I've been looking into CAM plants - notably the snake plant which is native to West Africa.

Upon researching the CAM photosynthesis cycle, I've found it fascinating that the plant stores CO2 at night and photosynthesizes during the day. But I'm a little confused as to how oxygen is a byproduct of this reaction. There seems to be no images of the cycle where oxygen is involved in any of the diagrams I've seen.

There was one question somewhere online that explained it, but I was nowhere near smart enough to understand their technical language and so I didn't really get an answer.

So here's my question.

Does a CAM plant release oxygen during the day? If so, is there a specific ppm value or some other value that that is applicable to a snake plant or another similar plant that I can use to calculate the approximate amount of oxygen released?

Your help is much appreciated. Thanks!


2 Answers 2


In the process of photosynthesis light is used as as a source of energy to generate sugar from carbon and water. A by-product is oxygen. enter image description here

This process can be broken into two cycles: light reaction and Calvin cycle. In the light reaction energy from photons is transformed into usable energy and reducing agents (ATP, NADPH) and water is used as a source of electron, this results in the release of oxygen. In the Calvin cycle this energy coins are used to produce the actual carbohydrates.

There are three known wide-spread mechanisms of photosynthesis: C3, C4 & CAM One can think of C3 as the "common" system and C4 & CAM as adaptations.
The CAM adaptation is a way to overcome dry, hot climates. The problem is that photosynthesis requires CO2 but opening the stomata allows water to escape. This is not acceptable. CAM plants separate the time of acquisition of CO2 and the actual fixation. They open the stomata at night, allowing oxygen to get out and CO2 to get in but fix the carbon, and thus create the oxygen, during the day. Although the Calvin cycle is not light dependent it needs substrates created in light conditions so it will not work in the dark under normal conditions.

This article has assimilation curves depending on temperature in different CO2 concentrations. You can use the above equation to estimate grosso modo the amount of oxygen released. They also supply graphs of oxygen change inside a bag following several hours. enter image description here enter image description here

Please remember that the amount of oxygen is less important that the concentration, especially compared with CO2

  • 1
    $\begingroup$ @user1136 This is the balanced equation. It caused a lot of confusion and many experiments were designed to prove your very important sentence in parenthesis. But We can't change the equation $\endgroup$
    – Hachiloni
    Jan 25, 2021 at 15:42
  • $\begingroup$ @user1136 that equation isn't more clear for me but i'm not against. I think editing gives your internet points. If you want you can edit my answer and I'll will approve $\endgroup$
    – Hachiloni
    Jan 25, 2021 at 17:24

The rationale behind CAM photosynthesis, as opposed to C3 photosynthesis, is to partition the "light" and "dark" reactions temporally to avoid production of phosphoglycolate by RuBisCO in the presence of oxygen. During photosynthesis, molecular oxygen is produced in the photosynthetic electron transport chain, or the "light" reactions. The components of the electron transport chain are very highly conserved across species, including CAM organisms. The enzyme responsible for producing oxygen, Photosystem II, uses light energy to oxidize water, in turn generating molecular oxygen. This means that light is a necessity for generating oxygen, and essentially constrains the highest levels of oxygen evolution to daytime.


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