Question

Cells with similar structures and functions work together to form

Answer 1

The basic unit of a living organism is a cell. Cells with the same function and structure comprises to makes up a tissue. A group of tissues combined with similar structure and forms makes up an organ. A group of organs with relative function makes up a system. Lastly, a group of system with relative functions make up an organism. To simplify:
Cell--> Tissue--> Organ--> System --> Living Organism.

Answer 2

Tissues. 
When large groups of tissues form up, they create tissues which the body will use to form organs.
Here is the cell levels in order for future reference:
Cells - Tissues - Organs - Organ Systems - Organisms