Chapter 7 - Human Health and Disease

Human Health and Disease explains the causes, transmission, prevention and biological effects of major human diseases. NCERT Class 12 Biology Chapter 7 also covers innate and acquired immunity, vaccination, allergies, autoimmunity, AIDS, cancer and substance misuse.

Teachoo’s chapter category organises diseases by pathogen, transmission, symptoms and prevention while explaining immune-system mechanisms. It includes NCERT solutions, disease tables, diagrams, important questions, case-based questions and NEET MCQs.

Health, pathogens and infectious disease

Health is a state of physical, mental and social well-being. Genetics, infection, lifestyle and environmental conditions can influence health. Disease-causing organisms include bacteria, viruses, protozoans, helminths and fungi.

The chapter examines important diseases such as:

• Typhoid

• Pneumonia

• Common cold

• Malaria

• Amoebiasis

• Ascariasis

• Filariasis

• Ringworm

Students should identify the causative organism, transmission route, major symptoms, vector or carrier where applicable and preventive measures.

The life cycle of Plasmodium is especially important. The parasite alternates between humans and female Anopheles mosquitoes. Liver cells and red blood cells are involved in the human phase, while the mosquito acts as both host and vector.

Innate immunity

Innate immunity is non-specific and present from birth. Its barriers include:

• Physical barriers such as skin and mucus

• Physiological barriers such as stomach acid and lysozyme

• Cellular barriers involving immune cells

• Cytokine barriers such as interferons

Students should connect each example to the appropriate barrier category.

Acquired immunity

Acquired immunity is specific and develops memory. The primary response occurs on first exposure, while subsequent exposure produces a faster and stronger secondary response.

B lymphocytes participate in antibody-mediated or humoral immunity. T lymphocytes contribute to cell-mediated immunity. Antibodies contain heavy and light chains and possess antigen-binding regions.

Active immunity develops when a person’s immune system responds to an antigen, as in infection or vaccination. Passive immunity results from receiving ready-made antibodies, as in maternal antibodies transferred to a baby.

Vaccination exposes the immune system to antigenic material safely enough to develop memory. Secondary immune responses then provide faster protection during later exposure.

Allergy and autoimmunity

Allergy is an exaggerated immune response to normally harmless environmental substances. Allergens can stimulate antibody-mediated responses and release of inflammatory chemicals.

In autoimmunity, the immune system reacts against the body’s own components. Students should not confuse allergy, autoimmunity and immunodeficiency.

AIDS

AIDS is caused by the human immunodeficiency virus. HIV is a retrovirus that infects important immune cells and progressively weakens cell-mediated immunity.

Transmission can occur through infected blood, shared contaminated needles, unprotected sexual exposure and mother-to-child transmission. It does not spread through ordinary social contact.

The chapter explains viral replication involving reverse transcription and the progressive loss of immune function. Prevention depends on safe behaviour, screened blood, sterile equipment, education and timely testing.

Cancer

Cancer results from uncontrolled cell proliferation and loss of normal growth regulation. Benign tumours remain localised, while malignant tumours invade surrounding tissues and may spread through metastasis.

Carcinogens may be physical, chemical or biological. Oncogenes and changes in growth-regulating genes contribute to transformation. Detection and treatment may involve imaging, biopsy, surgery, radiation, chemotherapy and immunological approaches.

Drugs and alcohol misuse

The chapter discusses opioids, cannabinoids, coca alkaloids and other psychoactive substances, along with dependence and harmful effects. Adolescents may be particularly vulnerable to experimentation, peer pressure and misinformation.

Prevention includes education, family and social support, professional counselling, early recognition and medical help. The aim is not moral labelling but evidence-based prevention and treatment.

Important diagrams and tables

• Plasmodium life cycle

• Antibody structure

• Primary and secondary immune response

• HIV replication

• Normal cells versus tumour growth

• Disease–pathogen–transmission comparison table

Why is this chapter important?

CBSE frequently asks case-based disease and immunity questions. NEET tests pathogens, vectors, immune cells, antibodies, AIDS, cancer, drugs and exact NCERT examples.

How should students study this chapter?

Create one disease table with pathogen, transmission, symptoms and prevention. Create another table comparing innate immunity, acquired immunity, active immunity, passive immunity, humoral immunity and cell-mediated immunity. Use flowcharts for Plasmodium and HIV.

Frequently Asked Questions

What is the difference between innate and acquired immunity?

Innate immunity is non-specific and present from birth. Acquired immunity is antigen-specific and develops memory after exposure.

Why is the secondary immune response stronger?

Memory cells formed during the primary response react rapidly and produce a stronger response upon re-exposure.

Is a mosquito that transmits malaria only a vector?

The female Anopheles mosquito is both a vector and a host because part of the parasite’s development occurs inside it.

Does HIV spread through touching or sharing food?

No. HIV does not spread through ordinary touch, social contact or sharing food.

What is metastasis?

Metastasis is the spread of malignant cancer cells from the original tumour to distant tissues or organs.

How should students remember disease examples?

Group them by pathogen type—bacterial, viral, protozoan, helminthic and fungal—and then attach transmission and symptoms to each.