A2 AQA, Biol4 exam, revision notes for respiration chapter 4

Heyy, these are just my notes from the Nelson Thornes textbook that I have summarised for me.

They do not have any diagrams, sorry but I hope it helps.

Please let me know if something need adding/removing.

Thanks, :D

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  • Created on: 24-12-12 23:18
Preview of A2 AQA, Biol4 exam, revision notes for respiration chapter 4

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Respiration ­ Chapter 4
4.1 Glycolysis
Glucose cannot be used as directly by cell as a source of energy so cells use ATP as their
immediate source of energy.
This conversion of glucose into ATP takes place during cellular respiration and there are 2
different forms of cellular respiration depending upon whether oxygen is available or
o Aerobic respiration requires oxygen and produces CO2, water and lots of ATP.
o Anaerobic respiration (fermentation) takes place in the absence of oxygen and
produces lactate or ethanol and CO2 but only a little ATP.
Aerobic has 4 stages:
1) Glycolysis ­ the splitting of the 6carbon glucose molecule into 2 3carbon
molecule pyruvate molecules.
2) Link reaction ­ the conversion of the 3carbon pyruvate molecule into CO2 and
a 2carbon molecule called acetylcoenzyme A.
3) Krebs cycle ­ the introduction of acetylcoenzyme A into a cycle of
oxidationreduction reactions that yield some ATP and a large number of
4) Electron Transport Chain ­ the use of the electrons produced in Krebs to
synthesis ATP with water produced as a byproduct.
Glycolysis is the initial stage of both aerobic and anaerobic respiration
It occurs in the cytoplasm of all living cells and is the process by which a hexose sugar,
usually glucose, is split into two molecules of pyruvate
Although there a number of smaller enzymecontrolled reactions in glycolysis, these can be
grouped into 4 stages:
1) Activation of glucose by phosphorylation. Before it can be split into two,
glucose must first be made more reactive by the addition of 2 phosphate
molecules (phosphorylation). The phosphate molecules come from the
hydrolysis of 2 ATP molecules to ADP. This provides the energy to activate
glucose (lowers the activation energy)
2) Splitting of the phosphorylated glucose. Each glucose molecule is split
into 2 3carbon molecules known as triose phosphate
3) Oxidation of triose phosphate. Hydrogen is removed from each of the 2
triose phosphate molecules and transferred to a hydrogencarrier molecule
known as NAD to form reduced NAD
4) The production of ATP. Enzymecontrolled reactions convert each triose
phosphate into another 3carbon molecule called pyruvate. In the process, 2
molecules of ATP are regenerated from ATP
Energy Yields from Glycolysis
The overall yield from one glucose molecule undergoing glycolysis is therefore
o 2 molecules of ATP (4 are produced but 2 were used in the initial phosphorylation of
glucose so the net increase is 2)
o 2 molecules of NADH (these go on into ETC)
o 2 molecule of pyruvate
Glycolysis is a universal feature of every living organism, the enzymes are found in the
cytoplasm of cells and so glycolysis does not need any organelle for it to take place.
It doesn't need oxygen and so can take place when it is present or not, in the absence of
oxygen the pyruvate can be converted into either lactate or ethanol and CO2.
4.2 Link Reaction and Krebs cycle

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Respiration ­ Chapter 4
The Link Reaction
The pyruvate molecules produced in the cytoplasm during glycolysis are actively transported
into the matrix of the mitochondria.
Here pyruvate undergoes a series of reactions during which the following changes take
o The pyruvate is oxidised by removing hydrogen. This hydrogen is accepted by NAD
producing NADH, which is later used to produce ATP.…read more

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Respiration ­ Chapter 4
o It regenerates the 4carbon molecule that combines with acetylcoenzyme A, which
would otherwise accumulate.
4.3 Electron Transport Chain
Hydrogen atoms from Krebs are taken into the ETC ­ where the energy of the electrons within
the hydrogen atoms is converted into ATP.…read more

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Respiration ­ Chapter 4
Production of Ethanol in Plants and Some Microorganisms
Anaerobic respiration leading to the production of ethanol occurs in organisms such as
certain bacteria and fungi (plus some plants in waterlogged conditions).
The pyruvate molecule formed at the end of glycolysis loses a molecule of CO2 and accepts
hydrogen from NADH to produce ethanol.…read more


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