AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), 2018: Question 1

Key topic

• Biotic vs abiotic factors
• Light intensity and photosynthesis
• Sampling with a quadrat
• Reading tables and spotting patterns

How marks are gained

• Recall correct science facts
• Use data from the table
• Give reasons, not just statements
• Show calculations clearly

✅ Correct answers

• Diseases → biotic
• Herbivores → biotic
• Temperature → abiotic
• Water → abiotic

💡 Key knowledge

• Biotic = living factors, or things caused by living organisms.
• Abiotic = non-living environmental factors.
• Diseases and herbivores involve living organisms, so they are biotic.
• Temperature and water are part of the environment, so they are abiotic.

🧠 Exam technique

• There are 2 marks, so you can get credit for any 2 or 3 correct labels.
• Tick carefully in the correct column.
• If you are unsure, think: living = biotic, non-living = abiotic.

❌ Common errors

• Calling water biotic because plants need it.
• Calling temperature biotic because it affects living things.
• Mixing up the meaning of “biotic” and “abiotic”.

✅ Full-mark answer

Leaves block light near the tree, so there is more light as you move outwards. More light means more photosynthesis. Photosynthesis makes more glucose, which plants use for growth.

💡 Key knowledge

• Under the tree canopy, less light reaches the plants.
• Light is needed for photosynthesis.
• More photosynthesis means more glucose is produced.
• Glucose is used to make biomass for growth, including proteins and other cell materials.

🧠 Exam technique

This is a 3-mark explain question. A strong answer links the ideas in a chain:

less light → more photosynthesis → more glucose → more growth

To get the marks, explain the cause and the effect, not just one word like “light”.

❌ Common errors

• Just writing “plants grow better in sunlight” without explaining why.
• Talking about the Sun instead of the light level under the tree.
• Saying “photosynthesis makes growth” without mentioning glucose or biomass.

✅ Correct answers

• A 0.5 m × 0.5 m square frame = quadrat
• An electronic device to measure light intensity = light meter

💡 Key knowledge

• A quadrat is used to sample plants in a fixed area.
• A light meter measures light intensity in a habitat.
• “Lux meter” or “light intensity meter” may also be accepted.

🧠 Exam technique

• Check the object’s purpose, then name it.
• Spelling matters for 1-mark recall answers.
• Answers must be in the correct order given on the paper.

❌ Common errors

• Writing “square” instead of quadrat.
• Writing “sensor” or “meter” without the right scientific name.
• Confusing the quadrat with the tape measure.

📐 Calculation

Step 1: Find the area of one quadrat

0.5 m × 0.5 m = 0.25 m²

Step 2: Count how many quadrats were used

They were placed every 2 m from 2 m to 10 m:

2, 4, 6, 8, 10 → 5 quadrats

Step 3: Multiply

0.25 × 5 = 1.25 m²

Answer: 1.25 m²

🧠 Exam technique

• Write the unit clearly: m².
• Method marks are based on the correct area of one quadrat and the correct number of samples.
• Even if your arithmetic is weak, show the working for credit.

❌ Common errors

• Using 0.5 + 0.5 instead of multiplying.
• Forgetting that area is in m², not m.
• Counting the wrong number of quadrats.
• Giving 12500 cm² without showing the conversion clearly.

✅ Correct answer

To keep the light intensity as similar as possible.

💡 Key knowledge

• Environmental conditions can change during an investigation.
• Light intensity can change as the time of day changes or clouds move.
• Doing the sampling quickly helps make the results fairer.

🧠 Exam technique

The mark scheme focuses on control of light intensity. A short, clear reason is enough for 1 mark.

❌ Common errors

• Talking only about temperature or weather, which the mark scheme does not require here.
• Saying “to save time” without linking it to fair testing.

✅ Acceptable improvements

• Repeat the investigation around the tree.
• Repeat the investigation for other trees or areas.
• Sample every one metre.
• Count the number of each species present rather than percentage cover.

💡 Key knowledge

• Repeating gives more reliable results.
• Sampling more often gives a better picture of distribution.
• Using multiple sites helps check whether the pattern is general.

🧠 Exam technique

• Give a practical improvement, not just “do more science”.
• Strong answers often mention repeat or more frequent sampling.

❌ Common errors

• “Use a bigger quadrat” — not accepted here.
• “Random sampling” — not accepted for this mark scheme.
• Repeats without explaining what is repeated.

✅ Correct answer

Daisy

💡 Key knowledge

• Daisy cover is 0 at low light levels and appears more at higher light.
• This suggests it needs more light to grow well.

🧠 Exam technique

Use the table to pick the species that only appears where light is high. One word is enough for the mark.

✅ Full-mark conclusion

As light intensity increased, the total percentage cover of plants increased, up to 100% at 175 arbitrary units.

💡 Key knowledge

• From the table, total plant cover rises from 16% at 37 units to 100% at 175 units.
• At 200+ units, plant cover stays at 100%.
• This shows a positive correlation.

🧠 Exam technique

• Always support the conclusion with data.
• Use comparative words: as... increased..., from... to...
• Do not say “directly proportional” unless the pattern is perfectly proportional.

❌ Common errors

• Saying “plants increase because of distance” without mentioning light intensity.
• Using only one value with no trend.
• Ignoring the plateau at 100%.

✅ Acceptable answers

• Water / rain / soil moisture – because the tree canopy or roots affect how much water reaches the area.
• Minerals / ions – because the tree roots absorb nutrients from the soil.
• Temperature – because it is cooler under the tree canopy.
• pH / acidity – because fallen leaves can make the soil more acidic.

💡 Key knowledge

• Plants need water and mineral ions for growth.
• Tree roots compete with other plants for resources.
• The canopy can reduce sunlight and also change local conditions like temperature and moisture.

🧠 Exam technique

This is a 2-mark answer: you need

• one factor, and
• one clear reason linked to the tree or habitat.

A good structure is: Factor: water then Reason: less rain reaches under the tree because the leaves block it .

❌ Common errors

• Choosing carbon dioxide — not accepted here.
• Choosing oxygen — not accepted.
• Giving a factor with no explanation.
• Writing an unrelated factor like “pollution” without linking it to the data.

Biotic vs abiotic

• Biotic = living things or their effects
• Abiotic = non-living factors

Light and growth

• More light → more photosynthesis
• More photosynthesis → more glucose
• More glucose → more growth

Fieldwork

• Quadrat = sampling frame
• Light meter = measures light intensity
• Repeat samples for reliability