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Specimen lab book: Photosynthesis
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Study Hack Lab
RP 6 · Biology
Photosynthesis
Lab book
Name
Specimen
Date
2 November 2026
Course
GCSE Biology
Board and specification
AQA GCSE Biology (8461), 4.4.1.2AQA GCSE Combined Science: Trilogy (8464), 4.4.1.2Apparatus and techniques: AT 1, AT 2, AT 3, AT 4, AT 5
Run
C29HO
Status
Finished: every stage done
Exam questions
30/30 marks
Aim
Investigate the effect of light intensity on the rate of photosynthesis in pondweed, by changing the distance between the pondweed and a lamp.
Contents
Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up
Exam questions on your data
Simulated data produced by Study Hack Lab from the student's own run (seed 20261004). Every reading, value and mark here is from that run; nothing has been retyped. Layout v1, practical v4. Original material; not affiliated with AQA, which has not reviewed it.
1 Plan and risk assessment
Photosynthesis uses light energy to make glucose from carbon dioxide and water, giving off oxygen. The faster the pondweed gives off oxygen, the faster it is photosynthesising. Moving the lamp away spreads its light over a bigger area, so less light reaches the pondweed: light intensity is proportional to 1 ÷ distance² (Higher). When light is the limiting factor, less light means a slower rate.
carbon dioxide + water → glucose + oxygen (light energy needed); light intensity ∝ 1 ÷ distance²
Variables
Independent (you change)
Light intensity, changed by the distance from the lamp to the pondweed in cm
Dependent (you measure)
Rate of photosynthesis: the volume of oxygen collected in a given time (or the number of bubbles in a given time) in cm³ in 5 minutes
Control (you keep the same)
Temperature of the solution; Carbon dioxide concentration; The pondweed; Time to adjust; Time for each reading; Other light
Prediction
As you move the lamp further from the pondweed (10, 20, 30 then 40 cm), what will happen to the rate of photosynthesis?
It will fall, quickly at first and then more slowly.Right first time
Your mean fell from 2.37 cm³ at 10 cm to 0.27 at 40 cm. Further from the lamp, less light reaches the pondweed. Light provides the energy for photosynthesis, so with less light the rate falls. The light falls off quickly at first (it spreads out over a bigger area), so the rate falls quickly at first too.
The lamp moves from 10 cm to 20 cm. What happens to the light intensity at the pondweed? (Higher)
It falls to a quarter: light intensity is proportional to 1 ÷ distance².Right first time
The inverse square law: light intensity ∝ 1 ÷ distance². At twice the distance the same light is spread over four times the area, so each part of the pondweed gets a quarter of the light. The rate does not always fall to a quarter: close to the lamp, light is not the only limiting factor. Your rate at 10 cm was 2.2 times your rate at 20 cm.
What gas is in the bubbles that come out of the pondweed?
Mainly oxygen, made in photosynthesis.Right first time
Photosynthesis: carbon dioxide + water → glucose + oxygen (light energy is needed). The oxygen leaves the leaves as a gas, so the bubbles are mainly oxygen.
Risk assessment
Hazard
Harm it could cause
Control you chose
Water near the lamp’s mains plug and lead
Electric shock
Keep the lead and plug away from the water, dry your hands before touching the switch, and mop up spills at once.Right first time
Hot bulb of a filament lamp
Burns to the fingers
Use an LED lamp, or do not touch the bulb, and let the lamp cool before you move it.Right first time
Sharp scalpel
Cuts to the fingers
Cut on a white tile, pressing down and away from your fingers, and carry the scalpel with the blade pointing down.Right first time
Glass boiling tube, beaker and tank
Cuts if the glass breaks
Clamp the tube, stand glassware away from the edge of the bench, and report any breakage.Right first time
Pondweed is an invasive plant
Harm to wildlife if it gets into ponds and rivers
Put it back in the class tank after the practical; never put it down the sink or into a pond.Right first time
A darkened room
Tripping over bags and stools
Put bags under the benches and stools away before the lights go off.Right first time
2 Apparatus
✓Pondweed (Cabomba or Elodea), about 10 cm sprigs The plant that photosynthesises.
✓Scalpel and white tile To cut a fresh end on each stem.
✓Boiling tube in a clamp, or a 400 cm³ beaker with a glass funnel Holds the pondweed in the solution.
✓10 cm³ measuring cylinder (resolution 0.2 cm³) Upturned over the funnel: collects the oxygen.
✓Glass rod Pushes the pondweed down into the solution.
✓0.2 % sodium hydrogencarbonate solution Supplies the carbon dioxide the pondweed needs.
✓Lamp (LED, or filament) The light source.
✓Glass tank of water A heat shield between a filament lamp and the pondweed.
✓Metre rule (resolution 1 mm) Sets the distance from the pondweed to the lamp.
✓Thermometer (resolution 0.5 °C) Checks the temperature of the solution stays the same.
✓Stopclock (resolution 1 s) Times each count or collection.
✓Hand tally counter Counts the bubbles without losing count.
3 Method: your choices
Which version are you doing?: AQA required practical 6: pondweed and a lampMeasure the oxygen the pondweed gives off at four distances from the lamp.
Cut the end of each stem: DoneAn old cut end is squashed and sealed, so the oxygen cannot get out of it. A fresh cut lets the bubbles stream out.
Choose how to measure the rate: Collect the oxygen: a bunch of pondweed under an upturned funnel, with an upturned 10 cm³ measuring cylinder over it. Measure the volume collected in 5 minutes.You measure the volume of oxygen itself, so it does not matter that bubbles are different sizes. Repeats usually agree to within about 0.1 to 0.2 cm³. At 40 cm only about 0.3 cm³ collects, so the cylinder’s 0.2 cm³ divisions limit how precisely you can read it.
Fill with the solution: Use 0.2 % sodium hydrogencarbonate solutionThe solution supplies carbon dioxide, so carbon dioxide does not limit the rate. Close to the lamp the rate still starts to level off, because something else (such as temperature) begins to limit it.
Choose which lamp to use: An LED lampAn LED gives out very little heat: the solution stays within about 0.5 °C of room temperature.
Measure the distance: Measure from the middle of the pondweed to the front of the lamp, where the light comes outEach distance is the real distance from the light (within about 3 mm).
Switch off the room lights: DoneLight from the room also reaches the pondweed. It would add to the light from the lamp.
Let the pondweed adjust: DoneThe pondweed takes a few minutes to settle to the rate that suits its new light intensity.
4 Results
16 of 16 readings taken.
Oxygen collected at each distance · At each distance: wait 5 minutes, read the thermometer, then collect the oxygen for 5 minutes, three times (refill the cylinder each time). Light intensity is 10 000 ÷ distance²: you work out the 30 cm value yourself in Analyse; the others fill in as each mean is done.
Distance from the lamp in cm
Temperature of the solution in °C
Volume 1 in cm³
Volume 2 in cm³
Volume 3 in cm³
Mean volume of oxygen in 5 minutes in cm³
Light intensity in a.u.
10
20.0
2.4
2.3
2.4
2.37
100.0
20
20.5
1.0
1.1
1.1
1.07
25.0
30
20.0
0.5
0.6
0.4
0.50
11.1
40
20.5
0.2
0.3
1.0, crossed out,0.3
0.27
6.3
0.0 Struck through: the anomaly, retaken; the new reading is beside it.
Anomaly: Volume of oxygen in 5 minutes at 40 cm (third), retaken. Likely cause: a bubble of air that was trapped among the leaves came out during that reading.
5 Graph
Rate against distanceRate against light intensity (Higher)
6 Analysis
Shape of the graph
Describe the shape of your curve.
It falls steeply at first, then less steeply as the distance increases.Right first time
Reading your curve
Go up from 25 cm to your curve, then across to the y-axis.
Use your curve to estimate the rate with the lamp at 25 cm, in cm³ in 5 minutes.
0.72 cm³Right first time
Relative light intensity (Higher)
light intensity ∝ 1 ÷ distance², so relative light intensity = 10 000 ÷ distance² (100 at 10 cm)
Calculate the relative light intensity with the lamp at 30 cm. Give your answer to 3 significant figures.
11.1 arbitrary unitsRight first time
Shape of the graph
Describe the shape of this curve.
It rises steeply at low light intensity, then less steeply: the rate starts to level off.Right first time
Four times the light, four times the rate?
rate at 10 cm ÷ rate at 20 cm
The light intensity at 10 cm is 4 times the light intensity at 20 cm. How many times bigger was your rate at 10 cm than at 20 cm? Give your answer to 2 significant figures.
2.2Right first time
Why not four times?
Four times the light gave you only 2.2 times the rate. Why?
Close to the lamp, light is not the only limiting factor: carbon dioxide or temperature limits the rate, so more light has less effect.Right first time
7 Conclusion and evaluation
Quantity
Your value
Accepted value
Rate at 10 cm ÷ rate at 20 cm (your pondweed, careful technique)
2.2
2.3
Mean at 10 cm, cm³ in 5 minutes (your pondweed, careful technique)
2.4 cm³
2.4 cm³
Conclusion
Which conclusion do your results support best?
As the distance from the lamp increases (light intensity decreases), the rate of photosynthesis decreases; close to the lamp it rises less than the light intensity does (2.2 times the rate for 4 times the light), because another factor starts to limit it.Right first time
Light provides the energy for photosynthesis, and the light falls off as 1 ÷ distance². Far from the lamp, light is the limiting factor; close to it, carbon dioxide concentration and temperature start to limit the rate, so it levels off.
Sources of error
Counting bubbles that are different sizes: systematic or random?
RandomRight first time
The same volume of oxygen can come out as more small bubbles or fewer big ones, so the counts scatter.
Heat from a filament lamp: systematic or random?
SystematicRight first time
The solution warms up most when the lamp is close, so the rates close to the lamp are too high: temperature is not controlled.
Light from the room: systematic or random?
SystematicRight first time
Room light adds to the lamp’s light at every distance, so the rates far from the lamp are too high.
Not waiting after moving the lamp: systematic or random?
SystematicRight first time
The first reading at each distance is still partly at the old rate, so it does not agree with the other two.
Measuring the distance to the lamp’s stand: systematic or random?
SystematicRight first time
The light is really 3 cm closer than recorded, so every rate is too high for its distance, most of all close up.
Not enough carbon dioxide (tap water): systematic or random?
SystematicRight first time
Carbon dioxide limits the rate, so the rates are low and level off close to the lamp.
A squashed cut end: systematic or random?
SystematicRight first time
Less gas leaves the cut end, so every reading is too low.
Only four distances, 10 cm apart: systematic or random?
RandomRight first time
The curve between 10 and 20 cm, where it changes most, is drawn from two points, so its shape there is a guess.
Improvement
Which change would most improve your results?
Add more distances close to the lamp (for example 15 and 25 cm), and repeat with other pieces of pondweed.Right first time
Repeatable or reproducible
Suppose the three readings at one distance are close to each other (any anomaly measured again or left out). This shows the results are…
RepeatableRight first time
Repeatable: the same person, method and equipment give similar results.
Another group, with a different piece of pondweed and a gas syringe, also found the rate fell steeply from 10 cm to 20 cm, then more slowly. This shows the results are…
ReproducibleRight first time
Reproducible: a different person, method or equipment gives similar results.
8 Make safe and clear up
Switch the lamp off at the wall and unplug it. Let a filament lamp cool before you move it
Put the pondweed back in the class tank. Never put it down the sink or into a pond or stream
Pour the solution down the sink and rinse the glassware
Put the scalpel and tile away, blade pointing down. Wipe up any spilt water, then switch the room lights back on
9 Exam questions on your data
On your own readings, self-marked against the mark scheme, with error carried forward where it applies. Total 30/30.
01.1[1 mark]
A student investigated the effect of light intensity on the rate of photosynthesis in pondweed. They put a lamp at different distances from the pondweed, in 0.2 % sodium hydrogencarbonate solution, and measured the oxygen the pondweed gave off.
Which gas is in the bubbles given off by the pondweed?
Tick (✓) one box.
Carbon dioxide
Nitrogen
✓ Oxygen (your choice)
Water vapour
Your answer
Oxygen
1/1
Oxygen
Full marks. Well done.
Model answer: Oxygen: it is a product of photosynthesis (carbon dioxide + water → glucose + oxygen).
01.2[1 mark]
A student investigated how the distance of a lamp from some pondweed affects the rate of photosynthesis. The pondweed was in sodium hydrogencarbonate solution, and the rate was found from the oxygen it gave off.
What was the independent variable in this investigation?
Your answer
The distance of the pondweed from the lamp
1/1 self-marked
Distance (of the pondweed) from the lamp / light intensity (ignore "light" on its own)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The distance of the pondweed from the lamp (the light intensity).
01.3[1 mark]
Describe how the oxygen given off can be used to measure the rate of photosynthesis.
Your answer
Measure the volume of oxygen given off in a set time, such as 5 minutes.
1/1 self-marked
Measure the volume of oxygen (or count the bubbles) given off in a given time (ignore "measure the amount" without a time)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: Measure the volume of oxygen given off in a given time (for example 5 minutes), or count the bubbles given off in 1 minute.
01.4[1 mark]
A student investigated how the distance of a lamp from some pondweed affects the rate of photosynthesis. The pondweed was in sodium hydrogencarbonate solution, and the rate was found from the oxygen it gave off.
Give one variable the student should control.
Your answer
The temperature of the solution
1/1 self-marked
Any one of: temperature; carbon dioxide concentration (concentration of sodium hydrogencarbonate); the same pondweed (mass, length, species); time to adjust; time of each reading; volume of solution (do not accept distance or light intensity)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The temperature of the solution (or the carbon dioxide concentration, the same piece of pondweed, the time to adjust).
01.5[2 marks]
The student used a mains lamp close to a tube of solution.
Give one harm this could cause, and one way to reduce the risk.
Your answer
An electric shock. Keep the plug and lead away from the water and dry your hands.
2/2 self-marked
Harm: electric shock (allow electrocution) / burns (from a hot bulb) (ignore "it is dangerous")
Control: keep water away from the lamp, lead and plug / dry hands before touching the switch / mop up spills / use an LED lamp / do not touch the bulb, let it cool
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: An electric shock. Keep the lamp’s plug and lead away from the water and dry your hands before touching the switch.
02.1[1 mark]
Table 1 shows the three readings you first took with the lamp at 40 cm.
Which reading is anomalous?
Select one row.
Table 1
Collection
Volume of oxygen collected in 5 minutes in cm³
1
0.2
2
0.3
3
1.0
Your answer
reading 3
1/1
Reading 3: much higher than the other two, which agree
Full marks. Clear and precise. Reading 3 (1.0) is far above the other two, which are close to each other.
Model answer: Reading 3. It is much higher than the other two, which agree with each other (probably a burst of trapped air).
02.2[2 marks]
Look again at Table 1: your first three readings at 40 cm, before any retake.
Calculate the mean volume of oxygen collected in 5 minutes.
Do not use the anomalous result. Give your answer to 2 decimal places.
Your answer
0.25
Working: mean = (0.2 + 0.3) ÷ 2
= 0.25 cm³
2/2
(0.2 + 0.3) ÷ 2 (the anomaly left out)
0.25
Full marks. Well done.
Model answer: mean = (0.2 + 0.3) ÷ 2
= 0.25 cm³
02.3[2 marks]
In your own results table (after any retake), your mean volume of oxygen at 30 cm was 0.50 cm³ in 5 minutes.
Calculate the rate of photosynthesis in cm³ of oxygen per hour.
Give your answer to 3 significant figures.
Your answer
6.00
Working: 5 minutes is 1/12 of an hour, so 0.50 × 12 = 6.000
= 6.00 cm³ per hour (3 s.f.)
2/2
0.50 × 12 (any correct rounding)
Given to 3 significant figures: 6.00
Full marks. Your answer meets all the points for this question.
Model answer: 5 minutes is 1/12 of an hour, so 0.50 × 12 = 6.000
= 6.00 cm³ per hour (3 s.f.)
02.4[1 mark]
Give one conclusion from these results.
Your answer
As the distance from the lamp increases, the rate of photosynthesis decreases.
1/1 self-marked
As the distance increases (light intensity decreases), the rate of photosynthesis decreases; or as light intensity increases, the rate increases (do not accept proportional)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: As the distance from the lamp increases (the light intensity decreases), the rate of photosynthesis decreases.
02.5[1 mark]
Figure 1 shows your means, with a curve of best fit.
Figure 1
Use Figure 1 to estimate the volume of oxygen in 5 minutes with the lamp at 25 cm.
Your answer
0.72
1/1
0.72 (read from the curve at 25 cm; ± half a small square)
Full marks. That is exactly what the mark scheme is looking for.
Model answer: About 0.72 cm³ of oxygen in 5 minutes, read from the curve at 25 cm.
03.1[3 marks]
Light intensity is inversely proportional to the square of the distance from the lamp: light intensity ∝ 1 ÷ distance².
Use calculations to show how many times greater the light intensity is with the lamp at 20 cm than at 40 cm.
Your answer
4
Working: 20² = 400 and 40² = 1600
light intensity ∝ 1 ÷ distance², so (1/400) ÷ (1/1600) = 1600 ÷ 400
= 4 times greater
3/3
40² = 1600 (or 1 ÷ 40² = 0.000625)
20² = 400 (or 1 ÷ 20² = 0.0025)
4 (times greater; the intensity at 40 cm is 1/4 of it)
Full marks. Your answer meets all the points for this question.
Model answer: 20² = 400 and 40² = 1600
light intensity ∝ 1 ÷ distance², so (1/400) ÷ (1/1600) = 1600 ÷ 400
= 4 times greater
03.2[2 marks]
Your mean was 2.37 cm³ in 5 minutes at 10 cm and 1.07 cm³ in 5 minutes at 20 cm: the rate at 10 cm was 2.2 times the rate at 20 cm (you worked out 2.21).
The light intensity at 10 cm is 4 times the light intensity at 20 cm.
Suggest why the rate at 10 cm was not 4 times the rate at 20 cm.
Your answer
At 10 cm another factor was limiting the rate, such as the carbon dioxide concentration or the temperature.
2/2 self-marked
At 10 cm light is not the only limiting factor / another factor limits the rate (allow "light is no longer limiting")
Names the factor: carbon dioxide concentration / temperature / (amount of) chlorophyll / enzymes
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: At 10 cm, light is not the only limiting factor: another factor, such as the carbon dioxide concentration or the temperature, limits the rate.
03.3[1 mark]
Another student put the pondweed in water baths at different temperatures. The rate of photosynthesis rose up to 35 °C, then fell sharply at 45 °C.
Explain why the rate of photosynthesis fell at 45 °C.
Your answer
The enzymes are denatured, so the active site changes shape.
1/1 self-marked
The enzymes (controlling photosynthesis) are denatured / the active site changes shape (do not accept the plant or cells denature, or killed)
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: The enzymes that control photosynthesis are denatured: the shape of their active site changes, so they no longer work.
04.1[2 marks]
You used an LED lamp.
Explain why an LED lamp is better than a filament lamp for this investigation.
Your answer
An LED gives off little heat so the temperature stays the same. Temperature affects the rate, so only the light intensity changes the rate.
2/2 self-marked
An LED gives off little heat, so the temperature of the solution stays the same
Temperature affects the rate of photosynthesis (enzymes), so only the light intensity changes the rate / it is a control variable / a fair test
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: An LED gives off very little heat, so the temperature of the solution stays the same. Temperature affects the rate of photosynthesis (enzymes), so only the light intensity changes the rate.
04.2[2 marks]
Another student counted the bubbles for 1 minute at each distance, instead of collecting the gas.
Suggest two ways the student could measure the rate of photosynthesis more accurately.
Your answer
Collect the gas in a gas syringe and measure the volume of oxygen. Collect it for longer, such as 5 minutes.
2/2 self-marked
Collect the gas and measure its volume (gas syringe / upturned measuring cylinder / capillary tube)
Count (or collect) for a longer time, e.g. 5 minutes
Video the pondweed and count the bubbles again from the recording
Repeat and calculate a mean (ignore "repeat" on its own)
Self-marked: 2 of 2 marks. This is your own judgement against the mark scheme.
Model answer: Collect the oxygen in a gas syringe (or an upturned measuring cylinder) and measure its volume, because bubbles are different sizes. Count or collect for longer, such as 5 minutes.
04.3[1 mark]
The method says: each time you move the lamp, wait 5 minutes before you start measuring.
Explain why you should wait 5 minutes after moving the lamp.
Your answer
So the pondweed adjusts to the new light intensity and the rate becomes steady.
1/1 self-marked
So the pondweed adjusts (acclimatises) to the new light intensity: its rate of photosynthesis becomes steady before you measure
Self-marked: 1 of 1 mark. This is your own judgement against the mark scheme.
Model answer: So the pondweed can adjust to the new light intensity, and its rate of photosynthesis is steady before the readings start.
05[6 marks]
A student wants to find out how the colour of light affects the rate of photosynthesis in pondweed.
The student has: pondweed, sodium hydrogencarbonate solution, a boiling tube, a lamp, red, blue, green and yellow filters, a gas syringe, a metre rule and a stopwatch.
Plan an investigation to find the effect of the colour of light on the rate of photosynthesis.
Your answer
1. Put a piece of pondweed in a boiling tube of sodium hydrogencarbonate solution, with an LED lamp 10 cm away, in a dark room.
2. Put a red filter in front of the lamp. Keep the lamp at the same distance for every colour.
3. Leave the pondweed for 5 minutes to adjust to the light.
4. Collect the oxygen in a gas syringe for 5 minutes, timed with a stopwatch, and record the volume.
5. Repeat three times and calculate the mean.
6. Repeat with blue, green and yellow filters, using the same pondweed and keeping the temperature the same.
6/6 self-marked
Put a coloured filter in front of the lamp (or use coloured LEDs) and change the colour
Keep the lamp the same distance from the pondweed (same light intensity)
Leave the pondweed to adjust (about 5 minutes) for each colour
Measure the volume of oxygen collected (or count the bubbles)
In a set time (e.g. 5 minutes), timed with a stopwatch
Repeat for each colour and calculate a mean
Control the temperature (LED, heat shield or water bath) and carbon dioxide (same solution); use the same pondweed
Darken the room so the lamp is the only light
Test at least three colours
Self-marked: Level 3, 6 of 6 marks. You ticked 9 of 9 indicative points. This is your own judgement against the mark scheme.
Model answer: 1. Put a piece of pondweed in a boiling tube of sodium hydrogencarbonate solution, with an LED lamp 10 cm away, in a dark room.
2. Put a red filter in front of the lamp. Keep the lamp at the same distance for every colour.
3. Leave the pondweed for 5 minutes to adjust to the light.
4. Collect the oxygen in a gas syringe for 5 minutes, timed with a stopwatch, and record the volume.
5. Repeat three times and calculate the mean.
6. Repeat with blue, green and yellow filters, using the same pondweed and keeping the temperature the same.
Unseen data: the same skills, new apparatus
01[2 marks]
In a separate simulated pondweed investigation, a lamp was 20 cm from the pondweed. Each of three oxygen collections lasted 5 minutes.
Three readings at 20 cm
Repeat
Oxygen volume in cm³
1
1.1
2
1.0
3
1.1
Using all three readings, calculate the mean rate in cm³/min.
Your answer
0.213
Working: 1.1 + 1 + 1.1 = 3.2
3.2 / 15 = 0.213
2/2
Adds the three readings: 3.2 cm³
Mean rate = 0.213 cm³/min
Full marks. Clear and precise.
Model answer: Total = 1.1 + 1.0 + 1.1 = 3.2 cm³.
Total measurement time = 3 × 5 = 15 min.
Mean rate = 3.2 ÷ 15 = 0.213 cm³/min.
02[1 mark]
Another simulated investigation used a filament lamp without a heat shield. The thermometer was read before collecting oxygen for 5 minutes at each distance. The table shows the first collection at each distance.
Recorded readings
Distance in cm
Temperature in °C
Oxygen volume in cm³ (5 minutes)
10
22.0
2.0
20
23.0
0.8
30
21.5
0.4
40
21.0
0.3
Which conclusion is supported by the recorded temperatures? Tick (✓) one box.
The temperatures stay within 0.5 °C (the thermometer’s reading precision), supporting temperature control at those measurement times.
✓ Temperature varied by more than 0.5 °C and may also affect oxygen production, so the results cannot isolate the effect of light alone. (your choice)
The lamp arrangement proves temperature was constant, regardless of the thermometer readings.
The readings prove that temperature alone caused all differences in oxygen production.
Your answer
Temperature varied by more than 0.5 °C and may also affect oxygen production, so the results cannot isolate the effect of light alone.
1/1
Temperature varied by more than 0.5 °C and may also affect oxygen production, so the results cannot isolate the effect of light alone.
Full marks. Well done.
Model answer: The recorded temperatures span 2.0 °C, more than one 0.5 °C reading step. Both temperature and light can affect photosynthesis, so the effect of light alone cannot be isolated.
03[1 mark]
Two separate simulated investigations used different pondweed samples: a sprig for counting bubbles and a bunch under a funnel for collecting oxygen. These are their first readings at 20 cm.
Two measurement methods
Method
Time in minutes
Reading
Bubble count
1
12 bubbles
Collected oxygen volume
5
1.2 cm³
For a new investigation comparing oxygen volume produced per minute at different distances, which method and reason are valid? Tick (✓) one box.
✓ Collect oxygen for 5 minutes at each distance and divide the volume by 5. This avoids assuming all bubbles have the same volume. (your choice)
Count for 1 minute and report the bubble count as cm³/min, because every bubble is 1 cm³.
Repeat the 1-minute bubble count and take a mean; averaging makes all bubbles equal in volume.
Choose whichever method gives the larger number in this table; a larger number proves a more valid measurement.
Your answer
Collect oxygen for 5 minutes at each distance and divide the volume by 5. This avoids assuming all bubbles have the same volume.
1/1
Collect oxygen for 5 minutes at each distance and divide the volume by 5. This avoids assuming all bubbles have the same volume.
Full marks. Well done.
Model answer: Collect oxygen for the same 5-minute interval at each distance, then divide each volume by 5 for cm³/min. Bubble sizes can differ, so counts cannot be treated as volumes. The two raw readings also have different units, times and pondweed samples.