Investigating the distribution of Pleurococcus

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Investigating the distribution of Pleurococcus

A green powdery growth is evidence of the presence of tiny single-celled plants called Pleurococcus growing on the trunk of a tree. Is the distribution of Pleurococcus on a tree trunk influenced by physical factors?


To find out whether the distribution of Pleurococcus is influenced by physical factors by using a quadrat to measure the percentage cover of Pleurococcus at different points around a tree trunk.


  • string, long enough to fasten around a tree (1.5–2 m), marked in 10 cm intervals


  • Wash your hands thoroughly after you have finished the activity.

What you need to do

1 Use your compass to find the direction of North.

2 Take your piece of string marked at 10 cm intervals. Fix it around the trunk of the tree about 1–1.5 m above the ground.

3 Place a 10 cm × 10 cm quadrat on the string at the north-facing point. Estimate percentage cover of Pleurococcus at this point.

4 Move the quadrat 10 cm along the string and repeat your estimation. Carry on until you have sampled the whole circumference of the tree.

5 Note which of your samples was taken from the trunk facing east, south and west respectively.

6 Display your results as a bar chart, plotting percentage cover against aspect (the direction in which that part of the trunk was facing).

Using the evidence

1 What conclusion can be drawn from your results? (1 mark)

2 What conditions do you think Pleurococcus needs to live? (3 marks)

3 How do environmental conditions, such as light and water, vary around the tree? (3 marks)

4 How might your answers to questions 1 and 2 explain the distribution of Pleurococcus? (1 mark)


5 a How could the method you used be made more reliable? (1 mark)

b How could the method you used be made more accurate? (1 mark)


6 a Write a hypothesis to explain the reason for the conclusion you made in question 1. (1 mark)

b Design an investigation to test your hypothesis. (6 marks)

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