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Which of the following is not a part of non-specific defence?
(A) Mucous membrane
(B) Phagocytosis
(C) Lysozyme
(D) Killer T-cells

Last updated date: 13th Jun 2024
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Hint: Immune response is how our body recognizes and defends itself against bacteria, viruses and other foreign particles. There are two types of immune responses, namely, specific and non-specific. Non-specific immunity protects the body of the individual against all antigens, irrespective of the nature of the pathogen. Specific immunity is where specific antibodies or cells are produced internally in order to defend that particular pathogen.

Complete answer:
Immunity refers to the ability of an individual organism to resist against any kind of pathogens or foreign particles. There are two types of immune responses. They are specific (acquired) immunity and non-specific (innate) respectively.

Non- specific immunity or innate immunity refers to protection of the body against all the foreign particles irrespective of their nature. It provides the first and second line of defence. First line of defence includes physical barriers and chemical barriers. Physical barriers include mucous membrane, skin, etc. Whereas, chemical barriers refers to oil, sweat, lysozyme and HCl secretion. After a pathogen or antigen escapes the first line of defence, it is now defended by the second line of defence. Second line of defence includes inflammatory response, complement system, production of interferon and phagocytosis.

Specific immunity or acquired immunity refers to production of cells and antibodies against specific antigens. It provides a third cell of defence. It includes cell mediated and antibody mediated immunity. Humoral or antibody mediated immunity refers to the production of antibodies by B-lymphocytes. While, cell mediated immunity refers to the involvement of T-lymphocytes to attack viruses and cancerous cells.

Understanding the options one by one,
(A) Mucous membrane – It is one of the physical barriers which provides protection against all kinds of infection in general. It is a type of non-specific immunity. This is not the correct answer.
(B) Phagocytosis – It is the process of cell-eating by neutrophils and monocytes. It is non-specific in nature and it is present from birth. This is not the correct answer.
(C) Lysozyme – Enzyme which has the ability to lyse the bacterial cell wall. It is found in body secretions like tears and saliva. Hence, this is not the correct answer.
(D) Killer T-cells – They are a part of acquired immunity. They are involved in the body's third line of defence. And, hence they are not a part of non-specific defence.

Therefore, the correct answer is option (D)

Note:It is important to remember the different types of plant, their characteristic features and examples. Majority of the lower plants (algae) reproduce vegetatively, asexually and sexually. It is essential to understand the varied types of spores, gametes (motile and non-motile) produced by the lower plants.