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Q6:
Name the primary and secondary lymphoid organs.
Solution :
1. Definitions and Theoretical Framework
Lymphoid organs are the anatomical sites where the origin, maturation, and proliferation of lymphocytes occur. They are categorized based on their functional role in the maturation process of $B$-lymphocytes and $T$-lymphocytes. [Per the principles of Immunology, the immune system follows a hierarchical structure to ensure self-tolerance and antigen recognition].
2. Primary Lymphoid Organs
Primary lymphoid organs provide the microenvironment for the development and maturation of antigen-specific lymphocytes from progenitor cells. Once maturation is complete, these lymphocytes migrate to secondary lymphoid organs.
- Bone Marrow: The site of hematopoiesis where all blood cells, including lymphocytes, are produced. It is the site for the maturation of $B$-lymphocytes.
- Thymus: A lobed organ located near the heart and beneath the breastbone. It is the site for the maturation of $T$-lymphocytes. [Note: The thymus is large at birth but gradually atrophies with age].
3. Secondary Lymphoid Organs
Secondary lymphoid organs provide the anatomical sites for the interaction of lymphocytes with antigens. This is where lymphocytes become activated and proliferate to form effector cells. [Mechanism: Clonal selection and expansion].
- Spleen: A large, bean-shaped organ containing lymphocytes and phagocytes. It acts as a filter for the blood by trapping blood-borne microorganisms.
- Lymph Nodes: Small solid structures located at different points along the lymphatic system. They trap microorganisms or antigens that enter the lymph and tissue fluid.
- MALT (Mucosa-Associated Lymphoid Tissue): Comprises approximately $50\%$ of the lymphoid tissue in the human body. It is located within the lining of major tracts, including the respiratory, digestive, and urogenital tracts.
4. Comparative Summary Table
| Category | Organs | Primary Function |
|---|---|---|
| Primary | Bone Marrow, Thymus | Antigen-independent maturation of lymphocytes |
| Secondary | Spleen, Lymph Nodes, MALT, Tonsils, Peyer's patches | Antigen-dependent activation and proliferation |
5. Visual Representation of Lymphoid Distribution
Final Solution: The primary lymphoid organs are the Bone Marrow and Thymus, where lymphocytes mature. The secondary lymphoid organs are the Spleen, Lymph Nodes, Tonsils, Peyer’s patches of the small intestine, and the Appendix (MALT), where lymphocytes interact with antigens to initiate an immune response.
More Questions from Class 12 Biology Human Health and Disease EXERCISES
- Q1: What are the various public health measures, which you would suggest as safeguard against infectious diseases?
- Q1: What are the various public health measures, which you would suggest as safeguard against infectious diseases?
- Q2: In which way has the study of biology helped us to control infectious diseases?
- Q2: In which way has the study of biology helped us to control infectious diseases?
- Q3(a): How does the transmission of each of the following diseases take place? (a) Amoebiasis
- Q3(a): How does the transmission of each of the following diseases take place? (a) Amoebiasis
- Q3(b): How does the transmission of each of the following diseases take place? (b) Malaria
- Q3(b): How does the transmission of each of the following diseases take place? (b) Malaria
- Q3(c): How does the transmission of each of the following diseases take place? (c) Ascariasis
- Q3(c): How does the transmission of each of the following diseases take place? (c) Ascariasis
- Q3(d): How does the transmission of each of the following diseases take place? (d) Pneumonia
- Q3(d): How does the transmission of each of the following diseases take place? (d) Pneumonia
- Q4: What measure would you take to prevent water-borne diseases?
- Q4: What measure would you take to prevent water-borne diseases?
- Q5: Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
- Q5: Discuss with your teacher what does ‘a suitable gene’ means, in the context of DNA vaccines.
- Q6: Name the primary and secondary lymphoid organs.
- Q7(a): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT
- Q7(a): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (a) MALT
- Q7(b): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (b) CMI
- Q7(b): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (b) CMI
- Q7(c): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (c) AIDS
- Q7(c): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (c) AIDS
- Q7(d): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (d) NACO
- Q7(d): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (d) NACO
- Q7(e): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (e) HIV
- Q7(e): The following are some well-known abbreviations, which have been used in this chapter. Expand each one to its full form: (e) HIV
- Q8(a): Differentiate the following and give examples of each: (a) Innate and acquired immunity
- Q8(a): Differentiate the following and give examples of each: (a) Innate and acquired immunity
- Q8(b): Differentiate the following and give examples of each: (b) Active and passive immunity
- Q8(b): Differentiate the following and give examples of each: (b) Active and passive immunity
- Q9: Draw a well-labelled diagram of an antibody molecule.
- Q9: Draw a well-labelled diagram of an antibody molecule.
- Q10: What are the various routes by which transmission of human immuno-deficiency virus takes place?
- Q10: What are the various routes by which transmission of human immuno-deficiency virus takes place?
- Q11: What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
- Q11: What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
- Q12: How is a cancerous cell different from a normal cell?
- Q12: How is a cancerous cell different from a normal cell?
- Q13: Explain what is meant by metastasis.
- Q13: Explain what is meant by metastasis.
- Q14: List the harmful effects caused by alcohol/drug abuse.
- Q14: List the harmful effects caused by alcohol/drug abuse.
- Q15: Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
- Q15: Do you think that friends can influence one to take alcohol/drugs? If yes, how may one protect himself/herself from such an influence?
- Q16: Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
- Q16: Why is that once a person starts taking alcohol or drugs, it is difficult to get rid of this habit? Discuss it with your teacher.
- Q17: In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
- Q17: In your view what motivates youngsters to take to alcohol or drugs and how can this be avoided?
CBSE Solutions for Class 12 Biology Human Health and Disease
Chapters in CBSE - Class 12 Biology
- Reproduction in Organisms
- Human Reproduction
- Reproductive Health
- Principles of Inheritance and Variation
- Molecular Basis of Inheritance
- Evolution
- Strategies for Enhancement in Food Production
- Microbes in Human Welfare
- Biotechnology: Principles and Processes
- Biotechnology and Its Applications
- Organisms and Populations
- Ecosystem
- Biodiversity and Conservation
- Environmental Issues
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