Which is the best definition of rate-determining step? an elementary step that often occurs in the reaction mechanism
the elementary step that limits how fast the overall reaction proceeds
an elementary step that is used to derive a rate law
the unimolecular step in a reaction mechanism

You exhale co2 which is produced during cellular respiration.  co2 combines with the water in your blood's plasma to make up one half of the body's most important buffer pair, carbonic acid.  the more physical activity you engage in, the more co2 your body is producing.  you can see this by putting some of the cabbage indicator in a glass and then blowing bubbles into it through a straw.  can you see a change in the color of the indicator?