Biology
CBSE
Biology — CBSE Class XII Sample Paper (2026-27)
Sample paper · 2026-27
Section A · Section B · Section C · Section D · Section E
This MCQ module is based on: Aids Cancer
TOPIC 32 OF 64
Aids Cancer
🎓 Class 12
Biology
CBSE
Theory
Ch 7 – Human Health and Disease
⏱ ~14 min
🌐 Language:
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Aids Cancer
8.19 AIDS — Acquired Immuno Deficiency Syndrome
AIDS means Acquired Immuno Deficiency Syndrome — a deficiency of the immune system acquired during a person's lifetime (it is not congenital). "Syndrome" means a group of symptoms. AIDS was first reported in 1981 and has killed more than 25 million people worldwide.
The Virus: HIV
AIDS is caused by the Human Immunodeficiency Virus (HIV) — a retrovirus with an envelope enclosing an RNA genome.
Transmission of HIV
HIV transmission occurs through:
- Sexual contact with an infected person.
- Transfusion of contaminated blood or blood products.
- Sharing infected needles (intravenous drug abusers).
- Infected mother to child through placenta.
High-risk groups: people with multiple sexual partners, intravenous drug users, recipients of repeated blood transfusions, and babies born to HIV-positive mothers.
Important: HIV/AIDS is not spread by casual touch or physical contact; it spreads only through body fluids. Therefore, HIV-positive persons should not be isolated from family and society — that is harmful and unnecessary.
The time between infection and onset of AIDS symptoms can range from a few months to many years — typically 5–10 years.
HIV Replication in the Human Host
Step-by-step replication:
- HIV enters the body and infects macrophages.
- Inside the macrophage, viral RNA is converted to viral DNA by the enzyme reverse transcriptase.
- This viral DNA integrates into the host cell's DNA (it becomes a "provirus").
- The infected macrophage now produces virus particles continuously — acting as an HIV factory.
- HIV also enters helper T-lymphocytes (TH), replicates inside them and produces progeny viruses.
- The new viruses attack more helper T-cells — the cycle repeats.
- The number of helper T-cells in the body decreases progressively.
- The patient suffers from fever, diarrhoea, weight loss and increasing susceptibility to opportunistic infections (Mycobacterium, fungi, parasites like Toxoplasma).
Diagnosis of AIDS
The widely used diagnostic test for AIDS is the ELISA (Enzyme-Linked Immuno-Sorbent Assay). A positive ELISA is typically confirmed by a Western blot test.
Treatment and Prevention
Treatment with anti-retroviral drugs is only partially effective — it can prolong life but cannot cure AIDS; death from opportunistic infections is eventually inevitable.
Prevention is the best option. In India, the National AIDS Control Organisation (NACO) and many NGOs educate the public. WHO measures include:
- Screening blood (blood banks) for HIV.
- Using only disposable needles and syringes.
- Free distribution of condoms.
- Controlling drug abuse.
- Advocating safe sex and regular HIV check-ups in susceptible populations.
The message is "Don't die of ignorance." HIV/AIDS-infected people deserve help and sympathy — not stigma.
8.20 Cancer
Cancer is one of the most dreaded human diseases and a major cause of death globally. More than a million Indians suffer from cancer and a large number die from it annually.
What is Cancer?
In normal cells, growth and differentiation are tightly controlled. Cancer cells lose this control:
- They lose contact inhibition — normal cells stop dividing when they touch neighbouring cells; cancer cells keep dividing.
- They form masses of cells called tumours.
Benign vs Malignant Tumours
| Feature | Benign | Malignant |
|---|---|---|
| Spread | Confined to original location | Invade surrounding tissues |
| Growth rate | Slow | Rapid |
| Damage | Little | Damage surrounding normal tissues; starve normal cells of nutrients |
| Metastasis | None | Yes — cells spread via blood to new sites and start new tumours |
| Examples | Common skin moles, lipomas | Carcinomas, sarcomas, leukemias, lymphomas |
The most feared property of malignant tumours is metastasis — cancer cells break off, travel through blood, lodge in distant organs and form secondary tumours.
Types of Cancer
| Type | Origin | Examples |
|---|---|---|
| Carcinoma | Epithelial tissues (skin, lining of organs) | Lung, breast, colon, stomach |
| Sarcoma | Connective tissues (bone, cartilage, muscle, fat) | Osteosarcoma (bone), liposarcoma (fat) |
| Leukemia | Blood-forming cells (bone marrow) | Acute leukemia, chronic leukemia |
| Lymphoma | Lymphoid tissue | Hodgkin's, non-Hodgkin's lymphoma |
Causes of Cancer
Normal cells become cancerous by induction from carcinogens — physical, chemical or biological agents:
- Ionising radiations — X-rays, gamma rays — cause DNA damage.
- Non-ionising radiations — UV light — causes skin cancer.
- Chemical carcinogens — especially in tobacco smoke (cause lung cancer).
- Biological agents — oncogenic viruses — have viral oncogenes (e.g., HPV → cervical cancer).
- Cellular oncogenes (c-onc) or proto-oncogenes — normal genes that, when activated abnormally, lead to oncogenic transformation.
Cancer Detection & Diagnosis
Early detection saves lives. Methods include:
- Biopsy and histopathology — a tissue sample is stained and examined under microscope.
- Blood and bone marrow tests — for leukemias (increased white cell counts).
- Radiography (X-rays), CT scan (Computed Tomography — 3D X-ray image), MRI (Magnetic Resonance Imaging — uses strong magnetic fields, non-ionising).
- Antibodies against cancer-specific antigens for certain cancers.
- Molecular biology techniques — detect genes that predispose to certain cancers (e.g., BRCA1/2 for breast cancer).
Cancer Treatment
Common approaches:
- Surgery — physical removal of tumour.
- Radiation therapy (radiotherapy) — tumour cells are irradiated lethally; care is taken to spare surrounding normal tissues.
- Chemotherapy — drugs that kill cancerous cells; some are specific to particular tumours. Side effects: hair loss, anaemia, nausea (because they also affect rapidly-dividing normal cells like hair follicles and blood cells).
- Immunotherapy — Tumour cells often evade the immune system. Patients are given biological response modifiers like α-interferon which activate the immune system to destroy the tumour.
Most cancers are treated by a combination of surgery, radiotherapy and chemotherapy.
Interactive: HIV/Cancer Concept Explorer
Pick a concept to see its key facts:
Definition: —
Relevance: —
Activity 8.3 — Predict-Observe-Explain: Why ARVs Don't Cure AIDS
Setup: A patient diagnosed with HIV starts taking anti-retroviral drugs (ARVs) regularly. ARVs target the enzyme reverse transcriptase. Within months her viral load drops dramatically and she feels healthy. Yet doctors say she still has HIV.
Predict: If ARVs stop the virus from copying itself, why is she not cured? What would happen if she stopped taking the drugs?
Key insight: When HIV infects a cell, its RNA is reverse-transcribed into DNA which integrates into the host cell's chromosome as a provirus. This integrated viral DNA is now permanent — it cannot be removed by any current drug.
What ARVs do: Block new virus production (by inhibiting reverse transcriptase or protease). They prevent existing infected cells from making more virus.
What ARVs CANNOT do: Remove the provirus DNA already in the patient's genome. Some infected cells are long-lived (latent reservoirs in memory T-cells).
If she stops ARVs: Latent infected cells reactivate; virus production resumes; viral load rebounds within weeks; T-cell decline restarts; AIDS eventually develops.
Conclusion: ARVs convert HIV from a death sentence to a manageable chronic infection, but lifelong adherence is essential. Research on "functional cures" (eliminating proviral DNA) is ongoing.
Worked Examples
Worked Example 1: How is HIV transmitted? List the routes.
HIV is transmitted only through body fluids — specifically:
- Sexual contact with an infected person.
- Blood transfusion with contaminated blood or blood products.
- Sharing needles/syringes (most commonly in intravenous drug users).
- Mother-to-child transmission — during pregnancy (placenta), childbirth, or breastfeeding.
Worked Example 2: How does cancer differ from a normal cell?
| Feature | Normal cell | Cancer cell |
|---|---|---|
| Cell division | Highly controlled | Uncontrolled, continuous |
| Contact inhibition | Present | Absent |
| Differentiation | Specialised | De-differentiated |
| Nucleus | Normal size | Large, abnormal shape |
| Lifespan | Limited (apoptosis at right time) | Immortal (avoids apoptosis) |
| Mobility | Stay in tissue of origin | Invade neighbours; metastasise to distant sites |
| Resource use | Cooperative | Compete with and starve normal cells |
Worked Example 3: Why does chemotherapy cause hair loss and anaemia?
Chemotherapy drugs target rapidly dividing cells — which is what cancer cells are. Unfortunately, several types of normal cells also divide rapidly:
- Hair follicle cells — divide fast to produce hair. Killed by chemo → hair loss.
- Bone marrow cells — divide fast to produce RBCs, WBCs, platelets. Killed by chemo → anaemia, infection susceptibility, bleeding tendency.
- Gut lining cells — divide fast to replace shedding cells. Killed by chemo → nausea, mouth sores, diarrhoea.
Competency-Based Questions
Q1. Which enzyme is unique to retroviruses like HIV? L1 Remember
Answer: (b) Reverse transcriptase. This enzyme makes a DNA copy from the viral RNA — the reverse of the normal direction of information flow. The DNA then integrates into the host genome.
Q2. ELISA is used to diagnose: L1 Remember
Answer: (b) AIDS. ELISA detects anti-HIV antibodies in patient's blood. Positive ELISA is usually confirmed by Western blot. (ELISA is also used for many other infections, but the NCERT-specific use mentioned for HIV diagnosis is the primary association.)
Q3. Short Answer: Differentiate between benign and malignant tumours. L2 Understand
Benign tumour: Slow-growing; confined to original site; does NOT metastasise; usually not life-threatening; surgical removal is often curative. Example: skin mole, lipoma.
Malignant tumour (cancer): Rapidly growing; invades surrounding tissues; metastasises via blood/lymph to distant organs; life-threatening; requires combination therapy. Examples: carcinomas, sarcomas, leukemias, lymphomas.
Malignant tumour (cancer): Rapidly growing; invades surrounding tissues; metastasises via blood/lymph to distant organs; life-threatening; requires combination therapy. Examples: carcinomas, sarcomas, leukemias, lymphomas.
Q4. Analyse: Why does HIV preferentially destroy helper T-cells (TH)? What is the consequence? L4 Analyse
Why TH cells: HIV's surface protein gp120 binds the CD4 receptor expressed on helper T-cells (and also on macrophages). This receptor specificity makes TH cells the primary target.
Consequence — why this is catastrophic: Helper T-cells are the central coordinators of the immune system. They:
Consequence — why this is catastrophic: Helper T-cells are the central coordinators of the immune system. They:
- Activate B-cells to produce antibodies.
- Activate cytotoxic T-cells.
- Activate macrophages.
Q5. HOT (Evaluate): A celebrity claims that "smokeless cigarettes" (vaping) are completely safe. Evaluate this claim using your knowledge of carcinogens. L5 Evaluate
Critique: The claim is misleading.
- "Smokeless" does not equal "carcinogen-free." Many e-cigarette vapours contain formaldehyde, acetaldehyde, acrolein and heavy metals (lead, nickel) — all classified as carcinogens or probable carcinogens by IARC.
- Nicotine itself is highly addictive — leading users to lifelong dependence and potentially graduating to tobacco products.
- EVALI (E-cigarette/Vaping Associated Lung Injury) — confirmed lung disease, including deaths, linked to vaping.
- Long-term safety data is unknown — vaping has only existed widely since ~2010; cancer typically develops over decades.
- Risk for youth — adolescent brain development is disrupted by nicotine; vaping is now an epidemic in schools.
Assertion–Reason Questions
Choose: (A) Both true, R explains A. (B) Both true, R doesn't explain A. (C) A true, R false. (D) A false, R true.
A: AIDS is not spread by mere touch or physical contact.
R: HIV spreads only through body fluids — sexual contact, blood, sharing needles, mother to child.
Answer: (A). Both true; R explains A. Stigmatising HIV-positive people is therefore both medically wrong and socially harmful.
A: Cancer cells form tumours by uncontrolled division.
R: Cancer cells have lost the property of contact inhibition that normally limits cell division.
Answer: (A). Both true; R explains A. Normal cells stop dividing when they touch neighbours; cancer cells ignore this signal and pile up into masses.
A: α-interferon is sometimes used in cancer treatment.
R: α-interferon is a chemotherapy drug that directly kills tumour cells.
Answer: (C). A is TRUE — α-interferon is used as immunotherapy in some cancers. R is FALSE — α-interferon is NOT a chemotherapy drug. It is a "biological response modifier" that activates the patient's own immune system to attack tumours. It works indirectly via immune activation, not by directly killing cancer cells.
Frequently Asked Questions - Aids Cancer
What is the main concept covered in Aids Cancer?
In NCERT Class 12 Biology Chapter on Human Health and Disease, "Aids Cancer" covers the core biological structures, processes, and pathways students need for board exam success. The MyAiSchool lesson explains the topic with definitions, labelled diagrams, comparison tables, and interactive simulations. Scientific terminology and physiological/genetic significance are highlighted throughout to build conceptual depth aligned with CBSE 2025-26 syllabus.
How is Aids Cancer useful in real-life or applied biology?
Real-life applications of "Aids Cancer" from NCERT Class 12 Biology Human Health and Disease include medical diagnostics, agriculture, biotechnology, public health, evolutionary insights, and ecological monitoring. The MyAiSchool lesson links every biological concept to a tangible application so students see biology as a problem-solving framework for living systems and real-world challenges.
What are the key terms students should memorize for Aids Cancer?
Key terms in "Aids Cancer" (NCERT Class 12 Biology Human Health and Disease) are tabulated in the MyAiSchool key-terms grid. Students should memorize each term with its precise definition, function, and example. Terminology is high-yield in CBSE board exams — 1-mark MCQs and 2-mark short answers test definitions directly. The Summary section provides a printable quick-reference card.
How does this part connect to other parts of the chapter?
NCERT Class 12 Biology Human Health and Disease is structured so each part builds biological understanding sequentially. "Aids Cancer" connects to neighbouring parts via shared mechanisms, structural hierarchies, and physiological processes. The MyAiSchool lesson cross-references related concepts with internal links so students can navigate the whole chapter as one connected biological story rather than disconnected fragments.
What types of CBSE board questions come from Aids Cancer?
CBSE board questions from "Aids Cancer" typically include: (1) 1-mark MCQs on definitions and processes, (2) 2-mark short-answer differences/comparisons, (3) 3-mark labelled-diagram questions, (4) 5-mark long-answer essays combining mechanism + diagram + significance. The MyAiSchool lesson tags each Competency-Based Question (CBQ) with Bloom level (L1-L6) so students know how to study for each weight.
How can students use the interactive simulation effectively?
The interactive simulation in the "Aids Cancer" lesson allows students to explore biological processes, classifications, or pathways using selectors and sliders, with live visual feedback. To use it effectively: (1) explore each option/state, (2) compare with textbook diagrams, (3) note the function/outcome changes, (4) try the integrated practice quiz. The simulation reinforces visual-spatial understanding that pure text-based study cannot.
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