A virus's ability to infect an animal cell depends primarily upon the:

• A. number of mitochondria in the host cell
• B. presence of specific receptors on the host cell surface
• C. rate of host cell division
• D. size of the viral genome

Answer: (B)

Verified step by step guidance

1. Understand that a virus infects a host cell by first attaching to it. This attachment is highly specific and depends on the interaction between viral surface proteins and molecules on the host cell surface.
2. Recognize that the host cell must have specific receptors on its surface that the virus can bind to. These receptors act like 'docking stations' allowing the virus to attach and subsequently enter the cell.
3. Note that the number of mitochondria in the host cell is not directly related to viral infection because mitochondria are involved in energy production, not viral entry.
4. Consider that the rate of host cell division does not primarily influence whether a virus can infect the cell, although it may affect viral replication after infection.
5. Understand that the size of the viral genome affects the virus's genetic information but does not determine its ability to infect a host cell; infection depends on receptor presence.