1. Define respiration as the chemical reactions that break down nutrient molecules in living cells to release energy.

The definition is pretty much given in the point!


  1. State the uses of energy in the body of humans: muscle contraction, protein synthesis, cell division, growth, the passage of nerve impulses and the maintenance of a constant body temperature.

Muscle contraction, protein synthesis, cell division, the passage of nerve impulses and the maintenance of a constant body temperature all require energy.


  1. State the word equation for aerobic respiration.

Glucose + oxygen  carbon dioxide + water


  1. Define aerobic respiration as the release of a relatively large amount of energy in cells by the breakdown of food substances in the presence of oxygen.

This is a pretty self-explanatory point!


  1. State the equation for aerobic respiration, using symbols:

(C6H12O6 + 6O26CO2 + 6H2O).

I don’t think this point requires an explanation either.


  1. Define anaerobic respiration as the release of a relatively small amount of energy by the breakdown of food substances in the absence of oxygen.

This topic certainly has plenty of self-explanatory points.


  1. State the word equation for anaerobic respiration in muscles during hard exercise (glucose → lactic acid) and the microorganism yeast (glucose → alcohol + carbon dioxide).

In muscles, glucose is respired into two lactic acid molecules. Yeast respires glucose into alcohol and carbon dioxide.


  1. Describe the effect of lactic acid in muscles during exercise (include oxygen debt in outline only).

During vigorous exercise, your heart can’t pump blood around your body fast enough for enough oxygen to be supplied to your muscles – your muscles require too much energy. In order to gain enough energy, in addition to respiring aerobically, your muscle cells also respire anaerobically, resulting in the build-up of lactic acid.

In higher concentrations, lactic acid can prove to be toxic to muscles cells, causing cramps, muscle fatigue, soreness, etc. Therefore, after exercise, we continue to breathe hard and our heart rate remains high for some time, to supply your muscles with enough oxygen to further break down lactic acid into carbon dioxide and water. This is called the oxygen debt – an easy way to remember this is, during exercise, you ‘borrowed’ extra energy without ‘paying’ for it with oxygen.

So in simple words, oxygen debt is the extra oxygen required by your body to break down the lactic acid produced by your body after strenuous exercise.

Your breathing rate and heart rate return to normal after you finish breaking down all the lactic acid.


  1. Describe the role of anaerobic respiration in yeast during brewing and bread making.


Yeast is dissolved into a warm maltose-containing solution. The yeast respires anaerobically (this is fermentation). It produces the alcohol called ethanol, making the drink alcoholic, and carbon dioxide, making it fizzy.

Bread making:

The first stage of bread making usually involves mixing yeast, water and sugar. This activates the yeast to begin respiring anaerobically. After flour is added to make the dough, it is left in a warm place to rise. The dough rises due to the carbon dioxide produced during respiration.

Baking kills the yeast and evaporates any alcohol formed.

  1. Compare aerobic respiration and anaerobic respiration in terms of relative amounts of energy released.

Usually, in biology, the amount of energy released in respiration is proportional to the number of C-H bonds broken in the substance respired.

Since aerobic respiration allows the breaking of all C-H bonds to form CO2 and H2O, and anaerobic means that a lot of the C-H bonds may not be broken, more energy is released in aerobic respiration.




Notes submitted by Sarah.

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