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Vaccination, memory cells and clotting

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Vaccines prepare the immune system in advance. Platelets seal wounds to stop blood loss and keep pathogens out.

How vaccination works

A vaccine contains dead or weakened pathogens, or their antigens.
Lymphocytes respond by making antibodies, and some become memory cells.
Memory cells stay in the blood for a long time.

The secondary response

If the real pathogen enters later, memory cells make antibodies sooner, faster and in greater quantity.
The pathogen is destroyed before it can cause illness.

Blood clotting

When a blood vessel is damaged, platelets help form a clot.
A chain of reactions turns a soluble protein (fibrinogen) into insoluble fibrin threads. These form a mesh that traps red blood cells.
The clot prevents blood loss and stops microorganisms entering the wound. It dries into a scab.
Worked example

Explain why a vaccinated person does not become ill when infected by the pathogen.

  1. The vaccine caused memory cells to form.
  2. On infection, memory cells make antibodies sooner, faster and in greater amounts.
  3. The pathogen is destroyed before it can cause symptoms.

Answer: Memory cells give a rapid, large antibody response that destroys the pathogen before illness develops.

Key idea

Vaccination makes lymphocytes form memory cells. On a later infection, antibodies are made sooner, faster and in greater quantity. Platelets start clotting: fibrin threads trap red cells, preventing blood loss and the entry of microorganisms.

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