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![Page 1: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/1.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Photosynthesis: Capturing Energy
Unit 3 ContinuedChapter 8
![Page 2: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/2.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Carbon Fixation
• Carbon fixation is the process of building complex carbon compounds from simple carbon compounds.
• Organisms that fix carbon are autotrophs – they use carbon dioxide as a carbon source, and combine it with water
![Page 3: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/3.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Name the type of organism that…
• Uses C02 as a carbon source• Cannot fix carbon• Uses light energy as an energy source• Uses organic compounds as sources of energy• Absorbs and converts light energy into
chemical energy• Uses light energy, but can’t do carbon fixation• Obtain energy from H2S, N02 or NH2• Use organic molecules as a source of energy
and carbon
![Page 4: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/4.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Photoautotrophs, Heterotrophs, and Chemoautotrophs
• Photoautotrophs: Organisms that gain energy from light in order to carry out carbon fixation• Photosynthetic plants, algae and bacteria• Use light energy to make ATP and carbohydrate
• Chemoautotrophs: Organisms that use chemical energy only to cause carbon fixation and to build structure• Certain bacteria
• Heterotrophs: Organisms that gain energy by eating other organisms, including autotrophs• Animals, nonphotosynthetic plants,
nonphotosynthetic unicellular organisms(such as protists), bacteria, and fungi
![Page 5: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/5.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
What is the Electromagnetic Spectrum?
• Complete range of radiant energy
![Page 6: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/6.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
• Order is ROYGBIV•Range is 380 – 760 nm•Violet has a shorter wavelength than red•Tiny packets of this energy is called a photon•Photons of light can energize an electron
Characteristics of Visible Light
![Page 7: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/7.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Relationship Between Photon Energy Capture and
Electrons• Electrons can absorb photon energy.• When they do so, they hop to a higher
shell.• When they release energy, they release a
photon, and drop back to the lower shell.• The released photon has less energy than
the one that was absorbed• The released photon has a longer
wavelength• Light released this way is fluorescence.
![Page 8: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/8.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Sun• The sun is a star• It has very high surface temperatures • It produces a vast amount of electromagnetic
radiation of widely varying frequencies• Gamma-rays, which have very short wavelengths • To the far-infrared (much longer )
![Page 9: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/9.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Absorption of Light Energy
• Light energy is absorbed by electrons in energy-absorbing atoms
• The energy causes electrons to change shells; the more energy absorbed, the further electrons move fromthe nucleus
• The energy may be shed as fluorescence ...
• Or transferred in the form of an electron to another molecule
![Page 10: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/10.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Leaf Structure
• Leaves have a layered organization
• The mesophyll tissue (middle layers of cells) is the main site of photosynthesis
![Page 11: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/11.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy The
Chloroplast
•The site of light harvesting & carbohydrate synthesis
![Page 12: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/12.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Parts of a Chloroplast• Thylakoid - Disc like
structure that contains the chlorophyll which absorbs the light
• Grana – stacks of thylakoids
• Purpose is to increase the amount of light that can be absorbed
• Stroma – middle fluid part that contains the enzymes needed for photosynthesis
![Page 13: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/13.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Chlorophyll
• Chlorophyll collects light energy (absorbs it) in a resonant porphyrin group that hangs out like a kite on the surface of the thylakoid
• Chlorophyll a initiates the light-dependent reactions• Bright green
• Chlorophyll b is an accessory pigment • Duller green
• Carotenoids are yellow and orange pigments that capture light energy and pass electrons to chlorophyll• Xanthophyll (yellow)• Carotene (orange)
![Page 14: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/14.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Chlorophyll Structure
• Note the double bonds and the Mg2+ ion
• The positive charges on the Mg2+ ion attract electrons
• The electrons become delocalized over the porphyrin ring (so they can reside there for some time, then can move easily on)
![Page 15: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/15.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Two types of Chlorophyll
1. Light antenna• These chlorophyll’s are the ones that
gather the light energy• When the light hits it, the chlorophyll
vibrates and the molecules move rapidly to the reaction center
2. Reaction Center• These chlorphylls are the ones that boost
the electrons to a higher energy state
![Page 16: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/16.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
![Page 17: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/17.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Antenna-Complex
Energy Funnel
• About 200 chlorophylls ‘inhabit’ an antenna complex
• Electrons move from one chlorophyll to another, losing energy (depicted by a red-shift in the electrons in this diagram)
h
Reaction center
![Page 18: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/18.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Each photosynthetic Unit contains a slightly different type of antenna and
reaction center
There are 2 types of photosynthetic units, or
photosystems
![Page 19: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/19.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Photosystems
• Photosystem I• Also called P700• Absorbs light that
has a 700 nm wavelength
• Can operate independently so probably evolved first
• Photosystem II• Also called P680• Absorbs light that
has a 680 nm wavelength
![Page 20: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/20.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Overview of Photosynthesis
• Photosynthesis is a redox reaction:
• Carbon dioxide is reduced to sugar• Water is oxidized to molecular
oxygen
6 CO2 + 12 H2O C6H12O6 + 6O2 + 6H2O
C6H12O6 + 6O26 CO2 + 6 H2O
Reduction
Oxidation
![Page 21: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/21.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Function in the Chloroplast• The light-dependent reactions (the harvesting
of light) occur on thylakoid membranes• The carbon fixation reactions (formation of
carbohydrate) occur in the stroma
![Page 22: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/22.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Two Energy Carriers of Photosynthesis
• ATP, and…• NADPH:
• Much like NADH except that it bears a phosphate
• Phosphate is attached to the sugar group
• NADPH is characteristic of anabolic redox processes
H added
PO4
NADH
NADPH
![Page 23: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/23.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Two Different Photosynthesis Reaction Sets
1. Cyclic photophosphorylation• e- run in a cycle• (photophosphorylation of ADP to make ATP) by
chemiosmosis• No carbohydrate made• Uses only P700
2. Noncyclic photophosphorylation• e- derived from splitting of water• Releases molecular oxygen• Makes ATP• Makes carbohydrate b/c NADPH (terminal e- acceptor)
passes to the Calvin Cycle• Uses P700 and P680
![Page 24: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/24.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Summary Equation for light dependent reactions of
photosynthesis
12H20 + 12 NADP+ + 18 ADP + 18Pi
602 + 12 NADPH + 18ATP
![Page 25: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/25.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
How Photosynthesis Starts• Sunlight hits chloroplast in a leaf
(Remember the sun is the ultimate source of energy on earth)
• Automatically, water goes through photolysis and splits• H20 02 + H+ + e-
• This provides O2 for the atmosphere and H+ ions and electron’s for photosystem II
• Antenna chlorophyll A associated with PII absorbs the photon
• This absorbed energy moves from one chlorphyll to another and eventually falls into the reaction center
![Page 26: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/26.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
• In the reaction center, an electron gets energized and moves to a higher energy level
• Energized electrons get accepted to a primary electron acceptor and moved through the electron transport chain
![Page 27: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/27.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
![Page 28: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/28.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
• The primary electron acceptor passes the electron to plastoquinone then to cytochrome complex than to plastocyanin. Each step of the electron transport chain creates ATP by chemiosmosis
![Page 29: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/29.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
![Page 30: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/30.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
• Now the “tired” electron needs more energy, so it travels to Photosystem I and received more sunlight
• It gets energized and accepted by a primary electron acceptor
• Primary electron acceptor passes the electron to 6 different electron acceptors, with the final acceptor as ferredoxin
• Ferredoxin transfers the electron to NADP+ forming NADPH which is released into the stroma**Sometimes Ferredoxin transfers the electron back to PI, so
the light dependent reactions can be referred to as being cyclic
![Page 31: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/31.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Noncyclic Photophosphorylation
![Page 32: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/32.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Protons Build up Inside Thylakoids
• The activity of the ETC causes a gradient of protons across the thylakoid membrane
![Page 33: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/33.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Chloroplast ATP Synthase
• Protons fall back through the chloroplast ATP synthase
• Makes ATP by combining ADP and phosphate in a process called chemiosmosis
• Much like the mitochondrial ATP synthase
![Page 34: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/34.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy The Electron Transport Chain and
Chemiosmosis
![Page 35: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/35.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Ok so now what
• All the light dependent phase did was transfer the energy from the sun into ATP and NADPH.
• The carbon fixation stage is next and will use this energy to make glucose!
![Page 36: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/36.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Dark Reactions• So-called because they do not directly need
light• They occur in the stroma of the chloroplast• They fix carbon to make carbohydrate• They are the Calvin-Benson Cycle reactions
![Page 37: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/37.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Calvin Cycle
• Melvin Calvin discovered it and received the nobel prize in 1961
• Calvin Cycle means “fixing carbon” or putting together carbons
• (not as difficult and complex as the Krebs)
![Page 38: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/38.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Summary Equation for the Dark Phase (i.e. Calvin Cycle)
12 NADPH + 18 ATP + 6C02
C6H1206 + 12 NADP+ + 18 ADP + 18Pi + 6H20
![Page 39: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/39.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
3 phases of Calvin Cycle
1. Carbon dioxide Uptake2. Carbon reduction3. RuBP regeneration
![Page 40: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/40.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Carbon Dioxide Uptake
• Carbon dioxide reacts with a 5C molecule called RuBP (ribulose biphosphate)
• This reaction is catalyzed by the enzyme Rubisco. (ribulose bisphosphate carboxylase) This enzyme is present in the chloroplast in large amounts
• The product is an unstable 6C molecule which immediately breaks down to 2 molecules of PGA (stands for phosphoglycerate). Each of these PGA molecules have 3C each.
![Page 41: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/41.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Carbon Reduction
• PGA is converted to G3P (glyceraldehyde 3 phosphate) – which is also nicknamed PGAL
• This reaction requires a lot of ATP and NADPH
• G3P is then converted to sugars like glucose! (and other carbohydrates)
• Not all G3P’s make sugar some go on to phase 3
![Page 43: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/43.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Regeneration of RuBP
• G3P converts to RP (ribulose phosphate)• RP then converts to RuBP using ATP• Now RuBP is available to join again with
CO2
![Page 45: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/45.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The Calvin Cycle
![Page 46: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/46.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Calvin Cycle = C3 Pathway
• Its named this way because the intermediate product G3P has 3 carbons
• This pathway is very inefficient; less than 1% of the light energy that reaches the chloroplast is found in glucose
• It’s all Rubisco’s fault!
![Page 48: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/48.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
When RUBISCO Doesn’t Work• In high light and temperature:
• Photosynthesis is very active• Water is easily lost• Leaf stomata close (small pores on the
underside of the leaf) to protect against water loss
• Oxygen builds up• Ribulose bisphosphate carboxylase (=
RUBISCO) (it’s a carboxylase because it adds a -COOH) has mixed affinity for oxygen and CO2
• It binds to O2 when O2 is abundant
• G3P is NOT produced
![Page 49: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/49.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Photorespiration• And as a result, photorespiration occurs:• In the presence of oxygen and light,
carbohydrates are oxidized and therefore No carbohydrate is produced
• Instead, CO2 and H2O are produced
• In C3 plants, 50% of the glucose made may be reoxidized back into Co2 due to this
• So photorespiration reduces the efficiency of C3 plants because Rubisco can bind to O2 as much as it binds to C02
• In C4, Co2 is very concentrated, so photorespiration is limited
![Page 50: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/50.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Evolutionary “Work-Arounds” Avoid Photorespiration
1. The C4 pathway• Physically sequesters the carbon dioxide-
requiring RUBISCO (carbon fixation) away from high oxygen
• Uses compartmentation with biological membranes (in different cells)
• In crabgrass, corn, and sugar cane2. Crassulacean acid metabolism (CAM)
• Carries out C fixation separated in time from high temperature and high oxygen
• In desert plants: succulents and cacti (also lilies and orchids)
![Page 51: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/51.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
C4 Pathway• CO2 is used by PEP
carboxylase to convert PEP (3C) to oxaloacetate (4C)
• Oxaloacetate is reduced to malate (4C) by NADPH
• Malate is transported via plasmodesmata to RUBISCO in the bundle sheath cell
• Malate is decarboxylated to yield CO2 (1C) and pyruvate (3C), which is transported to the mesophyll cell (C3 pathway)
• Pyruvate is phosphorylated to PEP by ATP
• PEP carboxylase has a higher affinity for C02 than Rubisco in C3. So PEP carboxylase is faster at obtaining Co2
![Page 52: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/52.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
C3 vs. C4 Leaf Anatomy
• C3• Have Rubisco in
mesophyll cells• Bundle sheath cells
have few chloroplasts and no Rubisco; so they can’t fix C02
• C4• Have PEP carboxylase
in mesophyll cells• Bundle sheath cells
have Rubisco!• Bundle sheath cells
are close to mesophyll cells which permits C02 transfer from mesophyll to bundle sheath cells for Calvin Cycle
![Page 53: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/53.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
C3 versus C4 Anatomy
• Bundle sheath cells are arranged differently in C3 and C4 plants
![Page 54: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/54.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Comparing C3 and C4 Pathways
• Extensive Photorespiration
• Does Calvin Cycle• RuBP accepts Co2• Enzyme Rubisco
• First product of C02 fixation is PGA (3C)
• Moderate affinity for C02• Occurs in mesophyll cells
• Minimal photorespiration• Does Calvin Cycle• PEP accepts C02• Enzymes Rubisco and
PEP carboxylase• First product of C02
fixation is Oxaloacetate (4c)
• High affinity for C02• Occurs in mesophyll and
bundle sheath cells
![Page 55: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/55.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
The CAM pathway• Seen in xeric plants (very dry conditions; desert)• Separation of function by TIME instead of
location / compartmentation• PEP carboxylase works at night when the
stomata are open (they close during the day in desert plants)
• Oxaloacetate is made and malate derived from it is stored in the vacuole
• During the day, CO2 is derived from the malate and made available to the Calvin cycle.
• Not as efficient at supporting rapid growth as is seen in C4 plants like crabgrass and corn, is good adaptation for desert plants
![Page 56: Copyright 2002 by Harcourt College Publishers, a division of Thomson Learning Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy Photosynthesis:](https://reader036.fdocuments.in/reader036/viewer/2022062517/56649e925503460f94b982f2/html5/thumbnails/56.jpg)
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Biology, Sixth Edition Chapter 8, Photosynthesis: Capturing Energy
Calvin cycle is all-important!
• In C3, C4 and CAM plants, the Calvin Cycle always receives the carbon dioxide that is made into carbohydrate...
• . . . under all conditions!
• Scientists are very interested in getting C4 chemistry genetically introduced into plants to increase crop efficiency.