Photosynthesis Lab: What to Expect

As mentioned earlier, the rate of photosynthesis should increase when you give the plant more light, more carbon dioxide and the optimum temperature. However, at high light and high carbon dioxide, photosynthesis will reach its maximum rate and won't go any higher.

For more details, check this page on photosynthesis:
(I will eventually get around to writing more about photosynthesis on this website).

Other Important Points

Here are some extra notes about photosynthesis that could come in handy when discussing your results and writing your conclusion and evaluation sections.

  • Plants carry out respiration (the opposite of photosynthesis!) the entire time to make energy, and so they constantly USE oxygen and MAKE carbon dioxide (which lowers the pH). At low photosynthesis rates (e.g. in the dark), they are respiring but not photosynthesizing. You will only start to see bubbles or pH changes when the rate of photosynthesis is higher than the rate of respiration.

  • Having different number of leaves or mass of the plant cutting will affect your results. More leaves mean more photosynthesis! Also, they should all be healthy cuttings.

  • Remember to take your measurements only after a few minutes of exposing your plant to light so that it will be photosynthesizing at a constant rate. Similarly, be careful not to expose all your plant cuttings to light while running an experiment on one of them!

  • If you are using a pH probe, it needs to be properly calibrated before starting your experiments. If you are not able to do this, just remember that it might be a source of error...

Try to make a list of all the things you will need to run the experiment. Think about what you need to keep constant. You should also have a control experiment where photosynthesis won't happen (no source of light or carbon dioxide, or a dead plant, for example).

Read more about setting up your experiment, and what variables you can measure.

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