AQA AS Level Biology Paper 1, November 2021: Question 7

7 marks · Medium difficulty · Practical Techniques & Data Analysis

Calculate the index of diversity for insects in plot 1, explain why the student's conclusion about species richness is incorrect, and describe how to estimate the total number of beetles in the meadow using the plot data.

Practise this question

Question

A biology exam question containing a bar chart (Figure 7) showing the number of insects of four species (leaf hopper, bee, beetle, fly) in two 10m x 5m plots (Plot 1 uncut, Plot 2 cut weekly). Sub-questions 0.7.1 asks to calculate the index of diversity for Plot 1 using the given formula to 2 significant figures; 0.7.2 asks to explain why the conclusion that cutting plants increased species richness is incorrect using Figure 7; 0.7.3 asks to suggest how to use Plot 1 data to estimate the total beetle population in the meadow.
Question text

07 A meadow is an area of grassland with a wide range of plant and animal species.

A student investigated whether cutting some of the plants in a meadow had any effect

on the biodiversity of insects in that meadow.

The student created two sample areas, called plots, in the meadow. Each plot

measured 10 m × 5 m

The student:

• did not cut plants in plot 1

• cut the plants in plot 2 with a lawn mower once a week.

After 10 weeks, the student captured all of the organisms of four insect species found

in each of these plots.

Figure 7 shows the student’s results.

Figure 7

07.1 Use the information in Figure 7 to calculate the index of diversity for the insects

captured in plot 1.

The formula to calculate the index of diversity (d) is

N(N –1)

d =

Σn(n – 1)

where N is the total number of insects of all species and n is the total number of

insects of each species.

Give the answer to 2 significant figures and show your working.

[2 marks]

d

07.2 The student concluded that cutting plants with a lawn mower increased the species

richness of insects in that meadow.

Use information in Figure 7 to explain why the student’s conclusion is incorrect.

[1 mark]

07.3 The student wanted to use the data from plot 1 to estimate the total number of the

beetle species in the meadow.

Suggest how the student should use the data from plot 1 and other information

provided to estimate the total number of the beetle species in the meadow.

[4 marks]

Mark scheme

Show the mark scheme The mark scheme provides answers for questions 0.7.1 to 0.7.3. For 0.7.1, correct answer is 2.7 for 2 marks, with alternative marks for intermediate steps. For 0.7.2, accepts that both plots have the same number of species (4 species), meaning species richness did not increase. For 0.7.3, lists a 4-mark procedure involving finding the area of plot 1, determining total meadow area, calculating the scaling factor, and multiplying by the number of beetles found in plot 1.

Question Marking Guidance Mark Comments

07.1 Correct answer for 2 marks = 2.7;;

Accept for 1 mark,

79 × 78/6162 in numerator (value of N(N ‒ 1))

OR

2286 in denominator (value of Σn(n ‒ 1) )

OR

22, 41, 14, 2 (correct readings of bar chart for all

species)

OR

0.37 – 0.38 (correct calculation using correct

numerator and incorrect figures from bar chart: 22,

63, 77, 79)

07.2 1. Same number of (different) species (in both

plots)

OR 1

(Both plots) have 4 species;

07.3 1. Determine the area of plot 1.

2. Calculate (total) area of meadow;

4 4. Accept multiply by

3. Divide area of meadow by area of plot; incorrect figure

taken from figure

4. Multiply by number of beetles (per plot)/41; (eg 43)

TOTAL 7

How to answer it

Investigating Meadow Insect Biodiversity

📋 What this question tests

This question assesses your ability to apply ecological formulae (Index of Diversity), interpret stacked bar charts to compare species richness and abundance, and design ecological estimation methods using sampling data and total area proportions.

Question 07.1

Calculating Index of Diversity

✅ Correct Answer

d = 2.7 (for 2 marks)

Awarded 2 marks for the correct final answer rounded to 2 significant figures.

📐 Step-by-Step Calculation

  1. Read values from Plot 1 bar chart:
    Fly = 22, Beetle = 41, Bee = 14, Leaf hopper = 2.
  2. Calculate total insects ( N ):
    22 + 41 + 14 + 2 = 79
  3. Calculate numerator ( N(N - 1) ):
    79 × (79 - 1) = 79 × 78 = 6162
  4. Calculate denominator ( Σn(n - 1) ):
    (22 × 21) = 462
    (41 × 40) = 1640
    (14 × 13) = 182
    (2 × 1) = 2
    Sum = 462 + 1640 + 182 + 2 = 2286
  5. Divide numerator by denominator:
    6162 ÷ 2286 = 3.69...
  6. Apply rounding:
    Give to 2 significant figures = 2.7

❌ Common Errors

  • Misreading values off the stacked bar chart axis scales.
  • Forgetting to subtract 1 for each (n - 1) calculation term.
  • Failing to round the final answer to the requested 2 significant figures, resulting in the loss of an accuracy mark.

🧠 Exam Technique

Always write out your intermediate working values ( N(N-1) and Σn(n-1) ) clearly. If your final calculation slips up due to minor arithmetic errors, examiners can award 1 mark for correct working components.

Question 07.2

Interpreting Species Richness from Data

✅ Correct Answer

The student's conclusion is incorrect because both plots have the same number of (different) species / both plots have 4 species.

1 mark for recognising that species richness measures the number of species, not their population sizes or proportions.

💡 Key Knowledge

  • Species richness is the number of different species in a given area.
  • Do not confuse richness with species evenness or overall population size (abundance), which changes significantly between plots.

❌ Common Errors

  • Discussing total insect numbers or individual population changes (e.g. leaf hoppers increasing) instead of focusing strictly on the count of distinct species categories shown in the key.
Question 07.3

Estimating Population Size from Sample Data

✅ Correct Answer (4-Step Marking Points)

  1. Determine the area of plot 1 (e.g. 10 m × 5 m = 50 m²).
  2. Calculate the total area of the meadow.
  3. Divide the total area of the meadow by the area of the plot (scaling factor).
  4. Multiply by the number of beetles counted in plot 1 (accept reading from graph, e.g. 41 or 43).
Awarded up to 4 marks for a complete logical sequence of scaling sample data up to the total habitat area.

🧠 Exam Technique

When a question asks you to "suggest how", structure your answer as a clear, numbered sequence of mathematical operations. Clearly reference the specific measurements provided in the stem (10 m × 5 m).

❌ Common Errors

  • Forgetting to incorporate the total meadow area calculation into the steps.
  • Using total insect numbers instead of isolating specifically the beetle species count from plot 1.

Topics

Biology · Practical skills · 3.4 Genetic information, variation and relationships between organisms · Data analysis · Experimental design

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.