Open Curriculum
Open Curriculum: Excretory System
This article helps students define homeostasis and excretion, and why they are necessary for life.
CK-12 Foundation
Ck 12: Life Science: Excretion
[Free Registration/Login may be required to access all resource tools.] You might have noticed that sometimes your urine is darker than usual. This can happens when your body is low on water and trying to reduce the amount of water lost...