Bio II Elodea Lab: Photosynthesis and Cellular Respiration

What could be limiting the rate of photosynthesis at light intensities where a graph shows no increase in Absorbance with an increase in light intensity? What is the name of the point at which your line of best fit crosses the x-axis, what is happening at this light intensity, and what is its significance for the photosynthesising organism? ................
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