A virus is an infectious agent with its genome is uncoated from the protein and injected into the host cell. This means they can only replicate within a host organism, literally taking over the host's functions. Then the viral genome hijacks the host cell's machinery, and to produce viral proteins, it forces the cell to replicate the viral genome. So, viruses depend on the host cells that they infect to reproduce.
<u>B) is a plant cell and D) is an animal cell.</u> They are both structural and functional unit of all living organisms, they do not need another cell to copy its genetic material. <u>And C) is a bacteria</u>, which reproduces by binary fission. In this process the bacterium divides into two identical daughter cells, and the DNA of the bacterium divides into two. <u>So none of them needs a host cell to copy its genetic material and protein coat.</u>
The virus' DNA becomes a part of the host cell's DNA, and every time the host cell copies and divides, it also copies viral DNA. The viral DNA may remain inactive (a provirus) for a long time, but it can become active when it frees itself from the host's chromosome, which triggers the lytic cycle.
The most appropiate unit of measurement fro most types of cells is CD4 counts are measured in cells per cubic millimetre = cells/mm3. A cubic millimetre (mm3) = mm3 = 1 mm x 1 mm x 1 mm.
