Download Photosynthesis and Respiration

Photosynthesis
& Respiration
Photosynthesis Pathway
http://www.ualr.edu/~botany/photosynthesis.gif
Leaves & Leaf Structure
• Raw Materials of
Photosynthesis
Enter Cells of Leaf
• Visible Light only Small Portion of
Electromagnetic Spectrum
• Plants Use Light Energy mostly in Visible
Light Range for PS
• Red & Blue Wavelengths most Important for
PS
– Water & Carbon
Dioxide
• Products of
Photosynthesis
Leave Leaf
– Captured by Chloroplasts & Used to Initiate PS
Reactions
– Sugar & Oxygen
http://techalive.mtu.edu/meec/module19/Page4.htm
Photosynthetic Reactions
•
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Nature of Light
Photos (light)
Synthesis (to put together)
Light Energy to Chemical Energy
Life on Earth Depends on this Process
Supplies Our Oxygen
Overall Equation
http://www.coloradocollege.edu/dept/ev/courses/EV112/ImagesII/image003.gif
• Overall Equation
Deceptively Simple
• Complex Set of Physical
& Chemical Reactions
must Occur in
Coordinated Manner for
Synthesis of
Carbohydrates
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Chlorophyll
Accessory Pigments
• Chlorophyll Is a Complex
Molecule
• All Photosynthetic Organisms
Have Chlorophyll a
• Accessory Pigments Absorb
Energy that Chlorophyll a Does
not Absorb
• Pigment Is any Substance
that Absorbs Light
• Color of the Pigment
Comes from Wavelengths
of Light Reflected
• Chlorophyll
– Green Pigment Common to
all Photosynthetic Cells
– Absorbs all Wavelengths of
Visible Light Except Green
– Chlorophyll b
– Xanthophylls
– Carotenoids (Beta-Carotene)
http://www.nyu.edu/pages/mathmol/library/photo/
• If a Pigment Absorbs
Light Energy, 1 of 3
Things Will Occur
• Energy Is Dissipated
as Heat
• The Energy may Be
Emitted Immediately
as a Longer
Wavelength
• Energy may Trigger a Chemical Reaction, as
in PS
Chloroplasts
• Organelles in a
Plant Cell
• Location of
Photosynthesis
– Chlorophyll Triggers a Chemical Reaction when
It Is Associated with Proteins Embedded in a
Membrane (as in a Chloroplast)
http://www.ualr.edu/~botany/chlorophyll.jpg
• Chloroplast Has 3
Membrane Systems
http://www.lclark.edu/~seavey/Bio100_03/Lecture%20notes/lecture_Feb_11.h
tml
Photosynthesis Stages
– Form 3
Compartments
• 2-Stage Process
1. Outer Membrane
2. Inner Membrane
3. Intertwined &
Stacked Network
of more Membranes
– Light Reactions
• Require Light to Occur
• Involves Actual Harnessing of Light Energy
• Occur in\on Grana
– Dark Reactions
– Thylakoids: Wafer-Like Structures
– Granum/Grana: Stack of Thylakoids
– Stroma: Areas between Grana
• Photosynthesis Takes Place in the Structures
http://www.wellesley.edu/Biology/Courses/Plant/chloro.html
• Do not Need Light to Occur
• Involve Creation of Carbohydrates
• Uses Products of Light Reaction to Form C-C Bonds
of Carbohydrates
• Occur in Stroma
http://www.daviddarling.info/images/chloroplast.jpg
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2. Photophosphorylation
Light
Reactions
1. Electron Transfer
– Light Strikes Magnesium (Mg) Atom in Center of
Chlorophyll Molecule
– Light’s Energy Excites Mg Electron & It Leaves
Orbit from Mg Atom
– Electron Can Be Converted to Useful Chemical
Energy
– Excited Electron (plus
Additional Light Energy)
Provides Energy
– Phosphate Group Can
Be Added to Compound
Called Adenosine
Diphosphate (ADP)
– Yields Adenosine
Triphosphate (ATP)
– ATP Is Important Stored
Energy Molecule
http://bioweb.wku.edu/courses/Biol120/images/Photophosphryl.htm
http://www.sirinet.net/~jgjohnso/lightreactionproject.html
ATP
• ATP = Adenosine---(PO4-)---(PO4-)---(PO42-)
• String of 3 Phosphate Groups Is Held
Together by Covalent Bonds
• When Bond that Attaches 1 of the
Phosphate Groups onto ATP Is Broken, It
Becomes ADP
• Adenosine---(PO4-)---(PO42) + (PO42) + Energy
3. Photolysis (Hill Reaction)
– 2 Water Molecules Are Split into H & O
– H Is Attached to a Molecule Called Nicotinamide
Adenine Dinucleotide Phosphate (NADP)
– It Becomes NADPH2
– O Is Given off as O Gas
– 2 H20 + NADP + light  NADPH2 + O2
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookatp.html
• ATP & NADPH2 Are Common Energy-Carrying
Molecules in all Plant & Animal Cells
• ATP Gives up the Phosphate Group when It Is
Involved in a Chemical Reaction
• Same Thing Happens when NADPH2 Gives off
the Hydrogen Atoms as Part of a Reaction
• ATP & NADPH2 Are Renewable or Recyclable
Energy Sources
http://plantphys.info/plant_physiology/lightrxn.shtml
Dark Reactions
• ‘Calvin Cycle’
• ‘Carbon Reactions
Pathway’
• Do not Require
Light Energy to
Occur
– Do Require Energy
Captured by Light
Reactions
http://www.ualr.edu/~botany/calvincycle.gif
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• Occur at same Time as Light Reactions
• Cease Soon if Light Energy Is not Available
to Make Light Reaction Products
– Exception: some Xerophytes
• 2 Main Steps
– Carbon Dioxide Fixation
– Sugar Formation
• Occur in the Stroma of the Chloroplasts
• C4 Plants
– CO2 Fixation for Many Plants of
Dry or Tropical Origins
– Plants Use a Different Enzyme
Called PEP Carboxylase for CO2
Fixation
• Much Higher Affinity for CO 2 than Rubisco
• At Low CO2 Pressures, Rubisco Doesn’t Distinguish
Well between O2 & CO2 so Stomata usually Have to Be
Wide Open for PS to Occur
Calvin Cycle/Dark Reactions
1. Carbon Dioxide Fixation
• CO2 Incorporated into a 3-Carbon or 4Carbon Chain
• C3 Plants
– Most Plants Use Enzyme Called RuBP Carboxylase
(RuBisCo) to Carry out CO2 Fixation
– Occurs in Mesophyll Cells
– Creates a 3-Carbon Product Ready for Sugar
Formation
– Called C3 Plants because 1st Stable Carbon Chain
Made from CO2 Has 3 Carbons
• PEP Carboxylase’s Transport of CO2 to Bundle
Sheath Allows C4 Plants to Build Up Higher
Concentration of CO2 than Normally Found in
the Mesophyll Cells of C3 or C4 Plants
• Where Does 1st Part of Calvin Cycle Occur?
– Bundle Sheath Cells of C4 Plants
– Mesophyll Cells of C3 Plants
– Creates a 4-Carbon Product
– 4-Carbon Chain Transported into Bundle Sheath
Cells where CO2 Is Released & then Immediately
Fixed by Rubisco as Part of C3 Cycle
– Same Fixation with Rubisco as in C3 Plants but in
Bundle Sheath Cells, not Mesophyll Cells
http://www2.mcdaniel.edu/Biology/botf99/photodark/c4.htm
PEP Carboxylase vs. Rubisco
• PEP Carboxylase Works Well at Warm Temps
but Not Optimum at Cool Temps
• Why C4 Grasses Called ‘Warm Season’
Grasses & Why They Don’t Compete Well
with C3 Grasses at Cooler Temps
• C4 Grasses Have an Edge in Dry Warm Sites or
Open Sunny Sites
C3 & C4 Plants Differ in Water Use
• C4 Plants Can Produce 3 Times as Much Dry
Matter/Unit of Water as C3 Plants
– Can Keep Leaf Stomata Closed during Mid-Day &
Extract every Last CO2 Molecule in the Leaf
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• Stomata Closed during the Day
CAM Plants
– CO2 Is Released from the 4-Carbon Product
– Normal Light & Dark Reactions occur without
Stomata Opening
– Allows the
Plants to
Conserve
Water during
the Day
• Crassulacean Acid
Metabolism
• Another Type of C4 PS
Carried out only by
Xerophytes
• Stomata Open at Night
• When Water Is
Adequate,
these Plants
usually Carry
out C3 PS
– Plants Fix CO2 into a 4Carbon Product
– 4-Carbon Product
Stored Overnight in
Vacuole
http://www.ualr.edu/~botany/c4andcam.jpg
Calvin Cycle/Dark Reactions
2. Sugar Formation
Photosynthesis Logistics
•
• Carbon Chain Formed in
Step 1 Is Converted to
Glucose
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Carbon Dioxide Source
– CO2 Enters Leaves through Stomata by Diffusion
– Dissolves in Water to Become HCO3-
– C6H12O6
• Water Source
– From Roots Upward
• Oxygen Output
– Diffuse out through Stomata
– Used in Respiration or other Reactions
– Plants Are Net Oxygen Producer
http://www.ualr.edu/~botany/starch_sucrose.jpg
http://www.westga.edu/~geosci/wgmc/plants_pics.htm
• 6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
Factors Affecting Photosynthesis
• Water Output
– Fate of Water Produced by PS
• Used in other Reactions or Plant Transport
• Water Vapor out of Stomata
• Sugar/Glucose Output
• Converted to Sucrose
– Main Plant Sugar, Water Soluble
• Converted to Starch or other Storage Carbs
– Water-Soluble
– Common Form of Stored Carbs
• Converted to Cellulose or other Structural
Carbohydrate
– Not Water Soluble
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Availability of CO2
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CO2 Supply Diminishes if Stomata Close
Air Movement Replaces CO2 Taken up by Plants
Normal [CO2] Is ~400 ppm (0.04%)
Increase Can Increase Photosynthetic Rates
Occurring due to Environmental Changes
• Availability of Water
– Water not a Limiting Factor for PS
– Water Stress Can Causes Stomata to Close
plantbiology.stanford.edu/ imagecollection.html
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•
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Temperature
• Light Quality (Color)
– Increasing Temp will Increase Rate of PS, within Normal
Ranges
– Below Normal Ranges, PS Slows or Stops
– Chlorophyll Absorbs Red & Blue
Wavelengths
– Called Photosynthetically Active Radiation (PAR)
• Cytoplasm (Liquid inside Cells) Slows Moving
– Above Normal Ranges
• Light Duration (Photoperiod)
• Light Intensity (Brightness)
• Proteins may Change Shape
• Membranes may Become too Leaky
– Light Saturation Point
• PS Reaches Its Maximum Point
• Increasing Light Intensity no Longer Increases PS Rate
• Leaf Chlorophyll Content
– About 20 to 100 Chloroplasts/Leaf Mesophyll Cell
http://www.firstrays.com/plants_and_light.htm
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
•
• C3 Plants Have Optimum PS from about 5575°F
– Can Carry out PS from 32-95°F
– C3 Grasses Called Cool-Season
• C4 Plants Optimum PS 75-95°F
– Can Carry out PS from 55-105°F
– PEP Enzyme Deactivates below 55°F
– C4 Grasses Called Warm-Season
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Carbohydrate Translocation
– Sugars not Moved out of Mesophyll
Cells can Inhibit PS
– As more Sugars Are Needed, It
can Increase the Rate of PS
• ‘Source-Sink Relationship’
• Leaf Age
– Young, Mature Leaves Have Greatest Rate & Output of
PS
– Young, Immature Leaves Have High Rate of PS but Use
more of what They Produce for Their Own Growth
– Mature Leaves have Slower PS Rates
– Defoliation of Young or Young + Mature Leaves of a
Plant Drains the Plant
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/pressflo.jpg
Respiration
• Free Energy Is Released
& Incorporated into Form
that Can Be Readily
Used for Maintenance
& Development
• Net Reaction Appears
Reverse of PS
• C6H12O6 + 6O2 + 40 ADP + 40 Phosphates →
6 CO2 + 6 H2O + 40 ATP
• Turns Carbs into Usable Chemical Energy
(ATP) for many Other Plant Reactions
including PS
• All Living Plant & Animal Cells Carry Out
Respiration
• When Does Respiration Occur?
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–
–
–
Same Time as PS
During Night
Developing & Ripening Fruit
Dormant Seeds
http://www.biol.lu.se/cellorgbiol/dehydrogenase/pop_sv.html
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Mitochondria
Aerobic Respiration
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•
•
•
• Occurs in Mitochondria
• Membrane-Enclosed
Organelles Distributed
through Cytosol of Most
Eukaryotic Cells
• Convert Potential Energy
of Food Molecules into
ATP
Requires Oxygen
Main Type of Respiration in most Situations
Breakdown of Glucose back to CO2 & Water
Not All Energy in Glucose Is Converted to
ATP Formation
– Only about 40% Efficient
– Extra Energy Is Given off as Heat
http://www.kathleensworld.com/mitochondria.jpg
http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0077.JPG
2. Krebs Cycle
3 Main Steps
1. Glycolysis
– Breakdown of Glucose to a 3-Carbon
Compound Called Pyruvate
– Occurs in Cytosol
– Some ATP & NADH Are also Formed
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–
–
–
‘Tricarboxylic Acid Cycle (TCA Cycle)’
‘Citric Acid Cycle’
Occurs in Mitochondrial Matrix
Cyclic Series of Rxs Break Down
Pyruvate to CO2 & Carbon Skeletons
– Skeletons Used in other Metabolic Pathways
– Step where CO2 Is Given off by Plant
– 10 NADH Are Generated
• Storage Energy Molecules
– NADH Is Formed from NAD
– Similar Type of Energy-Storing Rx as NADP +
H2 → NADPH2
• NAD + H → NADH
http://www.med.unibs.it/~marchesi/glycpth2.gif
3. Electron Transport Chain
–
–
‘Oxidative
Phosphorylation’
Series of Proteins in
Mitochondria Helps
Transfer Electrons (e-) from NADH to Oxygen
• Releases a Lot of Energy
–
–
Occurs on Mitochondrial Inner Membrane
(Proteins Bound to Membrane)
Released Energy Is Used to Drive Reaction ADP
+ P → ATP
http://www.sp.uconn.edu/~bi107vc/images/mol/krebs_cycle.gif
Anaerobic Respiration
• ‘Fermentation’
• Low-Oxygen Environments
– Wet or Compacted Soils
– After Strong Exertion
• ATP Still Produced from Glucose but Not as
Efficiently as with Aerobic Respiration
• Many ATP Are Made
–
–
Oxygen Is Required for this Step
Water Is Produced
http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter%205/ch05.htm
http://www.jracademy.com/~vinjama/2003pics/fermentation%5B1%5D.jpg
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• C6H12O6 + O2 → 2 CH2O5 + 2 H2O + 2 ATP
• Same Rx Used to Produce Alcohol from Corn
or to Make Wine or other Consumed Alcohol
Photorespiration
Aerobic:
C6H12O6 + 6O2 + 40 ADP + 40 Phosphates → 6 CO2 + 6 H2O + 40 ATP
• Only 2 ATP Are Formed Instead of 40 from
Aerobic Respiration
– Plant Soon Runs out of Energy
– Can Suffer from Toxic Levels of Ethanol
http://www.marietta.edu/~spilatrs/biol103/photolab/photresp.html
• Respiration Driven by Light Energy
• Scientists Realized that Some Plants Have
Faster Respiration Rate in Light than in Dark
• Occurs in Chloroplasts & Other Structures in
a Photosynthetic Cell
• Rubisco can React with Oxygen to Start
Slightly Different Series of Rxs
– Result in Loss or No Net Gain of Dry Matter for
Plant
– Less ATP Is Produced
Factors Influencing
Photorespiration
• O2 : CO2 Ratio
– C4 Plants Have Little Photorespiration
• Light Intensity
– Increasing Light Intensity Will Increase
Energy for Photorespiration Process & for PS
– C3 Plants Light-Saturate at Lower Light
Intensities than C4 Plants
• Temperature
– Aerobic Respiration & Photorespiration
Increase with Temp
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
• Net Photosynthesis Rate
– C4 Plants Generally Have Net of 2 to 3 Times
that of C3 Plants
– C4 Plants often Called Efficient Plants & C3
Plants Called Non-Efficient Plants
– A Few C3 Plants Have Low Respiration & Similar
Rates as C4 Plants
– Cooler Temps Are the only Time when C3 Plants
Have Higher Net Rates than C4 Plants
Factors Affecting Respiration
• Kind of Cell or Tissue
– Young & Developing Cells (Meristematic Areas)
usually Have Higher Respiration Rates
– Developing & Ripening Fruit & Seeds, too
• Temperature Inside Plant Cell
– Can Have Net Dry Matter Loss at High Temps
where Respiration Exceeds PS
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
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• Oxygen
– Low O2 Can Reduce Aerobic Respiration
– Low O2 Can Reduce Photorespiration
• Light
– Can Enhance Rate of Photorespiration
– No Direct Effect on other Forms of Respiration
• [Glucose]
– Need Adequate # to Carry out Respiration
– Reductions can Occur
Light Compensation Point
• [CO2]
– Higher CO2 Levels Reduce Rate of Respiration
– Seldom Occurs except if O2 Levels Are Limited
• [ATP]
– Higher [ATP] Reduces Rate of Respiration
– Usually Occurs when Other Metabolic Processes
Have Slowed or Stopped
• Plant Injury
– Injury Increases Respiration
– Plant’s Growth Rate Increases in Attempt to
Recover
– Synthesizes Compounds to Fight Pests
– Some Herbicides Kill Plants by Disrupting or
Affecting Respiration
Endosymbiotic Theory
• Level of Light Intensity where Rate of
Respiration (CO2 Produced) Equals Rate of PS
(CO2 Consumed)
• Greater Light Intensity = Net Dry Matter
(Carbohydrate Accumulation)
• Lower Light Intensity = Net Dry Matter Loss
• Generally Reached for Plants Grown
Outdoors
• Maybe Not for Full Sun Plants Grown in
Shade or Houseplants Grown Indoors in
Inadequate Light
http://www.daviddarling.info/encyclopedia
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