Carbon dioxide crosses the plasma membrane by simple diffusion. the rate at which carbon dioxide enters the cell is determined by the

google my dude. if it doesn't show up ask me.

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.