Investigating populationsAQA A-Level Biology: Subtopic test

1. 1
   An ecologist wants to estimate the number of dandelion plants in a meadow of area 2000 m². She places a 0.5 m × 0.5 m quadrat at 20 positions in the meadow and counts a total of 130 dandelion plants in the 20 quadrats.

   (a)

   Which method of choosing the quadrat positions would avoid bias?

   [1 mark]

   • APlacing quadrats where the dandelions look most dense
   • BPlacing quadrats at regular intervals starting from the gate
   • CUsing random numbers as coordinates on a grid laid over the meadow
   • DUsing the positions that are easiest to reach

   (b)

   Why is the quadrat method suitable for estimating the number of dandelions?

   [1 mark]

   • ADandelions are non-motile, so they stay in place while they are counted
   • BDandelions can be marked with paint and then released
   • CDandelions move too quickly to be counted by eye
   • DA quadrat counts every dandelion in the whole meadow

   (c)

   Calculate an estimate of the total number of dandelion plants in the meadow. Show your working.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A student investigates how the percentage cover of a moss species changes along a 20 m line running from the edge of a woodland into an open field. She suspects that light intensity affects the distribution of the moss.

   (a)

   Which of the following describes a belt transect?

   [1 mark]

   • AQuadrats placed at random coordinates across the whole area
   • BOnly the organisms touching a tape measure are recorded
   • COrganisms are marked, released and later recaptured
   • DQuadrats placed at regular intervals along a line, to show change in abundance across an environmental gradient

   (b)

   Which measurement should the student take at each quadrat position to test her idea?

   [1 mark]

   • AAir pressure
   • BLight intensity at ground level
   • CThe total number of species in the field
   • DThe length of the transect

   (c)

   Suggest two other abiotic factors that the student should measure or control to be confident that light intensity is responsible for the distribution of the moss.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Ground beetles in a field were sampled using pitfall traps. On day 1, 86 beetles were caught, marked with a small dot of non-toxic paint on the underside of the body and released where they were caught. Three days later, 74 beetles were caught, of which 19 were marked.

   (a)

   Calculate an estimate of the population size of the beetles. Show your working.

   [3 marks]

   (b)

   State two assumptions made when using this method. Explain how the estimate would be affected if the marked beetles were more likely to be eaten by predators than unmarked beetles.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school field slopes gradually from a dry hilltop to a damp valley bottom. A student thinks that soil water content affects the distribution of creeping buttercup in the field and plans to investigate this.

   (a)

   Describe how the student could investigate the effect of soil water content on the distribution of creeping buttercup in the field.

   [6 marks]

   (b)

   The student's results showed that the percentage cover of buttercup increased from 2% at the hilltop to 48% at the valley bottom, while soil water content rose from 12% to 41%. A Spearman's rank correlation test on the 10 sampling positions gave a coefficient of +0.91. The critical value at p = 0.05 is 0.648. The valley bottom was also shadier and the soil there had a higher pH. Evaluate the conclusion that soil water content determines the distribution of creeping buttercup in the field.

   [6 marks]

   Total for question 4: 12 marks

End of questions