Answer:
During exercise the muscle cells use up more oxygen and produce increased amounts of carbon dioxide. Your lungs and heart have to work harder to supply the extra oxygen and remove the carbon dioxide. Your breathing rate increases and you breathe more deeply. Heart rate also increases in order to transport the oxygenated blood to the muscles.
Muscle cell respiration increases - more oxygen is used up and levels of carbon dioxide rise. The brain detects increasing levels of carbon dioxide - a signal is sent to the lungs to increase breathing. Breathing rate and the volume of air in each breath increase - This means that more gaseous exchange takes place. The brain also tells the heart to beat faster so that more blood is pumped to the lungs for gaseous exchange. More oxygenated blood is gets to the muscles and more carbon dioxide is removed.