What substance in red blood cells carries oxygen and gives blood its red color?

Hemoglobin is the substance in red blood cells that is primarily responsible for carrying oxygen throughout the body. It is a specialized protein that can bind to oxygen molecules in the lungs and release them in the tissues where they are needed for cellular respiration. The high concentration of hemoglobin in red blood cells not only allows for efficient oxygen transport but also gives blood its characteristic red color.

Myoglobin, while similar to hemoglobin, is found in muscle tissues and serves the purpose of storing oxygen for short bursts of high-demand activity, but it is not present in red blood cells and does not contribute to blood color. Albumin is a protein in plasma that helps to maintain blood volume and pressure but is not involved in oxygen transport. Cholesterol is a type of fat present in the blood, but it does not have a role in oxygen transportation and does not contribute to the color of the blood.

Thus, hemoglobin is the correct answer, highlighting its essential function in the circulatory system, both in terms of oxygen transport and the distinctive coloring of the blood.