IB DP Biology: SL复习笔记2.7.1 Cellular Respiration

Cellular Respiration Defined

  • Cell respiration is the controlled release of energy from organic compounds to produce ATP
  • Respiration is a series of chemical reactions that happens in every cell
  • Its purpose is to release energy in usable forms from the chemical energy stored in food e.g. glucose
  • Respiration is a catabolic process
  • Glucose is the main respiratory fuel used in cells
    • Lipids and proteins can also be used
  • Organic food substances contain a lot of chemical energy
  • This energy cannot be released in one, uncontrolled step in cells, which would cause cell damage and tissue death
  • Enzymes control the release of energy through a series of chemical reactions called a pathway
  • This ends in the production of ATP (adenosine triphosphate)
    • To make ATP, a phosphate group is linked to adenosine diphosphate (ADP)
    • This process requires energy which comes from the breakdown of organic molecules
  • The energy that is released is used for
    • Fuelling anabolic processes
    • Muscle contraction
    • Fuelling active transport
    • Moving molecules around the cell
    • Generating heat to maintain body temperature in warm-blooded animals

Exam Tip

Respiration is often confused with breathing, but remember, respiration is a chemical process, breathing is a method of moving air in and out of the body


  • ATP is a source of energy for cellular processes
  • The energy can be released immediately, exactly when it is required
  • All organisms require a constant supply of energy to maintain their cells and stay alive
  • This energy is required:
    • In anabolic reactions – synthesizing larger molecules from smaller molecules
    • To move molecules across the cell membrane (active transport)
    • To move substances and organelles within the cell
    • In animals, energy is required:
      • For muscle contraction – to coordinate movement at the whole-organism level
      • In the conduction of nerve impulses, as well as many other cellular processes
  • In all known forms of life, ATP from respiration is used to transfer energy in all energy-requiring processes in cells
  • ATP is converted to ADP and phosphate when releasing its energy
    • ADP and phosphate can then be re-converted to ATP during respiration
  • Organisms require a constant supply of ATP because much of the energy is dissipated (lost to the surroundings) as heat


The constant cycling of ATP and ADP+Pi within a cell