In this experiment, I will test to see how heat affects the rate of photosynthesis in a water plant as a limiting factor

Photosynthesis is the process by which chlorophyll containing organisms, (namely green plants, algae, and some bacteria), capture energy in the form of light and convert it to chemical energy. Virtually all the energy available for life in the earth’s biosphere, (the zone in which life can exist), is made available through photosynthesis.

A generalized chemical equation for photosynthesis is:

Carbon Dioxide + Water + light energy = Sugar (Glucose) + Oxygen + Water

This can be seen as two different chains of reactions…

One involves the transfer of light energy into chemical energy that is light intensity dependant – if it is lighter the reaction happens more efficiently.

The other shows the creation of glucose and is heat dependant. The glucose is created by carbon dioxide and water, and the reaction is powered by the chemical energy converted from solar energy. The carbon dioxide must be broken down using enzymes to form the basics of the glucose. This is heat dependant because enzymes work better at higher temperatures. This creates glucose (C6H12O6) and waste products, oxygen (O2) and a little water (H2O).

Artificial Photosynthesis

If chemists were able to duplicate photosynthesis by artificial means it would result in systems having enormous potential for tapping solar energy on a large scale.

Much research is now being devoted to this effort. An artificial molecule that remains polarized sufficiently long enough to react usefully with other molecules has not yet been perfected, but the prospects of this are promising.


I predict that more heat will increase the rate of photosynthesis.

I predict that at 0�C there will be few bubbles and at around 40�C, it will be at its peak. After 40�C the rate of photosynthesis will again drop. I can show this in a simple graph:

I think this because the enzyme that breaks down the carbon dioxide stops working or is even obliterated by temperatures over 40�C as shown in my background knowledge. When the enzyme stops working the carbon dioxide is not broken down, so less glucose and oxygen are produced.

Apparatus List:

Boiling Tube

Elodea (Canadian Pondweed)






Beaker Kettle (Boiling Water)


To show how I will assemble the equipment for this experiment I will draw a diagram.


I am going to count the bubbles at each level of heat for 2 minutes and see if there is any relationship between my results. The temperatures I will use are 0�C, 10�C, 20�C, 30�C, 40�C, 50�C and 60�C.

I am counting the bubbles because I think that if there are more bubbles then the rate of photosynthesis is increased, because the bubbles are oxygen and the more oxygen the plant is giving off the higher the rate of photosynthesis. To make sure that any bubbles are not missed there will be 2 counters of bubbles to get a precise measurement.


Input: – I will change the temperature of the water that the plant is in by adding ice or hot water.

Control: – I will keep the light intensity the same by measuring the space between the lamp and the pondweed before each test. If the light intensity changes, the rate of photosynthesis would be affected, because light is a factor which photosynthesis relies on and if there is a high light intensity it increases the rate of photosynthesis because the energy from the light source would increase the rate.

I will also keep the amount of carbon dioxide in the water constant by changing the water after each test. If there is too little carbon dioxide in the water then the rate is decreased because the plant has no carbon dioxide to use in the photosynthesis reaction.

I will keep the plant the same length of 5cm and the same species of pondweed (Elodea).

Outcome: – I will measure the temperature of the water with a thermometer to get an accurate fair temperature for the plant to be in. I will also count the number of bubbles that the plant gives off.

To keep it fair I will obey the variables and do the test at each temperature 3 times to clear any anomalous results. This will be so that if are any anomalous results then I can reject them without creating a gap in my results.

To keep this experiment safe I will mop up any water that I drop near the lamp or plug to stop any chance of electrocution. I will also keep in mind the heat that the lamp generates so I will be careful to not touch it.