4.2.3 Metabolism

• What is metabolism?

  Sum of all chemical reactions in a cell or the body

  Metabolic rate = rate of these reactions
• How else do cells use energy transferred by respiration?

  To continually carry out enzyme-controlled processes of metabolism that synthesise new molecules
• examples of metabolic reactions

  Smaller →

  larger

  molecules

  1. )Many glucose molecules converted (joined together) into:

  ● Starch (a storage molecule in plant cells)

  ● Glycogen (a storage molecule in animal cells)

  ● Cellulose (a component of plant cell walls)
• examples of metabolic reactions

  2) 1 glycerol molecule + 3 fatty acid molecules → a lipid molecule
• examples of metabolic reactions

  3) Glucose + nitrate ions → amino acids → used to synthesise proteins
• examples of metabolic reactions

  Larger →

  smaller

  molecules

  4 )Respiration
• Why is this statement wrong?

  “Metabolism is how quickly food is

  broken down.”

  Metabolism is the sum of all chemical reactions in a cell or organism.
• Organisms A and B both keep a constant

  body temperature. The surface area to

  volume ratio is higher in organism A.

  Explain why organism A’s metabolic rate

  is greater. (4)

  ● Larger surface area to volume ratio so lose heat more

  quickly

  ● So need to generate more heat (to keep warm)

  ● So requires greater rate of respiration

  ● Respiration is a (large) part of metabolism
• Plants convert glucose into starch, and

  animals convert glucose into glycogen.

  Explain why this is necessary. (2)

  ● Both storage molecules

  ● Converted back to glucose when energy needed