Why is it that during changing weather, one is advised to avoid closed, crowded and air conditioned places like cinema halls, etc.?
OR
(a) It is generally observed that the children who had suffered from chickenpox in their childhood may not contract the same disease in their adulthood. Explain giving reasons the basis of such immunity in an individual. Name this kind of immunity.
(b) What are Interferons? Mention their role.

Shift in temperatures is a common observation as the seasons change. This phenomenon is ideal for different groups of viruses to flourish, which then spread contagious diseases. The moisture in air-conditioned and closed spaces is another favorable factor for the growth of many pathogens. With more people living in dense conditions (crowding), there is more frequent contact between more individuals, allowing disease transmission to easily occur. Air-borne infections spread when an infected person talks, coughs or sneezes and the small droplets they produce contain pathogens. The droplets travel a short distance before falling. The droplets may be breathed in by people who are near, or may fall and contaminate an object or surface. Incidence of infections which spread by contact also raise in crowded areas. It is a common observation that many people suffer from common cold and flu during changing seasons. This is the reason why one is advised to avoid crowded places like cinema halls or air conditioned places during changing seasons.

OR

(a) A child who suffered from chickenpox develops immunity against the chickenpox. During the first attack by the virus, the body develops memory cells. Memory B- and T-cells recognise
the pathogen quickly on subsequent exposure and overwhelm the invaders with a massive production of antibodies. This is highly intense and fast secondary immune response. It is a naturally acquired active immunity.
(b) Interferons are proteins that are secreted by virus infected cells which protect the healthy cells from the virus attack.