Ch 7Human Health and Diseases — Class 12 Biology, concept-first.

Health is far more than simply "not being sick" — the World Health Organization defines it as a state of complete physical, mental, and social well-being.

Innate immunity is the body's built-in, non-specific system of defence. It is called "innate" because a person is born with it, and unlike acquired immunity it does not need any prior contact with a p…

Where innate immunity treats every threat in roughly the same way, acquired immunity (also called adaptive or specific immunity) is tailor-made for each individual pathogen the body meets, and — most…

An antigen-antibody reaction is what happens the moment a matching antibody finds its target antigen. Because each antibody's binding site has a shape that complements one particular epitope on an ant…

Depending on how the antibodies protecting a person actually came to be present in their body, immunity is classified into two broad kinds: active immunity and passive immunity.

Vaccination puts the immune system's memory (section 7.3) to work before a person is ever exposed to a real, disease-causing pathogen.

A large share of the disease burden covered in the WBCHSE syllabus for this chapter comes from parasites — organisms, either single-celled protozoans or multicellular worms, that live in or on a human…

Dengue and chikungunya are grouped together in this section because they share the same vector — the day-biting Aedes aegypti mosquito — even though they are caused by two entirely different viruses a…

Typhoid and pneumonia are two important human diseases caused by bacteria, but they differ sharply in how they spread and which part of the body they primarily affect.

This section covers two viral diseases of the respiratory tract that differ enormously in severity — the everyday common cold, and SARS (COVID-19), a disease that became a defining global health event…

Ringworm is one of the most common skin infections encountered in a hot, humid climate such as that of West Bengal, and despite its name, it has nothing to do with any worm at all — it is a fungal inf…

An allergy is what happens when the immune system responds to a substance that is, for most people, entirely harmless, as though it were a dangerous invader.

The immune system normally relies on a careful ability to distinguish the body's own cells and molecules ("self") from anything foreign ("non-self"), attacking only the latter.

Cancer is not one single disease but a large group of diseases that share one defining feature: the uncontrolled and abnormal division of cells.

HIV, the Human Immunodeficiency Virus, is a retrovirus — meaning its genetic material is RNA rather than DNA, and it carries a special enzyme, reverse transcriptase, that lets it convert its RNA into…

Adolescence, roughly the second decade of life, is a period of rapid physical growth, emotional development, and social change, as a young person moves from childhood towards adulthood.

This chapter surveyed how the human body defends itself and the major diseases named in the WBCHSE syllabus for Chapter 7.

Sample papers and previous-year board questions for this subject.