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If a chemical reaction requires an input of energy rather than releasing energy, then the ∆G for that reaction will be a positive value. In this case, the products have more free energy than the reactants. Thus, the products of these reactions can be thought of as energy-storing molecules. These chemical reactions are called endergonic reactions , and they are non-spontaneous. An endergonic reaction will not take place on its own without the addition of free energy.

Let’s revisit the example of the synthesis and breakdown of the food molecule, glucose. Remember that the building of complex molecules, such as sugars, from simpler ones is an anabolic process and requires energy. Therefore, the chemical reactions involved in anabolic processes are endergonic reactions. On the other hand, the catabolic process of breaking sugar down into simpler molecules releases energy in a series of exergonic reactions. Like the example of rust above, the breakdown of sugar involves spontaneous reactions, but these reactions don’t occur instantaneously. [link] shows some other examples of endergonic and exergonic reactions. Later sections will provide more information about what else is required to make even spontaneous reactions happen more efficiently.

 Four photos show (a) a compost pile, (b) a baby chick emerging from a fertilized egg, (c) sand art, and (d) a ball rolling downhill.
Shown are some examples of endergonic processes (ones that require energy) and exergonic processes (ones that release energy). These include (a) a compost pile decomposing, (b) a chick hatching from a fertilized egg, (c) sand art being destroyed, and (d) a ball rolling down a hill. (credit a: modification of work by Natalie Maynor; credit b: modification of work by USDA; credit c: modification of work by “Athlex”/Flickr; credit d: modification of work by Harry Malsch)

An important concept in the study of metabolism and energy is that of chemical equilibrium. Most chemical reactions are reversible. They can proceed in both directions, releasing energy into their environment in one direction, and absorbing it from the environment in the other direction ( [link] ). The same is true for the chemical reactions involved in cell metabolism, such as the breaking down and building up of proteins into and from individual amino acids, respectively. Reactants within a closed system will undergo chemical reactions in both directions until a state of equilibrium is reached. This state of equilibrium is one of the lowest possible free energy and a state of maximal entropy. Energy must be put into the system to push the reactants and products away from a state of equilibrium. Either reactants or products must be added, removed, or changed. If a cell were a closed system, its chemical reactions would reach equilibrium, and it would die because there would be insufficient free energy left to perform the work needed to maintain life. In a living cell, chemical reactions are constantly moving towards equilibrium, but never reach it. This is because a living cell is an open system. Materials pass in and out, the cell recycles the products of certain chemical reactions into other reactions, and chemical equilibrium is never reached. In this way, living organisms are in a constant energy-requiring, uphill battle against equilibrium and entropy. This constant supply of energy ultimately comes from sunlight, which is used to produce nutrients in the process of photosynthesis.

The two plots show the change in Gibbs free energy as reactants are converted to products. Gibbs free energy decreases with time for an exergonic reaction (left), and the reaction is spontaneous. Gibbs free energy increases with time for an exergonic reaction (right), and the reaction is not spontaneous
Exergonic and endergonic reactions result in changes in Gibbs free energy. Exergonic reactions release energy; endergonic reactions require energy to proceed.

Questions & Answers

who is the first person who discover the cell
Etornam Reply
what's the difference between DNA and RNA
moffat Reply
DNA is double strained And RNA is singled strained
what is a fungi
Anaba Reply
What is meant by adaptation?
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Ferkah Reply
Charles D
complete the table below based on the levels of biological organization
Lovely Reply
Give me Examples of living thing which have 2 or more flagella?
Mahesh Reply
insect and plants
bacteria and chlamydompnas
reproduction it's full meaning
Gift Reply
full meaning of ATP
A life process in which living things increase their population through sexual or non sexual intercouse
please explaination
Gifty ATP means Adenosine tri phosphate
the process by which organisms produce their own kind.
who is the father of Biology
reproduction is the process where living organisms producess their offspring
jerry Reply
what is reproduction
Nmesoma Reply
why some kinds of students are failed
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lack of concentration
lack of guidance and counseling
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don't mind about reading
lack of focus
Inability to study at their own pace.📒
Inability to study at their own pace.📒
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Kisaky Reply
Giving a specific section of the alimentary canal,describe 3 ways in which physical digestion occurs.
mouth when chewing
what is population
Ivy Reply
total number of people living in an area
a number of people lives in one catigorize area or named area
total number of people living in a specific geographical area.📕
total number of people living in a specific geographical area.📕
what is a cell
Chiko Reply
basic and functional unit of life
cell is tissues that makes up functional life in human or un animal.
is the smallest basic unit of life.
Is the smallest baic unit. o
why cell is very important to human body
what is diffusion
diffusion is a process of mix of particles from higher concentration to the lower one,to make the body functional normal
what is effusion
what is soil
Is the finely divided material covering the earth crust.
is the upper moist of layer of the earth surface
The natural material that covers the surface of the earth crust.📖
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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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