NCERT Solutions for Class 12 Biology Chapter 7 Human Health and Disease

Short Note:

• Diseases can be caused by pathogens such as bacteria (e.g. typhoid, pneumonia), viruses (e.g. common cold), protozoans (e.g. malaria caused by Plasmodium, transmitted by female Anopheles mosquitoes), and helminths (e.g. ascariasis, elephantiasis).

• Understanding the mode of transmission (airborne, waterborne, vector-borne) and life cycle of pathogens is essential for designing effective prevention and control strategies, such as vaccination, sanitation, and vector control.

Short Note:

• The human immune system provides innate immunity (non-specific, present from birth, including physical barriers, phagocytic cells) and acquired immunity (specific, pathogen-directed, and possessing memory).

• Acquired immunity can be active (antibodies produced by the individual's own immune system, as in natural infection or vaccination) or passive (ready-made antibodies given directly, as in a mother's antibodies passed to a baby through breast milk).

Short Note:

• AIDS (Acquired Immuno Deficiency Syndrome) is caused by the Human Immunodeficiency Virus (HIV), which attacks and destroys helper T-lymphocytes, severely weakening the immune system and making the body vulnerable to opportunistic infections.

• Cancer results from uncontrolled cell division caused by genetic mutations affecting proto-oncogenes and tumour suppressor genes; cancer cells can invade surrounding tissue and, in malignant cases, spread to other parts of the body through metastasis.

Short Note:

• Drug and alcohol abuse refers to the use of substances that lead to adverse effects on the individual's physical, mental and social wellbeing, often resulting in addiction and dependence.

• Commonly abused substances include opioids, cannabinoids, and coca alkaloids (like cocaine), and preventive measures include avoiding peer pressure, seeking professional counselling, and being aware of warning signs of substance abuse.