BIOLOGY · Stage 8 · Chapter 5: Respiration and the Respiratory System
Biology 5.10 Transport in the blood — Red Blood Cells, Plasma and White Blood Cells — Alhussan International Academy - Biology (Stages 7-9) Revision Notes & Topical Questions
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Biology 5.10 Transport in the blood — Red Blood Cells, Plasma and White Blood Cells — Alhussan International Academy — Biology (Stages 7–9) notes: Describe the components of blood and explain how each is adapted to its function.Humans — big, active multicellular animals whose cel…
- Other substances
- Need for blood
- Haemoglobin
- Adaptations
- Phagocytes
- Lymphocytes
Section 1 of 7Why blood is needed
- Humans
- big, active multicellular animals whose cells need lots of digested food and oxygen and produce many waste products to be removed.
- Blood
- it transports these substances around the body and protects against many diseases.
- Volume
- an adult has about 5 litres of blood, which is not a simple red liquid.
Section 2 of 7The parts of blood
| Component | Description | Function |
|---|---|---|
| Plasma | Yellow, straw-coloured liquid, about 55% of blood volume, mostly water | Carries blood cells, platelets, dissolved food, carbon dioxide, urea, hormones, antibodies and heat |
| Red blood cells | About 44% of blood volume, disc-shaped, no nucleus | Carry oxygen |
| White blood cells | About 1% of blood volume, large, with a nucleus | Defend against pathogens |
| Platelets | Tiny pieces of cells, less than 1% of blood volume | Help the blood to clot |
Section 3 of 7Plasma
- Transport
- plasma carries dissolved food and other substances to cells, and toxic carbon dioxide away from cells to the lungs.
- Urea
- this waste product is carried from the liver to the kidneys, where it is removed in urine.
- Other substances
- hormones from glands to target organs and heat from the muscles and liver to the skin.
- Need for blood
- diffusion alone is too slow over long distances, so blood supplies all the cells of large organisms.
| Substance | Carried in | From → to |
|---|---|---|
| Oxygen | Red blood cells | Lungs → body cells |
| Carbon dioxide | Plasma | Cells → lungs |
| Digested food | Plasma | Small intestine → cells |
| Urea | Plasma | Liver → kidneys |
Section 4 of 7Red blood cells
- Number
- you have more red blood cells than any other type of cell, and they are the smallest cells in the body.
- Haemoglobin
- the red molecule that carries oxygen from the alveoli of the lungs to body cells for aerobic respiration.
- It combines with oxygen in the lungs and releases it in the tissues where oxygen is low.
- Adaptations
- their disc shape and lack of a nucleus leave lots of room for haemoglobin.
- The biconcave shape gives a large surface area for rapid diffusion.
- Their small, flexible shape lets them squeeze through very small blood vessels one at a time.
- Life
- they live about 120 days and are made in the bone marrow.
- Anaemia
- too few red blood cells or too little iron for haemoglobin causes tiredness and pale skin.
Section 5 of 7White blood cells
- Structure
- all white blood cells are big and have a nucleus.
- Role
- they protect the body against pathogens, which are microorganisms that get into the body and cause infectious diseases.
- Phagocytes
- some flow round and digest microorganisms, which is phagocytosis.
- Lymphocytes
- others make antibodies, special proteins that stick to microorganisms so they cannot cause disease.
- Some lymphocytes become memory cells that give immunity.
Section 6 of 7Platelets
- Structure
- tiny pieces of cells, less than 1% of blood volume.
- Clotting
- they make blood clot if you cut yourself, so you do not bleed to death.
- They release chemicals that form a mesh of fibrin fibres, trapping blood cells.
- Clots form scabs, which cover damaged tissue, protect the wound and stop microorganisms getting in, so the body can repair itself.
- Protection
- platelets and white blood cells both help to protect against disease.
Section 7 of 7Functions of blood
- Transporting oxygen, digested food and other nutrients.
- Removing wastes such as carbon dioxide and urea.
- Defending against disease, clotting to seal wounds and spreading heat.
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