1. Chapter 8 Photosynthesis General Biology I BSC 2010
credit: modification of work by David Nance
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The processes in all organisms– from bacteria to humans– require energy.
credit: modification of work by Steve VanRiper, U.S. Fish and Wildlife Service
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3. To get this energy, many organisms access stored energy by eating food (other organisms).
credit: Associaçäo Brasileira de Supermercados
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4. Photosynthesis is the only process that can capture energy that originates in outer space and convert it into energy stored as chemical compounds (food).
credit: modification of work by Julie Magro
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Photosynthesis
a series of chemical reactions
results in production of food
consumes carbon dioxide
releases oxygen
occurs in plants, some bacteria, and some protists
credit: modification of work by Steve Hillebrand, U.S. Fish and Wildlife Service
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6. Photosynthesis Locations
Eukaryotes: occurs in chloroplasts
Prokaryotes: occurs in association with cell membranes
Chloroplasts arose by endosymbiosis of photosynthetic bacteria.
credit: modification of work by Todd Petit
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7. Photosynthesis: Global Distribution
credit: modification of work by SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE
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Chlorophyll Concentrations

8. “Trophy” = Feeding energy source “photo-” “chemo-” “auto-” “hetero-”
energy from light
energy from molecules (food)
“auto-”
photoautotrophs
plants
algae
cyanobacteria
chemoautotrophs
some bacteria and archaea
carbon from carbon dioxide (CO2) gas
“hetero-”
photoheterotrophs
some types of bacteria
chemoheterotrophs
animals, fungi
some protists
some prokaryotes
carbon from solid molecules (food)
carbon source

9. Photosynthesis Powers Ecosystems*
It converts light energy into food energy.
Both plants and animals depend on the food it produces as parts of food chains or food webs.
*99% of known ecosystems are powered by sunlight. Deep sea hydrothermal vent ecosystems are an example of the other 1%.
credit: Gerry Atwell
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Photosynthesis uses solar energy, carbon dioxide, and water to produce energy-storing carbohydrates. Oxygen is generated as a waste product of photosynthesis.
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11. The Photosynthesis Equation
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Plant Leaf Structure
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credit a: modification of work by Louisa Howard, Rippel Electron Microscope Facility, Dartmouth College; credit b: modification of work by June Kwak, University of Maryland; scale-bar data from Matt Russell

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Chloroplasts
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14. Photosynthesis Has Two Stages
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The light-dependent reactions
The light-independent reactions (Calvin Cycle)

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Visible Light
is a form of electromagnetic radiation
exists in different wavelengths
Different wavelengths correspond to different colors.
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16. The Electromagnetic Spectrum
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Absorption of Light
Pigment molecules absorb light energy.
Different pigments absorb different wavelengths, as seen in the absorption spectrum graph.
Photosynthesis pigments include chlorophylls a and b and carotenoids.
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Absorption of Light
Chlorophyll reflects (does not absorb) green light.
Plants with lots of chlorophyll reflect green light and appear green.
Carotenoids absorb some of the other wavelengths.
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19. credit: Jason Hollinger
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Plants that commonly grow in shade have adapted to low levels of light by changing the relative concentrations of their pigments.

20. The Light-Dependent Reactions
the first stage of photosynthesis
harvest light energy to make NADPH and ATP*
occur in photosystems embedded in the thylakoid membrane
include 2 types of photosystems (type II and type I)
* Yes! Some ATP is made in chloroplasts. However, it is used in the chloroplast. Chloroplasts are not an ATP “powerhouse” like mitochondria are.
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21. Photosystems are Light-Harvesting Complexes
structure includes an antenna complex made of proteins and pigment molecules
pigment molecules pass energy to the reaction center
a photon is a “packet” of light energy
pigments absorb photons and the molecule becomes excited in a high-energy state
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22. The Photoact and Electron Capture
The excited reaction center gives up an electron.
This is an oxidation event.
The electron is captured by the primary electron acceptor.
The electron is sent through an electron transport chain.

23. Light Reactions in the Thylakoid
Water is split
to get electrons.
This releases oxygen.
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24. The Light-Independent Reactions
the second stage of photosynthesis
uses NADPH and ATP to build carbohydrate molecules (food)
occurs in the stroma
accomplishes carbon fixation
also known as the Calvin cycle
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25. The Calvin Cycle Has Three Parts
1. Fixation: CO2 from air is “fixed” into solid 3-PGA molecules.
2. Reduction: ATP energy and NADPH are used to reduce the 3-PGA to make G3P*.
3. Regeneration: More ATP is used to regenerate the starting material.
*Where have you seen G3P before? In glycolysis, a 6-carbon glucose is first split into two 3-carbon G3P molecules.

26. Calvin Cycle, Part 1: Fixation
“RuBisCo” is the enzyme called ribulose-1,5- bisphosphate carboxylase/oxygenase. It does the carbon fixation.
A carbon atom from air is added to RuBP (ribulose bisphosphate), which then splits into two 3-PGA molecules.
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27. Calvin Cycle, Part 2: Reduction
“G3P” (or GA3P) is the product of the Calvin cycle.
ATP and NADPH are used.
For every six G3P made, one leaves the cycle and can become part of foods like glucose.
The rest of the G3P is recycled back into RuBP so the cycle can continue.
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28. Calvin Cycle, Part 3: Regeneration
More ATP is used to regenerate RuBP.
This allows to Calvin cycle to continue.
Note: It takes two 3-carbon G3P to make one 6-carbon glucose.
Since each turn of the cycle fixes only one carbon, it actually takes three turns of the cycle to make one G3P and six turns of the cycle to make one glucose.
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29. Recall: Photosynthesis Has Two Stages
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The light-dependent reactions
The light-independent reactions (Calvin Cycle)

30. Photosynthesis and aerobic respiration play important roles in the carbon cycle.
credit: modification of work by Stuart Bassil
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31. Chloroplasts and Mitochondria
O2 and glucose
CO2
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