Plastid

Plastids are a class of organelles found in plant and algal cells. The may differentiate into several forms depending upon which function they need to play in the cell. Undifferentiated plastids are called proplasts and may develop into any of the following plastids:

• Amyloplasts[?]: for starch storage
• Chloroplasts: for photosynthesis
• Etioplasts[?]: chloroplasts that have not been exposed to light
• Leucoplasts[?]: for monoterpenes synthesis
• Chromoplasts[?]: for pigment synthesis and storage

Plastids are thought to have originated from endosymbiotic cyanobacteria. Chloroplasts are presumably the ancestral type.