Lysosomes were first discovered by Christian de Duve. Unlike other organelles which were detected by microscbpe, these were first discovered biochemically. Later, electron microscope and biochemical methods shed more light on their nature and their participationin cell activities.These particles were called lysosomes (lysis= dissolution, soma = body) due to their hydrolytic activity. A lysosome is a single membrane bound vesicle that either buds off from the releasing face of Golgi apparatus or arises directly from ER. The Lysosomes are rich in hydrolases. specially acid phosphahse, of about 50 different types which digest all the - significant groups of macro molecules. These enzymes are active at pH 5 within the organelle. The enzymes, which escapes from lysosomes, become slow in their action because the pH of cytoplasm is 7.0. This large pH difference is a device to protect the cell from digestion.