Metabolic waste

Metabolic waste

Metabolic wastes or excretes are substances left over from excretory 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, sulfates, insoles, medicals, 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 abscissa leaves also carry wastes away from the parent plant. In this way, Ford argues that the shed leaf acts as an excretory (= 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.

Nitrogen wastes

The nitrogen 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 and kidney.

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 diapsids. Such 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 gases

These compounds form during the catabolism of carbohydrates and lipids in condensation reactions, and in some other metabolic reactions of the amino acids. Oxygen is produced by plants and some bacteria in photosynthesis, while CO2 is a waste product of all animals and plants in darkness. Nitrogen gases are produced by denitrifying bacteria and as a waste product, and bacteria for decaying yield ammonia, as do most invertebrates and vertebrates. Water is the only liquid waste from animals and photosynthesizing plants in the dark.[1]

Solids

Nitrates and nitrites are wastes produced by nitritfying bacteria, just as sulfur and sulfates are produced by sulfur bacteria. Insoluble iron waste can be made by iron bacteria by using soluble forms. In plants, resins, fats, waxes, and complex organic chemicals are ejcted from plants, e.g., the latex from rubber trees and milkweeds. Solid waste products may be manufactured as organic pigments derived from breakdown of pigments like hemoglobin, and inorganic salts like carbonates, biicarbonates, and phosphate, whether in ionic or molecular form, are excreted as solids.[1]

  1. ^ a b "excretion." Encyclopædia Britannica. Encyclopaedia Britannica Ultimate Reference Suite. Chicago: Encyclopædia Britannica, 2010.

Wikimedia Foundation. 2010.

Игры ⚽ Нужно сделать НИР?

Look at other dictionaries:

  • Metabolic rift — is a term developed by John Bellamy Foster and other theorists to refer to Karl Marx’s understanding of ecological disruption under capitalism. While Marx never employed the term itself in his writings, he did write of an irreparable rift in the… …   Wikipedia

  • metabolic disease — ▪ pathology Introduction       any of the diseases or disorders that disrupt normal metabolism, the process of converting food to energy on a cellular (cell) level. Thousands of enzymes participating in numerous interdependent metabolic pathways… …   Universalium

  • Metabolic engineering — Cellular metabolism can be optimized for industrial use. Metabolic engineering is the practice of optimizing genetic and regulatory processes within cells to increase the cells production of a certain substance. Metabolic engineers commonly work… …   Wikipedia

  • Excretion — is the process of eliminating waste products of metabolism and other non useful materials.cite book | last = Beckett | first = B. S. | authorlink = | coauthors = | title = Biology: A Modern Introduction | publisher = Oxford University Press |… …   Wikipedia

  • Topic outline of cell biology — [ micrograph of a moss s leaf cells at 400X magnification.] : For a more comprehensive list, see the List of cell biology topics. Cell biology (formerly cytology, from the Greek kytos , container ) is an academic discipline that studies cells –… …   Wikipedia

  • Outline of cell biology — Light micrograph of a moss s leaf cells at 400X magnification. The following outline is provided as an overview of and topical guide to cell biology: Cell biology (formerly cytology, from the Greek kytos, container ) – academic discipline that… …   Wikipedia

  • Glossary of terms associated with diabetes — This page lists and explains terms connected with diabetes. NOTOC A *Acanthosis nigricans A brown to black, poorly defined, velvety hyperpigmentation of the skin, usually present in the posterior and lateral folds of the neck, the axilla, groin,… …   Wikipedia

  • metabolite — Any product or substrate (foodstuff, intermediate, waste product) of metabolism, especially of catabolism. SYN: metabolin. primary m. a m. synthesized in a step in primary metabolism. secondary m. a …   Medical dictionary

  • Glossary of diabetes — See also: Diabetes (disambiguation) The following is a glossary of diabetes which explains terms connected with diabetes. Contents: Top · 0–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z …   Wikipedia

  • nervous system disease — Introduction       any of the diseases or disorders that affect the functioning of the human nervous system (nervous system, human). Everything that humans sense, consider, and effect and all the unlearned reflexes of the body depend on the… …   Universalium

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”