EVERYDAY SCIENCE

Detailed explanation-1: -Blood does change color somewhat as oxygen is absorbed and replenished. But it doesn’t change from red to blue. It changes from red to dark red. It is true that veins, which are sometimes visible through the skin, may look bluish.

Detailed explanation-2: -Most of the time, nearly all red blood cells in the arteries carry a full supply of oxygen. These blood cells are bright red and the skin is pinkish or red. Blood that has lost its oxygen is dark bluish-red. People whose blood is low in oxygen tend to have a bluish color to their skin.

Detailed explanation-3: -Blue blood does flow through the veins of a few living things, including horseshoe crabs and octopuses. (The blood in those animals uses a copper-containing protein called hemocyanin to carry oxygen, which explains the blue color.)

Detailed explanation-4: -Blood that has been oxygenated (mostly flowing through the arteries) is bright red and blood that has lost its oxygen (mostly flowing through the veins) is dark red. Anyone who has donated blood or had their blood drawn by a nurse can attest that deoxygenated blood is dark red and not blue.

Detailed explanation-5: -Over 95% of hemoglobin in arterial blood is in the oxy-Hb form; the level in venous blood averages between 50-80%. The colors of arterial and venous blood are different. Oxygenated (arterial) blood is bright red, while dexoygenated (venous) blood is dark reddish-purple.