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Fossil Fuels and the Carbon Cycle

Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, and Judith Dresden, MS.
Showing Results for: nitrogen Return to Presentation

Human Excretory System

Normal metabolic activity generates waste products that must be eliminated to sustain homeostasis. Ammonia (a product of protein metabolism) is converted to urea for elimination. Carbon dioxide, generated from cellular respiration, is removed from the lungs. Excess water and salts must be eliminated in order to maintain osmotic and pH balance.

The skin removes water, salts and nitrogen wastes in the form of sweat. 

The lungs eliminate carbon dioxide, water vapor and heat in exhaled air.

The kidneys excrete the majority of metabolic waste products from the body. Each kidney contains about one million functional filtering units called nephrons.


Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

My Health My World: National Dissemination
Grant Number: 5R25ES009259
The Environment as a Context for Opportunities in Schools
Grant Number: 5R25ES010698, R25ES06932


Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education