KLB BIOLOGY BK 2 https://www.biotopics.co.uk/human2/homkid.html http://www.kcse-online.info/Form%202%20Biology/Form%202%20Biology10.html http://www.elimu.net/Secondary/Kenya/KCSE_Student/Biology/Form2/Excretion/KCSE%20Biology%20Curriculum%20Form%20I-Excretion.htm https://homeostasisinhumans.weebly.com/excretion-during-homeostasis.html