Each cell contains a single chloroplast which transforms light energy in and uses it to make energy rich molecules thru the process of photosynthesis (eg. atp) Light is the portion of the electromagnetic spectrum that human can detect with their eyes. Light behaves as a stream of energy particles, protons. Light interacts with matter, by going thru them, reflecting off the object, or being absorbed by the object. Molecule that can absorb photons of light is called a pigment, different pigments can absorb different lights. Color of pigment is determined by the wavelengths of light it cannot absorb. Action spectrum- graph showing the effectiveness of light at each wavelength for photosynthesis. Photon is absorbed, electron inside pigment molecule is excited. Excited electron energy is used in photosynthesis to create nadph, and atp. Energy is then used to create other biological molecules. Prokaryotes called halobacterium use light to power their proton pumps along the membrane.