Embryonic and early fetal development occurs in the trimester.

Cells destroy body cells infected by a virus or bacteria.

When you run, you begin to breathe heavier and faster. your heart beats more quickly, bringing more oxygen to your cells. which organ systems are working together here?

Directions: read the descriptions of the four islands presented in the lesson. 1. list two new traits that each new species of rat might demonstrate as it adapts to the conditions on each island. 2. introduce one of the four new rat species to another island and describe one challenge it would encounter and one success as it adapts to its new environment.