Hardest IGCSE Biology Questions & How to Answer Them

Ever stared at a Biology exam question and had no idea where to start? You’re not alone. Many IGCSE students struggle most with the hardest questions, especially when aiming for top grades (7–9 or A*/A).

These questions go beyond simple recall. They often combine topics, use unfamiliar scenarios, or ask you to explain ideas in new ways. The good news is that even the hardest IGCSE Biology questions follow clear patterns. Once you understand what makes them challenging and how examiners expect you to respond, they become far more manageable.

In this guide, you’ll see examples of difficult IGCSE Biology questions and learn the strategies that help students access full marks.

Key Takeaways

• The hardest IGCSE Biology questions test application and analysis, not just memorisation

• They often involve unfamiliar contexts, data interpretation, or multi-step reasoning

• Success depends on understanding command words and structuring answers clearly

• Regular practice with past papers and mark schemes builds confidence

What Makes a Biology Question Hard?

The toughest questions share common features:

• Unfamiliar scenarios that require applying knowledge, not recalling facts

• Multi-part questions where each part builds on the last

• Data interpretation, such as analysing graphs, tables, or experimental results

• Challenging command words like explain, evaluate, or compare

• Precise terminology, where inaccurate wording loses marks

• Abstract concepts (e.g. hormones, genetics, ecosystems) that are harder to visualise

How to Approach Difficult IGCSE Biology Questions

When you're faced with a tough question, having a clear strategy makesthe difference. Here are some steps I have shared with students over the years:

Step 1: Read the question carefully. This sounds obvious, but it's where most mistakes happen. Underline key information and circle the command word. Are you being asked to "describe," "explain," or "suggest"?

Step 2: Check the mark value. This tells you how much detail is expected.

Step 3: Identify the topic being tested. Once you know the topic, you can access the relevant information you've revised.

Step 4: Break multi-part questions down. If there's part (a), (b), and (c), treat each one separately and make sure you answer every part.

Step 5: Plan extended answers.. Spend 30 seconds jotting down key points before you write. This helps you structure a clear response.

Step 6: Use scientific terminology. Show the examiner you know your stuff by using the correct biological terms.

Step 7: Check your answer. Does it actually answer the question asked? Have you included enough detail for the marks available?

Examples of the Hardest IGCSE Biology Questions

Let's look at some genuinely challenging questions. We'll use a mix of past paper questions and realistic examples that reflect the toughest content in the IGCSE Biology specifications.

Question 1 – Respiration Data Interpretation (Original Example)

Question:

A scientist investigates oxygen consumption in germinating seeds and non-germinating seeds at 20°C and 30°C. The results are shown in the table below.

(a) Compare the oxygen consumption of germinating seeds at 20°C and 30°C. [2 marks]

(b) Explain why germinating seeds consume more oxygen than non-germinating seeds. [3 marks]

(c) Predict what would happen to oxygen consumption if the temperature was increased to 50°C. Explain your answer. [3 marks]

Why This Is Difficult:

This question combines data interpretation with an understanding of respiration and enzyme activity. Part (c) is particularly challenging because it requires you to predict an outcome and explain your reasoning using knowledge of enzymes and temperature.

Model Answer:

(a) Germinating seeds at 30°C consume more oxygen than at 20°C (0.28 cm³/min compared to 0.15 cm³/min). The oxygen consumption is nearly double at the higher temperature. [2 marks—for comparison using data]

(b) Germinating seeds are growing, which requires energy. To release this energy, the seeds carry out more aerobic respiration. Aerobic respiration requires oxygen, so germinating seeds consume more oxygen than non-germinating seeds, which are dormant and not actively growing. [3 marks]

(c) Oxygen consumption would likely decrease or stop completely. At 50°C, the enzymes involved in respiration would start to denature. This means the active sites change shape and can no longer bind to substrates. Without functioning enzymes, respiration slows down or stops, so less oxygen is consumed. [3 marks—for prediction and full explanation]

Examiner Tips:

• Always quote data from tables or graphs when asked to compare

• Use comparative language: "more than," "less than," "higher," "lower"

• Link respiration to energy requirements—don't just say "they respire more"

• Remember that very high temperatures denature enzymes

Question 2 – Genetic Crosses (Past Paper Style)

Question:

In tomato plants, the allele for red fruit (R) is dominant to the allele for yellow fruit (r).

A farmer crosses two tomato plants. Both parent plants have red fruit. The offspring produced include some plants with yellow fruit.

(a) Explain how two red-fruited parent plants can produce offspring with yellow fruit. [3 marks]

(b) One of the parent plants is heterozygous (Rr). Use a genetic diagram to show the cross between this plant and a homozygous red-fruited plant (RR). Show the genotypes and phenotypes of the offspring. [4 marks]

(c) Calculate the expected ratio of red-fruited to yellow-fruited plants if both parents are heterozygous. Show your working. [3 marks]

Why This Is Difficult:

Genetics questions require multiple steps and careful working out. You need to understand dominant and recessive alleles, work out parent genotypes from offspring information, construct accurate genetic diagrams, and calculate ratios. One small mistake early on affects all your subsequent answers.

Model Answer:

(a) Both parent plants must be heterozygous (Rr). They both have red fruit because red is dominant. When they reproduce, some offspring inherit a recessive allele (r) from each parent, giving them the genotype rr. These offspring have yellow fruit because they don't have a dominant R allele. [3 marks]

(b)

Parents: Rr × RR

Gametes: R or r from first parent; R from second parent

Punnett square:

Genotypes: 2 RR : 2 Rr (or 1:1 ratio)

Phenotypes: All offspring have red fruit [4 marks—for correct gametes, Punnett square, genotypes, and phenotypes]

(c) If both parents are Rr:

Parents: Rr × Rr

Punnett square:

Genotypes: 1 RR : 2 Rr : 1 rr

Phenotypes: 3 red : 1 yellow

The ratio of red-fruited to yellow-fruited plants is 3:1 [3 marks—for correct working and ratio]

Examiner Tips:

• Always show your Punnett square—even if you make a mistake, you can earn method marks

• Write out the parents' genotypes clearly at the start

• Remember to give both genotypes and phenotypes when asked

• Don't forget to simplify ratios (e.g., 2:2 becomes 1:1)

Question 3 – Homeostasis and Kidney Function (Original Example)

Question:

A person drinks a large volume of water quickly. After 30 minutes, they produce a large volume of dilute urine.

(a) Describe what happens to the concentration of the blood as the person drinks the water. [1 mark]

(b) Explain how the kidneys respond to produce dilute urine. Your answer should include the role of ADH (antidiuretic hormone). [5 marks]

(c) A different person has kidney damage and cannot produce concentrated urine. Suggest why this person needs to drink water more frequently than a healthy person. [2 marks]

Why This Is Difficult:

This question requires understanding of a complex homeostatic mechanism involving the brain, pituitary gland, and kidneys. You need to explain a sequence of events and understand negative feedback. Part (b) is worth 5 marks, so you need substantial detail. Part (c) asks you to apply your knowledge to predict consequences of organ damage.

Model Answer:

(a) The blood becomes more dilute (or: water concentration increases / solute concentration decreases). [1 mark]

(b) The hypothalamus in the brain detects that the blood has become too dilute. This causes the pituitary gland to release less ADH into the bloodstream. ADH normally makes the kidney tubules more permeable to water, allowing more water to be reabsorbed back into the blood. When less ADH is present, the kidney tubules become less permeable to water. This means less water is reabsorbed from the kidney tubules. Therefore, more water remains in the tubules and is excreted as dilute urine. [5 marks—for detection, ADH release, effect on tubules, permeability change, and outcome]

(c) A healthy person can produce concentrated urine by reabsorbing more water back into the blood when needed. A person with kidney damage cannot do this, so they lose more water in their urine. To replace this lost water and prevent dehydration, they need to drink more frequently. [2 marks]

Examiner Tips:

• For homeostasis questions, describe the full sequence: detection → hormone release → effect on target organ → outcome

• Use the word "permeable" when discussing water reabsorption in kidneys

• Explain cause and effect clearly using words like "therefore," "this causes," "as a result"

• Don't confuse ADH with other hormones like insulin

Understanding the Mark Scheme

Knowing how marks are awarded helps you write higher-scoring answers.

Each mark in a mark scheme usually equals one clear point. For example, a 3-mark question needs three distinct ideas. Keywords matter — if the mark scheme says concentration gradient, vague phrases like difference in concentration may not gain credit.

For “explain” questions, description alone is not enough. You must show cause and effect by explaining why something happens.

Longer questions (5–6 marks) often use levels-based mark schemes, where examiners judge:

• accuracy and detail

• application of knowledge

• clarity and structure

Cambridge IGCSE Biology mark schemes (opens in a new tab) reward:

• correct scientific terminology

• clear, logical explanations

• appropriate use of data

• correct structure (e.g. genetic diagrams)

Even partial answers can gain marks, so always write what you know.

Frequently Asked Questions

What Are the Hardest Topics in IGCSE Biology?

Students commonly find these topics challenging:

• Genetics and inheritance – ratios, crosses, alleles

• Respiration and photosynthesis – multi-stage processes

• Homeostasis – negative feedback and hormonal control

• Transport in plants – xylem vs phloem, transpiration

• Ecology – food webs, energy transfer, populations

These topics often appear in harder questions because they test application and analysis.

Do These Questions Appear in Every Exam?

Yes. Every paper includes:

• easier recall questions

• medium-difficulty application questions

• harder questions (often at the end or in later parts)

The question style changes each year, but the skills tested stay the same, which is why past papers are so useful.

How Can I Improve at Difficult Biology Questions?

• Secure your basic knowledge first

• Build difficulty gradually

• Study model answers

• Focus on explain and evaluate questions

• Practise experimental design

• Get feedback from teachers or mark schemes

Are Extended Questions Only for Extended Tier?

No, but they differ in difficulty:

• Core tier: Core content, shorter structured questions

• Extended tier: Core plus Supplement content, deeper explanations and higher mark questions

Check your tier entry with your teacher so you can target your revision effectively.

Final Thoughts

Hard IGCSE Biology questions are challenging by design — but they’re also your chance to show real understanding.

These questions test the same skills again and again: application, data interpretation, logical explanation, and precision. Once you recognise those patterns and practise them regularly, even the toughest questions become manageable.

Mistakes during revision are part of the process. Every error you fix now is a mark you won’t lose in the exam. With the right strategies and consistent practice, you can handle even the hardest IGCSE Biology questions with confidence.

For more support with your IGCSE Biology revision, check out our IGCSE Biology Revision Notes, exam technique guides, and practice question banks designed to help you achieve your best possible grade.

References

• Cambridge IGCSE Biology (0610) Syllabus and Resources (opens in a new tab) – Cambridge Assessment International Education

• Pearson Edexcel International GCSE in Biology (4BI1) Syllabus  (opens in a new tab)

• OxfordAQA International GCSEs (opens in a new tab) - Biology