Cells

A cell is the structural and functional unit of all known living things. It is the simplest unit of an organism that is classified as living, and is sometimes called the "building block of life."

Types of cells

• Eukaryotic cells
  

Eukaryotic cells are usually found in multicellular organisms. The major difference between prokaryotes and eukaryotes is that eukaryotic cells contain membrane-bound compartments in which specific metabolic activities take place. Most important among these is the presence of a cell nucleus, a membrane-delineated compartment that houses the eukaryotic cell's DNA. It is this nucleus that gives the eukaryote its name, which means "true nucleus".

• Prokaryotic cells
  

Prokaryotes are distinguished from eukaryotes on the basis of nuclear organization, specifically their lack of a nuclear membrane. Prokaryotes also lack most of the intracellular organelles and structures that are characteristic of eukaryotic cells. Most functions of organelles, such as mitochondria, chloroplasts, and the Golgi apparatus, are taken over by the prokaryotic plasma membrane. Prokaryotic cells have three architectural regions: appendages called flagella and pili — proteins tha are attached to the cell surface; a cell envelope ,consisting of a capsule, a cell wall , and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions.

Taken from: http://en.wikipedia.org/wiki/Cell_%28biology%29