Any of the chlorophyll-containing organelles (see plastid) that are found in large numbers in those plant and algal cells undergoing photosynthesis. Plant chloroplasts are typically lens-shaped and bounded by a double membrane. They contain membranous structures called thylakoids, which are piled up into stacks (see granum), surrounded by a gel-like matrix (stroma). The light-dependent reactions of photosynthesis occur on the thylakoid membranes while the light-independent reactions take place in the stroma. Chloroplasts contain multiple copies of a DNA molecule, typically 120–200 kbp in size and carrying genes required for chloroplast functions.