food has been broken down into individual molecules by the time it reaches a cell, cells still need to deal with larger complexes of organic material. Intracellular digestion is carried out by organelles called lysosomes. There are several contexts in which cells need to carry out digestion. They include the recycling of cellular organelles and the breakdown of viruses and other cellular invaders. Single-celled organisms such as amoebas use lysosomes to digest their food as they have no process for extracellular digestion. Lysosomes are analogous to the human stomach. The pH within a lysosome is very acidic and the enzymes within work most effectively in this environment. The components of a lysosome have evolved specific conformations that make them resistant to break down by the enzymes within the lysosome.