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Q11:
What is the mechanism by which the AIDS virus causes deficiency of immune system of the infected person?
Solution :
1. The Pathogen and Entry Mechanism
The causative agent of AIDS (Acquired Immuno Deficiency Syndrome) is the Human Immunodeficiency Virus (HIV), a member of the group of viruses called retroviruses, which possess an envelope enclosing the RNA genome [Per the Baltimore Classification of Viruses]. Upon entry into the human body, the virus gains access to macrophages, which function as an HIV factory [Biological mechanism of viral pathogenesis].
2. Viral Replication Cycle within Host Cells
The mechanism of immune system degradation proceeds through the following sequential steps:
- Entry and Reverse Transcription: After entering the macrophage, the viral RNA genome is transcribed into viral DNA by the enzyme reverse transcriptase [$RNA \xrightarrow{\text{Reverse Transcriptase}} DNA$].
- Integration: The newly formed viral DNA is incorporated into the host cell's genome, directing the infected cells to produce new virus particles [Integration via viral integrase enzyme].
- The Factory Effect: Macrophages continue to produce virus particles without immediate lysis, effectively turning the cell into a viral reservoir.
3. Target-Specific Destruction of T-Helper Lymphocytes
The critical factor in immune deficiency is the secondary infection of $CD4^+$ T-helper lymphocytes. The HIV virus enters these cells and replicates further, producing a massive number of progeny viruses. This leads to the following physiological outcome:
- Cell Lysis: The high rate of viral replication leads to the destruction (lysis) of the T-helper cells.
- Numerical Decline: As the virus spreads, the population of T-helper lymphocytes decreases drastically in the host.
- Immune Collapse: T-helper cells are the central coordinators of the adaptive immune response. Their reduction renders the person susceptible to opportunistic infections, such as those caused by Mycobacterium, viruses, fungi, and parasites like Toxoplasma [Clinical consequence of cellular immunodeficiency].
4. Summary of Pathogenesis
| Stage | Mechanism |
|---|---|
| Viral Entry | HIV enters macrophages/CD4+ T-cells via surface receptors. |
| Synthesis | Viral RNA converts to DNA; integration into host nucleus. |
| Immune Impact | Destruction of T-helper cells reduces cell-mediated and humoral immunity. |
Final Solution: The AIDS virus (HIV) causes immune deficiency by utilizing macrophages as viral factories and subsequently infecting and destroying $CD4^+$ T-helper lymphocytes. The progressive loss of these T-cells, which are essential for coordinating the immune response, leaves the body defenseless against opportunistic infections and malignancies.
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.
- 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?
- 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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