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OCR Gateway Combined Science A assesses your practical work entirely within the six written papers — there is no separate practical exam. Across the course you carry out a set of required practical activities, often called PAGs (Practical Activity Groups), spanning biology, chemistry and physics. Questions about them can appear on any of the six papers, and they can ask you to describe a method, identify variables, spot sources of error, interpret results, evaluate an investigation, suggest improvements, or do a calculation from practical data. Because the skills are common to all three sciences, learning them once pays off everywhere.
By the end of this lesson you should be fluent in the language of working scientifically, know the standard required practicals in each science and their most common exam question, and be able to identify apparatus, variables and errors confidently.
Required-practical questions mostly target AO1 (recalling a method and apparatus) and AO2 (applying it to identify variables or errors), rising to AO3 when you evaluate an investigation or suggest improvements.
Exam Tip: Practical questions are not always flagged as "practical" — they appear as ordinary structured or 6-mark questions. Recognise them from the context (apparatus, a method, a results table) and reach for your working-scientifically vocabulary.
Almost every practical question, in any science, rewards the same handful of ideas. Learn them as a checklist you can apply to any investigation:
| Term | Definition | Watch out for |
|---|---|---|
| Accuracy | How close a measurement is to the true value | A precise result can still be inaccurate (e.g. a balance reading 2 g too high every time) |
| Precision | How close repeated measurements are to each other | Precision alone does not prove correctness |
| Repeatability | Same person, same method, similar results | Improved by repeats and controlling variables |
| Reproducibility | Different people/equipment, similar results | Stronger evidence than repeatability alone |
Exam Tip: "Suggest one improvement to this method" is one of the most frequent practical questions in every science. Strong answers name a specific control variable the method missed, add repeats and a mean, or use equipment of higher resolution — never just "be more careful".
The activities below are the standard set you meet in the biology topics. Always check your specification and your school's practical record for the exact activities you completed.
| Practical | Aim | Key variables | Common exam question |
|---|---|---|---|
| Microscopy | Observe and draw cells | IV = magnification; DV = detail seen | Calculate actual size or magnification; draw a labelled diagram |
| Osmosis in plant tissue | Effect of concentration on potato mass | IV = concentration; DV = % change in mass | Explain mass change; calculate % change |
| Food tests | Identify starch, sugars, protein, lipid | IV = food sample; DV = colour change | Describe the test and positive result for each molecule |
| Enzymes | Effect of pH or temperature on amylase | IV = pH/temperature; DV = time to digest starch | Explain the rate curve using denaturation |
| Photosynthesis | Effect of light intensity on pondweed | IV = lamp distance; DV = bubbles per minute | Explain why the rate levels off (a limiting factor) |
| Sampling (quadrats/transects) | Estimate abundance or distribution | IV = location; DV = number/% cover | Estimate a population; explain random sampling |
A worked reminder of two frequent biology moves:
Exam Tip: For any biology enzyme or photosynthesis practical, the mark-winning explanation is almost always denaturation (active site changes shape) or a limiting factor (the rate can only go as fast as its slowest-supplied requirement). Have both phrases ready.
| Practical | Aim | Key variables | Common exam question |
|---|---|---|---|
| Making a soluble salt | Prepare a pure, dry salt | Technique-based (no IV/DV) | Describe the method: excess base → filter → evaporate → crystallise |
| Titration | Find a neutralisation volume | IV = volume of one solution; DV = end point | Describe the method; read a burette; calculate concentration |
| Temperature changes | Exothermic vs endothermic reactions | IV = reaction/type; DV = temperature change | Interpret a temperature–time graph |
| Rates of reaction | Effect of concentration on rate | IV = concentration; DV = time for a change | Calculate rate; explain using collision theory |
| Chromatography | Separate and identify a mixture | IV = substance; DV = distance moved / Rf | Calculate an Rf value; identify components |
| Electrolysis | Products at the electrodes | IV = solution; DV = products formed | Predict products; link to reactivity |
Two frequent chemistry moves worth rehearsing:
Exam Tip: In a titration, name the equipment precisely — burette, pipette, conical flask, white tile — and describe the end point (a permanent colour change of the indicator). "Container" and "when it changes colour a bit" will not score.
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