Contents Respiration Releasing energy Aerobic respiration Rate of

Contents Respiration Releasing energy Aerobic respiration Rate of respiration Anaerobic respiration Summary activities 1 of 36 © Boardworks Ltd 2004

Not enough oxygen! Most of the time the body’s cells has a good supply of oxygen and is able to release energy by aerobic respiration. glucose oxygen carbon dioxide water energy Sometimes, during strenuous exercise, the breathing rate and blood flow are not able to deliver enough oxygen to the body’s cells. How does this affect the release of energy? 2 of 36 © Boardworks Ltd 2004

Not enough oxygen! If the body is not able to supply enough oxygen, aerobic respiration cannot take place and energy is not released! glucose oxygen carbon dioxide water energy The body still has a supply of glucose, so how does it continue to get energy? When there is not enough oxygen, energy can still be released from glucose by another type of respiration called anaerobic respiration. 3 of 36 © Boardworks Ltd 2004

Respiration without oxygen During anaerobic respiration, glucose breaks down into a substance called lactic acid and some energy is released. glucose lactic acid energy What do you think anaerobic means? anaerobic = ‘without oxygen’ Anaerobic respiration involves the incomplete breakdown of glucose and so releases less energy than aerobic respiration. Our bodies can only release energy without oxygen for a short period of time. 4 of 36 © Boardworks Ltd 2004

Anaerobic respiration: word equation glucose lactic acid energy glucose 5 of 36 lactic acid © Boardworks Ltd 2004

The problems with anaerobic respiration Anaerobic respiration is useful to the body when energy is needed in a hurry. glucose lactic acid energy There are two problems with anaerobic respiration: l Anaerobic respiration releases much less energy from glucose compared to aerobic respiration. l Lactic acid is a poisonous waste product. Why is anaerobic respiration not the best way to get energy from glucose? 6 of 36 © Boardworks Ltd 2004

Why is lactic acid so harmful? Lactic acid is the product of anaerobic respiration and is harmful because it can stop muscles from doing their job. If lactic acid builds up in muscle cells, it stops muscles from contracting and relaxing and they become fatigued. The muscles ache and the body experiences cramp, which forces the body to stop what it is doing and rest. Why can anaerobic respiration only be carried out for short periods of time? 7 of 36 © Boardworks Ltd 2004

Recovery and getting rid of lactic acid After anaerobic respiration, the body is in recovery and must get rid lactic acid. glucose lactic acid energy The body is now at rest but the breathing rate and heart rate remain high. Why does this happen? Oxygen is needed to get rid of lactic acid by turning it into carbon dioxide and water. lactic acid oxygen carbon dioxide water Why do the breathing and heart rates return to normal after a few minutes of recovery? 8 of 36 © Boardworks Ltd 2004

Oxygen debt – build up During aerobic respiration, muscles get energy from glucose by ‘paying’ for it with oxygen. glucose oxygen carbon dioxide water energy During anaerobic respiration, muscles get energy from glucose but do not ‘pay’ for it with oxygen. glucose lactic acid energy This means that an oxygen debt is created. When and how is this oxygen debt ‘paid off’? 9 of 36 © Boardworks Ltd 2004

Oxygen debt – pay off The oxygen debt caused by anaerobic respiration is paid off during the recovery period after exercise. It is the oxygen needed to get rid of lactic acid that pays back the oxygen debt. lactic acid oxygen carbon dioxide water oxygen to pay back ‘oxygen debt’ When is the oxygen debt completely paid off? 10 of 36 © Boardworks Ltd 2004

Anaerobic respiration: word equation activity 11 of 36 © Boardworks Ltd 2004

tasks • What is anaerobic respiration? ? • What is the word equation for anaerobic respiration ? ? • What is lactic acid? • What is oxygen debt? • How does the body get rid of lactic acid? 12 of 36 © Boardworks Ltd 2004