Photosynthesis - Light & CO2
This practical lesson covers:
- The effect of light on net gas exchange from a leaf, using a hydrogen-carbonate indicator.
Investigating the effect of light intensity on gas exchange from a leaf.
Aim:
To investigate the effect of light on net gas exchange from a leaf, using a hydrogen-carbonate indicator.
Background information:
Photosynthesis is the fundamental process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. This practical investigates the effect of light intensity on photosynthesis by observing changes in a bicarbonate indicator, which responds to pH shifts due to varying CO2 levels around pondweed. By adjusting the distance between the light source and the pondweed, we explore how light intensity influences the rate of photosynthesis.
Variables:
- Independent variable - Distance between light source and pondweed.
- Dependent variable - Colour change and pH shift of the bicarbonate indicator solution.
- Control variables - Type of pondweed, duration of light exposure, temperature of the environment, type of lighting.
Equipment:
- Boiling tube
- Pondweed
- Lamp
- Ruler
- Test tube rack
- Timer
- Glass rod
- Measuring cylinder
- Bicarbonate indicator solution
- Bicarbonate indicator colour standard chart
Method:
- Place a test tube rack containing a boiling tube 10 cm away from the light source, measured using the ruler.
- Fill the boiling tube with a fixed volume of bicarbonate indicator.
- Place the cut pondweed into the boiling tube with the cut end at the top. Gently push the pondweed down with the glass rod.
- Record the initial colour and pH (using the colour standard) of the solution and start timing.
- After 30 minutes, record the final colour and pH (using the colour standard) of the solution.
- Repeat steps 1-5 for 3 more distances (20, 30, 40 cm) of the boiling tube from the light source.
What process do plants use sunlight to convert carbon dioxide and water into glucose and oxygen?
fermentation
respiration
photosynthesis
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What is the independent variable in the experiment?
colour change and pH shift of the bicarbonate indicator solution
type of pondweed
distance between light source and pondweed
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What is the dependent variable in the experiment?
type of pondweed
colour change and pH shift of the bicarbonate indicator solution
distance between light source and pondweed
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What is the purpose of the bicarbonate indicator solution in the experiment?
to measure the light intensity
to measure the pH shifts due to varying CO2 levels
to measure the temperature of the environment
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