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Chapter 12: Respiration
Leaving Certificate Biology
Higher Level
Respiration
• Internal versus external:
– Internal respiration is the enzyme-controlled
release of energy from food
– External respiration is the exchange of gases
with environment
• Aerobic versus anaerobic:
– Aerobic respiration is the enzyme-controlled
release of energy from food using oxygen
– Anaerobic respiration is the enzyme-controlled
release of energy from food without the use of
oxygen
Aerobic Respiration
• Two stage process:
1. Glycolysis
2. Krebs cycle & Electron Transport Chain
Stage 1: Glycolysis
• Oxygen-independent (can occur in presence
or absence of oxygen)
• Occurs in cytosol
• Glucose (a 6-carbon molecule) is changed into
two 3-carbon molecules (pyruvate)
– This breaking down of glucose releases high energy
electrons – they are mopped up by NAD+ to become
NADH
– NADH is an energy carrier but cannot release its
energy to power metabolic reactions and so it needs
to pass it on to ATP
– NADH powers the production of 3 ATP molecules
– Glycolysis produces 2 molecules of ATP directly
Stage 1: Glycolysis
GLUCOSE
2ADP + 2P
2ATP
2NAD+
2NADH
H2O
Metabolism
2 PYRUVATE
Electron
Transport
Chain
Stage 2: Krebs Cycle
• Oxygen-dependent (can only occur in the presence of O2)
• Occurs in the lumen of the mitochondrion (matrix)
• Pyruvate enters mitochondrion and converted to 2-C
molecule (acetyl-coA) with release of NADH and CO2
• The acetyl-coA then joins with 4-C molecule from the
previous Krebs cycle to form 6-C molecule
• The 6-C molecule is then broken down into 5-C molecule
with release of CO2 and NADH
• The 5-C molecule is then broken down into 4-C molecule
with release of ATP, CO2, 2NADH and 1FADH2
– The ATP goes to power metabolism
– The NADH and the FADH2 energy carriers go to the electron
transport chain to pass their energy onto ATP molecules
– The 4-C molecule goes into the next Krebs cycle
Stage 2: Krebs Cycle
PYRUVATE
CO2
PYRUVATE
NADH
CO2
Acetyl-CoA (2C)
2C +4C
Acetyl-CoA (2C)
2C + 4C
CoA
6C
4C
NADH
CoA
6C
4C
2NADH
2NADH
CO2
ATP
CO2
Metabolism
5C
NADH
CO2
ATP
CO2
Metabolism
5C
NADH
Stage 2: Electron Transport Chain
• NADH molecules from glycolysis and
Krebs cycle travel to the inner membrane
(cristae) of mitochondrion
• The high-energy electrons release their
energy slowly to power the production of
ATP
• 3 ATP molecules are produced from each
NADH
Stage 2: Electron Transport Chain
NADH
3ADP + 3P
Inner mitochondrial membrane
NAD+
3ATP
Metabolism
H+ , 2e–
O2
H2O
Aerobic respiration
produces a total of 38
ATP molecules
Anaerobic Respiration
• Anaerobic respiration occurs when no
oxygen or limited oxygen is present
• Two stages:
– Glycolysis
– Lactic acid fermentation/Alcohol fermentation
Animals
and some
bacteria
Plants, fungi,
and some
bacteria
Anaerobic Respiration
GLUCOSE
2ADP + 2P
2NAD+ + 4e- + 2H+
2NADH
2ATP
H2O
Metabolism
2 x PYRUVATE
NADH
NAD+
2 x Lactate
Electron
Transport
Chain
NADH
2CO2
NAD+
2 x Ethanol
Summary
Mandatory Experiment: To produce
and test for alcohol
• Set up the apparatus as shown
• Leave for a number of days, or
until the carbon dioxide is no
longer produced
• Test for alcohol by filtering and
taking 3 ml of filtrate; then
adding 3 ml potassium iodide
solution followed by 5 ml
sodium hypochlorite solution
• Heat gently and the production
of pale yellow crystals indicates
the presence of alcohol