The difference between 'excretion' and 'egestion' is that whereas excretion is the process of removing toxic waste by-products of the body's metabolism, egestion is the removal of indigestible remains/substances through the alimentary canal. Through egestion, substances that were not able to be used in the body are removed, and through excretion, waste products of used substances which are potentially harmful are removed.

The principal waste products generated by metabolic activities in most animals are water, carbon dioxide, and nitrogenous wastes. Carbon dioxide is mainly excreted by gills, lungs, or other respiratory surfaces. Excretory organs such as kidneys excrete most of the water and nitrogenous wastes. Nitrogenous wastes include ammonia, uric acid, and urea. In a process called deamination, the amino group is removed from amino acids and is converted to ammonia. Ammonia is highly toxic and it may harm the organism if permitted to accumulate inside the body. Since it is very soluble, in many organisms it's quickly converted to some less toxic nitrogenous waste product such as

uric acid or urea. Other waste products of the body include carbon dioxide, which is the product of cellular respiration in which oxygen is used up. Carbon dioxide is carried by the plasma, in the form of hydrogen carbonates, or a smaller portion in the haemoglobin. It is carried to the lungs, where it is excreted from the body.

Here is a table of the excretory organs found in mammals and the excretory substances which they remove:

Some common words found in the essay are:
System Aim, Carbon Dioxide, Lungs Excess, Kidney Skin, Kidney Birds, Organ Excess, Kidney Ammonia, Water Modified, Skin Salts/urea, waste products, carbon dioxide, modified tear gland, Organ Substance, tear gland, renal tubules, excess salt, modified tear, nitrogenous wastes, uric acid, excretory organs, substance removed, excretory organs found, organ substance removed, carrying blood kidney, waste products blood,
Approximate Word count = 877
Approximate Pages = 4 (250 words per page double spaced)