Ch 13 explores why we fall ill — the difference between being healthy and disease-free, causes of disease, how infectious diseases spread, and the role of the immune system and prevention.
Health is a state of complete physical, mental, and social well-being (WHO). Disease means "dis-ease" — disturbed ease. Acute diseases: short-lived (common cold, diarrhoea). Chronic diseases: last long (TB, diabetes). Infectious: caused by microorganisms and can spread. Non-infectious: caused by internal factors (cancer, allergies).
Caused by: bacteria (TB, typhoid), viruses (cold, COVID, AIDS), fungi (skin infections), protozoa (malaria, kala-azar). Spread through: air (droplets — TB, cold), water/food (contaminated — cholera, typhoid), contact (skin — ringworm), vectors (mosquito → malaria/dengue, fly → cholera).
First line: barriers (skin, mucus, HCl in stomach). Immune system: WBCs identify and fight pathogens. Vaccination: introducing weakened/dead pathogens to train immunity without causing disease. Public health: clean water supply, sanitation, hygiene, awareness campaigns, isolation of infected.
Download: https://ncert.nic.in/textbook/pdf/iesc113.pdf | Complete book: https://ncert.nic.in/textbook/pdf/iesc1ps.zip
Antibiotics block biochemical pathways important for bacteria (e.g., cell wall synthesis) without affecting human cells. They can kill bacteria or prevent them from reproducing. Antibiotics do NOT work against viruses because viruses live inside host cells and have different biochemistry.
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