Cellular Respiration
Main Ideas
Details
Cellular Respiration (also called Aerobic respiration)
 Occurs in autotrophs AND heterotrophs
 Converts chemical energy stored in molecules of glucose to
cellular energy (ATP)
 Requires oxygen
 Produces 36 ATP molecules
 Equation: C6H12O6 + 6O2  6CO2 +6H2O +36ATP
3 Stages of Cellular Respiration
 Glycolysis
 Krebs cycle
 Electron transport chain (ETC)
Glycolysis - Glyco = glucose, Lysis = to split
 Process in which one molecule of glucose is broken in half,
producing two molecules of pyruvic acid, a 3-carbon compound
 Glycolysis occurs in the cytoplasm
 Total energy yield = 4 ATP, but 2 ATP used in process so
Net ATP gain = 2 ATP
 Advantages - Reaction is fast, cells can produce thousands of
ATP molecules in a few milliseconds, Does not require oxygen
What comes next depends on whether conditions are aerobic (with
O2) or anaerobic (without O2).
 In presence of O2, molecules enter Krebs Cycle and ETC
releasing additional ATP
 In the absence of O2, glycolysis is followed by fermentation
with NO additional energy production
Krebs Cycle - In the presence of oxygen, pyruvic acid is broken
down into CO2, 2 more ATP produced, NADH produced for last
step.
SUMMARY:
Electron Transport Chain (ETC) – Electrons from hydrogen are
carried by NADH from Krebs cycle and passed down an electron
transport chain (ETC), where high-energy electrons convert ADP
to ATP, 32 more ATP produced.
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Krebs Cycle and ETC occur in the mitochondria of all organisms

Structure of mitochondria
– Matrix = liquid portion
– Cristae – inner membrane where majority of ATP is
produced
pH of the mitochondria is lower (acidic) in matrix of inner
membrane than in between outer membrane and cristae
As ETC processes occur and positive ions are moved across
membranes the mitochondria becomes more acidic
-

If no oxygen is present there is no Krebs Cycle or ETC, instead
Anaerobic respiration (also called fermentation) will occur.
– Does not use O2
- Produces 2 ATP Net (from glycolysis)
- There are two types of fermentation
Alcoholic fermentation – produces alcohol
Lactic acid fermentation – produces lactic acid, it is
an acid, when produced in skeletal muscles the
muscles do not contract as easily (& are sore!)
Energy and Exercise
 Quick energy – body uses limited supply of ATP produced
during glycolysis which last a few seconds
 For the first 90 seconds the body produces ATP by lactic acid
fermentation
 Longer-term energy – cellular respiration produces ATP for
exercise over 90 seconds
– Cellular respiration is slower than fermentation.
 Human bodies begin breaking down glycogen for the first 1520 minutes of exercise to give glucose to fuel cellular
respiration
 After that, human bodies begin breaking down fats and other
molecules for energy
Oxygen debt – caused when there is a shortage of oxygen due
to lactic acid being produced as a byproduct. When exercise is
finished the body must repay the debt with heavy breathing.
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SUMMARY:
Cellular Respiration Summary:
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Organelles
Reactants
Products
Energy Transformation
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SUMMARY:
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