AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), June 2025: Question 3

✅ Correct Answer

Quadrat (Tick the middle box)

💡 Key Knowledge

• A quadrat is a square frame (often 0.5 m × 0.5 m or divided into smaller grid squares) placed on the ground to sample stationary organisms.
• A transect is a line (e.g. a tape measure) along which samples are taken to investigate how distribution changes along an environmental gradient.

❌ Common Errors

Confusing the physical equipment (quadrat) with the line along which it is placed (transect) or simply calling it a generic "grid".

📐 Step-by-Step Calculation

1. Count qualifying squares: Identify every square that is at least half (≥ 50%) covered by buttercups in the 10 m quadrat.
   Squares meeting the rule = 7 squares.
2. Multiply by percentage per square:
   7 × 4% = 28%
   Alternative method: (7 / 25) × 100 = 28%
3. Final Answer: 28%

🧠 Exam Technique & Partial Marks

Always show your working! If you miscount and count 5, 6, 8, 9, or 10 squares, but clearly multiply that number by 4 (e.g. 8 × 4 = 32% ), you still receive 1 compensation mark for applying the correct calculation method.

❌ Common Errors

• Counting tiny edges of plants that do not cover at least half of the small square.
• Forgetting to multiply the count by 4% (e.g. leaving the final answer as "7").

✅ Correct Answer

Distance from the tree (Tick the first box)

💡 Key Knowledge

• Independent Variable: The factor that is intentionally changed by the investigator (here: 1 m and 10 m away from the tree).
• Dependent Variable: The factor that is measured (percentage cover of buttercup plants).
• Control Variables: Factors kept constant to ensure valid results (e.g. quadrat size, time of year).

✅ Correct Answer

Percentage cover is affected by the number and size of individual plants. (Tick the first box)

🧠 Exam Technique

When plants spread out or clump together via runners or stems (like buttercups, grass, or clover), it is extremely difficult to separate and count individual plants. Percentage cover gives a more realistic picture of ground biomass and coverage because it factors in both plant size and number.

📐 Step-by-Step Calculation

1. Sum the five repeats for distance 1 m:
   12 + 8 + 4 + 12 + 4 = 40
2. Divide by the number of repeats (5):
   40 / 5 = 8
3. Final Answer: X = 8 (%)

❌ Common Errors

• Dividing by the wrong number (e.g. dividing by 4 or 6).
• Entering 12 + 8 + 4 + 12 + 4 ÷ 5 into a standard calculator without brackets, which performs 4 ÷ 5 first! Always total the numbers before dividing.

✅ Correct Answer

Any one of the following clear comparative statements:

• There is a higher percentage cover 10 m from the tree (compared to 1 m).
• There is lower percentage cover closer to the tree (at 1 m).
• The percentage cover at 10 m is double the cover at 1 m (16% vs 8%).

🧠 Exam Technique

Make sure your conclusion states a clear comparative relationship. Don't just list data values (e.g. "at 1m it is 8% and at 10m it is 16%") without stating what that means (e.g. "therefore, cover increases as distance increases").

✅ Accepted Answers (Give any TWO)

• Light intensity / shade (e.g. light blocked by tree canopy)
• Water / moisture / rain
• Mineral ions / nutrients (e.g. nitrates / fertiliser)
• Soil pH / acidity
• Temperature
• Competition from other plant species
• Herbivores / grazing animals / insects
• Tree canopy size / fallen leaves covering seedlings

❌ What the Examiner Rejects

• "Distance from tree": Expressly forbidden by the question rubric!
• "Weather" or "Climate": Too vague — you must name a specific factor like temperature or rainfall.
• "Space": Avoid writing "space" on biology papers; specify competition for light/water.
• "Sun": Must refer to light, sunlight, or shade.
• "Carbon dioxide": Atmospheric CO₂ is generally uniform across an open field and does not explain local variation around a tree.

✅ Suggested Improvements (Give any TWO)

• Sample at more distances along the transect (e.g. every 1 m or 2 m between 0 m and 10 m, or beyond 10 m) to identify trends more accurately.
• Repeat at each distance more than 5 times (e.g. 10 repeats) to calculate a more reliable mean and spot anomalies easily.
• Repeat the investigation around different trees / other tree species to see if the pattern is generalisable.
• Measure other environmental factors at each location (e.g. measuring soil pH, light intensity with a light meter, or soil moisture).

❌ Common Errors

• Writing simply "repeat 5 times" — the table shows they already did 5 repeats! You must say more than 5 repeats.
• Writing vague ideas like "use a better quadrat" or "be more careful".