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KS4 Biology
Respiration
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Contents
Respiration
An energy-making process
Waste products
What is respiration?
Aerobic respiration
Anaerobic respiration
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An energy-making process
We know that we breathe constantly throughout life.
Also, we know that if we stopped breathing we would
eventually die.
So, breathing in oxygen (O2) must be linked to something
that we need constantly and without it our bodies would die.
The answer is ENERGY making.
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Ingredients to make energy
The energy-making process depends on the breathing
system and the digestive system.
Imagine a fire...
This will produce energy in the form of heat but only if
it is supplied with 2 main ingredients.
FUEL
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OXYGEN
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Our fuel
The bodies energy-making reaction needs similar
things to the energy-making process of fire.
Like the fire, the body needs oxygen and a fuel.
the oxygen is
supplied by the
breathing
system
+
and the fuel (in the form of
digested food) comes courtesy
of the digestive system.
2
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Our pipelines to the cells
If we now think back over the journey of oxygen and
digested food through the human body, we will
realise that they both end up in the same place.
food
oxygen
breathing
system
these substances
eventually arrive
at the body cells
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digestive
system
BLOOD
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Every living cell needs to respire
Therefore, the raw materials for the energy-making
process eventually arrive at the body cells.
This energy-making process is known as...
RESPIRATION
Each living cell is supplied with food and oxygen in
order to generate energy.
capillary
blood
oxygen
+
food
muscle cell
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Contents
Respiration
An energy-making process
Waste products
What is respiration?
Aerobic respiration
Anaerobic respiration
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Waste products
No chemical reaction is 100% efficient.
Therefore, as well as producing the useful energy, respiration
also produces waste products.
These waste products
must be removed
from the body.
If the process of breathing in is used to obtain the
O2 for respiration, it would make sense for the body
to use the process of breathing out to remove these
waste products of this reaction.
This is exactly what happens!
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What’s the waste?
If we study the composition of the air that is breathed
out, we will identify the waste products of respiration.
Two tests help us identify these waste products.
Test One
Blow gently through a
straw into a test tube filled
with lime water.
straw
Before you start
exhaling, the lime
water is a clear liquid
After a short while,
the lime water
becomes cloudy.
lime water
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Identification of the first waste product
If a gas is bubbles through lime water and the liquid
becomes cloudy, the gas is identified as….
carbon dioxide (CO2)
This is the first of our waste products of respiration.
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Seeing your breath
The air you breathe out is visible
because the mystery waste product
condenses back into a liquid.
Test Two
On a freezing
cold day, watch
what happens
when you
breathe out.
This waste product is water vapour and so our final
waste product of the process of respiration is...
water
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The equation for respiration
Using this information, we can now write out the full equation
for respiration.
FOOD
(GLUCOSE)
from
digestive
system
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+
OXYGEN
from
breathing
system
CARBON
DIOXIDE
waste
product
exhaled
+ WATER +
waste
product
exhaled
ENERGY
USEFUL!
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Contents
Respiration
An energy-making process
Waste products
What is respiration?
Aerobic respiration
Anaerobic respiration
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When is energy needed?
However, to call this reaction just ‘respiration’ is not
quite correct.
Let us try to understand why….. Think about what you
do in an average day.
sometimes you
are resting
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low energy
requirements
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A busy day!
sometimes
you are active
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high energy
requirements
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Food and fuel flexibility
Your body requires different amounts of energy at
different times.
Therefore…
this is exactly
what happens
our rate of breathing will change
the blood will have to flow
at different speeds
according to demand
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the process of respiration
must be able to ‘speed
up’ and ‘slow down’
this will mean that
we need different
amounts of food to
feed the reaction
it will also mean that we
need different amounts of
oxygen to feed the reaction
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Throughout the day…
It seems that the process of respiration changes
during the course of the day.
Let’s take two extreme examples human activity and
see how the process of respiration change...
1.
sleeping
2.
running a
marathon
This is not the daily activities of an average human, but
this scenario will help us understand the process of
respiration in more depth.
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Sleeping
SLEEPING
When we sleep, our body is at rest.
There is a low demand for energy.
low
energy
demand
low demand
for food and
oxygen
blood flow
does not
have to be
rapid
the breathing
rate remains
normal
In other words, the body has plenty of time to inhale the
oxygen that it needs. It also has time to completely digest
food to release the important chemicals (e.g glucose). The
blood can efficiently transport these substances to the cells
without increasing its rate of flow.
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Contents
Respiration
An energy-making process
Waste products
What is respiration?
Aerobic respiration
Anaerobic respiration
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Aerobic respiration
When the body is performing respiration in such a way, it
is given a special name.
When the body…
O2
has plenty of oxygen
is able to completely digest food
can supply the cells with the oxygen and
food that they need
We say it is performing AEROBIC respiration.
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Equation for aerobic respiration
So our original equation for the process of respiration
is actually the equation for aerobic respiration.
Glucose + Oxygen
Carbon Dioxide + Water + Energy
This is an efficient process... enough energy is made to
supply the whole body.
Our bodies perform aerobic respiration for much of the day.
In fact, as long as the supply of oxygen remains high
enough, we will continue to perform aerobic respiration.
Of course, the amount of energy we produce will drop if
the level of oxygen drops.
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Exercise: before - during - after
So, now we know that there is a form of respiration which is
performed when there is a supply of oxygen to the body.
But, what happens in situation 2?
Remember the runners?
Are they performing aerobic respiration?
Well, in order to answer that question, we have to think
about what their bodies are doing during the race.
before
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during
after
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Physical activity dictates energy demands
What’s happening?
before
Energy
demands
Oxygen
available
Form of
respiration
low
high
aerobic
high
low / none
aerobic
(but slowing)
during
after
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dropping
none / low
?
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Running out of the good stuff
?
How can the body perform aerobic
respiration in this situation?
Aerobic respiration requires oxygen but when you have
been running a race or doing strenuous exercise, you
cannot inhale enough oxygen for this reaction.
Glucose + Oxygen
Carbon Dioxide + Water + Energy
This process fails!
But, if this process fails when the oxygen levels drop, the
body would be left with absolutely no energy.
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Oxygen levels at zero
No energy would lead the body to stop working!
The body would stop working
whenever it became short of oxygen.
The problem is that we often do exercise and our
bodies continue working.
What must be happening when our oxygen levels
drop to zero?
The body must be able to keep working through
short periods of low/no oxygen.
But how?
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Oxygen shortage at the cellular level
With aerobic respiration, the cells supply of oxygen and
food is relatively constant.
oxygen
When this supply is
cut off, the cell is left
with excess food
and lacks energy.
food
blood
cell
It solves this problem by making energy from just the food
alone!
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Contents
Respiration
An energy-making process
Waste products
What is respiration?
Aerobic respiration
Anaerobic respiration
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Anaerobic respiration
Now because it is releasing energy from food, it is still
performing respiration.
But it is not aerobic respiration because there is
no oxygen present. (aero- means of air)
Therefore we call it ANAEROBIC respiration.
The energy being made by breaking down the food
without oxygen.
This seems a better process!
To be able to make energy without needing oxygen would
be very beneficial.
However, there is a problem.
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Hitting the wall
Remember the last time you ran a race, carried a
heavy weight or swam under water for too long and
ran short of breath.
It probably felt uncomfortable.
Well, if anaerobic respiration was as efficient as it
sounds, this lack of comfort would not happen.
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What’s wrong with anaerobic respiration?
So, what is the problem with anaerobic respiration?
When the cell breaks down the food to release the
energy, it also makes a potentially harmful waste
product.
The breakdown of the food is also incomplete.
It is not an efficient process.
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The anaerobic equation
This waste product is known as LACTIC ACID.
Therefore the equation for anaerobic respiration is…
Glucose
from the
digestive system
Lactic Acid + (some) Energy
waste
product
not as much energy
as with aerobic
respiration
You will notice that this reaction is only an option for short
periods of time.
This is because the waste product is harmful and not
enough energy is made to satisfy the body.
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Why is lactic acid so harmful?
Well, this chemical can stop muscles within the body,
from contracting and relaxing.
relaxation
The lactic acid soaks the muscle cells and
prevents the muscle cell from doing its job.
contraction
If the muscles in your body stop contracting and
relaxing they are said to be fatigued.
They eventually seize and you experience cramp.
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Striking the right balance
If you want to consider the full impact of damage caused
by the presence of lactic acid, just remember that the
heart is made of muscle cells!
This leaves us with a problem...
if we want to do exercise
We want the energy
that anaerobic
respiration produces
YES
NO
But we don’t want the
lactic acid waste
product
So the answer is for anaerobic respiration to be a ‘gap-fill’
during periods of very low / no oxygen availability.
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Oxygen debt
rest
aerobic
exercise
stops
oxygen
levels
anaerobic
exercise
time
Anaerobic respiration keeps our bodies going until we
can breathe in more oxygen again.
Whilst we are performing anaerobic respiration, our
bodies are building up a ‘debt’ of oxygen.
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Paying it off
This is rather like owing the bank some money.
Once you get some money, you have to pay off that
debt.
We can think of that debt as being the presence of
lactic acid in the body.
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Doing the sums
When our bodies convert
from aerobic to anaerobic
respiration, we start
making lactic acid.
As soon as this begins, the
body starts building an
oxygen debt.
This is equivalent to the
amount of oxygen it would
have used if aerobic
respiration had continued.
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Dealing with the lactic acid build-up
This oxygen debt will have to be repaid when the
exercise stops.
Oxygen will be used to break down the lactic acid that is
present in the body.
The oxygen ‘oxidises’ the lactic acid.
In fact, the lactic acid is oxidised into carbon dioxide
and water.
In this way, the process of aerobic respiration can be converted into
The process of anaerobic respiration which can then turn back into...
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Respiration summary
The body has the ability to produce energy, despite changes
in the supply of oxygen.
Here are the two forms of respiration.
Aerobic respiration (complete breakdown of food)
glucose + oxygen
carbon dioxide + water + energy
Anaerobic respiration (incomplete breakdown of food)
glucose + oxygen
carbon dioxide + water + lactic
acid + little energy
Aerobic respiration is performed when oxygen is present.
Anaerobic respiration is performed when oxygen is absent.
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Respiration…do I really need oxygen?
Work through the following tasks, filling the missing words
or crossing out the wrong words where necessary.
A
The body can perform two types of respiration.
These are:
1. ____________ respiration (performed in plenty of O2)
2. ____________ respiration (performed in little or no O2)
B
Aerobic Respiration
_______ + ______
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_______ _______ + ______ + ______
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Respiration…do I really need oxygen?
C
Aerobic respiration is performed when the supply of
oxygen to the cells is HIGH / LOW.
It is the COMPLETE / INCOMPLETE breakdown of food
and so is very INEFFICIENT / EFFICIENT.
It is a method of respiration that produces LOTS /
LITTLE energy for the body.
If the body does not get enough oxygen to the cells it
CAN / CAN’T perform aerobic respiration.
Instead it has to perform __________ respiration for a
LONG / SHORT period of time.
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Why would the body be short of oxygen?
Two common reasons for the body being short of energy
would be if a human was performing…
D
1. HEAVY / LIGHT exercise for LONG / SHORT periods of
time.
2. HEAVY / LIGHT exercise for LONG / SHORT periods of
time.
E
Anaerobic Respiration
_______ + ______
_______ _______ + ______
waste product
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useful
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Why would the body be short of oxygen?
F
Anaerobic respiration is performed when the supply
of oxygen of the cells is HIGH / LOW.
It is the COMPLETE / INCOMPLETE break down of
food and so is very INEFFICENT / EFFICIENT.
It is a method of respiration that produces LOTS /
LITTLE energy for the body.
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The acid test
fatigued
aerobic
oxygen
muscle
contracting
anaerobic
broken
This is poisonous. It can build up in _________ cells and
stop them ___________ and relaxing. We say the cell is
tired or __________.
If we then relax and breathe again the body recovers. The
supply of ___________ increases and the lactic acid is
___________ down. The body can now stop performing
___________ respiration and go back to performing
__________ respiration.
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Multiple choice section
Multiple choice questions
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1. Which of the following is a definition of respiration?
A breathing
B the release of energy from food
C obtaining oxygen and releasing carbon dioxide
D exchanging gases
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2. Aerobic respiration is a type of respiration that uses
up…
A oxygen.
B energy.
C carbon dioxide.
D water.
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3. Which of the following are the raw materials for the
process of aerobic respiration?
A carbon dioxide, water and glucose
B glucose and carbon dioxide
C oxygen, water and energy
D oxygen and glucose
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4. Which of the following are the waste products of
aerobic respiration?
A oxygen and carbon dioxide
B glucose and energy
C carbon dioxide and water
D oxygen, water and energy
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5. Which of the following is a useful product of aerobic
respiration?
A oxygen
B energy
C carbon dioxide
D glucose
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6. Which of the following is an accurate equation for this
process of aerobic respiration?
A Glucose + Carbon Dioxide  Water + Energy + Oxygen
B Oxygen + Carbon Dioxide  Glucose + Sugar + Energy
C Water + Energy + Sugar  Carbon Dioxide + Oxygen
D Glucose + Oxygen  Carbon Dioxide + Water + Energy
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7. Animals perform anaerobic respiration when the
body is short of…
A energy.
B carbon dioxide.
C food.
D oxygen.
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8. The main waste product from the process of
anaerobic respiration is…
A lactic acid.
B carbon dioxide.
C urea.
D water.
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9. Which of the following statements accurately
describes one use of the energy released during
respiration?
A The breakdown of protein into muscle from which
amino acids are made.
B The building of amino acids from proteins.
C The building of protein from amino acids, with these
proteins then being used to make muscle.
D The building of carbohydrates from fatty acids to
make organs.
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10. One further use of the energy that is
generated by respiration is in…
A the lowering of the body temperature on a cold
day.
B the raising of the body temperature on a hot
day.
C allowing the body temperature to change to
match the air temperature.
D maintaining a steady body temperature despite
changes in the air temperature.
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11. What causes the inefficient contraction of muscle
that can occur during anaerobic respiration?
A The complete breakdown of glucose (releasing
more energy than aerobic respiration) and the build
up of lactic acid.
B The incomplete breakdown of glucose (releasing
less energy than aerobic respiration) and the build
up of lactic acid.
C The incomplete breakdown of glucose (releasing
more energy than aerobic respiration) and the
breakdown of lactic acid.
D The complete breakdown of glucose (releasing
more energy than aerobic respiration) and the
breakdown of lactic acid.
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12. David Beckham has just come off the pitch at Old
Trafford after a tiring game.
He is breathing heavily in order to…
A carry out a series of chemical reactions that result
in the complete oxidation of lactic acid to carbon
dioxide and water.
B slow down anaerobic respiration.
C speed up anaerobic respiration.
D increase the “oxygen debt”.
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