B3 - Respiration

• Respiration releases energy from food and this energy is trapped in a molecule called ATP. ATP can then be used to provide the energy for many different processes in living organisms.

• Aerobic respiration involves the use of oxygen. The symbol equation for aerobic respiration is: 

C6 H12 06 + 6O2 --> 6CO2 + 6H20

• During exercise, despite an increase in breathing rate and heart rate, the muscles often do not recieve enough oxygen. They start to use anaerobic respiration in addition to earobic respiration.
• The word equation for anaerobic respiration is:

glucose ---> lactic acid (+energy)

• Anearobic respiration has two main disadvantages over aerobic respiration.

- the lactic acid that is made by anaerobic respiration builds up in muscles and causes pain and fatigue.

- anaerobic respiration releases much less energy per glucose molecule than aerobic respiration.

• The incomplete breakdown of glucose resulting in lactic acid is called oxygen debt.
• During recovery the breathing rate and heart rate stay so high that:

- rapid blood flow can carry lactic acid away to the liver

- extra oxygen can be supplied, enabling the liver to break down the lactic acid.

• Two experiments the measure respiration:

- measuring how much oxygen is used up - the faster it is consumed - the fatser the respiration rate

- the rate at which carbon dioxide is made.

• Scientists use this to calculate the respiratory quotient.

- RQ = carbon dioxide produced

oxygen used

• The metabolic rate is described as the sum of all the reactions taking place in the body. If the metabollic rate is high, more oxygen is needed, as aerobic respiration is faster.
• Changes in temperature and pH can also affect respiration rate, as they affect enzymes, and respiration is controlled by enzymes.