AQA GCSE Biology Trilogy: Respiration

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.

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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.

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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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