A '''Lysosomelysosome''' ({{IPAc-en|ˈ|l|aɪ|s|ə|ˌ|s|oʊ|m}}) is a [[membrane-bound organelle]] found in many<!--Human red blood cells and some other specialized cells don't have lysosomes--> animal [[Cell (biology)|cell]]s.<ref>By convention similar cells in plants are called [[vacuoles]], see {{Section link||Controversy in botany}}</ref> They are spherical [[Vesicle (biology and chemistry)|vesicles]] that contain [[Hydrolysis|hydrolytic]] [[enzyme]]s that can break down many kinds of [[biomolecule]]s. A lysosome has a specific composition, of both its [[membrane protein]]s, and its [[lumen (anatomy)|lumenal]] proteins. The lumen's pH (~4.5–5.0)<ref>{{cite journal | vauthors = Ohkuma S, Poole B | title = Fluorescence probe measurement of the intralysosomal pH in living cells and the perturbation of pH by various agents | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 75 | issue = 7 | pages = 3327–31 | date = July 1978 | pmid = 28524 | pmc = 392768 | doi=10.1073/pnas.75.7.3327| bibcode = 1978PNAS...75.3327O | doi-access = free }}</ref> is optimal for the enzymes involved in hydrolysis, analogous to the activity of the [[stomach]]. Besides degradation of polymers, the lysosome is involved in various cell processes, including secretion, [[plasma membrane]] repair, [[apoptosis]], [[cell signaling]], and [[energy metabolism]].<ref>{{cite journal | vauthors = Settembre C, Fraldi A, Medina DL, Ballabio A | title = Signals from the lysosome: a control centre for cellular clearance and energy metabolism | journal = Nature Reviews Molecular Cell Biology | volume = 14 | issue = 5 | pages = 283–96 | date = May 2013 | pmid = 23609508 | pmc = 4387238 | doi = 10.1038/nrm3565 }}</ref>
[[File:Lysosomes Digestion.svg|thumb|Lysosomes digest materials taken into the cell and recycle intracellular materials. Step one shows material entering a food vacuole through the plasma membrane, a process known as endocytosis. In step two a lysosome with an active hydrolytic enzyme comes into the picture as the food vacuole moves away from the plasma membrane. Step three consists of the lysosome fusing with the food vacuole and hydrolytic enzymes entering the food vacuole. In the final step, step four, hydrolytic enzymes digest the food particles.<ref>{{cite book | vauthors = Holtzclaw FW, etal | title = AP* Biology: to Accompany Biology | edition = 8th AP | publisher = Pearson Benjamin Cummings | date = 2008 }}</ref>]]
