What occurs during internal respiration?

During internal respiration, oxygen moves from the blood into the body cells. This process occurs at the cellular level when oxygen that has been transported through the circulatory system is delivered to tissues and organs where it is used for metabolic processes, particularly cellular respiration. In this context, oxygen is essential for the production of ATP, the energy currency of cells, as it participates in the biochemical reactions that convert glucose and other substrates into energy.

This stage distinguishes itself from external respiration, which involves the exchange of gases between the atmosphere and the lungs, specifically the inhalation of oxygen and the expulsion of carbon dioxide from the lungs into the atmosphere. Internal respiration is vital for maintaining cellular function and ultimately supports the overall energy needs of the organism.

The other options do not accurately describe internal respiration. For instance, the intake of oxygen from the atmosphere is part of external respiration, and the expulsion of carbon dioxide from the lungs is also linked to external respiration. The process of blood filtration in the kidneys pertains to the urinary system and does not relate to respiration at all. Thus, the correct choice highlights the crucial function of oxygen delivery to cells, a fundamental aspect of sustaining life.