Which of the following is not part of the cell theory? A. All organisms are composed of one or more cells.

B. Cells are the basic unit of life for all living things.

C. All cells come from pre-existing cells.

D. All cells contain a nucleus.

the answer is D. All cells contain a nucleus

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.