Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pond weed.
The effect of light intensity on photosynthesis can be investigated in water plants. Use Cabomba or Elodea, which are sold in aquarium shops.
The plants will release bubbles of oxygen - a product of photosynthesis - which can be counted.
A lamp with an LED bulb is set up at different distances from the plant in a beaker of water.
The bubbles produced over one minute periods are recorded.
To investigate the effect of light intensity on the rate of photosynthesis.
Care must be taken when using water near electrical equipment. Ensure that your hands are dry when handling the lamp.
The volume of oxygen produced could be measured by collecting the gas produced in a gas syringe.
The changes in the oxygen or carbon dioxide concentration in the water could be measured using datalogging equipment.
You could investigate the effect of different wavelengths of light on photosynthesis.
Use coloured acetate filters to investigate the effects of the blue, green and red parts of the spectrum on photosynthesis.
The effect of the presence or absence of chlorophyll on photosynthesis can be investigated using a variegated plant. Variegated plants have regions of their leaves with and without chlorophyll.
Only those areas of the leaf with chlorophyll photosynthesise. They will test positive for starch, which is built up from the glucose produced.
Care must be taken when using boiling ethanol. Make sure that no Bunsen burners are turned on as the ethanol is highly flammable.
To investigate if a plant needs carbon dioxide for photosynthesis, we need to create conditions for the plants where carbon dioxide is present in one test and absent in another. The air contains 0.04% carbon dioxide. Scientists can use sodium hydroxide to absorb carbon dioxide from the air so that it is unavailable for the plants to use in photosynthesis.
In this particular experiment, a de-starched plant is covered using a transparent plastic bag or a glass jar. The chemical, sodium hydroxide, is placed in the bag with the plant to absorb the carbon dioxide. The plant is left for 24 hours and the leaves are tested for starch using iodine. The leaves will show that no starch has been made, as no photosynthesis has occurred.
What is the purpose of a control in this experiment?
The control is a comparison to show the results with and without sodium hydroxide; all other variables are kept the same. It shows it is the sodium hydroxide removing the carbon dioxide that affects the production of starch and not any other factor.