Class 12th Biology 2011 Set3 Delhi Board Paper Solution

(a) The stage of Plasmodium that gains entry into the human body is sporozoites.

(b) Plasmodium requires two hosts to complete its life cycle. 

When the Anopheles mosquito bites a diseased person, gametocytes of Plasmodium are introduced into the mosquito.

Gametocytes fertilise and develop inside the intestine of mosquito to form sporozoites.

Sporozoites are stored in the salivary glands of mosquito and are released into a healthy person who is bitten by the mosquito.

(c) Parasites initially multiply within the liver cells and then attack the red blood cells resulting in their rupture. The rupture of RBCs is associated with the release of a toxic substance called haemozoin. Haemozoin is responsible for the chill and high fever recurring every three to four days.

 

OR

 

Events occurring in the human host after the entry of HIV:

After entering in the human body, viruses enter into the macrophages.

Macrophages become a virtual HIV factory.

Thereafter, HIV enters helper T-lymphocytes, replicates, and produces progenies.

As the progenies are released, they attack other T-lymphocytes.

Therefore, T-lymphocytes start decreasing in number and immune response of the person becomes weak.

Even infections that could be overcome easily start aggravating.