Chloroplast

Definition

Chloroplast is a chlorophyll-containing organelle of phototrophic eukaryotes responsible for the generation of energy from radiation. A major feature of eukaryotic cells, absent from prokaryotic cells, is the presence of membrane-enclosed structures called organelles. These include mitochondria and chloroplasts, the latter only in photosynthetic cells. Like mitochondria, chloroplasts have a permeable outermost membrane, a much less permeable inner membrane, and an intermembrane space. The inner membrane surrounds the lumen of the chloroplast, called stroma. Chlorophyll and all other components needed for photosynthesis are located in a series of flattened membrane disks called thylakoids. The thylakoid membrane is highly impermeable to ions and other metabolites because its function is to establish the proton motive force necessary for ATP synthesis. In green algaeand plants, thylakoids are typically stacked into discrete structural units called grana. The chloroplast...