crucial caveat, in Ofqual's own framing: statistical "difficulty" measures should not be read in isolation, because they cannot separate harsh grading from differences in teaching, motivation and who chooses the subject. So "Chemistry is more severely graded" is well-evidenced, but it is a cohort-level statistical statement — not a claim that every Chemistry question is harder than every Biology one.

And here my marking experience cuts the other way. At the level of an individual written answer, Biology is the more tightly marked of the two. Examiners are pickier in Biology because a single word in a paragraph can change the whole meaning of a sentence, so the same idea can score or fail on phrasing alone. Chemistry candidates usually write less, and apart from a few specific scientific terms, the marking is more flexible. So Biology can be "easier-graded" at cohort level yet "harder-marked" on the page — both are true, and holding them together is the complete answer.

What makes A-level biology and chemistry hard?

Each subject is hard in its own way: Biology punishes imprecise writing across a huge content load, while Chemistry punishes shaky concepts and unscaffolded calculation. Knowing which failure mode you are prone to matters more than any league table.

What makes A-level Biology hard?

Biology is hard because of the sheer volume of content and the precision the mark scheme demands when you write about it. The marks students lose most are on the long-answer questions — the ones asking you to describe and explain data within a given scenario. Those extended items are where I see candidates struggle most: they know the biology but cannot marshal it into the exact points the mark scheme wants.

A typical, avoidable example is the enzyme question. A student who writes that enzymes are biological catalysts that speed up the rate of reaction scores nothing close to full marks — to earn the discussion marks, they have to explain why, by stating that enzymes lower the activation energy of the reaction. The biology is "right" in spirit and still loses marks because the specific mechanism is missing. Training that habit of answering the exact question asked is most of what my free IAL Biology class drills, alongside the structured walkthroughs in the IAL notes eBooks.

What makes A-level Chemistry hard?

Chemistry is hard because concepts build on each other, so a shaky foundation compounds — and because the long calculation questions give no scaffolding. The marks students lose most are on mole problems, especially the multi-step ones with no guidance: the five- or six-mark questions where you have to plan the route to the answer yourself, ideal-gas calculations being a classic. The saving grace is that these are marked by method, so writing out your steps clearly still banks several marks even if the final number is wrong — a point I hammer in the free IAL Chemistry class.

Notice what is not on that list: raw maths. In my experience mathematics is rarely the limiting factor on a student's grade. The maths in Biology is straightforward, and the maths in Chemistry comes down to a few laws and formulae that any student can learn; plenty score well even when numbers are not their strength. What trips people up is not the arithmetic but planning a multi-step problem under exam conditions — a reasoning skill, not a mathematical one.

Is Edexcel IAL chemistry harder than IAL biology?

The same pattern holds for Edexcel IAL, with one important wrinkle: the IAL mark scheme is stricter than Cambridge's. Across the IAL Biology units (WBI11–WBI16) and Chemistry units (WCH11–WCH16), Biology remains the content-and-precision subject and Chemistry the concept-and-calculation subject — but Edexcel tends to accept fewer marking points per question than Cambridge, whose mark schemes are more flexible.

That stricter, more specific marking is felt most in IAL Biology's long describe-and-explain items, where there is less room to phrase an idea loosely and still be credited. If you are coming to IAL from a Cambridge IGCSE background, this is the adjustment that catches students out: the same standard of understanding earns fewer marks unless the wording lands exactly. There is no published IAL-specific difficulty ranking the way there is for UK A-levels, so the UK grading evidence above is the best available proxy — but the marking-precision gap is something I see directly from sitting on both sides.

Chemistry or biology: which should you choose?

For most science and medicine routes the realistic answer is "both", so the real decision is where your revision time will hurt least. If you are stronger at memorising and applying detail with precise wording, Biology will feel more natural; if you are stronger at reasoning through abstract ideas and multi-step problems, Chemistry will. Neither choice is "safer" for your grades once you account for the cohort effects above.

A useful pattern I see: students who arrive strong on content but loose on exam technique tend to plateau in Biology until they fix their phrasing, while students who arrive strong on understanding but rushed tend to plateau in Chemistry until they slow down and show their working. Both ceilings are technique problems, not ability problems — which is good news, because technique is teachable. If you want a steer for your own situation, message me on WhatsApp at +965 5137 5709 or email admin@chem-bio.info and I will point you to the right starting place.

FAQ

Is chemistry or biology better for medicine? Most medical schools want Chemistry as a hard requirement and Biology as the strongly preferred second science, so the usual answer is to take both. Check each university's exact requirements, as a minority accept Biology in place of Chemistry.

Which has more maths, A-level chemistry or biology? Chemistry has noticeably more calculation — moles, energetics and rates — while Biology's maths is lighter and mostly statistical. That said, the maths in either is learnable and rarely the deciding factor in a student's final grade.

Which gives the higher average grade? Chemistry, on the raw numbers: 32.0% of entries reached A*/A in 2025 versus 27.6% in Biology. But that reflects Chemistry's stronger cohort rather than easier marking, so it does not mean an individual will find Chemistry easier.

Can you self-study A-level biology or chemistry? Both are self-studiable with the right structure, though Chemistry's cumulative concepts make a clear sequence more important, and Biology's volume makes disciplined recall essential. Structured notes and marked practice close the gap faster than reading alone.