115px|Metabolic network

Metabolism is the set of chemical reactions that happen in living organisms to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The chemical reactions of metabolism are organized into metabolic pathways, in which one chemical is transformed through a series of steps into another chemical, by a sequence of enzymes. Enzymes are crucial to metabolism because they allow organisms to drive desirable reactions that require energy and will not occur by themselves, by coupling them to spontaneous reactions that release energy. As enzymes act as catalysts they allow these reactions to proceed quickly and efficiently. Enzymes also allow the regulation of metabolic pathways in response to changes in the cell's environment or signals from other cells. The metabolism of an organism determines which substances it will find nutritious and which it will find poisonous. The speed of metabolism, the metabolic rate, also influences how much food an organism will require. (more...)

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_______________________________ Today's selected anniversaries:

1781:

American Revolutionary War: French naval forces handed Britain an major strategic defeat in the Battle of the Chesapeake. http://en.wikipedia.org/wiki/Battle_of_the_Chesapeake

1943:

World War II: American and Australian forces made an airborne landing at Nadzab as part of the New Guinea campaign against Japan. http://en.wikipedia.org/wiki/landing_at_Nadzab

1960:

Senegalese poet Léopold Sédar Senghor was elected as the first President of Senegal. http://en.wikipedia.org/wiki/L%C3%A9opold_S%C3%A9dar_Senghor

1972:

The Palestinian militant group Black September took hostage eleven Israeli athletes and coaches at the Olympic Games in Munich, West Germany; all of the hostages were killed less than 24 hours later. http://en.wikipedia.org/wiki/Munich_massacre

1977:

NASA launched the robotic space probe Voyager 1, currently the man-made object most distant from Earth. http://en.wikipedia.org/wiki/Voyager_1

_____________________________ Wiktionary's word of the day:

thermoception (n): The sense of heat and cold http://en.wiktionary.org/wiki/thermoception

___________________________ Wikiquote quote of the day:

Crazy Horse dreamed and went into the world where there is nothing but the spirits of all things. That is the real world that is behind this one, and everything we see here is something like a shadow from that one. --Black Elk http://en.wikiquote.org/wiki/Black_Elk