GCSE Biology Required Practicals: Microscopy, Osmosis and Food Tests

Questions about required practical activities make up a significant share of the marks in GCSE Biology, and many of them are calculations. This material covers the practicals from the cell biology and organisation topics: using a light microscope, investigating osmosis in plant tissue, testing foods for starch, sugars, protein and lipids, and, for students taking separate Biology, growing bacteria with aseptic technique to test the effect of antiseptics or antibiotics.

For each practical the questions focus on what examiners ask about: the method in the right order, the independent, dependent and control variables, safety, and how to process the results. In microscopy you calculate magnification from image size and real size, convert between millimetres and micrometres, and write sizes in standard form. In the osmosis practical you calculate percentage change in mass (keeping the negative sign when the tissue loses water), explain why percentage change and blotting improve the comparison, and read the concentration of the cell contents from the point where the change in mass is zero. The food tests section matches each reagent to its positive result and covers the heating step in the Benedict's test and the flammability of ethanol. The microbiology section covers sterilising the loop, taping the lid without sealing it, incubating at no more than 25 °C in a school laboratory, calculating the area of a clear zone with πr², and working out bacterial numbers after a number of divisions.

The content follows the practical activities listed in the DfE GCSE biology subject content, organised as in the exam-board specifications (for example, the AQA required practicals on microscopy, microbiology, osmosis and food tests). The aseptic technique practical is part of separate GCSE Biology and not Combined Science for most boards.

Four formats are offered. The quiz has twelve questions with full explanations and worked calculations. The flashcards cover the key terms and formulae, from magnification and resolution to zone of inhibition. The printable written sheet has eight longer questions — method descriptions, a table of osmosis results to process, zone areas to compare and a bacterial growth calculation — to answer by hand and photograph for feedback. The oral exam lets you explain the methods to an examiner who asks one question at a time and gives short feedback at the end.

All data in the questions are illustrative, written to practise the calculations rather than to reproduce real class results. Use the material after doing the practicals in class, or before a mock, to check that you can describe each method clearly and handle the numbers with confidence.

• Calculate magnification, real size and image size, converting between mm, µm and standard form
• Describe how to prepare and observe an onion epidermis slide
• Identify variables in the osmosis practical and calculate percentage change in mass
• Estimate the concentration of plant cell contents from osmosis results
• Describe the food tests for starch, reducing sugars, protein and lipids with their positive results
• Describe aseptic technique and calculate the area of a clear zone and bacterial numbers after n divisions

Practice material written by Zestly, based on the practical activities in the DfE GCSE biology subject content and the corresponding exam-board required practicals (for example, AQA GCSE Biology 8461: microscopy, microbiology, osmosis and food tests). All data are illustrative.