Book 1, Question 12
Why Is Blood Red? The Iron and Oxygen Secret!
What makes blood so bright red? Blood travels around your body delivering oxygen, and inside red blood cells a protein called hemoglobin holds iron that grabs onto oxygen. When iron and oxygen team up, the result looks red. The page also clears up a common mix-up: veins look blue through your skin, but the blood inside is always red. Try looking at the veins on your wrist with a grown-up and think about why they look blue.
From the book
Page from A Million Whys Book 1
More fun facts
- Blood is made of blood cells floating in plasma. Plasma is a yellowish liquid that carries nutrients, proteins, hormones, and waste.
- Red blood cells are shaped like flattened disks that are slightly pushed in on each side.
- Blood turns its brightest red when hemoglobin picks up oxygen in your lungs.
- As blood travels around your body, hemoglobin lets go of oxygen so each body part can keep working.
- Red blood cells are made inside your bones, in a soft part called the bone marrow.
- White blood cells are part of your immune system. You have far fewer of them than red blood cells, but your body can make more when it is fighting an infection.
- The science name for red blood cells is erythrocytes.
Sources: KidsHealth (Nemours)
Questions kids ask
Where are red blood cells made?
Inside your bones, in the soft bone marrow.
When is blood the brightest red?
When hemoglobin in your red blood cells has just picked up oxygen in your lungs.