Summary

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

The immune system rests on the antigen-antibody partnership: antigens are foreign substances the body recognises as a threat, and antibodies are the specific proteins the immune system makes to neutralise them. Innate immunity provides a fast, non-specific first line of defence through physical, physiological, cellular, and cytokine barriers, present from birth. Acquired immunity, mediated by B- and T-lymphocytes, is specific to each pathogen and — thanks to memory cells — becomes stronger and faster on repeat exposure. Immunity itself may be active (the body makes its own antibodies, either after natural infection or after vaccination) or passive (ready-made antibodies are received from an outside source, such as a mother or an antitoxin injection); vaccination exploits immunological memory to protect people without ever making them go through the disease itself, and, at a population level, produces herd immunity.

The chapter then covered eleven named diseases caused by pathogens, spanning protozoans (malaria, amoebiasis), helminth worms (filariasis, ascariasis), viruses (dengue, chikungunya, common cold, SARS/COVID-19), bacteria (typhoid, pneumonia), and a fungus (ringworm) — each with its own causative agent, mode of transmission, symptoms, and preventive measures, consolidated in the summary table in section 7.7.

Beyond infectious disease, the chapter examined conditions where the immune system itself misfires — allergy, where an overactive response to a harmless allergen produces symptoms through histamine release, and autoimmune disorders such as rheumatoid arthritis, where the immune system mistakenly attacks the body's own tissue. It examined cancer, the uncontrolled and abnormal division of cells, and the methods used to detect and treat it, and HIV and AIDS, where a specific retrovirus progressively destroys the helper T-lymphocytes central to acquired immunity. …