The number of cells that make up an organism varies greatly depending on the size and complexity of the organism. Here's a general idea:

* Single-celled organisms: These are the simplest life forms, like bacteria and amoebas, and are composed of only one cell.

* Multicellular organisms: These include plants, animals, fungi, and algae, and consist of trillions of cells.

Here are some examples:

* Human: A human body is estimated to contain around 37.2 trillion cells.

* Fruit fly: A fruit fly has approximately 100,000 cells.

* Bacterium: A single bacterium is a single-celled organism.

It's important to note that the number of cells in an organism can change throughout its life cycle, depending on growth, development, and cell division.