Digestion begins in the mouth, which chews food into smaller pieces for easier digestion. Proteins were found to yield amino acids after enzymatic digestion or acid hydrolysis. The intestine completes the process of digestion and nutrient absorption. Unexplained weight loss may occur from a lack of pancreatic enzymes hindering digestion. Lysosomes are organelles that contain hydrolytic enzymes that are used for intracellular digestion. Absence of enteropeptidase results in intestinal digestion impairment. This mucus causes problems with breathing and with the digestion and absorption of nutrients. The stomach and liver have to function normally in order for proper digestion. The small intestine is where most chemical digestion takes place. Most of the digestion of food takes place in the small intestine. Pancreatic sPLA2 serve for the initial digestion of phospholipid compounds in dietary fat. Carboxypeptidase cleaves peptide linkages during digestion of proteins. Sewage can be converted to biogas using anaerobic digestion. The liver has many functions some of which are important to digestion. Some systems incorporate both anaerobic digestion and composting.