Chloroplasts areorganelles, specialized compartments, inplantandalgalcells. The main role of chloroplasts is to conductphotosynthesis, where the photosynthetic pigmentchlorophyllcaptures theenergyfromsunlightand converts it and stores it in the energy-storage moleculesATPandNADPHwhile freeingoxygenfrom water. They then use the ATP and NADPH to make organic molecules fromcarbon dioxidein a process known as theCalvin cycle. Chloroplasts carry out a number of other functions, includingfatty acid synthesis, muchamino acidsynthesis, and theimmune responsein plants. The number of chloroplasts per cell varies from one, in unicellular algae, up to 100 in plants likeArabidopsisandwheat.

A chloroplast is a type of organelle known as aplastid, characterized byits two membranesand a high concentration ofchlorophyll. Other plastid types, such as theleucoplastand thechromoplast, contain little chlorophyll and do not carry out photosynthesis.

Chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionallypinch in twoto reproduce. Their behavior is strongly influenced by environmental factors like light color and intensity. Chloroplasts, likemitochondria, contain their ownDNA, which is thought to be inherited from their ancestor—a photosyntheticcyanobacteriumthat was engulfed by an earlyeukaryoticcell. Chloroplasts cannot be made by the plant cell and must be inherited by each daughter cell during cell division.

With one exception (theamoeboidPaulinellachromatophora), all chloroplasts can probably be traced back to a singleendosymbiotic event, when a cyanobacterium was engulfed by the eukaryote. Despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of manysecondaryand eventertiary endosymbiotic events.

The wordchloroplastis derived from the Greek wordschloros, which means green, andplastes, which means "the one who form".