Urea and fertilizers containing urea are excellent sources of nitrogen for crop production.

When the weather is hot, our body system tries to keep our body cool by evaporating the water along with unwanted things (sweating) through the skin in the form of perspiration. So, skin helps the kidney by sharing its work of cleaning the body in hot weather. In cold conditions, as sweating is much decreased, there is no perspiration and the kidney has to bear the entire burden of excretion and hence we urinate frequently.

How the lungs work

Every cell in your body needs oxygen to live. The air we breathe contains oxygen and other gases. The respiratory system's main job is to move fresh air into your body while removing waste gases.

Once in the lungs, oxygen is moved into the bloodstream and carried through your body. At each cell in your body, oxygen is exchanged for a waste gas called carbon dioxide. Your bloodstream then carries this waste gas back to the lungs where it is removed from the bloodstream and then exhaled. Your lungs and respiratory system automatically perform this vital process, called gas exchange.

The liver is the largest solid organ in the body. It removes toxins from the body’s blood supply, maintains healthy blood sugar levels, regulates blood clotting, and performs hundreds of other vital functions. It is located beneath the rib cage in the right upper abdomen.

Key Facts
1. The liver filters all of the blood in the body and breaks down poisonous substances, such as alcohol and drugs.
2. The liver also produces bile, a fluid that helps digest fats and carry away waste.

Humans take in oxygen and releases carbon dioxide as a waste product by the lungs.

Excretion involves the separation and elimination of metabolic waste products from the body. Various organs are involved in this process: the lungs, gills, skin, etc. The kidneys and their ducts are the major full-time excretory organs and comprise the excretory system.