CBSE · Class 12 · Biology · Human Health and DiseasesDefine immunity. Distinguish between innate and acquired immunity. Explain the two types of acquired immune responses (humoral and cell-mediated immunity) in detail.
Step-by-Step Solution
Definition of Immunity
Immunity is the overall ability of a host organism to resist and defend itself against disease-causing pathogenic microorganisms (such as bacteria, viruses, fungi, and parasites) through its immune system.
Difference Between Innate and Acquired Immunity
| Feature | Innate Immunity | Acquired Immunity |
|---|---|---|
| Nature | Non-specific type of defense mechanism. | Pathogen-specific defense mechanism. |
| Presence | Present from birth (congenital). | Developed during the organism's lifetime. |
| Memory | Does not exhibit immunological memory. | Characterized by immunological memory. |
| Components | Physical, physiological, cellular, and cytokine barriers. | Antibodies (B-lymphocytes) and T-lymphocytes. |
Types of Acquired Immune Responses
\nAcquired immunity is carried out by two special types of lymphocytes present in our blood:
1. Humoral Immune Response (Antibody-Mediated Immunity):
- Mediating Cells: Primary role played by B-lymphocytes (B-cells).
- Mechanism: When pathogens enter the bloodstream, B-cells produce an army of proteins called antibodies into body fluids (like blood plasma and lymph).
- Structure: Each antibody molecule consists of four peptide chains—two small light (L) chains and two longer heavy (H) chains ($H_2L_2$).
- Function: These antibodies bind specifically to antigens on pathogens to neutralize, agglutinate, or precipitate them for destruction.
2. Cell-Mediated Immune Response (CMI):
- Mediating Cells: Mediated primarily by T-lymphocytes (T-cells).
- Mechanism: T-cells do not secrete antibodies directly but assist B-cells to produce them and directly attack infected host cells, cancer cells, or foreign tissues.
- Key Role: CMI is responsible for the body's ability to differentiate between 'self' and 'non-self'. It is primarily responsible for graft rejection during organ transplantation. Immunosuppressive drugs are administered to patients to prevent this response.
💡 Study Guide: This question tests core syllabus concepts from Human Health and Diseases. For formulas, key summaries, and mock exam reference guides, read the full Human Health and Diseases Revision Notes.