Exhalation in Humans and Animals: The Role of Carbon Dioxide

Introduction:
Exhalation is the process by which air is expelled from the lungs during breathing. It is an important physiological process that helps to remove waste gases from the body. In humans and most animals, the primary waste gas that is exhaled is carbon dioxide (CO2).

Carbon Dioxide:
Carbon dioxide is a byproduct of cellular respiration, which is the process by which cells convert oxygen and nutrients into energy. During this process, cells break down glucose molecules and release carbon dioxide as a waste product. The carbon dioxide then diffuses out of the cells and into the bloodstream.

Transport of Carbon Dioxide:
Once in the bloodstream, carbon dioxide is transported to the lungs. It binds to hemoglobin molecules in red blood cells and is carried back to the lungs. In the lungs, carbon dioxide is exchanged for oxygen through a process called gas exchange. Oxygen is taken up by the red blood cells, while carbon dioxide is released from the blood and into the alveoli, tiny air sacs in the lungs.

Exhalation of Carbon Dioxide:
During exhalation, the diaphragm and intercostal muscles contract, causing the volume of the thoracic cavity to decrease. This increase in pressure forces air out of the lungs, along with the carbon dioxide that has accumulated in the alveoli. The exhaled air, containing carbon dioxide, is then expelled through the nose or mouth.

Other Gases Exhaled:
While carbon dioxide is the primary waste gas exhaled by humans and animals, it is not the only gas that is exhaled. The exhaled air also contains small amounts of other gases, such as oxygen and nitrogen. However, the concentration of these gases is much lower compared to carbon dioxide.

Conclusion:
In conclusion, the correct answer to the question is option 'C' - carbon dioxide. During exhalation, humans and animals primarily exhale carbon dioxide, which is a waste product of cellular respiration. While small amounts of other gases, such as oxygen and nitrogen, are also exhaled, carbon dioxide is the main waste gas expelled from the body.