All organisms need energy to function. Heterotrophic organisms obtain their energy by oxidizing reduced organic compounds and recovering the energy stored in the C-H bonds. However, those C-H bonds were originally created using energy from sunlight, by a process called photosynthesis. Photosynthesis is described in greater detail in chapter 10 of your text and topic 7 of your lab manual.
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. Plants have two photosystems, Photosystem I and Photosystem II . In cyclic photophosphorylation electrons transferred from P700 to the electron transport system are returned to P700.