Life on Earth

Chapter 4
Energy Flow in the Life of a Cell
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Energy and the Ability to Do Work
  • The laws of thermodynamics describe the basic properties of energy.
  • Living things use the energy of sunlight to create the low-entropy conditions characteristic of life.

    Energy Flow in Chemical Reactions
  • Exergonic reactions release energy.
  • Endergonic reactions require an input of energy.
  • Coupled reactions link exergonic with endergonic reactions.
  • Chemical reactions are reversible.

    Controlling the Metabolism of Living Cells
  • At body temperatures, high activation energy makes spontaneous reactions proceed too slowly to sustain life.
  • Catalysts reduce activation energy.
  • Enzymes are biological catalysts.

    Coupled Reactions and Energy-Carrier Molecules
  • ATP is the principal energy carrier in a cell.



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