Required Practicals — Overview and Common Questions

The AQA GCSE Combined Science: Trilogy specification (8464) includes 21 required practicals (8 Biology, 8 Chemistry, 5 Physics). Although you do not sit a separate practical exam, questions about these practicals appear on every paper and account for approximately 15% of the total marks. This lesson provides an overview of all 21 practicals and the types of questions you can expect.

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Why Required Practicals Matter

• At least 15% of marks (around 63 marks out of 420) are directly linked to practical skills.
• Questions may ask about the method, variables, results, evaluation or improvements.
• Even if you did not carry out a practical in class, you are still expected to know it for the exam.

Exam Tip: You do not need to memorise every practical word-for-word. Instead, focus on understanding the purpose, key variables, method summary, expected results and potential sources of error for each one.

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The 21 Required Practicals

Biology Required Practicals (Papers 1 and 2)

#	Practical	Paper	Key variables
1	Microscopy — using a light microscope to observe cells	Paper 1	Magnification (IV), cell features observed (DV)
2	Microbiology — investigating the effect of antiseptics on bacterial growth	Paper 1	Type of antiseptic (IV), zone of inhibition diameter (DV)
3	Osmosis — investigating the effect of concentration on mass change in plant tissue	Paper 1	Concentration of sucrose solution (IV), percentage change in mass (DV)
4	Food tests — testing for starch, sugars, proteins and lipids	Paper 1	Type of food sample (IV), colour change (DV)
5	Enzymes — investigating the effect of pH on enzyme activity	Paper 1	pH (IV), time to react / rate of reaction (DV)
6	Photosynthesis — investigating the effect of light intensity on the rate of photosynthesis	Paper 1	Light intensity / distance (IV), rate of oxygen production (DV)
7	Reaction time — investigating factors affecting human reaction time	Paper 2	Factor tested e.g. caffeine (IV), reaction time (DV)
8	Plant responses — investigating the effect of light or gravity on seedling growth	Paper 2	Direction of light / gravity (IV), direction of growth (DV)

Chemistry Required Practicals (Papers 3 and 4)

#	Practical	Paper	Key variables
9	Making salts — preparing a pure, dry sample of a soluble salt	Paper 3	N/A — technique-based practical
10	Electrolysis — investigating electrolysis of aqueous solutions	Paper 3	Type of solution / concentration (IV), products at electrodes (DV)
11	Temperature changes — investigating exothermic and endothermic reactions	Paper 3	Type of reaction (IV), temperature change (DV)
12	Rates of reaction — investigating factors affecting rate (e.g. concentration, temperature)	Paper 4	Concentration / temperature (IV), time for reaction / rate (DV)
13	Chromatography — investigating the composition of inks and food colourings	Paper 4	Type of substance (IV), Rf value (DV)
14	Identifying ions — testing for cations and anions	Paper 4	Unknown sample (IV), observation / precipitate colour (DV)
15	Water purification — analysis and purification of water samples	Paper 4	Method of purification (IV), purity of water (DV)
16	Neutralisation — investigating strong acid and strong alkali titrations	Paper 3	Volume of alkali (IV), end point / colour change (DV)

Physics Required Practicals (Papers 5 and 6)

#	Practical	Paper	Key variables
17	Specific heat capacity — investigating the relationship between energy, mass and temperature change	Paper 5	Type of material / mass (IV), temperature change (DV)
18	Resistance — investigating factors affecting resistance (length, type of wire)	Paper 5	Length of wire (IV), resistance / current (DV)
19	I-V characteristics — investigating current-voltage for a resistor, lamp and diode	Paper 5	Voltage (IV), current (DV)
20	Density — investigating the densities of regular and irregular solids and liquids	Paper 5	Type of material (IV), density (DV)
21	Force and extension — investigating the relationship between force and extension of a spring	Paper 6	Force applied (IV), extension (DV)

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Common Practical Questions in the Exam

Exam questions on required practicals fall into predictable categories. Here is what to expect:

1. Variables Questions

"Identify the independent variable, dependent variable and one control variable."

• Independent variable (IV): What you deliberately change.
• Dependent variable (DV): What you measure.
• Control variables: What you keep the same to make it a fair test.

2. Method Questions

"Describe how you would carry out this practical."

• Write in logical order, step by step.
• Name specific equipment (e.g. "measuring cylinder" not "container").
• State how you would measure the DV.
• Include how you would make it a fair test.

3. Results and Data Questions

"Calculate the mean / Plot a graph / Describe the pattern."

• Know how to calculate a mean (ignore anomalies).
• Know how to plot graphs with labelled axes and a line of best fit.
• Know how to describe trends using data from the question.

4. Evaluation Questions

"Suggest one improvement to increase the accuracy / reliability of the results."

Improvement	Why it helps
Take more repeats and calculate a mean	Reduces the effect of random errors; makes results more reliable
Use a data logger instead of manual readings	Reduces human error; more precise
Use a larger range of the IV	Allows you to see the full trend
Use smaller intervals of the IV	Gives more data points; smoother graph
Control temperature with a water bath	Reduces a confounding variable

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Key Practical Skills Assessed

The specification defines a set of practical skills that are assessed across all papers:

flowchart TD
    A["Practical Skills"] --> B["Planning"]
    A --> C["Recording"]
    A --> D["Analysing"]
    A --> E["Evaluating"]
    B --> B1["Identify variables"]
    B --> B2["Write a method"]
    B --> B3["Risk assessment"]
    C --> C1["Tables with headings and units"]
    C --> C2["Appropriate precision"]
    D --> D1["Calculate means"]
    D --> D2["Plot graphs"]
    D --> D3["Identify patterns"]
    E --> E1["Identify anomalies"]
    E --> E2["Suggest improvements"]
    E --> E3["Evaluate accuracy and precision"]

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Good vs Poor Practical Answers

Question: "A student investigated osmosis using potato chips in different concentrations of sucrose solution. Describe the results you would expect."

Poor answer: "The potato would change mass."

Good answer: "In dilute sucrose solutions (lower concentration than the cell contents), water moves into the potato cells by osmosis, so the chips gain mass. In concentrated sucrose solutions (higher concentration than the cell contents), water moves out of the cells by osmosis, so the chips lose mass. At the point where the solution concentration equals the concentration inside the cells, there is no net movement of water and the mass stays the same."