Immunity (NCERT) - NEET Biology Class 12 Free MCQ Test with solutions

The given figure is a structure of an antibody molecule

Malignant malaria is caused by plasmodium falciparum. The incubation period of plasmodium falciparum is about 12 days. recurrence of fever is after every 48 hours. Active immunity is developed when the person's own cells produce antibodies in response to infection.it is slow and takes time to give its full effective response. Saliva in the mouth acts as physiological barrier for pathogens. it contains lysozyme that attacks bacteria and dissolves their cells walls.

Innate immunity is the type of immunity that is present in the organism by birth. Acquired immunity is the immunity that an individual acquires during life. B-lymphocytes are involved in acquired immunity and produce antibodies.

vaccination refers to the administration of a vaccine or toxoid, while immunisation is the process by which the body produces antibodies against the vaccine preventable diseases through administration of specific vaccines. Polio, tetnus, diphtheria and pneumonia have been controlled by vaccines and immunisation

Skin and mucous membrane are the physical barriers that provide the first line of defence or the external defence. These barriers prevent the entry of microorganisms into the body. Outer tough layer of the skin, the stratumm corneum prevents the entry of bacteria and viruses. Mucus secreted by mucous membrane traps the microorganisms and immobilises them.

Antibodies are immunoglobulins produced in response to antigenic stimulation. An antibody is made up of four peptide chains. Of the four chains, there are two long chains, called heavy chains and two short chains called light chains.

Hepatitis B vaccine is produced from transgenic yeast by recombinant DNA technology. It is the first commercially available human vaccine that is produced by the genetic engineering technology.

The substances to which an exaggerated response of the immune system occurs are called allergens. The antibodies produced to these are of IgE type.

Antibodies are immunoglobulins which are produced in response to antigenic stimulation. Antibodies are produced by B-lymphocytes. Antibodies direct the antibody-mediated immunity

Primary immune response is produced by the initial contact of an animal with an antigen. It takes relatively longer time, is of low intensity and declines rapidly.

Humoral immunity consists of antibodies that circulate in the blood and lymph. B-lyphocytes produce antibodies that regulate humoral immunity.

Acquired immunity is the type of immunity acquired during life time. Both cell-mediated immunity (mediated by T-cells) and humoral immunity (mediated by B-cells) are responsible for acquired immunity. Acquired immunity is characterised by memory. This means that when our body encounters a pathogen for the first time, it produces a response called primary response which is of low intensity. Active immunity and passive immunity are types of acquired immunity. Polymorphonuclear leucocytes and natural killer cells are involved in innate immunity. These cells phagocytose and destroy microbes.

 The spleen is a secondary lymphoid organ, not a primary one, which makes statement (iii) incorrect. However, the spleen does primarily contain lymphocytes and phagocytes, acts as a reservoir of erythrocytes, and functions as a filter for blood-borne microorganisms. Therefore, statements (i), (ii), and (iv) are correct.

Macrophages are large phagocytic cells that play a crucial role in the immune system. They are responsible for engulfing and digesting invading microorganisms. Unlike epithelial cells, which produce mucus, macrophages focus on defending the body against pathogens.

• Phagocytic cells: These cells can ingest and destroy harmful invaders.
• Function: Macrophages help to protect the body by eliminating bacteria and viruses.
• Comparison: Epithelial cells secrete mucus, while macrophages actively digest pathogens.

If the immune system fails to recognize 'self from non-self and starts destroying the body's own cells, this leads to some malfunctions, which are termed as autoimmune diseases. Both rheumatoid arthritis and myasthenia gravis are autoimmune diseases. In rheumatoid arthritis, inflammation of the synovial membrane in synovial joints occurs. When this membrane, which is the source of synovial fluid, becomes inflamed, it produces too much fluid. Thus, the joints swell and become extremely painful. Myasthenia gravis is a chronic disease marked by abnormal fatigability and weakness of selected muscles. The degree of fatigue is so extreme that these muscles are temporarily paralysed. In this disease, antibodies bind to cholinergic receptors on muscle cells, which impairs the ability of the neurotransmitter acetylcholine to induce muscle contraction.

Diabetes mellitus (type-l) and rheumatic fever are the auto-immune diseases of B-cells of pancreas and heart cells respectively.

Transfer of immune products like antibodies and immunoglobulins to a recipient is called passive immunity. Colostrum, a yellowish milk secreted by mother during the initial days of lactation has abundant antibodies to protect the infant. In tetanus, we need to directly inject the preformed antibodies or antitoxin (a preparation containing antibodies to the toxin). These both are examples of passive immunity.

The process of introduction of vaccine into an individual to provide protection against a disease is called vaccination. Vaccine is a preparation or extract of an inactivated/ attenuated (weakened) pathogen of a disease which on inoculation into a healthy person provides immunity by inducing antibodies production.

IgG is the only maternal immunoglobulin that can cross the placenta and provide natural passive immunity to the fetus. IgG is the most abundant class of immunoglobulins in the body constituting 75% of the lgs.

Allergy is the hypersentivensess of a person to some foreign substance coming in contact with or entering the body. Allergy involvers mainly lgE antibodies and histamine. Histamine is released by mast cells. Mast cells are large cells present in the connective tissue. Their granules contain chemicals heparin, histamine and serotonin which are released during allergic and inflammatory response.

'A'-lymph nodes, 'B'-Thymus, 'C'-spleen, 'D'-Bone marrow. Thymus and bone marrow are the primary lymphoid organs where maturation of T-cells and B-cells take place respectively. Lymph nodes and spleen are the secondary lymphoid organs where T-cells and B-cells undergo proliferation and differentiation.

Thymus is a soft, pinkish, bilobed mass of lymphoid tissue. It is a prominent gland at the time of birth but it gradually atrophies in the adult. It secretes a hormone thymosin that is involved in producing immunity. It also acts as a primary lymphoid organ where T-cells mature

Mucous membrane lining the respiratory, gastrointestinal and uriogenital tracts helps in trapping the microbes and constitute physical barriers of our body.

When a host is exposed to antigens, which may be in the form of living or dead microbes or other proteins, antibodies are produced in the host body. This type of immunity is called active immunity. Injecting the microbes deliberately during immunisation/vaccination induces active immunity e.g., polio vaccine

Antibodies are made up of four polypeptide chains two heavy and two light chains. Light and heavy chains are subdivided into variable and constant regions. The variable portion is used for binding to antigen and a constant portion determines its adherence and diffusivity.