Edexcel International GCSE science practicals: tested in writing

Edexcel International GCSE Biology 4BI1 and Chemistry 4CH1 each have two written papers and nothing else. You never sit a practical exam in a laboratory. But practical work is not left out. Questions about experiments appear in both Paper 1 and Paper 2, mixed in with everything else.

These questions ask you to describe how an experiment is done, name the variables, fill in or read a results table, plot or read a graph, draw a conclusion from data, or say how a method could be improved. Together, the skills they test carry around a fifth of the marks. That is too many marks to leave to luck.

Each specification lists the practicals you must know. In 4BI1 they include food tests, the effect of temperature on enzyme activity, and sampling with quadrats (specification points 2.9, 2.12 and 5.2). In 4CH1 they include paper chromatography, finding the percentage of oxygen in air, and the electrolysis of solutions. Take the full list from your own specification, and make one page of notes for each practical with five headings:

1. Aim: what the experiment finds out, in one sentence.
2. Method: the steps in order, with the apparatus named and the quantities given.
3. Variables: what you change, what you measure and what you keep the same.
4. Results: what a typical table looks like and what the results usually show.
5. Improvement: one specific way to make the results more accurate or more reliable.

If you can write that page from memory, you can answer most questions about that practical, whether or not you did it at school.

Variables

The independent variable is the one you change. The dependent variable is the one you measure. The control variables are everything you keep the same so the test is fair. Name control variables precisely: "the volume of enzyme solution" earns more than "the amount".

Results tables

Put the quantity and its unit in each column heading, for example "temperature / °C". Keep the unit out of the body of the table. Record every reading in one column to the same number of decimal places.

Conclusions

A conclusion says what the data shows, and backs it up with figures from the data. "As the temperature increased from 20 °C to 40 °C, the time taken fell from 180 s to 60 s" is stronger than "the enzyme worked faster". If the question asks you to explain the conclusion, add the science: why the change happens.

Improvement questions reward answers that fit the experiment in front of you. "Be more careful", "human error" and "use better equipment" rarely earn anything.

Pair each problem with the fix for it:

• The colour change was hard to judge, so compare each tube against a white tile.
• The temperature fell during the experiment, so use a thermostatically controlled water bath.
• The readings varied a lot, so repeat each measurement and calculate a mean, leaving out any anomalous result.
• A scale read from an angle gives a parallax error, so read it at eye level.

A quick test: could someone else carry out your improvement without asking what you meant? If so, it is specific enough.

Plenty of students have not done every practical, especially private candidates and students at schools with little lab time. The marks are all in the written papers, so you can still prepare properly:

• Learn the one-page notes above until you can write them from memory.
• Sketch the apparatus, labelled, for each practical.
• Answer past-paper questions on practicals and mark them against the mark scheme. The wording that earns marks often repeats from year to year.
• Draw the table and graph for each practical from made-up but sensible data, then write a conclusion from it.

On Eudika Learn, some of these practicals are also virtual labs, including food tests, enzymes and temperature and an acid-alkali titration. You record what you observe or measure, and answer questions on it: in the enzyme and titration labs that includes a results table and an improvement. They help you learn the method and handle data. They are not a school laboratory, and doing the real experiment is still better when you can.

If you are entering as a private candidate, ask your exam centre about anything to do with your entry.

This guide is about Biology 4BI1 and Chemistry 4CH1, the two specifications we have checked. Edexcel International GCSE Physics is 4PH1, and we do not give its paper details or weightings here. Check the 4PH1 specification yourself, or ask your teacher.

The general skills, from variables and tables to specific improvements, are the same in any science.