# Cell --- A **cell** is the basic unit of [[biology|life]], and having cells is one of the five fundamental critea for being considered truly [[biology|alive]]. Even in vastly complex multicellular organism, each individual cell is considered alive on it's own. In the [[anatomy & physiology|biological organization]], the cellular level is one more complex than the chemical level, and the next most complex level is the [[tissue]], where many similar cells come together for a common function. The **cell theory** was revolutionized the field of biology, which first was suggested after we gained the [[light microscope|technology]] to see individual cell. >[! theory] Cell Theory > - **All organisms** are made of **one or more cells**. > - The cell is the **fundamental** living unit. > - All cells arise from **preexisting cells**. There are over 200 different types of cells in a human, and they all different in size, shape, subcellular components and function. ## Features of All Cells Cells can become highly specilized to cary out specific functions across all the organisims on earth. - All cells are dedicated to building, breaking down, storing and assembling the four basic [[macromolecules]]. - All cells follow the [[central dogma of biology]]: DNA is transcribed into RNA, RNA is translated into proteins. - All cells have [[ribosome|ribosomes]]. - All cells have a [[plasma membrane]]. - All cells have [[cytoplasm]]. In general the body of the cell is called the **soma** and anything that projects out from the soma is called a **process**. ## Prokaryotic vs Eukaryotic Cells All cells can be classified as either **prokaryotic** or **eukaryotic** as defined by the presence or absence of a [[nucleus]] and membrane-bound [[organelle|organelles]]. Organisms that lack a nucleus and organelles are called [[prokaryote|prokaryotes]], and those that do have a nucleus and organelles are called [[eukaryote|eukaryotes]]. All unicellular organisms are prokaryotes, and all multicellular organisms are eukaryotes, but there are some eukaryotic organisms that are unicellular. In addition to having a nucleus and organelles, eukaryotic cells are much more complex than prokaryotic cells. For example, humans have two copies each of 23 different [[chromosome|chromosomes]] with about 25k [[gene|genes]] total. Bacteria on the other hand have just 1 chromosome with 3-5k genes. In order to fit all this complexity, eukaryotic cells are much larger than prokaryotic cells. ![[eukaryote vs prokaryote.png]] ___