The Effects of Concentration of CO2 on Photosynthesis in C3 (Sunflower) and C4 (Corn Plants)


Corn and sunflowers are the plants that grow in the areas that have sufficient nutrient and water supply. These environments provide variable conditions in ambient concentration of CO2 that is necessary for transpiration and respiration. Photosynthesis is the process through which plants utilize sunlight rays that help in synthesizing CO2 and water and producing energy and oxygen. It is important in both the plants’ and animals’ lives (Sadras et al. 170). It produces the oxygen required by animals and that allows the plants to eliminate the CO2 gas from the environment. As a factor in the process of photosynthesis, the concentration of CO2 plays an important role in the process. Notably, it varies across different plants. The experiment sought to investigate the effects of the concentration of CO2 on photosynthesis using sunflower and corn plants as the major crops growing in the field. Predominantly, most scientific researchers established that the rate of photosynthesis in most C3 plants increases with a raise in the concentration of CO2. Therefore, the experiment was conducted under ambient conditions of room temperature and pressure within the biology laboratory. Two variables are important in this experiment: the concentration of CO2 and the gaseous exchange rate in the plant leaves (Schmid et al. 81).

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The processes of photosynthesis, respiration, and transpiration of elements help the plants develop and grow in the environment. Photosynthesis takes place in the green pigments, which explains why the experiment has focused on the leaves of the two plants in the ecosystem. Thus, any factor that affects the normal function of the leaf will change the rate of photosynthesis and consequently the level of growth and development within the plants in the environments. Several experimental reports have indicated differences among different species regarding the rate of photosynthesis, irradiance, and baseline reactions to a variation of the conditions in the environment (Busch et al. 200).

Materials and Methods


  • C4- corn plants (Zea maize) leaf
  • C3- sunflower (Helianthus annulus) leaf
  • 500 ml of water
  • Qubit/ Vernie system
  • Thermometer
  • Leaf chamber
  • Plastic syringes
  • Drier et solution
  • Vaseline gel
  • LED output system


Three conditions were set in the laboratory to help in the investigation of the variations in the concentrations of CO2 and its effects on the rate of photosynthesis. First, there was low concentration of CO2 setup. Second, a high concentration of CO2 was established in the laboratory. Finally, an ambient concentration condition was present in the environment. Afterwards, a bypass was established for all the conditions in the laboratory to help attain a stable baseline for both plant leaves. The vaseline gel was smeared on leaves, which were placed in their respective chambers in the laboratory. They were allowed to stay there for a few minutes until the level of CO2 concentration became stable in both cases in the setting. The variation in the concentrations of CO2 was then measured and recorded as shown in the Excel files of the experiment. The setup was monitored for the duration of time, and the findings were documented in the class reports.


The difference in the concentration of CO2 was derived by subtracting the final concentrations from the initial one in the laboratory manuals. The results are enumerated in the Excel files. On balance, there was a significant change in the level of variation witnessed in this study. The ambient conditions for the experiment represented the normal field growth provisions for the process of photosynthesis in the plants. The results showed that C3 experienced a higher rate of photosynthesis with the increase in the concentration of the CO2. Moreover, there was an improved response to a higher concentration of CO2 as opposed to the ambient air conditions during the experiment. At irradiance above 1000, the average rate of flow becomes higher compared to when it is lower than 1000. The temperature levels slightly change with the rising level of the sun.

However, at the ambient baseline conditions, C3 has a higher rate of metabolic processes as compared to C4. Prominently, at the baseline of 195, the irradiance for C3 was 800.84, while that of C4 was 800. Indeed, C3 recorded lower rates than C4 under the same conditions in the environment. Moreover, with increased concentrations in the ambient levels, the rate of photosynthesis raises progressively with the change in flow rates in the chamber.


The experiment shows that the rate of photosynthesis is normally affected by both the respiratory and transpiration elements in the environment. The ambient concentration of the CO2 acted as the case control for the study setup in establishing the concentration of the CO2 and its effect on the process of photosynthesis in the laboratory. Vaseline was applied to reduce the rate of water loss and avoid the shrinking of the plant leaves (Kramer 31). The difference in the variations of the rate of leaf response and the natural environmental setup helps explain the organization of the stomata cells. The one of the sunflowers enables the leaf to respond faster than the corn in the experimental study, which implies that various species display different rates of photosynthetic rates and other metabolic activities in the ecosystem (Killi et al. 134).

Naturally, the increase in the CO2 concentration triggers a number of activities in the plants’ life. It initiates the metabolic activity of the stomata cells that boost the rate of cellular mechanisms within the cells. Such irradiance differences in photosynthetic component illustrate the dynamisms of the role of the environment in the rate of metabolic activities in photosynthesis (Lawlor and Mitchell 808). Typically, it takes place at the initiation of the basic elements of the environment, which include sunlight, water, and CO2. From the experiment, it is evident that the rate of photosynthesis directly depends on both the internal environmental conditions and the internal structure of the leaf. Importantly, the rate of gaseous exchange and water loss influences the level of photosynthesis in all leaves in the environment (Vanaja et al. 84).


Therefore, the level of concentration of CO2 affects the rate of photosynthesis in the plant leaves. Notably, the study shows that the higher the irradiance, the greater the rate of photosynthesis in the environment (Morison and Gifford 789). Thus, the level of energy absorption and development depends on the metabolic mechanisms within the environment. From this study, it is clear that the rate of photosynthesis varies among plant species in the living environments. C4 plants respond faster to the increase in the concentrations compared to C3 plants within similar conditions. The experiment demonstrates the differences in the structure of the stomata openings as well as the concentration of the green matter of the plant, chlorophyll. Notably, leaves play a great role in the growth and development of other organs. Thus, this experiment is crucial in explaining the relationship between the concentration of CO2 and the rate of photosynthesis between the two species of plants in a similar environment.


Works Cited

Busch, Florian A., et al. “C3 Plants Enhance Rates of Photosynthesis by Reassimilating Photorespired and Respired CO2.” Plant, Cell & Environment, vol. 36, no. 1, 2013, pp. 200-212.

Killi, Dilek, et al. “Adaptation to High Temperature Mitigates the Impact of water deficit during Combined Heat and Drought Stress in C3 Sunflower and C4 Maize Varieties with Contrasting Drought Tolerance.” Physiologia Plantarum, vol. 159, no. 2, 2016, pp. 130-147.

Kramer, Paul J. “Carbon Dioxide Concentration, Photosynthesis, and Dry Matter Production.” BioScience, vol. 31, no. 1, 2011, pp. 29-33.

Lawlor, D. W., and R. A. C. Mitchell. “The Effects of Increasing CO2 on Crop Photosynthesis and Productivity: A Review of Field Studies.” Plant, Cell & Environment, vol. 14, no. 8, 1991, pp. 807-818.

Morison, James, and Roger M. Gifford. “Stomatal Sensitivity to Carbon Dioxide and Humidity a Comparison of Two C3 and Two C4 Grass Species.” Plant Physiology, vol. 71, no. 4, 2013, pp. 789-796.

Sadras, Victor O., Francisco J. Villalobos, and Elias Fereres. “Radiation Interception, Radiation Use Efficiency and Crop Productivity.” In Principles of Agronomy for Sustainable Agriculture (pp. 169-188). Springer International Publishing.

Schmid, I., et al. “Effects of CO2 Enrichment and Drought on Photosynthesis, Growth and Yield of an Old and a Modern Barley Cultivar.” Journal of Agronomy and Crop Science, vol. 202, no. 2, 2016, pp. 81-95.

Vanaja, M., et al. “Increasing Atmospheric Carbon Dioxide and Temperature—Threats and Opportunities for Rainfed Agriculture.” Agriculture under Climate Change: Threats, Strategies and Policies, vol. 1, no. 1, 2017, p. 84.

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