Science
How Well Do You Really Know Blood?
It's never blue. It contains gold. And your body makes 2 million red blood cells per second.
It's never blue. It contains gold. And your body makes 2 million red blood cells per second.
The human body produces approximately 2 million new red blood cells every single second — manufactured in the bone marrow and each one living about 120 days before being recycled by the spleen. This quiz covers 50 questions on blood composition, types, transfusion history, and surprising facts.
You'll discover why blood is never actually blue, how Karl Landsteiner's Nobel Prize-winning discovery made surgery safe, the evolutionary advantage hidden in sickle cell disease, why George Washington's doctors may have killed him, and how your body contains trace amounts of gold.
No — blood is never blue. Deoxygenated blood is dark red, not blue. Veins appear blue through the skin because of how light interacts with tissue: blue wavelengths are reflected back to your eyes while red wavelengths are absorbed by the skin.
AB-negative is the rarest blood type, found in roughly 1% of the global population. However, rarity varies by ethnicity and region. The Rh-null blood type ('golden blood') is even rarer — fewer than 50 people worldwide have it.
In most countries, you can donate whole blood every 56 days (8 weeks). It takes your body about 4-6 weeks to fully replenish the red blood cells lost during donation, though plasma volume recovers within 24-48 hours.
Last updated: March 2026