biology

• Cellular respiration is an exothermic reaction which is continuously occurring in living cells
• Cellular respiration


  The chemical process that releases energy
• Organisms need energy for

  • Chemical reactions
  • Muscle contraction
  • Keeping warm
• Aerobic respiration


  Respiration in cells that uses oxygen to transfer energy; glucose is reacted with oxygen in this process
• Aerobic respiration


  Glucose + Oxygen → Carbon dioxide + Water
• Aerobic respiration


  • Takes place in the mitochondria
• Anaerobic respiration


  Respiration in cells that takes place without oxygen, involving the incomplete breakdown of glucose into lactic acid
• Anaerobic respiration in animals

  Glucose → Lactic acid
• Anaerobic respiration in plants & yeast

  Breaking down glucose in the absence of oxygen to produce ethanol and carbon dioxide
• Anaerobic respiration takes place without the need of oxygen
• Anaerobic respiration produces much less energy than aerobic respiration
• Cellular respiration is not breathing; it is a chemical process of transferring energy from glucose in all living cells
• When exercising, the number of muscle contractions increases, therefore there is a greater energy demand, which means that the muscles need a greater supply of oxygen for aerobic respiration
• Human body's reactions to increased oxygen demand during exercise


  1. Breathing rate and breath volume increase to increase oxygen absorption and carbon dioxide removal

  2. Heart rate increases to supply more oxygenated blood to muscles
• If exercising vigorously, the body may not be able to supply sufficient oxygen to the muscles to meet the demand for energy
• Anaerobic respiration


  Incomplete breakdown of glucose without oxygen, releases much less energy than aerobic respiration and results in formation of lactic acid
• Oxygen debt


  Extra oxygen needed after exercising vigorously to react with the lactic acid produced via anaerobic respiration and remove it from the cells
• During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently as a result of increased levels of lactic acid building up
• How the body deals with lactic acid

  1. It can be oxidised (reacted with oxygen) to form carbon dioxide and water

  2. Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose
• The "oxygen debt" is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells
• It is relatively simple to investigate the effects of exercise on the body in the classroom by measuring breathing rate and heart rate before and after an activity
• It is important that the time over which breathing rate and pulse rate are measured is consistent, and that individuals fully recover (rest) before starting a new activity
• Metabolism is the sum of all the reactions in a cell or the body – these reactions happen all of the time
• The energy transferred by respiration in cells is used by the organism for the continual enzyme controlled processes of metabolism that synthesise new molecules
• Enzymes control all of the reactions occurring in cells; often the products of one reaction are the reactants for another (and so on)
• Metabolic Substrates


  The products of digestion are used to build substances, and some of these are then broken down – this is metabolism
• Metabolism includes


  • Conversion of glucose to cellulose in plants to build and strengthen cell walls
  • Conversion of glucose into glycogen in animals and starch in plants for storage
  • The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids to form triglycerides which are used for energy storage and as insulation in animals
  • In plants: the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins required by cells (such as enzymes)
  • Glucose is broken down in the process of respiration to release energy in all cells
  • In animals, the breakdown of excess proteins to form urea for excretion
• All of the features of metabolism listed are covered in more detail in the relevant topics but you should be aware of how they all link together here