Final answer:
Bacteria cells are usually larger than viruses, but some viruses can be larger than the smallest bacteria. Viruses have smaller sizes which allow them to efficiently infect host cells and reproduce, but they are not considered alive because they can't reproduce independently. The influenza virus keeps its host cell alive to maintain the environment it requires for continued infection.
Step-by-step explanation:
In comparison, bacteria cells are generally larger than viruses. For instance, most bacteria measure between 1,000 to 2,000 millimicrons, while viruses such as the foot and mouth disease virus can be as small as 21 millimicrons in diameter. However, some exceptions exist like the Mimivirus, which can be larger than the smallest bacteria.
The small size and simplicity of viruses provide an evolutionary advantage by allowing them to efficiently hijack their host's cellular machinery for replication. Unlike bacteria, which can reproduce independently, viruses must infect the cells of a host organism to multiply. This mode of reproduction allows viruses to quickly adapt to host defenses, making them highly effective at spreading and causing disease.
As for how they differ from living organisms, viruses lack many characteristics of life, such as not being able to reproduce independently and not having a metabolism. They do share some features with living organisms, including the presence of nucleic acids—either DNA or RNA. The question of whether viruses are truly "alive" is still debated, although the discovery of giant viruses with more complex genomes has challenged traditional views.
One way that the influenza virus increases its fitness is by exiting host cells without destroying them. This strategy helps to maintain a viable environment for the virus to continue its life cycle, ensuring ongoing infection and transmission.