Photosynthesis - LECTURE(2!4!13)
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Transcript of Photosynthesis - LECTURE(2!4!13)
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PHOTOSYNTHESIS
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THE SUN: MAIN SOURCE OF
ENERGY FOR LIFE ON EARTH
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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
THE BASICS OF PHOTOSYNTHESIS
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Light Energy Harvested by Plants &
Other Photosynthetic Autotrophs
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Different wavelengths of visible light are seen bythe human eye as different colors.
WHY ARE PLANTS GREEN?
Gamma
raysX-rays UV Infrared
Micro-
waves
Radio
waves
Visible light
Wavelength (nm)
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What color of light is least effective
in driving photosynthesis?
ANS. GREEN
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Sunlight minus absorbedwavelengths or colors
equals the apparent color
of an object.
The feathers of male cardinals
are loaded with carotenoid
pigments. These pigments
absorb some wavelengths of
light and reflect others.
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Why are plants green?
Transmitted light
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WHY ARE PLANTS GREEN?
Plant Cellshave Green
Chloroplasts
The thylakoid
membrane of the
chloroplast isimpregnated with
photosynthetic
pigments (i.e.,chlorophylls,
carotenoids).
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Chloroplasts
absorb light
energy andconvert it to
chemical energy
Light Reflectedlight
Absorbedlight
Transmittedlight Chloroplast
THE COLOR OF LIGHT SEEN IS THE
COLOR NOT ABSORBED
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The location and structure of chloroplasts
LEAF
CHLOROPLAST
StromaGrana
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The location and structure of chloroplasts
LEAF CROSS SECTIONMESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Innermembrane
Thylakoid
compartmentThylakoidStroma
Granum
StromaGrana
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Chloroplasts: Sites of Photosynthesis
Photosynthesis Occurs in chloroplasts, organelles in certain
plants
All green plant parts have chloroplasts and carryout photosynthesis
The leaves have the most chloroplasts
The green color comes from chlorophyll in the
chloroplasts The pigments absorb light energy
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In most plants, photosynthesis occursprimarily in the leaves, in the chloroplasts
A chloroplast contains:
stroma, a fluid grana, stacks of thylakoids
The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captureslight for photosynthesis
Photosynthesis occurs in chloroplasts
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Chloroplasts contain several pigments
Chloroplast Pigments
Chlorophyll a = absorbs blue-violet and red light
Chlorophyll b = absorbs blue and orange light
Carotenoids = absorbs blue-green light
Figure 7.7
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The Calvin cycle makessugar from carbon
dioxide ATP generated by the light
reactions provides the energyfor sugar synthesis
The NADPH produced by the
light reactions provides the
electrons for the reduction of
carbon dioxide to glucose
Light
Chloroplast
Lightreactions
Calvincycle
NADP
ADP+ P
The light reactions
convert solarenergy to chemicalenergy Produce ATP & NADPH
AN OVERVIEW OF PHOTOSYNTHESIS
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Chlorophyll a & bChl a has a methyl
group
Chl b has a carbonyl
group
Porphyrin ring
delocalized e-
Phytol tail
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Primary
electron acceptor
Photon
Reaction
center
PHOTOSYSTEM
Pigment
molecules
of antenna
Molecular Game of Hot Potato
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Cyclic Photophosphorylation Process for ATP generation associated with
some Photosynthetic Bacteria Reaction Center => 700 nm
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Water-splittingphotosystem NADPH-producingphotosystem
ATPmill
Two types of
photosystems
cooperate in the
light reactions
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Primaryelectron acceptor
Primaryelectron acceptor
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy forsynthesis of
Noncyclic Photophosphorylation Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product
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The O2 liberated by photosynthesis is madefrom the oxygen in water (H+ and e-)
Plants produce O2 gas by splitting H2O
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2 H+ 1/2
Water-splittingphotosystem
Reaction-center
chlorophyll
Light
Primaryelectronacceptor
Energyto make
Primaryelectronacceptor
Primaryelectronacceptor
NADPH-producingphotosystem
Light
NADP
1
2
3
How the Light Reactions Generate ATP and NADPH
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In the light reactions, there is a flow ofelectrons from____ molecules to ____,
which is reduced to ____, the source of
electron for sugar synthesis in the ____
cycle.
ANS. Water, NADP+, NADPH, Calvin
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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
In the light reactions, electron transport
chains generate ATP, NADPH, & O2
Ch i i ATP
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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
Chemiosmosis powers ATP
synthesis in the light reactions
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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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What is the advantage of the lightreactions producing NADPH and ATP on
the stroma side of the thylakoid
membrane?
ANS. The Calvin cycle, which consumes
the NADPH and ATP, occurs in the
stroma.
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Review: Photosynthesis uses light
energy to make food molecules
Light
Chloroplast
Photosystem IIElectrontransport
chainsPhotosystem I
CALVINCYCLE Stroma
LIGHT REACTIONS CALVIN CYCLE
Cellularrespiration
Cellulose
Starch
Otherorganiccompounds
A summary of
the chemical
processes ofphotosynthesis
http://www.flickr.com/photos/ghonet/27421952/ -
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It's not that
easy bein'
green but itis essential for
life on earth!
http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/http://www.flickr.com/photos/ghonet/27421952/