respiration (B9)

• Cellular respiration is an exothermic reaction that occurs continuously in the mitochondria of living cells to supply the cells with energy
• Energy released during respiration is needed for all living processes, including:

  • Chemical reactions to build larger molecules, for example, making proteins from amino acids
  • Muscle contraction for movement
  • Keeping warm
• Respiration in cells can take place aerobically (using oxygen) or anaerobically (without oxygen)
• Anaerobic respiration in plant and yeast cells is represented by the equation glucose ➞ ethanol + carbon dioxide
• Type of respiration:

  • Aerobic: complete oxidation of glucose, large amount of energy released
  • Anaerobic: incomplete oxidation of glucose, much less energy released per glucose molecule than in aerobic respiration
• Aerobic respiration:

  glucose + oxygen ➞ carbon dioxide + water

  C6H12O6 + 6O2 ➞ 6CO2 + 6H2O
• Anaerobic respiration in muscles:

  glucose ➞ lactic acid

  C6H12O6 ➞ 2C3H6O3
• Anaerobic respiration in yeast cells is called fermentation (important for bread and alcoholic drinks)
• Mitochondria contain the enzymes for aerobic respiration
• Cell membrane allows gases and water to pass freely into and out of the cell, controls the passage of other molecules
• Cytoplasm is where enzymes are made and location of reactions in anaerobic respiration
• Nucleus holds genetic code for enzymes involved in respiration
• Metabolism is the sum of all the reactions in a cell or the body
• Metabolic processes include the synthesis and breakdown of:

  • Carbohydrates: synthesis of larger carbohydrates from sugars (starch, glycogen, and cellulose), breakdown of glucose in respiration to release energy
  • Proteins: synthesis of amino acids from glucose and nitrate ions, amino acids used to form proteins, excess proteins broken down to form urea for excretion
  • Lipids: synthesis of lipids from one molecule of glycerol and three molecules of fatty acid
• Oxygen debt is the amount of oxygen needed to react with the lactic acid to remove it from cells
• During exercise, the human body reacts to the increased demand for energy by increasing heart rate, breathing rate, and breath volume
• Lactic acid builds up in muscles during anaerobic respiration
• Muscles become fatigued and stop contracting efficiently during long periods of activity
• Lactic acid in muscles is transported to the liver in the blood and converted back to glucose
• Oxygen debt is the 'extra' oxygen required to pay off the oxygen debt
• Metabolism produces new molecules through enzyme-controlled processes
• Aerobic respiration


  An exothermic reaction in which glucose reacts with oxygen to release energy which can be used by cells
• Aerobic respiration


  Glucose + oxygen → carbon dioxide + water (+energy)
• Anaerobic respiration


  An exothermic reaction in which glucose is broken down to release energy in the absence of oxygen
• Anaerobic respiration


  Glucose → lactic acid (+energy)
• Anaerobic respiration is less efficient than aerobic respiration
• Reason anaerobic respiration is less efficient


  Glucose is not completely broken down, so less energy is transferred
• Anaerobic respiration


  Leads to muscle fatigue due to lactic acid build up
• Oxygen debt


  The amount of oxygen needed to convert lactic acid into back into glucose after anaerobic respiration
• Fermentation


  A type of anaerobic respiration that occurs in yeast cells
• Fermentation


  Glucose → ethanol + carbon dioxide (+energy)
• Importance of fermentation


  Used in the production of bread and alcoholic drinks
• Differences between aerobic and anaerobic respiration

  • Aerobic requires oxygen; anaerobic does not
  • Aerobic produces CO2 and water; anaerobic produces lactic acid or ethanol + CO2
  • Aerobic transfers a greater amount of energy
• How muscles store glucose

  As glycogen
• Changes when muscular activity increases


  1. Heart rate increases and arteries dilate - increases flow of oxygenated blood to muscles

  2. Breathing rate increases and breathing is deeper - increases the rate of gaseous exchange

  3. Stored glycogen is converted back into glucose
• Lactic acid is transported away from muscles to the liver, where it is oxidised back to glucose
• Metabolism


  The sum of all the reactions that take place in a cell or an organism
• How cells use energy from respiration


  To continuously carry out enzyme-controlled processes which lead to the synthesis of new molecules
• Examples of metabolic reactions


  • Glucose into starch/glycogen/cellulose
  • Glycerol and fatty acids into lipids
  • Glucose and nitrate ions into amino acids
  • Photosynthesis
  • Respiration
  • Breakdown of excess proteins into urea