Aerobic respiration is a chemical reaction that takes place in cells to release stored chemical energy. It involves glucose reacting with oxygen to produce carbon dioxide, water, and release energy. Anaerobic respiration occurs when cells do not get enough oxygen, resulting in incomplete breakdown of glucose and lactic acid production, but less energy is released. The rate of aerobic respiration increases with more intense physical activity as cells need more energy, requiring faster breathing and heart rate to supply increased oxygen and glucose.

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KS4 Biology
Respiration

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Contents
Respiration
Anaerobic respiration
Summary activities
Releasing energy
Rate of respiration
Aerobic respiration

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Energy for life
Every living cell in your body needs energy. The average
adult has about 50 million million cells – that’s a lot of energy!
In body cells, the energy needed for life comes from the
chemical energy stored in glucose.
energy
Where does all this energy come from?

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What is needed for releasing energy?
What other substance is needed for energy to be released
from this fuel?
Burning is a chemical reaction in which energy is released
in the form of heat.
?fuel oxygen

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What does the body need for releasing energy?
The body’s energy-releasing process depends on the
digestive system and the breathing system.
How does the body’s energy-releasing process compare
with releasing energy from wood?
What are the substances supplied by these systems?
? ??
glucose is the fuel
supplied by
the digestive system
oxygenoxygen
is supplied by
the breathing system

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Glucose and oxygen enter the body
in different ways,
Where are these substances needed
and how do they get there?
Glucose and oxygen are
transported around the body
by the circulatory system.
Blood flowing in blood vessels
takes these important substances
to where they are needed – the
body’s cells.
Transport around the body
but are needed at
the same destinations.

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In the body’s cells, the chemical energy stored in glucose
is usually released by a chemical reaction with oxygen.
The body’s energy-releasing process
What is this energy-releasing process called?
glucose
oxygen
energy
respiration
Why does every living cell need a constant supply of
glucose and oxygen?

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Contents
Respiration
Anaerobic respiration
Summary activities
Releasing energy
Rate of respiration
Aerobic respiration

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Respiration is the process used by the body’s cells
to release the chemical energy stored in glucose.
When oxygen is involved in this energy-releasing process,
it is called aerobic respiration.
What do you think aerobic means?
Aerobic respiration is an efficient process that generates
enough energy to supply the whole body.
Our bodies perform aerobic respiration most of the time,
as long as the supply of oxygen remains high enough.
What is aerobic respiration?
aerobic = ‘with oxygen’

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Waste products of aerobic respiration
Breathing in obtains the oxygen needed for aerobic
respiration. How does the body get rid of the waste products?
Breathing out removes the waste products of aerobic
respiration.
How can the waste products of this reaction be identified?
Aerobic respiration releases energy that is useful.
This process is a chemical reaction between glucose and
oxygen which also generates waste products.
?glucose oxygen ? energy

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Waste products – limewater test
Limewater turns cloudy when carbon dioxide passes through.
What does this test tell you about aerobic respiration?
One waste product of aerobic respiration must be…
2. Blow gently
through a straw
into the limewater.
3. After a short time,
the limewater
turns cloudy.
limewater
straw
1. Take a test tube
of limewater,
a clear liquid.
…carbon dioxide.

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Waste products – see your breath test
Water vapour condenses into a liquid and becomes visible.
What does this test tell you about aerobic respiration?
Another waste product of aerobic respiration must be…
What happens when you
breathe out onto a cold
pane of glass?
What happens when you
breathe out on a freezing
cold day?
In both cases, you can see some of the air that you have
breathed out. Why?
water vapour
…water.

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Aerobic respiration: summary
Summarize the process of aerobic respiration in a sentence.
Aerobic respiration is a chemical reaction so it can also be
summarized in a word equation.
What is the word equation for this vital chemical reaction?
Aerobic respiration is a chemical reaction
that takes place in all living cells,
in which glucose reacts with oxygen
to produce carbon dioxide and water
and stored chemical energy is released.

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Aerobic respiration: word equation
carbon
dioxideglucose oxygen water
carbon
dioxide
wateroxygen
glucose
energy
energy

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Aerobic respiration: word equation activity

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Aerobic respiration: quiz

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Contents
Respiration
Anaerobic respiration
Summary activities
Releasing energy
Rate of respiration
Aerobic respiration

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The rate of respiration
Aerobic respiration is a chemical reaction and so has a rate.
Is the rate of this reaction always the same?
Your body requires different amounts of energy depending
on how active you are. So the rate of aerobic respiration
changes depending on the amount of energy needed.
During what type of activities, does the rate of aerobic
respiration increase so that more energy can be released?
carbon
dioxideglucose oxygen water energy

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When does the body need to release more energy?
How much energy is needed?
During which type of activities is the rate of aerobic
respiration higher?
not very active
= low energy
requirements
very active
= high energy
requirements

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Different energy needs
How does the body respond to these different rates of
aerobic respiration?
high energy need
These extremely different activities both need energy from
aerobic respiration but is the rate of this reaction the same?
low energy need
= low rate of
aerobic respiration
= high rate of
aerobic respiration

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The body’s response to low energy needs
During sleep, the body’s energy needs are low
and so the rate of aerobic respiration is slow
but steady.
How does this affect the amount of glucose
and oxygen needed?
How does this affect the heart rate and breathing rate?
Under these resting conditions, the body has plenty of time
to inhale oxygen and the blood is able to supply enough
low energy
need
low rate of
aerobic
respiration
low demand
for glucose
and oxygen
slow heart
and breathing
rates
glucose and oxygen to the body’s cells.

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The body’s response to high energy needs
During running, the body’s energy needs are high
and so the rate of respiration increases to meet
this demand.
How does this affect the amount of glucose and
oxygen needed?
How does this affect the heart rate and breathing rate?
high energy
need
high rate of
aerobic
respiration
high demand
for glucose
and oxygen
fast heart
and breathing
rates
Under these tougher conditions, the body has to work hard
to supply enough glucose and oxygen to the body’s cells
for aerobic respiration to produce enough energy.

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Contents
Respiration
Anaerobic respiration
Summary activities
Releasing energy
Rate of respiration
Aerobic respiration

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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.
carbon
dioxideglucose oxygen 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!
carbon
dioxideglucose oxygen 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.
What do you think anaerobic means?
lactic
acid energyglucose
Our bodies can only release energy without oxygen for a
short period of time.
anaerobic = ‘without oxygen’
Anaerobic respiration involves the incomplete breakdown
of glucose and so releases less energy than aerobic
respiration.

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Anaerobic respiration: word equation
lactic
acidglucose
lactic
acidglucose
energy
energy

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The problems with anaerobic respiration
Anaerobic respiration is useful to the body when energy is
needed in a hurry.
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?
lactic
acidglucose energy

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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.
The body is now at rest but the breathing rate
and heart rate remain high. Why does this happen?
carbon
dioxide
lactic
acid oxygen water
Why do the breathing and heart rates return to normal
after a few minutes of recovery?
lactic
acid energyglucose
Oxygen is needed to get rid of lactic acid by turning it
into carbon dioxide and water.

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

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It is the oxygen needed to get rid of lactic
acid that pays back the oxygen debt.
Oxygen debt – pay off
The oxygen debt caused by anaerobic
respiration is paid off during the recovery
period after exercise.
carbon
dioxide
lactic
acid oxygen 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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Contents
Respiration
Anaerobic respiration
Summary activities
Releasing energy
Rate of respiration
Aerobic respiration

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Which type of respiration?

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Multiple-choice quiz