False-colour transmission electron micrograph (TEM) of a group of human lymphocytes, the smallest of the white blood cells. The central nucleus (brown) is slightly indented & the chromatin (genetic material - DNA) is moderately condensed; the darker coloured chromatin is seen towards the nuclear wall. The cytoplasm (yellow) is sparse, but contains a few mitochondria (small green, cigar-shaped bodies - the site of energy production & storage within the cell). The outer plasma membranes support a few microvilli (projections). Lymphocytes undergo transformations when activated in their role in immunological defence. Magnification x1650 at 35mm size.