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Metabolic Waste (代謝產物)
From Wikipedia


Metabolic wastes or excretes are substances left over from metabolic processes, which cannot be used by the organism (they are surplus or have lethal effect), and must therefore be excreted. This includes NITROGEN COMPOUNDS, WATER, CO2, PHOSPHATES, SULPHATES, INDOLES, MEDICAL, FOOD ADDITIVES etc. Animals treat these compounds as excretes. Plants have chemical "machinery" which transforms some of them (primarily the nitrogen compounds) into useful substances, and it has been shown by Brian J. Ford that abscised leaves also carry wastes away from the parent plant. In this way, Ford argues that the shed leaf avcts as an excretophore (= organ carrying away excretory products).

All the metabolic wastes are excreted in a form of water solutes through the excretory organs (nephridia, Malpighian tubules, kidneys), with the exception of CO2, which is excreted together with the water vapor throughout the lungs. The elimination of these compounds enables the chemical homeostasis of the organism.


Nitogen Compounds

The nitogen compounds through which the very toxic nitrogen is eliminated from the organism are ammonia, urea and uric acid. All of these substances are product from the protein metabolism.

Ammonia forms with the oxidation of amino groups (NH2), which are removed from the proteins when they convert into carbohydrates. It is a very toxic substance and only one nitrogen atom is removed with it. A lot of water is needed for the ammonia excretion. Thus, the marine organisms excrete ammonia directly in the water (aminothelic organisms), while the terrestrial (mainly amphibians and mammals) convert ammonia into urea, a process which occurs in the liver.

Urea is a less toxic compound than ammonia; two nitrogen atoms are eliminated through it and less water is needed for its excretion. Urea is a protein metabolism product at vertebrates and part of the invertebrates. These organisms are called ureothelic.

Uric acid is a protein metabolism product of terrestrial invertebrates, birds and terrestrial reptiles. This is the reason of which these animals are called uricothelic organisms. In humans and anthropoides, this acid is purine metabolism product. Uric acid is less toxic than ammonia or urea; it contains four nitrogen atoms and a small amount of water is needed for its excretion. Out of solute, it precipitates and forms crystals.


Water and Carbon Dioxide

These compounds form during the catabolism of carbohydrates and lipids, and in some other metabolic reactions of the amino acids


Phosphate

refer: http://en.wikipedia.org/wiki/Phosphate


Sulfate

refer: http://en.wikipedia.org/wiki/Sulphate


Indole

refer: http://en.wikipedia.org/wiki/Indole


Food Additive

refer: http://en.wikipedia.org/wiki/Food_additive


代謝產物

微生物在代謝過程中，會產生多種代謝產物。根據代謝產物與微生物生長繁殖的關係，可以分爲初級代謝產物和次級代謝產物兩類。 初級代謝產物是指微生物通過代謝活動產生的、自身生長和繁殖所必須的物質，如胺基酸、核苷酸、多糖、脂質、維生素等。在不同種類的微生物細胞中，初級代謝產物的種類基本相同。 次級代謝產物是指微生物生長到一定階段才產生的化學結構十分複雜，對該微生物無明顯生理功能，或並非是微生物生長和繁殖所必須的物質，如抗生素、毒素、激素、色素等。不同種類的微生物所產生的次級代謝產物不相同，它們可能積累在細胞內，也可能排到外環境中。

metabolic waste係"經過身體metabolized";之後既廢棄物,,metabolization 分anabolism (build up) and catabloism(break down)
例如co2

而例如 植物既cellulose,,如果食左,,咁人消化唔到,,自然冇metabloized過,,咁就算排出體外,都當然唔係metabolic waste

or 空氣既Nitrogen,因為冇用過,所以都唔係