AQA GCSE Biology Biology Paper 2 (Foundation), June 2022: Question 9

✅ Mark Scheme Accepted Answers

Abiotic factors (Any 2 for 2 marks):

• Water / moisture / humidity / rain(fall) / dryness
• Oxygen / air content (in soil)
• pH (of soil) / acidity / alkalinity
• Temperature
• Minerals / mineral ions / soil salinity
• Soil texture / particle size / soil type

Biotic factors (Any 2 for 2 marks):

• Food / amount of dead and decaying plant matter
• Predators / carnivores (e.g. birds, hedgehogs)
• Disease / pathogens / bacteria / fungi / parasites

💡 Key Biology Knowledge

• Abiotic = Physical (non-living) conditions. The stem tells us earthworms have "moist skin" and "exchange gases through skin" → soil moisture and oxygen levels are critical!
• Biotic = Living factors. The stem states earthworms "feed on dead and decaying plant matter" → availability of food or competition from other decomposers directly limits population size.

❌ Common Errors & Mark Traps

• Vague words: Stating just "weather" , "environment" , or "space" scores zero. You must name specific factors.
• Writing "nutrients": Under both abiotic and biotic headings, examiners ignore the single word "nutrients". Specify mineral ions (abiotic) or food / decaying leaves (biotic).
• Mixing up categories: Writing predators under abiotic or temperature under biotic.

🧠 Exam Technique Tip

Always re-read the short introductory bullet points at the start of Question 9! Examiners gave you clues: "soft, moist skin" (water/humidity), "exchange gases" (oxygen), and "feed on dead plant matter" (food availability).

✅ The Ideal Step-by-Step Method (Full 6 Marks)

1. Setup Grid: Lay out two tape measures at right angles to create a coordinate grid across Area A.
2. Random Coordinates: Use a random number generator to obtain pairs of coordinates to place a 1 m² quadrat (or 0.25 m² quadrat).
3. Control Chemical X: Pour a fixed, measured volume (e.g. 500 cm³) of Chemical X at a specified concentration evenly over the quadrat area.
4. Standardise Time: Wait a set amount of time (e.g. 5 minutes) and collect all worms that surface within a set collection window.
5. Count and Record: Count and record the number of worms gathered in that quadrat.
6. Repeat: Repeat steps 2–5 at least 5 times in Area A.
7. Investigate Area B: Carry out the exact same procedure in Area B using the same volume, concentration, quadrat size, and wait time.
8. Data Analysis: Calculate the mean number of earthworms per m² for Area A and Area B, then compare the values.

🧠 Level Marking Criteria & Strategy

This is a 6-mark extended response marked in three levels:

• Level 3 (5–6 marks): The method would lead to a valid outcome. Key steps are identified, fully controlled, and logically sequenced.
• Level 2 (3–4 marks): Most steps are present, but missing key controls or sampling logic (might not lead to a valid outcome).
• Level 1 (1–2 marks): Isolated points mentioned (e.g. just "pour chemical and count worms") without systematic structure.

📐 Calculations & Unit Conversion Step

The question specifies comparing earthworms per m²:

1. If using a 1 m² quadrat:
   Mean = Total worms counted ÷ Number of quadrat throws
2. If using a 0.5 m × 0.5 m (0.25 m²) quadrat:
   Step 1: Calculate mean per quadrat (0.25 m²).
   Step 2: Multiply by 4 to get population per 1 m²:
   Worms per m² = Mean per quadrat × 4

❌ Where Students Lose Marks

• Saying "throw the quadrat randomly": In GCSE Biology, throwing a quadrat is considered biased and dangerous. Always state: use a random number generator to select coordinates.
• Forgetting control variables: Failing to specify that the concentration and volume of Chemical X must be identical in both areas.
• No repeats: Sampling only once in each area means anomalies cannot be identified and a valid mean cannot be calculated. Always state at least 5 repeats.
• Stopping at the count: Forgetting to conclude with: "calculate the mean per m² and compare Area A to Area B".