Download Introduction to Photosynthesis

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Organisms capture and store free energy for use in
biological processes
Introduction to
Photosynthesis
• Autotrophs capture free energy from physical sources in the
environment
• Photosynthesis versus chemosynthesis
• Heterotrophs capture free energy present in carbon
compounds produced by other organisms
• Metabolism of carbohydrates, lipids, and proteins
• Fermentation produces organic compounds (alcohol and lactic
acid) and occurs in the absence of oxygen
• Different energy-capturing processes use different types of
electron acceptors
• NADP+ in photosynthesis
• Oxygen in cellular respiration
Photosynthesis: light-dependent reactions + the
Calvin cycle
1.
2.
3.
4.
5.
Chlorophylls absorb free energy from light, boosting
electrons to a higher energy level in photosystems I and II
These photosystems are embedded in the internal
membranes of chloroplasts (thylakoids) and are connected
by the transfer of higher free energy electrons through an
electron transport chain (ETC)
As electrons pass through the ETC an electrochemical
gradient of hydrogen ions (protons) across the thylakoid
membrane is established
This proton gradient is linked to the synthesis of ATP from
ADP and inorganic phosphate via ATP synthase
The energy captured in the light reactions as ATP and
NADPH powers the production of carbohydrates from CO2
in the Calvin cycle, which occurs in the stroma of the
chloroplast
Take a mental journey…..
Photosynthesis
• First evolved in prokaryotic organisms
• Evidence supports that prokaryotic (bacterial)
photosynthesis was responsible for the production of
an oxygenated atmosphere
• Prokaryotic photosynthetic pathways were the
foundation of eukaryotic photosynthesis
Biological Hierarchy of a Plant
Using the structures involved in
photosynthesis, put in order from largest
(organism) to smallest (molecule).
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Biological Hierarchy of a Plant
• Organism – plant
• Organ system – shoot system (leaves, buds, stems,
flowers)
• Organs – leaves
• Tissues - vascular (xylem & phloem), dermal, ground
• Cells – Parenchyma cells  mesophyll cells are
photosynthetic  palisade & spongy mesophyll
• Organelles – chloroplasts (thylakoid membranes &
stroma)
• Molecules – chlorophylls & proteins embedded in
thylakoid membranes move around photons (particle of
light energy)
Use this diagram and page 461 to label the cross section of a leaf.
Define – pgs. 101-107
• Autotroph
• Pigment
• Chlorophyll a
• Chloroplast
• Thylakoid membrane
• Stroma
• Photosystems
• Photolysis
• The energy captured
photosynthesis forms the
Photosynthesis
&through
Ecology
• Photosynthesis
is the process
which
Photosynthesis:
ThebyBIG
Picture
PHOTOAUTOTROPHS convert the energy in SUNLIGHT into
the energy stored in ORGANIC COMPOUNDS.
basis of the ecological pyramid.
• The biomass that is generated by
producers supports nearly all
the living organisms on the
planet.
• Autotrophs capture energy and
“fix” it into organic compounds;
heterotrophs consume
compounds produced by other
organisms to obtain energy.
Don’t forget the 1st Law
of Thermodynamics,
which says…
What is an autotroph?
What is an organic compound?
light
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Leaves:
The
Photosynthetic
Organs
of Plants
• Leaves
perform most
of the
photosynthesis in plants.
• In eukaryotes,Structure:
photosynthesis
place inside
Chloroplast
Atakes
Review
chloroplasts inside cells (inside leaves).
• Chloroplasts have 3 membranes:
cuticle
• Outer membrane
• Inner membrane
• Thylakoid membrane,
folded to form thylakoids
• Thylakoids are
arranged in stacks
called grana.
upper epidermis
palisade mesophyll
spongy mesophyll
lower epidermis
stoma
Bundlesheath cells
Xylem &
phloem
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Light & Pigments
Granum
• Chlorophyll and other pigments involved in photosynthesis
are embedded in the thylakoid membrane.
Light & Pigments
• Visible light is made up of different colors of light
with different wavelengths.
• Pigments are molecules that absorb
light energy.
• Different pigments absorb light of
different wavelengths.
• Light has a
dual
nature.
• Accessory pigments:
 Chlorophyll B
 Carotenoids
• Light exhibits
properties of
both waves
and particles
(photons).
• Xanthophyll
• Carotenes
• Major photosynthetic pigment:
 Chlorophyll A
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Light & Pigments
What is the advantage
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Light &
Pigments
What
to having multiple
pigments?
information
does this
ABSORPTION
SPECTRUM tell
you?
Which colors of light
are absorbed well?
Not well?
What
information
does this
ACTION
SPECTRUM tell
you?
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Photosynthesis: An Overview
• The net overall equation for photosynthesis is:
6 CO2 + 6 H2O
light
C6H12O6 + 6 O2
• Photosynthesis occurs in 2 “stages”:
1. The Light Reactions (or Light-Dependent Reactions)
2. The Calvin Cycle (or Calvin-Benson Cycle or Dark Reactions
or Light-Independent Reactions)
Is photosynthesis
an ENDERGONIC
or EXERGONIC
reaction?
Photosynthesis: An Overview
• Follow the energy in photosynthesis,
Summary of Photosynthesis
Stage
Location
Starting
Ending
1st
Thylakoid
membranes
H2O
ADP
NADP+
O2
ATP
NADPH
– Lightdependent
Reactions
2nd – Calvin
cycle (Lightindependent
reactions)
Stroma
CO2
ATP
NADPH
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Light
Reactions
light
thylakoids
light
ATP
NADPH
Calvin
Cycle
stroma
Organic
compounds
(carbs)
C6H12O6
ADP
NADP+
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