AQA Biology
3.5.2 Respiration
Name: ______________________
Lesson
Exam Question Homework Date
Marks
Checked
/30
Lesson 1 – Mitochondrial Structure
Lesson 2 – Stage 1: Glycolysis
/35
Lesson 3 – Stage 2: Link Reaction
/13
Lesson 4 – Stage 3: Krebs cycle
/29
Lesson 5 – Stage 4: Oxidative Phosphorylation/ETC
/36
Lesson 6 – RQ and Respiratory Substrates
/10
End of Topic Test
Page 1 of 42
Specification Section
3.5.2 Respiration
Respiration produces ATP.
Glycolysis is the first stage of anaerobic and aerobic respiration. It occurs in the cytoplasm and is an
anaerobic process.
Glycolysis involves the following stages:



phosphorylation of glucose to glucose phosphate, using ATP
production of triose phosphate
oxidation of triose phosphate to pyruvate with a net gain of ATP and reduced NAD.
If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The
oxidised NAD produced in this way can be used in further glycolysis.
If respiration is aerobic, pyruvate from glycolysis enters the mitochondrial matrix by active transport.
Aerobic respiration in such detail as to show that:





pyruvate is oxidised to acetate, producing reduced NAD in the process
acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A
acetylcoenzyme A reacts with a four-carbon molecule, releasing coenzyme A and producing a sixcarbon molecule that enters the Krebs cycle
in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP
by substrate-level phosphorylation, and carbon dioxide is lost
synthesis of ATP by oxidative phosphorylation is associated with the transfer of electrons down the
electron transfer chain and passage of protons across inner mitochondrial membranes and is
catalysed by ATP synthase embedded in these membranes (chemiosomotic theory)
other respiratory substrates include the breakdown products of lipids and amino acids, which enter the
Krebs cycle.
Page 2 of 42
Key word list for 3.5.2
Aerobic
Anaerobic
ATP (adenosine
triphosphate)
Diffusion
Electron
Electron carrier
molecule
Electron
Transport Chain
Facilitated
diffusion
Glycolysis
Hydrolysis
Krebs cycle
Link reaction
Metabolism
NAD
(nicotinamide
adenine
dinucleotide)
Oxidation
Oxidationreduction
Oxidative
phosphorylation
Substrate
Substrate-level
phosphorylation
Connective with the presence of free oxygen. Aerobic respiration requires
free oxygen to release energy from glucose
Connected with the absence of oxygen. Anaerobic respiration releases
energy from glucose or other foods without the presence of oxygen
Nucleotide found in all living organisms, which is produced during
respiration and is important in the transfer of energy
The movement of molecules or ions form a region where there are in high
concentration to one where their concentration is lower
Negatively charged sub-atomic particle that orbits the positively charged
nucleus of all atoms
A chain of carrier molecules along which electrons pass, released energy in
the form of ATP as they do so
Use of electrons from the Krebs Cycle to synthesise ATP via a series of
oxidation-reduction reactions
Diffusion involving the presence of protein carrier molecules to allow the
passive movement of substances across plasma membranes
First part of cellular respiration in which glucose is broken down
anaerobically in the cytoplasm to two molecules of pyruvate
The breaking down of large molecules into smaller ones by the addition of
water molecules
Series of aerobic biochemical reactions in the matrix of the mitochondria of
most eukaryotic cells by which energy is obtained through the oxidation of
acetylcoenzyme A produced from the breakdown of glucose
The process linking glycolysis with the Krebs cycle in which hydrogen and
carbon dioxide are removed from pyruvate to form acetylcoenzyme A in the
matrix of the mitochondria
All the chemical processes that take place in living organisms
A molecule that carriers electrons and hydrogen ions during aerobic
respiration
Chemical reaction involving the loss of electrons
A chemical reaction I which electrons are transferred from one substance to
another substance. Losing electrons is oxidised, gaining electrons is
reduced
The formation of ATP in the electron transport system of aerobic respiration
A substance that is acted on or used by another substance or process
The formation of ATP by the direct transfer of a phosphate group from a
reactive intermediate to ADP
Page 3 of 42
Lesson 1 – Mitochondria Structure
By the end of this lesson you should be able to:


Describe respiration as a metabolic pathway
Describe and explain the structure of the mitochondrion and its adaptations for respiration
Notes:
Respiration Recap:
All living cells respire. During respiration a chemical reaction occurs in which sugars are oxidised to release
energy. Carbon dioxide and water are released during these reactions. Glucose enters cells by diffusion
and facilitated diffusion. When there is a shortage of oxygen, anaerobic respiration in muscles produces
lactate.
Carbohydrates and fats store chemical energy, these organic molecules are broken down. The energy that
is released from breaking the bonds is used to synthesise ATP. ATP is known as the universal energy
currency and drives biological processes and chemical reactions that occur within cells. The sum of
chemical reactions that occur in the body is known as metabolism. Metabolic reactions can either be
anabolic or catabolic.
● Anabolic – building larger molecules from smaller molecules – requires energy as its making bonds
● Catabolic – breaking larger molecules into smaller molecules – releases energy as its breaking bonds
Respiration is known as a metabolic pathway as it is a many stepped process with each step controlled and
catalysed by a specific enzyme.
Mitochondria Structure and Function




Found in all eukaryotic cell types.
Found in higher numbers in cells that have
higher energy demands.
1µm diameter 10µm long.
Mitochondrial DNA
Some cells e.g muscle cells, sperm cells, epithelial cells in small intestine, and nerve cells, will have large
amounts of mitochondria to provide the large amounts of ATP they require for: building complex molecules,
protein synthesis, movement (active transport, swimming or muscle contraction), cell division,
endo/exocytosis (e.g cells that secrete substances) and transmitting nerve impulses.
Page 4 of 42
Stages of Respiration
The process of respiration can be split into 4
stages:
1. Glycolysis = In the cytoplasm of the cell.
2. Link reaction = In the Matrix of the
mitochondria.
3. Krebs Cycle = Also in the matrix.
4. Electron Transport Chain = Proteins found in
the membrane of the cristae in the
mitochondria.
Recall Questions:
1.
2.
3.
4.
5.
6.
7.
8.
What is aerobic respiration?
What is a metabolic pathway?
Describe the membrane of the mitochondria
What is the name of the fluid inside the mitochondria?
What is contained in the matrix?
How is the inner membrane adapted for respiration?
The membrane also contains proteins for the ETC. What is an ETC?
Oxidative phosphorylation in mitochondria is similar to
photophosphorylation in chloroplasts. These processes are involved in
the formation of what compound?
9. What is the name of the enzyme that is involved in synthesising this compound?
10. Chemiosmosis (covered in photosynthesis) depends on the creation of proton concentration
gradients. What sub-atomic particle provides the energy to maintain this gradient?
11. What cells contain the most mitochondria? Give an example and explain.
12. The figure above is a transverse section of a sperm cell. The mitochondria of sperm cells form a
spiral around the central flagellum. Identify the structures labelled U, W, and Z
13. Where do most of the stages of respiration take place in the cell?
14. What are the stages of respiration?
15. The matrix is the fluid filled space inside the mitochondria. Which 2 reactions take place here?
Exam Questions:
Q1. (b)
The table shows features of a mitochondrion and a chloroplast. Complete the table with ticks
where a feature is present.
(3)
Feature
Mitochondrion
Chloroplast
Double outer
membrane
Starch grains
Diffusion of oxygen into
the organelle
Page 5 of 42
(c)
Give the function of a mitochondrion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
Q2. During respiration where, exactly, in a cell does each of the following occur?
(i)
Glycolysis
______________________________________________________________
(1)
(ii)
Electron transfer chain
______________________________________________________________
(1)
Q3. The diagram shows a mitochondrion.
(a)
Name the parts labelled X and Y.
(i)
X ______________________________
(ii)
Y ______________________________
(2)
Scientists isolated mitochondria from liver cells. They broke the cells open in an ice-cold,
isotonic solution. They then used a centrifuge to separate the cell organelles. The diagram
shows some of the steps in the process of centrifugation.
(b)
Suggest which pellet, A, B or C contained the mitochondria.
Page 6 of 42
(1)
(c)
Explain why the solution used was
(i)
ice-cold
______________________________________________________________
______________________________________________________________
(1)
(ii)
isotonic.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(d)
People with mitochondrial disease have mitochondria that do not function properly.
Some people with mitochondrial disease can only exercise for a short time. Explain why a
person with mitochondrial disease can only exercise for a short time.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
Q4. (b)
The diagram is of a mitochondrion at a magnification of × 30 000.
Calculate the actual length of this mitochondrion in micrometres (µm). Show your working.
Answer = ____________________ µm (2)
(c)
Some scientists support the theory that mitochondria are organelles that evolved from
prokaryotic cells.
(i)
Give one piece of evidence that supports the theory that mitochondria evolved from
prokaryotic cells.
______________________________________________________________
______________________________________________________________
______________________________________________________________ (1)
Page 7 of 42
(ii)
What is the advantage to cells of having mitochondria?
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Q5. Cells constantly hydrolyse ATP to provide energy.
(a)
Describe how ATP is resynthesised in cells.
___________________________________________________________________
___________________________________________________________________
(2)
(b)
Give two ways in which the hydrolysis of ATP is used in cells.
1. _________________________________________________________________
___________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________
(2)
(c)
This is a photograph (micrograph) of a mitochondrion taken using a scanning electron
microscope.
Page 8 of 42
What is the evidence that a scanning electron microscope was used to take this
photograph?
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(1)
(d)
Name the part of the mitochondrion labelled X in the photograph.
___________________________________________________________________
(1)
(e)
The actual length of the mitochondrion between points A and B in the photograph is 4
μm.
What is the magnification of the mitochondrion in the photograph?
Show your working.
Magnification ____________________ (2)
Q6. The diagram shows the structure of a mitochondrion.
(a)
In which part of the mitochondrion does the Krebs cycle take place?
___________________________________________________________________
(1)
(c)
The mitochondria in muscles contain many cristae. Explain the advantage of this.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________(2)
Page 9 of 42
Homework:
Watch the following videos to learn how mitochondrial DNA can be used to map human evolution
Mother of Humanity -Mitochondrial Eve (2:15) https://www.youtube.com/watch?v=rx_oUd-05ys
TED Talk: A family tree for humanity (8:27) https://bit.ly/30YamqU
Recall Question Answers:
splitting of glucose to release CO2 as a waste product and
combining H2 with atmospheric O2 with the release of a
large amount of energy
many stepped process with each step controlled and
catalysed by a specific intracellular enzyme
Double membrane, inner membrane folded to form cristae.
What is aerobic respiration?
What is a metabolic pathway?
Describe the membrane of the mitochondria
What is the name of the fluid inside the
mitochondria?
What is found in the fluid inside the
mitochondria?
Matrix
Ribosomes, Mitochondrial DNA, Enzymes for the link
reaction and Krebs cycle
Highly folded to increase surface area for ATP production.
Lots of membrane bound electron carrier proteins and ATP
synthase enzymes for generating ATP.
A series of membrane bound proteins that can transfer
electrons between them
How is the inner membrane adapted for
respiration?
The membrane contains proteins for the ETC.
What is an ETC?
Oxidative phosphorylation in mitochondria is
similar to photophosphorylation in chloroplasts.
These processes are involved in the formation of
what compound?
What is the name of the enzyme that is involved
in synthesising this compound?
ATP
ATP synthase
Chemiosmosis (covered in photosynthesis)
depends on the creation of proton
concentration gradients. What sub-atomic
particle provides the energy to maintain this
gradient?
What cells contain the most mitochondria? Give
an example and explain.
The figure above is a transverse section of a
sperm cell. The mitochondria of sperm cells form
a spiral around the central flagellum. Identify the
structures labelled U, W, and Z
Where do most of the stages of respiration take
place in the cell?
H+ ions
Cells which require large amounts of ATP e.g muscle cells
(for movement), sperm cells (for movement), root cells (for
active transport), epithelial cells of small intestine (for
active transport)
U = matrix
W = Cristae
Z= Outer membrane/intermembrane space
What are the stages of respiration?
The mitochondria
Glycolysis, link reaction, Krebs cycle, electron transport
chain
The matrix is the fluid filled space inside the
mitochondria. Which 2 reactions take place
here?
The link reaction and the Krebs cycle
Page 10 of 42
Lesson 2 – Stage 1: Glycolysis
By the end of this lesson you should be able to:


Describe the process of glycolysis
Describe the products of anaerobic respiration
Video: BioRach – Glycolysis - https://bit.ly/3g3QWVH
Notes:
Glycolysis (Glyco - glucose and Lysis – splitting) is the first stage of aerobic respiration AND anaerobic
respiration as it does not require oxygen. It occurs outside of the mitochondria in the cytoplasm of all living
cells. There are two stages: phosphorylation (1-2) and oxidation (4). You will notice this is the reverse of the
Calvin cycle in photosynthesis!
Glucose is phosphorylated by adding 2 phosphates from
2 molecules of ATP. This makes it a more reactive
molecule.
It splits to produce 2 x 3C molecules of TP
The triose phosphate is oxidised (loses hydrogen and
phosphate) to form 2 molecules of pyruvate.
NAD collects the hydrogen ions forming 2 reduced NAD
4 ATP are produced, but 2 were used at the start, so
there’s a net gain of 2ATP
Products of glycolysis (for 1 molecule of glucose):
 2 reduced NAD – goes to the ETC
 2 Pyruvate – Actively transported into the mitochondria for the link reaction
 2 ATP – Used for energy
Anaerobic Respiration
During anaerobic respiration the products of glycolysis are converted into ethanol or lactate using reduced
NAD.
Lactate fermentation occurs in animal cells
Alcoholic fermentation occurs in plants and yeast
and bacteria
Anaerobic respiration regenerates NAD so that glycolysis can continue even when there isn’t enough
oxygen – this allows a small amount of ATP to be produced to allow some biological processes to continue.
After a period of anaerobic respiration lactate is oxidised back into pyruvate. The oxygen needed to do this
is known as the oxygen debt and it is the reason you breathe heavier after a period of intense exercise.
Pyruvate can be oxidised back into CO2 and H2O via the Krebs Cycle. Some lactate is converted to
glycogen and stored in muscle or liver cells.
Page 11 of 42
Recall Questions:
1. What is the first stage of respiration?
2. Where does the first stage take place in the cell?
3. What happens during phosphorylation in glycolysis?
4. What happens during oxidation in glycolysis?
5. How many ATP molecules are produced during glycolysis?
6. What is the only stage of respiration common to aerobic and anaerobic respiration?
7. What are the productsof glycolysis?
8. Why is the production of reduced NAD important?
9. Where do the products of glycolysis go?
10. Why is the ATP from glycolysis only 2?
11. What happens to lactate after a period of anaerobic respiration?
12. What is oxygen debt?
Exam Questions:
Q1. (a)
The main stages in anaerobic respiration in yeast are shown in the diagram.
(i)
Name process X.
______________________________________________________________
(1)
(ii)
Give one piece of evidence from the diagram which suggests that the conversion of
pyruvate to ethanol involves reduction.
______________________________________________________________
______________________________________________________________
(1)
(iii)
Explain why converting pyruvate to ethanol is important in allowing the continued
production of ATP in anaerobic respiration.
______________________________________________________________
Page 12 of 42
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(b)
Give two ways in which anaerobic respiration of glucose in yeast is
(i)
similar to anaerobic respiration of glucose in a muscle cell;
1. ____________________________________________________________
______________________________________________________________
2. ____________________________________________________________
______________________________________________________________
(2)
(ii)
different from anaerobic respiration of glucose in a muscle cell.
1. ____________________________________________________________
______________________________________________________________
2. ____________________________________________________________
______________________________________________________________
(2)
Q2. The diagram summarises the process of anaerobic respiration in yeast cells.
(a) (i)
In anaerobic respiration, what is the net yield of
ATP molecules per molecule of glucose?
________________________________________________
__________________________________________ (1)
(ii) Give two advantages of ATP as an energy-storage
molecule within a cell.
1.________________________________________________
________________________________________________
2.________________________________________________
________________________________________________
(2)
(b)
Describe how NAD is regenerated in anaerobic
respiration in yeast cells.
___________________________________________________________________
___________________________________________________________________(1)
Page 13 of 42
Q3. (a)
Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain the
advantage of mitochondria in muscle cells having more cristae.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(b)
Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X
has three carbon atoms.
(i)
Name substance X.
______________________________________________________________
(1)
Q4.
(a)
Name the two substances produced by anaerobic respiration in humans.
1. _________________________________________________________________
2. _________________________________________________________________
(2)
(b)
When an athlete runs in a 100 metre race, 90% of the energy needed is provided by
anaerobic respiration.
(i)
Explain why most of the energy is provided by anaerobic respiration rather than
aerobic respiration.
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)
The athlete continues to breathe deeply for several minutes after the race ends.
Explain why this is necessary.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Q5.
(a)
Pyruvate is formed in the breakdown of glucose during respiration. When there is
sufficient oxygen, this pyruvate is fully broken down. Name two substances formed from
the pyruvate.
1. _________________________________________________________________
2. _________________________________________________________________ (1)
Page 14 of 42
(b)
(i)
If there is a shortage of oxygen in muscle cells during exercise, some pyruvate is
converted into lactate. Explain why muscles become fatigued when insufficient
oxygen is available.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)
Some of the lactate is oxidised to pyruvate by muscles when they are well-supplied
with oxygen. Suggest an advantage of the lactate being oxidised in the muscles.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Q6. (a)
During respiration where, exactly, in a cell does each of the following occur?
(i)
Glycolysis
______________________________________________________________
(1)
(ii)
Electron transfer chain
______________________________________________________________
(1)
(b)
Without oxygen, less ATP is produced by respiration. Explain why.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
Q7. When one mole of glucose is burned, 2800 kJ of energy are released. However, when one mole of
glucose is respired aerobically, only 40% of the energy released is incorporated into ATP. Each mole of
glucose respired aerobically produces 38 moles of ATP.
(a)
(i)
Calculate how much energy is incorporated into each mole of ATP. Show your
working.
Answer ____________________ kJ
(2)
Page 15 of 42
(ii)
When glucose is respired what happens to the energy which is not incorporated into
ATP?
______________________________________________________________
(1)
(b)
(i)
When one mole of glucose is respired anaerobically, only 2 moles of ATP are
produced. Explain why less energy is released in anaerobic respiration.
______________________________________________________________
______________________________________________________________
(1)
(ii)
At the end of a sprint race, a runner continues to breathe rapidly for some time.
Explain the advantage of this.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Homework:
Page 16 of 42
Recall Question Answers - Glycolysis:
What is the first stage of respiration?
Glycolysis
Where does the first stage take place in the cell?
Cell cytoplasm
Glucose is phosphorylated by adding 2 phosphate groups from 2
ATP molecules.
Triose phosphate is oxidised forming 2 pyruvate molecules. 2
NAD molecules are reduced to 2 NADH.
What happens during phosphorylation in glycolysis?
What happens during oxidation in glycolysis?
How many ATP molecules are produced during
glycolysis?
What is the only stage of respiration common to
aerobic and anaerobic respiration?
What are the productsof glycolysis?
Why is the production of reduced NAD important?
Where do the products of glycolysis go?
Why is the ATP from glycolysis only 2?
What happens to lactate after a period of anaerobic
respiration?
What is oxygen debt?
4 ATP are produced but the net gain is 2ATP
Glycolysis
2 molecules of pyruvate, 2 reduced NAD and 2 ATP
It is needed for the ETC to produce ATP


2 reduced NAD – goes to the ETC
2 Pyruvate – Actively transported into the mitochondria
for the link reaction
2 ATP are used to phosphorylate the glucose to make it more
reactive, four ATP molecules are produced but the net (overall
total) is 2.
Lactate is oxidised back into pyruvate. It is directly oxidised into
CO2 and H2O via Krebs Cycle. Some lactate is converted to
glycogen and stored in muscle or liver cells.
The oxygen needed to oxidise lactic acid in the period of recovery
after exercise
Recall Question Answers – Link Reactoin:
What is the second stage of
respiration?
The link reaction
What are the products of the link
reaction?
CO2, Acetyl CoA, and reduced NAD
Pyruvate is oxidised and carboxylated to form acetate which combined
What happens in the link reaction?
with Coenzyme A to form Acetyl coenzyme A.
What are the products of the link
reaction?
Acetyl CoA + reduced NAD + CO2
How many times do the Link
reaction occur for every glucose
molecule?
twice
2 acetyl coenzyme A (goes to Krebs cycle)
For each glucose molecule where do 2 CO2 released as waste
the products go?
2 Reduced NAD – goes to ETC
What is the role of coenzyme A in
the link reaction?
Transports Acetate to the Krebs cycle
Page 17 of 42
Lesson 3 – Stage 2: Link Reaction
By the end of this lesson you should be able to:

Describe the process of the link reaction
Notes:
The link reaction is the second stage of respiration, it LINKS glycolysis to the Krebs cycle. The products of
the link reaction enter the Krebs cycle.
Products from the glycolysis are:
● 2x net ATP
● 2x reduced NAD (NADH)
● 2x Pyruvate
If oxygen is present pyruvate is transported into the mitochondrial matrix via active transport (so this
requires energy.
Oxidative carboxylation:
Removal of a CO2 and H+ from pyruvate
producing acetate. The H+ ion is accepted by
NAD forming reduced NAD.
The acetate combines with coenzyme A to form
acetylcoenzyme A – this then enters the Krebs
cycle.,
1 pyruvate molecule produces:
o 1x CO2 = released as waste
o 1x reduced NAD = goes to the ETC
o 1x acetyl CoA = Goes into the Krebs cycle
For each glucose molecule used in glycolysis, two pyruvate molecules are made, but the link reaction uses
only one pyruvate molecule, so the link reaction and the Krebs cycle happen twice for every glucose
molecule which goes through glycolysis.
Recall Questions:
1.
2.
3.
4.
5.
6.
What is the second stage of respiration?
What are the products of the link reaction?
What happens in the link reaction?
What are the products of the link reaction?
How many times do the Link reaction occur for every glucose molecule?
For each glucose molecule where do the products go?
7. What is the role of coenzyme A in the link reaction?
Page 18 of 42
Exam Questions:
Q1. (a)
Describe how acetylcoenzyme A is formed in the link reaction.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(c)
In muscles, pyruvate is converted to lactate during anaerobic respiration.
(i)
Explain why converting pyruvate to lactate allows the continued production of ATP
during anaerobic respiration.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)
In muscles, some of the lactate is converted back to pyruvate when they are well
supplied with oxygen. Suggest one advantage of this.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(1)
Q2. The biochemical pathway of aerobic respiration involves a number of different steps.
Name one step in which carbon dioxide is produced.
___________________________________________________________________
(1)
Page 19 of 42
Q3. The diagram represents two of the stages of aerobic respiration that take place in a mitochondrion.
(a)
Name substance X.
___________________________________________________________________
(1)
(b)
Which stage of aerobic respiration takes place inside a mitochondrion and is not
represented on the diagram?
___________________________________________________________________
(1)
Q5.
(a)
Mitochondria in muscle cells have more cristae than mitochondria in skin cells. Explain
the advantage of mitochondria in muscle cells having more cristae.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(2)
(b)
Substance X enters the mitochondrion from the cytoplasm. Each molecule of substance X
has three carbon atoms.
(i)
Name substance X.
______________________________________________________________
(1)
(ii)
In the link reaction substance X is converted to a substance with molecules
effectively containing only two carbon atoms. Describe what happens in this
process.
______________________________________________________________
______________________________________________________________
______________________________________________________________ (2)
Page 20 of 42
Homework:
Introduction
This activity gives you the chance to analyse a data set that shows the relationship
between storage temperature and respiration rate in a range of fruits and vegetables.
The data have implications for how commercial crops are stored and transported, and
for the potential use of hormone treatments to manipulate ripening. You will be
employing skills you have developed during the course, such as recognising patterns,
explaining causal relationships, and interpreting evidence.
Learning outcome
After completing this worksheet you should be able to:

describe, calculate, and explain patterns, relationships, and evidence in data for
respiration rate and temperature.
Background
Fruits and vegetables can continue to respire once they have been harvested and
stored. Cellular respiration can enable ripening to continue when the product is stored.
The rate of respiration varies between species. The table below shows the respiration
rates of various types of fruit and vegetable at different storage temperatures.
Type of fruit
or vegetable
Respiration rate (mg CO2 kg1 h1)
At 0 °C
At 5 °C
At 10 °C
At 15 °C
At 20 °C
Apple
3
6
9
15
20
Asparagus
60
105
215
235
270
Blackberry
19
36
62
75
115
Cauliflower
17
21
34
44
69
Onion
3
5
7
7
8
Orange
4
6
8
18
28
Parsnip
12
13
22
37
n/a
Potato
n/a
12
16
17
22
Turnip
8
10
16
23
25
Questions
1
Describe how respiration rate changes as temperature increases in:
a asparagus
(3 marks)
b onion.
Page 21 of 42
(4 marks)
2
Which fruit or vegetable shows:
a the greatest percentage increase in respiration rate between 0 °C and 20 °C?
Show your working.
(2 marks)
b the smallest percentage increase in respiration rate between 0 °C and 20 °C?
Show your working.
(2 marks)
3
Calculate the respiration rate in mg CO2 g1 s1 of:
a blackberry at 20 °C.
(3 marks)
b parsnip at 15 C.
(3 marks)
Give your answers in standard form and to two significant figures.
4
What can you conclude from the data about:
a the optimal storage conditions for harvested fruits and vegetables?
(2 marks)
b which fruit(s) or vegetable(s) would be the easiest to store and maintain in an
edible condition at room temperature in a cupboard? Explain your answer.
(3 marks)
Page 22 of 42
Lesson 4 – Sage 3: Krebs Cycle
By the end of this lesson you should be able to:
• Describe the Krebs cycle
• Explain the importance of coenzymes in respiration
Video: BioRach - Link reaction and Krebs cycle: https://bit.ly/30ZFZR6
Notes:
1. Acetate is removed from the CoenzymeA and combines
with a 4C molecule of oxaloacetic acid to form a 6C sugar
called citrate. Coenzyme A goes back to the link reaction.
2. Citrate is decarboxylated and dehydrogenated – 2 H+
ions are used to reduce NAD
3. Now a 5C compound it is decarboxylated and
dehydrogenated again to produce another CO2 and
another reduced NAD.
4. Now a 4C molecule, a phosphate is removed and used
to generate a molecule of ATP. This is known as
substrate-level phosphorylation
5. The 4C compound is dehydrogenated again and 2 H+ ions reduce FAD.
6. Finally one more dehydrogenation produces oxaloacetate.
For each molecule of glucose the Krebs cycle turns twice, producing:




4 carbon dioxides – waste product
6 x reduced NAD – to the ETC
2 x reduced FAD – to the ETC
2 x ATP
Most of the ATP in respiration is made in the ETC!
Page 23 of 42
Importance of coenzymes in cellular respiration:
Coenzyme A NAD
Stages
Link reaction Glycolysis x2
Link reaction x 2
Krebs x6
What it transports
Acetyl group
1 H+
Role in ETC
Oxidised at the start of ETC
Amount of ATP
synthesised per
molecule
3 ATP
FAD
Krebs x 1
2 H+
Oxidised further along the
ETC
2 ATP
Recall Questions:
1.
2.
3.
4.
5.
6.
7.
8.
Where does the Krebs cycle takes place?
How is citrate formed?
How many molecules of reduced NAD are produced in the Krebs cycle per molecule of glucose?
Name the coenzymes used within the Krebs cycle
What are the products of one Krebs cycle?
What is released from NADH and FADH2 when they are oxidised?
How many turns of the Krebs cycle for one molecule of glucose?
Which coenzyme can synthesise more ATP?
Exam Questions:
Q1. (b)
In the Krebs cycle, acetylcoenzyme A combines with four-carbon oxaloacetate to form sixcarbon citrate. This reaction is catalysed by the enzyme citrate synthase.
(i)
Oxaloacetate is the first substrate to bind with the enzyme citrate synthase. This
induces a change in the enzyme, which enables the acetylcoenzyme A to bind.
Explain how oxaloacetate enables the acetylcoenzyme A to then bind to the
enzyme.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(ii)
Another substance in the Krebs cycle is called succinyl coenzyme A. This substance
has a very similar shape to acetylcoenzyme A.
Suggest how production of succinyl coenzyme A could control the rate of the
reaction catalysed by citrate synthase.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
Page 24 of 42
(2)
Q2. (a) The table contains statements about three stages of respiration.
Complete the table with a tick if the statement in the first column is true for each stage of
respiration in an animal.
Glycolysis
Link reaction
Krebs cycle
Occurs in
mitochondria
Carbon dioxide
produced
NAD is reduced
(3)
Q3. The boxes in the diagram represent substances in glycolysis, the link reaction and the Krebs cycle.
(a)
Complete the diagram to show the number of carbon atoms present in one molecule of
each compound.
(2)
(b)
Other substances are produced in the Krebs cycle in addition to the carbon compounds
shown in the diagram. Name three of these other products.
1. _________________________________________________________________
2. _________________________________________________________________
3. _________________________________________________________________
(3)
Page 25 of 42
Q4. (a)
The flow chart shows the main stages in aerobic respiration.
(i)
Complete the flow chart by writing, in the appropriate boxes, the number of carbon
atoms in substance P and the name of substance Q.
(2)
Page 26 of 42
Q5. The diagram gives an outline of the process of aerobic respiration.
(a)
Name substances X, Y and Z.
X ________________________________________________________________
Y ________________________________________________________________
Z ________________________________________________________________(3)
Page 27 of 42
(b)
Give the location of each of the following in a liver cell.
(i)
Glycolysis ____________________________________________________
(ii)
The Krebs cycle _______________________________________________
(2)
(c)
(i)
Write the letter A on the diagram to show one step where ATP is used.
(ii)
Write the letter B on the diagram at two steps where ATP is produced.
(3)
(d)
Apart from respiration, give three uses of ATP in a liver cell.
1. _________________________________________________________________
2. _________________________________________________________________
3. _________________________________________________________________
(3)
Q6. The table contains some statements relating to biochemical processes in a plant cell. Complete the
table with a tick if the statement is true or a cross if it is not true for each biochemical process (4)
Statement
Glycolysis
NAD is reduced
NADP is reduced
ATP is produced
ATP is required
Homework:
Page 28 of 42
Krebs
cycle
Light-dependent
reaction of
photosynthesis
Recall Question Answers Lesson 4:
Where does the Krebs cycle takes place?
How is citrate formed?
Matrix inside mitochondria
Acetate from acetyl coenzyme A combines
with oxaloacetate
How many molecules of reduced NAD are produced in the
Krebs cycle per molecule of glucose?
Name the coenzymes used within the Krebs cycle
6
What are the products of one Krebs cycle?
What is released from NADH and FADH2 when they are
oxidised?
How many turns of the Krebs cycle for one molecule of glucose?
CoEnzyme A, NAD, FAD
ATP, 2 CO2, 3 reduced NAD and reduced FAD
Hydrogen atoms
2
NAD
Which coenzyme can synthesise more ATP?
Recall Question Answers Lesson 5:
What is chemiosmosis?
What is oxidative phosphorylation ?
Where do the electrons come from at the start of the
electron transport chain?
What is the energy released from electrons as they
move down their electron transport chain used for?
How is ATP made in electron transport chain?
What is the final electron acceptor in respiration ?
How much ATP is produced from the ETC?
How much ATP is produced in total?
What happens to energy that is not used to make
ATP?
How efficient is respiration (%)?
Give a reason why respiration is not more efficient
The movement of hydrogen ions across a selectively
permeable membrane down their electrochemical
gradient to generate ATP
The process where the energy carried by electrons
from NADH and FADH2 is used to make ATP
Oxidation of reduced NAD and reduced FAD
Used by electron carriers to pump H+ ions into the
intermembrane space
H+ ions move down the electrochemical gradient back
into the mitochondrial matrix via the ATP synthase
enzyme. This movement drives the synthesis of ATP
Oxygen
28
32
Generates heat
32%
 Some ATP is used up moving hydrogen from
reduced NAD made during glycolysis into the
mitochondria.
 Some ATP is used up moving pyruvate into the
mitochondria by active transport.
 Some energy is lost as heat. This heat helps to
maintain a suitable body temperature for
enzyme-controlled reactions
Page 29 of 42
Lesson 5 – Stage 4: Oxidative Phosphorylation
By the end of this lesson you should be able to:

Describe and explain how ATP is produced in the mitochondria
Videos: BioRach: Oxidative phosphorylation - https://bit.ly/3aqfjfk summary video - https://bit.ly/2CvtR0F
Notes:
Oxidative phosphorylation is the process where the energy carried by electrons from reduced coenzymes is used to
make ATP., it relies on chemiosmotic theory. The theory of chemiosmosis states that the energy in a chemical
gradient established by electron movement is used to generate ATP. This movement of protons (H+) down the
concentration gradient releases energy that is used to create ATP from ADP + Pi in cellular respiration as well as
photosynthesis.
Chemiosmosis depends on the creation of proton concentration gradient. This energy comes from high-energy
(excited) electrons. Electrons are raised to this higher energy level in 2 ways.
● Photosynthesis – Electrons found within pigment molecules in chloroplasts (e.g. Chlorophyll) are excited by
absorbing light from the Sun
● Respiration – High energy electrons are released when chemical bonds in glucose are broken down within
mitochondria.
In respiration OP takes place within the folded inner membrane of the mitochondria called cristae. Excited electrons
are taken to an electron transport chain (ETC) in the mitochondrial membrane by the reduced coenzymes NAD and
FAD. When they are oxidised, they release protons and electrons. The electrons pass along the ETC through a series
of redox reactions, releasing energy. The energy is used to move protons into the intermembrane space. They
diffuse back, down the concentration gradient, through ATP synthase which combines ADP and Pi to produce ATP.
Three protons are required to synthesis one ATP molecule.
At the end of the ETC the electrons, protons and oxygen (from the blood) combine to form water. This means that
oxygen is the final electron acceptor in the ETC.
Intermembrane
space
Evidence to support chemiosmotic theory:



The proton gradient across the inner membrane can be measured as it corresponds to a pH
gradient.
Isolated ATP synthase enzymes can produce ATP using a proton gradient even if no electron
transport is occurring.
Chemicals that block the ETC inhibit the formation of a proton gradient and prevent ATP synthesis.
Page 30 of 42
Calculating the Total ATP
ATP produced before the ETC:


4 molecules of ATP are produced in glycolysis (2 are used up so NET is only 2)
2 molecules of ATP are produced from two turns of the Krebs cycle.
Each reduced NAD can produce 2.5 ATP and each reduced FAD can produce 1.5 ATP.
ATP produced in the ETC:




Glycolysis = 2 x reduced NAD = 5 ATP
Link Reaction = 2 x reduced NAD = 5 ATP
Krebs Cycle = 6 x reduced NAD = 15 ATP
Krebs Cycle = 2 reduced FAD = 3 ATP
Respiration Total = 32 ATP
Efficiency:
The theoretical yield of 32 ATPs for each glucose molecule is rarely achieved. In fact, respiration is only
about 32% efficient because:



Some ATP is used up moving hydrogen from reduced NAD made during glycolysis into the
mitochondria.
Some ATP is used up moving pyruvate into the mitochondria by active transport.
Some energy is used to generate heat. This helps to maintain a suitable body temperature for
enzyme-controlled reactions.
Recall Questions:
1. What is oxidative phosphorylation?
2. What is chemiosmosis?
3. Where do the electrons come from at the start of the electron transport chain?
4. What is the energy released from electrons in the electron transport chain used to do?
5. How is ATP made in electron transport chain?
6. What is the final electron acceptor in respiration?
7. How much ATP is produced from the ETC?
8. How much ATP is produced in respiration in total?
9. What happens to energy that is not used to make ATP?
10. How efficient is respiration (%)?
11. Give a reason why respiration is not more efficient
Exam Questions:
Q2. Describe the role of oxygen in aerobic respiration.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________ (2)
Page 31 of 42
Q7. (b)
Describe how ATP is made in mitochondria.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(6)
(c)
Plants produce ATP in their chloroplasts during photosynthesis. They also produce ATP
during respiration. Explain why it is important for plants to produce ATP during respiration
in addition to during photosynthesis.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(5)
Page 32 of 42
Q3. The diagram shows some of the stages in two processes that produce ATP.
(a)
In Process 1, what causes substance X to lose electrons (e–)?
___________________________________________________________________
(1)
(b)
Where precisely, within a cell, does electron transport take place in Process 2?
___________________________________________________________________
___________________________________________________________________(1)
Q8. Explain why oxygen is needed for the production of ATP on the cristae of the mitochondrion.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________ (3)
Page 33 of 42
Q6.
(a)
Describe the part played by the inner membrane of a mitochondrion in producing ATP.
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
___________________________________________________________________
(3)
Q4.
(a)
The table contains some statements relating to biochemical processes in a plant cell.
Complete the table with a tick if the statement is true or a cross if it is not true for each
biochemical process.
Statement
Glycolysis
Krebs
cycle
Light-dependent
reaction of
photosynthesis
NAD is reduced
NADP is reduced
ATP is produced
ATP is required
(4)
(b)
An investigation was carried out into the production of ATP by mitochondria. ADP,
phosphate, excess substrate and oxygen were added to a suspension of isolated
mitochondria.
(i)
Suggest the substrate used for this investigation.
______________________________________________________________
(1)
(ii)
Explain why the concentration of oxygen and amount of ADP fell during the
investigation.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Page 34 of 42
(iii)
A further investigation was carried out into the effect of three inhibitors, A, B and C,
on the electron transport chain in these mitochondria. In each of three experiments,
a different inhibitor was added. The table shows the state of the electron carriers,
W–Z, after the addition of inhibitor.
Inhibitor
added
Electron carrier
W
X
Y
Z
A
oxidised
reduced
reduced
oxidised
B
oxidised
oxidised
reduced
oxidised
C
reduced
reduced
reduced
oxidised
Give the order of the electron carriers in this electron transport chain. Explain your
answer.
Order
_______
_______
_______
_______
Explanation ____________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Q5. (a)
The table contains statements about three biological processes.
Complete the table with a tick if the statement in the first column is true, for each process.
Photosynthesis
Anaerobic
respiration
Aerobic
respiration
ATP produced
Occurs in
organelles
Electron transport
chain involved
(3)
(b)
Write a simple equation to show how ATP is synthesised from ADP.
___________________________________________________________________
(1)
(c)
Give two ways in which the properties of ATP make it a suitable source of energy in
biological processes.
1. _________________________________________________________________
2. _________________________________________________________________
___________________________________________________________________ (2)
Page 35 of 42
Summary Video Bozeman Science: http://www.bozemanscience.com/cellular-respiration
Homework:
Page 36 of 42
Lesson 6 – Respiratory Quotient and Respiratory Substrates
By the end of this lesson you should be able to:


Describe how to calculate the respiratory quotient
Explain how other respiratory substrates can be used for respiration
Videos: BioRach-Respiratory substrates: https://bit.ly/2EaZXiQ
Notes:
A respiratory substrate is any organic molecule broken
down to release energy for the synthesis of ATP.
Lipids
● Triglycerides are hydrolysed into fatty acids, and
glycerol by lipase enzymes.
● Glycerol is converted to pyruvate before
undergoing oxidative decarboxylation, producing
an acetyl group which binds with coenzyme A and
forms Acetyl CoA.
● Fatty acids are converted to Acetyl CoA.
● Lipids store and release 2x as much energy as
carbohydrates.
Proteins
● Proteins have to be hydrolysed into amino acids
● Then deaminated (removal of amine group)
before they can enter the respiratory pathway via
pyruvate.
● This requires ATP, so the net production of ATP
from protein is reduced.
Gram for gram, in terms of net energy release biological macromolecules are arranged in this order.
Lipids > Alcohols > Proteins > Carbohydrates
The respiratory quotient of a substrate is the ratio of CO2 to O2 produced/consumed to break down that molecule.
RQ=
𝐶𝑂2 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑
𝑂2 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑
The balanced symbol equation for aerobic respiration is
Carbohydrates RQ=
𝐶𝑂2 𝑝𝑟𝑜𝑑𝑢𝑐𝑒𝑑
𝑂2 𝑐𝑜𝑛𝑠𝑢𝑚𝑒𝑑
6O2 + C6H12O6  6CO2 + 6H2O
therefore:
6
= RQ= 6 = 1.0
RQ Proteins = 0.8-0.9
RQ Lipids = 0.7
If the respiratory quotient is calculated to be greater than one, it indicates anaerobic respiration is occurring because
more carbon dioxide is being produced than oxygen being consumed.
Page 37 of 42
Practice Questions:
1. Suggest what the following RQ values indicate about the type of respiration occurring in an organism:
a. 1.10
b. 0.98
c. 0.77
2. Calculate the RQ of the insect at rest and in flight
3. Which substrate is used being used when at rest an in flight?
4. Use the data in the table to suggest the likely diet of each genus of honeypot ant:
Exam Question:
Q1.
In an investigation, the effects of caffeine on performance during exercise were measured. One
group of athletes (A) was given a drink of decaffeinated coffee. Another group (B) was given a
drink of decaffeinated coffee with caffeine added. One hour later the athletes started riding an
exercise bike and continued until too exhausted to carry on. Three days later the same athletes
repeated the experiment, with the drinks exchanged.
(a)
(i)
The researchers added caffeine to decaffeinated coffee. Explain why they did not
just use normal coffee.
______________________________________________________________
______________________________________________________________
(1)
(ii)
The performance of the athletes might have been influenced by how they expected
the caffeine to affect them. How could the researchers avoid this possibility?
______________________________________________________________
______________________________________________________________
(1)
Page 38 of 42
During the exercise the concentrations of glycerol and fatty acids in the blood plasma were
measured. The results are shown in the table.
Drink
Mean time to
exhaustion
/minutes
Mean
concentration of
blood glycerol/
mmol dm–3
Mean
concentration of
blood fatty
acids/
mmol dm–3
With caffeine
90.2
0.20
0.53
Without caffeine
75.5
0.09
0.31
(b)
(i)
Describe the effect of caffeine on exercise performance.
______________________________________________________________
______________________________________________________________
(1)
(ii)
Suggest one explanation for the higher glycerol and fatty acid concentrations in the
blood plasma of the athletes after they were given caffeine.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
(c)
The researchers measured the volumes of carbon dioxide exhaled and oxygen inhaled
during the exercise. From the results they calculated the respiratory quotient (RQ), using
the formula
When a person is respiring carbohydrate only, RQ = 1.0
When a person is respiring fatty acids only, RQ = 0.7
(i)
The basic equation for the respiration of glucose is
C6H12O6 + 6O2 → 6CO2 + 6H2O
Explain why the RQ for glucose is 1.0.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(2)
Page 39 of 42
(ii)
The researchers found that, when the athletes were given the drink containing
caffeine, their mean RQ was 0.85. When given the drink without caffeine their mean
RQ was 0.92.
The researchers concluded that when the athletes had caffeine they used glycogen
more slowly than when they did not have caffeine, and that the store of glycogen in
their muscles was used up less quickly during the exercise.
Explain the evidence from the information above and from the table which supports
these conclusions.
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
(3
Homework:
Introduction
This worksheet asks you to look at alternative substrates for respiration. This will give
you a more realistic idea of respiration, as it rarely just involves the metabolism of
glucose or carbohydrates. You will need a good knowledge of aerobic respiration. You
will also need your knowledge of common biological molecules.
Learning outcomes
After completing this worksheet you should be able to:





describe and apply the difference in relative energy values of carbohydrates, lipids,
and proteins as respiratory substrates
apply knowledge and understanding of practical investigations into the effect of
factors such as temperature, substrate concentration, and different respiratory
substrates on the rate of respiration
state that glucose is not the only substrate available for respiration
explain the different ATP outputs from the different substrates
explain what the respiratory quotient is.
Background
Respiratory substrates
The normal substrate for respiration is glucose. Although there is some glucose in the
blood, most is stored as glycogen in the liver and muscles. When these reserves run
low, many animal cells are able to use fats without the need to convert them to sugars.
The fats are first broken down into fatty acids and glycerol. Cells can also use protein
as a respiratory substrate. This is only when carbohydrate and fat stores have been
used up. Proteins must first be broken down into amino acids and then the amine
group removed via a process called deamination. This produces molecules called keto
acids.
Page 40 of 42
Glycerol, fatty acids, and keto acids do not enter the respiratory pathway at the same
place that glucose would. In fact there are several places where each can enter the
pathway. The diagram below shows how some of these molecules can be utilised during
aerobic respiration.
Figure 1
Just like glucose, glycerol must undergo phosphorylation for its conversion to triose
phosphate. This process requires the hydrolysis of one ATP molecule but also
generates three ATP molecules.
Fatty acids are converted to acetyl coenzyme A in a process called β-oxidation. Each
acetyl coenzyme A molecule produced only requires two carbon atoms from the fatty
acid chain, so each molecule of acid can produce many molecules of acetyl coenzyme
A. These then enter the Krebs cycle as usual.
The respiratory quotient (RQ) is one way of finding which substrate is being used for
respiration. RQ is the ratio of the amount of carbon dioxide produced to the amount of
oxygen used up. During the respiration of glucose, six molecules of carbon dioxide are
produced for every six molecules of oxygen used, so the ratio is one to one or 1.0. The
table below shows the RQ values of common substrates.
Substrate
RQ
Glucose
1.0
Protein
0.9
Fats
0.7
C6H12O6 + 6O2 → 6CO2 + 6H2O so:
6CO2
= 1.0
6O2
Page 41 of 42
Questions
1
State the net gain of ATP molecules during glycolysis from where glycerol enters
the chemical pathway, and describe it.
(3 marks)
2
About 200 molecules of ATP are produced during the respiration of a molecule of
fat. Explain how so many ATP molecules are produced.
(3 marks)
3
Using your knowledge of anaerobic and aerobic respiration together with the
information provided, determine whether any of glycerol, fatty acids, or keto acids
can be used in anaerobic respiration. Using your knowledge of where glycerol, fatty
acids, and keto acids join the respiratory pathway and which parts of aerobic
respiration stop when there is no oxygen available, determine whether these
molecules can be used for anaerobic respiration.
(2 marks)
4
Palmitin (C51H98O6) is a fat. It requires 145 molecules of oxygen for every two
molecules that are respired. Explain, using a balanced chemical equation, why the
RQ for this fat would be lower than the RQ for glucose.
(2 marks)
5
Glucose is more readily used than fats or proteins as a respiratory substrate.
Suggest why.
(2 marks)
6
The respiration of fats requires more oxygen than the respiration of glucose.
Suggest why.
(3 marks)
Page 42 of 42