Chapter 9: Cellular Respiration
and Fermentation
p.248-265
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Voc Terms
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Cellular respiration
Aerobic
Anaerobic
Glycolysis
NAD+
Krebs cycle
Matrix
Fermentation
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Chapter 9: Big Idea
Cellular Basis of life- How do organisms obtain
Energy
9.1- Why do most organisms undergo the
process of cellular respiration?
9.2- How do cell release energy from food in the
presence of oxygen?
9.3- How do cells release energy from food
without oxygen?
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THINK ABOUT IT
– You feel weak when you are hungry
because food serves as a source of
energy. How does the food you eat get
converted into a usable form of energy for
your cells?
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Harvesting Chemical Energy
• Cellular respirationcomplex process in which cells make ATP by
breaking down organic cpds.
• What are Autotrophs?
use photosynthesis to convert light energy
from the sun into chemical energy, stored
organic cpds
Both auto and heterotrophs undergo cellular
respiration to break organic cpds into simpler
molecules to release energy
(ATP and work)
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Chemical Energy and Food
– Where do organisms get energy?
– Organisms get the energy they need from
food.
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Chemical Energy and Food
– Food provides living things with the
chemical building blocks they need to grow
and reproduce.
– Food molecules contain chemical energy
that is released when its chemical bonds
are broken.
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Chemical Energy and Food
–
Energy stored in food is expressed in units of calories. A
Calorie is the amount of energy needed to raise the
temperature of 1 gram of water by 1 degree Celsius. 1000
calories = 1 kilocalorie, or Calorie.
–
Cells use all sorts of molecules for food, including fats,
proteins, and carbohydrates. The energy stored in each of
these molecules varies because their chemical structures,
and therefore their energy-storing bonds, differ.
–
Cells break down food molecules gradually and use the
energy stored in the chemical bonds to produce compounds
such as ATP that power the activities of the cell.
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Overview of Cellular Respiration
What is cellular respiration?
– Cellular respiration is the process that
releases energy from food in the presence of
oxygen.
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Glycolysis
•
Is a biochemical pathway in which one 6C
molecule of glucose is oxidized to produce
two 3C molecule
Terms:
1. Pyruvic acid- 3 carbon molecule
2. NADH/FADH2- electron carrier molecule
3. Anaerobic- does not require the presence of
oxygen
4. Aerobic- requires oxygen
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Overview of Cellular Respiration
–
If oxygen is available, organisms can obtain energy from
food by a process called cellular respiration. The summary
of cellular respiration is presented below.
– In symbols:
6 O2 + C6H12O6  6 CO2 + 6 H2O + Energy
–
–
In words:
Oxygen + Glucose  Carbon dioxide + Water + Energy
–
The cell has to release the chemical energy in food
molecules (like glucose) gradually, otherwise most of the
energy would be lost in the form of heat and light.
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Stages of Cellular Respiration
The three main stages of
cellular respiration:
1. Glycolysis
2. Krebs cycle
3. Electron transport
chain.
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Stages of Cellular Respiration
Glycolysis produces
only a small amount of
energy. Most of
glucose’s energy (90%)
remains locked in the
chemical bonds of
pyruvic acid at the end
of glycolysis.
(2 net ATP)
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Stages of Cellular Respiration
– During the Krebs
cycle, a little more
energy is generated
from pyruvic acid.
– (2 Net ATP)
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Stages of Cellular Respiration
The electron
transport chain
produces the bulk of
the energy in cellular
respiration by using
oxygen, a powerful
electron acceptor.
(34- 36 Net ATP)
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Oxygen and Energy
– Pathways of cellular
respiration that
require oxygen are
called aerobic. The
Krebs cycle and
electron transport
chain are both
aerobic processes.
Both processes take
place inside the
mitochondria.
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Oxygen and Energy
– Gylcolysis is an
anaerobic process. It
does not directly require
oxygen, nor does it rely
on an oxygen-requiring
process to run.
However, it is still
considered part of
cellular respiration.
Glycolysis takes place
in the cytoplasm of a
cell.
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Comparing Photosynthesis and
Cellular Respiration
– What is the relationship between
photosynthesis and cellular respiration?
– Photosynthesis removes carbon dioxide from
the atmosphere, and cellular respiration puts it
back. Photosynthesis releases oxygen into the
atmosphere, and cellular respiration uses that
oxygen to release energy from food.
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Comparing Photosynthesis and
Cellular Respiration
–
Photosynthesis and cellular
respiration are opposite
processes.
–
The energy flows in opposite
directions. Photosynthesis
“deposits” energy, and cellular
respiration “withdraws”
energy.
–
The reactants of cellular
respiration are the products of
photosynthesis and vice
versa.
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Comparing Photosynthesis and
Cellular Respiration
– The release of energy
by cellular respiration
takes place in plants,
animals, fungi, protists,
and most bacteria.
– Energy capture by
photosynthesis occurs
only in plants, algae,
and some bacteria.
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THINK ABOUT IT
– Food burns! How does a living cell extract
the energy stored in food without setting a
fire or blowing things up?
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Glycolysis
What happens during the process of glycolysis?
– During glycolysis, 1 molecule of glucose, a 6carbon compound, is transformed into 2
molecules of pyruvic acid, a 3-carbon
compound.
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Glycolysis
Glycolysis is the first stage
of cellular respiration.
–
During glycolysis, glucose
is broken down into 2
molecules of the 3-carbon
molecule pyruvic acid.
Pyruvic acid is a reactant in
the Krebs cycle.
–
ATP and NADH are
produced as part of the
process.
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The Advantages of Glycolysis
– Glycolysis produces ATP very fast, which is
an advantage when the energy demands of
the cell suddenly increase.
– Glycolysis does not require oxygen, so it can
quickly supply energy to cells when oxygen is
unavailable.
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The Krebs Cycle
What happens during the Krebs cycle?
– During the Krebs cycle, pyruvic acid is broken
down into carbon dioxide in a series of energyextracting reactions.
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Krebs Cycle
• Biochemical pathway that breaks down acetyl Co A,
producing CO2, hydrogen atoms, and ATP
• Hans Krebs (1900-1981), German biochemist
Five main steps that occur in the mitochondrial matrix,
aerobic process that oxidizes pyruvates to CO2
** this process yields 2 ATP same as glycolysis, but it
does give 10NADH molecules and 2 FADH2 molecules
which will drive the next stage ETC , where most
energy is transferred from glucose to ATP
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The Krebs Cycle
– During the Krebs cycle,
the second stage of cellular
respiration, pyruvic acid
produced in glycolysis is
broken down into carbon
dioxide in a series of
energy-extracting reactions.
– The Krebs cycle is also
known as the citric acid
cycle because citric acid is
the first compound formed
in this series of reactions.
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chapter 7 biology notes
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Energy Extraction
–
Remember! Each
molecule of glucose
results in 2 molecules of
pyruvic acid, which enter
the Krebs cycle. So each
molecule of glucose
results in two complete
“turns” of the Krebs cycle.
–
Therefore, for each
glucose molecule, 6 CO2
molecules, 2 ATP
molecules, 8 NADH
molecules, and 2 FADH2
molecules are produced.
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Electron Transport and ATP
Synthesis
How does the electron transport chain use highenergy electrons from glycolysis and the Krebs
cycle?
– The electron transport chain uses the highenergy electrons from glycolysis and the Krebs
cycle to convert ADP into ATP.
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chapter 7 biology notes
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Electron Transport
– NADH and FADH2 pass their high-energy
electrons to electron carrier proteins in the
electron transport chain.
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Importance of oxygen
• ATP can be synthesized by chemiosmosis only
if electrons continue to move from molecule
to molecule in the ETC.
• The last molecule in the ETC must pass e- on
to a final electron acceptor. If not it will stop!!
• The oxygen allows for additional electron to
pass along the chain, ATP can continue to be
made through chemiosmosis
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The Totals
How much energy does cellular respiration
generate?
– Together, glycolysis, the Krebs cycle, and the
electron transport chain release about 36-38
molecules of ATP per molecule of glucose.
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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.
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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.
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Efficiency of cellular respiration
• glycolysis and the Krebs cycle give a max yield
of 38 ATP molecules per molecule of glucose
• It can vary from cell to cell
• As a result most euk cells produce only 36 ATP
(39% efficiency) (38 x7)/ 686
**Cellular resp is 20x more efficient than
glycolysis alone
chapter 7 biology notes
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chapter 7 biology notes
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THINK ABOUT IT
– We use oxygen to release chemical energy
from the food we eat, but what if oxygen is
not around?
– Is there a pathway that allows cells to
extract energy from food in the absence of
oxygen?
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Fermentation
How do organisms generate energy when
oxygen is not available?
– In the absence of oxygen, fermentation
releases energy from food molecules by
producing NAD+ to regenerate glycolysis.
– Takes place in the cytoplasm of the cell
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Fermentation
– Under anaerobic conditions, fermentation
follows glycolysis. During fermentation, cells
convert NADH produced by glycolysis back into
the electron carrier NAD+, which allows
glycolysis to continue producing ATP.
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Rumen Microbes
• The rumen is a special stomach chamber in
cows and other large hoofed mammals. It acts
as a fermentation vat and has been estimated
in some cows to contain as many as 8.2 X
10^15 microbes, including over 200 species of
bacteria, protozoa and fungi!! (adaptation for
digesting plants)
chapter 7 biology notes
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Fermentation
• When O2 is present CR continues as pyruvic
acid enter the pathways of aerobic
respiration.
• When no O2 is present- anaerobic
environment cells must convert pyruvic acid
into other cpds through additional
biochemical pathways that occur in the
cytoplasm
• The combination of glycolysis and these
pathways that regenerate NAD+ is
fermentation
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Fermentation cont:
• Additional pathways do not produce ATP
• If there were not a cellular process that
recycled NAD+ from NADH, glycolysis would
quickly use up all the NAD+ in the cell
• Glycolysis would STOP! ATP production
would STOP!! fermentation pathways allow
for the continued production of ATP
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Fermentation cont:
•
•
There are many fermentation pathways
They differ in terms of enzymes that are
used
• They differ in the cpds that are made from
pyruvic acid
Two common fermentation pathways result in
the production of
1. Lactic acid
2. Ethyl alcohol
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chapter 7 biology notes
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Alcoholic Fermentation
– 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.
Chemical equation:
Pyruvic acid + NADH  Alcohol + CO2 + NAD
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Alcoholic Fermentation cont
• The ethyl alcohol is the alcohol in alcoholic beverages
• To make wines, the CO2 that is generated is allowed
to escape
• If you make champagne it is retained for the
carbonation
• Bread making also depends on alcoholic
fermentation performed by yeast cells, CO2
produced makes the bread rise because of the
bubbles produced the ethyl alcohol evaporates
during the baking process
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Lactic Acid Fermentation
– Most organisms, including humans, carry out
fermentation using a chemical reaction that
converts pyruvic acid to lactic acid.
Chemical equation:
Pyruvic acid + NADH  Lactic acid + NAD+
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Lactic Acid Fermentation cont:
• Why is this important
LA fermentation by microorganisms play an
essential role in the manufacture of many
dairy products
Ex. Fermentation of milk spoiling, if controlled
we can use it to make buttermilk, cheese,
yogurt, sour cream
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Lactic Acid Fermentation cont
• Also occurs in your body
Muscle cells during strenuous exercise
Muscle cells use up O2 more rapidly than it can be
delivered to them
O2 becomes depleted, muscles switch from cellular
respiration to LAF
This LA accumulated in the muscle making the cytosol
more acidic, this increased acidity may reduce the
cells ability to contract causing cramping pain,
fatigue, later id will diffuse into the blood and is
transported to the liver to be converted back to
pyruvic acid
chapter 7 biology notes
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Energy and Exercise
How does the body produce ATP during
different stages of exercise?
– For short, quick bursts of energy, the body
uses ATP already in muscles as well as ATP
made by lactic acid fermentation.
– For exercise longer than about 90 seconds,
cellular respiration is the only way to continue
generating a supply of ATP.
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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.
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Long-Term Energy
– For intense 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.
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Long-Term Energy
– Hibernating animals like this brown bear
depend on stored fat for energy when they
sleep through the winter.
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chapter 7 biology notes
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