Fat cell. Coloured scanning electron micrograph (SEM) of a brown fat cell (adipocyte) surrounded by capillaries. This type of fat cell is mainly found in infants. Its function is to produce heat (thermogenesis). Brown adipocytes have an irregular shape. The fat is stored as many lipid droplets suspended in the cell's cytoplasm. Also in the cytoplasm are the mitochondria that generate heat from the fat. Magnification: x2850 when printed at 10 centimetres wide.