Metabolism

• All chemical reactions that occur in an organism; most occur in cells and use intracellular enzymes, e.g. phagocytic white blood cells use them to digest bacteria that they engulf; a way that enzymes are used as a defense mechanism
• Sometimes enzymes are secreted from cells to catalyze reactions outside called extracellular enzymes e.g. in animal digestion, like mammals, within internal digestive systems
• Organisms such as fungi feed as saprophytes - release digestive enzymes onto the large/insoluble food molecules and absorb the smaller/soluble products