Answer:
My guess would be H₂O/ water, since osmosis is a form of passive transport and I can't see the model the question references. Gases like O₂/ oxygen, CO₂/ carbon dioxide, and simple sugars like glucose can also pass through a cell membrane with passive transport though.
Respiration is a process of exchanging gas.
Enzymes are catalysts for reactions Their activity (how well they work) increases and decreases with temperature
