2.7.1 Cellular Respiration

• 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

• 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