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Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 6
Where It Starts – Photosynthesis
©
Learning2015
2015
© Cengage
Cengage Learning
6.1 How Do Photosynthesizers Absorb
Light?
• Energy flow through ecosystems begins
when photosynthesizers intercept sunlight
• Autotrophs are producers
– Make food using energy from environment
and carbon from inorganic molecules
• Heterotrophs are consumers
– Obtain carbon from organic compounds
assembled by other organisms
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2
Properties of Light
visible light
gamma
rays
x-rays
ultraviolet
radiation
near-infrared
radiation
infrared
radiation
400 nm
B
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radio waves
longest wavelengths
(lowest energy)
shortest wavelengths
(highest energy)
A
microwaves
500 nm
600 nm
700 nm
Capturing a Rainbow
• Photosynthesizers use pigments to
capture light of specific wavelengths
• Chlorophyll α: most common
photosynthetic pigment in plants and
protists
– Absorbs violet, red, and orange light
– Reflects green light (appears as green)
• Accessory pigments harvest additional
light wavelengths
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4
6.2 Why Do Cells Use More Than One
Photosynthetic Pigment?
• In 1882, Theodor Engelmann tested the
hypothesis that the color of light affects the
rate of photosynthesis
– Used motile, oxygen-requiring bacteria to
identify where photosynthesis was taking
place
– Directed a spectrum of light across individual
strands of green algae
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5
Why Do Cells Use More Than One
Photosynthetic Pigment?
• In Engelmann’s experiment, oxygenrequiring bacteria gathered where blue
and red light fell across the algal cells
• Conclusion:
– Blue and red light are best light for driving
photosynthesis in these algal cells
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Why Do Cells Use More Than One Photosynthetic Pigment?
A
phycoerythrobilin
phycocyanobilin
chlorophyll b
chlorophyll a
β-carotene
bacteria
algae
400nm
500nm
600nm
700nm
400nm
500nm
600nm
700nm
Wavelength
B
C
7
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Why Do Cells Use More Than One
Photosynthetic Pigment?
• The combination of pigments used for
photosynthesis differs among species
– Photosynthetic species are adapted to the
environment in which they evolved
– Light that reaches different environments
varies in its proportions of wavelengths
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6.3 What Happens During
Photosynthesis?
• Photosynthesis converts the energy of
light into the energy of chemical bonds
• Unlike light, chemical energy can power
the reactions of life, and it can be stored
for use at a later time
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What Happens During Photosynthesis?
• In eukaryotes, photosynthesis takes place
in chloroplasts
– Thylakoid membrane: a chloroplast’s
continuous highly folded inner membrane
system
– Stroma: cytoplasm-like fluid between the
thylakoid membrane and the two outer
membranes of a chloroplast
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10
What Happens During Photosynthesis?
• Photosynthesis is often summarized as:
– CO2 + water
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light energy
sugars + O2
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Adaptations to Climate
• Stomata are tiny gateways for gases
– Open stomata:
• Allow CO2 to diffuse from the air into
photosynthetic tissues
• Allow O2 to diffuse out of these tissues into the air
– Closed stomata:
• Conserve water on hot, dry days
• Limit the availability of CO2 for the lightindependent reactions; sugar synthesis slows
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6.6 Application: Green Energy
• With fossil fuel prices soaring, there is an
increasing demand for biofuels:
– Oils, gases, or alcohols made from organic
matter that is not fossilized
• Most materials we use for biofuel
production today consist of food crops:
– Mainly corn, soybeans, and sugarcane
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Application: Green Energy
• Fossil fuels:
– Petroleum, coal, and natural gas
– Formed from the remains of ancient swamp
forests that decayed and compacted over
millions of years
– Consist of molecules originally assembled by
ancient plants
“Non-renewable”
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Application: Green Energy
• The process of using fossil fuels or
biofuels are fundamentally the same:
– Release energy by breaking the bonds of
organic molecules
– Use oxygen to break those bonds
– Produce carbon dioxide
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Application: Green Energy
• Biofuels are a renewable source of energy
– Growing more plants creates more sources of
biofuels
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Application: Green Energy
• Biofuels do not contribute to global climate
change
– Growing plant matter for fuel recycles carbon
that is already in the atmosphere
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Application: Green Energy
• Corn and other food crops are rich in oils,
starches, and sugars that can be easily
converted to biofuels
– Starch from corn kernels can be broken down
to glucose, which is converted to ethanol by
bacteria or yeast
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Application: Green Energy
• Making biofuels from some plants require
additional steps, because these materials
contain a higher proportion of cellulose
– Researchers are currently working on costeffective ways to break down the abundant
cellulose in fast-growing weeds
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Application: Green Energy
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Application: Green Energy
• According to tropical forest scientist Willie
Smits, the Arenga sugar palm has the
potential to serve as the core of a wastefree system
– Produces premium organic sugar and ethanol
for fuel
– Provides food products and jobs to villagers
– Helps preserve the existing native rain forest
© Cengage Learning 2015
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Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 7
How Cells Release
Chemical Energy
©
Learning2015
2015
© Cengage
Cengage Learning
7.1 How Do Cells Access the Chemical
Energy in Sugars?
• In order to use the energy stored in
sugars, cells must first transfer it to ATP
– The energy transfer occurs when the bonds of
a sugar’s carbon backbone are broken,
driving ATP synthesis
– Chemical Energy
© Cengage Learning 2015
Usable Energy
How Do Cells Access the Chemical Energy
in Sugars?
• There are two main mechanisms by which
organisms break down sugars to make
ATP:
– Aerobic respiration
– Fermentation (anaerobic respiration)
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Aerobic Respiration and Fermentation
Compared
• Aerobic respiration: requires oxygen to
break down sugars to make ATP
– Main energy-releasing pathway in nearly all
eukaryotes and some bacteria
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Aerobic Respiration and Fermentation
Compared
• The three stages of aerobic respiration
produce thirty-six ATP:
– Glycolysis
• Occurs in the cytoplasm; net yield is two ATP
– Krebs cycle
• Occurs in the mitochondria; net yield is two ATP
– Electron transfer phosphorylation
• Occurs in the mitochondria; net yield is thirty-two
ATP
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Aerobic Respiration and Fermentation
Compared
• Fermentation: sugar breakdown pathway
that does not require oxygen to make ATP
– Like aerobic respiration, fermentation begins
with glycolysis in cytoplasm
– Unlike aerobic respiration, fermentation
occurs entirely in cytoplasm, and does not
include electron transfer chains
– Net yield is two ATP, which provides enough
ATP to sustain many single-celled species
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How Did Energy-Releasing Pathways
Evolve?
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What Is Fermentation?
• Two fermentation pathways:
– Alcoholic fermentation: anaerobic sugar
breakdown pathway that produces ATP, CO2,
and ethanol
– Lactate fermentation: anaerobic sugar
breakdown pathway that produces ATP and
lactate
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Alcoholic Fermentation
• Alcoholic fermentation in a fungus,
Saccharomyces cerevisiae, sustains these
yeast cells as they grow and reproduce
– Used to produce beer, wine, and bread
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Lactate Fermentation
• Animal muscle cells carry out aerobic
respiration and/or lactate fermentation
– Red muscle fibers: many mitochondria and
myoglobin; produce ATP mainly by aerobic
respiration
• Sustains prolonged activity
– White muscle fibers: contain few mitochondria
and no myoglobin; most ATP produced by
lactate fermentation
• Useful for quick, strenuous activities
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Lactate Fermentation
B
C
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7.7 Can the Body Use Any Organic
Molecule for Energy?
• Energy from dietary molecules
– Aerobic respiration generates a lot of ATP by
fully oxidizing glucose, completely dismantling
it carbon by carbon
• Cells also dismantle other organic molecules by
oxidizing them
– Complex carbohydrates, fats, and proteins in
food can be converted to molecules that enter
glycolysis or the Krebs cycle
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Complex Carbohydrates
• Starches and other complex
carbohydrates are broken down into
monosaccharides
• Sugars are converted to glucose-6phosphate for glycolysis
– A high concentration of ATP causes glucose6-phosphate to be diverted away from
glycolysis and into the formation of glycogen
stores
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Fats
• Fats are dismantled by first breaking the
bonds that connect the fatty acid tails to
the glycerol head
• Free fatty acids are oxidized by splitting
their backbones into two-carbon fragments
– These fragments are converted to acetyl–
CoA, which can enter the Krebs cycle
• Glycerol gets converted to PGAL, an
intermediate of glycolysis
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Proteins
• Dietary proteins are split into their amino
acid subunits
– Ammonia (NH3), formed as a waste product,
is eliminated in urine
– The carbon backbone is split, and acetyl–
CoA, pyruvate, or an intermediate of the
Krebs cycle forms
– These molecules enter aerobic respiration’s
second stage
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Food
7.7 Can the Body Use Any Organic
Molecule for Energy? (cont’d.)
a triglyceride (fat)
glycerol
head
Fats
fatty acids
2
acetyl–CoA
glycerol
3
Complex Carbohydrates
Proteins
glucose, other simple sugars
amino acids
1
4
acetyl–CoA
PGAL
fatty acid
tails
NADH pyruvate
intermediate
of Krebs cycle
NADH, FADH2
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• Photosynthesis =
Light Energy
Chemical Energy
• Cell Respiration =
Chemical Energy
© Cengage Learning 2015
Usable Energy
In the setup shown below,
which color light will
cause the plant to
produce the smallest
number of gas bubbles?
A) red
B) orange
C) blue
D) green
© Cengage Learning 2015
In the setup shown below,
which color light will
cause the plant to
produce the smallest
number of gas bubbles?
A) red
B) orange
C) blue
D) green
© Cengage Learning 2015
An investigation was carried out and the results are shown below.
Substance X resulted from a metabolic process that produces ATP in yeast (a singlecelled fungus).
Which statement best describes substance X?
A) It is oxygen released by protein synthesis.
B) It is glucose that was produced in photosynthesis.
C) It is starch that was produced during digestion.
D) It is carbon dioxide released by respiration.
© Cengage Learning 2015
An investigation was carried out and the results are shown below.
Substance X resulted from a metabolic process that produces ATP in yeast (a singlecelled fungus).
Which statement best describes substance X?
A) It is oxygen released by protein synthesis.
B) It is glucose that was produced in photosynthesis.
C) It is starch that was produced during digestion.
D) It is carbon dioxide released by respiration.
© Cengage Learning 2015
The diagram represents a system in a space station that includes a tank containing
algae. An astronaut from a spaceship boards the space station.
A- State two changes in the chemical composition of the space station atmosphere
that would result from turning on more lights.
B- State two changes in the chemical composition of the space station atmosphere as
a result of the astronaut coming on board the space station.
C- Identify one process being controlled in the setup shown in the diagram.
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The diagram represents a system in a space station that includes a tank containing algae. An
astronaut from a spaceship boards the space station.
A- State two changes in the chemical composition of the space station atmosphere that would
result from turning on more lights.
Less CO2 / More O2
B- State two changes in the chemical composition of the space station atmosphere as a result of
the astronaut coming on board the space station.
Less O2 / More CO2 / More water vapor
C- Identify one process being controlled in the setup shown in the diagram.
Photosynthesis
© Cengage Learning 2015