Question

Which of the following reproduces only inside a host cell?
A. Bacteria
B. Virus
C. Protist
D. Fungus

Answer 1

Reproduction is the biological process by which new individual organisms ie. "offspring" are produced from their "parents". A host is an organism that harbors a parasitic, a mutualistic, or a commensalism guest.

Step by step answer: Bacteria-Bacteria reproduce by binary fission. In this process, the bacterium, which is a single cell, divides into two identical daughter cells.
Virus- A virus cannot replicate alone. Viruses must infect cells and use components of the host cell to make copies of themselves. Often, they kill the host cell in the process and cause damage to the host organism.
Protist-Most Protists reproduce sexually using gametes, while others reproduce asexually by binary fission. Some species, for example, Plasmodium falciparum, have extremely complex life cycles that involve multiple forms of the organism, some of which reproduce sexually and others asexually.
Fungus-Fungi reproduces asexually by fragmentation, budding, or producing spores. Sexual reproduction also occurs in virtually all fungi. This involves mating between two haploid hyphae.
So, the answer is B. Virus, that reproduce inside a host cell.

Note: Viruses replicate by lytic and lysogenic cycle. In the lytic cycle, the virus attaches to the host cell and injects its DNA. Using the host's cellular metabolism, the viral DNA begins to replicate and form proteins. Then fully formed viruses assemble. These viruses break, or lyse, the cell and spread to other cells to continue the cycle. A lysogenic virus can remain inactive for a period of time. In lysogenic infection, viral DNA gets integrated with the host cell's DNA, where it is copied along with the host cell's DNA when the host cell replicates. Viral DNA multiplies as the host cell multiplies. Each new daughter cell created is infected with the virus' DNA.