Write a fact related to the given fact, based on the given topic word. Note that, your fact should have at least one word in common with the given fact. All facts in this task refer to scientific facts. Your related fact must form a chain with the given fact. Chains form when two facts connect together to produce the third fact. An example of a chain is: "pesticides cause pollution" (given fact) + "pollution can harm animals" (related fact) → "pesticides can harm animals" (connected chain). Avoid creating simple paraphrases of the given fact. While your generated fact should be related to the input fact, they must describe slightly different scientific phenomena. It's okay if your related fact includes some irrelevant information, provided that it has some overlap with the given fact and it contains some words corresponding to the provided topic.

Fact: Prokaryotes are single-celled organisms that lack a nucleus. 
Topic: nucleus.
Inside the nucleus are the genes.

Fact: when a hemisphere is tilted away from the sun , that hemisphere receives less direct sunlight. 
Topic: hemisphere receives less direct sunlight.
Because of this tilt, the northern hemisphere receives less direct sunlight (creating winter) while the southern hemisphere receives more direct sunlight (creating summer).

Fact: Plants respond to daily and seasonal cycles and to disease. 
Topic: plant type cactus.

Cactuses are one type of succulent plants, although they are usually referred to separately.