During internal respiration, what happens to O2 in the blood?

During internal respiration, oxygen (O2) is transported from the blood into the cells of the body. This process occurs at the cellular level, where oxygen is exchanged for carbon dioxide (CO2) produced as a metabolic byproduct of cellular respiration. The cells utilize oxygen for energy production through aerobic metabolism. This is crucial for maintaining the energy needs of the body tissues.

The other choices do not accurately describe the process associated with internal respiration. Oxygen is not released into the air since that occurs during external respiration in the lungs. It also does not combine directly with carbon dioxide in a way that signifies internal respiration. Instead, CO2 is released by the cells into the blood for transport back to the lungs, where it will be expelled from the body during external respiration. Thus, the correct understanding of internal respiration focuses on the uptake of oxygen by the cells, highlighting the vital role of oxygen in cellular metabolism.