Q.What causes AIDS? Explain the mode of action of AIDS virus. OR Explain the role of microbes in energy generation.
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Let’s start with an everyday picture. Think of your body as a country, and your immune system as its army and police force. This army is always on patrol, looking for invaders — viruses, bacteria, fungi — and destroying them before they can cause trouble. Now imagine a spy so clever that it doesn’t just attack the army; it actually enters the army’s command centre, takes over the generals, and slowly disables the entire defence system. That is exactly what the HIV virus does.
HIV stands for Human Immunodeficiency Virus. The key word is immunodeficiency — a deficiency, or shortage, of immunity. The virus does not kill you directly. Instead, it systematically destroys the very cells that coordinate your body’s defence, leaving you defenceless against even mild infections.
The precise mechanism
The immune system has many types of soldiers. The most important commander cell is the helper T-cell (also called CD4+ T-cell). This cell does not kill germs itself; it sends signals that activate other cells — the killer T-cells and antibody-producing B-cells — to attack.
HIV has a special protein on its surface that fits perfectly into a receptor on the helper T-cell, like a key into a lock. Once inside, the virus hijacks the cell’s machinery. It forces the cell to produce thousands of copies of the virus. Eventually, the cell bursts open and dies, releasing new viruses that go on to infect more helper T-cells.
Over months or years, the number of helper T-cells in the blood drops steadily. When the count falls below a critical level (around 200 cells per microlitre of blood), the immune system can no longer mount a proper defence. At this stage, the person is said to have AIDS — Acquired Immunodeficiency Syndrome.
HIV causes immune deficiency by destroying helper T-cells, the master switches of the immune system. The body does not die from HIV itself, but from opportunistic infections — diseases that a healthy immune system would easily stop, such as tuberculosis, pneumonia, or certain cancers.
Why it matters
A person with HIV can look and feel healthy for many years. During this asymptomatic phase, the virus is still active, but the body is producing new T-cells to replace the ones being destroyed. This is a losing battle — eventually, production cannot keep up.
The virus is transmitted only through specific routes:
- Unprotected sexual contact
- Sharing of infected needles (common among drug users)
- From an infected mother to her child during pregnancy, childbirth, or breastfeeding
- Transfusion of infected blood (rare now due to screening)
It is not transmitted by casual contact — shaking hands, sharing food, mosquito bites, or living in the same room. …
AIDS (Acquired Immuno Deficiency Syndrome) is caused by HIV (Human Immunodeficiency Virus), a retrovirus. HIV specifically infects and progressively destroys helper T-lymphocytes (a type of white blood cell essential for coordinating the immune response), using reverse transcriptase to make a DNA copy of its RNA genome, which integrates into the host cell's DNA and directs the production of new virus particles, eventually so severely reducing the number of helper T-cells that the person becomes immuno-compromised and susceptible to …
HIV, a retrovirus, infects and destroys helper T-cells using reverse transcriptase, progressively collapsing the immune system to cause AIDS.
Cause of AIDS: AIDS is caused by HIV (Human Immunodeficiency Virus), a retrovirus, transmitted through sexual contact with an infected person, transfusion of contaminated blood/blood products, sharing of infected needles/syringes, and from an infected mother to her child during pregnancy, birth, or breastfeeding.
Mode of action of the HIV virus:
- After entering the human body (usually via body fluids), HIV enters macrophages, where its RNA genome, using the viral enzyme reverse transcriptase, is used to synthesise viral DNA, which then gets incorporated into the host cell's (macrophage's) DNA.
- This DNA directs the synthesis of new viral RNA and proteins, producing many copies of the virus. The infected macrophages continue producing virus particles, acting like an HIV "factory."
- HIV also infects helper T-lymphocytes (T4 or CD4+ cells), replicating within them and progressively destroying them, using them to make more copies of the virus.
- Because helper T-cells play a central, coordinating role in mounting the body's immune response (both cell-mediated and humoral), the continuous decrease in their number over time (typically over several years) leads to a progressive decline in the person's immune capability. …
Showing the 12 most recent of 19 on this concept.
- CBSE 2026Set V11 markQ.Human immuno deficiency virus replicates in ___________.
›Reveal solutionSolution
HIV first enters and replicates within macrophages, so the word-bank answer for 'Human immunodeficiency virus replicates in ___' is macrophages.
After entering the body, the human immunodeficiency virus (HIV) enters macrophages. Inside a macrophage its single-stranded RNA genome is reverse-transcribed into viral DNA (by the enzyme reverse transcriptase); this viral DNA is incorporated into the host cell's DNA and directs the production of new virus particles. The infected macrophage keeps releasing virus and in this sense behaves as an HIV 'factory'. The virus then also enters and multipl …
- CBSE 2026Set A1 markMCQQ.Which of the following viruses has reverse transcriptase enzyme?(a) TMV(b) Bacteriophage(c) HIV(d) All of these
›Reveal solutionSolution
HIV is a retrovirus and carries reverse transcriptase; the correct option is (c).
Reverse transcriptase is the enzyme that synthesises DNA using an RNA template — the reverse of normal transcription. It is characteristic of retroviruses.
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- CBSE 2026Set ZOOLOGY1 markMCQQ.Which is the genetic material of HIV?(a) Single-stranded RNA(b) Single-stranded DNA(c) Double-stranded DNA(d) Double-stranded RNA
›Reveal solutionSolution
HIV (Human Immunodeficiency Virus) is a retrovirus carrying single-stranded RNA as its genome.
HIV belongs to the retrovirus group, meaning its genetic material is RNA, not DNA. Specifically, HIV carries two copies of single-stranded (+)sense RNA enclosed within a protein capsid. On infecting a helper T-lymphocyte (CD4+ cell), the viral enzyme reverse transcriptase uses this RNA as a template to synthesize viral DNA, which then integrates into the host cell's genome as a provirus. This DNA subsequently directs the pro …
- CBSE 2026Set ANNUAL1 markMCQQ.Test for AIDS is :(a) Widal test(b) Biopsy test(c) ELISA test(d) CRY organism test
›Reveal solutionSolution
AIDS (caused by HIV) is diagnosed using the ELISA (Enzyme-Linked Immunosorbent Assay) test.
ELISA (Enzyme-Linked Immunosorbent Assay) detects the presence of HIV antigens or the antibodies produced by the body's immune system against HIV in a patient's blood serum. It is the standard screening test for AIDS. (Widal test is for typhoid; biopsy is for examining tissue, e.g. for c …
- CBSE 2025Set ANNUAL1 markMCQQ.The type of HIV virus is -(a) Adenovirus(b) Bacteriophage virus(c) Retrovirus(d) Rotavirus
›Reveal solutionSolution
HIV carries its genome as RNA and uses reverse transcriptase to make a DNA copy inside the host cell, the defining feature of a retrovirus.
HIV (Human Immunodeficiency Virus) belongs to the retrovirus group: its genetic material is single-stranded RNA, and on infecting a host lymphocyte (helper T-cell) it uses the enzyme reverse transcriptase to synthesise viral DNA from the RNA template, which then integrates into the host genome. This 'reverse' flow of information ( …
- CBSE 2024Set ANNUAL1 markQ.[Case/Source-based passage] The word AIDS stands for Acquired Immuno Deficiency Syndrome. AIDS was first reported in 1981. AIDS mainly caused by the HIV (Human Immunodeficiency Virus). It is also called retrovirus. HIV infection mainly occurs by sexual contact with infected person. It is transmitted from the infected mother to her child through the Placenta. AIDS has no cure, but prevention is the best care. In our country, the National AIDS Control Organisation (NACO) and in states, the State AIDS Control Organisations (SACO) are making people aware towards AIDS education. World Health Organisation (WHO) has started a number of programmes to prevent the spreading of HIV infection. For this, we have need to aware and alert, so that India could lead forward in the direction of Human Welfare. On 1st day of December, AIDS day is celebrated. Read the above passage carefully and answer the questions given below:(a) How AIDS spreads from one infected person to others?
›Reveal solutionSolution
AIDS spreads mainly through sexual contact with an infected person and from an infected mother to her child via the placenta.
As stated in the passage, HIV infection mainly spreads through sexual contact with an infected person. It can also be transmitted from an infected mother to her child through the placenta during pregnancy. Beyond the passage, HIV can also spread through transfusion of contaminated blood/blood products, and through sharing of infected/contaminated needles an …
- CBSE 2024Set ANNUAL1 markQ.(Same passage as Q26.)(b) "Prevention is the best cure" - Clarify in context to AIDS.
›Reveal solutionSolution
Since AIDS has no cure, avoiding exposure to HIV through preventive practices is the only effective way to protect against it.
As the passage states, 'AIDS has no cure, but prevention is the best care.' Since there is currently no drug or vaccine that can cure or fully eliminate HIV infection from the body, the only truly effective strategy against AIDS is to prevent oneself from getting infected in the first place — for example, by avoiding unprotected/casual sexual contact, using precautions such as condoms, ensuring blood used for transfusion is screened, and avoiding the sharing of needles/syringes. This is why awareness and safe practices, rather than treatment aft …
- CBSE 2024Set E1 markMCQQ.HIV attacks on which of the following cells?(a) B-cells(b) T-cells(c) Epithelial cell(d) T-helper cell
›Reveal solutionSolution
HIV attacks the helper T-lymphocytes (CD4+ cells), destroying immunity and causing AIDS.
After entering the body, HIV enters macrophages and then attacks the helper T-lymphocytes (T-helper cells, which carry CD4 receptors). Inside them the viral RNA is reverse-transcribed to DNA, integrated into the host genome, and made to produce more virus particles. The progressive destruction of helper T-cells cripples the immune system, …
- CBSE 2023Set ANNUAL1 markMCQQ.Retrovirus is the pathogen of which of the following diseases?(a) filariasis(b) syphilis(c) AIDS(d) both(b) and (c)
›Reveal solutionSolution
A retrovirus (HIV) causes AIDS.
Retroviruses are RNA viruses that carry the enzyme reverse transcriptase, which makes a DNA copy of their RNA genome inside the host cell. The Human Immunodeficiency Virus (HIV), the cause of AIDS, is such a retrovirus; it infects and destroys helper T-cells, weakening immunit …
- CBSE 2022Set ANNUAL1 markMCQQ.HIV is not transmitted by(a) Blood transfusion(b) Sharing of injection(c) Hugging(d) Infected mother to child
›Reveal solutionSolution
HIV spreads only through body-fluid exchange, never through casual contact like hugging.
HIV (Human Immunodeficiency Virus), the causative agent of AIDS, is transmitted through: (i) sexual contact with an infected person, (ii) transfusion of contaminated blood, (iii) sharing of infected needles/syringes (commonly among intravenous drug users), and (iv) from an infected mother to her child through the placenta, or during birth/breastfeeding. It is NOT transmitted by casual social contact such as …
- CBSE 2022Set ANNUAL1 markMCQQ.The genetic material of the AIDS virus is(a) a single-stranded DNA(b) a single-stranded RNA(c) a double-stranded DNA(d) a double-stranded RNA
›Reveal solutionSolution
HIV is a retrovirus carrying single-stranded RNA, so the answer is (B).
AIDS is caused by the Human Immunodeficiency Virus (HIV), a retrovirus. Its genome consists of single-stranded RNA together with the enzyme reverse transcriptase. After entering a host helper T-cell, reverse transcriptase makes a DNA copy of the viral RNA, which integrates into th …
- CBSE 2022Set ZOOLOGY1 markMCQQ.Which is the genetic material of AIDS virus?(i) Double-stranded DNA(ii) Single-stranded DNA(iii) Single-stranded RNA(iv) Double-stranded RNA
›Reveal solutionSolution
HIV, the AIDS virus, carries its genetic information as single-stranded RNA.
AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV), which belongs to the group of retroviruses. A retrovirus carries single-stranded RNA as its genome, along with the enzyme reverse transcriptase. After entering a host cell (helper T-lymphocyte/macrophage), the enzyme reverse-transcribes the viral RNA into a DNA copy, which integ …
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