Class XII Biology Lecture Notes

1. HUMAN HEALTH & DISEASES L04
Immunity:
It is the ability of an organism to resist or defend itself from the development of a disease.
Types of Immunity:
1. Innate immunity:
 It is present from the birth and is inherited from the parents.
 It is non-specific.
 It consists of the following barriers:
a. Physical barriers
They are barriers which do not allow the entry of pathogens and other foreign
agents into the body. Eg. Skin, mucous membranes of digestive tract, respiratory
tract and urogenital tracts.
b. Physiological barriers:
Sweat, tears, acid in the stomach, saliva help to prevent microbial growth.
c. Cellular barriers:
WBCs (PMNL and monocytes, NK lymphocytes) and macrophages can phagocytose
and destroy microbes.
d. Cytokine barriers:
Interferons produced by virus infected cells protect non-infected cells from further
viral infections.
2. Acquired Immunity:
 It is not present from the birth but acquired by either contracting the disease or by
vaccination.
 It is pathogen specific.
 Has the ability to distinguish among various types of foreign molecules or antigens.
 When the immune system encounters a pathogen for the first time, produces a
response called a primary response and memory of this encounter with the same
pathogen produces antibodies immediately to counter it.

2.  The primary and secondary immune responses are carried out with the help of B and T
lymphocytes.
 B-lymphocytes produce specialized proteins called as antibodies.
 These antibodies are found in the blood and the lymph, the response is thus called
humoral antibody mediated immunity (AMI).
 T-lymphocytes are responsible for cellular immunity and it is called cell-mediated
immunity (CMI).
 T-cells do not produce antibodies but help B-cells to produce it.
 T-cells are of three types: Killer/ helper/ suppressor cells.
Antibodies:
 The antibodies are protein molecules called immunoglobulins (Igs) and are of various types like
IgA, IgM, IgE, IgG, IgD etc.
 Each antibody molecule consists of four polypeptide chains, two are long called heavy chain (H-
chain) while the other two are short called light (L) chains. Both are arranged together in the
shape of an Y, hence, antibody can be represented as H2L2.

3. MCQs
1. The substance produced by a cell in viral infection that can protect other cells from further
infection is:
A. Serotonin
B. Colostrum
C. Interferon
D. Histamine
2. Transplantation of tissues/organs to save certain patients often fails due to rejection. Which
type of immune response is responsible for such rejections?
a. Auto-immune response
b. Humoral immune response
c. Physiological immune response
d. Cell-mediated immune response.
3. Antibodies present in colostrum which protect the new born from certain diseases is of
a. IgG type
b. IgA type
c. IgD type
d. IgE type
4. Hemozoin is?
a. Precursor to hemoglobin
b. Toxin from Streptococcus
c. Toxin from Plasmodium sp.
d. Toxin from Haemophilus sp.
5. One of the following is not the causal organism of ringworm
a. Microsporum
b. Trichophyton
c. Epidermophyton
d. Macrosporum
Descriptive type questions
1. Pathogens are tissue/organ specific. Justify the statement with suitable examples.
2. What are interferons? How do interferons check infection of new cells?
3. Why is an antibody molecule represented as H2L2?
4. Explain “memory of the immune system”.
5. For an organ transplant, it is advised to have identical twins. WHY?