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LYSOSOMAL OCCURRENCE
Prokaryotes do not have a well defined membrane system. organelles comparable to those of eukaryotic cells, including lysosomes, therefore appear to be absent. Prokaryotes are, however, known to secrete extra-cellular enzymes. Some hydrolases have been located outside the cell membrane. this has led to the suggestion that such prokaryotic cells are surrounded by an extra cytoplasmic lysosome. Digestion would thus take place outside the cell, at the site of the location of hydrolases.

Electron microscope and cytochemical studies have revealed the presence of membrane bound structures containing acid phosphotase in the protozoa. A number of lysosomal hydrolases have been found in the food vacuoles of many protozoa, including amoeba, paramecium, stentor and tetrahymena. The food vacuoles are equivalent to a type of secondary lysosomes. It has been demonstrated that the protozoa contain heterogeneous populations of lysosomes.

Slime moulds contain particles which appear to be lysosomes. Lysosomal localisation of acid phosphatase has been demonstrated in hyphae of many fungi. The fungi secrete a wide variety of extracellular enzymes, among which are acid hydrolases. Among the algae, acid phosphotase has been located in the lysosomes of euglena ans a few other species.

lysosomes have been reported in several groups of vertebrates and invertebrates. Almost every algae tissue investigated has yeilded evidence of presence of lysosomes.