Leaves that develop in full sunlight might be expected to develop mechanisms for protection that are less obvious or absent from leaves that develop in full shade. To address this question, the instructor will select a type of plant that grows in full sun, but that is dense enough that many of its leaves are constantly in full shade. Green shrubs growing as a hedge in full sun are good candidates for the study. You will measure the photosynthetic rate for sun and shade leaves taken from a single plant, throughout a range of light intensities. For a null hypothesis, let us suggest that there is no difference in photosynthetic efficiency between sun and shade leaves.
Every leaf has a saturation intensity.
That is, there is a limited quantity of pigment per unit area that is capable of capturing photons, or there could be a limit to the rate at which the captured energy can be utilized to fix carbon. Either way, above the saturation intensity the photosynthetic rate cannot be increased, and it may even drop if the leaf is readily injured by strong light. Among the alternative hypotheses, you might suggest that shade leaves fix carbon faster than sun leaves at low light intensities. You can also suggest that sun leaves have a higher saturation point than shade leaves. The first hypothesis makes sense, since you might expect shade leaves to develop mechanisms for more efficient photon capture in low light.