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Capturing Solar Energy:
Photosynthesis
Capturing Solar Energy:
Photosynthesis
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Photosynthesis Photosynthesis
Light energy captured and stored as chemical potential energy in the covalent bonds of carbohydrate molecules
6 CO2 + 6 H2O + light C6H12O6 + 6 O2
Light energy captured and stored as chemical potential energy in the covalent bonds of carbohydrate molecules
6 CO2 + 6 H2O + light C6H12O6 + 6 O2
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Photosynthesis Photosynthesis Less Than 1% of the Sun's Energy Is Captured
in Photosynthesis Sun energy drives reduction of carrier
molecules Electrons in respiration loose energy going
from sugar to oxygen Mitochondria use released energy to make
ATP Electrons in photosynthesis must gain energy
going from water to sugar Energy provided by the sun Occurs in 1 million billionths of a second
Less Than 1% of the Sun's Energy Is Captured in Photosynthesis
Sun energy drives reduction of carrier molecules
Electrons in respiration loose energy going from sugar to oxygen
Mitochondria use released energy to make ATP
Electrons in photosynthesis must gain energy going from water to sugar
Energy provided by the sun Occurs in 1 million billionths of a second
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PhotosynthesisPhotosynthesis
LightLight A. Light consists of units of energy called photonsA. Light consists of units of energy called photons B. Photons possess differing amounts of energy B. Photons possess differing amounts of energy C. Energy in visible lightC. Energy in visible light 1.1. VioletViolet has short wavelength and high energy has short wavelength and high energy
photonsphotons 2.2. Red Red has long wavelength and low energy has long wavelength and low energy
photonsphotons D. D. AbsorbedAbsorbed vs reflected vs reflected E. Specific atoms can absorb only certain photons E. Specific atoms can absorb only certain photons
of lightof light
LightLight A. Light consists of units of energy called photonsA. Light consists of units of energy called photons B. Photons possess differing amounts of energy B. Photons possess differing amounts of energy C. Energy in visible lightC. Energy in visible light 1.1. VioletViolet has short wavelength and high energy has short wavelength and high energy
photonsphotons 2.2. Red Red has long wavelength and low energy has long wavelength and low energy
photonsphotons D. D. AbsorbedAbsorbed vs reflected vs reflected E. Specific atoms can absorb only certain photons E. Specific atoms can absorb only certain photons
of lightof light
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Pigments-molecules that Pigments-molecules that absorb lightabsorb light
Pigments-molecules that Pigments-molecules that absorb lightabsorb light
A. Molecules that absorb lightA. Molecules that absorb light B. TypesB. Types 1. 1. CarotenoidsCarotenoids-absorbs some green-absorbs some green a. Absorb photons over a broad range, not highly efficienta. Absorb photons over a broad range, not highly efficient b. Include beta-carotene, vitamin A and retinalb. Include beta-carotene, vitamin A and retinal 2. 2. ChlorophyllsChlorophylls a. Absorb photons by excitation like the photoelectric effecta. Absorb photons by excitation like the photoelectric effect 1. Complex ring structure called a porphyrin ring1. Complex ring structure called a porphyrin ring 2. Metal ion within a network of alternating single and double 2. Metal ion within a network of alternating single and double
bonds(Fe)bonds(Fe) b. Absorb photons over a narrow rangeb. Absorb photons over a narrow range 1. 1. Chlorophyll Chlorophyll aa absorbs in violet-blue range absorbs in violet-blue range 2. 2. Chlorophyll Chlorophyll bb absorbs in the red range absorbs in the red range 3. Wavelength not absorbed by chlorophylls reflected as green3. Wavelength not absorbed by chlorophylls reflected as green 4. Chlorophyll absorbs in a narrow range, but with great 4. Chlorophyll absorbs in a narrow range, but with great
efficiencyefficiency c. c. xanthrophyllxanthrophyll
A. Molecules that absorb lightA. Molecules that absorb light B. TypesB. Types 1. 1. CarotenoidsCarotenoids-absorbs some green-absorbs some green a. Absorb photons over a broad range, not highly efficienta. Absorb photons over a broad range, not highly efficient b. Include beta-carotene, vitamin A and retinalb. Include beta-carotene, vitamin A and retinal 2. 2. ChlorophyllsChlorophylls a. Absorb photons by excitation like the photoelectric effecta. Absorb photons by excitation like the photoelectric effect 1. Complex ring structure called a porphyrin ring1. Complex ring structure called a porphyrin ring 2. Metal ion within a network of alternating single and double 2. Metal ion within a network of alternating single and double
bonds(Fe)bonds(Fe) b. Absorb photons over a narrow rangeb. Absorb photons over a narrow range 1. 1. Chlorophyll Chlorophyll aa absorbs in violet-blue range absorbs in violet-blue range 2. 2. Chlorophyll Chlorophyll bb absorbs in the red range absorbs in the red range 3. Wavelength not absorbed by chlorophylls reflected as green3. Wavelength not absorbed by chlorophylls reflected as green 4. Chlorophyll absorbs in a narrow range, but with great 4. Chlorophyll absorbs in a narrow range, but with great
efficiencyefficiency c. c. xanthrophyllxanthrophyll
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Life depends on photosynthesis Life depends on photosynthesis
A. Foundation of energy for most ecosystems
B. Source of oxygen
C. Key component of the carbon cycle
A. Foundation of energy for most ecosystems
B. Source of oxygen
C. Key component of the carbon cycle
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The mechanism of photosynthesis
The mechanism of photosynthesis
Chloroplasts are the sites of photosynthesis
Have a membrane system within internal space (stroma)
Arranged in disk-shaped sacks (thylakoids)
The thylakoids contain light-harvesting photosynthetic pigments & enzymes
Internal membranes define space (lumen) that is separate from the rest of the stroma
Chloroplasts are the sites of photosynthesis
Have a membrane system within internal space (stroma)
Arranged in disk-shaped sacks (thylakoids)
The thylakoids contain light-harvesting photosynthetic pigments & enzymes
Internal membranes define space (lumen) that is separate from the rest of the stroma
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The mechanism of photosynthesis
The mechanism of photosynthesis
Photosynthesis occurs in two steps
1. Light-dependent reactions
a. Provides the energy necessary to fix carbon
b. Occurs in the thylakoid membranes
c. Generates ATP
Photosynthesis occurs in two steps
1. Light-dependent reactions
a. Provides the energy necessary to fix carbon
b. Occurs in the thylakoid membranes
c. Generates ATP
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LIMITATIONSLIMITATIONS
1.1. Geared only towards Geared only towards energy production(ATP)energy production(ATP)
2.2. Does not provide for Does not provide for biosynthesis(glucose biosynthesis(glucose synthesis)synthesis)
1.1. Geared only towards Geared only towards energy production(ATP)energy production(ATP)
2.2. Does not provide for Does not provide for biosynthesis(glucose biosynthesis(glucose synthesis)synthesis)
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CYCLIC PHOTOSYNTHESISCYCLIC PHOTOSYNTHESIS
PRIMATIVE FORMCOMES IN TO PLAY ON ITS OWN IN
FALL IN HIGHER PLANTS.
PRIMATIVE FORMCOMES IN TO PLAY ON ITS OWN IN
FALL IN HIGHER PLANTS.
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Light-Dependent Reactions
Light-Dependent Reactions
What happens during light reactions?
During transport of electrons from PS II to PS I
Some energy is harnessed to produce ATP
Eventually, chlorophyll from PS II is oxidized
Gets replacement electrons from water-photolysis
What happens during light reactions?
During transport of electrons from PS II to PS I
Some energy is harnessed to produce ATP
Eventually, chlorophyll from PS II is oxidized
Gets replacement electrons from water-photolysis
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Light-Dependent Reactions
Light-Dependent Reactions
Energy of light has thus been captured in two forms:
The synthesis of NADPH from NADP+
Proton gradient across the thylakoid membraneCannot be used directly to make foodMust first be converted to ATP by chloroplast
ATP synthase
Energy of light has thus been captured in two forms:
The synthesis of NADPH from NADP+
Proton gradient across the thylakoid membraneCannot be used directly to make foodMust first be converted to ATP by chloroplast
ATP synthase
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The mechanism of photosynthesis
The mechanism of photosynthesis
Energy carriers ATP and NADPH transport energy from the light-dependent reactions to the light-independent reactions
Energy carriers ATP and NADPH transport energy from the light-dependent reactions to the light-independent reactions
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The mechanism of photosynthesis
The mechanism of photosynthesis
2. Light-independent reactions
a. Uses energy of the light-dependent reaction to make sugar from CO2
b. Occurs in the stroma
2. Light-independent reactions
a. Uses energy of the light-dependent reaction to make sugar from CO2
b. Occurs in the stroma
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Light-Independent Reactions
Light-Independent Reactions
Steps in Light-Independent Reactions:
CO2 joins with RuBP forming an unstable 6-C molecule
Breaks into two 3-C PGA molecules
This first step in Calvin-Benson/C3 cycle is catalyzed by enzyme
Called ribulose biphosphate carboxylase (Rubisco)
Steps in Light-Independent Reactions:
CO2 joins with RuBP forming an unstable 6-C molecule
Breaks into two 3-C PGA molecules
This first step in Calvin-Benson/C3 cycle is catalyzed by enzyme
Called ribulose biphosphate carboxylase (Rubisco)
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2 G3P availablefor synthesis oforganic molecules.
3 RuBP regeneration uses energy and 10 G3P.
2 G3P synthesis uses energy.
1 Carbon fixation combines CO2
with RuBP.
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PHOTORESPIRATIONPHOTORESPIRATION
Many land plants take up oxygen and release CO2 in the light. There is a superficial resemblance to true respiration, but the process is much faster. However, it is normally masked by photosynthesis, which is even faster. Photorespiration differs from true respiration. Although plants do respire normally (with mitochondria, etc.) this is useful (produces ATP and NADH), and occurs mostly in the dark. In contrast, photorespiration is wasteful and occurs mostly in the light. Photorespiration appears to serve no useful purpose. Its main effect is to reduce the apparent rate of photosynthesis. Most of our important crops photorespire about half of their potential yield away!
Many land plants take up oxygen and release CO2 in the light. There is a superficial resemblance to true respiration, but the process is much faster. However, it is normally masked by photosynthesis, which is even faster. Photorespiration differs from true respiration. Although plants do respire normally (with mitochondria, etc.) this is useful (produces ATP and NADH), and occurs mostly in the dark. In contrast, photorespiration is wasteful and occurs mostly in the light. Photorespiration appears to serve no useful purpose. Its main effect is to reduce the apparent rate of photosynthesis. Most of our important crops photorespire about half of their potential yield away!
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PHOTORESPIRATIONPHOTORESPIRATION
A.A. OO22 competes for CO competes for CO2 2 with RuBP oxidizes it-with RuBP oxidizes it-high high oxygen low carbon dioxideoxygen low carbon dioxide
B.B. COCO2 2 released without ATP or NADPHreleased without ATP or NADPH C.C. C3 lose 1/4 to 1/2 of carbon fixed-40%C3 lose 1/4 to 1/2 of carbon fixed-40% D. C4 And CAM plants adapted to counter act D. C4 And CAM plants adapted to counter act
this this problemproblem E.E. Rubisco takes oxygen makes Rubisco takes oxygen makes
phosphoglycerate and phosphoglycerate and glycolateglycolate F.F. Goes to perioxisome-takes oxygen and Goes to perioxisome-takes oxygen and
makes a makes a compound that goes to compound that goes to mitochondria to make mitochondria to make carbon dioxide carbon dioxide like respiration.like respiration.
A.A. OO22 competes for CO competes for CO2 2 with RuBP oxidizes it-with RuBP oxidizes it-high high oxygen low carbon dioxideoxygen low carbon dioxide
B.B. COCO2 2 released without ATP or NADPHreleased without ATP or NADPH C.C. C3 lose 1/4 to 1/2 of carbon fixed-40%C3 lose 1/4 to 1/2 of carbon fixed-40% D. C4 And CAM plants adapted to counter act D. C4 And CAM plants adapted to counter act
this this problemproblem E.E. Rubisco takes oxygen makes Rubisco takes oxygen makes
phosphoglycerate and phosphoglycerate and glycolateglycolate F.F. Goes to perioxisome-takes oxygen and Goes to perioxisome-takes oxygen and
makes a makes a compound that goes to compound that goes to mitochondria to make mitochondria to make carbon dioxide carbon dioxide like respiration.like respiration.
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Much photorespirationoccurs under hot,dry conditions.
CO2 is capturedwith a highlyspecific enzyme.
Almost nophotorespirationoccurs in hot,dry conditions.Much glucose
synthesis occurs.
mesophyll cell in C4 plant
mesophyll cell in C3 plant
bundle-sheath cell in C4 plant
bundle-sheath cells
C3 plants use the C3 pathway
C4 plants use the C4 pathway
In a C3 plant, most chloroplasts are in mesophyll cells.
In a C4 plant, both mesophyll and bundle-sheath cells contain chloroplasts.
(a)
(b)
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ADAPTATIONSADAPTATIONS
C4C4 plants- plants-Hatch Slack plantsHatch Slack plants a. Different leaf structurea. Different leaf structure
b. Bundle sheath surrounded by palisade mesophyllb. Bundle sheath surrounded by palisade mesophyll c. Grasses-Found in hot climates, lots of sun,above 300 Cc. Grasses-Found in hot climates, lots of sun,above 300 C d. Uses about 2x ATP but stores COd. Uses about 2x ATP but stores CO22 at night or anytime at night or anytime
stomates are open. Saves CO stomates are open. Saves CO22 when plant when plant can can
e. Cyclee. Cycle 1. CO1. CO2 2 is picked up by PEP in mesophyll-is picked up by PEP in mesophyll-no rubiscono rubisco 2. Converted to oxaloacetic acid then malic acid2. Converted to oxaloacetic acid then malic acid 3. Stored in this stable form3. Stored in this stable form 4. Malic converted to Pyruvic acid + CO4. Malic converted to Pyruvic acid + CO22 5. Pumped into bundle sheath thru plasmodesmata 5. Pumped into bundle sheath thru plasmodesmata 6. Deeper than surface because there is less 6. Deeper than surface because there is less
oxygen to oxygen to cause photorespiration to occur cause photorespiration to occur
C4C4 plants- plants-Hatch Slack plantsHatch Slack plants a. Different leaf structurea. Different leaf structure
b. Bundle sheath surrounded by palisade mesophyllb. Bundle sheath surrounded by palisade mesophyll c. Grasses-Found in hot climates, lots of sun,above 300 Cc. Grasses-Found in hot climates, lots of sun,above 300 C d. Uses about 2x ATP but stores COd. Uses about 2x ATP but stores CO22 at night or anytime at night or anytime
stomates are open. Saves CO stomates are open. Saves CO22 when plant when plant can can
e. Cyclee. Cycle 1. CO1. CO2 2 is picked up by PEP in mesophyll-is picked up by PEP in mesophyll-no rubiscono rubisco 2. Converted to oxaloacetic acid then malic acid2. Converted to oxaloacetic acid then malic acid 3. Stored in this stable form3. Stored in this stable form 4. Malic converted to Pyruvic acid + CO4. Malic converted to Pyruvic acid + CO22 5. Pumped into bundle sheath thru plasmodesmata 5. Pumped into bundle sheath thru plasmodesmata 6. Deeper than surface because there is less 6. Deeper than surface because there is less
oxygen to oxygen to cause photorespiration to occur cause photorespiration to occur
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C4 plants/Hatch SlackC4 plants/Hatch Slack
Utilize an alternate pathway to make sugars in dry environments
Closing stomata to conserve water results in photorespiration in C3 plants
Utilize an alternate pathway to make sugars in dry environments
Closing stomata to conserve water results in photorespiration in C3 plants
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CAM PLANTSCAM PLANTS
a. Hot(desert) climates-a. Hot(desert) climates-high daytime high daytime temps, temps, low soil moisture,intense lightlow soil moisture,intense light
b. Stomates only open at nightb. Stomates only open at night c. Central Vacuole stores malic acidc. Central Vacuole stores malic acid d. Leaves vacuole and and releases COd. Leaves vacuole and and releases CO22
DiatomsDiatoms 1. Have both C3 and C4 cycles1. Have both C3 and C4 cycles 2. C3 in chloroplasts2. C3 in chloroplasts 3. C4 in cytosol3. C4 in cytosol 4. Uses because of low CO4. Uses because of low CO2 2 in the oceanin the ocean
a. Hot(desert) climates-a. Hot(desert) climates-high daytime high daytime temps, temps, low soil moisture,intense lightlow soil moisture,intense light
b. Stomates only open at nightb. Stomates only open at night c. Central Vacuole stores malic acidc. Central Vacuole stores malic acid d. Leaves vacuole and and releases COd. Leaves vacuole and and releases CO22
DiatomsDiatoms 1. Have both C3 and C4 cycles1. Have both C3 and C4 cycles 2. C3 in chloroplasts2. C3 in chloroplasts 3. C4 in cytosol3. C4 in cytosol 4. Uses because of low CO4. Uses because of low CO2 2 in the oceanin the ocean