IGCSE Chemistry vs Biology vs Physics: Which Science Should Kenyan Students Take?

Information current as of Term 2, 2026.

One of the most consequential early decisions for an IGCSE student is which sciences to take. Most Nairobi and Kenyan IGCSE schools require at least one science, and many ambitious students take two or all three. But Chemistry (0620), Biology (0610) and Physics (0625) are genuinely different subjects, demanding different cognitive strengths: memory, calculation, spatial reasoning: in different proportions. This guide explains each syllabus in detail, compares real difficulty with worked examples, and tells you exactly which combination suits which career path.

IGCSE Biology (0610): What It Covers and Who Thrives

Biology is the study of living organisms and life processes. The Cambridge IGCSE Biology syllabus (0610) covers:

• Characteristics of living things, cells and organisation
• Movement into and out of cells (osmosis, diffusion, active transport)
• Biological molecules and enzymes
• Plant nutrition (photosynthesis) and animal nutrition
• Respiration, gas exchange and transport systems (heart, blood)
• Diseases, immunity and defence mechanisms
• Excretion and homeostasis
• Reproduction (plant and animal), genetics and inheritance
• Evolution and biodiversity
• Ecology and the environment

Who thrives in Biology: Students with strong memory skills and a genuine interest in how the human body and natural world function. Biology has the highest content volume of the three sciences: there is a great deal to memorise, and Cambridge examiners expect precise terminology, not approximate descriptions.

Mathematics demand: Low to moderate. Some genetics ratio calculations, graph interpretation and data analysis appear, but there is no calculus and minimal algebra.

Worked Example: Biology: A Genetics Cross

A common IGCSE Biology question type: "Brown eye colour (B) is dominant over blue eye colour (b). Two heterozygous (Bb) parents have a child. What is the probability the child has blue eyes?"

Method: Each parent is Bb. A Punnett square cross of Bb × Bb gives four equally likely combinations: BB, Bb, bB, bb. Only bb produces the recessive blue-eye phenotype.

Answer: 1 out of 4 combinations is bb, so the probability is 25% (or 1 in 4).

This illustrates Biology's typical demand: understanding a biological concept (dominant/recessive alleles) and applying simple, structured logic: not heavy computation.

IGCSE Chemistry (0620): What It Covers and Who Thrives

Chemistry is the study of matter, its properties and its reactions. Cambridge IGCSE Chemistry (0620) covers:

• States of matter, atomic structure and the Periodic Table
• Chemical bonding (ionic, covalent, metallic)
• Stoichiometry: moles, formula masses, equation balancing
• Electrochemistry (electrolysis, cells)
• Energetics (exothermic/endothermic reactions)
• Chemical kinetics (rate of reaction, factors affecting rate)
• Acids, bases and salts (preparation, reactions, pH)
• The atmosphere and environment
• Organic Chemistry (alkanes, alkenes, alcohols, polymers)
• Experimental techniques and analysis

Who thrives in Chemistry: Students who are comfortable with both memorisation and problem-solving. Chemistry requires understanding abstract concepts (why ionic bonds form, why reaction rates change) AND performing calculations (moles, yield, concentration). It genuinely bridges Biology and Physics in cognitive demand, which is why many students find it the most "balanced" of the three.

Mathematics demand: Moderate. Stoichiometry and concentration calculations, percentage yield, and graph work are manageable with solid numeracy but do require real fluency, not just formula substitution.

Worked Example: Chemistry: A Moles Calculation

A typical Paper 4 (Extended) style question: "Calculate the mass of carbon dioxide produced when 10 g of calcium carbonate (CaCO₃) is fully decomposed by heat. (Relative atomic masses: Ca = 40, C = 12, O = 16.)"

Step 1: Write the equation: CaCO₃ → CaO + CO₂

Step 2: Molar mass of CaCO₃ = 40 + 12 + (16×3) = 100 g/mol. Molar mass of CO₂ = 12 + (16×2) = 44 g/mol.

Step 3: Moles of CaCO₃ = 10 g ÷ 100 g/mol = 0.1 mol. The equation shows a 1:1 ratio, so moles of CO₂ produced = 0.1 mol.

Step 4: Mass of CO₂ = 0.1 mol × 44 g/mol = 4.4 g.

This is the exact style of multi-step calculation that costs Kenyan candidates marks when working is skipped: Cambridge mark schemes award marks at each step, not just for the final number.

IGCSE Physics (0625): What It Covers and Who Thrives

Physics is the study of matter, energy and forces. Cambridge IGCSE Physics (0625) covers:

• Measurements and units
• Motion (velocity, acceleration, Newton's laws)
• Forces (pressure, density, turning effects)
• Energy (work, power, efficiency, energy sources)
• Thermal physics (temperature, heat transfer, gas laws)
• Waves (properties, light, sound)
• Electricity and magnetism (circuits, Ohm's law, electromagnetic induction)
• Nuclear physics (radioactivity, fission, fusion)
• Space physics (Extended only)

Who thrives in Physics: Students with strong mathematical ability and logical, analytical thinking. Physics is the most mathematical of the three sciences at IGCSE level: almost every topic involves a calculation, and questions frequently combine two or three formulae in a single problem.

Mathematics demand: High. Speed, acceleration, force, electrical and wave calculations all require confident, fast manipulation of formulae under timed conditions.

Worked Example: Physics: A Motion Calculation

A standard Paper 2/4 style question: "A car accelerates uniformly from 5 m/s to 25 m/s in 8 seconds. Calculate (a) the acceleration, and (b) the distance travelled during this time."

Part (a): Acceleration = (final velocity − initial velocity) ÷ time = (25 − 5) ÷ 8 = 20 ÷ 8 = 2.5 m/s².

Part (b): Using distance = average velocity × time, average velocity = (5 + 25) ÷ 2 = 15 m/s. Distance = 15 × 8 = 120 metres.

Notice this single question already requires two separate formulae applied correctly in sequence: typical of why students who are less confident with algebra find Physics the most demanding of the three sciences, even though the underlying concept (acceleration) is conceptually simple.

Difficulty Comparison

*Difficulty varies significantly by individual strengths: these are broad generalisations based on historical grade boundary patterns, not a guarantee for any specific student. See our companion article on how Cambridge grade boundaries actually work for the full picture on how "hardness" translates into the grade you actually receive.

Common Mistakes Students Make When Choosing Sciences

• Choosing based on which teacher is more popular, not the subject's actual demands. A likeable teacher does not change the underlying skill the subject requires.
• Assuming Combined Science (0653) is always the "safe" option. It is lighter, but check it actually satisfies your target degree's entry requirement before relying on it: some Medicine and Engineering programmes require separate, full IGCSE sciences.
• Dropping Physics too early because it "feels hard now." Early Physics often feels harder than Biology because the mathematical foundation is still being built: it frequently clicks once core formulae become automatic, typically by the second term.
• Not checking university requirements before Grade 10 subject selection. Subject choices made at IGCSE constrain A Level options, which in turn constrain degree options: work backwards from the target career, not forwards from current comfort.
• Underusing past papers per subject. Each science has its own command-word patterns and mark-scheme habits; treating revision the same way across all three wastes time. See Flashcards vs Past Papers: Which Actually Works for IGCSE Revision? for a subject-specific breakdown.

Which Science for Which University Course?

A Practical Path: How to Decide This Term

1. List 3–5 realistic career directions your child is currently considering: not a single fixed choice, since interests change.
2. Cross-reference against the table above to see which sciences appear most often across those directions.
3. Talk honestly about mathematical confidence. If Mathematics is currently a weaker subject, Physics will demand the most remedial work alongside the new content: factor this into the decision, not as a reason to avoid Physics outright, but as a planning input.
4. Ask the school for a trial period or taster lessons if genuinely undecided between two sciences: many Nairobi IGCSE schools allow a few weeks of overlap before final subject confirmation.
5. Revisit the decision at the end of Term 1 using actual test results, not just first impressions, before it becomes costly to switch.

Frequently Asked Questions

Can I take all three sciences at IGCSE?

Yes, and many strong students do. Taking all three gives maximum flexibility for future subject choices at A Level. However, it increases workload significantly across three separate sets of practicals, coursework and revision schedules. Discuss with your school whether this is genuinely manageable alongside your other subjects before committing.

What is Cambridge Combined Science (0653)?

Cambridge IGCSE Combined Science (0653) covers reduced content from all three sciences across two examination papers, awarding a single combined IGCSE grade. It is a sound option for students who want a broad science foundation without the full commitment of three separate science IGCSEs. However, it may not satisfy entry requirements for Medicine, Dentistry, Pharmacy or some Engineering degree programmes: always check the specific university's requirements first.

My child is strong in Biology but struggles with Physics: do they have to take Physics?

No. Subject choice should reflect the learner's genuine strengths and interests. However, check that not taking Physics does not quietly close doors they may want to open later, particularly in Engineering or the Physical Sciences, where Physics is frequently a hard university entry requirement rather than a preference.

Which IGCSE science has the best grade boundaries: is one "easier" to score an A* in?

Grade boundaries shift every examination session based on how the whole global cohort performed on that specific paper, so there is no permanently "easier" science. See our full explainer on how Cambridge grade boundaries are set for the mechanics behind this.

Do Kenyan IGCSE schools all offer the same three sciences?

Most do, but not all schools offer Combined Science as an alternative, and some smaller schools may not offer all three separate sciences due to staffing or laboratory capacity. Confirm exact availability with each school directly: see our guide to choosing an IGCSE school in Nairobi for what else to check before enrolling.

How should I revise differently for Biology versus Physics?

Biology revision benefits most from active recall techniques (flashcards, self-testing on definitions and processes) given its memorisation load. Physics revision benefits most from repeated worked-example practice under timed conditions, since fluency with formulae only comes from doing many calculations, not from reading about them. Chemistry needs a mix of both. For a structured comparison of these techniques, see Flashcards vs Past Papers: Which Actually Works for IGCSE Revision?

Is it true that Physics has the highest grade boundaries (i.e. is hardest to get an A* in)?

Not necessarily highest boundaries, but Physics typically requires the most consistent mathematical accuracy across an entire paper, since marks are lost incrementally at each calculation step rather than on isolated recall questions. This is different from "high boundaries": it is about the unforgiving nature of multi-step numerical answers.

Bottom Line

There is no single "best" IGCSE science: only the best fit for your child's strengths and intended career direction. Biology rewards disciplined memorisation, Chemistry rewards a balance of concept and calculation, and Physics rewards mathematical confidence and precision. Whichever combination your child takes, consistent topic-by-topic practice beats last-minute cramming every time. For full revision support across all three sciences, explore the IGCSE Science notes catalogue, or get instant, subject-specific help any time with Somo, our AI tutor: KSH 300/month, 30 questions a day.