The Importance of Respiration

• Why do humans need energy

  • Humans and other mammals need energy to keep warm 
  • We also need energy for chemical reactions to build larger molecules  
  • For example proteins are made by chemically joining amino acids

  
• What is respiration and what type of reaction is it

  • The energy that humans need is supplied by a process called cellular respiration (or just respiration) 
  • Respiration is an example of an exothermic reaction
  • This is because it releases energy from glucose molecules for use by the body  
  • And it takes place continually in all living cells
• Why do organisms need the energy released from respiration

  • Organisms need it to build larger molecules 
  • Organisms need it to keep warm 
  • Organisms need it for movement
• Describe what happens in aerobic respiration

  • If oxygen is present cells carry out aerobic respiration 
  • In aerobic respiration, the sugar glucose is reacted with oxygen gas  
  • This produces carbon dioxide and water and releases energy

  
• How much energy does aerobic respiration release and why

  • Aerobic respiration releases a large amount of energy  
  • This is because the glucose molecule has been completely broken down / oxidised 
• What is the word equation for aerobic respiration?

  glucose + oxygen → carbon dioxide + water 
• What is the symbol equation for aerobic respiration?

  C₆H₁₂O₆ + O₂ → CO₂ + H₂O
• Why does anaerobic respiration take place in muscle cells, instead of aerobic respiration?

  • If not enough oxygen is present, then cells carry out anaerobic respiration 
  • In humans, muscle cells need a great deal of energy for contraction  
  • But under certain conditions the amount of oxygen is limited 
  • When there is a shortage oxygen, muscle cells respire anaerobically

  
• Describe what happens in anaerobic respiration in animals/muscles

  • During anaerobic respiration in muscles , the sugar glucose is converted to lactic acid  
  • This releases energy 
  • Anaerobic respiration does not require oxygen

  
• How much energy does anaerobic respiration release and why?

  • Anaerobic respiration releases less energy than aerobic respiration 
  • This is because in anaerobic energy, the glucose molecule has not been completely broken down / oxidised
• What is the word equation for the anaerobic respiration in animals/muscle cells

  Glucose → lactic acid
• Describe what happens when anaerobic respiration takes place in yeast and plant cells

  • Anaerobic respiration can also take place in plant cells and yeast cells 
  • Anaerobic respiration in yeast cells is called fermentation 
  • In this reaction, the sugar glucose is converted to ethanol and carbon dioxide - and this releases energy
  •  No oxygen is required for anaerobic respiration in plants and yeast

  
• What is the word equation for anaerobic respiration in plant cells and yeast cells?


  Glucose → ethanol + carbon dioxide
• What is the symbol equation for anaerobic respiration in plant cells and yeast cells?

  C₆H₁₂O₆ → C₂H₅OH + CO₂
• Why is fermentation important?

  • We use anaerobic respiration in yeast (fermentation) to make alcoholic drinks such as beer 
  • The alcohol in these drinks is ethanol 
  • The carbon dioxide in this reaction is useful as it can be trapped to make the drink fizzy 
  • It can also be useful when yeast is used to make bread , as it creates bubbles in the dough causing the bread to rise