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1.1 Cell structure

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Question 22

A water-treatment laboratory estimated the number of bacterial cells in a sample from a storage tank.

A technician spread the same volume of the diluted sample over each of two sterile nutrient agar plates. Both plates were incubated for the same time and at the same temperature, but in different positions.

PlatePosition of agar during incubationNumber of well-separated coloniesNumber of areas where colonies had joined
PAbove the lid862
QBelow the lid3914

Using the results, explain why plate P gives a more reliable estimate of the number of bacterial cells in the diluted sample than plate Q.

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Markscheme

1.1 Cell structure Questions

  1. GCSE
  2. /Biology
  3. /1.1 Cell structure

282 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.

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