In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. There is a "main" tissue, parenchyma, and "sporadic" tissues, stroma. The main tissue is the one that is unique for the specific organ. For example, the main tissue in the heart is the myocardium, while sporadic tissues include the nerves, blood and connective tissues. Functionally related organs often cooperate to form whole organ systems. Organs exist in all higher biological organisms, in particular they are not restricted to animals, but can also be identified in plants. In single-cell organisms like bacteria, the functional analogues of organs are called organelles. A hollow organ is a visceral organ that is a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity, like the heart or urinary bladder. Wikipedia [ - ]

In biology, an organ is a collection of tissues joined in a structural unit to serve a common... [ + ]