Photosynthesis

What is the aim of this practical?

To investigate how light intensity affects the rate of photosynthesis

What equipment is required?

• Bright lamp

• Small tank of water (if lamp is hot, this will absorb the heat produced)

• Screw top bottles (one for each distance)

• Algal balls (20 per bottle)

• Universal indicator solution

• Metre ruler

• pH colour chart for indicator

What is the method?

1. Place 20 algal balls and the same volume of indicator solution in each bottle, and replace the screw tops

2. Check the colour of the indicator against the colour chart and record the starting pH

3. If using a hot lamp, place the water tank next to the lamp

4. Use the metre ruler to place the uncovered bottles at specific distances from the lamp, on the opposite side of the tanj

5. Leave the bottles for 1-2 hours

How do you record the results?

• Record distance pH of each bottle, using the colour chart for identifying the pH

• Calculate the rate of change in pH per hour for each bottle

• Draw a graph of your results to show distance against rate of change in pH

What is the conclusion?

As the distance increases, light intensity falls and so the rate of photosynthesis decreases. This is because energy transferred by light is needed for photosynthesis to take place