Which molecule is crucial for transporting oxygen in the blood?

Hemoglobin is the molecule crucial for transporting oxygen in the blood. It is a protein found in red blood cells that binds to oxygen molecules in the lungs and then carries them through the bloodstream to tissues and organs that need oxygen. Hemoglobin has a unique structure that allows it to efficiently pick up oxygen where it is abundant (such as in the lungs) and release it in areas where it is needed most (such as actively respiring tissues).

This protein's ability to undergo conformational changes when binding and releasing oxygen enhances its functionality. Without hemoglobin, the oxygen delivery system in the body would be severely compromised, affecting cellular respiration and overall metabolism, which is essential for life.

The other molecules listed do not play a direct role in oxygen transport. For instance, glucose is primarily an energy source for cells and does not have any function related to oxygen transport. Collagen serves structural purposes in connective tissues, while cholesterol is a vital component of cell membranes and a precursor for steroid hormones but does not participate in transporting oxygen in the bloodstream.