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Subject - cell biology
Chloroplasts are green organelles found in photosynthetically active cells. A typical plant cell contains up to 50 chloroplasts. They are usually lenticular with a diameter of 2 to 8 µm. Their green color comes from chlorophyll. With an optical microscope, it is possible to differentiate denser areas in the chloroplasts, called grana, from more transparent areas known as stroma. Chloroplasts are surrounded by a shell made of two membranes. The outer membrane seems to originate from eukaryotes, whereas the inner membrane has typically prokaryotic characteristics (endosymbiotic theory). The membranes contain the leaf pigment chlorophyll. When irradiated, isolated chloroplasts produce oxygen and carbohydrates. They can thus also be photosynthetically active outside of the cell. Chloroplasts contain all of the enzymes necessary to carry out photosynthesis.
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