Estimating population size in the field and the laboratory

Overview

Capture–mark–recapture technique, relationship used to estimate population size from a capture–mark–recapture study and three assumptions made when using capture–mark–recapture.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What is a haemocytometer?

   Model answer

   A haemocytometer is a thick microscope slide with a counting grid of known dimensions etched on it and a coverslip held a known depth above that grid.

2. 2

   What must a culture medium supply if a yeast population is to grow in it?

   Model answer

   It must supply a carbohydrate such as glucose as an energy source, a source of nitrogen for making amino acids, mineral ions and water, at a suitable pH and temperature.

3. 3

   Why must the depth of liquid beneath the coverslip of a haemocytometer be fixed?

   Model answer

   A known depth combined with a known area gives a known volume, and it is the volume that turns a count of cells into a cell density.

4. 4

   The central grid of a haemocytometer measures 1 mm by 1 mm and the liquid above it is 0.1 mm deep. Calculate the volume counted.

   Model answer

   The volume counted is 0.1 mm³.

5. 5

   A total of 250 yeast cells is counted over a grid holding 0.1 mm³ of suspension. Calculate the cell density in cells per mm³.

   Model answer

   The cell density is 2500 cells mm⁻³.

6. 6

   Express a yeast density of 2500 cells mm⁻³ in cells per cm³.

   Model answer

   A density of 2500 cells mm⁻³ is 2.5 × 10⁶ cells cm⁻³.

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