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Contents
Respiration
Releasing energy
Aerobic respiration
Rate of respiration
Anaerobic respiration
Summary activities
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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?
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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.
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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.
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Anaerobic respiration: word equation
glucose
lactic
acid
energy
energy
glucose
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lactic
acid
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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:
 Anaerobic respiration releases much less energy from
glucose compared to aerobic respiration.
 Lactic acid is a poisonous waste product.
Why is anaerobic respiration not the best way to get energy
from glucose?
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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?
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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?
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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’?
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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?
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Anaerobic respiration: word equation activity
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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?
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