The diffusion of water into or out of a cell is called solubility
solubility

osmosis
osmosis

selective transport
selective transport

endocytosis

i am going to guess that it is co2.

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.