DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY
Transmission electron micrograph of Rhizobium leguminosarum, the nitrogen-fixing bacteria, within the cell of a root nodule of the pea plant, Pisum sativum. The large structure in the picture is the cell nucleus. It is surrounded by Rhizobium bacteroids, enlarged forms of the bacteria that occur once the bacteria have entered the root of the plant. The bacteroids release an enzyme, nitrogenase, which converts atmospheric nitrogen into a usable organic form - something the plant cannot do for itself. Around each bacteroid is a transparent envelope provided by the plant tissue. Magnification: x1430 at 35mm size, x10, 000 at 8x10-inch size. Reference: MICROCOSMOS, figure 5.19, page 98.
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