AQA GCSE Combined Science: Trilogy Biology Paper 2 (Foundation), 2022: Question 2
16 marks · Standard Demand difficulty · Extended Answer
Describe how to use quadrats to estimate population size and investigate the effect of abiotic factors on plant growth.
Practise this questionQuestion
Question text
02 On a school field:
• one area of the soil was usually wet
• another area of the soil was usually dry.
Students investigated the effect of water in the soil on the number of buttercup plants
growing in each area.
On the field the students marked out:
• an area of 10 m by 10 m on the wet soil
• an area of 10 m by 10 m on the dry soil.
02.1 Describe how a quadrat can be used to measure the size of the buttercup population
on the wet soil area.
[4 marks]
02.2 What type of factor is water in the soil?
[1 mark]
Tick ( ) one box.
A biotic factor
A control factor
An abiotic factor
02.3 Give two factors which might affect the number of buttercups growing on the
school field.
Do not refer to water in your answer.
[2 marks]
02.4 Complete the sentence.
Choose the answer from the box.
[1 mark]
a control the dependent the independent
In this investigation the number of buttercups in each quadrat was
variable.
Figure 2 shows a quadrat on an area of the school field.
Figure 2
02.5 Calculate the area of the quadrat.
[1 mark]
Area of the quadrat = m2
02.6 The mean number of buttercups in one quadrat was 8
Calculate the number of buttercups per m2
Use your answer from Question 02.5
[2 marks]
10 2
Number of buttercups = per m
In a laboratory another group of students investigated the effect of soil acidity on the
growth of beans.
This is the method used.
1. Put soil with a neutral pH in two large boxes.
2. Add acid to the soil in one box.
3. Plant some bean seeds in each box.
4. Water the seeds over 3 weeks.
5. After 3 weeks, measure the height of the bean plants in each box.
6. Calculate the mean height of bean plants in each box.
02.7 Give two improvements the students could make to the method to give
more valid results.
[2 marks]
The students then carried out a valid investigation.
Table 1 shows the students’ results.
Table 1
Height of bean plants in cm
Bean plant Acid soil Neutral soil
18 11
26 12
34 11
4 10 17
57 19
Mean 7 X
02.8 Calculate mean value X in Table 1.
[2 marks]
X = cm
02.9 What conclusion can the students make about the effect of acid soil on the growth of
bean plants?
[1 mark]
Mark scheme
Show the mark scheme
Question 2
AO /
Question Answers Mark
Spec. Ref.
02.1 Level 2: The method would lead to the production of a valid 3–4 AO1
outcome. All key steps are identified and logically sequenced. 4.7.2.1
RPA 7
Level 1: The method would not lead to a valid outcome. Some 1–2
relevant steps are identified, but links are not made clear.
No relevant content 0
Indicative content
• place quadrat randomly / systematically
• description of how randomness is achieved
or
description of how systematic placement is achieved
• count number of buttercups in quadrat
• record number
• repeat quadrat (in another location in the same wet soil area)
• (repeat) at least 5 times
• calculate a mean number of buttercups per quadrat
• the area of the wet soil area is 100 m2
• estimate the buttercup population using the area of the quadrat
AO /
Question Answers Extra information Mark
Spec. Ref.
02.2 an abiotic factor 1 AO2
4.7.1.2
– OMBINED SCIENCE: TRILOGY – – RPA7
AO /
Spec. Ref.
ignore rain / water / weather
02.3 any two from: 2 AO2
• light (intensity) allow shade 4.7.1.2
ignore sun 4.7.1.3
• temperature RPA7
• competition allow other plants growing there
• herbivores / grazing allow pests or named pest
• pollinators allow insects or named
pollinator
• trampling / mowing
• wind (direction / strength)
• soil pH or soil type
• ions / minerals / nutrients in allow named mineral
the soil
• pathogens allow infection
ignore disease unqualified
• herbicides allow pesticides
AO /
Spec. Ref.
02.4 (the) dependent 1 AO2
4.7.1.2
– OMBINED SCIENCE: TRILOGY – – RPA7
AO /
Spec. Ref.
02.5 0.25 (m2) 1 AO2
mark with 4.7.1.2
02.6 RPA7
AO /
Spec. Ref.
02.6 allow ecf from question 02.5 AO2
mark with 4.7.1.2
02.5 8 ÷ 0.25 allow 8 × 4 1 RPA7
32 (buttercups per m2) 1
AO /
Spec. Ref.
02.7 any two from: 2 AO3
• repeat 4.7.1.2
• same volume of water allow same amount of water RPA7
• same mass / volume of soil allow same amount of soil
• more acidity / pH levels
• same number of bean seeds
• same spacing / depth of
seeds
• same species / variety / type
of bean seeds
• same size boxes
• same light (intensity) if neither marking point
• same temperature awarded, allow put them in
the same place eg
– OMBINED SCIENCE: TRIgreenhouseLOGY – –
AO /
Spec. Ref.
02.8 11+12+11+17+19 1 AO2
5 4.7.1.2
RPA7
or
12 70
14 (cm) 1
AO /
Spec. Ref.
02.9 bean plants grow less well allow converse 1 AO3
(in acid soil) 4.7.1.2
or RPA7
bean plants are shorter (in acid
soil)
Total Question 2 16
How to answer it
Investigating Ecosystems: Quadrats and Plant Growth
What this question tests
This question assesses your knowledge of Required Practical 7 (Ecology), including random sampling techniques, identifying abiotic factors, understanding experimental variables, and performing basic biological calculations (area, mean, and scaling up populations).
Sampling with Quadrats
Describe how a quadrat can be used to measure the size of the buttercup population.
Model Answer (4 Marks)
- Place the quadrat randomly (e.g., using a random number generator for coordinates).
- Count the number of buttercups inside the quadrat.
- Repeat this process at least 5 times (or more) in the area.
- Calculate a mean number of buttercups per quadrat and multiply by the total area to estimate the population.
Exam Technique
To get full marks on "Method" questions, your steps must be in a logical sequence. Always mention randomness to avoid bias and repeats to make the results more representative.
Factors and Variables
02.2 Abiotic Factors
Water is an abiotic factor because it is a non-living part of the environment.
Biotic would be living things like predators or competition.
02.3 Other Factors
Two factors (excluding water) that affect growth:
- Light intensity
- Temperature
- Soil pH or Mineral ions
- Competition from other plants
Common Errors
Do not use vague terms like "weather" or "sun". Use scientific terms like light intensity or wind speed. The examiner will ignore "rain" as the question asked you to exclude water.
02.4 Identifying Variables
The number of buttercups is the dependent variable because it is the thing you are measuring as a result of the changes.
Calculations: Area and Density
02.5 Calculate Area
The quadrat is 0.5 m by 0.5 m.
1. Area = Length × Width
2. 0.5 × 0.5 = 0.25 m²
02.6 Calculate Density
Mean = 8 buttercups per quadrat.
1. Density = Mean ÷ Area of 1 quadrat
2. 8 ÷ 0.25 = 32 per m²
Experimental Design & Data
02.7 Improving Validity
To make the bean growth experiment more valid, students should:
- Repeat the experiment and calculate a mean.
- Control variables: Use the same volume of water, same temperature, or same light intensity for both boxes.
02.8 Calculate Mean (X)
1. Add the values: 11 + 12 + 11 + 17 + 19 = 70
2. Divide by the number of plants: 70 ÷ 5
3. X = 14 cm
02.9 Conclusion
Conclusion: Bean plants grow less well (or are shorter) in acid soil compared to neutral soil.
Topics
Biology · B7: Ecology
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Foundation), 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.