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6.2.6Unit 6: Practical Skills in Biology II

Developing Immunity — IAL Edexcel Linear Revision Notes & Topical Questions

5 min read 5 parts Lesson 12 of 48 Unit quiz

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Part 1 of 5Primary Response

6.2.6 Developing Immunity

The first meeting with an antigen is slow because few suitable lymphocytes are present.

1
On first exposure to an antigen, few lymphocytes have the right receptor.
2
Activated T and B cells must divide and differentiate, which takes several days.
3
Plasma cells then start to make antibodies, so the person usually has symptoms.
4
Memory cells are formed during this response and remain in the blood.
5
The person is now immune to that pathogen.

Part 2 of 5Secondary Response

Faster
  • Memory cells are more numerous than the original matching lymphocytes, so they detect and respond to the antigen quickly.
Stronger
  • More plasma cells form, so antibodies are made faster and in larger quantity.
Outcome
  • The pathogen is often removed before symptoms develop.
Memory
  • This long-term protection depends on memory cells staying in the body.
Antibody level
  • The antibody concentration in the blood rises much higher and more quickly in the secondary response than in the primary one.

Part 3 of 5Active and Passive Immunity

In passive immunity, no memory cells are produced, so protection is short lived.

Active and Passive Immunity
Active natural
  • Gained by catching the disease, when the person makes their own antibodies and memory cells.
Active artificial
  • Gained through vaccination, which triggers the immune response without causing the disease.
Passive natural
  • Antibodies pass from mother to foetus across the placenta or to a baby in breast milk.
Passive artificial
  • Antibodies are injected, as in an antitoxin, and give quick but temporary protection.
FeatureActivePassive
Antibodies made byThe personAnother source
Memory cellsYesNo
ProtectionLong termShort term

Part 4 of 5Vaccination

Vaccines are the main application of the primary and secondary response.

Content
  • Vaccines contain antigens, in the form of weakened or dead pathogens, antigens alone, or genetic material coding for them.
Effect
  • The primary response creates memory cells, so a later infection triggers a rapid secondary response.
Delivery
  • Vaccines are given by injection or by mouth.
Antigenic variation
  • Mutations change pathogen antigens, so some vaccines must be updated regularly.
Herd effect
  • When many people are vaccinated, fewer people can pass on the pathogen, which also protects those who are not immune.

Part 5 of 5Exam Checklist & Tips

6.2.6 – Key Points for the Exam

  • Primary response The slower immune response when an antigen is first encountered.
  • Secondary response The faster, larger response when the same antigen is met again.
  • Vaccine A preparation containing antigens that is given to produce immunity.
  • Passive immunity Protection from antibodies obtained from another source.
  • Memory cell A long-lived lymphocyte that remains after an infection and enables a faster secondary response.

Common Mistakes

  • Writing that vaccines contain antibodies; most contain antigens.
  • Saying passive immunity makes memory cells, when it does not.
  • Forgetting that the secondary response is faster because memory cells are already present.
  • Describing the primary response as having no symptoms; symptoms usually occur while it builds.

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