What might cause a virus in the lysogenic cycle to suddenly enter the lytic cycle?

The correct answer would be the "stressful conditions of the host cell."

In the lysogenic cycle, the viral genome gets attached and integrated into host cell chromosomes and the virus becomes dormant and is termed as a prophage.

However, environmental stress to the host cell such as exposure to a toxic substance, starvation et cetera may cause the prophage to be excised which then enters the lytic cycle.

a symbiotic relationship with the mitochondria