Answer:
cell - basic unit of structure and function of all living things
tissue - a group of cells that work together to perform a common function
organ - a group of tissues that work together to perform a common function
organ system - group of organs that work together to perform a common function
Explanation:
What you have there is the biological level of organization. It is how living things are organized from the simplest to the most complex. Each level makes up another level.
As you can see in your exercise, the basic unit of life is the cell and cells make up tissues, while tissues make up organs and so forth. There are higher levels of organizations passed organ system.
Cell - tissue - organ - organ system - organism - population - community - ecosystem - biosphere
