In your cells, cellular respiration happens in a special organelle called the mitochondrion. But as mentioned, prokaryotic organisms don't have organelles. Rather than taking place in the mitochondrion, cellular respiration happens either in the cytoplasm or across the plasma membrane of the cell.
Answer:
In animals, oxygen combines with food in the cells to produce energy for daily activity and then gives off carbon. The carbon combines with oxygen to form carbon dioxide (CO2) and is released back into the atmosphere as a waste product when animals breathe and exhale.