Nitrogenous Waste

Excretion: the removal from the body of waste products made in the cells during metabolism. The main excretory organs are the Kidneys and bladder although the Liver metabolizes many waste materials, one process carried out by the liver is called deamination.

Deamination: Excessive amino acids are metabolized by the liver, the amino group forms ammonia and the remainder enters the Krebs cycle or is stored.

Types of Nitrogenous Waste

Ammonia is highly toxic, aquatic animals can readily excrete it to their environment because of the water that is available.
Terrestrial animals use energy to turn ammonia into urea (in the liver), urea is VERY soluble and not very toxic so it can be excreted with a small volume of water.
Desert terrestrial animals and birds that do not have access to much water or that cannot carry much water (weight) exert more energy to make Uric acid. It is not toxic and is excreted as crystals, requires very little water.

Textbook Practice

p.445#4-6