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

For a long time, health was understood through the idea of bodily 'humors' being in balance — a view held by early Greek physicians like Hippocrates and by the Indian Ayurvedic tradition alike.

This section introduces the most common infectious diseases that affect humans — their causative agents, modes of transmission, symptoms, and basic preventive measures.

The body’s ability to fight disease-causing organisms is called immunity. This is not a single mechanism but a coordinated system of cells, tissues, and chemical signals that recognise and neutralise…

Innate immunity is the body's first line of defence — it is present from birth and works against any foreign agent, regardless of what it is.

Acquired immunity is fundamentally different from innate immunity. While innate immunity is a general, non-specific defence that works against any invader, acquired immunity is pathogen specific — it…

The body’s immune system can be divided into two broad types based on how immunity is acquired: active immunity and passive immunity.

The immune system has a remarkable property: it remembers. Once your body fights off a pathogen, it keeps a stock of memory B-cells and T-cells that recognise that same invader instantly if it ever re…

When you walk into a new place and start sneezing or wheezing for no obvious reason, only to have the symptoms vanish when you leave — that is a classic allergic reaction.

The immune system of higher vertebrates — including humans — has a remarkable ability: it can tell the difference between the body's own cells (self) and foreign invaders (non-self), such as bacteria,…

The immune system is not a single organ but a distributed network. It includes lymphoid organs, tissues, cells, and soluble molecules like antibodies.

AIDS stands for Acquired Immuno Deficiency Syndrome. The name itself tells you what it is: a deficiency of the immune system that is acquired during a person's lifetime — it is not a congenital (inher…

Cancer is not a single disease but a broad term for a collection of related diseases. In all types of cancer, some of the body’s cells begin to divide without stopping and spread into surrounding tiss…

Health is not just the absence of disease — it is a state of complete physical, mental and social well-being. Drug and alcohol abuse directly attacks all three dimensions.

Adolescence is not just a stretch of years — it is a transition. The word itself means both a period and a process, during which a child matures in attitudes and beliefs, learning to participate effec…

The core idea here is that drugs and alcohol are not just harmful in the moment — they trap the user through two distinct but linked mechanisms: addiction and dependence.

Drug and alcohol abuse does not only harm the person consuming them — the effects ripple outward, damaging relationships, families, and society.

The central idea in preventing drug and alcohol abuse is the old saying: prevention is better than cure.

- Health and its dimensions: Health is a state of complete physical, mental and social well-being, not merely the absence of disease.

Higher-order thinking problems from the NCERT Exemplar.

Questions from official CBSE sample papers.