Chlorophyll is a pigment residing in the chloroplasts of plant cells. More specifically, the outer layer of the thylakoids--tiny organs found within each chloroplast that resemble stacks of pancakes--is home to the chlorophyll molecules.
Chlorophyll and the Light Reactions
The first steps in photosynthesis are the light reactions, in which chlorophyll plays an important role. Chlorophyll not only helps to absorb the energy from the sun but also ejects an electron in the presence of this energy. This ejected electron is crucial to the production of energy-rich glucose.
The various types of pigments include chlorophylls, carotenoids and phycobilins. Each pigment absorbs different wavelengths of sunlight, ensuring that plants get as much energy as possible from sunlight. The accumulation of this light energy leads to the ejection of electrons. Chlorophylls absorb a wide range of wavelengths, with the exception of wavelengths in the green range, which are reflected. The reflection of green light explains why chlorophylls are associated with the green color of plants.
Types of Chlorophyll
“Chlorophyll” describes a class of pigment molecules rather than a specific molecule. The chlorophylls include chlorophyll a and chlorophyll b--as well as c, d and e in certain other non-plant species. All the chlorophylls, except chlorophyll a, harvest light; they absorb light energy and eventually transfer it to the electron-releasing molecule. Chlorophyll a plays a different role. Found in all photosynthetic organisms, chlorophyll a molecules are the electron-releasing molecules and are found in what is called the reaction center.
Chlorophyll A in the Reaction Center
The reaction center consists of chlorophyll a and various proteins. When the energy that has been gathered gets transferred to this reaction center, the chlorophyll a molecules become so excited that they release electrons. Normally, the molecules would return to ground state from this excited state, emitting light energy, but the proteins in the reaction center catalyze the energy to be released in the form of an ejected electron. This electron drives the later steps of photosynthesis, so chlorophylls play crucial roles in photosynthesis.