Tissue

From EvoWiki

A tissue is a group of specialized cells of the same type in a multicellular organism.

It is one of the five hierarchical levels of organization of multicellular organisms. Groups of tissues that function together to perform a set of specialized tasks within an organism are called organs.

Usually tissues contain partially undifferentiated stem cells to allow regeneration of lost cells. Other times, as in the case of some brain tissue, dead cells are never replaced. In still other cases, as with human blood cells, creation of new cells occurs in other tissues.