Answer:
(a) Pneumonia and common cold are two airborne diseases.
Spreading of disease-causing microbes occurs through the
little droplets thrown out by an infected person who sneezes or coughs. Someone
standing close by can breathe in these droplets and microbes get a chance to
start new infection.
(b) HIV virus (AIDS) spread among human beings by
following ways
(i) Through transfusion of blood contaminated with HIV
virus.
(ii) Infected mother can transmit the virus to her child
during pregnancy or during birth.
(ii) Through sexual contact with an infected person.
(c) When infectious microbes enter into our body, then
body's immune system get activated in response to infection. An active immune
system recruits many cells to the affected tissue to kill off the disease
causing microbes. This recruitment process is called inflammation and it
produces pain, fever, swelling as a part of this process,
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