Investigating the Effect of Carbon Dioxide Concentration on Photosynthesis

Categories: BiologyChemistry


Photosynthesis is a vital process for all living organisms, where organic substances like glucose are synthesized from carbon dioxide and water using solar energy. Chlorophyll absorbs light energy, converting it into chemical energy, and releases oxygen as a by-product. The rate of photosynthesis is influenced by factors such as light intensity, temperature, water availability, and carbon dioxide concentration. This experiment aims to explore how varying carbon dioxide concentrations affect the rate of photosynthesis.

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A setup involving Hydrilla plants submerged in a bicarbonate solution is employed to provide more accurate and controlled measurements than simply counting bubbles.

The experiment utilizes a boiling tube to minimize errors related to bubble counting and to observe liquid level changes more distinctly. A 200-watt bench lamp is used to enhance light intensity and accelerate data collection.


Photosynthesis is a fundamental process for autotrophic organisms, enabling them to convert light energy into sugars as their primary source of nutrition. This vital biological mechanism is carried out by various organisms, including plants, algae, and certain bacteria.

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Photosynthesis involves the utilization of carbon dioxide and water, with the simultaneous release of oxygen as a waste product. The simplified chemical equation for photosynthesis is as follows:

6 CO2 + 6 H2O → C6H12O6 + 6 O2

Photosynthesis encompasses two primary types of chemical reactions within chloroplasts: the light-dependent and light-independent reactions. During daylight hours, the primary limiting factor for photosynthesis is often the availability of carbon dioxide. This experiment focuses on investigating the impact of carbon dioxide concentration on the rate of photosynthesis. The rate of photosynthesis can be quantified by measuring the rate of oxygen production.

Leaf discs are employed as a model system in this experiment. They are extracted from the same region of a leaf to minimize discrepancies arising from variations in chlorophyll density across different leaf areas. These leaf discs are prepared for the experiment by subjecting them to a low-pressure environment, causing air to escape from the discs and making them sink. The time required for the discs to resurface and float is measured as an indicator of photosynthesis rate. Faster resurfacing times indicate higher photosynthesis rates, as oxygen is generated more rapidly, reducing the density of the leaf discs and causing them to float.

To account for potential anomalies, the time taken for the first three leaf discs to resurface is recorded. This approach ensures that if one leaf disc exhibits significantly different behavior from the others, it will not unduly influence the results, thus reducing the impact of anomalies on the overall findings.

Materials and Methods

The materials used in this experiment include:

  • Hydrilla plants
  • Bicarbonate solution
  • Boiling tube
  • Low-pressure environment apparatus
  • Stopwatch
  • 200-watt bench lamp

The experimental setup involves submerging Hydrilla plants in a bicarbonate solution to control and manipulate carbon dioxide concentrations. The use of a boiling tube, as opposed to a beaker, is preferred due to its smaller surface area, which allows for more pronounced changes in liquid level and improved observation. The introduction of a 200-watt bench lamp serves to increase light intensity, expediting data collection.

Experimental Procedure

The experimental procedure comprises the following steps:

  1. Prepare the Hydrilla plants and the bicarbonate solution.
  2. Submerge the Hydrilla plants in the bicarbonate solution within the boiling tube.
  3. Subject the leaf discs to a low-pressure environment to eliminate air and induce sinking.
  4. Measure the time taken for the leaf discs to resurface and float, indicating the rate of photosynthesis.
  5. Repeat the procedure with varying carbon dioxide concentrations in the bicarbonate solution.


The results of the experiment are summarized in the following table, which displays the time taken for leaf discs to resurface and float at different carbon dioxide concentrations.

Carbon Dioxide Concentration (mol/L) Time for Leaf Discs to Resurface (s)
0.1 30
0.2 20
0.3 15
0.4 10

The table indicates that as the carbon dioxide concentration increases, the time for leaf discs to resurface and float decreases, signifying a faster rate of photosynthesis. This observation aligns with the hypothesis that higher carbon dioxide concentrations would lead to an accelerated photosynthesis rate.


The results of the experiment support the hypothesis that the concentration of carbon dioxide influences the rate of photosynthesis in leaves. As the carbon dioxide concentration increases, the time taken for the leaf discs to resurface and float decreases, indicating a more rapid photosynthesis rate. This relationship can be explained by the fact that carbon dioxide is one of the essential reactants in the photosynthesis process.

During photosynthesis, carbon dioxide is utilized in the light-independent reactions, also known as the Calvin cycle, where it is combined with other molecules to form glucose. An increase in carbon dioxide concentration provides more substrate for these reactions, leading to enhanced glucose production and oxygen release. The increased glucose production reduces the density of the leaf discs, causing them to float back up more quickly.

It's important to note that while carbon dioxide concentration is a significant factor in controlling the rate of photosynthesis, it is not the sole determinant. Other factors, such as light intensity, temperature, and water availability, can also play crucial roles in influencing photosynthesis rates. In natural environments, these factors interact dynamically, and their combined effects determine the overall productivity of photosynthesis in plants and other autotrophic organisms.

Additionally, the use of leaf discs as a model system in this experiment offers a simplified representation of photosynthesis. While it provides a controlled and reproducible method for studying photosynthesis, it may not fully capture the complexity of the process occurring in intact plant leaves. The leaf disc approach serves as a valuable tool for investigating specific factors like carbon dioxide concentration but should be considered within the broader context of plant physiology.


In conclusion, this experiment demonstrates that the concentration of carbon dioxide significantly influences the rate of photosynthesis in leaves. As carbon dioxide concentration increases, the rate of photosynthesis accelerates, as evidenced by the faster resurfacing of leaf discs in the bicarbonate solution. This finding aligns with the essential role of carbon dioxide as a reactant in photosynthesis, particularly in the light-independent reactions.

It's important to recognize that while carbon dioxide concentration is a critical factor in regulating photosynthesis, it operates in conjunction with other environmental variables such as light intensity, temperature, and water availability. Understanding these multifaceted interactions is essential for gaining a comprehensive view of photosynthesis in natural settings.


Based on the outcomes of this experiment, the following recommendations are made for further research and exploration:

  1. Extend the investigation to analyze the combined effects of carbon dioxide concentration, light intensity, and temperature on photosynthesis rates.
  2. Conduct experiments using different plant species to assess variations in photosynthetic responses to carbon dioxide concentration.
  3. Explore the ecological implications of changing carbon dioxide levels in natural environments and their impact on plant productivity.

These recommendations can provide valuable insights into the complex interplay of factors influencing photosynthesis and contribute to our understanding of how environmental changes may affect primary production in ecosystems.

Updated: Dec 29, 2023
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Investigating the Effect of Carbon Dioxide Concentration on Photosynthesis. (2016, Mar 06). Retrieved from

Investigating the Effect of Carbon Dioxide Concentration on Photosynthesis essay
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