Cellular Respiration
How do living things release energy from
the foods they consume or produce?
Objectives
Compare the reactants and products of
photosynthesis and cellular respiration in
terms of energy and matter (TEKS 9B)
• What is cellular respiration?
• Describe what happens during the process of
glycolysis.
• Describe what happens during the Krebs cycle
• Explain how high-energy electrons are used by the
electron transport chain
• Compare photosynthesis and cellular respiration
Cellular Respiration
Cellular respiration is the process that releases
energy by breaking down glucose and other food
molecules in the presence of oxygen.
Cellular RespirationOverview
There are 3 major
steps to cellular
respiration:
1. Glycolysis
2. Krebs cycle
3. Electron
Transport Chain
Objectives
Compare the reactants and products of
photosynthesis and cellular respiration in
terms of energy and matter (TEKS 9B)
• What is cellular respiration?
• Describe what happens during the process of
glycolysis.
• Describe what happens during the Krebs cycle
• Explain how high-energy electrons are used by the
electron transport chain
• Compare photosynthesis and cellular respiration
Chemical Energy and Food
How much energy is actually present in food?
Quite a lot. 1 gram of glucose when burned in the
presence of oxygen can release 3811 calories of
heat energy
A calorie is the amount of energy needed to raise
the temperature of 1 gram of water 1 degree
Celsius.
The “Calorie” used on food labels is actually a
kilocalorie or 1000 calories.
Cellular RespirationGlycolysis
• Cells don’t “burn” glucose. They gradually release the
energy from glucose and other food compounds.
• This process begins with glycolysis.
• Glycolysis is the process in which 1 molecule of glucose (a
6-carbon compound) is broken in half, producing 2
molecules of pyruvic acid (a 3-carbon compound).
Cellular RespirationGlycolysis
• Glycolysis occurs in the cytoplasm of a cell.
• 2 ATP molecules are used to get the process
going.
• 4 ATP molecules are produced at the end of
glycolysis
 This means the cell, overall, gains 2 ATP
molecules from this process.
• NAD+ is an electron carrier used to carry 4 highenergy electrons (turns into NADH) to the
electron transport chain
• Glycolysis is very fast. Cells can produce
thousands of ATP molecules in just a few
milliseconds.
• No oxygen is needed (Anaerobic).
 This means that cells can supply chemical
energy to cells even when oxygen isn’t
available
Glycolysis-Fermentation
If oxygen is NOT present, glycolysis is
followed by a process called
fermentation instead of the Krebs cycle
and the electron transport chain.
Fermentation releases energy from
food molecules by producing ATP in the
absence of oxygen.
 Produces much less ATP than if
oxygen were present; only 2 ATP
total, whereas aerobic cellular
respiration can produce up to 38 ATP
molecules.
It is an anaerobic process because it
does not require oxygen.
Glycolysis-Fermentation
Two types of fermentation:
Lactic acid fermentation –
Occurs in muscle cells
(makes muscles tired)
Alcohol fermentation Occurs in yeast and a few
other microorganisms to
make ethyl alcohol
Objectives
Compare the reactants and products of
photosynthesis and cellular respiration in
terms of energy and matter (TEKS 9B)
• What is cellular respiration?
• Describe what happens during the process of
glycolysis.
• Describe what happens during the Krebs cycle
• Explain how high-energy electrons are used by the
electron transport chain
• Compare photosynthesis and cellular respiration
Cellular Respiration –
The Krebs Cycle
• At the end of glycolysis, about 90% of
the chemical energy available in glucose
is still unused.
• Oxygen is one of the most powerful
electron acceptors.
• Since the remaining pathways of cellular
respiration require oxygen, they are
aerobic.
• The Krebs cycle (also called the citric
acid cycle) is the step that follows
glycolysis when oxygen is present.
• During the Krebs cycle, pyruvic acid is
broken down into CO2 in a series of
energy-extracting reactions.
The Krebs Cycle Summary
• Takes place in matrix of
mitochondria
• Requires Oxygen (Aerobic)
• Cyclical series of oxidation
reactions that give off CO2 and
produce one ATP per cycle
• Turns twice per glucose molecule
• Produces two ATP
• Each turn of the Krebs Cycle also
produces 3NADH, 1FADH2, and
2CO2
• Therefore, For each Glucose
molecule, the Krebs Cycle
produces 6NADH, 2FADH2,
4CO2, and 2ATP
Pyruvic acid
enters the
mitochondrion
The other 2 carbons
combine with coenzyme
A to form acetyl-CoA
1 carbon atom from
pyruvic acid becomes
part of a CO2 molecule
Acetyl-CoA then
combines with a 4carbon compound to
form citric acid
Citric acid is broken
down , releasing more
CO2, and electrons are
transferred to energy
carriers (NAD+ and FAD)
2 ATP molecules
are produced
during the Krebs
cycle
All the high-energy
electrons in carriers
(NADH and FADH2) are
then transported to the
electron transport chain
where huge amounts of
ATP can be made.
Objectives
Compare the reactants and products of
photosynthesis and cellular respiration in
terms of energy and matter (TEKS 9B)
• What is cellular respiration?
• Describe what happens during the process of
glycolysis.
• Describe what happens during the Krebs cycle
• Explain how high-energy electrons are used by the
electron transport chain
• Compare photosynthesis and cellular respiration
Cellular Respiration- The
Electron Transport Chain
The electron transport chain
uses the high-energy electrons
from the Krebs cycle to convert
ADP into ATP.
Overview:
• Occurs Across Inner
Mitochondrial membrane
• 34 ATP Produced
• H2O Produced
• Uses coenzymes NAD+ and FAD+
to accept e- from glucose
• NADH = 3 ATP’s
• FADH2 = 2 ATP’s
A. High-energy electrons
from NADH and FADH2 are
passed along the electron
transport chain.
B. For every 2 high-energy electrons,
their energy is used to transport H+
across the membrane. H+ build up in the
intermembrane space making it positively
charged.
At the end of the chain is an enzyme
that combines these electrons with
hydrogen ions (H+) and oxygen to form
water.
C. As H+ escape the ATP
synthase spins. Each time it
rotates, it grabs an ADP and
attached a phosphate to create
ATP.
Cellular Respiration Overview
= 38
ATP
Objectives
Compare the reactants and products of
photosynthesis and cellular respiration in
terms of energy and matter (TEKS 9B)
• What is cellular respiration?
• Describe what happens during the process of
glycolysis.
• Describe what happens during the Krebs cycle
• Explain how high-energy electrons are used by the
electron transport chain
• Compare photosynthesis and cellular respiration
6CO2 + 6H2O
LIGHT
C6H12O6 + 6O2