AQA GCSE Biology Biology Paper 2 (Higher), June 2022: Question 2

10 marks · Standard Demand difficulty · Extended Answer

Identify abiotic and biotic factors affecting an earthworm population and plan an investigation using a chemical irritant to compare population density between two areas.

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Question

Question 02 begins with background information on earthworms: they live in soil, feed on dead and decaying plant matter, have soft, moist skin, and exchange gases through their skin. Question 02.1 asks candidates to give two abiotic factors and two biotic factors that could affect the size of an earthworm population, worth 4 marks. Question 02.2 describes an investigation where students compare earthworm populations in a grass lawn (Area A) and a farmer's field (Area B) using harmless chemical X that brings worms to the surface, asking students to plan an investigation to compare the number of earthworms per square metre in both areas, worth 6 marks.
Question text

02 Earthworms:

• live in soil

• feed on dead and decaying plant matter

• have soft, moist skin

• exchange gases through their skin.

02.1 Give two abiotic factors and two biotic factors that could affect the size of an

earthworm population.

[4 marks]

Abiotic factors

Biotic factors

02.2 Students investigated the populations of earthworms in the soil in two different areas:

• Area A: a grass lawn

• Area B: a farmer’s field.

Chemical X can be mixed with water and poured onto the soil.

The mixture brings earthworms to the surface of the soil but does not harm

the earthworms.

Plan an investigation using chemical X to compare the number of earthworms per m2

in areas A and B.

[6 marks]

Mark scheme

Show the mark scheme Mark scheme for Question 02. 02.1: Abiotic factors (any two from water/moisture, oxygen/air in soil, pH, minerals/ions, temperature, soil texture/type) for 2 marks; Biotic factors (any two from food, predators/carnivores, disease/pathogens/bacteria/fungi) for 2 marks. 02.2: A 6-mark level-of-response marking grid (Levels 1 to 3). Indicative content includes controlled variables (volume/concentration of chemical X, size of area sampled using a quadrat, time allowed), random sampling method using coordinates, counting worms in both areas, repeating at least 5 times, and calculating and comparing the mean number of earthworms per m².

Question 2

AO /

Question Answers Extra information Mark

Spec. Ref.

02.1 abiotic AO1

any two from: 2 4.7.1.1

4.7.1.2

• water allow moisture / humidity /

4.7.1.3

rain(fall)

allow dryness

• oxygen / air (in soil) ignore carbon dioxide

• pH (of soil) allow acidity / alkalinity (of soil)

• minerals / ions allow salts

allow named example of an ion

ignore nutrients

• temperature

• size of soil particles or texture allow named example of soil

/ type of soil type

ignore space / toxins / weather

biotic 2

any two from:

• food allow amount of dead / decaying

matter (in soil)

ignore nutrients

• predators / consumers / allow example – such as birds

carnivores

• disease / pathogens / bacteria allow microorganisms /

/ fungi microbes / parasites

if no other marks awarded allow

2 marks for four factors in

reverse categories

AO /

Question Answers Mark

Spec. Ref.

02.2 Level 3: The method would lead to the production of a valid 5–6 AO2

outcome. The key steps are identified and logically sequenced.

Level 2: The method would not necessarily lead to a valid 3–4 AO2

outcome. Most steps are identified, but the method is not fully

logically sequenced. 9

Level 1: The method would not lead to a valid outcome. Some 1–2 AO1

relevant steps are identified, but links are not made clear.

No relevant content 0

Indicative content 4.7.2.1

RPA9

• same concentration of chemical / X applied to the soil

• same volume / amount of chemical / X applied to the soil

• same size of area sampled – eg 1 m2 or 0.25 m2

• use of a quadrat

• same time between application and collecting worms

• same time allowed for collecting worms after application

• each sample area selected randomly

• method of achieving randomness – eg random coordinates

• (collect and) count worms in each of areas A and B

• at least 5 repeats in each of areas A and B

• calculate mean (per unit area) or total for each of areas A and B

• compare means / totals for areas A and B

Total Question 2 10

How to answer it

Ecology: Earthworm Population Factors & Sampling

📋 What This Question Tests

This question assesses key skills from Topic 7: Ecology (Adaptations, Interdependence, and Required Practical 9):

  • Recall & Categorisation: Identifying and distinguishing between abiotic (non-living physical/chemical) and biotic (living) factors affecting a specific organism.
  • Practical Investigation Design (6 marks): Writing an ordered, logical method to compare populations in two habitats using random sampling (quadrats), controlling variables, repeating samples, and calculating means per m².
Part 02.1 • 4 Marks

Abiotic and Biotic Factors

Give two abiotic factors and two biotic factors that could affect the size of an earthworm population.

✅ Mark Scheme Accepted Answers

Abiotic factors (Any 2, 1 mark each):

  • Water / moisture / soil humidity / rainfall
  • Oxygen / air content in the soil
  • pH of the soil (acidity or alkalinity)
  • Soil temperature
  • Soil texture / particle size / soil type
  • Mineral ion content / salts

Biotic factors (Any 2, 1 mark each):

  • Availability of food (dead / decaying plant matter)
  • Predators / carnivores (e.g. birds, badgers)
  • Pathogens / disease / harmful soil microbes

💡 Key Knowledge

  • Abiotic: Non-living physical and chemical conditions. Earthworms breathe through moist skin, so soil moisture, aeration (oxygen), and temperature directly control survival.
  • Biotic: Living organisms that influence the population. These include food sources (leaves/plant debris), predators eating them, and pathogens infecting them.

❌ Common Errors & Traps

  • Writing "Nutrients": The mark scheme specifically states "ignore nutrients" for both categories because it is too ambiguous. Specify minerals/ions for abiotic or food / decaying plants for biotic.
  • Writing "Weather": Too vague. Must specify temperature or rainfall.
  • Carbon dioxide: Earthworms require oxygen for aerobic respiration; carbon dioxide is specifically ignored.
  • Swapping categories: Putting food under abiotic and temperature under biotic loses marks. (Examiner note: full credit is only saved if all 4 are reversed, which scores a maximum of 2).

🧠 Exam Technique

Always link your answers directly to the facts provided in the introduction:

  • Intro says: "feed on dead plant matter" → Food availability (Biotic).
  • Intro says: "soft, moist skin / gas exchange" → Soil moisture and Oxygen (Abiotic).
Mark Breakdown: 2 marks for two correct abiotic factors + 2 marks for two correct biotic factors = 4 marks total.
Part 02.2 • 6 Marks

Planning a Field Investigation

Plan an investigation using chemical X to compare the number of earthworms per m² in areas A (lawn) and B (farmer's field).

📐 Step-by-Step 6-Mark Method Template

To reach Level 3 (5–6 marks), your method must be a coherent, logical recipe that someone else could follow to obtain valid, comparable results:

  1. 1 Define Sample Unit: Place a quadrat of known size (e.g. 1 m × 1 m = 1 m², or 0.5 m × 0.5 m = 0.25 m²) on the ground in Area A.
  2. 2 Random Sampling: Lay out tape measures at right angles to form a grid and use a random number generator to select coordinates. Avoid bias!
  3. 3 Controlled Application: Pour a fixed volume (e.g. 2 dm³) and fixed concentration of chemical X solution evenly over the quadrat area.
  4. 4 Standardised Waiting & Collection: Wait a set period of time (e.g. 5 minutes) for earthworms to surface, then collect and count all emerged worms.
  5. 5 Replication: Repeat this process at least 5 times (or 10 times) at different random coordinates within Area A.
  6. 6 Repeat in Area B: Carry out the exact same procedure in Area B, using identical volumes and concentrations of chemical X.
  7. 7 Data Processing & Comparison: Calculate the mean number of earthworms per m² for Area A and for Area B, then compare the two values.

🧠 How Examiners Grade This (Levels of Response)

  • Level 3 (5–6 marks): Comprehensive and logically sequenced. Clearly mentions random coordinates, fixed area (quadrat), controlled chemical application (volume & concentration), repeats (at least 5), and calculating/comparing means per m².
  • Level 2 (3–4 marks): Most key steps included (e.g. pouring chemical, counting, comparing), but misses key controls (like standardising volume/time) or fails to explain how sampling is randomised.
  • Level 1 (1–2 marks): Fragmented steps without a logical sequence (e.g. "pour chemical on lawn and field and see which has more").

❌ Common Mistakes to Avoid

  • Forgetting to specify control variables: Failing to state that the volume and concentration of chemical X must be the same in both areas.
  • "Throwing" a quadrat: Writing "throw the quadrat randomly" loses marks in modern exams. Always state: set up a grid using tape measures and use a random number generator to pick coordinates.
  • Not converting to per m²: If you specify a 0.25 m² (50 cm × 50 cm) quadrat, remember that you must multiply the count by 4 to get earthworms per m². Sticking to a 1 m² quadrat is safer!
  • Saying "repeat until reliable": Always give a concrete number of repeats: "at least 5 repeats in each area".
Examiner Tip for 6/6: Check that your final sentence directly answers the prompt: "Calculate the mean number of earthworms per m² for both the lawn and the field and compare the results to see which habitat supports a higher population."

Topics

Biology · Required Practicals · B7: Ecology · Required Practicals

Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Higher), June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.