To investigate and identify the factors that affect the rate at which photosynthesis happens.
Photosynthesis is a series of chemical reactions that uses energy from sunlight to produce food. The product or ‘food’ is Glucose which is a sugar, photosynthesis happens in the cells in green parts of plants, for example in leaf cells. Photosynthesis can also occur in some microorganisms, for example phytoplankton. Chlorophyll is needed for photosynthesis, it is a green substance which absorbs sunlight and allows the energy to be used to convert carbon dioxide and water into glucose. Oxygen is a waste product of photosynthesis. The equations for photosynthesis are:
Carbon Dioxide + Water Glucose + Oxygen Light Energy 6CO2 + 6H20 C6H1206 + 6O2
Organisms that do photosynthesis form the start of food chains. They make the energy from the Sun available to other organisms by converting it to glucose, this energy is transferred when these organisms are eaten.
Plants use the glucose in three main ways:
1. Glucose is used for Respiration:
Plants use some of this Glucose for respiration, this process releases energy from the Glucose.
2. Glucose is used to make chemicals for growth:
-Glucose is converted into cellulose for making cell walls, especially in a rapidly growing plant. Glucose is combined with nitrogen (from nitrates taken up from the soil by plant roots) to make amino acids, which are then made into proteins. Glucose is also used to help make Chlorophyll. 3. Glucose is stored as Starch:
- Glucose is turned into Starch and stored in roots, stems and leaves. It’s used at times when the rate of photosynthesis is slower, like in the winter.
There are three factors that affect the rate of Photosynthesis:
Amount of light
Amount of Carbon Dioxide (CO2)
Each of these factors can become the limiting factor. This just means that it stops photosynthesis from happening any faster. Which factor is limiting at a particular time depends on the environmental conditions. For example:
At night, light is the limiting factor.
In winter it’s often the temperature.
If the other two conditions (Light and Temperature) are fine, then Carbon Dioxide (CO2) is usually limiting.
If there is not enough light, then it will slow down the rate of Photosynthesis. This is because light provides the energy needed for Photosynthesis. As the light level is raised, the rate of Photosynthesis steadily increases but only up to a certain point. After that, it won’t make any difference because then it will either be the temperature or the Carbon Dioxide (CO2) levels which are the limiting factors.
If there is too little Carbon Dioxide (CO2), then the rate of Photosynthesis will slow down. This is because Carbon Dioxide (CO2) is one of the raw materials needed for Photosynthesis. Similarly with light intensity, the amount of CO2 will only increase the rate of Photosynthesis up to a point. After this CO2 will no longer be the limiting factor, but instead light and CO2 will.
Usually, if the temperature is the limiting factor, it is because it’s too low. Due to this the enzymes work more slowly at low temperatures. However if the plant gets too hot, the enzymes it needs for Photosynthesis and its other reactions will be denatured, this happens at approximately 450C.
As you increase the distance from the light source, the plant will produce less bubbles of oxygen since the rate of Photosynthesis will decrease. This is because as you increase the distance of the light source away from the plant, it will become a limiting factor and this will decrease the rate of Photosynthesis.
Light Source (Electric lamp, torch, etc.)
Measuring ruler (cm)
Sodium Hydrogen Carbonate