Activity 8b: To examine the effect of carbon dioxide concentration on the rate of photosynthesis

Chapter 8

Step 1

Take some pondweed and place it in a beaker of pure water

Step 2

Keep the light intensity constant by placing a lamp at a fixed distance from the beaker. Place the whole apparatus in a water bath to keep the temperature constant

Step 3

Cover the pondweed with an upturned filter funnel and invert a test tube filled with water over the nozzle of the funnel

Step 4

Move the lamp to a set distance (50cm) from the pondweed and allow it to sit for five minutes to give the plant time to adjust to the conditions

Step 5

The rate is found by counting the number of bubbles rising from the pondweed per minute. Repeat the count three times and record the average

Step 6

Change the concentration of biocarbonate solution by adding a teaspoon of concentrated biocarbonate solution to the beaker and stirring gently. Leave for five minutes to give the plant time to adjust to the new conditions

Step 7

Count the number of bubbles per minute rising from the pondweed. Repeat the count three times and record the average

Step 8

Repeat this after adding another teaspoon of biocarbonate solution

Result

As the CO2 concentration increases, so does the rate of photosynthesis. Then a limiting factor comes into effect. I’m this case it can be light intensity or temperature