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CHAPTER 6
Cellular Respiration:
Obtaining Energy from Food
PowerPoint® Lectures for
Essential Biology, Third Edition
– Neil Campbell, Jane Reece, and Eric Simon
Essential Biology with Physiology, Second Edition
– Neil Campbell, Jane Reece, and Eric Simon
Lectures by Chris C. Romero
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Biology and Society: Feeling the Burn
• When you exercise,
– Muscles need energy in order to perform work.
– Your cells use oxygen to release energy from the
sugar glucose.
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• Aerobic metabolism
– Occurs when enough oxygen reaches cells to
support energy needs.
• Anaerobic metabolism
– Occurs when the demand for oxygen outstrips the
body’s ability to deliver it.
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• Anaerobic metabolism
– Without enough oxygen, muscle cells break down
glucose to produce lactic acid.
– Lactic acid is associated with the “burn”
associated with heavy exercise.
– If too much lactic acid builds up, your muscles
give out.
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• Physical conditioning allows your body to adapt to
increased activity.
– The body can increase its ability to deliver
oxygen to muscles.
• Long-distance runners wait until the final sprint to
exceed their aerobic capacity.
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Figure 6.1
Energy Flow and Chemical Cycling
in the Biosphere
• Fuel molecules in food represent solar energy.
– Energy stored in food can be traced back to the
sun.
• Animals depend on plants to convert solar energy
to chemical energy.
– This chemical energy is in the form of sugars and
other organic molecules.
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Producers and Consumers
• Photosynthesis
– Uses light energy from the sun to power a
chemical process that makes organic molecules.
– Occurs in the leaves of terrestrial plants.
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• Autotrophs
– Are “self-feeders.”
– Include plants and other organisms that make all
their own organic matter from inorganic nutrients.
• Heterotrophs
– Are “other-feeders.”
– Include humans and other animals that cannot
make organic molecules from inorganic ones.
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• Producers
– Biologists refer to plants and other autotrophs as
the producers in an ecosystem.
• Consumers
– Heterotrophs are consumers, because they eat
plants or other animals.
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Figure 6.2
Chemical Cycling between Photosynthesis and
Cellular Respiration
• The ingredients for photosynthesis are carbon
dioxide and water.
– CO2 is obtained from the air by a plant’s leaves.
– H2O is obtained from the damp soil by a plant’s
roots.
• Chloroplasts rearrange the atoms of these
ingredients to produce sugars (glucose) and other
organic molecules.
– Oxygen gas is a by-product of photosynthesis.
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• Both plants and animals perform cellular
respiration.
– Cellular respiration is a chemical process that
harvests energy from organic molecules.
– Cellular respiration occurs in mitochondria.
• The waste products of cellular respiration, CO2 and
H2O, are used in photosynthesis.
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Figure 6.3
Cellular Respiration: Aerobic Harvest
of Food Energy
• Cellular respiration
– Is the main way that chemical energy is harvested
from food and converted to ATP.
– Is an aerobic process—it requires oxygen.
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The Relationship between Cellular Respiration and
Breathing
• Cellular respiration and breathing are closely
related.
– Cellular respiration requires a cell to exchange
gases with its surroundings.
– Breathing exchanges these gases between the
blood and outside air.
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Figure 6.4
The Overall Equation for Cellular Respiration
• A common fuel molecule for cellular respiration is
glucose.
– The overall equation for what happens to glucose
during cellular respiration
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Unnumbered Figure 6.1
The Role of Oxygen in Cellular Respiration
• During cellular respiration, hydrogen and its
bonding electrons change partners.
– Hydrogen and its electrons go from sugar to
oxygen, forming water.
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Redox Reactions
• Chemical reactions that transfer electrons from one
substance to another are called oxidation-reduction
reactions,
– Or redox reactions for short.
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• The loss of electrons during a redox reaction is
called oxidation.
• The acceptance of electrons during a redox reaction
is called reduction.
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Unnumbered Figure 6.2
• Why does electron transfer to oxygen release
energy?
– When electrons move from glucose to oxygen, it
is as though they were falling.
– This “fall” of electrons releases energy during
cellular respiration.
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Figure 6.5
NADH and Electron Transport Chains
• The path that electrons take on their way down
from glucose to oxygen involves many steps.
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Figure 6.6
• The first step is an electron acceptor called NAD+.
– The transfer of electrons from organic fuel to
NAD+ reduces it to NADH.
• The rest of the path consists of an electron
transport chain.
– This chain involves a series of redox reactions.
– These lead ultimately to the production of large
amounts of ATP.
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The Metabolic Pathway of Cellular Respiration
• Cellular respiration is an example of a metabolic
pathway,
– A series of chemical reactions in cells.
• All of the reactions involved in cellular respiration
can be grouped into three main stages:
– Glycolysis
– The citric acid cycle
– Electron transport
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A Road Map for Cellular Respiration
• The path of glucose through cellular respiration
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Figure 6.7
Stage 1: Glycolysis
• A molecule of glucose is split into two molecules
of pyruvic acid.
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• Glycolysis breaks a six-carbon glucose into two
three-carbon molecules.
– These molecules then donate high energy
electrons to NAD+, forming NADH.
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Figure 6.8
• Glycolysis makes some ATP directly when
enzymes transfer phosphate groups from fuel
molecules to ADP.
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Figure 6.9
Stage 2: The Citric Acid Cycle
• The citric acid cycle completes the breakdown of
sugar.
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• In the citric acid cycle, pyruvic acid from
glycolysis is first “prepped” into a usable form,
Acetyl CoA.
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Figure 6.10
• The citric acid cycle extracts the energy of sugar by
breaking the acetic acid molecules all the way
down to CO2.
– The cycle uses some of this energy to make ATP.
– The cycle also forms NADH and FADH2.
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Figure 6.11
Stage 3: Electron Transport
• Electron transport releases the energy your cells
need to make most of their ATP.
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• The molecules of electron transport chains are built
into the inner membranes of mitochondria.
– The chain functions as a chemical machine that
uses energy released by the “fall” of electrons to
pump hydrogen ions across the inner
mitochondrial membrane.
– These ions store potential energy.
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• When the hydrogen ions flow back through the
membrane, they release energy.
– The ions flow through ATP synthase.
– ATP synthase takes the energy from this flow, and
synthesizes ATP.
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Figure 6.12
The Versatility of Cellular Respiration
• Cellular respiration can “burn” other kinds of
molecules besides glucose:
– Diverse types of carbohydrates
– Fats
– Proteins
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Figure 6.13
Adding Up the ATP from Cellular Respiration
• A summary of ATP yield during cellular respiration
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Figure 6.14
Fermentation: Anaerobic Harvest of Food Energy
• Some of your cells can actually work for short
periods without oxygen.
• Fermentation
– Is the anaerobic harvest of food energy.
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Fermentation in Human Muscle Cells
• After functioning anaerobically for about 15
seconds,
– Muscle cells will begin to generate ATP by the
process of fermentation.
• Fermentation relies on glycolysis to produce ATP.
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• Glycolysis is the metabolic pathway that provides
ATP during fermentation.
– Pyruvic acid is reduced by NADH, producing
NAD+, which keeps glycolysis going.
– In human muscle cells, lactic acid is a by-product.
Fermentation Overview
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Figure 6.15a
Fermentation in Microorganisms
• Various types of microorganisms perform
fermentation.
– Yeast cells carry out a slightly different type of
fermentation pathway.
– This pathway produces CO2 and ethyl alcohol.
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Figure 6.15b
• The food industry uses yeast to produce various
food products.
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Figure 6.16
Evolution Connection:
Life on an Anaerobic Earth
• Ancient bacteria probably used glycolysis to make
ATP long before oxygen was present in Earth’s
atmosphere.
– Glycolysis is a metabolic heirloom from the
earliest cells that continues to function today in
the harvest of food energy.
Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings