AQA GCSE Combined Science: Trilogy Biology Paper 1 (Foundation), 2023: Question 3
8 marks · Standard Demand difficulty · Short Answer
Analyze water loss in plants through transpiration, including calculating mass loss from a table, interpreting a rate from a graph, and predicting the effect of environmental factors.
Practise this questionQuestion
Question text
03 Plants need water for photosynthesis.
03.1 Where do plants obtain water for photosynthesis from?
[1 mark]
Plants lose water from their leaves through small pores called stomata.
03.2 What is the evaporation of water from leaves called?
[1 mark]
Tick ( ) one box.
Active transport
Respiration
Transpiration 14
A student investigated the mass of water lost from a plant.
Figure 4 shows the apparatus.
Figure 4
*13* This is the method used.
1. Seal a plastic bag around the pot of a potted plant.
2. Place the plant on a balance in a room at 20 °C.
3. Record the mass.
4. Record the mass every hour for 5 hours.
5. Calculate the total mass of water lost from the plant after each hour.
Table 1 shows the results.
Table 1
Total mass of water
Time in hours Mass in grams
lost in grams
0 510.7 0.0
1 508.9 1.8
2 507.1 3.6
3 505.3 5.4
4 503.5 7.2
5 X 9.0
03.3 Calculate mass X in Table 1.
[2 marks]
Mass X = grams
Figure 5 shows the results.
Figure 5
03.4 What was the rate of water loss from the plant?
[1 mark]
Tick ( ) one box.
0.9 grams/hour
1.8 grams/hour
9.0 grams/hour
03.5 The investigation was repeated at a lower temperature.
Draw one line on Figure 5 to show how the results would be different at a
lower temperature.
[2 marks]
03.6 Suggest one change to the investigation that would increase the rate of water loss
from the plant.
Do not refer to temperature in your answer.
[1 mark]
Mark scheme
Show the mark scheme
Question 3
AO /
Question Answers Extra information Mark
Spec. Ref.
03.1 soil allow ground 1 AO1
ignore air 4.4.1.1
ignore rain 4.2.3.2
ignore roots
AO /
Spec. Ref.
03.2 transpiration 1 AO1
4.2.3.2
AO /
Spec. Ref.
03.3 510.7 – 9(.0) 1 AO2
or 4.2.3.2
503.5 – 1.8
501.7 (grams) 1
AO /
Spec. Ref.
03.4 1.8 grams/hour 1 AO2
4.2.3.2
AO /
Spec. Ref.
03.5 straight line drawn from 0,0 to 5 ignore any extrapolations 1 AO2
hours
at a less steep gradient below 1 AO3
the line on Figure 5
4.2.3.2
AO /
Spec. Ref.
03.6 ignore references to AO3
temperature 4.2.3.2
ignore references to the bag
any one from: 1
• increase air movement allow descriptions of how
• increase light intensity changes could be achieved
• decrease humidity experimentally eg use a fan
Total Question 3 8
How to answer it
Plant Transport and Transpiration
What this question tests
This question assesses your understanding of the transpiration stream. You need to know how plants obtain water, the process of evaporation from leaves, how to interpret experimental data from a balance, and the factors that change the rate of water loss.
Water Uptake
Correct Answer
Soil (or ground)
Key Knowledge
- Water is absorbed from the soil by root hair cells.
- This happens via osmosis.
Common Errors
Do not say "rain" or "the air". While rain provides water to the soil, the plant specifically obtains it from the soil.
Defining the Process
Correct Answer
Transpiration
Exam Technique
This is a "Tick one box" question. If you tick more than one, you will get 0 marks even if one of them is correct. Read the options carefully!
What is Transpiration?
It is the evaporation of water from the surface of the leaf (mostly through stomata) and the subsequent movement of water through the plant in the xylem.
Calculating Mass Loss
Finding the value of X in Table 1
Step-by-Step Calculation
- Identify the starting mass: At 0 hours, the mass was 510.7 g .
- Identify the total loss: At 5 hours, the "Total mass of water lost" is 9.0 g .
- Subtract: 510.7 - 9.0 = 501.7
Mass X = 501.7 grams
Mark Breakdown
1 Mark for the correct subtraction method.
1 Mark for the correct final answer.
Common Trap
Students often try to subtract the previous hour's mass (503.5) from the starting mass. Always check the column headings to see if you are looking at "Total Loss" or "Mass in grams".
Rate of Water Loss
Correct Answer
1.8 grams/hour
How to find it
Look at the "Total mass of water lost" column. Every hour, the loss increases by exactly 1.8g (e.g., 1.8, 3.6, 5.4...). This is the rate.
Graphing Variables
Effect of Lower Temperature
What to draw
You must draw a straight line starting at the origin (0,0) that is less steep than the original line (it should sit below the original line on the graph).
The Science
Lower temperatures mean water molecules have less kinetic energy, so evaporation happens more slowly. A slower rate of loss results in a shallower gradient on the graph.
Examiner Tip
Use a ruler! Many students lose marks for "sketchy" or curved lines when the data shows a constant rate (a straight line).
Increasing Transpiration
Correct Answers (Choose one)
- Increase air movement (e.g., use a fan)
- Increase light intensity (e.g., move the lamp closer)
- Decrease humidity
The "Forbidden" Answer
The question explicitly says: "Do not refer to temperature". If you write "increase temperature", you will get 0 marks, even though it is scientifically true.
Why these work
Light causes stomata to open wider for photosynthesis, allowing more water to escape. Wind moves water vapour away from the leaf surface, maintaining a steep concentration gradient.
Topics
Biology · B4: Bioenergetics · B2: Organisation
Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 1 (Foundation), 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.