In a test of three antiseptics, one paper disc is soaked in sterile water instead of antiseptic. Why is this disc included?
To show that the bacteria used in the investigation are able to grow on the agar
To keep the number of paper discs on this agar plate the same as on other plates
To give a fixed point from which the diameter of each clear zone is measured
To show that any clear zone is caused by the antiseptic and not by the paper disc
163 exam-style questions on AQA GCSE Biology 1.1 Cell structure, covering 1.1.1 Eukaryotes and prokaryotes, 1.1.2 Animal and plant cells, 1.1.3 Cell specialisation, 1.1.4 Cell differentiation, 1.1.5 Microscopy, and 1.1.6 Culturing microorganisms. Each one has a worked solution and a mark scheme showing where the marks go.