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Q6:
Name the primary and secondary lymphoid organs.
Solution :
1. Definitions of Lymphoid Organs
Lymphoid organs are sites where the maturation, differentiation, and proliferation of lymphocytes occur. They are categorized based on their physiological role in the immune system into primary (central) and secondary (peripheral) organs. [Ref: Immunology Fundamentals, Adaptive Immune System Architecture].
2. Primary Lymphoid Organs
Primary lymphoid organs are the environments where immature lymphocytes originate, proliferate, and differentiate into mature, antigen-committed lymphocytes. These organs provide the necessary microenvironment for the development of $T$-lymphocytes and $B$-lymphocytes.
- Bone Marrow: The primary site for hematopoiesis where all blood cells, including B-lymphocytes, are produced and where B-cells undergo maturation. [Per Biological Principle of Hematopoietic Stem Cell (HSC) niche].
- Thymus: A lobed organ located near the heart and beneath the breastbone. It is the site where immature T-lymphocytes, generated in the bone marrow, migrate to undergo maturation and selection. [Per Thymic Selection/Education Process].
3. Secondary Lymphoid Organs
Secondary lymphoid organs are the sites where mature lymphocytes encounter antigens, become activated, and undergo clonal expansion into effector cells. These organs act as filters for antigens present in the blood, lymph, or mucosal surfaces.
- Spleen: A large, bean-shaped organ that acts as a reservoir for erythrocytes and filters blood by trapping blood-borne microorganisms. It contains a large pool of lymphocytes and phagocytes.
- Lymph Nodes: Small, solid structures located at different points along the lymphatic system. They serve to trap microorganisms or other antigens that enter the lymph and tissue fluid.
- MALT (Mucosa-Associated Lymphoid Tissue): Located within the lining of major tracts (respiratory, digestive, and urogenital). It constitutes approximately $50\%$ of the lymphoid tissue in the human body.
- Tonsils, Peyer’s Patches, and Appendix: Specialized clusters of lymphoid tissue embedded in the mucosal linings that provide localized immune responses.
4. Comparative Structural Overview
| Organ Category | Primary Role | Key Examples |
|---|---|---|
| Primary | Antigen-independent maturation of lymphocytes | Bone Marrow, Thymus |
| Secondary | Antigen-dependent activation of lymphocytes | Spleen, Lymph Nodes, MALT |
5. Visual Representation of Lymphoid Distribution
Final Solution: The primary lymphoid organs are the Bone Marrow and the Thymus, where lymphocytes mature. The secondary lymphoid organs, where lymphocytes interact with antigens and become activated, include the Spleen, Lymph Nodes, MALT, Tonsils, Peyer’s Patches, and the Appendix.
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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