Which sequence best represents the different levels of organization of multicellular organisms from least complex to most complex?

The sequence would be as follows:
cells - tissues - organs - organ system - organisms

Let's take a look at each of these levels:
Level 1: Cell
Cells are the smallest building unit of any structure within the organism. 
Level 2: Tissue
a tissue is a group of cells having the same function and structure that are bound together to perform a certain function in the body
Level 3: Organ
an organ is a group of tissues bound together to perform a certain function
Level 4: Organ system
groups of two or more organs that work together to serve a certain function in the body
Level 5: Organism
the entire living thing formed of different organ systems