Mistakes I Learnt From the 2026 A-Level Biology Exams

Every year, when the AQA A-Level Biology examiners’ reports are released, I go through them carefully to find out where students lost marks — and, more importantly, why.

The 2026 exams were no exception.

Some of the mistakes students made were genuinely surprising. Not because the biology was particularly difficult, but because students often seemed to understand the concept and still lost marks through imprecise language, incomplete explanations or avoidable errors.

And that is the frustrating thing about A-Level Biology: you can understand the biology and still lose marks if you don't express your answer in the way the mark scheme requires.

In this blog, I’m sharing some of the key mistakes highlighted in the AQA A-Level Biology examiners’ reports for Papers 1, 2 and 3, along with practical tips to help you avoid making the same mistakes in your own exams.

Let’s get into it!

1. Heart Contraction and Pressure: Explain WHY, Not Just WHAT

One of the most poorly answered questions in Paper 1 concerned the unidirectional flow of blood through the heart.

According to the examiners’ report, only around 2% of students achieved full marks, while over 40% scored zero.

So, what went wrong?

Many students described the pressure in a chamber of the heart as simply being “high” or “low”. However, the question required students to make comparisons and explain the relationship between the force of contraction, the volume of the chamber and the pressure generated.

The key idea is that the left ventricle has a thicker muscular wall than the right ventricle. It contracts more forcefully, generating the high pressure needed to pump blood around the entire body.

When explaining the relationship between contraction and pressure, think about the full chain of reasoning:

More forceful contraction → smaller ventricular volume → higher pressure → blood is pushed out of the ventricle.

Simply stating that the pressure is high may not be enough. You need to explain how the pressure is generated and, where relevant, compare the left and right ventricles.

Other heart mistakes to avoid

A few other basic misconceptions also caused problems:

• The aorta connects to the left ventricle, not the right ventricle.

• Valves do not contract. Cardiac muscle contracts, while valves open and close in response to pressure differences.

• Be careful when naming the atrioventricular valves. The bicuspid valve is on the left side of the heart, while the tricuspid valve is on the right.

Exam tip: When explaining a physiological process, don't stop at describing what happens. Explain why it happens and link each step logically to the next.

2. Alveoli: Focus on the Epithelium

Most students know that the lungs contain millions of alveoli, providing a large surface area for gas exchange.

However, when a question specifically asks about the alveolar epithelium, you need to focus on the epithelium itself rather than simply describing the lungs as a whole.

The alveolar epithelium is one cell thick, creating a short diffusion pathway. Its extensive surface area also allows gases to diffuse across the exchange surface.

A strong answer needs to link the structural feature to its consequence.

For example:

• The epithelium is one cell thick.

• This creates a short diffusion pathway.

• This increases the rate of diffusion of gases across the surface.

Similarly, if you refer to surface area, make the consequence explicit: a large surface area allows more gas to diffuse per unit time, provided the other relevant conditions are comparable.

Simply writing “there is a large surface area for diffusion” may leave your explanation incomplete if the question requires you to explain how this improves gas exchange.

Don't confuse the epithelium with other structures

There are two additional points worth remembering:

• Capillary walls are separate from the alveolar epithelium. Both contribute to the overall gas exchange barrier, but they are distinct structures.

• Microvilli are not a feature of the alveolar epithelium. They are associated with surfaces such as the epithelial lining of the small intestine, where they increase surface area for absorption.

Exam tip: Always pay attention to the exact structure named in the question. If the question asks about the epithelium, make sure your answer refers directly to the epithelium.

3. Condensation Reactions: Say “Chemical Bond”

This is a small detail that can make a surprisingly big difference.

When describing a condensation reaction, students often write that “a bond forms”. However, the expected terminology may require you to state explicitly that a chemical bond forms.

This applies to processes involving the formation of molecules such as polypeptides and carbohydrates, as well as the formation of phosphodiester bonds in nucleic acids.

For example, when amino acids join together in a condensation reaction, a peptide bond forms and a molecule of water is released.

The important lesson is that a correct general idea does not always guarantee the mark. You need to use the terminology required by the question and mark scheme.

Exam tip: Learn your specification definitions accurately. Understanding the gist of a definition is important, but being able to recall the precise biological terminology can help you secure those extra marks.

4. More Definitions and Terminology That Cost Marks

The examiners’ reports highlighted several other examples of students losing marks through inaccurate terminology.

These are all worth adding to your revision list.

DNA replication: Hydrogen bonds, not hydrolysis

During DNA replication, helicase breaks the hydrogen bonds between complementary bases, allowing the two DNA strands to separate.

Do not say that helicase hydrolyses the bonds. Hydrolysis involves breaking a bond through a reaction with water, whereas helicase separates the DNA strands by disrupting hydrogen bonds.

Also, remember the difference between adenine and adenosine. Adenine is a nitrogenous base, while adenosine consists of adenine attached to a ribose sugar.

Nerve impulses: Use the word diffusion

During an action potential, ions move across the cell-surface membrane down their electrochemical gradients through appropriate ion channels.

If a question asks about the movement of ions by diffusion, simply stating “influx” or “efflux” may not be sufficient.

Be precise about the process involved and explain the direction of movement where relevant.

Blood glucose regulation: Concentration, not level

In your exam answers, use the phrase blood glucose concentration rather than relying on the more general expression “blood glucose level”.

This is a simple terminology change that can help make your answers more precise.

Oxidative phosphorylation: Energy is released, not produced

This is a common source of confusion.

In respiration, energy is transferred and released through metabolic processes, and this energy is used to synthesise ATP.

Avoid saying that energy is “produced”. Instead, explain that energy is released or transferred and that ATP is synthesised.

For oxidative phosphorylation, be prepared to explain the roles of the electron transport chain, the proton gradient and ATP synthase.

Water potential and reabsorption: Explain where it happens

When discussing water reabsorption in the nephron, it is important to identify the relevant locations.

Instead of writing only that water is “reabsorbed”, explain that it moves from the filtrate in the nephron into the surrounding tissue and blood, where appropriate to the question.

Water moves by osmosis down a water potential gradient across a partially permeable membrane.

Make sure your answer identifies the relevant structures and explains the direction of movement.

Restriction endonucleases: Cut at specific sites

Restriction endonucleases recognise particular DNA base sequences and cut the DNA at specific restriction sites.

Avoid writing that they simply “cut the gene”. The enzyme recognises a particular sequence, which may be within a gene or elsewhere in the DNA.

Crossing over: New combinations, not new alleles

Crossing over during meiosis can produce new combinations of existing alleles.

It does not, by itself, create new alleles. New alleles arise through mutation.

This is an important distinction when answering questions about genetic variation.

Chemiosmosis: Name the structures

When explaining chemiosmosis in respiration or photosynthesis, be precise about the relevant membranes, compartments and direction of proton movement.

For example, during oxidative phosphorylation, protons are pumped from the mitochondrial matrix into the intermembrane space and then flow back into the matrix through ATP synthase.

During photophosphorylation, protons accumulate in the thylakoid space and flow back into the stroma through ATP synthase.

Don't leave the examiner guessing which structure you mean.

5. Maths and Data Handling: Small Details, Lost Marks

Biology is not just about memorising content. The mathematical and statistical elements of the course can also make a significant difference to your final grade.

Here are some mistakes to watch out for.

Check what the answer needs to be expressed per

When completing percentage-change calculations, logarithmic calculations or other mathematical questions, read the final instruction carefully.

You may need to express a result per gene, per hour or in another specified unit.

Even if your calculation is otherwise correct, failing to complete the final conversion can cost you marks.

My advice: Before submitting a numerical answer, ask yourself three questions:

1. Have I completed every step of the calculation?

2. Have I used the correct units?

3. Have I expressed the answer in the exact form requested?

Make improvements relevant to the experiment

When evaluating an investigation, avoid automatically suggesting that the researcher should repeat the experiment, increase the sample size or carry out a statistical test.

These suggestions are not always wrong, but they need to address the limitations of the specific method described.

For example, if the experiment uses only one banana, think carefully about whether the limitation relates to biological variation between bananas, the reliability of the measurements or another factor.

Your improvement should solve the problem you have identified.

Pay attention to instructions that rule out an answer

If a question explicitly tells you not to suggest a particular improvement, do not include it anyway.

The instruction is there for a reason: the examiner wants you to consider a different approach.

Read the whole question before deciding what to write.

Be precise about statistical significance

There is an important difference between stating that “the results are significant” and stating that “the difference between the results is statistically significant”.

When interpreting statistical tests, explain what the result tells you about the comparison being made.

Remember that statistical significance does not automatically mean a difference is biologically important or that one variable caused another.

6. A-Level Biology Essay Mistakes: Paper 3

If you are preparing for the extended essay in AQA A-Level Biology Paper 3, there are a few additional misconceptions and essay-writing habits to address.

Enzymes do more than break molecules down

It is easy to associate enzymes primarily with hydrolysis, but enzymes catalyse a wide range of reactions.

Some break molecules down, while others join molecules together.

For example, DNA polymerase catalyses the formation of phosphodiester bonds during DNA replication.

When writing an essay about enzymes, include examples of both types of reaction where relevant.

ATP cannot be transported around the body as a general energy supply

ATP is continually synthesised and used within cells. It is not transported around the body as a general energy source in the way that glucose can be transported in the blood.

Instead, cells produce ATP close to where it is required, using metabolic pathways suited to their needs.

This is a useful point to remember when writing essays about respiration, muscle contraction, active transport and metabolism.

DNA helicase and transcription are not interchangeable

During DNA replication, helicase helps separate the DNA strands by breaking the hydrogen bonds between complementary bases.

During transcription, RNA polymerase locally unwinds the DNA as it synthesises an RNA strand from a DNA template.

Be careful not to mix up the enzymes and processes involved in replication and transcription.

Oestrogen and gene expression

When discussing oestrogen and cancer, avoid making the blanket claim that oestrogen typically switches on tumour suppressor genes.

Oestrogen can influence gene expression through its receptors, including the expression of genes involved in cell growth and survival. In certain hormone-sensitive cancers, these signalling pathways can contribute to tumour development.

The exact effects depend on the biological context, so be specific about the mechanism you are describing.

Your AO2 paragraph needs to add something new

This is an important point about essay structure.

Your AO1 paragraphs demonstrate your biological knowledge, while your AO2 content explains the significance, relevance or importance of that knowledge.

A common mistake is to repeat an AO1 point in reverse and present it as a new AO2 point.

For example, if you explain that ATP is required for active transport, simply stating that active transport would not occur without ATP may not add a sufficiently distinct point.

Instead, extend your explanation by exploring a different consequence, application or biological connection.

Essay tip: After writing each paragraph, ask yourself: “Have I added a new biological point, or have I just repeated what I already said?”

7. How to Avoid These Mistakes in Your Next Biology Exam

Looking across these examples, one thing becomes clear: many lost marks come down to precision rather than a complete lack of knowledge.

So, what can you do about it?

1. Learn definitions accurately

Return to the AQA specification and identify the definitions and processes you need to know.

Practise recalling them without looking at your notes, paying particular attention to the key terms that distinguish one process from another.

2. Use mark schemes actively

Don't just check whether your answer was correct or incorrect.

Compare your answer with the mark scheme and identify exactly which words, links or explanations you missed.

Then rewrite your answer to include those points.

3. Practise explaining cause and effect

For processes such as ventilation, circulation, nerve impulses and respiration, practise building logical chains of explanation.

Ask yourself what happens, why it happens and what the consequence is.

This is particularly useful for questions worth several marks.

4. Read the question carefully

Identify the command word, the structure or process named in the question, and any restrictions on your answer.

A question about the alveolar epithelium requires a different focus from a question about the entire gas exchange system.

5. Keep a personal mistake log

Every time you lose a mark, record the mistake and the corrected answer.

Organise your mistakes into categories such as terminology, incomplete explanations, maths, practical work and essay technique.

Revisit the list regularly. Your own recurring mistakes are often more useful to revise than another round of reading through the textbook.

Final Thoughts

If there is one lesson I want you to take away from the 2026 AQA A-Level Biology exams, it is this:

Knowing the biology is only half the battle. You also need to communicate it precisely.

Remember to use chemical bond, not just bond, where the question requires it. Compare pressure rather than simply describing it as high or low. Explain diffusion, identify the correct structures and distinguish between processes such as replication and transcription.

These may seem like small details, but small details can make a difference when you are aiming for the highest grades.

Go back to your specification, practise exam questions, use the mark schemes to understand where marks are awarded, and learn from every mistake you make along the way.

And remember: making mistakes during revision is not a bad thing. It gives you the opportunity to correct them before they matter in the exam.

Which of these mistakes surprised you the most? Let me know, and keep an eye out for more AQA A-Level Biology exam tips from Miss Estruch Biology.

Source: AQA A-Level Biology (7402) examiners’ reports, June 2026 series — Papers 1, 2 and 3.

P.S. Are You A Visual Learner? 

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