Final answer:
The life cycle of bacteriophages includes two cycles: the lytic cycle, which results in host cell lysis, and the lysogenic cycle, where the virus integrates into the host genome. Environmental stress can trigger the switch from lysogenic to lytic.
Step-by-step explanation:
The life cycle of a virus comprises two primary cycles: the lytic cycle and the lysogenic cycle. In the lytic cycle, bacteriophages inject their DNA into a host cell, replicate themselves, and eventually cause cell lysis, releasing new viral particles. This cycle generally leads to the death of the host cell. On the other hand, during the lysogenic cycle, the phage's DNA becomes integrated into the host's chromosome, known as a prophage, where it is replicated along with the cell's DNA. This cycle can be dormant for extended periods.
Temperate bacteriophages can switch between these two cycles. Various environmental stressors such as starvation or exposure to toxic chemicals can trigger a prophage to excise from the host genome and enter back into the lytic cycle, resulting in the production of new virus particles and the destruction of the host cell. An example of a lytic bacteriophage is T4, while an example of a lysogenic bacteriophage is the lambda virus.
Viruses, including bacteriophages, are characterized as obligate intracellular parasites because they require a host cell to replicate and propagate. The replication process differs significantly from that of other living organisms due to this dependency on the host's cellular machinery.