Functional organisation refers to the organisational structure of living organisms used to divide them into different groups based on their functions. Based on this organisation living organisms can be classified into unicellular and multicellular organisms.
In unicellular organisms, all the life processes are carried out by single cell. In multicellular organisms, these cells combine to form tissues, organs, organ systems which finally form entire organism. In these organisms, the different types of cell or tissues work together to perform all the life processes.