Question

Blood is red in colour. Oxygen-rich blood is bright red as it leaves the heart. When it returns to veins without oxygen, it turns blue. Does it mean that the haemoglobin is turned off in the absence of oxygen?

• A. Yes, haemoglobin is turned off in the absence of oxygen.
• B. Haemoglobin gets activated in the presence of carbon dioxide.
• C. Because of oxygen, haemoglobin looks in red colour. Otherwise it is blue in colour.
• D. Haemoglobin is never turned off, blood is always red.

Answer 1

The correct option is D

Haemoglobin is never turned off, blood is always red.

Blood is always red. Oxygen-rich blood is bright red as it leaves the heart. When it returns in veins with less oxygen, it's still red, but it's a deeper, darker red, so veins look blue. It is all about light. Veins appear blue because blue light is reflected back to our eyes because of deoxyhaemoglobin.