What gives blood its red color?

• A. Hemoglobin-iron complex
• B. Plasma proteins
• C. White blood cells
• D. Platelets

Answer: (A)

The red color of blood comes from hemoglobin, the iron-containing pigment in red blood cells. The iron in the heme groups binds oxygen to form oxyhemoglobin, which reflects red light and gives arterial blood its bright red hue. When oxygen is released, deoxyhemoglobin is a darker red, which makes venous blood appear deeper in color. Plasma proteins, white blood cells, and platelets don’t contribute the same pigmented color, so they don’t determine blood’s overall red appearance.