Respiration:

• Cellular respiration is an exothermic reaction which is continuously occurring in living cells.

• The energy transferred supplies all the energy needed for living processes, such as -

  • Chemical reactions to build larger molecules

  • Movement

  • Keeping warm

Aerobic Respiration:

Anaerobic Respiration:

• Anaerobic respiration in yeast cells is called fermentation and has economic importance in the manufacture of bread and alcoholic drinks.

Responses to Exercise:

• During exercise, the human body reacts to the increased demand for energy.

• The heart rate, breathing rate and breath volume increase during exercise to supply the muscles with more oxygenated blood.

• If insufficient oxygen is supplied anaerobic respiration takes place in muscles.

• The incomplete oxidation of glucose causes a build-up of lactic acid and creates an oxygen debt.

• During long periods of vigorous activity, muscles become fatigued and stop contracting efficiently.

• Blood flowing through the muscles transports the lactic acid to the liver where it is converted back into glucose.

• Oxygen debt is the amount of extra oxygen the body needs after exercise to react with the accumulated lactic acid and remove it from the cells.

Metabolism:

• Metabolism - the sum of all the reactions in a cell or the body.

• The energy transferred by respiration in cells is used by the organism for the continual enzyme-controlled processes of metabolism that synthesise new molecules.

• Metabolism includes -

  • Conversion of glucose to starch, glycogen and cellulose

  • Formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids

  • The use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins

  • Respiration

  • Breakdown of excess proteins to form urea for excretion.

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