Learning outcomes:
2.33
understand that the process of respiration releases energy in living organisms
2.34
describe the differences between aerobic and anaerobic respiration
2.35
write the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms
2.36
write the word equation for anaerobic respiration in plants and in animals
2.37
describe experiments to investigate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms.
Respiration is the process that releases energy into every living cell of every organism. The energy is essential for keeping the cell alive as it powers processes like protein synthesis, growth, repair, division etc.

Oxygen + Glucose ---> Carbon Dioxide + Water

6O2 + C6H12O6 ---> 6CO2 + 6H2O

Some cells have the ability to respire without using oxygen. This is called anaerobic respiration. Only liver and muscle cells can do this in humans. Anaerobic respiration allows the cell to carry on working despite there being a shortage of oxygen (this is very useful in muscle cells – particularly if you are running for your life!)

Glucose ---> Lactic Acid

C6H12O6 ---> 2CH3CHOHCOOH (interest only – don’t learn)

Anaerobic respiration produces Lactic Acid, which is poisonous. Lactic acid builds up inside muscle cells and quickly leads to muscle fatigue and cramp. Eventually the muscle cell will stop working. During recovery the lactic acid is transported to the liver via the bloodstream. The liver breaks the lactic acid into CO2 and water. Oxygen is required for this, which is called the Oxygen Debt.
Yeast also respire anaerobically, except they do not produce lactic acid like humans. Instead they make ethanol. This type of anaerobic respiration is also called alcoholic fermentation. It is used in the baking and brewing processes.

Glucose ---> Ethanol + Carbon Dioxide

C6H12O6 ---> 2CH3CH2OH + 2CO2 (interest only)

You need to know an experiment that shows that living organisms produce CO2 through respiration. The best example is to suspend some maggots or seeds near the top of a test tube sealed with a bung (suspend the maggots / seeds in a wire mesh). A small amount of lime water in the bottom of the test tube will turn milky over time, indicating that CO2 has been produced.

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