2. Visited by pollinating insects over the course of its life, the head of the student who refused to drop finally dried out, fell to the ground and spilled it's seeds on the ground.

Ans.2. Visited by pollinating insects over the course of its life, the head of the student who refused to drop finally dried out, fell to the ground, and spilled its seeds on the ground.

1.In a series of verbs like " dried out, fell to the ground, and spilled" a comma must be placed between the second and third item.

2. it's = it is. In this context we are using the possessive, and for this construction, there is no apostrophe. It is simply "its"