Cellular Respiration and
Fermentation
Chapter 9
Where do organisms get their energy?
• For all organisms, food molecules contain
chemical energy that is released when its
chemical bonds are broken.
• Heterotrophs need to eat food to obtain energy.
How is this different than autotrophs?
• Energy stored in food is expressed in units of
calories: the amount of energy needed to raise the
temperature of 1 gram of water by 1 degree
Celsius. 1000 calories = 1 kilocalorie, or Calorie.
• fats, proteins, and carbohydrates all store energy
• The energy stored in each molecule varies because their
chemical structures, and therefore their energy-storing
bonds, differ.
• Carbs and protein: 4 Calories of energy per gram
• Fats: 9 Calories of energy per gram
• Cells break down food molecules and use the
energy stored in the chemical bonds to produce
compounds such as ATP that power the activities of
the cell.
• How do cells use energy?
1. Movement
2. Making new parts for the cell
3. Repairing cell parts
4. Transport of food and wastes
via active transport
5. Heat production in warm
blooded animals
How Do We Get Energy From ATP?
By breaking the
high- energy
bonds between
the last two
phosphates in
ATP
ATP
• The foods we eat contain usable energy
• If oxygen is available, organisms can break
down food and generate energy by the
process of cellular respiration.
Equation:
• Why doesn’t Earth run out of oxygen?
• Where does all the carbon dioxide waste
product go?
• As cellular respiration happens, it is balanced
by another process ____________________.
• The energy flows in opposite directions.
Photosynthesis “deposits” energy, and cellular
respiration “withdraws” energy.
The release of energy
by cellular respiration
takes place in plants,
animals, fungi,
protists, and most
bacteria.
• There are three stages
of cellular respiration
– Glycolysis
– Krebs Cycle
– Electron Transport
Chain
– Where does most
cellular respiration
take place?
Mitochondria
•
•
•
•
Inner Membrane
Outer membrane
Cristae
Matrix
1. Glycolysis
• Glycolysis means “sugar
breaking”
• Glucose breaks into 2
molecules of pyruvate.
• Happens in the
cytoplasm of the cell
• In the process of glycolysis 2 ATP are produced
and 2 NADH are produced.
• NAD+ accepts electrons from the breaking of
glucose.
• NADH carries the high-energy electrons to the
electron transport chain, where they can be
used to produce more ATP
Glucose
Although oxygen is
required for cellular
respiration, glycolysis is
anaerobic because it
does not require
oxygen to function.
NAD+
ADP
ATP
NADH
Pyruvic acid
2. Krebs Cycle (Citric acid cycle)
• Pyruvate enters the mitochondrial matrix
– The inner most compartment of the mitochondria
• Pyruvate is broken
down into carbon dioxide
and other molecules
• 2 ATP released
• Electron carriers NADH
and FADH2 are produced
High energy electron carriers NADH and
FADH2 make their way to the ETC
FAD
NAD+
FADH2
NADH
Cytoplasm
CO2
Matrix
• The Krebs cycle is aerobic (with the presence
of oxygen), a process that requires oxygen.
Even though the Krebs cycle does not directly
require oxygen, we call it aerobic because it
would not run with out the oxygen requiring
ETC.
• What is the last step in cellular respiration?
Where are we going to get most of the ATP
our cells need?
3. The Electron Transport Chain
• The ETC occurs in the inner membrane of the
mitochondria
NADH
ETC
FADH2
• NADH and FADH2 pass
their high energy electrons
to the ETC
• A total of 32 ATP are
made
• After the electrons pass through the ETC,
Oxygen takes them and combines with
hydrogen to form water.
• Oxygen is the final electron acceptor.
• Without oxygen, the Krebs cycle and the ETC
will not function. Why?
– What is made in the Krebs cycle?
– Why is oxygen a requirement in the ETC?
C6H12O6 + 6O2
•
•
•
•
6CO2 + 6H2O + ENERGY
Reactants?
Products?
Where do each of the reactants come from?
Where do each of the products come from?
Note: NADH and FADH2 go to the ETC
Energy Totals
– In the presence of
oxygen, the complete
breakdown of glucose
through cellular
respiration results in the
production of 36 ATP
molecules.
– This represents about
36 percent of the total
energy of glucose. The
remaining 64 percent is
released as heat.
Energy Totals
– The cell can generate ATP from just about
any source, even though we’ve modeled it
using only glucose. Complex carbohydrates
are broken down into simple sugars like
glucose. Lipids and proteins can be broken
down into molecules that enter the Krebs
cycle or glycolysis at one of several places.
Fermentation 9.3
• Cellular respiration requires oxygen. The Krebs
cycle and the ETC would not work with out it.
• What happens when we hold our breath and dive
under water?
• What happens if we can not replace oxygen fast
enough?
• What about microorganisms that live in places
where oxygen isn’t available?
• How do organisms generate energy when oxygen
is not available?
• Fermentation is a process by which energy can
be released from food molecules in the absence
of oxygen.
• Anaerobic process that occurs in the cytoplasm
• Two types of fermentation:
– Alcoholic Fermentation
– Lactic acid fermentation
Alcoholic Fermentation
• 1. Alcoholic Fermentation: pyruvate is broken
down to ethanol and in the process it releases
CO2
• Yeast and a few other
microorganisms use
alcoholic fermentation
that produces ethyl
alcohol and carbon
dioxide.
• This process is used
to produce alcoholic
beverages and causes
bread dough to rise.
Holes from release of
carbon dioxide
• Ethanol is toxic to yeast and a concentration of
about 12% ethanol kills yeast. This is why
naturally fermented wine contains about 12%
alcohol.
• 2. Lactic Acid Fermentation: In lactic acid
fermentation, pyruvate is converted into lactic acid
• Does not give off carbon dioxide
• Humans produce lactic acid when we undergo
strenuous exercise
• Prokaryotes (bacteria) produce lactic acid and
are used in the production of dairy products.
• Cheese, yogurt,
buttermilk, sour cream,
pickles, sauerkraut and
kimchi are all examples
of foods we eat that
are produced from
lactic acid
fermentation.
Energy and Exercise
•
•
•
•
Humans have three main sources of ATP:
1. ATP in the muscles
2. ATP made by lactic acid fermentation
3. ATP produced by cellular respiration
Quick Energy
– Cells normally contain small amounts of ATP
produced during cellular respiration, enough
for a few seconds of intense activity.
– Lactic acid fermentation can supply enough
ATP to last about 90 seconds. However, extra
oxygen is required to get rid of the lactic acid
produced. Following intense exercise, a person
will huff and puff for several minutes in order to
pay back the built-up “oxygen debt” and clear
the lactic acid from the body.
Long-Term Energy
– For exercise lasting longer than 90 seconds,
cellular respiration is required to continue
production of ATP.
– Cellular respiration releases energy more
slowly than fermentation does.
– The body stores energy in the form of the
carbohydrate glycogen. These glycogen stores
are enough to last for 15 to 20 minutes of
activity. After that, the body begins to break
down other stored molecules, including fats, for
energy.
Long-Term Energy
– Hibernating animals like this brown bear rely
on stored fat for energy when they sleep
through the winter.