Respiration (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Respiration

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

• The chemical process of cellular respiration releases energy

• The energy transferred supplies all the energy needed for living processes to occur within cells and organisms as a whole

• Organisms need energy for:

  • Chemical reactions to build larger molecules from smaller molecules

  • Muscle contraction to allow movement

  • Keeping warm (to maintain a constant temperature suitable for enzyme activity)

Uses of the energy released from respiration

Aerobic Respiration

• Respiration in cells can take place aerobically (using oxygen) to transfer energy; glucose is reacted with oxygen in this process

• The equations that summarise the chemical reactions of respiration that release energy from glucose are:

Word equation for aerobic respiration

• Aerobic respiration uses oxygen and most of the reaction takes place in the mitochondria (these are shown above the arrow in the equations)

Anaerobic Respiration in Animals

• Respiration in cells can take place anaerobically (without oxygen), to transfer energy; it simply involves the incomplete breakdown of glucose into lactic acid

• This occurs when the body can’t supply enough oxygen for aerobic respiration, such as during vigorous exercise

• Anaerobic respiration is represented by the equation:

Word equation for anaerobic respiration in animals – some bacterial cells respire in this way too

• As the oxidation of glucose is incomplete in anaerobic respiration much less energy is transferred than in aerobic respiration

• Anaerobic respiration takes place without the need of oxygen

Oxygen debt

• Oxygen debt occurs when the body cannot supply enough oxygen to meet its energy demands, often during exercise

• As a result, the muscles carry out anaerobic respiration, which produces lactic acid as a by-product

  • This lactic acid can cause muscle fatigue and discomfort

• After exercise, extra oxygen is needed to break down the lactic acid and restore the body to its normal state

  • This is why breathing and heart rate remain high for a while after intense activity—to “repay” the oxygen debt

Comparing Anaerobic & Aerobic Respiration

• You need to be able to compare the processes of aerobic and anaerobic respiration with regard to the need for oxygen, the differing products and the relative amounts of energy transferred: