Is it correct to say: Calling AIDS a bacterial disease?

AIDS is caused by HIV — a retrovirus. Bacteria are entirely different pathogens.

Is it correct to say: Treating benign and malignant tumours as the same?

Benign tumours remain localised. Malignant tumours invade neighbouring tissue and metastasise via blood/lymph — this is the defining trait.

Is it correct to say: Confusing active with passive immunity?

Active = host makes antibodies (slow, long). Passive = ready-made antibodies given (fast, short). Colostrum and antivenom are passive; vaccines and infections induce active.

Is it correct to say: Believing memory cells make antibodies directly?

Memory cells stay dormant until re-exposure. On second contact they proliferate rapidly into antibody-secreting plasma cells (basis of vaccination).

Is it correct to say: Mixing up interferon and interleukin?

Interferons are antiviral cytokines released by infected cells. Interleukins are cell-signalling molecules between leukocytes.

Is it correct to say: Stating that opioids and cocaine act by the same mechanism?

Opioids (morphine, heroin) bind opioid receptors and depress the CNS. Cocaine blocks reuptake of dopamine and is a CNS stimulant.

Human Health and Disease

Pathogens, immune system, vaccines, HIV/AIDS, cancer, drug and alcohol abuse — NCERT Class 12 Biology Ch 7

📐 10 formulas✏️ 3 examples🎯 6 practice⚖️ 5-7 marks🏫 CBSE📚 Class 12✓ 2025–26 syllabus

💡

Board Exam Tips

→Learn diseases with their causative agents in tabular form — one mark each for correct pairs.
→Antibody structure H2L2 with labelled diagram is a 3-mark favourite.
→Distinguish active vs passive and innate vs acquired immunity — very common comparative question.
→HIV replication cycle (with reverse transcriptase) is a 5-mark diagram question.
→Do not confuse benign with malignant tumours; metastasis is the defining feature of malignant.

📐 Formulas(10)

Antibody Structure★ Board fav

Antibody = H_{2} L_{2} (2 heavy + 2 light chains)

Five Classes of Immunoglobulins★ Board fav

IgG, IgA, IgM, IgE, IgD

Types of Immunity

Innate (non-specific) + Acquired (specific: active/passive)

HIV Genome and Enzyme★ Board fav

HIV = ssRNA + reverse transcriptase (RT); RNA RT DNA

AIDS Detection Test★ Board fav

ELISA (Enzyme-Linked Immunosorbent Assay)

Cancer Cell Trait★ Board fav

Loss of contact inhibition + uncontrolled division + metastasis (malignant)

Cancer Detection Techniques

Biopsy, histopathology, CT, MRI, PET, tumour-marker antibodies

Drug Chemical Formulas

Morphine (opioid): C_{17} H_{19} NO_{3}; Cocaine: C_{17} H_{21} NO_{4}

Interferon Function

Virus-infected cell \to Interferon \to Protects neighbouring cells

Vaccination Principle

Antigen (weakened/killed) \to Memory B and T cells \to Rapid secondary response

✏️ Solved Examples

1Solved Exampleeasy4 steps

Name the causative organism and one symptom of (i) malaria, (ii) typhoid, (iii) pneumonia, (iv) amoebiasis.

Malaria

Plasmodium (P. vivax, P. falciparum) \to cyclic high fever with chills

2Solved Exampleboard5 steps

Distinguish active immunity from passive immunity with one example each and state which offers longer protection. (3 marks)

Define active immunity

Antigen enters body \to body makes its own antibodies

3Solved ExampleHOTS5 steps

A patient's blood tests positive for HIV antibodies by ELISA. Explain why this does not necessarily mean the person will immediately develop symptoms of AIDS. Trace the cellular events from infection to full-blown AIDS.

Entry of virus

HIV binds gp120 on helper T (CD4^{+}) cells

⚠️ Traps & Common Mistakes

⚠️Common Mistakes6

1
Calling AIDS a bacterial disease
✓AIDS is caused by HIV — a retrovirus. Bacteria are entirely different pathogens.
2
Treating benign and malignant tumours as the same
✓Benign tumours remain localised. Malignant tumours invade neighbouring tissue and metastasise via blood/lymph — this is the defining trait.
3
Confusing active with passive immunity
✓Active = host makes antibodies (slow, long). Passive = ready-made antibodies given (fast, short). Colostrum and antivenom are passive; vaccines and infections induce active.
4
Believing memory cells make antibodies directly
✓Memory cells stay dormant until re-exposure. On second contact they proliferate rapidly into antibody-secreting plasma cells (basis of vaccination).
5
Mixing up interferon and interleukin
✓Interferons are antiviral cytokines released by infected cells. Interleukins are cell-signalling molecules between leukocytes.
6
Stating that opioids and cocaine act by the same mechanism
✓Opioids (morphine, heroin) bind opioid receptors and depress the CNS. Cocaine blocks reuptake of dopamine and is a CNS stimulant.

🎯 Practice Yourself

🎯Practice Yourself6 questions

Q1
Name the vector of malaria and the stage of the parasite that enters a human when the vector bites.
Q2
What are the two 'B' and 'T' cells of the acquired immune system and where do they mature?
Q3
Give two examples each of drugs classified as opioids, cannabinoids and coca alkaloids.
Q4
Which cells does HIV primarily attack and what does the term AIDS stand for?
Q5
Name any four vaccine-preventable diseases in the Indian immunisation schedule.
Q6
What are proto-oncogenes? How can they cause cancer?

📝 Notes

Human Health and Disease

NCERT Chapter 7 covers common pathogens of India, the working of the immune system, and modern challenges like HIV, cancer and substance abuse.

Common human diseases and their pathogens

| Disease | Pathogen | Vector/mode | |---------|----------|-------------| | Malaria | Plasmodium (protozoan) | Female Anopheles | | Typhoid | Salmonella typhi (bacterium) | Contaminated food/water | | Pneumonia | Streptococcus pneumoniae, Haemophilus influenzae | Droplets | | Common cold | Rhinoviruses | Droplets | | Amoebiasis | Entamoeba histolytica | Contaminated food/water; housefly | | Ascariasis | Ascaris lumbricoides | Contaminated food/water | | Filariasis | Wuchereria (nematode) | Culex mosquito | | Ringworm | Microsporum, Trichophyton, Epidermophyton | Direct contact/fomites |

Levels of defence

Innate immunity (non-specific): physical barriers (skin, mucus), physiological (HCl, saliva), cellular (neutrophils, macrophages, NK cells) and cytokine barriers (interferons).
Acquired immunity (specific): B lymphocytes → antibodies (humoral); T lymphocytes → cell-mediated. Primary response is slow; secondary is rapid and strong because of memory cells.

Antibody = H₂L₂

Y-shaped glycoprotein — two heavy + two light chains, held by disulphide bonds. The variable tips bind antigen; the Fc stem recruits effector functions. Five classes: IgG, IgA, IgM, IgE, IgD.

Active vs passive immunity

Active — host makes its own antibodies after antigen exposure (vaccine or infection). Slow but long-lasting.
Passive — ready-made antibodies transferred (colostrum, anti-venom). Fast but short-lived.

AIDS

Caused by Human Immunodeficiency Virus (HIV) — a retrovirus.
Genome = ssRNA + reverse transcriptase.
Attacks helper T (CD4⁺) cells; on integration as provirus, virus replicates and destroys T-cells.
Diagnosed by ELISA (detects antibodies) confirmed by Western blot.
Treatment: antiretroviral therapy (ART) — cocktails targeting RT, protease and integrase.

Cancer

Loss of contact inhibition → uncontrolled cell proliferation → tumour.
Benign tumours stay local; malignant tumours invade tissues and metastasise via blood/lymph.
Causes: carcinogens (chemicals, ionising radiation, UV), oncogenic viruses.
Detection: biopsy + histopathology, imaging (CT/MRI/PET), tumour marker antibodies.
Treatment: surgery, radiotherapy, chemotherapy, immunotherapy (α-interferons).

Drugs and alcohol abuse

Opioids (heroin, morphine) — bind opioid receptors, depress CNS.
Cannabinoids (marijuana, hashish) — act on cannabinoid receptors.
Coca alkaloids (cocaine, crack) — block dopamine reuptake, stimulate CNS.
Adolescent risk factors: peer pressure, curiosity, stress. Warning signs: falling academic performance, social withdrawal, mood swings.