Unusual photosynthesis lab results

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ldustin004
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Joined: Tue Mar 30, 2021 6:00 am
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Unusual photosynthesis lab results

Post by ldustin004 »

In executing a lab where the rate of photosynthesis was to be measured as per the impact of controllable variables, my group obtained inconclusive results that we can't seem to definitively justify. In theory, variables aside, the results produced by measuring O2 levels over time should have indicated an upward trend - however in our control group, where we were simply observing the rate at which photosynthesis naturally occurred, our results identified a decline in oxygen concentration. The readily available CO2 should have been a contributing factor in producing increases in oxygen levels, rather than the subsequent decrease we identified.
Plants don't consume O2 - it is expelled as a waste product.
What error would have attributed to these results?
koneill18
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Joined: Thu Aug 06, 2020 8:22 am
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Re: Unusual photosynthesis lab results

Post by koneill18 »

Hello!

To help me answer your question, I have a few questions about your experimental design. Where were the control plants located and what type of plants are they? Also, how did you measure O2 levels? At what time intervals did you take the measurements? Did the O2 levels go up at all over the course of the experiment, or did they consistently decrease? Temperature and light intensity are two variables that affect the rate of photosynthesis. If the temperature gets above around 68 degrees Fahrenheit, the rate of photosynthesis will slow down. Reduced exposure to light also reduces the rate of photosynthesis. Is it possible there were some weather changes over the course of your experiment that may have influenced your results? I might be able to give you some better suggestions once I know more about how you performed your experiment!

Katelyn
ldustin004
Posts: 2
Joined: Tue Mar 30, 2021 6:00 am
Occupation: Student

Re: Unusual photosynthesis lab results

Post by ldustin004 »

Hi Katelyn,

The control plants were spinach leaves, contained within a clear plastic chamber located beneath a source of LED light in an indoor lab with a controlled, consistent temperature. We utilized a digital oxygen gas sensor inserted into the mouth of the chamber, where results were digitally conveyed and graphed in 20 second intervals over a 6 minute period - consistently over all trials, the oxygen concentration consistently decreased and there were no identifiable increases in the quantitative data.

Thank you for your time :)
koneill18
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Posts: 188
Joined: Thu Aug 06, 2020 8:22 am
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Re: Unusual photosynthesis lab results

Post by koneill18 »

Hello,

Thank you for the extra information! When you added the spinach leaves to the chamber, did you make sure to fully line the bottom of the chamber with leaves? Maximizing the leaf surface area helps the oxygen gas sensor detect oxygen concentration better. Just make sure that the leaves aren't stacked on top of each other. Did you make sure that the leaves were fresh and kept cool up until the start of the experiment? Sometimes lamps can produce too much heat and that inhibits photosynthesis. LED plant lights don't produce that much heat though, so that probably wasn't the issue.

Was there a reason why you stopped taking measurements after only 6 minutes? My guess is that you didn't allow enough time for photosynthesis to get started. Keep in mind that plants alternate between cellular respiration and photosynthesis. When plants carry out photosynthesis, they're converting CO2 and water into oxygen and glucose. The plant then uses the oxygen and glucose to carry out cellular respiration, which is the process that the plant uses to produce energy in the form of ATP molecules. CO2 and water get released as byproducts, and the plant picks them up to start the process of photosynthesis again. So the plant is continuously cycling between photosynthesis and cellular respiration.

There can be a several minute lag time when the plants are shifting between cellular respiration and photosynthesis. If you have time to do the experiment again, I would recommend taking 1-2 measurements per minute up to 20 minutes. If you observe the plants for a little longer, I think you should see them start to release more oxygen as they switch to photosynthesis.

I hope this helps!
Katelyn
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