AIDS and cancer are high-frequency NEET topics where terminology traps cost marks. The common trap: confusing which test screens for HIV versus which confirms it — and mixing up what CD4+ T cell count actually tells a clinician.
AIDS — the biology. HIV (Human Immunodeficiency Virus) is a retrovirus that selectively destroys helper T lymphocytes (CD4+ T cells). Transmission occurs through sexual contact, contaminated blood/needles, and from infected mother to child (transplacental or through breast milk). HIV is NOT transmitted by touch, mosquito bites, or sharing food (NCERT Class 12 Biology Chapter 7, page 164).
The diagnostic sequence matters. ELISA (Enzyme-Linked Immunosorbent Assay) is the screening test — it is cheap, sensitive, and used first. A positive ELISA alone does not confirm HIV. Western blot is the confirmatory test. CD4+ T cell count is neither screening nor confirmatory — it monitors disease progression. When CD4+ count drops below 200 cells/µL, the condition is classified as AIDS.
Cancer — key facts. Cancer results from uncontrolled cell division caused by activation of oncogenes or inactivation of tumour suppressor genes. Benign tumours remain localised; malignant tumours (cancers) show metastasis — spread to distant sites via blood and lymph. Carcinogens include physical agents (UV, X-rays), chemical agents (tobacco smoke compounds), and biological agents (oncogenic viruses).
Prevention and detection. Cancer detection methods include biopsy, radiography, CT, MRI, and molecular markers. AIDS prevention centres on safe practices, screening of blood before transfusion, use of disposable needles, and public awareness — no vaccine is available for HIV as of the NCERT syllabus.
Watch out: NEET questions on AIDS frequently test the ELISA-vs-Western-blot-vs-CD4 distinction. Read the stem carefully for whether it asks about screening, confirmation, or monitoring — each maps to a different answer.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which of the following is the causative agent of AIDS?
Which of the following is NOT a route of HIV transmission?
Which type of cells does HIV primarily destroy in the human body?
A patient tests positive on ELISA for HIV. The physician orders a second test before confirming HIV status. Which test is most appropriate as the confirmatory step?
An HIV-positive patient has a CD4+ T cell count of 180 cells/µL. What does this value indicate about the patient's condition?
Which of the following correctly distinguishes a benign tumour from a malignant tumour?
A researcher discovers that a particular gene, when activated, causes uncontrolled cell proliferation. This gene is best classified as:
A NEET question states: "An individual is diagnosed HIV-positive. Over the next several years, which sequence of events correctly describes disease progression?"
Given
- ELISA result: positive - CD4+ T cell count: 450 cells/µL
Required
Determine the correct interpretation of these two results together.
Concept
ELISA is a screening test for HIV antibodies. CD4+ T cell count monitors immune status. AIDS is classified when CD4+ drops below 200 cells/µL. A positive ELISA requires Western blot confirmation before HIV-positive status is established.
Formula/Rule
- ELISA positive → proceed to Western blot for confirmation - CD4+ < 200 cells/µL → AIDS classification - CD4+ ≥ 200 cells/µL in an HIV-positive individual → HIV-positive but not yet AIDS
Substitution
CD4+ count = 450 cells/µL → 450 > 200 → does NOT meet AIDS threshold.
Calculation
This is a logical reasoning problem, not an arithmetic one. The two data points are evaluated against clinical thresholds: - Positive ELISA → HIV exposure likely (pending confirmation) - CD4+ = 450 → above the 200 threshold → not AIDS
Final answer
**(B) The person is HIV-positive but has not progressed to AIDS.** (Strictly, the person requires Western blot confirmation of HIV status, but among the given options, B is the most accurate — the CD4+ count of 450 rules out AIDS.)
Common trap
Selecting option (A) by assuming a positive ELISA + any CD4+ reading = AIDS. The threshold is specifically <200 cells/µL. At 450, the immune system is impaired but has not collapsed to AIDS levels. Another trap: selecting (C) by assuming ELISA is unreliable — ELISA is highly sensitive; while false positives exist, a positive result is not "definitely" false.
Similar NEET-style question
"A patient shows positive Western blot and CD4+ count of 150 cells/µL. The patient is most likely suffering from: (A) Hepatitis B, (B) Tuberculosis, (C) AIDS, (D) Typhoid." Answer: (C) — Western blot confirms HIV, and CD4+ < 200 = AIDS. ---
AIDS: HIV (retrovirus); attacks helper T (CD4) cells; transmission — sexual, blood, mother-to-child. Diagnosis: ELISA / Western blot. Cancer: uncontrolled cell division; benign vs malignant; oncogenes; metastasis. Hallmarks: contact inhibition lost.
-- NCERT Class 12 Biology, Ch. 7, p. 164These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Similar Terms
ELISA = screening (cheap, sensitive); Western blot = confirmation. CD4+ T cell count tracks disease progression.
Question on which test confirms HIV vs which monitors progression.
ELISA first (screening); Western blot confirms; CD4+ count = monitoring marker (<200/µL = AIDS).
Category: Similar Terms
Active: own immune response (vaccination, infection). Passive: pre-formed antibodies received (colostrum, antiserum injection).
Question on immunity type from vaccination, antiserum, mother's milk.
Active = body produces; passive = body receives. Vaccination → active. Mother's milk → passive (IgA).
Root cause: term confusion
Vaccination = ACTIVE (body produces antibodies in response to antigen). Antiserum = passive. Maternal IgA in milk = passive.
Root cause: term confusion
Anopheles = vector (transmits). Plasmodium = causative agent (causes disease). Female Anopheles bite is the transmission route.
29 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.
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The capacity to generate a whole plant from any cell of the plant is called:
Which one of the following is NOT an advantage of inbreeding?
Identify the asexual reproductive structure associated with Penicillium :
Select the incorrect statement with respect to acquired immunity.
Which of the following plants is monoecious? (b) Plant tissue culture (ii) Pomato
Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.
active vs passive immunity confusion
Vaccination triggers the body to produce its own antibodies (active immunity), but students interpret 'given externally' as passive. Passive immunity (antiserum, colostrum IgA from mother's milk) provides preformed antibodies with no immune response from the recipient. Questions that pair vaccination, antiserum, and colostrum expose students who cannot classify by mechanism rather than by route of administration.
vector vs causative agent confusion
Questions name both the vector (organism that transmits) and the causative agent (organism that causes disease) as answer options. Students who associate 'Anopheles = malaria' select Anopheles as the causative agent rather than recognising it as the vector; Plasmodium is the causative agent. The distinction -- vector transmits, causative agent infects -- is lost when both options are plausible from partial recall.
microbe product pair swap
Match-list questions pair 10 or more microbe names with industrial or household products. Students confuse Lactobacillus (lactic acid fermentation, curd) with Saccharomyces cerevisiae (ethanol, bread), or Aspergillus niger (citric acid) with Clostridium butylicum (butyric acid). Partial recall of one-to-one mappings produces swapped pairs, especially when two products share the same chemical class.
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