A student wants to estimate the concentration of bacteria in a liquid culture using a counting chamber under a microscope. The table below shows the number of bacteria counted in four separate samples using the counting chamber:
| Sample | Number of bacteria in counting chamber |
|---|---|
| 1 | 22 |
| 2 | 18 |
| 3 | 25 |
| 4 | 15 |
The dimensions of the counting chamber are:
Calculate the mean number of bacteria in the four samples.
Calculate the total area of the counting chamber in mm2\text{mm}^2mm2.
Calculate the volume of the counting chamber in mm3\text{mm}^3mm3 using the equation:
volume=area×depth \text{volume} = \text{area} \times \text{depth} volume=area×depthCalculate the mean number of bacteria per mm3\text{mm}^3mm3 of the culture using the equation:
mean number of bacteria per mm3=mean number of bacteriavolume of counting chamber \text{mean number of bacteria per }\text{mm}^3 = \frac{\text{mean number of bacteria}}{\text{volume of counting chamber}} mean number of bacteria per mm3=volume of counting chambermean number of bacteria163 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.