A phyloGENETIC tree is not the same thing as a taxonomic tree, which is what Cal described. rRNA and molecular studies are used in phylogenetics to determine relations between species.
1 As the light intensity increases, the rate of photosynthesis increases. 2  However, the rate will not increase beyond a certain level of light intensity. 3  At high light intensities the rate becomes constant, even with further increases in light intensity, there are no increases in the rate.
Gradually the rate falls of and at a certain light intensity the rate of photosynthesis stay constant (from point B to C on the graph). Here a rise in light intensity has no affect on the rate of photosynthesis as the other factors such as temperature and carbon dioxide become limiting.