CELLULAR
RESPIRATION
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worksheets
(include answers)
CELLULAR RESPIRATION
1.
(a) Fill in the missing words:
Cellular respira�on is the process by which all living things - plants, animals, fungi, pro�sts and
bacteria - create energy in the form of ________________. This involves the breaking down of
__________________, a complex organic molecule, into __________________ __________________
and __________________, releasing energy. The complete breakdown of __________________ also
requires __________________.
(b) Complete the following cellular respira�on equa�on:
C6H12O6 + ___O2
___CO2 + ___H2O (+ 30 ATP)
2. Cellular respira�on occurs in three stages: glycolysis, Krebs cycle and electron transport. Glycolysis, which
occurs in the cell cytosol, can be summarised as follows:
Glucose
NAD
ADP + Pi
Hydrogen
(energy)
gy)
(ener
ATP
NADH
pyruvate
(a) On the diagram, highlight the (i) inputs and (ii) outputs of glycolysis using two different colours.
(b) What appears to be the role of the molecule NAD?
_________________________________________________________________________________
(c) Which important requirement of cellular respira�on does not take part in glycolysis?
_________________________________________________________________________________
3. The second stage of cellular respira�on, Krebs cycle, which occurs in the matrix of the mitochondria, can
be summarised as follows:
pyruvate
NAD
ADP + Pi
Hydrogen
rgy)
(ene
gy)
(ener
Hydrogen
FAD
)
gy
(ener
NADH
ATP
FADH2
Carbondioxide
© Ac�ve Science
(a) On the diagram, highlight the (i) inputs and (ii) outputs of the Krebs cycle, using two different
colours.
(b) The Krebs cycle involves not one, but two ‘carrier’ molecules. Name these molecules and state
their role.
_________________________________________________________________________________
_________________________________________________________________________________
(c) By the end of the Krebs cycle, which product of cellular respira�on is yet to be produced?
_________________________________________________________________________________
4. The third stage of cellular respira�on, electron transport, which occurs on the inner membranes of the
mitochondria, can be summarised as follows:
NADH
eH+
ADP + Pi
FADH2
FAD
ed
(accept by)
NAD
electron transport
chain
Water
O2-
(energy
)
ATP
oxygen
(a) On the diagram, highlight the (i) inputs and (ii) outputs of the electron transport stage, using two
different colours.
(b) According to the diagram, what happens to the hydrogen atoms released by NADH and FADH2?
_________________________________________________________________________________
(c) Explain how water is produced during electron transport.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
(d) Lots of ATP is made during the electron transport stage of cellular respira�on, a process that
requires energy. Where does this energy come from?
_________________________________________________________________________________
_________________________________________________________________________________
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5. The following diagram shows the structure of a mitochondrion:
1. ____________________
2. ____________________
3. ____________________
6. ____________________
5. ____________________
4. ____________________
(a) Label the structures 1 - 6.
(b) Explain how the structure of a mitochondrion makes it well suited to its func�on.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
6.
(a) Oxygen is a ‘limi�ng factor’ in the process of cellular respira�on. Explain this statement.
_________________________________________________________________________________
_________________________________________________________________________________
(b) Name two other factors that can limit cellular respira�on.
_________________________________________________________________________________
7.
Like chloroplasts, mitochondria are also believed to have once been free-living microbes that were
engulfed by a host cell in the process of endosymbiosis. What is the evidence for this?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
8. True or False?
(a)
(b)
(c)
(d)
(e)
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Cellular respira�on is an endergonic process.
Cellular respira�on can be aerobic or anaerobic.
Glycolysis is an aerobic process.
About 60% of the chemical energy of glucose is transferred to ATP,
while the rest is lost as heat.
The folds in a mitochondrion’s inner membrane are known as ‘cristae’.
ANAEROBIC RESPIRATION
1. Fill in the missing words:
Environments where there is a complete absence of oxygen, such as the deep ocean, can be described
as __________________. Organisms that live in these sorts of environments cannot carry out aerobic
respira�on, but must instead rely on __________________ __________________. For some
organisms, such as certain microbes, oxygen is actually toxic; these organisms are termed
__________________ __________________. Other organisms, known as __________________
__________________, are able to survive whether oxygen is present or not and can switch from
__________________ to __________________ respira�on.
When glucose is broken down in the absence of oxygen, only __________________
_________________ can occur. This type of cellular respira�on produces much less ______________
energy than ________________ respira�on, but it produces it more ________________.
During both aerobic and anaerobic respira�on, glucose is first broken down into __________________.
If oxygen is unavailable however, the complete breakdown of glucose into __________________
__________________ and __________________ cannot occur and instead, the __________________
is converted into __________________ __________________ (mammals) or __________________
(yeasts). In mammals, anaerobic respira�on is known as __________________ __________________
__________________, while in yeasts, it is called __________________ __________________.
2. Complete the table outlining the differences between aerobic and anaerobic respira�on in mammals:
Aerobic respira�on
Anaerobic respira�on
Inputs: ________________________________ Inputs: _________________________________
Outputs: _______________________________ Outputs: _______________________________
_____ ATP produced per molecule of glucose.
_____ ATP produced per molecule of glucose.
__________________ rate of ATP produc�on.
__________________ rate of ATP produc�on.
__________________ efficient energy transfer.
__________________ efficient energy transfer.
Occurs in the __________________.
Occurs in the __________________.
3. What do aerobic and anaerobic respira�on have in common?
_________________________________________________________________________________
_________________________________________________________________________________
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4. You are walking home from school when you see your bus, about 200m away, already at the bus stop. You
break into a run, sprin�ng towards the bus as fast as you can.
(a) While walking, are your leg muscle cells carrying out aerobic or anaerobic respira�on? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
(b) As you sprint towards the bus, what sort of cellular respira�on is happening in your muscle cells?
Explain.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
(c) Why is it that anaerobic respira�on can be sustained for very short amounts of �me only?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
(d) What causes the ‘burning legs’ sensa�on you some�mes feel during or at the end of a vigorous
workout? Explain.
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
5. Explain why mammals and yeasts produce different end products in anaerobic respira�on.
_________________________________________________________________________________
_________________________________________________________________________________
6. The following are chemical equa�ons for (i) lac�c acid fermenta�on and (ii) alcoholic fermenta�on. Fill in
the missing numbers.
(i)
C6H12O6
___C3H6O3 + (___ ATP)
(ii)
C6H12O6
___C2H5OH + ___CO2 + (___ATP)
© Ac�ve Science
CELLULAR RESPIRATION
(answers)
1.
(a) Cellular respira�on is the process by which all living things - plants, animals, fungi, pro�sts and
bacteria - create energy in the form of ATP. This involves the breaking down of glucose,
a complex organic molecule, into carbon dioxide and water, releasing energy. The complete
breakdown of glucose also requires oxygen.
(b)
C6H12O6 + 6O2
6CO2 + 6H2O (+ 30 ATP)
2.
Glucose
Inputs
NAD
ADP + Pi
Hydrogen
Outputs
(energy)
gy)
(ener
ATP
NADH
pyruvate
(a) See above diagram.
(b) NAD picks up hydrogen to become NADH. This hydrogen will be needed later for electron transport.
(c) Oxygen.
3.
pyruvate
NAD
Inputs
ADP + Pi
Hydrogen
rgy)
(ene
Outputs
gy)
(ener
Hydrogen
FAD
)
gy
(ener
NADH
ATP
FADH2
Carbondioxide
(a) See above diagram.
(b) The carrier molecules are NAD and FAD. They pick up hydrogen to become NADH and FADH2
respec�vely. This hydrogen will be needed later for electron transport.
(c) Water.
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4.
Inputs
NADH
e-
Outputs
H+
electron transport
chain
ADP + Pi
FADH2
FAD
ed
(accept by)
NAD
(energy
)
ATP
Water
oxygen
O2-
(a) See above diagram.
(b) The hydrogen atoms released by NADH and FADH2 are split into hydrogen ions (H+) and electrons
(e-).
(c) Water is produced when the oxygen ions (O2-) combine with hydrogen ions (H+). The oxygen ions
formed when oxygen atoms accepted the electrons that were transferred along the electron
transport chain.
(d) The energy required to produce ATP during electron transport comes from the transfer of electrons
along the electron transport chain.
5.
(a)
1. DNA
2. outer membrane
6. ribosome
5. matrix
3. inner membrane
4. intermembrane space
(b) The inner membrane of the mitochondrion is highly folded, providing a large surface area on
which important chemical reac�ons can occur, par�cularly those associated with the electron
transport stage of cellular respira�on.
6.
(a) Oxygen is said to be a limi�ng factor in cellular respira�on because it is one of the requirements
of the process, and a lack of it decreases the rate of the reac�on.
(b) Any two of: (i) glucose (ii) temperature (iii) NAD (iv) FAD (v) ADP + Pi
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7.
Evidence for this includes: (i) mitochondria contain circular molecules of DNA similar to that found
in bacteria (ii) mitochondria also contain ribosomes, meaning that they can make their own
proteins; these ribosomes are similar in size to those found in bacteria (iii) mitochondria, like
bacteria,divide by binary fission(iv) mitochondrial DNA replicates independently of the host cell’s
DNA (v)mitochondria are similar in size to bacteria.
8.
(a)
(b)
(c)
(d)
False
True
False
False
(e)
True
© Ac�ve Science
(cellular respira�on is exergonic; it releases energy)
(glycolysis is anaerobic; it does not require oxygen)
(about 40% of the chemical energy in glucose is transferred to ATP; the rest
is lost as heat)
ANAEROBIC RESPIRATION
(answers)
1.
Environments where there is a complete absence of oxygen, such as the deep ocean, can be described
as anoxic. Organisms that live in these sorts of environments cannot carry out aerobic respira�on,
but must instead rely on anaerobic respira�on. For some organisms, such as certain microbes, oxygen
is actually toxic; these organisms are termed obligate anaerobes. Other organisms, known as
faculta�ve anaerobes, are able to survive whether oxygen is present or not, and can switch from
anaerobic to aerobic respira�on.
When glucose is broken down in the absence of oxygen, only anaerobic respira�on can occur. This
type of cellular respira�on produces much less ATP energy than aerobic respira�on, but it produces
it more rapidly.
During both aerobic and anaerobic respira�on, glucose is first broken down into pyruvate. If oxygen
is unavailable however, the complete breakdown of glucose into carbon dioxide and water cannot
occur and instead, the pyruvate is converted into lac�c acid (mammals) or ethanol (yeasts). In
mammals, anaerobic respira�on is known as lac�c acid fermenta�on, while in yeasts, it is called
alcoholic fermenta�on.
2.
Aerobic respira�on
Anaerobic respira�on
Inputs: glucose and oxygen
Inputs: glucose (no oxygen required)
Outputs: carbon dioxide, water and ATP
Outputs: lac�c acid and ATP
30 ATP produced per molecule of glucose.
2 ATP produced per molecule of glucose.
Slower rate of ATP produc�on.
Faster rate of ATP produc�on.
More efficient energy transfer.
Less efficient energy transfer.
Occurs in the mitochondria.
Occurs in the cytosol.
3.
Aerobic and anaerobic respira�on both produce ATP, they are both involved in energy transfer and
both break down glucose into pyruvate.
4.
(a) While walking, you are carrying out aerobic respira�on. This is because your muscle cells are
working or contrac�ng at a steady rate and their demand for oxygen is being met by the body’s
circulatory system.
(b) As you sprint towards the bus your muscle cells are carrying out anaerobic respira�on. This is
because they are working so hard that their demand for oxygen can no longer be met by the
body’s circulatory system. Oxygen becomes depleted and cellular respira�on must occur in its
absence.
© Ac�ve Science
(c) Anaerobic respira�on can be sustained for only very short amounts of �me because the lack of
oxygen results in a build up of lac�c acid in the muscles that eventually causes pain and fa�gue.
This forces a person to stop exercising.
(d) The ‘burning legs’ sensa�on o�en experienced during or a�er vigorous exercise is due to the
build up of lac�c acid in your muscles, which lowers the pH as acidity increases. This can lead to
acidosis, the symptoms of which include a burning feeling in the legs, as well as cramps and
weakness.
5.
Mammals and yeasts produce different products of anaerobic respira�on because they have different
enzymes in their cell cytosol, resul�ng in different chemical reac�ons occurring.
6.
(i)
(ii)
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C6H12O6
C6H12O6
2C3H6O3 + (2 ATP)
(lac�c acid)
2C2H5OH + 2CO2 + (2ATP)
(ethanol)
Published in Australia
by ACTIVE SCIENCE
Heidelberg VIC 3084
Australia
First published 2021
All worksheets and answer sheets designed and created by Ariana Fabris
Text © Ariana Fabris
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The copyright for all text and diagrams in this document is the property of A. Fabris/Active Science.
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