photosynthesis lecture ppt
TRANSCRIPT
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LECTURE ONPHOTOSYNTHESIS
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By the end of this lecture you will be able to:
1. Understand that ENERGY can be transformed from one form to another.2. Know that energy exist in two forms; free energy - available for doing work
or as heat - a form unavailable for doing work.
3. Appreciate that the Sun provides most of the energy needed for life onEarth.
4. Explain why photosynthesis is so important to energy and material flow forlife on earth.
5. Know why plants tend to be green in appearance.
LEARNING OBJECTIVES
. quate t e organe e o p otosynt es s n eu aryotes w t t e c orop ast.7. Describe the organization of the chloroplast.8. Understand that photosynthesis is a two fold process composed of the
light-dependent reactions (i.e., light reactions) and the lightindependent reactions (i.e. Calvin Cycle or Dark Reactions).
9. Tell where the light reactions and the CO2 fixation reactions occur in the
chloroplast.10. Define chlorophylls giving their basic composition and structure.11. Draw the absorption spectrum of chlorophyll and compare it to the action
spectrum of photosynthesis.12. Define the Reaction Centers and Antennae and describe how it operates.13. Describe cyclic photophosphorylation of photosynthesis.
14. Describe noncyclic photophosphorylation of photosynthesis.
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Energy can be transformed fromone form to another
FREE ENERGY
(available for work)vs.
HEATnot available for work
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THE SUN: MAIN SOURCE OFENERGY FOR LIFE ON EARTH
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Almost all plants are photosynthetic autotrophs, asare 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
(a) Mosses, ferns, andflowering plants
(b) Kelp
(c) Euglena (d) Cyanobacteria
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Light Energy Harvested by Plants &Other Photosynthetic Autotrophs
6 CO2 + 6 H2O + light energy C6H12O6 + 6O2
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Food Chain
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THE FOOD WEB
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WHWHY ARY ARE PE PLANLANTS GTS GREREEN?EN?
It's not that easy bein' greenHaving to spend each day the color of the leavesWhen I think it could be nicer being red or yellow or goldOr something much more colorful like that
Kermit the Frog
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Electromagnetic Spectrum andVisible 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 AREARE PLAPLANTSNTS GREGREEN?EN?
Gamma
raysX-rays UV Infrared
Micro-
waves
Radio
waves
Visible light
Wavelength (nm)
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The feathers of male cardinals
are loaded with carotenoidpigments. These pigmentsabsorb some wavelengths of
light and reflect others.
Sunlight minus absorbedSunlight minus absorbedwavelengths or colorswavelengths or colorsequals the apparent colorequals the apparent colorof an object.of an object.
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Why are plants green?
Transmitted light
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WHYWHY AREARE PLAPLANTSNTS GREGREEN?EN?
Plant Cells
have GreenChloroplasts
The thylakoidmembrane of thechloroplast is
impregnated withphotosyntheticpigments (i.e.,chlorophylls,carotenoids).
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Chloroplastsabsorb lightenergy and Light
Reflectedlight
THE COLOR OF LIGHT SEEN IS THE
COLOR NOT ABSORBED
convert it tochemical energy
Absorbedlight
Transmittedlight
Chloroplast
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Photosynthesis is the process by which
autotrophic organisms use light energy tomake sugar and oxygen gas from carbon
AN OVERVIEW OF PHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
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Th lvin l m k
Light
Chloroplast
LightCalvinc cle
NADP++++
ADP+ P
The light reactionsconvert solarenergy to chemical
energy Produce ATP & NADPH
AN OVERVIEW OF PHOTOSYNTHESIS
sugar from carbondioxide ATP generated by the light
reactions provides the energyfor sugar synthesis
The NADPH produced by thelight reactions provides theelectrons for the reduction of
carbon dioxide to glucose
reactions
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Chloroplasts: Sites of Photosynthesis Photosynthesis
Occurs in chloroplasts, organelles in certainplants
All green plant parts have chloroplasts and carry
out p otosynt es s The leaves have the most chloroplasts
The green color comes from chlorophyll in thechloroplasts
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
Photosynthesis occurs in chloroplasts
grana, stacks of thylakoids The thylakoids contain chlorophyll
Chlorophyll is the green pigment that captures
light for photosynthesis
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The location and structure of chloroplasts
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
Thylakoid
compartmentThylakoidStroma
Granum
StromaGrana
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Chloroplasts contain several pigments
Chloroplast Pigments
Chlorophyll a Chlorophyll b
Carotenoids
Figure 7.7
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Chlorophyll a & b Chl a has a methylgroup
Chl b has a carbonylgroup
orp yr n r ngdelocalized e-
Phytol tail
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Different pigments absorb light
differently
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Excitedstate
e
Heat
Light
2
Excitation of chlorophyll
in a chloroplast
Loss of energy due to heatcauses the photons of light to be
less energetic.Less energy translates into
longer wavelength.
Energy = (Plancks constant) x
(velocity of light)/(wavelength oflight)
Transition toward the red end of
the visible spectrum.
e
Photon
Light
(fluorescence)
Chlorophyllmolecule
Groundstate
(a) Absorption of a photon
(b) fluorescence of isolated chlorophyll in solution
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Primaryelectron acceptor
Molecular Game of Hot Potato
Photon
Reactioncenter
PHOTOSYSTEM
Pigmentmolecules
of antenna
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Cyclic Photophosphorylation Process for ATP generation associated with
some Photosynthetic Bacteria
Reaction Center => 700 nm
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Two types of
photosystemscooperate in the
Water-splittingphotosystem
NADPH-producingphotosystem
ATPmill
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Primaryelectron acceptor
Primaryelectron acceptor
Noncyclic Photophosphorylation Photosystem II regains electrons by splitting
water, leaving O2 gas as a by-product
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy forsynthesis of
by chemiosmosis
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The O2 liberated by photosynthesis is made
from the oxygen in water (H+
and e-
)
Plants produce OPlants produce O22
gas by splitting Hgas by splitting H22OO
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Primaryelectronacceptor
Energyto make
Primaryelectronacceptor
Light
NADP++++
2
3
How the Light Reactions Generate ATP and NADPH
2 H++++ + 1/2
Water-splittingphotosystem
Reaction-center
chlorophyll
Light
Primaryelectronacceptor
NADPH-producingphotosystem1
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Two connected photosystems collectphotons of light and transfer the energy to
In the light reactions, electron transportIn the light reactions, electron transportchains generate ATP, NADPH, & Ochains generate ATP, NADPH, & O22
The excited electrons are passed from theprimary electron acceptor to electron
transport chains Their energy ends up in ATP and NADPH
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The electron transport chains are arranged
with the photosystems in the thylakoidmembranes and pump H+ through that
Chemiosmosis powers ATP
synthesis in the light reactions
The flow of H+ back through the membrane isharnessed by ATP synthase to make ATP
In the stroma, the H+ ions combine with NADP+
to form NADPH
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The production of ATP by chemiosmosis in
photosynthesis
Thylakoidcompartment(high H+) Light Light
Thylakoid
membrane
Stroma(low H+)
Antennamolecules
ELECTRON TRANSPORTCHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
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A Photosynthesis Road Map
Chloroplast
Light
Stack ofthylakoids ADP
+ P
NADP++++
Stroma
reactions cycle
Sugar used for
Cellular respiration
Cellulose
Starch
Other organic compounds
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Review: Photosynthesis uses lightenergy to make food molecules
Light
Chloroplast A summary of
the chemical
Photosystem IIElectrontransport
chainsPhotosystem I
CALVINCYCLE Stroma
LIGHT REACTIONS CALVIN CYCLE
Cellularrespiration
Cellulose
Starch
Otherorganiccompounds
photosynthesis
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It's not thatIt's not that
easy bein'easy bein'
is essential foris essential for
life on earth!life on earth!