Levels of Organization

• Cells: generally considered to be the smallest living entities with all cells coming from pre-existing cells and all organisms being composed of one or more cells.

 
• Tissues: composed of similar cells that perform a common function(s). Examples are:
• epithelial tissue
• nervous tissue
• muscle tissue
• connective tissue (bone, blood, adipose, cartilage, and others)

 
• Organs: composed of tissues that together perform a common function (s). Examples are:
• stomach
• pancreas
• heart
• skin

 
• Organ-Systems: groups of organs that together perform a common function (s). Some organs, such as the pancreas, are members of more than one organ-system. Examples of organ-systems are:
• nervous system
• muscular system
• integumentary system
• digestive system
• respiratory system
• reproductive system
• lympathic system
• circulatory system
• endocrine system

 
• The Organism