Respiration
You should be able to use and define the following terms:
Acetyl coA: two carbon transfer molecule in the link reaction.
Adenosine triphosphate (ATP): an activated nucleotide found in all living cells that acts as an energy carrier.
The hydrolysis of ATP leads to the formation of adenosine diphosphate (ADP) and inorganic phosphate, with
the release of energy.
Aerobic: connected with the presence of free oxygen. Aerobic respiration requires free oxygen to release
energy from glucose. See also anaerobic.
Anaerobic: connected with the absence of oxygen. Anaerobic respiration releases energy from glucose or
other foods without the presence of oxygen. See also aerobic.
ATP synthase: enzyme used to synthesise ATP from ADP + Pi.
Citrate: six carbon molecule formed in the Krebs cycle.
Cristae: folded inner membrane structure in the mitochondria. Site of the electron transport chain.
Electron transport chain: use of electrons from the Krebs Cycle to synthesise ATP via a series of oxidationreduction reactions.
Ethanol: product of anaerobic respiration in plants and microorganisms.
Glycolysis: first part of cellular respiration in which glucose is broken down anaerobically in the cytoplasm
to two molecules of pyruvate.
Krebs cycle: 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.
Lactate: product of anaerobic respiration in animals.
Link reaction: process linking Glycolysis to the Krebs Cycle (in the matrix of the mitochondria), where the
two molecules of pyruvate are converted to CO2 and acetylcoenzyme A.
Matrix: liquid portion of the mitochondria. Site of the Krebs cycle.
Mitochondria: organelle where aerobic respiration takes place.
NAD: a molecule that carries electrons and hydrogen ions during aerobic respiration.
Oxaloacetate: four carbon molecule formed in the Krebs cycle.
Oxidative phosphorylation: the formation of ATP in the electron transport system of aerobic respiration.
Pyruvate: three carbon molecule. Final product of glycolysis.
Reduced NAD: activated version of NAD. Produced when hydrogen is combined with NAD in glycolysis, the
link reaction and the Krebs cycle.
Triose phosphate: three carbon intermediate in glycolysis. Produced from phosphorylated glucose, used to
produce pyruvate.
Complete the sentences using the words in bold:
4C
6C
acetyl
anaerobic
ATP
ATPase
carbon dioxide
CO2
coenzyme A
concentration gradient
cristae
cytoplasm
electrons
electrons
energy
ethanol
glycolysis
hydrolysed
inner
lactate
matrix
matrix
muscle contraction
NAD
organisms
oxidative phosphorylation
oxygen
pump
pyruvate
quickly
reactions
reduced
reduced
soluble
triose phosphate
water
Adenosine triphosphate (ATP) is the main cellular energy storage molecule. ATP:
●
Is very __________
●
Allows energy to be released __________
●
Stores less energy than glucose, making it easier to utilise
It is used to provide energy for most cellular processes e.g. __________ ____________, active transport,
synthesis of proteins/enzymes and synthesis of DNA. The energy in ATP is released when it is
_____________ by an _________ enzyme: ATP ADP + Pi. Most of the ATP used by cells is produced during
respiration. ATP is also useful because when it donates a phosphate group to another molecule it makes
that molecule more reactive.
There are two forms of respiration: aerobic (in the presence of oxygen) and anaerobic (in the absence of
oxygen). Aerobic respiration is the most common form and can be broken down into four stages:
Glycolysis
Glycolysis takes place in the cell ____________ (i.e. outside of the mitochondria). During glycolysis:
1. Glucose is phosphorylated twice (by ATP) to form glucose phosphate, which immediately splits into
two _________ ___________ (3C) sugars.
2. Each triose sugar is changed through oxidation over several steps to form ___________, another
3C compound.
3. In these steps some energy is released to form 2 molecules of ATP and 1 molecule of ___________
NAD (NADH) per triose phosphate
The link reaction
This step links glycolysis and the Krebs cycle and takes place in the mitochondrial __________. During the
link reaction:
1. Pyruvate (3C) is converted to _________ (2C) that binds with __________ __ to form acetyl CoA.
2. Pyruvate loses electrons that are used to form a molecule of ____________ NAD.
3. Pyruvate also loses a _____ molecule that diffuses into the blood, where it is carried to the lungs
for removal.
The Krebs cycle
This cycle of reactions takes place in the mitochondrial __________. During the Krebs cycle:
1. Acetyl coA enters the Krebs Cycle where the acetate (2C) is transferred from acetyl coA to a ___
molecule to form a ___ molecule.
2. The 6C molecule is broken down in a series of oxidation-reduction reactions to reform the 4C
molecule, releasing CO2 and ____________. ATP is also made by substrate-level phosphorylation.
3. The CO2 diffuses out the cell and the electrons are taken up by _______ (to form reduced NAD), or
by an alternative electron carrier called FAD to form reduced FAD.
The electron transfer chain
The proteins required for the electron transport chain are embedded in the ________ mitochondrial
membrane (i.e. in the _________). During the electron transfer chain:
1. NADH and FADH pass __________ to proteins on the inner mitochondrial membrane and release
H+ ions
2. As the electrons are passed between proteins they release __________ that is used to ________
the H+ ions into the inter-mitochondrial membrane space
3. The electrons are eventually used to form ________ from H+ and oxygen.
4. As the H+ ions flow down their _______________ ___________ through the ATPase enzyme they
release energy used to synthesise ATP (known as _____________ _________________). This flow
of electrons is known as chemiosmosis.
Anaerobic respiration
In certain circumstances oxygen may not be available (_____________ conditions). Despite oxygen only
being required as the final electron acceptor in the process of aerobic respiration, its absence prevents
most of the ___________ from taking place. If there is no oxygen then NADH cannot unload hydrogen in
the electron transport chain; without free NAD some of the enzymes of the Krebs cycle and glycolysis
cannot work, so respiration stops. In these circumstances anaerobic respiration adds an extra step to the
end of glycolysis that regenerates NAD, so allowing ___________ to continue and some ATP to be made.
Different ____________ use the pyruvate produced in glycolysis in different ways.
In animals and bacteria pyruvate is converted to __________ (or lactic acid). NADH is used and NAD is
regenerated, to be used in glycolysis to release ________. The reaction is reversible, so the energy
remaining in the lactate molecule can be retrieved when __________ becomes available.
In plants and fungi pyruvate is converted to __________. NADH is used and NAD is regenerated, to be used
in glycolysis to release ATP. Ethanol is a two-carbon compound and _________ __________ is also formed.
This means the reaction is irreversible.
Diagrams
1. Label the diagram. [7]
2. Complete the diagrams to indicate the number of carbon atoms. [9]
Answer the questions
1. Where in the cell does glycolysis, the link reaction, the Kreb’s cycle and the electron transport chain
occur?
……………………………………………………………………………………………………………….
2. What is formed when glucose phosphate breaks down?
……………………………………………………………………………………………………………….
3. What is the final product produced in glycolysis?
……………………………………………………………………………………………………………….
4. What is the final product in the link reaction?
……………………………………………………………………………………………………………….
5. What is the name given to the formation of ATP in the Kreb’s cycle, when the phosphate group is
donated to ADP from another molecule?
……………………………………………………………………………………………………………….
6. What is the final electron acceptor in the electron transport chain of aerobic respiration?
……………………………………………………………………………………………………………….
7. What is the name given to the flow of protons through the ATP synthase enzyme by facilitated
diffusion?
……………………………………………………………………………………………………………….
8. What is the name given to the formation of ATP in aerobic respiration via the method described
above?
……………………………………………………………………………………………………………….
9. What is the final product produced during anaerobic respiration in a) animals, and b) plants?
……………………………………………………………………………………………………………….
10. What molecule is resynthesised during anaerobic respiration, so allowing glycolysis to continue?
……………………………………………………………………………………………………………….
Answer the exam questions
Q1.
The diagram gives an outline of the process of aerobic respiration.
(a)
Name substances X, Y and Z.
X ...................................................................................................................
Y ...................................................................................................................
Z ...................................................................................................................
(3)
(b)
Give the location of each of the following in a liver cell.
(i)
Glycolysis ............................................................................................
(ii)
The Krebs cycle ..................................................................................
(2)
(c)
(i)
(ii)
Write the letter A on the diagram to show one step where ATP is used.
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)
(e)
Human skeletal muscle can respire both aerobically and anaerobically. Describe what happens
to pyruvate in anaerobic conditions and explain why anaerobic respiration is advantageous to
human skeletal muscle.
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(4)
(Total 15 marks)
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)
(b)
The following reaction occurs in the Krebs cycle.
A scientist investigated the effect of the enzyme inhibitor malonate on this reaction. The
structure of malonate is very similar to the structure of succinate. The scientist added
malonate and the respiratory substrate, pyruvate, to a suspension of isolated mitochondria.
She also bubbled oxygen through the suspension.
(i)
Explain why the scientist did not use glucose as the respiratory substrate for these
isolated mitochondria.
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(2)
(ii)
Explain how malonate inhibits the formation of fumarate from succinate.
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(2)
(iii) The scientist measured the uptake of oxygen by the mitochondria during the
investigation. The uptake of oxygen decreased when malonate was added. Explain why.
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(2)
(Total 9 marks)
Q3.Yeast is a single-celled organism. A student investigated respiration in a population of yeast growing in a
sealed container. His results are shown in the graph.
(a)
Calculate the rate of oxygen uptake in arbitrary units per hour between 2 and 4 hours.
Answer ...................................... arbitrary units per hour
(1)
(b)
(i)
Use the information provided to explain the changes in oxygen uptake during this
investigation.
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(3)
(ii)
Use the information provided to explain the changes in production of ethanol during this
investigation.
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(2)
(c)
Sodium azide is a substance that inhibits the electron transport chain in respiration.The student
repeated the investigation but added sodium azide after 4 hours. Suggest and explain how the
addition of sodium azide would affect oxygen uptake and the production of ethanol.
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(3)
(Total 9 marks)
Q4.
(a)
A student measured the rate of aerobic respiration of a woodlouse using the apparatus
shown in the diagram.
(i)
The student closed the tap. After thirty minutes the drop of coloured liquid had moved to
the left. Explain why the drop of coloured liquid moved to the left.
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(3)
(ii)
What measurements should the student have taken to calculate the rate of aerobic
respiration in mm3 of oxygen g–1 h–1?
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(3)
(b)
DNP inhibits respiration by preventing a proton gradient being maintained across membranes.
When DNP was added to isolated mitochondria the following changes were observed
•
•
•
less ATP was produced
more heat was produced
the uptake of oxygen remained constant.
Explain how DNP caused these changes.
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(3)
(Total 9 marks)
Gap fill mark scheme
soluble quickly muscle contraction hydrolysed ATPase cytoplasm triose phosphate pyruvate reduced
matrix acetate coenzyme A reduced CO2 matrix 4C 6C electrons NAD inner cristae electrons energy
pump water concentration gradient oxidative phosphorylation anaerobic reactions glycolysis
organisms lactate ATP oxygen ethanol carbon dioxide
Diagrams mark scheme
For the labelled mitochondrion:
Outer membrane
Inner membrane
Cristae
Matrix
ATP synthase
Ribosome
Plasmid
For glycolysis: 6C 3C 3C
For the link reaction: 3C 1C 2C
For the Kreb’s cycle: 2C 6C 4C
Questions mark scheme
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Cytoplasm, mitochondrial matrix, mitochondrial matrix, intermitochondrial membrane
Triose phosphate
Pyruvate
Acetyl CoA
Substrate level phosphorylation
Oxygen
Chemiosmosis
Oxidative phosphorylation
Lactate (or lactic acid), ethanol and carbon dioxide
NAD (or oxidised NAD)
Exam questions mark scheme
M1.
(a) X = Carbon dioxide;
Y = Acetyl coenzyme A;
(ACCEPT Acetyl CoA)
Z = Water;
3
(b)
(i)
Cytoplasm;
1
(ii)
Mitochondrion;
(IGNORE named part)
1
(c)
On the diagram:
(i)
‘A’ (ATP used) – between glucose and triose phosphate;
1
(ii)
‘B’ Any two from:
(ATP produced) – between triose phosphate and pyruvate;
in Krebs cycle;
from electron carriers
(to right of bracket & not below grey box);
max 2
(d)
Any three from:
Source of energy/of phosphate;
Active transport;
Phagocytosis / endo- /exocytosis / pinocytosis;
Bile production;
Cell division / mitosis;
Synthesis of: glycogen;
protein / enzymes;
DNA / RNA;
lipid / cholesterol;
urea;
max 3
(e)
Any four from:
Forms lactate; [extras – C2H5OH / CO2 – CANCEL]
Use of reduced NAD / NADH;
Regenerates NAD;
NAD can be re-used to oxidise more respiratory substrate / correct e.g./ allows glycolysis
to continue;
Can still release energy/form ATP when oxygen in short supply/when no oxygen;
max 4
[15]
M2.(a)
Glycolysis
Link reaction
Krebs cycle
Occurs in
mitochondria
√
√
Carbon dioxide
produced
√
√
√
√
NAD is reduced
√
Mark horizontally
3
(b)
(i)
1.
Glucose is used / broken down during glycolysis / in cytoplasm;
1. Accept: glucose to pyruvate or glucose not converted to
pyruvate for one mark
2.
Glucose cannot cross mitochondrial membrane(s) / pyruvate can cross
mitochondrial membrane(s);
2
(ii)
1.
Is a competitive inhibitor / attaches to active site;
1 Accept: inhibitor / malonate attaches to active site to form an
enzyme-substrate complex
2.
Reduces / prevents enzyme-substrate / E-S complex forming;
2 Accept: substrate / succinate cannot bind to enzyme
2 Accept mark point 2, but not mp1 in context of noncompetitive inhibition
2
(iii) 1.
Krebs cycle inhibited;
2.
NAD / Coenzyme / FAD not / less reduced;
3.
Hydrogens not passed to ETC;
4.
Oxygen used as final / terminal (electron) acceptor;
4 Accept: oxygen combines with electrons and protons /
hydrogen ions without reference to final acceptor
Neutral: oxygen is used in the Krebs cycle
2 max
[9]
M3.(a) 0.8;
1
(b) (i)
1.
Aerobic respiration;
1. Allow description e.g. respiration using oxygen
1. Accept ‘oxidative phosphorylation’
2.
Increase in uptake (of oxygen) with growth / reproduction / division of
yeast cells;
3.
Glucose / nutrients / oxygen decreases / becomes limiting / cells die /
ethanol/toxins form / heat produced / anaerobic respiration occurs;
3. Ignore any reference to time
3. Accept decrease in oxygen being linked to oxygen being
‘used up’ or equivalent
3
(ii)
1.
(Ethanol produced) by anaerobic respiration / from pyruvate
in anaerobic conditions;
1. ‘Fermentation’ is not enough on its own
2.
(Ethanol / anaerobic respiration) increases as oxygen (uptake /
concentration) decreased;
3.
Decreases as glucose is used up / ethanol kills cells;
2 max
(c)
1.
Oxygen uptake decreases / stopped;
2.
Oxygen is final (electron) acceptor / combines with electrons (and protons);
3.
Ethanol produced sooner / more ethanol produced;
3. Accept ethanol produced at any specified time before 16
hours
3
[9]
M4.
(a)
(i)
1.
Oxygen taken up/used (by woodlouse);
2.
Carbon dioxide (given out) is absorbed by solution/potassium
hydroxide;
3.
Decrease/change in pressure;
Reference to vacuum negates last marking point
Reject reference to pressure increasing inside tube
3
(ii)
1.
Distance (drop moves) and time;
2.
Mass of woodlouse;
3.
Diameter/radius/bore of tubing/lumen/cross-sectional area;
If answer refers to measuring volume using the syringe allow 2
max –
one mark for measuring volume;
one mark for mass of woodlouse;
3
(b)
1.
Less/no proton/H+ movement so less/no ATP produced;
2.
Heat released from electron transport/redox reactions/energy not
used to produce ATP is released as heat;
3.
Oxygen used as final electron acceptor/combines with
electrons (and protons);
3
J[9]