What is Photosynthesis ? Plants use sunlight and water with Carbon Dioxide to make food. They store sugar as starch grains in the chloroplasts. Oxygen gas is produced in all plants, even those which live under water. 6CO2 + 6H2O  C6 H12 O6 + 6O2 light

What happens inside the leaf? sunlight Light is absorbed by the green coloured chlorophyll, and the leaf uses the energy in the light to combine carbon dioxide and oxygen.

Where Does the Light Come From? Plants normally get their light from the Sun, but in this experiment the light source is an electric bulb. The energy changes in a light bulb are : ELECTRICAL  LIGHT + HEAT Might the heat of the light bulb have an effect? Is there anything that could be done to get rid of the effect of the heat?

What About the Colour of the Light? The light bulb gives out white light, which is made of different colours & each colour has its own wavelength. Chlorophyll is green in colour, so green light is reflected away from the leaf – how could you test to see which colour is best for photosynthesis?

The Experiment The pondweed gives off oxygen when the light is on. Once the two minutes are up, the syringe is pulled out and the amount of oxygen is measured. The light is moved to different positions so that the light intensity changes.

The Results

Evaluation Explain what was done to make the experiment as accurate as possible. Why were the experiments repeated? Can you think of any extra measurements that could have been carried out. Did the prediction come true? Can you think of how the experiment can be improved?

Improvements? Putting sodium Bicarbonate into the water to saturate it with Carbon dioxide. Using an oxygen probe to measure the concentration in the water. Carbon filament lamps give out better wavelength distributions. Darken room to ensure that light intensity is constant. Putting a glass block between the plant and the light source to prevent the heat reaching the plant.

How can the experiment be extended? Once you have identified the best distance then you can identify the best Carbon Dioxide concentration. Add different concentrations of Carbon Dioxide into the water to see how it affects the rate of photosynthesis. Using the oxygen probe to measure the % Dissolved Oxygen concentration in the water.

ALL THE BEST