1. health and fitness
2. exercise

KS4 Biology
Respiration
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Contents
Respiration
Releasing energy
Aerobic respiration
Rate of respiration
Anaerobic respiration
Summary activities
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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!
energy
Where does all this energy come from?
In body cells, the energy needed for life comes from the
chemical energy stored in glucose.
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What is needed for releasing energy?
Burning is a chemical reaction in which energy is released
in the form of heat.
What other substance is needed for energy to be released
from this fuel?
fuel
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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.
What are the substances supplied by these systems?
glucose is the fuel
supplied
? by
the digestive system
oxygen
is supplied
?
by
the breathing system
How does the body’s energy-releasing process compare
with releasing energy from wood?
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Transport around the body
Glucose and oxygen enter the body
in different ways, but are needed at
the same destinations.
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.
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The body’s energy-releasing process
In the body’s cells, the chemical energy stored in glucose
is usually released by a chemical reaction with oxygen.
What is this energy-releasing process called?
respiration
glucose
oxygen
energy
Why does every living cell need a constant supply of
glucose and oxygen?
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Contents
Respiration
Releasing energy
Aerobic respiration
Rate of respiration
Anaerobic respiration
Summary activities
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What is aerobic respiration?
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 = ‘with oxygen’
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.
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Waste products of aerobic respiration
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
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?
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Waste products – limewater test
1. Take a test tube
of limewater,
a clear liquid.
3. After a short time,
2. Blow gently
the limewater
through a straw
turns cloudy.
into the limewater.
straw
limewater
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…
…carbon dioxide.
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Waste products – see your breath test
What happens when you
breathe out onto a cold
pane of glass?
What happens when you
breathe out on a freezing
cold day?
water vapour
In both cases, you can see some of the air that you have
breathed out. Why?
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…
…water.
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Aerobic respiration: summary
Summarize the process of aerobic respiration in a sentence.
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.
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?
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Aerobic respiration: word equation
glucose
oxygen
carbon
dioxide
water
energy
energy
glucose
oxygen
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carbon
dioxide
water
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Aerobic respiration: word equation activity
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Aerobic respiration: quiz
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Contents
Respiration
Releasing energy
Aerobic respiration
Rate of respiration
Anaerobic respiration
Summary activities
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The rate of respiration
Aerobic respiration is a chemical reaction and so has a rate.
glucose
oxygen
carbon
dioxide
water
energy
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?
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How much energy is needed?
When does the body need to release more energy?
not very active
= low energy
requirements
very active
= high energy
requirements
During which type of activities is the rate of aerobic
respiration higher?
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Different energy needs
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 energy need
= high rate of
aerobic respiration
How does the body respond to these different rates 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?
low energy
need
low rate of
aerobic
respiration
low demand
for glucose
and oxygen
slow heart
and breathing
rates
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
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?
high energy
need
high rate of
aerobic
respiration
high demand
for glucose
and oxygen
fast heart
and breathing
rates
How does this affect the heart rate and breathing rate?
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
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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Contents
Respiration
Releasing energy
Aerobic respiration
Rate of respiration
Anaerobic respiration
Summary activities
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Which type of respiration?
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Multiple-choice quiz
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