Title: Summary Notes - Topic 12 Respiration - CIE Biology IGCSE
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CIE Biology GCSE
# 12: Respiration
# Notes www.pmt.education Respiration is a chemical reaction which happens in almost all cells in the body to produce energy from nutrient molecules . This energy can be used in a variety of processes including:
Muscle contraction
Protein synthesis
Cell division
Active transport
Growth
Nerve impulses
Maintaining body temperature
Respiration usually occurs with the presence of oxygen ( aerobic respiration ), although it can occur in the absence of oxygen ( anaerobic respiration ). Anaerobic respiration is less efficient
and leads to fatigue in humans. Both types of respiration are catalysed by enzymes . This means that the rate of respiration can be influenced by factors such as temperature and pH .
Aerobic Respiration:
Aerobic respiration occurs in the presence of oxygen . Glucose is broken down into carbon dioxide, water and energy with the help of oxygen. This occurs in the cell mitochondria . Cells which require lots of energy, such as muscle cells, therefore have high amounts of mitochondria.
Equations for aerobic respiration:
glucose + oxygen carbon dioxide + water
>
C 6 H12 O6 + 6O 2 6CO 2 + 6H 2 O
Anaerobic respiration:
Anaerobic respiration occurs when oxygen is not present . It is less efficient than aerobic respiration and produces less energy per glucose molecule. It occurs in the cell cytoplasm and thus does not require mitochondria.
Animal cells undergo anaerobic respiration during vigorous exercise as not enough oxygen is delivered to muscles. In this reaction, glucose is broken down to produce lactic acid, as well as releasing energy. This lactic acid builds up in muscles and causes muscle fatigue. Anaerobic respiration also produces an oxygen debt . To repay this, the lactic acid must be transported to the liver where it is broken down into carbon dioxide and water using oxygen. This is the reason why the breathing and heart rates remain high after exercise. www.pmt.education Microorganisms, such as yeast , also undergo anaerobic respiration. Yeast breaks down anaerobically to form alcohol and carbon dioxide instead of lactic acid.
Equations for anaerobic respiration in yeast:
glucose alcohol + carbon dioxide
C 6 H12 O6 2C 2 H 5 OH + 2CO 2
Equation for anaerobic respiration in animal cells:
glucose lactic acid www.pmt.education