Biology – Investigation of limiting factors | e-Consult

Variables:

• Independent Variable: Carbon dioxide concentration (e.g., varying the concentration of sodium bicarbonate in the water).
• Dependent Variable: Rate of photosynthesis (measured as the rate of oxygen production).
• Controlled Variables:

  • Light intensity: Maintain a constant light intensity.
  • Temperature: Maintain a constant temperature.
  • Plant species and size: Use the same species and approximately the same size of plant.
  • Volume of water: Use the same volume of water for each trial.
  • Carbon dioxide source: Ensure the carbon dioxide is supplied consistently (e.g., by using a sodium bicarbonate solution).

Method:

1. Prepare several beakers, each containing a plant (e.g., a small potted plant) in a closed system. The system should allow for the collection of oxygen produced.
2. Prepare solutions of sodium bicarbonate with varying concentrations (e.g., 0.1M, 0.2M, 0.3M). The sodium bicarbonate will provide the carbon dioxide for photosynthesis.
3. Fill each beaker with the sodium bicarbonate solution of a specific concentration.
4. Expose the plants to a constant light intensity.
5. Allow the plants to photosynthesize for a set period (e.g., 30 minutes).
6. Collect the oxygen produced by the plants in an inverted graduated cylinder placed over the opening of the beaker.
7. Measure the volume of oxygen collected in each beaker.
8. Repeat the experiment multiple times (e.g., 3-5 replicates) for each carbon dioxide concentration.

Analysis:

The rate of photosynthesis can be calculated as the volume of oxygen produced per unit time (e.g., mL of O2 per minute). This data can be plotted on a graph with carbon dioxide concentration on the x-axis and the rate of photosynthesis on the y-axis. A scatter graph is appropriate. A trend line can be drawn to show the relationship between carbon dioxide concentration and the rate of photosynthesis. Statistical analysis (e.g., calculating the mean and standard deviation) should be used to assess the reliability of the results. A clear conclusion should be drawn about the effect of carbon dioxide concentration on the rate of photosynthesis, referencing the data and the trend line. The relationship is likely to be non-linear, with a point of diminishing returns.