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LAUNCH · SCIENCE · Lesson 7 of 10

Can light change what a plant makes?

Learning intention

Describe photosynthesis and investigate how light intensity affects a measured proxy for its rate.

Mission: make a prediction, test the method and defend a conclusion.

A good investigation records a limit as well as a pattern.

Success looks like

  • State the reactants, products and energy source for photosynthesis.
  • Explain a fair light investigation with a measured outcome and controls.
  • Calculate a mean bubble rate and explain its limitation as a proxy.
Retrieval

LAUNCH · SCIENCE · Lesson 7 of 10

Materials, energy and measurement

R1. Where is chlorophyll found in plant cells?

R2. What does a control variable do?

R3. What does “per minute” tell us?

I do

LAUNCH · SCIENCE · Lesson 7 of 10

Read the reaction accurately

Carbon dioxide + water → glucose + oxygen.

Light energy is absorbed by chlorophyll.

Photosynthesis takes in energy.

Matter changes; light supplies the energyPhotosynthesis word equation. Carbon dioxide and water are converted into glucose and oxygen using light energy absorbed by chlorophyll. The process takes in energy; light is not a material reactant.Matter changes; light supplies the energyCarbon dioxide+ waterLight energychlorophyllGlucose+ oxygenGlucose can build biomass or be used in respiration.Photosynthesis takes in energy.
Matter changes; light supplies the energy
Diagram description

Photosynthesis word equation. Carbon dioxide and water are converted into glucose and oxygen using light energy absorbed by chlorophyll. The process takes in energy; light is not a material reactant.

I do

LAUNCH · SCIENCE · Lesson 7 of 10

I plan the measurement before moving the lamp

Change the light level and record it.

Count bubbles over equal one-minute intervals.

Keep the shoot and other conditions comparable.

Change light; monitor temperatureSchematic supervised pondweed setup with LED lamp, distance ruler, vessel of solution, shoot, bubbles, light sensor and thermometer. It models apparatus positions, not a scale drawing or an exact gas-volume method.Change light; monitor temperatureCool LEDlampPondweed + solutionMonitorwatertemperatureLight sensorfixed orientationMeasure distanceSame shoot, solution, timing and background light.
Change light; monitor temperature
Diagram description

Schematic supervised pondweed setup with LED lamp, distance ruler, vessel of solution, shoot, bubbles, light sensor and thermometer. It models apparatus positions, not a scale drawing or an exact gas-volume method.

I do

LAUNCH · SCIENCE · Lesson 7 of 10

Work a rate and a mean

Worked example:12 bubbles in 2 minutes =6 per minute.

Three one-minute counts 4,5,6 have mean 5.

Count is a proxy, not an exact oxygen volume.

Constructed results: compare mean bubble ratesConstructed sample means: at 300 lux 5 bubbles/min,600 lux 10 bubbles/min,1200 lux 17 bubbles/min. The categorical axis represents measured light levels. Bubble count is a proxy, not exact oxygen volume.Constructed results: compare mean bubble ratesMean bubbles per minute; light sensor level below051015205300 lux10600 lux171200 lux
Constructed results: compare mean bubble rates
Diagram description

Constructed sample means: at 300 lux 5 bubbles/min,600 lux 10 bubbles/min,1200 lux 17 bubbles/min. The categorical axis represents measured light levels. Bubble count is a proxy, not exact oxygen volume.

We do

LAUNCH · SCIENCE · Lesson 7 of 10

Investigation team: predict, then calculate

Go to interactive investigation

W1. Predict the largest mean rate.

Calculate the mean for each light level.

Constructed sample data; same shoot/solution and 20°C; counts are bubbles.
Lamp distance(cm)Mean sensor(lux)Three 1-min counts
403004,5,6
306009,10,11
20120016,17,18

Light lab: predict and inspect

Constructed conditions and bubble counts; not a live plant simulation.

Decision 1 of 3

Which supplied light level has the greatest mean count?

Choose, test, then explain together. Evidence diagrams appear only after your test. Diagram transitions explain the model; they do not represent real elapsed time. Use Pause model to stop transitions and model controls, or your device’s reduced-motion setting. The printed We do activity provides the paper route.

We do

LAUNCH · SCIENCE · Lesson 7 of 10

Method repair challenge

W2. A group changes the shoot and the lamp position together.

Can it isolate the light effect? Repair one step.

Change light; monitor temperatureSchematic supervised pondweed setup with LED lamp, distance ruler, vessel of solution, shoot, bubbles, light sensor and thermometer. It models apparatus positions, not a scale drawing or an exact gas-volume method.Change light; monitor temperatureCool LEDlampPondweed + solutionMonitorwatertemperatureLight sensorfixed orientationMeasure distanceSame shoot, solution, timing and background light.
Change light; monitor temperature
Diagram description

Schematic supervised pondweed setup with LED lamp, distance ruler, vessel of solution, shoot, bubbles, light sensor and thermometer. It models apparatus positions, not a scale drawing or an exact gas-volume method.

We do

LAUNCH · SCIENCE · Lesson 7 of 10

Which conclusion earns its claim?

W3. “Within this range, higher measured light gave a higher mean count.”

Does that prove unlimited growth or exact oxygen volume?

Hinge

LAUNCH · SCIENCE · Lesson 7 of 10

A valid scientific conclusion

Choose the statement supported by the method.

You do

LAUNCH · SCIENCE · Lesson 7 of 10

Prepare your investigation brief

Choose your response route.

Include a reaction, method and evidence-based conclusion.

You do

LAUNCH · SCIENCE · Lesson 7 of 10

Use the evidence independently

Predict → calculate → explain → improve the method.

Keep constructed results separate from any actual observations.

Review

LAUNCH · SCIENCE · Lesson 7 of 10

Audience question: what did you measure?

L1. Show your conclusion.

Audience asks: “Count, volume, growth or photosynthesis itself?”

Review

LAUNCH · SCIENCE · Lesson 7 of 10

A strong brief names its limitation

The reaction explains the process.

The method determines what the evidence can show.

Exit

LAUNCH · SCIENCE · Lesson 7 of 10

Keep matter, energy and evidence distinct

E1. Name the two material reactants.

E2. Calculate 15 bubbles in 3 minutes.

E3. Name one control and one proxy limit.

Exit

LAUNCH · SCIENCE · Lesson 7 of 10

Next useful step

Reaction • rate • fair method • cautious conclusion.

Continue within this stage’s shared time.

My science task sheets

Choose one route with your teacher. Shared evidence and the exit sheet appear in every route. Your work stays here while the page is open; save it before closing.

Shared evidence | Light investigation

Constructed sample data. Same shoot, solution, one-minute intervals and 20°C water. Sensor readings are mean lux at the vessel; lux is a practical light indicator.

Distance(cm)Sensor(lux)Three bubble counts in 1 min
403004,5,6
306009,10,11
20120016,17,18

Method: use prepared shoot and same solution. Set light position; allow at least 2 minutes to adjust. Monitor temperature. Take three equal one-minute counts. For logging: sensor faces lamp in the same orientation; record once each second for 30 seconds and take its mean. Repeat at each position.

Paper route: analyse these values only. Optional demonstration uses teacher-prepared apparatus; record any real observations separately. Bubble sizes vary and some oxygen remains dissolved.

Supported route | Build the brief

Word bank: carbon dioxide; water; glucose; oxygen; light; same; rate; proxy.

Standard route | Investigation proposal

Use the constructed table and precise units.

Stretch route | How strong is the evidence?

Optional extension. A second constructed trial at 1200 lux gives one-minute counts 16,17,35. A note says the third bubble count may include two minutes of observation.

Exit and reflection | Process and measurement

Use one accurate sentence for each distinction.

Next useful step
Slide 1

TA Brief

Current stage

Objective

Describe photosynthesis and investigate how light intensity affects a measured proxy for its rate.

Preparation

Method precautions

Practical alternative

Analyse the supplied constructed table and apparatus diagram. Pupils make the same predictions, controls and evidence-based conclusions without using water, plants or electrical equipment.

Access and regulation

Supported: Same core scientific goal, with word bank, short prompts, read-aloud or pointing/dictation. Do not assign a route from diagnosis.

Standard: Use the supplied evidence to explain and justify an independent scientific decision.

Stretch: Optional challenge after secure core: evaluate a limitation and transfer the science. Higher-tier-only material, where present, is labelled explicitly.

Regulation: Preview the sequence. Offer solo or partner work, a pass and quiet response. Allow a brief reset and re-entry at the next numbered task; no compulsory disclosure, performance or speed competition.

Teacher answers

Retrieval

R1 chloroplasts. R2 a factor kept the same to improve fairness. R3 each 60 seconds.

W1–W3

W1 means 5,10,17 bubbles/min at 300,600,1200 lux. W2 use the same shoot/matched replicates and change the intended light level only, controlling temperature and solution. W3 count rises with measured light in this range; no unlimited-growth or exact-volume claim is justified.

Hinge

A false: light is energy, not a material reactant. B true: count indicates a pattern with bubble-size limitations. C false: different bubble sizes/dissolved gas. D false: changing shoots introduces another variable.

S1 / M1

Carbon dioxide + water → glucose + oxygen, with light energy absorbed by chlorophyll. Photosynthesis takes in energy; glucose can contribute to biomass or respiration.

S2 / M2

(4+5+6)/3=5;(9+10+11)/3=10;(16+17+18)/3=17 bubbles/min. From 300 to 1200 lux the mean increases by 12 bubbles/min. This is the observed range, not a universal proportionality.

S3 / M3

Change measured light level using lamp position. Count bubbles for equal one-minute intervals; repeat three times after adjustment. Same shoot, solution volume/concentration, background light and comparable temperature. Sensor orientation/location consistent; optional 30 second logging mean. Controls reduce alternative explanations.

S4 / M4

Higher measured light is associated with higher mean count here, for example 300 lux→5 and 1200 lux→17 bubbles/min. Counts do not equal exact gas volumes because sizes differ and gas may dissolve. Collect gas volume over a fixed time with appropriate apparatus to reduce the bubble-size limitation; maintain other controls.

T1

(16+17+35)/3=68/3≈22.7 bubbles/min only if all counts were truly one minute. If the 35 count lasted two minutes, averaging raw counts as equal rates is invalid. The note is uncertain; check the record before recalculating.

T2

Retain and annotate the original record; verify timing or repeat matched measurements with a clear timer/observer. Do not silently delete an inconvenient value or assume the cause from its size alone.

T3

Carbon dioxide availability or temperature could limit the rate. Example: compare matched carbon dioxide availability at the same light and temperature with repeats. The plateau alone does not identify which factor is limiting.

T4

Lux measures light weighted to human visual sensitivity, not glucose production or exact photosynthetic photon flux. Bubble counts indicate gas release, with volume/dissolution limits; glucose itself is not measured.

Exit and assessment

E1 carbon dioxide and water. E2 15÷3=5 bubbles/min. E3 valid controlled factor plus bubble-size/dissolved-gas limit. L1 accepts a specific evidence-based revision or justified label. Secure core = correct reaction, fair variable logic and proxy-aware conclusion.

Sources checked for this lesson

Word help

photosynthesis
Using light energy to make glucose from carbon dioxide and water, releasing oxygen.
chlorophyll
A pigment that absorbs light in photosynthesis.
rate
How much happens in a stated time.
proxy
A measurement used to indicate another quantity, with limitations.
control variable
A factor kept the same to make a comparison fairer.
limiting factor
A factor in short supply that restricts the rate of a process.

Cold Call

Give thinking time. Invite a response by voice, pointing or showing work. A pupil can pass; check in privately when useful.

Pause

Take a quiet pause.

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