Cell -the basic unit of structure and all living things-ex) a red blood cell
tissue-a group of similar cells working together to perform a single specific function-ex)Nervous tissue
organ-a group of different tissues working together to preform single or multiple functions-ex) our eyes are made up of epithelial tissue, nervous tissue, muscle tissue, and connective tissue.
organ system-A group-of organs working together to perform a function-ex) the digestive system
complex: Organism-all the organ systems working together to make the most complex level of life-ex) human
hope this helps :))