Organisms that are made up of many cells are called multicellular. There is agreat variety among multicellular organisms. All multicellular organisms depend on communication and cooperation among specialized cells. All of the members of the flora and the fauna are types ofmulticellular organisms that you can see with your own eyes without using a microscope or some types of lenses.
Biologists have identified levels of organization that make it easier to describe thecells within a multicellular organisms.
The levels of organization in order from the simplest from the complex: Cells, tissues, organs, organ system and organisms.
Cells are known as the basicunit of living things, tissues are similar groups of cells, organs are made up of many tissues groups, while the organ system is a group of organs working together for an specific function.
Then wewill see the process that multicellular organisms have in homeostasis how do they work together and which is their main function.
Homeostasis is the process in which organisms keep internalconditions, such as temperature and water content, fairly constant to survive. Homeostasis often involves internal feedback mechanisms that work in much the same way as a thermostat. 
CONTENTLevels of Organization of Multicellular Organisms
As we saw on the Introduction organisms have different levels of organization, next is an explanation of each one and an example or function.Multicellular organisms have the following 5 levels of organization ranging from simplest to most complex:
CELLS: LEVEL ONE
Cells are the collection of living matter enclosed by a barrier thatseparates the cell from its surroundings; basic unit of all forms of life.
TISSUES: LEVEL TWO
In any multicellular organism, cells rarely work alone. Cells that are similar in structure and...