Aerobic & Anaerobic Respiration (Edexcel IGCSE Biology): Revision Note

Aerobic Respiration

• Aerobic respiration requires oxygen and takes place in the mitochondria in the cell

  • It is defined as the chemical process in cells that uses oxygen to break down nutrient molecules to release energy in the form of ATP

• Aerobic respiration is the complete breakdown of glucose to release a relatively large amount of energy in the form of ATP for use in cellular processes and reactions.

• Carbon dioxide and water are also produced as waste products

Word equation for aerobic respiration

Symbol equation for aerobic respiration

• This equation can also be shown as a balanced chemical equation

  • One molecule of glucose reacts with six molecules of oxygen to produce six molecules of carbon dioxide and six molecules of water

Anaerobic Respiration

• Anaerobic respiration does not require oxygen

  • It is defined as the chemical process in cells that breaks down nutrient molecules to release energy without using oxygen

• It involves the incomplete breakdown of glucose and so releases a a smaller amount of energy in the form of ATP than aerobic respiration

• Different waste products are formed depending on the type of organism that the anaerobic respiration is taking place in

Anaerobic respiration in animals

• Anaerobic respiration mainly takes place in muscle cells during vigorous exercise

• When we exercise at high intensities, our muscles have a higher demand for energy

• Our bodies can only deliver so much oxygen to our muscle cells for aerobic respiration

• When oxygen supply is insufficient, some glucose is broken down without it anaerobically, producing lactic acid instead

• Glucose has not been fully broken down meaning there is still energy stored within the bonds of lactic acid molecules

  • Lactic acid builds up in muscle cells and lowers the pH of the muscle tissue (making the conditions more acidic)

    • Acidic conditions can denature the enzymes in cells

  • Lactic acid will eventually be broken down using oxygen to produce carbon dioxide and water as waste products

• Anaerobic respiration releases less energy than aerobic respiration

Anaerobic respiration in plants and fungi

• Plants and yeast can respire without oxygen as well, breaking down glucose in the absence of oxygen to produce ethanol and carbon dioxide

• Anaerobic respiration in yeast cells is called fermentation

  • Fermentation is economically important in the manufacture of bread (where the carbon dioxide produced helps the dough to rise)

Comparing Anaerobic & Aerobic Respiration

• The processes of aerobic and anaerobic respiration can be compared with regard to the need for oxygen, the products and the relative amounts of ATP produced/energy transferred