NCERT · Class 12 · Biology · Human Health and DiseasesDefine Immunity. Differentiate between Innate Immunity and Acquired Immunity. Detail the two types of acquired immune responses (Humoral and Cell-Mediated Immunity) and explain the structural components of an Antibody molecule.
Step-by-Step Solution
Immunity Definition\nImmunity refers to the overall ability of an organism (host) to resist and defend itself against disease-causing pathogenic microorganisms, mediated by its immune system.
Differences between Innate Immunity and Acquired Immunity
| Feature | Innate Immunity | Acquired Immunity |
|---|---|---|
| Origin | Present right from birth. | Developed during an individual's lifetime after exposure to pathogens. |
| Specificity | Non-specific type of defense. | Highly pathogen-specific. |
| Memory | Does not retain immunological memory. | Possesses immunological memory for rapid response upon re-exposure. |
| Barriers/Components | Involves physical, physiological, cellular, and cytokine barriers. | Involves B-lymphocytes and T-lymphocytes. |
Types of Acquired Immune Responses\nAcquired immunity operates through two main mechanisms:
-
Humoral Immune Response (Antibody-Mediated Immunity):
- Mediated by B-lymphocytes (B-cells).
- B-cells produce specific protein molecules called antibodies into body fluids (blood and lymph) in response to antigens.
- Effective against extracellular pathogens like bacteria and free viruses.
-
Cell-Mediated Immune Response (CMI):
- Mediated by T-lymphocytes (T-cells).
- T-cells do not secrete antibodies directly but help B-cells produce them and directly attack infected cells, cancer cells, or foreign grafts.
- CMI is responsible for the rejection of organ transplants (graft rejection). Modern immunosuppressants are used to manage this.
Structure of an Antibody Molecule\nAn antibody ($Ig$) is a 'Y'-shaped glycoprotein molecule consisting of four polypeptide chains:
- Two Light Chains (L): Smaller chains with lower molecular weight.
- Two Heavy Chains (H): Larger chains with higher molecular weight.
- Hence, an antibody molecule is represented as $H_2L_2$.
- Disulfide Bonds: The four chains are held together by inter-chain disulfide bonds.
- Variable and Constant Regions: The tips of the 'Y' shape contain the antigen-binding site (Paratope), which varies according to the target antigen. The base represents the constant region.
💡 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.