Common A-Level Biology Mistakes That Cost Students Marks
After marking thousands of Biology scripts across two exam boards, these are the 12 mistakes I see most often — with the exact corrections that turn lost marks into gained marks.
In this article
Every one of these mistakes appears in scripts from students who know the biology. That is what makes them so costly — and so fixable. They are not knowledge gaps. They are habits that, once identified, can be corrected in days rather than weeks.
Terminology Mistakes
These are the marks lost because of how you express the biology, not whether you understand it. They are the most common and the most preventable.
1 “The enzyme is killed”
TerminologyEnzymes are not alive, so they cannot be killed. The mark scheme will typically have R: killed/destroyed (Reject) next to the marking point. This single word costs a mark on almost every enzyme question, and enzyme questions appear on every paper. The correct term is denatured — meaning the tertiary structure has changed permanently so the active site no longer has a complementary shape to the substrate.
2 “Amount” instead of a specific term
Terminology“Amount” is too vague for A-Level. Examiners need to know whether you mean concentration, rate, volume, or number. Each has a different scientific meaning. Mark schemes routinely reject “amount” because it does not demonstrate understanding of what is actually changing. Get specific every time.
3 “The substance moves through the membrane”
TerminologyAt A-Level, you must specify the transport mechanism. Is it diffusion, facilitated diffusion, osmosis, active transport, or co-transport? Through which structural feature — channel protein, carrier protein, phospholipid bilayer? Down or against a concentration gradient? Every detail matters. “Moves through” earns zero marks because it could describe any process.
4 Confusing “cell wall” and “cell membrane”
TerminologyAnimal cells do not have cell walls. This is a GCSE-level distinction that still costs marks at A-Level because students write carelessly under time pressure. The cell membrane (or plasma membrane) controls what enters and leaves the cell. The cell wall (in plant, fungal, and bacterial cells) provides structural support and is freely permeable.
5 Using unapproved abbreviations
TerminologyYou can only use abbreviations that appear in your exam board’s specification. “TP” for triose phosphate is not in the AQA specification, so writing “TP” without first writing the full term will not be credited. ATP, DNA, RNA, mRNA, tRNA, ADP, NAD, NADP — these are in the specification and can be used freely. When in doubt, write the full term first.
Exam Technique Mistakes
These are the marks lost because of how you answer the question, not what you know about the biology.
6 Describing when asked to explain (and vice versa)
TechniqueDescribe means state what happens. Explain means state what happens and why. If a question says “Explain why the rate of reaction decreases,” writing “The rate of reaction decreases as temperature increases beyond the optimum” is a description, not an explanation. You have not said why. The explanation is that increased kinetic energy breaks hydrogen bonds, changing the tertiary structure and the shape of the active site. See my full guide to command words.
7 Writing everything you know about a topic
TechniqueA question worth 3 marks about enzyme inhibition does not want your entire knowledge of enzymes. It wants three specific marking points about inhibition. Writing a page-long answer wastes time you need for other questions and increases the risk of contradicting yourself — which triggers the “right + wrong = wrong” rule. Read the question, identify what is being asked, and answer only that.
8 Not using data from the graph or table
TechniqueWhen a question says “Use the data to…” or “Describe the results shown in Figure 1,” you must quote specific values from the data. Vague statements like “it increased” or “it was higher” without numbers lose marks. Always include values, units, and the conditions they relate to. If describing a trend, give at least the start value, end value, and any turning points.
9 Giving too many answers
TechniqueIf a question says “Name one function of the cell membrane,” give one answer. If you give two and one is wrong, you score zero. This is the “right + wrong = wrong” principle. Examiners see this constantly — students hedging their bets by writing multiple answers, not realising that every additional answer is a risk. If the question specifies a number, match it exactly.
Recognise Any of These?
Most students make 3–4 of these errors repeatedly. Fixing them can be worth an entire grade boundary. I can identify your specific patterns in a single session.
Book Free ConsultationContent Mistakes
These are genuine misunderstandings that need to be corrected through targeted revision.
10 Confusing where respiration stages occur
ContentGlycolysis occurs in the cytoplasm. The link reaction and Krebs cycle occur in the mitochondrial matrix. Oxidative phosphorylation occurs on the inner mitochondrial membrane (cristae). Students routinely place the Krebs cycle on the membrane or glycolysis in the mitochondria. This costs marks across multiple questions because the location is frequently a marking point.
11 Getting water potential direction wrong
ContentWater potential values are negative (except pure water at 0 kPa). A value of −200 kPa is lower than −100 kPa. Water moves from the higher (less negative) value to the lower (more negative) value. Students who think of “high concentration” from GCSE often reverse the direction because the negative numbers confuse them. Draw a number line if it helps: −100 is to the right of −200, so water moves from −100 towards −200.
12 Muddling transcription and translation
ContentTranscription (DNA → mRNA) occurs in the nucleus, using RNA polymerase. Translation (mRNA → polypeptide) occurs at ribosomes in the cytoplasm or on rough endoplasmic reticulum. The mRNA must leave the nucleus through a nuclear pore before translation can begin. Students who confuse these lose marks on gene expression questions, which appear on every paper.
How to Fix the Pattern
The reason these mistakes persist is not stupidity — it is that students do not have a system for identifying and correcting them. Here is one that works.
The mistake log
Every time you get a question wrong in practice, record three things: the topic, the type of mistake (terminology, technique, or content), and the correct mark scheme answer. After 2–3 papers, patterns will emerge. You might discover that you consistently lose terminology marks on transport topics, or that you always describe instead of explaining. Once you see the pattern, you can target it.
The correction flashcard
For every recurring error, make a flashcard with the wrong version on one side and the correct version on the other. “Killed → Denatured.” “Amount → Concentration / Rate / Volume.” Review these before every practice paper. The goal is to make the correct version automatic.
Get examiner-quality feedback
The fastest way to identify your specific patterns is to have someone who knows mark schemes mark your work. A teacher, tutor, or examiner can spot systematic errors in a single paper that you might never notice on your own. This is one of the most valuable things I do in my tutoring sessions — marking student answers the way an examiner would and showing them exactly where marks are won and lost.
Frequently Asked Questions
Three categories: terminology mistakes (vague language, “killed” instead of “denatured,” “amount” instead of specific terms), technique mistakes (ignoring command words, writing too much, not quoting data), and content mistakes (wrong locations for respiration stages, water potential direction errors, transcription/translation confusion).
Mark schemes require precise scientific terminology, not everyday language. Understanding the concept is necessary but not sufficient — you must express it in the specific way the mark scheme rewards. Exam technique (how you answer) accounts for a large proportion of lost marks.
Most “careless” mistakes are systematic errors. Keep a mistake log recording the topic, error type, and correct answer for every wrong question. Patterns will emerge after 2–3 papers. Make correction flashcards for recurring errors. Build in a 5-minute check at the end of each paper for true carelessness.
“Killed” instead of “denatured,” “amount” instead of concentration/rate/volume, “cell wall” instead of “cell membrane,” vague transport descriptions instead of specifying the mechanism, and unapproved abbreviations. Each costs 1–2 marks per occurrence and recurs across multiple questions.
Plan for 60 seconds before writing. Identify key terms, order them logically, aim for 8+ distinct points. Write connected prose, not a list. Use precise terminology. Match the command word. See the full 6-mark questions guide.
Respiration biochemistry (which reactions happen where), water potential (negative values and direction), gene expression (transcription vs translation), the immune response (T-cell and B-cell roles), and statistical tests (choosing and interpreting). These benefit most from active recall and past paper practice.