# Distinguish between the lytic and lysogenic cycles of a bacteriophage, with reference to the fate of the viral genome in each cycle.

> IB DP Biology Higher Level (2023 syllabus) — A2.3 Viruses (HL only) · Distinguish · 4 marks

## Mark scheme (4 marks)

1. In the lytic cycle the viral genome is replicated immediately and directs production of new phage components, whereas in the lysogenic cycle the viral genome is integrated into the host chromosome (as a prophage).
2. In the lytic cycle the host cell is lysed / destroyed at the end of the cycle, releasing new phage particles, whereas in the lysogenic cycle the host cell survives and continues to divide.
3. In the lysogenic cycle the prophage is replicated passively along with the host DNA each time the cell divides, so daughter cells inherit the viral genome, whereas in the lytic cycle no such vertical transmission occurs.
4. The lysogenic cycle can be induced / switched to the lytic cycle (e.g. by environmental stressors such as UV radiation), at which point the prophage excises from the host chromosome and enters the lytic pathway.

## Key terms

- [lysogenic cycle](https://www.gradenine.co.uk/glossary/lysogenic-cycle)
- [bacteriophage](https://www.gradenine.co.uk/glossary/bacteriophage)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Distinguish" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/distinguish-between-the-lytic-and-lysogenic-5dbc4a9c) · Published by Druglandscape Ltd.