Cells are the basic building blocks of living organisms. Although they are the smallest units of any living organism, cells are composed of different parts, each having a different function. Different cells also vary in structure and function.
There are two main categories of cells: prokaryotic and eukaryotic cells. Prokaryotic cells are cells whose DNA is not separated from the cytoplasm. All known prokaryotes are single cells. Eukaryotic cells are cells whose DNA is separated from the cytoplasm. Some eukaryotes are single-celled entities, while others, such as plants and humans, are multicellular organisms.
All cells, whether eukaryotic or prokaryotic, share some features. These include DNA, plasma membrane, cytoplasm and ribosomes. DNA is responsible for the genetic information about an organism. It is located in the nonmembrane-bound nucleoid region of prokaryotic cells, while in eukaryotic cells, it is located in the membrane-bound nucleus.
The plasma membrane, also referred to as the cell membrane, separates the internal and the external environment of a cell. It also functions as a selective barrier when it comes to the transport of materials in and out of the cell. The cytoplasm is the water-based internal environment of the cell. Ribosomes are responsible for creating proteins by processing the cell's genetic instructions.