Biology – Energy | e-Consult

Method: A simple respirometer can be constructed using a transparent container (e.g., a bottle or jar) filled with a solution of sodium hydroxide (NaOH). The NaOH solution absorbs carbon dioxide (CO2) produced during respiration. A small amount of germinating pea seeds are placed in the container, and the container is sealed, leaving a small tube open to allow air exchange. The volume of oxygen (O2) produced is measured by collecting the gas that is displaced in an inverted measuring cylinder placed over the open tube. The experiment is conducted in a controlled environment with a constant temperature. Multiple replicates are performed to improve reliability.

Variables to Control:

• Temperature: Maintain a constant temperature throughout the experiment using a water bath. Temperature significantly affects the rate of respiration.
• Light: Keep the seeds in darkness to prevent photosynthesis, which would artificially inflate the oxygen production.
• Seed Age/Viability: Use seeds of the same age and ensure they are viable to avoid variations in respiration rates.
• NaOH Concentration: Use a consistent concentration of NaOH to ensure all CO2 is absorbed.
• Volume of Seeds: Use a consistent mass of seeds in each replicate.

Measurements: The volume of O2 produced over a set time period (e.g., 30 minutes) is recorded. The RQ is calculated as: RQ = Volume of O2 produced / Volume of CO2 absorbed. Since the NaOH solution absorbs CO2, the volume of CO2 absorbed is equal to the volume of O2 produced. Therefore, the RQ is simply the volume of O2 produced.