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Acquired Immunity: Humoral, Cell-Mediated, Active and Passive

Acquired immunity is pathogen-specific immunity developed after exposure to an antigen, involving lymphocytes, antibodies, memory cells, and primary or secondary immune responses.

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Student-friendly explanation

Acquired immunity is specific and has memory. B-lymphocytes produce antibodies, giving humoral immunity through body fluids. T-lymphocytes support cell-mediated immunity, which is important against infected cells and in graft rejection. The primary response after first antigen exposure is slower and weaker, while the secondary response is faster and stronger because memory cells are already present. Active immunity develops when the body produces its own antibodies after infection or vaccination. Passive immunity is received ready-made, such as maternal antibodies or injected antibodies, and gives quick but usually short-term protection.

How to write this in exams

  1. 1

    Start with the exact idea

    Acquired immunity is pathogen-specific immunity developed after exposure to an antigen, involving lymphocytes, antibodies, memory cells, and primary or secondary immune responses.

  2. 2

    Then show how to use it

    Define acquired immunity. Mention antigen specificity and memory. Explain B-cell antibody response as humoral immunity. Explain T-cell response as cell-mediated immunity. Compare primary and secondary responses. Distinguish active and passive immunity using source, speed, duration, and memory.

  3. 3

    Add one concrete example

    A child receiving a vaccine develops active immunity because the child's immune system forms antibodies and memory cells. A newborn receiving maternal antibodies through colostrum receives passive immunity.

  4. 4

    Avoid this incomplete answer

    Calling vaccination passive immunity is wrong because vaccination stimulates the body to produce its own immune response and memory cells.

Definition

Acquired immunity is pathogen-specific immunity developed after exposure to an antigen, involving lymphocytes, antibodies, memory cells, and primary or secondary immune responses.

Example

A child receiving a vaccine develops active immunity because the child's immune system forms antibodies and memory cells. A newborn receiving maternal antibodies through colostrum receives passive immunity.

Rule to remember

Immune response rule: first exposure forms primary response and memory cells; later exposure triggers faster secondary response. Active immunity makes antibodies; passive immunity receives antibodies.

Memory hook

Active means your body acts; passive means protection is passed to you.

Examples and method

Worked example

Question: A person receives antivenom after a snake bite. Identify the immunity. Answer: It is passive immunity because ready-made antibodies are supplied for immediate protection.

Method to apply

Define acquired immunity. Mention antigen specificity and memory. Explain B-cell antibody response as humoral immunity. Explain T-cell response as cell-mediated immunity. Compare primary and secondary responses. Distinguish active and passive immunity using source, speed, duration, and memory.

Diagram support

A graph of antibody concentration versus time is important. Labels should include first exposure, primary response, memory cells, second exposure, secondary response, antibody level, and time.

How CBSE asks it

Asked through graph interpretation, active-passive comparison, humoral versus cell-mediated short answers, and assertion-reason questions on memory cells.

Avoid common mistakes

Common confusion

Students often write that passive immunity creates long-term memory. Passive immunity gives ready-made antibodies but does not usually produce lasting immune memory.

Common wrong answer

Calling vaccination passive immunity is wrong because vaccination stimulates the body to produce its own immune response and memory cells.

Exam tip

For active versus passive immunity, compare source of antibodies, speed of response, duration, and memory-cell formation.

Quick check

Why is the secondary immune response faster than the primary response?

The secondary immune response is faster because memory B-cells and T-cells formed after the first exposure recognise the antigen quickly and produce a stronger response.

Answer writing and exam use

1-mark answer

Define acquired immunity, mention specificity and memory, explain B-cell and T-cell roles, then compare active-passive or primary-secondary response as required by the question.

2-mark answer

Define acquired immunity, mention specificity and memory, explain B-cell and T-cell roles, then compare active-passive or primary-secondary response as required by the question.

3-mark answer

Define acquired immunity, mention specificity and memory, explain B-cell and T-cell roles, then compare active-passive or primary-secondary response as required by the question.
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