1) Respiration requires oxygen to fully oxidize nutrients and produce more ATP. It involves glycolysis, the Krebs cycle in mitochondria, and the electron transport chain, where ATP is generated by oxidative phosphorylation. 2) During aerobic respiration, glucose breakdown yields up to 36 ATP molecules, with most ATP generated in the mitochondria. Anaerobic respiration like fermentation only yields 2 ATP per glucose without oxygen. 3) The structure of mitochondria, with its inner and outer membranes, matrix, and cristae, allows for compartmentalization of redox reactions and generation of a proton gradient across the inner membrane for ATP production via chemiosmosis.

1. RESPIRATION
A summary to help with answering exam
questions.

2. Why do we need to respire?
 Active Transport
 Secretion (Exocytosis)
 Endocytosis
 Metabolic Reactions (Anabolism)
 DNA Replication
 Organelle Synthesis
 Movement
 Activation of Chemicals

3. ATP

4. ATP
 ATP is the ‘universal energy currency’ – it is small
and soluble. It transfers energy but also releases
it for metabolism (e.g. Active transport,
phosphorylation, glycolysis); energy is released in
small ‘packets’ to prevent cell damage.
 The phosphate can be removed by hydrolysis to
release 30kJ(molˉ1).

5. What is the importance of
coenzymes in respiration?
 Coenzymes aid in the oxidation and reduction of
reactions.
 NAD and FAD accept hydrogen and are
consequently reduced. The now reduced NAD
and FAD carry electrons to the electron transport
chain for oxidative phosphorylation and also carry
hydrogen ions for chemiosmosis. In addition,
coenzyme A carries acetate to the Krebs cycle.

6. Glycolysis
 Glycolysis takes place in the cytoplasm.
 An ATP molecule is hydrolysed, and the phosphorylation of glucose
takes place.
 Glucose-6-phosphate is changed into fructose-6-phosphate.
 Another ATP molecule is hydrolysed, and the phosphate group
attaches to C-1, forming fructose-1,6-bisphosphate.
 The hexose sugar is activated by the energy released from the
hydrolysed ATP so it cannot leave the cell and is known as hexose-
1,6-bisphosphate.
 It is split into two molecules of triose phosphate.
 Two hydrogen atoms are removed from each triose phosphate which
involved dehydrogenase enzymes.
 NAD combines with the hydrogen atoms to form reduced NAD and
two molecules of ATP are formed through substrate level
phosphorylation.

7. Rememb
er the
stages at
GGF
HTIP – so
you just
need to
remembe
r when
ATP is
made/use
d and
when
NAD is
reduced

8. Mitochondria
Intermembrane
space

9. How does the structure of mitochondria
enable it to perform its functions?
Matrix Inner
Membrane
Outer
Membrane
Electron
Transport Chain
•Enzymes that
catalyse the
stages of aerobic
respiration
•Coenzyme NAD
•Oxaloacetate
•Mitochondrial
DNA
•Mitochondria
Ribosomes
•A different lipid
composition than
the outer layer
which was
impermeable to
most small ions
•Folded into
cristae to give a
large surface
area
•It has many
embedded
electron carriers
and ATP
synthase
enzymes
•High
protein:phospholi
•Contains
proteins, some of
which form
channels or
carriers that
allow the
passage of
molecules (e.g.
Pyruvate)
•Contains
oxidoreductase
enzymes
•Some have a
coenzyme that
pumps protein
from the matrix
into the
intermembrane
space

10. The Link Reaction
 The link reaction takes place in the mitochondrial matrix.
 Pyruvate dehydrogenase removes hydrogen atoms from
pyruvate.
 Pyruvate decarboxylase removes a carboxyl group which
eventually becomes CO2.
 NAD accept the hydrogen atoms to become reduced.
 Coenzyme A (CoA) accepts the acetate to become Acetly CoA
which then enters the Krebs cycle.

11. The Krebs Cycle
 The Krebs cycle also takes place in the mitochondrial matrix.
 The acetate is offloaded from CoA and jois with oxaloacetate to form citrate.
 Citrate is decarboxylated and dehydrogenated to form a 5C compound. (the
hydrogen atoms are accepted by NAD – which becomes reduced – which take
them to the electron transport chain (etc) and the carboxyl group becomes CO2)
 The 5C compound is decarboxylated and dehydrogenated to form a 4C
compound.
 The 4C compound is changed into another 4C compound and a molecule of ADP
is phosphorylated to form ATP (substrate level phosphorylation).
 The second 4C compound is formed into another 4C compound and a pair of
hydrogen atoms are removed (dehydrogenation), reducing FAD.
 The third 4C compound is further dehydrogenated (reducing NAD) to regenerate
oxaloacetate.
 You can remember the Krebs Cycle as 65 44 44, so again, you just need to
remember where dehydrogenation and decarboxylation take place!

12. The number of molecules made from
one molecule of glucose...
Glycolysis Link Krebs
Reduced NAD 2 2 6
Reduced FAD 0 0 2
Carbon Dioxide 0 2 4
ATP 2 0 2

13. Oxidative Phosphorylation
 The final stage of respiration involves electron
carriers which are embedded in the mitochondrial
membrane.
 Oxidative Phosphorylation is the formation of ATP
by the addition of an inorganic phosphate to ADP
in the presence of oxygen. This occurs after
protons flow through ATP synthase and drive the
rotation part of the enzyme.
 The electrons are passed from the final electron
carrier to molecular oxygen, which is the final
electron acceptor.
 Hydrogen ions also join, so oxygen is reduced to
water.

14. Chemiosmosis
 Chemiosmosis is the diffusion of ions through a partially
permeable membrane.
 Reduced NAD and FAD donate hydrogens, which are split into
protons and electrons, to the electron carriers.
 The protons are pumped across the inner mitochondrial
membrane using energy released from the passing of electrons
down the electron transport chain.
 This builds up a proton gradient (pH gradient and
electrochemical gradient). So, potential energy builds up.
 The hydrogen ions cannot diffuse through the lipid part of the
inner membrane, but can diffuse through ATP synthase – an ion
channel in the membrane. This flow of hydrogen ions is
chemiosmosis.

15. Evaluate the evidence for
Chemiosmosis...
 Researchers isolated mitochondria and treated them by placing them in a
solution with a very low water potential. This meant the outer membrane
ruptured, releasing the contents of the intermembrane space (IMS). If they
further treated these mitoblasts with a strong detergent, they could release
the contents of the matrix. This allowed them to identify the enzymes in the
mitochondria, and work out that the link reaction and Krebs cycle took
place in the matrix. Also, that the enzymes for the electron transport chain
were embedded in the mitochondrial membrane.
 Electron transfer in mitoblasts didn’t produce ATP, so they could conclude
that the IMS was involved. ATP wasn’t made if the mushroom-shaped
parts of the stalked particles were removed from the inner membrane and
it wasn’t made in the presence of oligomycin, an antibiotic which is now
known to block the flow of protons through the ion channel part of ATP
synthase.
 In the mitochondria:
- The potential difference across the membrane was -200mV; more negative
on the matrix side than the IMS side.

16. Why is the theoretical maximum yield of ATP per
molecule of glucose rarely achieved in aerobic
respiration?
 Some hydrogens leak across the mitochondrial
membrane, so there are less protons to generate
the proton motive force.
 Some ATP is used to actively transport pyruvate
into the mitochondria.
 Some ATP is used to bring hydrogen from
reduced NAD made during glycolysis, into the
mitochondria.

17. Why does anaerobic respiration produce a
lower yield of ATP than aerobic?
 Because only glycolysis occurs.
 The electron transport chain cannot occur, as
there is no oxygen to act as the final electron
acceptor. As a result, the Krebs cycle stops
because all the NAD have been reduced. This
prevents the link reaction from occuring.
 On the other hand, anaerobic respiration takes
the pyruvate, and by reducing it, frees up the
NAD so glycolysis can continue, producing 2
molecules of ATP per molecule of glucose.

18. Alcohol Fermentation (Yeast)
CO2 (decarboxylation)
Combines with Hydrogen
from reduced NAD
Pyruvate Ethanal
Ethanol Alcohol
Dehydrogena
se

19. Lactate Fermentation (Mammals)
Combines with hydrogen (provided by
reduced NAD forming an oxidised NAD
also
Pyruvate 
Lactate
Lactate
Dehydrogen
ase

20. Mammal Yeast
Name of hydrogen
acceptor after
glycolysis
Pyruvate Ethanal
Is CO2 produced? No0 Yes
Final product Lactate Ethanol

21.  A respiratory substrate is an organic substance
that can be used for respiration.
 RQ = number of moles of carbon dioxide
number of moles of oxygen
used up
Respiratory Substrate Mean Energy Value/kJ gˉ1
Carbohydrate 15.8
Lipid 39.4
Protein 17.0

22. RQ Substrate
1.0 Carbohydrate
0.9 Protein
0.7 Fat

23. Respirometer