The small ball of dust and ice that is located at the center of a comet is called the

there are so many examples for that in different areas, like biology experiment carried out in our lab recently.

here's one link:

trachea, alveoli, lung capillaries, arteries

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.