A plastid in the cells of green plants and green algae that contains chlorophylls and carotenoid pigments and creates glucose through photosynthesis. In plants, chloroplasts are usually disk-shaped and can reorient themselves in the cell to vary their exposure to sunlight. Chloroplasts contain the saclike membranes known as thylakoids , which contain the chlorophyll and are arranged in stacklike structures known as grana. Besides conducting photosynthesis, plant chloroplasts store starch and are involved in amino acid synthesis. Like mitochondria, chloroplasts have their own DNA that is different from the DNA in the nucleus, and chloroplasts are therefore believed to have evolved from symbiont bacteria, their DNA being a remnant of their past existence as independent organisms.