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PhotosynthesisBiology
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1. Explain why photosynthesis is so important to energy and material flow for life on earth.
2. Know why plants tend to be green in appearance.3. Describe the organization of the chloroplast – the organelle of
photosynthesis in eukaryotes4. Understand that photosynthesis is a two fold process composed of
the light-dependent reactions and the light independent reactions 5. Explain where the light reactions and the CO2 fixation reactions
occur in the chloroplast.6. Define photosynthetic pigment composition and structure.7. Explain the absorption spectrum of chlorophyll and compare it to
the action spectrum of photosynthesis.
LEARNING OBJECTIVES
By the end of this lecture you will be able to:
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• Almost all plants are photosynthetic autotrophs, as are some bacteria and protists
– Autotrophs generate their own organic matter through photosynthesis– Sunlight energy is transformed to energy stored in the form of chemical
bonds
(a) Mosses, ferns, andflowering plants
(b) Kelp
(c) Euglena (d) Cyanobacteria
PHOTOSYNTHESISPHOTOSYNTHESIS
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Harvesting Light Energy
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2
PHOTOSYNTHESISPHOTOSYNTHESIS
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WHWHY ARY ARE PE PLANLANTS GTS GREREEN?EN?
It's not that easy bein' green Having to spend each day the color of the leaves When I think it could be nicer being red or yellow or gold Or something much more colorful like that…
Kermit the Frog
PHOTOSYNTHESISPHOTOSYNTHESIS
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Electromagnetic Spectrum and Visible Light
Gammarays X-rays UV
Infrared & Microwaves Radio waves
Visible light
Wavelength (nm)
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Different wavelengths of visible light are seen by the human eye as different colors.
WHYWHY ARE ARE PLA PLANTS NTS GREGREEN?EN?
Gammarays
X-rays UV Infrared Micro-waves
Radiowaves
Visible light
Wavelength (nm)
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Sunlight minus absorbed Sunlight minus absorbed wavelengths or colors equals wavelengths or colors equals the apparent color of an the apparent color of an object.object.
The feathers of male cardinals are loaded with carotenoid pigments. These pigments absorb some wavelengths of light and reflect others.
Reflected light
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Why are plants green?
Reflected lig
ht
Transmitted light
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WHYWHY ARE ARE PLA PLANTS NTS GREGREEN? EN? Plant Cells have Green Chloroplasts
The thylakoid The thylakoid membrane membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).
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Pigments
Pigments are lipids Plants use PIGMENTSPIGMENTS to
capture sun’s energy A pigment is a substance
that absorbs and reflects light.
The main pigment in plants is chlorophyll a Chlorophyll b Carotenoids
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Chlorophyll molecules are embedded in the thylakoid membrane
Act like a light “antenna”
These molecules can absorb sunlight energy
LightReflected
light
Absorbedlight
Transmittedlight
Chloroplast
THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED
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Chloroplast Chloroplast PigmentsPigments
Chloroplasts contain several pigments
– Chlorophyll a – Chlorophyll b – Carotenoids
Figure 7.7
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Different pigments absorb light differently
Chloroplast PigmentsChloroplast Pigments
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Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
PHOTOSYNTHESISPHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
carbon dioxide + water glucose + oxygen + water + energy
6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
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– All green plant parts have chloroplasts and carry out photosynthesis
• The leaves have the most chloroplasts
• The green color comes from chlorophyll in the chloroplasts
• The pigments absorb visible light energy
• What wavelength is reflected?
PHOTOSYNTHESISPHOTOSYNTHESIS
internal leaf structure
chloroplasts
outer membrane
inner membrane
thylakoid
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Chloroplasts: Sites of Photosynthesis In most plants,
photosynthesis occurs primarily in the chloroplasts in the leaves
A chloroplast contains: stroma, a fluid grana, stacks of
thylakoids The thylakoids contain
chlorophyll Chlorophyll is the green
pigment that captures light for photosynthesis
PHOTOSYNTHESISPHOTOSYNTHESIS
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LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana
Structure of Chloroplast
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LightChloroplast
Lightreactions
Calvincycle
NADP
ADP+ P
The light reactions light reactions convert solar energy to chemical energy
Produce ATP & NADPH
The Calvin cycle Calvin cycle makes sugar from carbon dioxide
ATP generated by the light reactions provides the energy for sugar synthesis
The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose
PHOTOSYNTHESIS
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Excitedstate
e
Heat
Light
Photon
Light(fluorescence)
Chlorophyllmolecule
Groundstate
2
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution
Excitation of chlorophyll in a chloroplast
Loss of energy due to heat causes the photons of light to be less energetic.
Less energy translates into longer wavelength.
Transition toward the red end of the visible spectrum.
ELECTRONS AGAIN!
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In the light reactions, electron In the light reactions, electron transport chains generate ATP, transport chains generate ATP, NADPH, & ONADPH, & O22
Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons
The excited electrons are passed from the primary electron acceptor to electron transport chains Their energy ends up
in ATP and NADPH
PhotosynthesisPhotosynthesis
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Reaction-center
chlorophyll
Primaryelectronacceptor
Primaryelectronacceptor
Primaryelectronacceptor
1
How the Light Reactions Generate ATP and NADPH
PhotosynthesisPhotosynthesis
Primaryelectron acceptor
Primaryelectron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy forsynthesis of
by chemiosmosis
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Plants produce OPlants produce O22 gas by splitting gas by splitting HH22OO
The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)
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Chemiosmosis powers ATP synthesis in the light reactions
The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane The flow of H+ back
through the membrane is harnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+ to form NADPH
PhotosynthesisPhotosynthesis
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The production of ATP by chemiosmosis in photosynthesis
Thylakoidcompartment(high H+)
Thylakoidmembrane
Stroma(low H+)
Light
Antennamolecules
Light
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
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The Calvin Cycle
.
a.k.a. the “dark reactions”
WARNING: DOES NOT ONLY TAKE PLACE IN THE DARK!
Accomplishes “carbon fixation” taking carbon from inorganic molecules and putting it into organic molecules (CO2 sugars)
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The Calvin Cycle
.
The quantities listed are for the production of one glucose molecule which is produced from six turns of the cycle
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Chloroplast
Light
Stack ofthylakoids ADP
+ P
NADP
Stroma
Lightreactions
Calvincycle
Sugar used for
Cellular respiration Cellulose
Starch
Other organic compounds
PhotosynthesisPhotosynthesis
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It's not that It's not that easy bein' easy bein' green… but it green… but it is essential for is essential for life on earth!life on earth!