Blood
What blood is made of
- Blood looks like a simple red liquid.
- It is really four parts working together.
- Three kinds of cell float in a liquid called plasma.
The four parts
| Part | Function |
|---|---|
| red blood cells | carry oxygen, using the pigment haemoglobin |
| white blood cells | defend the body against disease |
| platelets | help the blood to clot |
| plasma | liquid carrying cells, ions, nutrients, urea, hormones and carbon dioxide |
Practice
Red blood cells carry oxygen using:
Haemoglobin is the red pigment in red blood cells that carries oxygen.
Practice
Platelets help the blood to:
Platelets help the blood clot to seal wounds.
Practice
Plasma is a liquid that carries cells, nutrients, urea, hormones and carbon dioxide.
Plasma is the liquid part of blood that transports cells and dissolved substances.
Defence and clotting
- Phagocytes carry out phagocytosis — they surround and digest pathogens.
- Lymphocytes make antibodies, which stick to pathogens and destroy them.
- When you cut yourself, blood clots to seal the wound (stops blood loss and keeps pathogens out).
- (Supplement) In clotting, soluble fibrinogen turns into threads of fibrin that trap cells into a solid clot.
Practice
Match each white blood cell to what it does.
Phagocytes carry out phagocytosis; lymphocytes produce antibodies.
You've got it
Key idea
- blood = red cells (oxygen, haemoglobin) + white cells (defence) + platelets (clotting) + plasma (transport)
- phagocytes engulf pathogens; lymphocytes make antibodies
- clotting: fibrinogen → fibrin threads trap cells (Supplement)