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A membrane-bound sac (organelle) found in animal cells and in single-celled eukaryotes. It contains hydrolytic enzymes that degrade aged or defective cell components or material taken in by the cell from its environment, such as food particles or bacteria. The lysosomal enzymes are adapted to work in the acid conditions of the lysosome interior, which has a pH of about 4.8. This means that should the enzymes escape from the lysosome they are inactivated by the neutral pH of the cell cytosol, and so will not attack the cell contents. Primary lysosomes do not contain debris, but fuse with vesicles or organelles containing material for disposal, forming a secondary lysosome in which digestion takes place. In plant cells, the vacuole contains hydrolytic enzymes equivalent to those in the lysosome and can degrade materials in a manner similar to a lysosome.

Subjects: Biological Sciences.

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