Cells-the smallest structural and functional unit of an organism, typically microscopic and consisting of cytoplasm and a nucleus enclosed in a membrane. Microscopic organisms typically consist of a single cell, which is either eukaryotic or prokaryotic.

Cell Membrane-the semipermeable membrane enclosing thecytoplasm of a cell.

Cell Wall-a rigid layer of polysaccharides lying outside the plasma membrane of the cells of plants, fungi, and bacteria. In the algae and higher plants, it consists mainly of cellulose.

Organelle-Cell Biology. a specialized part of a cell havingsome specific function; a cell organ.

Tissue-Biology. an aggregate of similar cells and cellproducts forming a definite kind of structuralmaterial with a specific function, in a multicellularorganism.

Organ-Biology. a grouping of tissues into a distinctstructure, as a heart or kidney in animals or aleaf or stamen in plants, that performs aspecialized task.

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