Biology – Investigation of limiting factors | e-Consult
Investigation of limiting factors (1 questions)
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Experimental Procedure:
- Prepare a chloroplast suspension: Obtain chloroplasts from a spinach leaf by grinding the leaf in a suitable buffer solution (e.g., potassium phosphate buffer). Filter the suspension to remove cell debris.
- Set up the apparatus: Use a closed system, such as an inverted funnel placed over a test tube. The chloroplast suspension is introduced into the funnel. A light source (e.g., a lamp) is positioned at a fixed distance from the funnel.
- Measure oxygen production: As photosynthesis occurs, oxygen gas is produced. This gas will accumulate in the test tube. The volume of oxygen produced can be measured by collecting the gas over water using the inverted test tube and measuring the displacement of water. Alternatively, a dissolved oxygen sensor can be used to measure the concentration of oxygen in the solution.
- Vary light intensity: Adjust the distance between the light source and the funnel to vary the light intensity. Ensure that the temperature is kept constant throughout the experiment.
- Repeat measurements: Repeat the experiment for each light intensity at least three times to obtain reliable data.
Measuring the rate of photosynthesis: The rate of photosynthesis can be measured by determining the volume of oxygen produced per unit time (e.g., mL O2/min). This is a direct measure of the rate of oxygen evolution, which is a proxy for the rate of photosynthesis.
Independent Variables and Controls:
- Distance from the light source: This is the most direct way to manipulate light intensity. Control: Maintain a constant temperature throughout the experiment using a water bath.
- Wavelength of light: Use filters of different colours to isolate specific wavelengths of light (e.g., red, green, blue). Control: Ensure that the light intensity is the same for each wavelength tested.
- Carbon dioxide concentration: Use a solution with different concentrations of bicarbonate ions (HCO3-) to vary the availability of carbon dioxide. Control: Maintain a constant temperature and light intensity.