What is in blood?
Red cells, platelets and white cells.
A scratch on your knee
You scrape your knee. It bleeds, then the bleeding stops by itself. A day later a small cut looks red and swollen.
Is blood just red liquid?
What this lesson covers
The idea
Red blood cells contain haemoglobin, an iron-rich protein that makes blood red, live about 4 months and are replaced regularly; platelets help blood clot at an injury; white blood cells collect at infected areas, causing inflammation and pus.
A scratch on your knee
You scrape your knee. It bleeds, then the bleeding stops by itself. A day later a small cut looks red and swollen.
Is blood just red liquid?
- No. It has different cells with different jobs
- Yes, only a red liquid
- It is made of only one kind of cell
Cut and infection
Watch the blood flow. Then make a cut and let germs infect the skin.
Components of blood
Red blood cells (RBCs) contain haemoglobin, an iron-rich protein that makes blood red. RBCs live for about 4 months and are replaced regularly. Platelets help in blood clotting at the site of injury. White blood cells (WBCs) collect at infected areas, causing pus formation and inflammation (redness and swelling).
During exercise, muscles need more oxygen, so breathing becomes faster and blood flow increases. The face may look red.
Notes
RBCs: haemoglobin, red colour, live about 4 months. Platelets: clotting. WBCs: collect at infected areas (pus, inflammation).
Check yourself
What makes blood red?
Red blood cells live for about 4 months. About how many times are they replaced in one year (12 months)?
Answer: 3 times
12 ÷ 4 = 3 times a year.
A small wound becomes red, swollen and has pus. What has gathered there?
- White blood cells. White cells fight infection.
- Platelets. Platelets help clotting.
- Haemoglobin, an iron-rich protein in red blood cells — correct. Yes.
- Red blood cells only. RBCs carry haemoglobin; WBCs fight infection.
- White blood cells — correct. Yes. WBCs collect at infected areas.
- Platelets only. Platelets help clotting.