Home › Biology Class 12 › Human Health and Disease
Human Health and Disease
Biology · Class 12NCERT pp. 127–1472 sets × 25 questions
Key facts and formulas for Human Health and Disease, three worked sample questions, and two full practice sets. Every question has a hint, a reason for every option and a step-by-step solution, with a calculator or animation where one helps. English and Hinglish.
Key facts for this chapter
| Idea | Rule or fact |
|---|
| Health | Complete physical, mental and social well-being, not just absence of disease |
| Innate barriers | Physical (skin), physiological (acid, saliva, tears), cellular (NK cells), cytokine (interferon) |
| Lymphoid organs | Primary: bone marrow, thymus. Secondary: spleen, lymph nodes, tonsils, Peyer's patches, appendix |
| Antibody | H2L2, made by B-cells. IgG crosses placenta, IgA in colostrum, IgE in allergy, IgM first response |
| Active vs passive | Active: body makes antibodies (infection, vaccine). Passive: ready-made (colostrum, anti-venom, serum) |
| Malaria | Female Anopheles injects sporozoites, liver first, then RBCs. Haemozoin causes fever. P. malariae: 72 h |
| Vectors | Culex: filariasis. Aedes: dengue. Tsetse: sleeping sickness. Sandfly: kala-azar |
| HIV | RNA retrovirus, infects CD4 cells (macrophages, helper T-cells). ELISA screens, Western blot confirms, AZT blocks reverse transcriptase |
| Cancer | Loss of contact inhibition. Carcinoma: epithelium. Sarcoma: connective tissue. p53 is a tumour suppressor |
| Drugs | Heroin = acetylation of morphine (Papaver), depressant. Cocaine: Erythroxylum. Marijuana: Cannabis. LSD: ergot fungus |
Three sample questions
Q1. Which of the following best describes health?
- Absence of infection and disease
- A state of complete physical, mental and social well-being
- Freedom from genetic defects and good appetite
- Physical fitness and absence of stress
Hint and solution
Hint: Health has more than one dimension. Think of the three levels named by the World Health Organization.
- Health = physical + mental + social well-being — Health is not just absence of disease. It has three dimensions that must all be good.
- Option A, C, D cover only one or two levels — Option A talks only of disease, C of genes and appetite, D of fitness and stress. Each misses at least one level.
- All three levels together: Option B — Only option B names physical, mental and social well-being together. So the answer is Option B.
Answer: B. Health is not only the absence of disease or physical fitness; all three levels must be complete.
Q2. The 'good humor' hypothesis of health was discarded mainly because
- antibiotics were discovered
- vaccines were developed
- pathogens were seen under the microscope
- William Harvey's experiments showed blood circulation and thermometers showed normal temperature in 'blackbile' persons
Hint and solution
Hint: A hypothesis is dropped when experiments contradict it. Which option names experimental evidence?
- Good humor idea: body fluids decide health — Ancient belief said health depends on balance of four fluids, such as blood and black bile.
- Experiments tested the idea — William Harvey showed that blood circulates. Thermometers showed that 'blackbile' persons had normal body temperature.
- Evidence replaced speculation — This evidence contradicted the hypothesis, so it was discarded. Option D.
Answer: D. Evidence from experiments replaced speculation.
Q3. Choose the correct statement.
I. Cancer is the major cause of death among non-infectious diseases.
II. AIDS is an infectious disease.
III. Mental state cannot influence health.
- I and II only
- II and III only
- I and III only
- I, II and III
Hint and solution
Hint: Check each statement alone. One of them denies the mind-body link, which is known to exist.
- Statement I: cancer is the major non-infectious killer — Cancer is the major cause of death among non-infectious diseases. So I is true.
- Statement II: AIDS is infectious — AIDS is caused by HIV and spreads from person to person. So II is true.
- Statement III is false — Mental state affects the immune system through the neural and endocrine systems, so III is false. Only I and II are true. Option A.
Answer: A. The mind acts on the immune system through the neural and endocrine systems, so III is wrong.
How to use this chapter
Read the NCERT pages first, then attempt Set 1 without the hints. Note every wrong answer in a mistake list, read the reason for each option, and retry Set 2 two days later. A topic is solid when you can say why each wrong option is wrong.