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Cell respiration

Topic 2
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8

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Many bacteria and fungi rely on it, for example yeast

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Glycolysis takes place

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Each pyruvate is converted to an ethanol (2 carbons) molecule

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The lost 2 carbons form 2 carbon dioxide molecules

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Both ethanol and carbon dioxide are waste products
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Biology SL

That is why yeast is used in baking and in alcohol production

The only ATP produced comes from glycolysis

➢ Lactic acid fermentation
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Happens in organisms that use oxygen during cell respiration

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Some of the glucose entering into cell respiration will follow this anaerobic
pathway when the organism exceeds its body’s capacity to supply oxygen

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Lactic fermentation allows glycolysis to continue

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Glycolysis takes place

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2 3-carbon pyruvate molecules are converted into 2 3-carbon lactic acid

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There are converted back into pyruvate when oxygen levels rise and aerobic
respiration proceeds

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The only ATP produced comes from glycolysis

Aerobic respiration
➢ Occurs in mitochondria
➢ Oxygen is needed
➢ Process
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Glycolysis takes place

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The 2 pyruvate molecules enter a mitochondrion

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Each pyruvate loses a carbon dioxide and becomes acetyl-CoA
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Acetyl-coenzyme A has 2 carbon atoms

The 2 acetyl-CoA molecules enter the Krebs cycle
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A series of reactions

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A cycle because it starts and ends with the same molecule

Through many reactions the 2-carbon acetyl-CoA are broken down into 2
carbon dioxide molecules
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3 oxygens are needed to break down each acetyl-CoA

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30-36 ATP molecules are generated

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Aerobic cell respiration completely oxidizes a glucose molecule and the
end-products are carbon dioxide , water and ATP
C6H12O6 + 6O2 ⇒ 6CO2 + 6H2O
2

Cell respiration

Topic 2
...
As volume decreases, a water surface will rise
in the tube, which can be measured
➢ To deal with the carbon dioxide that is produced when the organisms breathe out,
we use an alkali (KOH) which will react with carbon dioxide
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Otherwise the volume would not change

3



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