Photosynthesis: Does it really happen?

We have read about photosynthesis on the computer... but how do we know it actually happens? People did not know about photosynthesis for a long time. How did they find out that it occured?

We aren't going to try to prove that photosynthesis happens with this experiment, but we will try to show you that something has to be happening in the plant in order for it to grow.

This experiment will require that you have a scale, small plant, some potting soil, a flower pot, and plenty of water. It will take several weeks to complete.

First take the plant, and very carefully remove as much dirt as possible from around its roots. You do not want to tear the tiny root hairs which are on each root, because that is how the plant gets its water.
Next, weigh the plant on the scale, and record its weight in grams. Now set aside the plant, and take the potting soil into which you are going to place your plant. Weigh out the soil on the scale. Write down the weight.
Plant your plant with the potting soil in the flower pot. Now weigh the soil, pot, and plant all together, and record that weight.

Put the plant in a place where it will get plenty of sunlight, and write down what you think will happen to the plant over the next several weeks. Do you think it will grow? Will it get heavier? Will the weight of the soil change? Write down your thoughts on these things. Remember to water the plant whenever the soil gets dry. Take a measuremennt of how much the potted plant weighs each week. Record this information.

Take the plant and weigh it.
Carefully unbury it from the soil. DO NOT LOSE ANY OF THE SOIL! Be sure to collect all of the soil, because you will want to weigh it.
Weigh the plant, and record its weight.
Weigh the soil. Record its weight.
Replant the plant. Compare the data, and write down what you notice about the results.

Go on to the Photosynthesis experiment results Let's go back for a different experiment! Let's go back to the Introductory page

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