AQA AS Level Biology Paper 1, June 2023: Question 7

8 marks · Medium difficulty · Practical Techniques & Data Analysis

Analyze prokaryotic biodiversity and agricultural impact using data from two farming methods, including definitions of biodiversity indices and evaluation of conservation versus farming balance.

Practise this question

Question

A three-part exam question about prokaryotic biodiversity in soil under two different farming methods. It includes Table 4 presenting data for mean species richness, mean index of diversity, mean total prokaryotic biomass, mean carbon stored, and mean wheat yield for farming method 1 and farming method 2, along with standard deviations. Question 07.1 asks to describe differences using standard deviation data and give definitions of species richness and index of diversity (4 marks). Question 07.2 asks to suggest why knowledge of prokaryotic biodiversity has increased given that most soil prokaryotes do not grow on agar plates (2 marks). Question 07.3 asks to evaluate the balance between conservation and farming for the two methods using Table 4 (2 marks).
Question text

07 Scientists investigated biodiversity in prokaryote communities found in soil.

The scientists:

• took soil samples from fields that had been managed for 20 years with two different

farming methods

• sequenced all the DNA that coded for prokaryotic ribosomal RNA in the soil

samples

• compared these base sequences to give a measure of species richness and an

index of diversity for the prokaryote community

• recorded the total prokaryotic biomass and the mass of stored carbon for each soil

sample

• obtained the mean wheat yield from the fields.

Table 4 shows the scientists’ results.

Table 4

Farming Farming

Data collected

method 1 method 2

Mean species richness 517 560

(± 2 × standard deviation) (± 17) (± 24)

Mean index of diversity 0.251 0.230

(± 2 × standard deviation) (± 0.011) (± 0.014)

Mean total prokaryotic biomass / kg m–3 0.24 0.40

Mean carbon stored in soil organisms / μg g–1 203 342

Mean wheat yield / g m–2 451 377

The mean ± 2 × standard deviation includes 95% of the data.

07.1 Using the standard deviation data from Table 4, describe the differences in

prokaryotic biodiversity found in the soil with these two farming methods.

In your answer, give the definitions of species richness and index of diversity.

[4 marks]

07.2 Genetic diversity in soil species was traditionally inferred by making observations after

growing prokaryotes on agar plates.

However, it is estimated that less than 10% of prokaryotes found in soil will grow if

spread on an agar plate in a laboratory.

In recent years, our knowledge of prokaryotic biodiversity in the soil has increased.

Suggest why.

[2 marks]

07.3 Evaluate the balance between conservation and farming for these two farming

methods.

Use the information provided in Table 4 (on page 16).

[2 marks]

Mark scheme

Show the mark scheme Mark scheme providing answers for questions 07.1, 07.2, and 07.3. For 07.1, it awards marks for definitions of species richness and index of diversity, and for noting whether standard deviation overlaps indicate significant differences. For 07.2, accepted answers include the use of DNA or genome sequencing to analyze species rather than relying on observable characteristics. For 07.3, it outlines points evaluating higher species richness and carbon storage versus lower wheat yield in farming method 2.

Question Marking Guidance Mark Comments

1. Species richness – number of species (in a

1. Reject number of

community/habitat/ecosystem/area);

species in a

2. Index of diversity – the relationship between the population.

number of species (in a community) and the

number of individuals in each species; 2. Accept equation

3. No SD overlap for species richness with N and n correctly

so significant difference shown explained

OR

No SD overlap for species richness so difference (2 x

07.1

not due to chance; AO1, 2

x AO2)

4. SD overlap so no significant difference in index

of diversity

OR

SD overlap so any difference shown due to

chance;

1. DNA/genome sequencing now used; 1. Accept RNA/amino

acid sequencing

2. (Now) can analyse every/more prokaryote 2 max

07.2 species (in the community); (2 x

2. Accept ‘identify’ for

AO2)

3. Rather than just recording analyse

measurable/observable characteristics;

(For farming method 2 has) Accept converse for

farming method 1

1. Better conservation as higher species richness,

higher (prokaryotic) biomass and more carbon

stored (than farming method 1);

2. More microbial mass – more organisms for food 2 max

07.3 web; (2 x

3. Higher species richness – more organisms for AO3)

food web;

4. More stored carbon, less CO2 in the atmosphere;

5. Lower yield so less food/less profit;

How to answer it

Investigating Biodiversity in Soil Prokaryote Communities

📌 What this question tests

This question assesses your understanding of ecological terminology (species richness vs. index of diversity), your ability to interpret standard deviation data to determine significant differences, how modern DNA sequencing has transformed microbiology compared to traditional culture-based methods, and how to evaluate complex trade-offs between agricultural yield and environmental conservation.

Question 07.1

Comparing Prokaryotic Biodiversity Using Standard Deviations

Analyze the differences in prokaryotic biodiversity using Table 4 data and provide key definitions.

✅ Correct Answer Structure

  • Species richness definition: The number of different species in a community/habitat/ecosystem/area.
  • Index of diversity definition: The relationship between the number of species in a community and the number of individuals in each species.
  • Species richness comparison: Farming method 2 has a significantly higher species richness than method 1 because their standard deviation ranges do not overlap.
  • Index of diversity comparison: There is no significant difference in the index of diversity between the two methods because their standard deviations overlap.

💡 Key Knowledge

  • Standard deviation indicates the spread of data around the mean.
  • When comparing data with mean ± 2 × standard deviation , non-overlapping ranges mean the difference is statistically significant (not due to chance).
  • Overlapping ranges mean any observed difference is likely due to chance.

🧠 Exam Technique

  • When asked to "describe differences using data", always quote or explicitly reference the statistical values (e.g., standard deviation overlap/non-overlap).
  • Make sure definitions are precise: never refer to species richness as "number of species in a population"—it must be a community or habitat.

❌ Common Errors

  • Confusing species richness with population size or species evenness.
  • Failing to mention standard deviation overlap when explaining why a difference is or isn't significant.
  • Using imprecise language like "amount of species" instead of "number of species".
Mark Allocation: 4 marks total (2 marks for definitions of ecological terms, 2 marks for data interpretation using standard deviations).
Question 07.2

Advances in Microbial Biodiversity Knowledge

Suggest why our knowledge of prokaryotic biodiversity in soil has increased in recent years.

✅ Correct Answer

  • DNA sequencing / genome sequencing is now used.
  • We can now analyze every or more prokaryote species present in the community.
  • Scientists can sequence DNA directly rather than relying on culturing organisms (overcoming the limitation that most soil prokaryotes do not grow on agar plates).

🧠 Exam Technique

  • Look at the stem clue: the introduction explicitly mentions that scientists "sequenced all the DNA that coded for prokaryotic ribosomal RNA". Connect this technique back to historical limitations (agar plates).
  • Accept alternative valid phrasing such as RNA sequencing or amino acid sequencing.
Mark Allocation: 2 marks max (Awarded for recognizing DNA sequencing technology and its ability to analyze unculturable species).
Question 07.3

Evaluating Conservation vs. Farming

Evaluate the balance between conservation and farming for these two farming methods using Table 4.

✅ Correct Answer

  • Farming Method 2 wins on Conservation: Higher species richness, higher prokaryotic biomass, and more carbon stored in soil organisms (reducing atmospheric CO₂).
  • Farming Method 1 wins on Agriculture: Higher wheat yield, producing more food and profit.
  • Biodiversity/conservation benefits include a larger microbial mass supporting more complex food webs.

💡 Key Knowledge

  • An "evaluate" question requires looking at both sides of the argument: the environmental/conservation benefits versus the agricultural/economic costs.
  • Higher carbon storage in soil helps mitigate climate change by locking away carbon that would otherwise form CO₂.

❌ Common Errors

  • Only discussing one side (e.g., only talking about how great method 2 is for biodiversity while completely ignoring wheat yield).
  • Failing to link data points from the table to broader ecological consequences (e.g., failing to link more stored carbon to less atmospheric CO₂).
Mark Allocation: 2 marks max (Awarded for balanced points covering both the conservation advantages of method 2 and the agricultural disadvantages/yield trade-offs).

Topics

Biology · 3.4 Genetic information, variation and relationships between organisms

Question and mark scheme from the AQA AS Level Biology examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.