(a) If a patient is advised anti-retroviral drug, name the possible infection he/she is likely to be suffering from. Name the causative organism.
(b) How do vaccines prevent subsequent microbial infection by the same pathogen?
(c) How does a cancerous cell differ from a normal cell?
(d) Many microbial pathogens enter the gut of humans along with food. Name the physiological barrier that protects the body from such pathogens.

Explanation

(a) AIDS caused by the Human Immuno deficiency Virus
(b) Vaccines prevent microbial infections by initiating production of antibodies against these antigens to neutralise the pathogenic agents during later actual infection. (1/2) The vaccines also generate memory – B and T-cells that recognize the pathogen quickly on subsequent exposure. (1/2)
(c) Normal cells show a property called contact inhibition by virtue of which contact with other cells inhibits their uncontrolled growth. Cancer cells appear to have lost this property.(1) These cells grow very rapidly, invading and damaging the surrounding normal tissues. Cells sloughed from such tumors reach distant sites through blood, and wherever they get lodged in the body, they start a new tumor there. This property called metastasis. (1)