This pre-lab will present some of the general concepts related to the measurement of the net rate of photosynthesis at different quantities (intensities) and qualities (wavelengths) of light by measuring carbon dioxide consumption.
General Purpose
Conceptual
The net amount of CO2 used by leaf tissue is a function of the rate of CO2 used by photosynthesis (specifically the Calvin cycle) and the rate of CO2 generated by cellular respiration. In the presence of light both processes will be at work. Depending on a number of factors the rate of photosynthesis will slow in the dark. It should be noted however that even though the light reactions quickly come to a halt in the absence of light, the Calvin cycle could proceed for some time in the dark because the intracellular ATP and NADPH pools are not immediately depleted.
Photosynthesis rates and the rate of CO2 used by photosynthesis is directly proportionate to the light available at low light intensities. This linear relationship is the result of the rate of photosynthesis being limited by the rate of the light reactions. Under lower light conditions the pigments in the leaf receive insufficient photons to produce enough ATP and NADPH to sustain maximum photosynthetic rates. At higher light intensities there is less of an increase in photosynthetic rate per unit increase in light intensity. Eventually photosynthesis reaches light saturation at the higher light intensities where light is no longer a limiting factor for the process of photosynthesis.
The photosynthetic rate and the rate of CO2 consumption by photosynthesis also varies with the wavelengths of light available. This is a function of two different aspects of the pigments associated with the light reactions: 1) not all wavelengths of light are absorbed equally by the pigments present in the plant and 2) not all absorbed wavelengths are equally effective at powering the light reactions. As a result of this, the rates of production of ATP and NADPH can vary as wavelength of light changes but this is not a linear relationship.
The effect of varying the quantity (intensity) and quality (wavelength) of light on the rate of net CO2 use by a plant will be investigated.
Proceed to the Pre-Lab Quiz