How to Revise Physics, Chemistry and Biology for Cambridge O Level: A Practical 6-Week Plan.
By Zaheer | Updated 10 October 2026
Disclosure: I created the Cambridge O Level Science membership mentioned at the end of this post and sell it on Gumroad. The revision guide below works without it.
Most O Level science students don't fail because they didn't study. They fail to improve because of how they study: re-reading notes, highlighting, and leaving past papers until the last week. Physics, Chemistry and Biology each reward slightly different habits, but the same core method works for all three. This guide sets out that method, then gives subject-specific tips with worked examples, a command-word table, and a short self-test.
Paper formats and syllabus codes differ by exam series and country, so check the current Cambridge syllabus and your school's guidance for exactly what your papers contain.
Why re-reading notes isn't enough
Reading feels productive because the material looks familiar. But familiarity is not the same as being able to recall and use it under exam conditions. Techniques that make you retrieve information from memory, such as closed-book questions and past papers, tend to work better than passive review. They also show you what you don't know while there is still time to fix it.
A simple revision method for all three sciences
- List the syllabus topics and rate each one red, amber or green for how confident you are. Start with red and amber.
- Learn a small chunk (one topic, 30 to 45 minutes) from your notes or textbook.
- Close the book and test yourself. Write down everything you can recall, then check what you missed.
- Do exam-style questions on that topic, then mark them against the mark scheme.
- Revisit it later. Come back after a few days and again after a couple of weeks. Spacing your practice helps memory last.
- Mix topics in later weeks. Exams don't arrive one topic at a time, so practise switching between them.
Physics: formula, substitute, unit
Many Physics marks are lost on presentation, not understanding. Write the formula, substitute the numbers, then give the answer with its unit.
Worked example: a car accelerates from 5 m/s to 25 m/s in 8 s. Calculate its acceleration.
- acceleration = change in speed ÷ time taken
- a = (25 − 5) ÷ 8 = 20 ÷ 8
- a = 2.5 m/s²
Common slips:
- Leaving out the unit, or using the wrong one.
- Not converting units first, such as km/h to m/s or g to kg.
- Mixing up mass (kg) and weight (N). Weight = mass × gravitational field strength. Use the value of g given on your paper, commonly 10 N/kg, so a 4 kg mass weighs 40 N.
Chemistry: balanced equations and mole calculations
Chemistry rewards accuracy. Balance every equation, include state symbols when asked, and set mole calculations out in clear steps.
Worked example: how many moles are in 25 g of calcium carbonate, CaCO3? (Ar: Ca = 40, C = 12, O = 16.)
- Mr of CaCO3 = 40 + 12 + (3 × 16) = 100
- moles = mass ÷ Mr = 25 ÷ 100
- moles = 0.25 mol
Learn the standard gas tests, because they appear often:
- Hydrogen: a lighted splint gives a squeaky pop.
- Oxygen: a glowing splint relights.
- Carbon dioxide: bubbled through limewater turns it milky (cloudy).
- Chlorine: bleaches damp litmus paper.
- Ammonia: turns damp red litmus paper blue.
Biology: precise wording
In Biology, the idea is often right but the wording loses the mark. Learn key definitions word for word, and use scientific terms rather than everyday ones.
- Diffusion: the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.
- Osmosis: the net movement of water molecules from a dilute solution to a more concentrated solution, through a partially permeable membrane.
Also watch for confusion between similar terms, such as respiration (a chemical reaction in cells that releases energy) and breathing (moving air in and out of the lungs). For a closer look at how wording costs marks, see my guide on why students lose marks on enzymes.
Practical skills count in every science
- Name the independent variable (what you change), the dependent variable (what you measure) and the control variables (what you keep the same).
- Read scales carefully and record units in table headings.
- When drawing graphs, label both axes with units, use most of the grid, plot points precisely and draw a smooth line or line of best fit.
- Say how you would make the results more reliable, for example by repeating the experiment and calculating a mean.
Know your command words
| Command word | What the examiner wants |
|---|---|
| State | A short, direct answer with no explanation |
| Describe | What happens or what you see, without giving reasons |
| Explain | Give reasons, usually with "because" or a scientific link between cause and effect |
| Calculate | Use numbers, show your working and include units |
| Suggest | Apply your knowledge to a situation you haven't seen before |
| Compare | Give similarities and differences, not just a description of each |
A 6-week revision plan
Adjust this to the time you have left before your exams.
| Week | Focus |
|---|---|
| 1 | List all topics, rate them red/amber/green, gather past papers and mark schemes |
| 2 to 3 | Work through red topics in all three subjects, using the method above |
| 4 | Amber topics, plus definitions, formulae and gas tests learned from memory |
| 5 | Full past-paper sections under timed conditions, then mark and list every lost mark |
| 6 | Fix the repeated errors, revisit weak topics and complete a full paper |
Try it yourself: 6-question self-test
- Physics: a cyclist speeds up from 2 m/s to 10 m/s in 4 s. Calculate the acceleration.
- Physics: find the weight of a 6 kg mass. (Use g = 10 N/kg.)
- Chemistry: calculate the moles in 50 g of CaCO3. (Ar: Ca = 40, C = 12, O = 16.)
- Chemistry: describe the test for carbon dioxide and the positive result.
- Biology: define diffusion.
- Biology: explain why a plant cell becomes turgid when placed in pure water.
Answers
- (10 − 2) ÷ 4 = 2 m/s²
- 6 × 10 = 60 N
- Mr = 100, so 50 ÷ 100 = 0.5 mol
- Bubble the gas through limewater; the limewater turns milky (cloudy).
- The net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random movement.
- Water enters the cell by osmosis, because the surrounding water is more dilute than the cell contents. The vacuole and cytoplasm swell and push against the cell wall, which stops the cell bursting, so the cell becomes firm (turgid).
Where my Cambridge O Level Science membership fits
I built the Cambridge O Level Science membership for students who want to practise actively rather than just read. It contains interactive labs across Physics, Chemistry and Biology. You can choose the subject you need or get all three at a lower combined rate, and new volumes are added automatically at no extra cost. It runs fully offline once downloaded, with no ads.
It is meant for O Level students revising on their own, parents helping at home, and tutors running structured sessions. It supports revision but doesn't replace your textbook, your teacher or Cambridge past papers, and you should always check topics against your own syllabus.
You can find it on Gumroad.
Frequently asked questions
How many hours a day should I revise?
There is no single right answer. Short, focused sessions with breaks, done consistently, usually beat long, tiring ones. Start with what you can sustain.
Should I revise one subject at a time or all three?
Early on, working topic by topic is fine. In the later weeks, mixing subjects and topics gives better practice for the exam.
What if I run out of past papers?
Redo old ones after a few weeks, this time closed-book, and focus on the questions you got wrong the first time.
Is there similar guidance for other
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