Tropism can be defined as the Choose one: A. ability to infect a particular type of cell within the host. B. mechanism of entry into a host cell for bacteriophages. C. emergence of a new type of virus. D. ability to infect a broad range of hosts.

A) ability to infect a particular type of cell within the host.

Explanation:

Viral tropism refers to the ability of a virus to infect a particular cell, tissue and a host species.

The viruses have to interact with a variety of negative and positive factors in the cell so the viral tropism is determined at different levels of the viral-host interaction that is during replication and viral progeny production.

The viral tropism occurs at two-step and based on this is of two types - the receptor-independent tropism which takes place intracellularly and the receptor-dependent tropism which takes place at the cell surface.

Thus, Option-A is the correct answer.

A. ability to infect a particular type of cell within the host.

Explanation:

In plants, tropism refers to the movement of a plant part in a particular direction in response to any stimulus. In microbiology, tropism refers to the ability of pathogen to infect a particular type of cell in the host.

The tropism in which a particular cell is infected is called cell tropism. The tropism in which a particular tissue is infected then it is cell tissue tropism. Host tropism is also seen in pathogen when they infect specific host. Stimulus is required for any tropism. So the right answer is A.