CBSE Class 12 Biology Chapter 8 Revision Notes Part 1

Chapter 8: Human Health and Diseases Revision Notes Part 1

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Multiple Choice Questions

  1. During an allergic response _________ antibody is generated.

  2. Which of these is an example of a congenital disease? _________

  3. __________ is a primary lymphoid organ.

  4. _______ is used to make the Hepatitis B vaccine.

  5. An infection disease spread from one person to another is also known as ____________

Reproductive Health

  • Health entails disease-free living and physical fitness.

  • Health is dependent on a few factors, and some of them are listed below:

    i. Genetic diseases that are inherited often affect an individual’s potential health ii. Microbes or other creatures that cause disease iii. Lifestyle choices – includes the foods and beverages we consume, physical activity levels, and sleep patterns

Disease types

There are two sorts of diseases: infectious and non-infectious.

Congenital diseases

  • Genetic disorders present at birth are known as congenital diseases.
  • This might result from a gene mutation, chromosomal abnormality, or environmental factors.
  • Defects in the chromosome and genes are passed on to the following generation.
  • Haemophilia, color blindness, Down syndrome, Turner’s syndrome, and other conditions are examples.

Acquired diseases

Diseases acquired during a lifetime are acquired diseases.

  1. Communicable: An infectious sickness is spread from one person to another.
  2. Non-communicable: Illness does not spread by infection.
  3. Deficiency disease: Anemia, kwashiorkor, beriberi, diabetes, and other deficiencies are caused by a lack of a key vitamin, enzyme, or hormone.
  4. Allergies: are a type of hypersensitivity to external particles such as pollen and dust.

Immunity and Related Disorders

  • Immunity refers to the body’s ability to defend itself against pathogens and other objects.
  • The immune system protects our bodies against infection.

Immunity can be divided into different categories:

Innate immunity

The immunity that is present from birth is known as innate immunity. There are four sorts of barriers in the human body’s defense mechanism.

  • Skin and mucous covering of respiratory, gastrointestinal, and urinary tract epithelial linings are physical barriers.
  • Saliva, tears, or stomach acid act as physiological barriers.
  • Neutrophils, monocytes, and natural killer lymphocytes are cellular barriers.
  • Interferons released by virus-infected cells form cytokine barriers.

Acquired immunity

Acquired immunity is pathogen-specific immunity that we develop throughout our lives.

  • After the initial interaction with a virus, the low-intensity primary reaction kicks in.
  • Due to the memory of the initial reaction, a recurrent infection causes a substantially increased secondary response or anamnestic response.
  • B-lymphocytes produce antibodies in response to foreign antigens.
  • Antibodies (H2L2) are Y-shaped protein molecules with two light and two heavy peptide strands.


Source: Antibodies

  • Humans have five different forms of antibodies or immunoglobulins: IgG, IgM, IgD, IgA, and IgE.
  • IgG is the most prevalent antibody in the blood, and it defends a fetus while its immunity builds.
  • IgA is plentiful in breast milk and colostrum, the yellowish fluid released at the beginning of breastfeeding.
  • IgE has a role in allergic reactions.
  • The humoral immune response is an antibody-mediated reaction.
  • Cell-mediated response, or CMI, is regulated by T-lymphocytes.
  • After transplantation, the cell-mediated response is crucial for discriminating among self and non-self and graft rejection.

Active immunity

  • Antibodies are created in the host’s body in response to antigen, and it takes time to respond effectively.
  • Vaccination, which involves injecting an attenuated pathogen, is an example of active immunity.

Types of Immunity


Passive immunity

  • Passive immunity is defined as providing pre-made antibodies to elicit a rapid response against a disease.
  • Passive immunization is achieved by injecting antitoxin for snakebite, including antibodies against the venom.
  • The use of recombinant DNA technology has aided in large-scale manufacturing vaccines. For example, yeast is used to make the hepatitis B vaccine.


  • Pollens, dust, mites, and other environmental antigens elicit an exaggerated immunological response.
  • During an allergic response, the IgE antibody is generated.
  • During an allergic response, the mast cell produces histamine and serotonin.
  • Antihistamines, adrenaline, and steroids all help to alleviate allergy symptoms.




  • Auto-immune illness occurs when the body attacks its own cells.
  • Rheumatoid arthritis is an autoimmune disease that affects the body’s immune system.

Autoimmune Diseases


Immune system: Lymphoid organs

  • The lymphoid organs, cells, and antibodies make up the human immune system.
  • Bone marrow and thymus are the primary lymphoid organs.
  • Lymphocytes grow, mature, and differentiate into antigen-specific lymphocytes in this area.
  • Spleen, lymph nodes, tonsils, Peyer’s patches in the small intestine, and appendix are secondary lymphoid organs.
  • These are the antigen-reaction sites, and following proliferation, they become effector cells.
  • The spleen functions as a blood filter. Lymphocytes and phagocytes are present, as well as a considerable number of erythrocytes.
  • Antigens in the lymph or tissue fluid are trapped in lymph nodes.
  • MALT (mucosa-associated lymphoid tissue): the mucosal lining of the respiratory, urinary, and digestive tracts accounts for half of all lymphoid tissues in the body.

Lymphatic System

Source: Lymphatic system

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