The organisation of a multicellular organism is as follows- Cells-Tissues-Organ-Organ System-Organism.

Cell are the smallest unit of life that carry out all the functions of living beings. Group of cells of the same type form tissue that perform specific function in the organism. Several types of tissue form organ which carry out particular functions. Several organs together form organ system which work together to perform a function. All the organ systems together form a multicellular organism.