In Which Part of the Chloroplast Does Each Stage Occur?
Photosynthesis takes place in the cell's chloroplast in two stages: the light stage and the dark stage. Each stage occurs in a different part of the chloroplast.
In the light stage of photosynthesis, the chloroplast absorbs the light of the sun. This sets off a series of chemical reactions, beginning by converting the sunlight to chemical energy. According to About.com, three types of energy are produced: ATP, NADPH and oxygen, all of which are used in the dark stage of photosynthesis. The light stage takes place in the grana's thylakoid stacks. Grana are visible under a microscope. Thylakoids contain chlorophyll, a green plant pigment that allows for the absorption of light. The thylakoids also contain important proteins that are needed in the photosynthesis process. These structures reside in the stroma, where the dark stage of photosynthesis takes place.
In the dark stage, carbon dioxide is converted to sugar or carbohydrates with the help of ATP and NADPH. The sugar in turn provides energy for the plant to perform its normal function. This process is also called the Calvin cycle, which in itself has three stages: carbon fixation, reduction and regeneration. The Calvin cycle takes place in the stroma, a dense fluid within the chloroplast that contains other structures such as the thylakoids and chloroplast DNA.