User:Hickymayhem98

 Units of life beyond the cell

 A cell is the smallest unit of an organsim capable of independent existence.

 Tissues are groups of cells, usually of the same type specialised to perform certain functions e.g. muscle, nerve, epithelium, exylem and bone. Organs are made of tissues coordinated to perform certain functions, e.g. heart, kidney and root.

 Organ systems are groups of organs which combine to perform their functions, e.g. digestive system, nervous systems.

Organisms depending on their complexity, may each be hust one cell, e.g. a bacterium, or millions of cells with the variety of functional units as above, e.g. an ash tree or a human being.