This exercise is designed to introduce you to techniques for measuring light-driven electron transport in chloroplasts, and to techniques for purifying organelles using their differences in density. It is also designed to reinforce your training in experimental design. Background Photosynthesis is the most important biochemical process on earth. Virtually all living organisms depend directly or indirectly on photosynthesis for energy, and all aerobic organisms also depend on photosynthesis for oxygen. O however, the reactions by which this is accomplished are diabolically complex.
Light is captured by pigments which absorb photons of certain wavelengths.
When this occurs, the energy of the photon is added to the energy of an electron within the pigment, which moves to an orbital more distant from the nucleus. Photosynthetic pigments are usually found in a precise array called a photosystem, which is constructed such that energy absorbed by any pigment within the photosystem is transferred by inductive resonance to a special pigment at the center of the array called the reaction center chlorophyll. The primary electron acceptor then passes the excited electron down an electron transport chain located on the thylakoid membrane. I the reaction center chlorophyll is called P700, while the reaction center chlorophyll in Photosystem II is called P680. In cyclic photophosphorylation electrons transferred from P700 to the electron transport system are returned to P700.