NCERT Class 12 Biology: Chapter – 8 Human Health and Diseases Part 4 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 3:

Where are B-cells and T-cells formed? How do they differ from each other?


B-cells are formed in bone marrow, while T-cells are formed in thymus. B-cells produce antibodies, while T-cells help B-cells in doing this

Question 4:

Given below are the pairs of pathogens and the diseases caused by them. Which out of these is not a matching pair and why?

Chapter-8- Question -4-Table of the Pairs of Pathogens and the Diseases
(a)VirusCommon cold

Answer: In the above question option ‘c’ is incorrectly matched. As Microsporum is a fungi which causes Ringworms, the disease՚s name is a misnomer as it is caused by fungi and not by worms. The disease Filariasis is caused by an infection caused by roundworms of Filarioidea genus.

Question 5:

What would happen to immune system, if thymus gland is removed from the body of a person?

Answer: Thymus gland is present in front of the sternum between the lungs. This gland is large in size at the time of birth and helps in the maturation of T-lymphocytes. If thymus gland is removed from the body of a person T-lymphocytes would not be able to mature. This would compromise the immune system and the individual would be more susceptible to various diseases.

Question 6:

Many microbial pathogens enter the gut of humans along with food. What are the preventive barriers to protect the body from such pathogens? What type of immunity do you observe in this case?


When we eat food, some microbes also enter our gut along with the food and may cause several diseases. To prevent these microbial pathogens from entering the gut, our body has preventive barriers which are as follows:

1. Lysozome present in saliva

2. Mucous coating on the epithelium lining of the gut.

3. Hydrochloric acid secreted by the parietal cells in the stomach.

This type of immunity is known as Innate Immunity. This immunity provides the body with a defence mechanism in response to the antigens produced in the body when any pathogen enters the body. It includes physical barriers like skin, chemical barriers like HCl, lysozome and immunity cells like T & B lymphocytes. It is present in a person since birth.

Question 7:

Why mother՚s milk is considered the most appropriate food for a new born infant?


Mother՚s milk is considered the most appropriate food for a new born infant because in the initial days the thick yellowish fluid called colostrum is produced. Colostrum has abundant antibodies in it like IgA, IgM & IgG etc. , which boosts the immune system of an infant.

Question 8:

What are interferons? How do interferons check infection of new cells?

Answer: Interferons are a group of natural proteins released by the host cell in the presence of any virus, tumour cells and parasites etc. In classic cases the viral infected cell releases interferon which heightens the antiviral response of the nearby cells.

Interferons check infection of new cells as:

1. Interferons inhibit viral replication within the host cells.

2. Which in turn activates the natural killer cells and macrophages .

3. This increases the presentation of antigens to lymphocytes.

4. Now, these antigens multiply and remove the pathogen.

Question 9:

In the figure, structure of an antibody molecule is shown. Name the parts A, B and C.

Show A, B and C in the diagram.

Chapter-8- Question -9- Structure of an Antibody Molecule


Site A is the constant region for heavy chain.

Site B is the constant region for light chain.

Site C is the variable region of light and heavy chain.

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