Question

Why the blood that flows from the lungs to the heart appears bright red rather than dark red?

• A. Oxygen makes it red.
• B. Carbon dioxide makes it red.
• C. Gastric juices produce the red color of blood.
• D. The lungs add a pigment to the blood as it flows through them.

Answer 1

The correct option is A Oxygen makes it red.

The blood that flows from the lungs to the heart is arterial blood. It is bright red in colour as it contains oxygen. Whereas blood that flows towards the lungs is venous blood. It is dark red in colour as it contains carbon dioxide. The red colour of blood comes from the haemoglobin. Hemoglobin binds to the oxygen. Carbon dioxide in deoxygenated blood makes it darker. This is due to the difference in colour between deoxyhemoglobin and oxyhemoglobin.

Thus, the correct answer is A.