An organism's excretory system is responsible for getting rid of waste and toxins that build up in the organism. The primary organs of excretion in the human body are the lungs, kidneys and skin. The lungs get rid of carbon dioxide, while the skin excretes waste in the form of sweat. The urinary system gets rid of waste in the form of urine. There are a variety of science projects that can demonstrate these principles and allow students to show an understanding of the systems.
Excretory System Model * In this project, students make a model of the excretory system that includes the kidneys, bladder, ureters and urethra, as well as the arteries and veins that bring blood to the kidneys for cleaning. The model can be three-dimensional, or it can be drawn and pasted onto a cardboard sheet. Let the students come up with innovative ways to represent the different organs. Give them a few tips and award extra points for students who can make their models out of recyclable materials. For example, a balloon can be used to represent the bladder and kidneys can be modeled from a basic dough that is colored with food dyes.

Filter System Project * This science project shows how the kidneys work together as a filtration system. It is a simple science project for younger students that demonstrates the concept of a filter and how it works. You will need either cheesecloth or filter paper, food coloring, a pound of fine-grained sand, a gallon of water and a tall, thin glass jar. Students mix the sand, water and food coloring together and set it aside. Fill the tall jar with water until it is about half full. Place the filter paper or cheesecloth over the top of the jar. Add the colorful sand and water mixture to the jar. Because of the action of the filter, only the colored water will be allowed through. The clear water changes color but the sand stays behind, stopped by the filter paper. Lift the filter paper and pour out the water. Add new water to the sand and water mixture and repeat the procedure. The color of the sand and water mixture will slowly fade with each change and this will demonstrate how the kidneys cleanse urea and toxins from the blood while the actual blood cells remain