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Year 11
Edexcel
Higher

The effect of light intensity on rate of photosynthesis in algae: practical

I can carry out an investigation into the effect of light intensity on the rate of photosynthesis in algae.

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New
New
Year 11
Edexcel
Higher

The effect of light intensity on rate of photosynthesis in algae: practical

I can carry out an investigation into the effect of light intensity on the rate of photosynthesis in algae.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. Following an appropriate method to vary light intensity and measure the colour change of indicator.
  2. Accurate measurement of variables (distance, time, colour change); control of variables that might affect the results.
  3. Comparison of indicator colour to a chart to determine pH.
  4. Record results in an appropriate table.

Common misconception

Some pupils do not consider how to control variables carefully enough. This means results are likely to be less accurate and so do not provide conclusions that can be used to support a hypothesis.

Each type of variable is considered during the lesson and repeated to help pupils to understand the differences between each type of variable.

Keywords

  • Light intensity - the amount of light reaching a given surface area in a period of time

  • Rate - a measure of how much change occurs per unit of time

  • Variable - a factor that can be changed during an experiment

  • Control variable - a factor that is kept the same during an experiment

  • Accurate - a measurement result is considered accurate if it is judged to be close to the true value

Get pupils to follow the same practical procedure so that results can be shared between groups. This will enable a mean change in pH to be calculated and will help to improve the reliability of results that are obtained.
Teacher tip

Equipment

Light source, beaker, bijou bottles, hydrogencarbonate indicator, measuring cylinder, algae immobilised in alginate beads, graduated pipette, spatula, pH indicator chart, foil, meter rule, stopclock.

Content guidance

  • Risk assessment required - equipment

Supervision

Adult supervision required

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

Video

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Starter quiz

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6 Questions

Q1.
Wat are the reactants in photosynthesis?
Correct answer: carbon dioxide and water
glucose and oxygen
water and oxygen
carbon dioxide and glucose
Q2.
As algae photosynthesise, what will happen to the concentration of carbon dioxide in the water?
Correct answer: it decreases
it increases
it remains constant
it fluctuates randomly
Q3.
What is an independent variable?
Correct answer: a factor that is changed during an experiment
a factor that is kept the same during an experiment
a factor that is measured during an experiment
Q4.
What is a control variable?
a factor that is changed during an experiment
Correct answer: a factor that is kept the same during an experiment
a factor that is measured during an experiment
Q5.
When investigating the effects of light intensity on the rate of photosynthesis, which of the following are control variables?
An image in a quiz
Correct answer: temperature
Correct answer: number of algal beads
light intensity
change in pH
Q6.
Why is it important to control the temperature in this experiment?
because temperature affects the amount of water
because temperature affects the colour of the pondweed
Correct answer: because temperature can affect the rate of photosynthesis
because temperature can affect the ight intensity

Exit quiz

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6 Questions

Q1.
What is an accurate measurement?
Correct answer: a measurement close to the true value
a measurement taken quickly
a measurement taken with a ruler
a measurement using more equipment
Q2.
How can you use the equipment shown to measure the rate of photosynthesis?
An image in a quiz
Correct answer: Count the number of bubbles of oxygen produced in a specific period of time.
Measure the volume of carbon dioxide produced in a specific period of time.
Measure the change in the pH, shown by the indicator of the indicator.
Q3.
Why does photosynthesis lead to a colour change in the indicator solution?
An image in a quiz
Photosynthesis gives out carbon dioxide which makes solutions more acidic.
Correct answer: Photosynthesis uses carbon dioxide which increases the pH of the solution.
Photosynthesis releases glucose, altering the solution's colour.
Light absorbed by the algal beads reacts with the indicator solution.
Q4.
How can you reduce the intensity of the light that the pondweed receives from the lamp?
An image in a quiz
Put a beaker of water between the pondweed and the lamp.
Increase the brightness of the lamp.
Correct answer: Move the pondweed away from the lamp.
Q5.
If the indicator changes from cherry red to purple, what does this tell you about the rate of photosynthesis?
there is no photosynthesis occurring
photosynthesis is happening at a low rate
Correct answer: photosynthesis is happening at a high rate
photosynthesis has stopped completely
Q6.
What is a logical prediction for this investigation?
An image in a quiz
As distance increases, the rate of photosynthesis will increase.
Correct answer: As distance increases, the rate of photosynthesis will decrease.
As distance increases, the rate of photosynthesis will stay the same.

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