Respiration is the process in which food is oxidized to release energy. Complex organic compounds are converted into simpler ones, e.g glucose into CO2 water and energy released.
Breathe in, breathe out. The oxygen that got in lungs is absorbed into blood and carbon dioxide diffuses out of blood into lungs. That's gaseous exchange.
Gaseous exchange is the diffusion of gases from a region of higher concentration to a region of lower one. It is used for the exchange of oxygen and CO2 between organism and its environment.
While using that oxygen to breakdown food and generate energy particles is respiration.
