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  • Created by: LucySPG
  • Created on: 18-04-14 14:19

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All living cells require energy and this energy is provided by the oxidation of glucose ­ respiration.
Why organisms need energy
Metabolism All the reactions that take place in living organisms
involve energy
Movement Both within an organisms and of the organism itself
Active transport Of ions and molecules against a concentration
gradient across plasma membrane
Maintenance, repair and Of cells and of organelles within the cells
Production of substances Used within organisms, for example, enzymes and
Maintenance of body These organisms are endothermic and need energy to
temperature replace that lost as heat to the environment
The flow of energy through living systems occurs in three stages:
1. Light energy from the Sun is converted by plants into chemical energy during photosynthesis
2. The chemical energy from photosynthesis, in the form of organic molecules, is converted into ATP
during respiration in all cells
3. ATP is used by cells to perform useful work
How ATP Stores Energy
Adenosine triphosphate has three phosphate groups.
The bonds between these phosphate groups are unstable and so have a low activation energy, which
means they are easily broken.
When they do break they release a considerable amount of energy.
The conversion of ATP to ADP is a reversible reaction and therefore energy can be used to add an
inorganic phosphate to ADP to re-form ATP.
As water is removed in this process, the reaction is known as a condensation reaction.

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The synthesis of ATP from ADP involves the addition of a phosphate molecule to ADP.
It occurs in three ways:
Synthesis of ATP
Photophosphorylation Takes place in chlorophyll-containing cells during photosynthesis
Oxidative phosphorylation Occurs in the mitochondria of plant and animal cells during the process of
electron transport
Substrate-level Occurs in plant and animal cells when phosphate groups are transferred from
phosphorylation donor molecules to ADP to make ATP
ATP is the immediate energy source of a cell.…read more


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