Class XII Biology Lecture Notes

1. HUMAN HEALTH & DISEASES L06
AIDS (Acquired Immuno Deficiency Syndrome)
 It was first reported in USA in 1981.
 It is caused by the Human Immunodeficiency Virus (HIV) which is a retrovirus having
envelope enclosing a RNA genome.
 Transmission:
i. Sexual contact with infected person.
ii. By transfusion of contaminated blood and blood particles.
iii. By sharing infected needles.
iv. From infected mother to her child through the placenta.
 High risk individuals:
i. Those having multiple sexual partners.
ii. Drug addicts taking drug intravenously.
iii. Individuals who require repeated blood transfusion.
iv. Children born to HIV infected mother.
 Life cycle of HIV
 After getting into the body of a person, the virus enters into macrophages, where
RNA replicates and form viral DNA by the help of an enzyme called as Reverse
Transctiptase.
 The viral DNA gets incorporated into the host cell’s DNA and directs the infected
cells to produce viruses.
 The macrophages continue to produce virus that enters the helper T-
lymphocytes.
 Thus, the number of helper T-lymphocytes progressively decreases in the body of
the infected persons.
 Thus, the person suffers from various pathogen like Mycobacterium, Viruses and
parasites like Toxoplasma.
 Diagnosis: Enzyme Linked Immuno Sorbent Assay (ELISA)
 Prevention of AIDS
i. NACO established in 1991 and other non-governmental organizations (NGOs) are
trying to educate people about AIDS.
ii. WHO has started a number of programs to prevent the spread of HIV infection.
iii. HIV free blood in the blood banks.
iv. Controlling drug abuse.
v. Advocating safe sex and promoting regular check-ups.
 Treatment of AIDS
i. Cichoric acid from green coffee beans prevent multiplication of HIV in human
body.

2. ii. Vaccines for preventing spread of HIV is also under preparation.
iii. Anti-retrovirals.
Descriptive questions
1. Name the two major group of cells required for attaining specific immunity. [CBSE
2005]
2. Name and explain the type of barriers of innate immunity when some cells releases
interferons when injected. [CBSE 2007]
3. A person has been diagnosed to be HIV+
i. Name the diagnostic test the patient has undergone.
ii. Write the full name of the pathogen involved and describe its structure.
iii. Which particular cells of this person are likely to get destroyed? [CBSE 2006]
4. What is the mechanism by which the AIDS virus causes deficiency in the immune
system of an infected person? [NCERT]
5. What is ELISA?