AQA A-level Biology: Biodiversity, Index of Diversity and Farming (7402) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover AQA A-level Biology (7402) section 3.4.6, Biodiversity within a community, from the AQA AS and A-level Biology specification for first teaching 2015, including maths skill MS 2.3. All data are invented. Use d = N(N − 1) ÷ Σn(n − 1), where N is the total number of organisms of all species and n is the number of organisms of each species. Teaching is in the study guide and the revision notes. Course pages: AQA A-level Biology hub and the printable checklist.

Questions

1. (a) Define the term species richness. [1] (b) A student says that richness is a full measure of a community’s diversity. Explain why this is not correct. [2]

2. Two ponds were sampled by netting for the same time. The numbers of individuals of each invertebrate species are shown.

Pond	Counts per species
A	16, 12, 9, 5, 3, 1
B	40, 4, 2, 1

(a) Calculate the index of diversity for pond A. Show your working and give your answer to 3 significant figures. [3] (b) The index of diversity for pond B is 1.37. Show that this value is correct. [3] (c) Compare the diversity of the two ponds. [2]

3. A woodland floor sample had six species with 11, 8, 6, 4, 3 and 2 individuals. (a) Show that the index of diversity is 5.2 to 2 significant figures. [3] (b) Suggest two ways of making the sample more representative of the whole woodland floor. [2]

4. Explain how each of the following farming techniques can reduce biodiversity. (a) Growing one crop species over a very large area year after year. [2] (b) Spraying a broad-spectrum insecticide over the crop. [2]

5. A sampling site on a coast had five species with 9 individuals each. (a) Calculate the index of diversity. [3] (b) A second site had five species and 45 individuals in total, but the counts were 41, 1, 1, 1 and 1. Calculate its index of diversity to 3 significant figures. [2] (c) Explain why the two sites have the same species richness but different values of the index. [1]

6. A roadside verge was sampled and the counts of five species were 22, 6, 3, 1 and 1. (a) Calculate the index of diversity to 3 significant figures. [3] (b) Explain why a species with only one individual contributes nothing to the denominator, and state what happens to the calculation if every species in a sample has only one individual. [2]

7. A stream beside an arable field was sampled for invertebrates before and after the crop was sprayed with insecticide. Before, the counts per species were 19, 14, 10, 7, 5 and 3. After, they were 27, 4 and 3, with no other species found. (a) Calculate the index of diversity before and after spraying, each to 3 significant figures. [4] (b) Using the rounded values from part (a), calculate the percentage change in the index. [1] (c) Suggest how the insecticide could have affected the stream community. [1]

8. A sample of 12 individuals from a grassland had four species, with 5, 4, 2 and 1 individuals. A much larger random sample of 240 individuals had five species and gave an index of 3.5. (a) Calculate the index of diversity for the sample of 12 to 3 significant figures. [3] (b) Explain why the larger sample gives a more reliable value of the index. [2]

9. Biodiversity can be described at a range of scales. Describe how biodiversity can be considered from a small local habitat up to the Earth, and explain why it would not be valid to compare the number of species in a single pond with the number of species in a whole country. [4]

10. In a trial on an arable farm, three fields were managed differently: field 1 had no sown margin, and fields 2 and 3 had native flowering plants sown on 6% and 12% of their area. Invertebrates were sampled with the same effort in each field.

Field	Sown margin (% of area)	Crop yield (tonnes per hectare)	Index of diversity
1	0	8.0	1.5
2	6	7.6	4.9
3	12	7.2	5.7

(a) Calculate the percentage change in yield between field 1 and field 2. [1] (b) Calculate the percentage change in the index of diversity between field 1 and field 2. [2] (c) Evaluate the use of sown margins on this farm, using the data and your own knowledge. [5]

11. Discuss the balance between conservation and farming. [6]

Answers

1. (a) A count of how many different species are present in a community [1]. [1] (b) It takes no account of the number of individuals of each species [1], so a community with an even spread and one dominated by a single species can have the same richness [1]. [2] Examiner insight: Say what richness leaves out (abundance), then show the consequence with a contrast.

2. (a) N = 16 + 12 + 9 + 5 + 3 + 1 = 46, so N(N − 1) = 46 × 45 = 2070 [1]. Σn(n − 1) = 240 + 132 + 72 + 20 + 6 + 0 = 470 [1]. d = 2070 ÷ 470 = 4.40 [1]. [3] (b) N = 40 + 4 + 2 + 1 = 47, so N(N − 1) = 47 × 46 = 2162 [1]. Σn(n − 1) = 1560 + 12 + 2 + 0 = 1574 [1]. d = 2162 ÷ 1574 = 1.373, which is 1.37 [1]. [3] (c) Pond A has more species (6 against 4) and a higher index (4.40 against 1.37), so A is more diverse [1]. In B one species makes up 40 of the 47 individuals [1]. [2] Examiner insight: In a “show that” question the answer is given, so list each n(n − 1) term to show the working.

3. (a) N = 34, so N(N − 1) = 34 × 33 = 1122 [1]. Σn(n − 1) = 110 + 56 + 30 + 12 + 6 + 2 = 216 [1]. d = 1122 ÷ 216 = 5.19, which is 5.2 to 2 significant figures [1]. [3] (b) Use random sampling, for example random coordinates for quadrat or trap positions [1]; take more samples from different parts of the woodland, and at more than one time of year [1]. [2] Examiner insight: “Take more samples” is stronger when it says where or when.

4. (a) There are fewer plant species [1], so fewer food sources and niches, which supports fewer animal species [1]. [2] (b) It kills non-target insects as well as the pest [1], reducing the food supply for animals that eat insects, so fewer species survive [1]. [2] Examiner insight: Give a chain from cause to effect; “kills wildlife” alone is too vague.

5. (a) N = 45, so N(N − 1) = 45 × 44 = 1980 [1]. Each species gives 9 × 8 = 72, so Σn(n − 1) = 5 × 72 = 360 [1]. d = 1980 ÷ 360 = 5.5 [1]. [3] (b) N(N − 1) = 1980 [1]. Σn(n − 1) = 1640 + 0 + 0 + 0 + 0 = 1640, so d = 1980 ÷ 1640 = 1.21 [1]. [2] (c) Richness counts only the number of species, but the index also depends on how the individuals are spread; in the second site one species dominates, so d is lower [1]. [1] Examiner insight: Name what each measure uses: species only, or species and numbers.

6. (a) N = 33, so N(N − 1) = 33 × 32 = 1056 [1]. Σn(n − 1) = 462 + 30 + 6 + 0 + 0 = 498 [1]. d = 1056 ÷ 498 = 2.12 [1]. [3] (b) For n = 1, n(n − 1) = 1 × 0 = 0 [1]. If every species has one individual, Σn(n − 1) = 0, so the division is by zero and d cannot be calculated (the sample is too small to use) [1]. [2] Examiner insight: Write single-individual terms as 0.

7. (a) Before: N = 58, N(N − 1) = 58 × 57 = 3306 [1]. Σn(n − 1) = 342 + 182 + 90 + 42 + 20 + 6 = 682, so d = 3306 ÷ 682 = 4.85 [1]. After: N = 34, N(N − 1) = 34 × 33 = 1122 [1]. Σn(n − 1) = 702 + 12 + 6 = 720, so d = 1122 ÷ 720 = 1.56 [1]. [4] (b) (1.56 − 4.85) ÷ 4.85 × 100 = −67.8% (a decrease of about 68%) [1]. [1] (c) Insecticide reaching the stream killed sensitive invertebrates, so richness fell from 6 to 3 and one species dominated [1]. [1] Examiner insight: Divide a percentage change by the old value and state rise or fall.

8. (a) N = 12, so N(N − 1) = 12 × 11 = 132 [1]. Σn(n − 1) = 20 + 12 + 2 + 0 = 34 [1]. d = 132 ÷ 34 = 3.88 [1]. [3] (b) A larger sample is more likely to include all the species, including rare ones [1], so it is more representative and less affected by chance [1]. [2] Examiner insight: Link sample size to species missed and chance variation.

9. Biodiversity can be considered in a small local habitat such as a pond [1], a larger habitat such as a woodland [1], a region or country, and the whole Earth [1]. It would not be valid to compare a pond with a country because the areas and sampling effort are very different, so any difference would reflect the scale of the area and not the habitat [1]. [4] Examiner insight: Give a reason about scale or effort.

10. (a) (7.6 − 8.0) ÷ 8.0 × 100 = −5.0% [1]. [1] (b) (4.9 − 1.5) ÷ 1.5 × 100 [1] = +227% (to 3 significant figures; about 227%) [1]. [2] (c) Sown margins of 6% raised the index by 227% for a 5.0% drop in yield, a large gain for a small cost [1]. Going from 6% to 12% raised the index by only about 16% but cut yield by a further 5.3% [1], so the extra margin gives less benefit for a similar cost [1]. The 6% margin appears the better compromise [1]. Limits: one trial and one year; only invertebrates sampled; no data on income or costs [1]. [5] Examiner insight: Use figures from the table, weigh benefit against cost, and state what the data cannot show.

11. Farming provides food for a growing population and income for farmers, and intensive methods give high yield from less land [1]. Monoculture, hedgerow removal and pesticides reduce biodiversity [1]. Conservation protects species and keeps ecosystems resilient [1], and wild species can help farming, for example pollinators and predators of pests [1]. Compromises include sown margins, kept hedgerows, crop rotation and reduced pesticide use [1]. The balance depends on evidence, such as the gain in diversity compared with the loss in yield, and a good answer ends with a reasoned conclusion [1]. [6] Examiner insight: Give both sides and finish with a reasoned judgement.

Where marks are usually lost

• Writing n² or N² instead of n(n − 1) and N(N − 1).
• Giving only the answer in a “show that” question, or ignoring the number of significant figures asked for.
• Counting a species with n = 0 as present, or dividing the wrong way round so d is below 1.
• Confusing richness (species only) with the index (species and abundance).
• Dividing a percentage change by the new value instead of the old one.
• Giving effects of farming with no mechanism, or one-sided answers on the balance.

Next steps

• Revisit the study guide and the revision notes.
• See the AQA A-level Biology hub and the printable checklist.
• Take all free 10-minute diagnostics to find what to revise next.
• Book a free trial class for help with this topic.

Official syllabus

AQA AS and A-level Biology specification (7401, 7402), for first teaching 2015, published by AQA. These questions are aligned to section 3.4.6 and maths skill MS 2.3.