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By the end of this section, you will be able to:
  • Explain what metabolic pathways are
  • State the first and second laws of thermodynamics
  • Explain the difference between kinetic and potential energy
  • Describe endergonic and exergonic reactions
  • Discuss how enzymes function as molecular catalysts

Scientists use the term bioenergetics    to describe the concept of energy flow ( [link] ) through living systems, such as cells. Cellular processes such as the building and breaking down of complex molecules occur through stepwise chemical reactions. Some of these chemical reactions are spontaneous and release energy, whereas others require energy to proceed. Just as living things must continually consume food to replenish their energy supplies, cells must continually produce more energy to replenish that used by the many energy-requiring chemical reactions that constantly take place. Together, all of the chemical reactions that take place inside cells, including those that consume or generate energy, are referred to as the cell’s metabolism    .

This diagram shows energy from the sun being transferred to producers, such as plants. The producers in turn transfer energy to consumers and decomposers. Animals also transfer energy to decomposers.
Ultimately, most life forms get their energy from the sun. Plants use photosynthesis to capture sunlight, and herbivores eat the plants to obtain energy. Carnivores eat the herbivores, and eventual decomposition of plant and animal material contributes to the nutrient pool.

Metabolic pathways

Consider the metabolism of sugar. This is a classic example of one of the many cellular processes that use and produce energy. Living things consume sugars as a major energy source, because sugar molecules have a great deal of energy stored within their bonds. For the most part, photosynthesizing organisms like plants produce these sugars. During photosynthesis, plants use energy (originally from sunlight) to convert carbon dioxide gas (CO 2 ) into sugar molecules (like glucose: C 6 H 12 O 6 ). They consume carbon dioxide and produce oxygen as a waste product. This reaction is summarized as:

6CO 2 + 6H 2 O --> C 6 H 12 O 6 + 6O 2 size 12{C rSub { size 8{6} } H rSub { size 8{12} } O rSub { size 8{2} } } {}

Because this process involves synthesizing an energy-storing molecule, it requires energy input to proceed. During the light reactions of photosynthesis, energy is provided by a molecule called adenosine triphosphate (ATP), which is the primary energy currency of all cells. Just as the dollar is used as currency to buy goods, cells use molecules of ATP as energy currency to perform immediate work. In contrast, energy-storage molecules such as glucose are consumed only to be broken down to use their energy. The reaction that harvests the energy of a sugar molecule in cells requiring oxygen to survive can be summarized by the reverse reaction to photosynthesis. In this reaction, oxygen is consumed and carbon dioxide is released as a waste product. The reaction is summarized as:

C 6 H 12 O 6 + 6O 2 --> 6H 2 O + 6CO 2 size 12{C rSub { size 8{6} } H rSub { size 8{12} } O rSub { size 8{2} } } {}

Both of these reactions involve many steps.

The processes of making and breaking down sugar molecules illustrate two examples of metabolic pathways. A metabolic pathway is a series of chemical reactions that takes a starting molecule and modifies it, step-by-step, through a series of metabolic intermediates, eventually yielding a final product. In the example of sugar metabolism, the first metabolic pathway synthesized sugar from smaller molecules, and the other pathway broke sugar down into smaller molecules. These two opposite processes—the first requiring energy and the second producing energy—are referred to as anabolic    pathways (building polymers) and catabolic    pathways (breaking down polymers into their monomers), respectively. Consequently, metabolism is composed of synthesis (anabolism) and degradation (catabolism) ( [link] ).

Questions & Answers

important of enocomic
Adu Reply
what is division of labour
Dennis Reply
division of labour can be defined as the separation of task to individuals in any economic system to specialize on it.
Ahmad
what is demand curve
Victoria Reply
demand curve is a downward sloping economic graph that shows the relationship between the price of product and the quantity of the product demanded.
Ahmad
What is demand
Frank Reply
It refers to the quantity of a commodity purchased in the market at a price and at a point of time.
Basanta
refers to amount of commodities a consumer is willing and able to buy at particular price within a period of time
Clifford
It is the ability and willingness a customer buys a product or service at a particular price, place and time while other things remaining constant or the same
kum
In which case is opportunity cost is zero
Francis Reply
where no alternative is available
Bhartendu
who is the father of economic
Omar Reply
Adam Smith
Suraj
ok
Tony
Adam Smith
Francis
Adam smith
Opana
Adam Smith
Basanta
What is monopoly
Mauthoor Reply
it an economic situation where one individual controls the essential commodities or value product for maximum profit
James
monopoly is a market situation in which there is only one producer of a good or service which has no close substitutes
eliano
is where only one person is solely the price taker
Francis
what is Monopoly
Dauda Reply
The word Monopoly is a Latin word. it is the combination of two words-Mono means single and Poly means seller. thus Monopoly means single seller. but this is not the full meaning of Monopoly. Monopoly must produce a product which does not have close substitute in the market.
Basanta
Monopoly is define as a firm in an industry with very high barriers to entry.
Favour
If close substitute is available, Monopoly will be a king without a crown.
Basanta
what does it array
Cbdishakur Reply
what are the differences between monopoly and.oligopoly
Onome Reply
what are the difference between monopoly and oligopoly
Cbdishakur
The deference between Monopoly and Oligopoly: Monopoly means:A single-firm-Industry producing and selling a product having no close business and Oligopoly means:A market structure where a few sellers compete with each other and each controls a significant portion of market .
Basanta
so that the price-output policy one affects the other.
Basanta
what are difference between physical policy and monotory policy
hon
what is economic
Emakpor Reply
what is economic
Cbdishakur
the word economic was derived from the Greek word oikos (a house)and mein(to manage) which in effect meant managing a household with the limited funds available 🙂.
Basanta
good excample about scarsity
hon
An Enquiry into the nature and causes of wealth Nations, this book clearly defined what economic is🙂🙂🙏🙏 thank you...
Basanta
good example about scarcity: money,time, energy, human or natural resources. Scarcity of resources implies that there supply is very much limited in relation to demand.
Basanta
equilibrium is a situation in which economic forces such as demand and supply are balanced and in the absence of external influences,the value of economic variables will not change
Onome Reply
hmnn
Emakpor
marginal cost and marginal revenue is equilibrium .
Kho
yessss
Basanta
what is equilibrium
Rodrice Reply
policy prescriptions for unemployment
Jeslyne Reply
Am working on it
Blacks
Study
Janelle
study
simeon
what are the factors effecting demand sedule
Kalimu Reply
we should talk about more important topics, you can search it on Google n u will find your answer we should try to focus on how we can improve our society using economics
shubham
so good night
hon
Why do people buy more grapes in December than in July?
lungi
because at time know money
Adu
While the American heart association suggests that meditation might be used in conjunction with more traditional treatments as a way to manage hypertension
Beverly Reply
in a comparison of the stages of meiosis to the stage of mitosis, which stages are unique to meiosis and which stages have the same event in botg meiosis and mitosis
Leah Reply
Researchers demonstrated that the hippocampus functions in memory processing by creating lesions in the hippocampi of rats, which resulted in ________.
Mapo Reply
The formulation of new memories is sometimes called ________, and the process of bringing up old memories is called ________.
Mapo Reply
Which of the following statements is true of epistasis
Houdini Reply
Why do phospolipids tend to spontaneously orient themselves into something resembling a membrane
catli Reply

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Source:  OpenStax, Concepts of biology for slcc biol 1010. OpenStax CNX. Aug 13, 2013 Download for free at https://legacy.cnx.org/content/col11555/1.1
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