HeLa cell. Coloured scanning electron micrograph (SEM) of a cultured Hela cell (centre) on MDCK kidney cells (background). HeLa cells are a continuously cultured cell line of human cancer cells, which are immortal and so thrive in the laboratory. Numerous microvilli (string-like) can be seen, which cancer cells use to enable them to move around and spread (metastasise) from one area to another. MDCK cells are a strain of cultured, normal kidney epithelial cells.
Credit: SCIENCE PHOTO LIBRARY