Macrophage. Comparison between a scanning election micrograph (SEM left) and transmission electron micrograph (TEM right) of a macrophage white blood cell. Macrophages are cells of the body's immune system. In the TEM image the cell's nucleus is light brown. Mitochondria (purple) in the cell's cytoplasm produce energy for the cell. Lysosomes (red) contain enzymes for digesting foreign particles. They are found in the tissues rather than in the circulating blood. Macrophages recognise foreign particles, including bacteria, pollen and dust, and phagocytose (engulf) and digest them. Magnification: x4000 when printed at 10 centimetres wide. For a series of comparisons between SEMs and TEMs see images C047/7006 to C047/7034.