Photosynthesis is the process plants use to convert sunlight into chemical energy. Light is absorbed by tiny organelles in the leaves of the plant, where it is processed via a series of chemical reactions and then stored in the plant. When consumed by herbivores, or plant-eating organisms, the energy stored in the plant is transferred to the consumer.
Photosynthesis is a two-part process. Each part is made up of several chemical reactions -- some that occur in daylight, called light reactions, and others that occur in the absence of light, called dark reactions. Carbon dioxide, water, light and minerals are processed through the various reactions to produce carbohydrates and oxygen. Carbohydrates are the energy-containing molecules that humans and animals ingest to power their own metabolic pathways. Oxygen, a waste product to plants, is necessary for respiration in mammals.
Chlorophyll is the pigment in plants and some bacteria that powers the reactions of photosynthesis. In higher plants such as grains, trees, shrubs, red, brown and yellow algae and even some bacteria such as the blue-green cyanobacterias, photosynthesis involves chlorophyll a. All of these photosynthesizers produce oxygen simultaneously with carbohydates. Some bacteria, such as purple and green bacteria, undergo photosynthesis but do not produce oxygen. These are called anoxygenic photosynthesizers; they use a type of chlorophyll called bacteriochlorophyll.
Chloroplasts are organelles in plant and bacteria cells that contain the chlorophyll used in photosynthesis. They are bound by a double membrane that contains many folds; this double membrane encloses many other membranous structures, called thylakoids. Thylakoids contain chlorophyll and are stacked as structures called grana. The chloroplasts' main function is to capture light and integrate it into the process of photosynthesis.