Photosynthesis Lab:Effects of Carbon Dioxide Levels in Different Environments

This experiment researched the effects of light concentration on the carbon dioxide levels in the container with leaves. The carbon dioxide respiration was measured at 3 distances: 6, 12, and 24 centimeters. We predicted that when the distance from the light source to the plant is smaller there would be a more significant decrease in the CO2 levels in the chamber. Light intensity is strongest when closer to the plant which should result in lower CO2 levels; however, similar studies have proven that too much light intensity can actually hinder plant growth (Barber and Andersson, 1992). This led us to support the idea that plants need specific conditions for optimal growth, meaning not too high or too little of a resource (Sharma, 2025). While this went against our initial hypothesis, plants in 6 cm and 24 cm groups had higher CO2 levels than those in the 12 cm group due to the lack or excess amount of light, further proving that the middle group enhanced photosynthesis the most.

Photosynthesis Lab: Effects of Carbon Dioxide Levels in Different Environments 

Plants rely on carbon dioxide from the atmosphere, sunlight, and water in the soil to grow needing adequate amounts to function efficiently. It is known that plants require sunlight to grow and thrive since it’s a key component in the process of photosynthesis. Farmers avoid planting in the winter because of the lack of sunlight makes photosynthesis harder to occur, decreasing the overall plant growth. But is there a such thing as too much sunlight? Will more concentrated forms of light prevent the plant from taking in more CO2 hindering photosynthesis? We formed the hypothesis that when the light is closer to the plant CO2 levels would decrease in the chamber due to the increased rate photosynthesis. However, this was proved wrong and came to the conclusion that plants require a certain amount of light and intensity and either too much or too little can negatively affect the rate of photosynthesis, ultimately requiring a “Goldilocks” amount. 

Method

Materials  

For this experiment the same, 3 spinach leaves were required for every trial and then placed inside a carbon dioxide chamber that measured the changing levels of CO2 with a CO2 sensor, it then reported that data into SparkVue. Each distance between the light and the chamber was measured using a ruler, starting with 6 centimeters, then 12, and lastly 24. Each trial was 7 minutes and there were 2 trials per group including the experimental and control to ensure reliability.

Procedure 

Prior to setting up the experiment in the lab, we connected the carbon dioxide sensor to the SparkVue app on the iPads, so the changes were seen on a graph. When taken to the lab the first distance group that was measured was 12 centimeters, we took 3 spinach leaves placed them into the chamber and placed it on a table with the sensor attached. The light was then installed above the sink and remained in that location for the duration of the experiment – staying constant. Next, we took a yardstick and measured 12 cm away from the light and placed the CO2 chamber with the leaves inside of it there. The light was turned on, and we waited 15 seconds until we started collecting data for the next 7 minutes. After those 7 minutes the first control group trial was complete, leading us to turn off the light source and removing the chamber from the table and refreshing it by waving it left and right, to air out the container. We repeated this process twice for each group, having 2 trials for each distance from the light source, and resulted in having 2 lines of data for each group on the SparkVue app. However, due to time constraints our last experimental group was left incomplete leaving us with only 1 line of data for our 24 cm group. In conclusion, our control group of 12 cm had 2 trials as well as our experimental group of 6 cm, but our other experimental group of 24 cm had only 1 trial which might affect the reliability of that trial.

Results

Data from the second trial of the 24 cm experimental group was unfinished, but the rest of the data is complete and led us to modify our previous hypothesis. We originally believed that the closer the chamber was to the light source, the more carbon dioxide would be absorbed by the plant in the chamber. However, our data showed that the 6 cm group, which was the closest to the light had -0.55 ppm/s which was a data point in between the 12 cm and 24 cm groups (see Figure 1). The 12 cm group was the control group and has the highest rate of change of CO2 in the chamber with -0.71 ppm/s. Lastly, the 24 cm distance had +0.19 ppm/s which was the most carbon dioxide left in the container after the light was placed from it. So as a result, 12 cm had the highest amount of CO2 taken from the chamber after the experiment was conducted, and the 24 cm had the lowest amount of CO2 taken from the container. We measured the rate of change in carbon dioxide in the chamber for the 7 minutes it was under the light for. This means that if the result is positive less change occurred, meaning photosynthesis occurred at a much slower rate. If the number is a lower negative number like -0.71 ppm/s more CO2 was absorbed by the plant meaning photosynthesis occurred at a much faster rate. In order, photosynthesis occurred the fastest 12 cm away from the light, and the slowest at 24 cm, with 6 cm away from the light being the middle result.

Conclusion/Discussion

The goal of this experiment was to see if photosynthesis would work at a faster rate with higher light intensity based on how close the plants were to the light source. While our results did not 100% match our original hypothesis it helped us modify our old hypothesis and then create a new one. Another factor that should be accounted in this experiment is that we did not complete 2 trials for our final experimental group of 24 cm. This didn’t directly alter the data, but there is a chance that it could’ve been an abnormal result, skewing our graph and we don’t have any other data from that trial to verify that. Our first hypothesis assumed that because there was more light in the plants surroundings, photosynthesis would occur at a faster rate; however, professor Jinfeng Zhang states, “Photoinhibition often occurs when light energy is excessive, which reduces photochemical efficiency and even causes photooxidative system damage.” This leads us to reevaluate our past hypothesis and change it so that if plants are exposed to light intensities above or below an optimal range, then their rate of photosynthesis will decrease due to insufficient energy amounts at low-light levels, and potential stress or photoinhibition at excessive-light levels. We have seen in our experiment that 12 cm away from the light source was the optimal range for the spinach leaves, and carried out photosynthesis at the fastest rate out of the 3 groups, resulting in the most CO2 being absorbed. 6 cm was far too intense for the spinach leaves and led to a slower rate photosynthesis and could’ve possibly left the plant with damage to the photooxidative system. Lastly, 24 cm was still not in an optimal range, being it was too far for the plant to collect the light energy, leading it to the be the group that had the least amount of carbon dioxide absorbed.

To conclude, this experiment resulted in different outcomes from what our original hypothesis predicted, leading us to alter our hypothesis and form a new reasoning. Plants have an optimal range for light intensity and when it’s over or under that range, the photosynthesis rates are inadequate. The control group being 12 cm away from the source of light had the highest rate of CO2 absorption and the experimental group of 24 cm had the least. It’s seen that when there is too much light intensity, the plant can actually get damaged, and when the light source is too far, photosynthesis occurs at a slower rate. 12 centimeters was in the middle of both experimental groups and was a ‘happy medium’ resulting in optimal carbon dioxide absorption.