The Blood

Section 1 of 13Components of blood

• Four components
  • blood consists of red blood cells, white blood cells, platelets and plasma.

Section 2 of 13Structure of each component

Component	Structure
Red blood cells	Biconcave discs with no nucleus, containing a large amount of the protein haemoglobin
White blood cells	Large cells with a large nucleus, with different types (phagocytes and lymphocytes) having slightly different structures
Platelets	Small fragments of cells with no nucleus
Plasma	Pale yellow (straw-coloured) liquid made mostly of water

Section 3 of 13Identifying red blood cells

Shape

• A biconcave disc providing a large surface area to volume ratio for efficient oxygen diffusion.

Nucleus

• Absent in mature red blood cells to maximize available space for hemoglobin.

Section 4 of 13Identifying white blood cells

Shape

• Shape usually round.

Nucleus

• Nucleus present, and large.

Size

• Size they are the largest blood cells.

Section 5 of 13Types of white blood cell

Types of white blood cell

Phagocytes

• Phagocytes have a multi-lobed nucleus and granular cytoplasm.

Lymphocytes

• Lymphocytes have a large round nucleus that fills nearly the whole cell and clear cytoplasm with no granules.

Section 6 of 13Platelets

Size

• Size much smaller than either type of cell.

Nature

• Nature fragments of cells, not whole cells.

Section 7 of 13Plasma carries

Blood cells

• Blood cells the red cells, white cells and platelets.

Nutrients

• Nutrients such as glucose and amino acids.

Waste

• Waste such as urea and carbon dioxide.

Other substances

• Other substances ions and hormones, and heat.

Section 8 of 13Where blood cells are made

• Bone marrow
  • red blood cells, phagocytes, lymphocytes and platelets are made in it.

Section 9 of 13More from the specification

More from the specification

Muscle

• Tissue that contracts to cause movement.

Ventricle

• A heart chamber that pumps blood out.

Circulatory system

• The organ system that transports blood.

Deoxygenated blood

• Blood with little oxygen.

Coronary artery

• An artery that supplies the heart muscle.

Oxygenated blood

• Blood carrying a lot of oxygen.

Pulmonary artery

• The artery that takes blood from the heart to the lungs.

Artery

• A vessel that carries blood away from the heart at high pressure.

Pressure

• Force acting on a unit area.

Valve

• A flap that stops blood flowing backwards.

Activity

• The rate at which the nuclei in a sample decay.

Capillary

• Very small blood vessel with a wall one cell thick.

Oxygen

• Gas that relights a glowing splint.

Section 10 of 13More on this topic

Component	Structure	Function
Red blood cells	Biconcave discs with no nucleus, full of haemoglobin	Carry oxygen
White blood cells	Large cells with a nucleus	Defend against pathogens
Platelets	Small cell fragments with no nucleus	Take part in clotting
Plasma	Pale yellow liquid, mostly water	Carries cells and dissolved substances

Section 11 of 13More from the specification

• Venous valves preventing retrograde flow
  • semilunar pocket valves along systemic veins assist muscular pumps returning portal blood toward the metabolic liver.

Section 12 of 13Key terms

Term	Meaning
Plasma	The pale yellow liquid part of blood.
Red blood cell	A biconcave cell with haemoglobin that carries oxygen.
White blood cell	A cell with a nucleus that defends against pathogens.
Platelet	A cell fragment involved in clotting.
Haemoglobin	The protein in red blood cells that binds oxygen.
Phagocyte	A white blood cell that engulfs pathogens.
Lymphocyte	A white blood cell that makes antibodies.

Section 13 of 13Exam technique

1

Saying red blood cells have a nucleus — they have none.

2

Calling platelets complete cells — they are cell fragments.

3

Saying plasma is made of cells — it is mostly water.

4

Mixing up phagocytes and lymphocytes — phagocytes engulf and lymphocytes make antibodies.