Coloured scanning electron micrograph (SEM) of Rhizobium leguminosarum nitrogen fixing bacteria (RED) in ruptured root nodule cells of a plant. These bacteria take nitrogen gas from the air and bind it up in compounds which the plant can use for its nutrition. They do this using an iron-containing protein called leghaemoglobin, similar to the haemoglobin found in red blood cells. The plant benefits from this symbiosis as it means they can grow in soils with a low nitrogen content, soils which are inaccessible to other plants. Magnification: x6,980 when printed at 10 centimetres wide.