Cell- 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 surrounding the cytoplasm 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- Any of a number of organized or specialized structures within a living cell.

Tissue- Any of the distinct types of material of which animals or plants are made, consisting of specialized cells and their products.

Organ- A part of an organism that is typically self-contained and has a specific vital function, such as the heart or liver in humans.

Unicellular- (of protozoans, certain algae and spores, etc.) consisting of a single cell.(of an evolutionary or developmental stage) characterized by the formation or presence of a single cell or cells.

Multicellular- (of an organism or part) having or consisting of many cells.

Autotroph- An organism that is able to form nutritional organic substances from simple inorganic substances such as carbon dioxide.

Heterotroph- An organism deriving its nutritional requirements from complex organic substances.

Prokaryotic- A prokaryote is a single-celled organism that lacks a membrane-bound nucleus (karyon), mitochondria, or any other membrane-bound organelles.

Eukaryotic- A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota.