Co2 level increase with plants

[linm0806]

When a plant is in the air tight container and lighted with fluorescent lamp, we thought the Co2 should be decrease because the rate of photosynthesis should be faster than respiration rate, but why the co2 level increases instead?

[Noorakhat]

Hello linm0806,

I'd happily guide you with this experiment. In order for your plant to grow, it needs carbon dioxide to make its sugars. They make carbon dioxide during respiration. Since the plant is in an airtight container, the plant re-suses its water and carbon dioxide for both cycles. Photosynthesis and respiration will both occur. However, cellular respiration can occur any time, while photosynthesis needs light to start its process. Also, in order for photosynthesis to occur, it needs carbon dioxide. You are right that the rate of photosynthesis is faster than respiration, but both of the cycles work together in keeping the plant alive. Since plants create more oxygen than they need, the CO2 levels should not exceed the oxygen levels.


Please let me know how else I can help.

[linm0806]

Thank you Noorakhat. This is what we did. We used an air tight container, but the bottom part was fill up with water to seal the air flow, and provide the water to the plant At the same time. Light was on whole day long, a Co2 meter and a plant were in it. The CO2 meter indicate the CO2 level kept going up. We thought the CO2 level supposed to go down because of the photosynthesis.

[LilGreenFrog]

Hi Linm,

So as Noorakhat mentioned, plants use gasses for two different processes. Photosynthesis, which uses CO2 and produces O2, and respiration (like we do) which uses O2 and PRDUCES CO2.

Even with the light on all day, the plant still needs to do respiration to keep its cells alive. So it uses CO2 during photosynthesis, and then excretes it during respiration. And then that same CO2 is used again in photosynthesis. Its cycled through the plant, over and over again.

Since plants need CO2 to live, and you can grow them in a sealed container where they can't get new CO2, it means that they use it, and make it, and use it, and make it. So while the levels will fluctuate during the day, I'm guessing the average CO2 level will remain pretty constant.

If you saw the levels go up and up, how many days did you measure the CO2 for, and how high did it get? Have you repeated the experiment to see if you get the same results, maybe with a second CO2 sensor? You could also try measuring the O2 in the container, since Noorakhat noted that CO2 shouldn't get higher than O2.

I'm not a plant scientist, so maybe someone else will have ideas as to why you saw your CO2 increasing.

[linm0806]

Hi LilGreenFrg, The Co2 meter is working because it has change to reading indoor, outdoor or when we open the container. So far we tested 2 plants. Both readings are going up. The current one, starting CO2 reading was 627, and after 24 hr, it has reached 2000. Not sure how to measure O2. The experiment was to measure the CO2 level with different plants, and see which one can absorb more, but both plants produce more CO2 if the experiment is correct.

[julieslake]

Hi linm0806,

I would continue to measure the CO2 levels for both of the plants for the next few days to see if CO2 levels continue to rise. Feel free to post an update!

[cnoonan180]

Hello!

For some extra context, the formula for photosynthesis is:

6CO2 + 6H20 ->C6H12O6 + O2

Notice that on the right side of the arrow are the products or the results of what is made by the reaction between the two molecules that the plant is starting with (carbon dioxide and water, which are on the left). What results from the reaction, or the products on the right, is glucose sugar and oxygen. Therefore, as long as the plant has sufficient water and light (or the reactants of photosynthesis on the left side of the equation plus heat/light), photosynthesis will continue to happen (the rate, or speed, depends on intensity of the light).

Similarly, the products, or what is released from cellular respiration in plants also includes oxygen. So, it makes sense that the oxygen levels in your closed system would increase as the plant remains to photosynthesize and create energy through cellular respiration. The most important thing to remember is that oxygen is a PRODUCT or what is RELEASED from both photosynthesis and cellular respiration in plants while carbon dioxide is a REACTANT, or is being taken out of the atmosphere in your closed system, so the reading for carbon dioxide will be less since it is being used up and not created. Oxygen is being created and released from chemical reactions.

For your experiment, I recommend you use both carbon dioxide and oxygen sensor readings (with oxygen being the most useful to try and find a change in gas levels). However, oxygen gas sensors can be expensive so I suggest you ask your science teacher if there is an oxygen gas sensor at your school you would be able to borrow.

Hope this helps and feel free to reach out with more questions!
-cnoonan180