Photosynthesis
and Respiration
http://www.ualr.edu/~botany/photosynthrxns.gif
Definitions
• Photosynthesis
– How a Plant Harnesses Light Energy to Make
Chemical Energy
• Respiration
– Turning Chemical Energy into Fuel for
Growth, Development and Reproduction
Photosynthesis
http://www.ualr.edu/~botany/photosynthesis.gif
Leaves and Leaf Structure
• The Raw Materials of
Photosynthesis Enter
the Cells of the Leaf
– Water and Carbon
Dioxide
• The Products of
Photosynthesis Leave
the Leaf
– Sugar and Oxygen
Nature of Light
• Visible Light Is only a
Small Portion of the
Electromagnetic
Spectrum
– p. 108, text
• Plants Use Light Energy
mostly in the Visible
Light Range for PS
Nature of Light
• When Light Hits an Object, 3 Possibilities
– Absorbed by Object
– Reflected off Object
– Transmitted through Object
• Colors We See Are actually Light
Reflected from an Object
– Something that Appears Green Is Reflecting
Green Light and either Absorbing or
Transmitting the other Wavelengths
– Plants Reflect Green, but Absorb other
Wavelengths for Use in PS
Nature of Light
• Plant Color Can Be an Indicator of
Plant Health
• Satellite Imagery (Remote Sensing)
Can Be Used to Indicate Crop
Health
• Measures some Visible Light but
also Measures Infrared
– Drought-Stressed Plants Give off more
Infrared Wavelengths
– Can Use this System to Indicate Weed
Impact and other Factors
Nature of Light
• Red and Blue
Wavelengths most
Important for PS
• Captured by
Chloroplasts and
Used to Initiate PS
Reactions
http://faculty.concord.edu/rockc/intro/sensate.htm
Photosynthetic Reactions
•
•
•
•
•
Photos (light)
Synthesis (to put together)
Light Energy to Chemical Energy
Life on Earth Depends on this Process
Supplies Our Oxygen
Photosynthetic Reactions
• Overall Equation
– C = Carbon
– O = Oxygen
– H = Hydrogen
Photosynthetic Reactions
• Overall Equation
– Carbon Dioxide Has 1 Carbon and 2 Oxygen Atoms,
Arranged O=C=O in the Molecule of Carbon Dioxide
– Water Has 2 Hydrogen and 1 Oxygen Atoms, Arranged
H=O=H in the Water Molecule
Photosynthetic Reactions
• The Overall Equation for PS Is Deceptively
Simple
• In Fact, a Complex Set of Physical and Chemical
Reactions must Occur in a Coordinated Manner
for the Synthesis of Carbohydrates
• To Produce a Sugar Molecule such as Sucrose,
Plants Require nearly 30 Distinct Proteins that
Work within a Complicated Membrane Structure
Chlorophyll and Accessory
Pigments
• A Pigment Is any Substance
that Absorbs Light
• The Color of the Pigment
Comes from the Wavelengths of
Light Reflected
• Chlorophyll, the Green Pigment
Common to all Photosynthetic
Cells, Absorbs all Wavelengths
of Visible Light Except Green,
which It Reflects to Be
Detected by Our Eyes
Chlorophyll and Accessory
Pigments
• Chlorophyll Is a Complex Molecule
– Several Modifications of Chlorophyll
Occur among Plants and other
Photosynthetic Organisms
• All Photosynthetic Organisms Have
Chlorophyll a
• Accessory Pigments Absorb Energy
that Chlorophyll a Does not Absorb
– Chlorophyll b
– Xanthophylls
– Carotenoids (Beta-Carotene)
http://www.nyu.edu/pages/mathmol/library/photo/
Chlorophyll and Accessory
Pigments
• 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 (a Phenomenon
Known as Fluorescence)
• Energy may Trigger a
Chemical Reaction, as in PS
– 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
Chloroplasts
• Organelles in a
Plant Cell
• Location of
Photosynthesis
http://www.lclark.edu/~seavey/Bio100_03/Lecture%20notes/lecture_Feb_11.h
Chloroplasts
• Inside the Chloroplast
– Intertwined and Stacked
Network of more
Membranes
– Thylakoids
• Wafer-Like Structures
– Granum/Grana
• Stack of Thylakoids
– Stroma
• Areas between Grana
• Chloroplast Has 3
Membrane Systems,
Forming 3 Compartments
http://www.wellesley.edu/Biology/Courses/Plant/chloro.html
Chloroplasts
• Photosynthesis
Takes Place inside
these Structures
http://www.wellesley.edu/Biology/Courses/Plant/chloro.html
Photosynthesis Stages
• 2-Stage Process
– Light Reactions
• Require Light to Occur
• Involves the Actual Harnessing of Light Energy
• Occur in\on the Grana
– Dark Reactions
• Do not Need Light to Occur
• Involve the Creation of the Carbohydrates
– Products of the Light Reaction Are Used to Form C-C
Covalent Bonds of Carbohydrates
– Occur in the Stroma
http://www.daviddarling.info/images/chloroplast.jpg
Light
Reactions
• Electron Transfer
– When Light Strikes Magnesium (Mg) Atom in
Center of Chlorophyll Molecule, the Light
Energy Excites a Mg Electron and It Leaves
Orbit from the Mg Atom
– The Electron Can Be Converted to Useful
Chemical Energy
http://www.sirinet.net/~jgjohnso/lightreactionproject.html
Light
Reactions
• Photophosphorylation
– The Excited Electron (plus Additional Light
Energy) eventually Provides Energy so a
Phosphate Group Can Be Added to a Compound
Called Adenosine Diphosphate (ADP), Yielding
Adenosine Triphosphate (ATP)
– ATP Is an Important Stored Energy Molecule
http://www.sirinet.net/~jgjohnso/lightreactionproject.html
ATP
• ATP = Adenosine - (PO4-) - (PO4-) - (PO42-)
• 3 Phosphate Groups Stuck off the End of an Adenosine Molecule
–
Fairly Simple Compound Containing Nitrogen
• The String of 3 Phosphate Groups Is Held Together by Covalent Bonds
–
–
–
All Macromolecules Are Held Together by Covalent Bonds
For some Reason, Phosphate Groups in a String Need a Really, Really Strong
Bond to Hold Them Together
So the Ones within the String Are Extremely Strong
• Think of the Bond Like a Rope in a Tug-of-War with 2 People Pulling on the
Rope in Opposite Directions
• If someone Comes along and Cuts the Rope the 2 People Will Go Flying
• They Go Flying off because Lots of Energy Was Being Stored in the Rope
and the Energy Was Released as the People Fell
• When the Bond that Attaches 1 of the Phosphate Groups onto ATP Is
Broken, It Becomes ADP
• Adenosine - (PO4-) - (PO42-)
+ (PO42-)
+ Energy
Light
Reactions
• Photolysis (Hill Reaction)
– The 2 Water Molecules Are Split into Hydrogen and
Oxygen
– The Hydrogen Is Attached to a Molecule Called
Nicotinamide Adenine Dinucleotide Phosphate (NADP)
• Produces NADPH2
– The Oxygen Is Given off as Oxygen Gas
– 2 H20 + NADP + light  NADPH2 + O2
http://www.sirinet.net/~jgjohnso/lightreactionproject.html
Light Reactions
• ATP and NADPH2 Are Common Energy-Carrying
Molecules in all Plant and Animal Cells
• ATP Gives up the Phosphate Group when It Is Involved in
a Chemical Reaction
– This Gives off a Lot of Energy which Helps the Needed Reaction
Occur
• Same Thing Happens when NADPH2 Gives off the
Hydrogen Atoms as Part of a Reaction
– It Provides Energy to Drive that Reaction
• ATP and NADPH2 Are Renewable or Recyclable Energy
Sources
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
Dark Reactions
• Occur at same Time
as Light Reactions
• Cease Soon if Light
Energy Is not
Available to Make
Light Reaction
Products
– Exception: some
Xerophytes
http://www.ualr.edu/~botany/thylakoidmembrane.gif
Dark Reactions
• 2 Main Steps
– Carbon Dioxide
Fixation
– Sugar Formation
• Occur in the Stroma
of the Chloroplasts
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-3/ch19_Dark-reactions.jpg
1. Carbon Dioxide Fixation
• ‘Carbon Dioxide
Assimilation’
• CO2 Is
Incorporated into
a 3-Carbon or 4Carbon Chain
– C3 Plants
– C4 Plants
http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0127.JPG
Carbon Dioxide Fixation
• C3 Plants
–
Most Plants Use an Enzyme Called RuBP
Carboxylase (RuBisCo) to Carry out the
CO2 Fixation
• Enzymes Are Natural Proteins that Help
Catalyze/Carry out Reactions
• Rubisco Is the most Abundant Enzyme on
Earth!
–
This Occurs in the Mesophyll Cells
• Palisade or Spongy
–
–
–
Creates a 3-Carbon Product Ready for
Sugar Formation
Called C3 Plants because the 1st Stable
Carbon Chain Made from CO2 Has 3
Carbons
C3 Crops
• Wheat, Soybeans, Cotton, Tobacco, Small
Grains, Legumes, Tomatoes, Potatoes,
Peppers, Cucurbits
http://www.uic.edu/classes/bios/bios100/lecturesf04am/rubisco01.jpg, http://www.palaeos.com/Eukarya/Lists/EuGlossary/Images/Rubisco.gif
• C4 Plants
– ‘Hatch-Slack Pathway’
– Process of CO2 Fixation
for many Plants of Dry
or Tropical Origins
– Plants Use a Different
Enzyme Called PEP in
the Mesophyll Cells for
CO2 Fixation
Carbon Dioxide
Fixation
• PEP Carboxylase Has a
much Higher Affinity
for CO2 than Does
Rubisco
• At Low CO2 Pressures,
Rubisco Doesn’t
Distinguish Well
between O2 and CO2 so
Stomata usually Have
to Be Wide Open for PS
to Occur
– Creates a 4-Carbon
Product
http://www.ualr.edu/~botany/c4pathway.gif
Carbon Dioxide Fixation
• C4 Plants
– This 4-Carbon Chain Is
then Transported into
Bundle Sheath Cells where
the CO2 Is Released and
then Immediately Fixed by
Rubisco as Part of the C3
Cycle
• Bundle Sheath Cells Are
Specialized Cells that
Surround the Vascular
Bundles in the Leaves
– Same Fixation with Rubisco
as in C3 Plants but Occurs
in the Bundle Sheath Cells,
not Mesophyll Cells
http://gemini.oscs.montana.edu/~mlavin/b434/graphic/Leafc4a.jpg, http://www.ualr.edu/~botany/c4pathway.gif
Carbon Dioxide Fixation
• Transport of CO2 to the Mesophyll Cells
Allows the C4 Plants to Build up a Higher
Concentration of CO2 in the Bundle
Sheath Cells than what Is Normally Found
in the Mesophyll Cells of C3 or C4 Plants
Carbon Dioxide Fixation
• 1st Part of Calvin Cycle Occurs in Bundle
Sheath Cells of C4 Plants and in Mesophyll
Cells of C3 Plants
PEP Carboxylase vs. Rubisco
• PEP Carboxylase Works Well at Warm Temperatures but
not Optimally at Cool Temps
• This Is the Reason why C4 Grasses Are Referred to as
Warm Season Grasses, and 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 as They Can Keep Leaf Stomata Closed
during Mid-Day and Extract every Last CO2 Molecule in
the Leaf
• In Contrast, C3 Grasses that Keep Stomata Closed in Dry
Sunny Sites Undergo High Amounts of Respiration
Carbon Dioxide Fixation
• Both Types of Plants Use Energy from ATP
and NADPH2 to Carry out the Reactions
• The Energy from ATP Is Given by ATP
Giving up Its 3rd Phosphorus
– ATP → ADP + P
• The Energy from NADPH2 Is Given by
NADPH2 Giving up Its Hydrogens
– NADPH2 → NADP + H2
2. Sugar Formation
• Carbon Chain Formed
in step 1 Is Converted
to Glucose
– C6H12O6
• Overall PS Reactions
and Energy Transfers
Can Be Seen in Text
http://www.ualr.edu/~botany/starch_sucrose.jpg
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Carbon Dioxide Source
– CO2 Enters Leaves
through Stomata by
Diffusion
• Passive Process
– Dissolves in Water Inside
the Plant to Become the
Bicarbonate Ion (HCO3-)
http://www.westga.edu/~geosci/wgmc/plants_pics.htm
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Water Source
– Water Enters the Plant
through the Roots
– Moves up through Plants
• Some Passive Movement
• Active Process (Requires
Chemical Energy to Occur)
during some Parts of the
Journey
http://catseye.blogs.com/catseye/2005/03/roots.html
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Oxygen Output
– Fate of Oxygen Produced by
PS
• Diffuse out through Stomata
• Be used in Respiration or other
Reactions
• Only about 40% of Oxygen
Produced Is Used by the Plant,
so Plants Are a Net Oxygen
Producer
http://home.vicnet.net.au/~grange/images/stomata.jpg
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Water Output
– Fate of Water Produced by PS
• Used in other Reactions or Plant
Transport
• Diffuses as Water Vapor out of Leaf
through Stomata
plantbiology.stanford.edu/ imagecollection.html
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Sugar/Glucose Output
–
Fate of Glucose Produced by PS
1. Converted to Sucrose
–
–
–
Main Plant Sugar Used by Plants for Growth and Reproduction
Common Table Sugar
Water Soluble and Readily Transported to Sinks
2. Converted to Starch or other Storage Carbs
–
–
–
Starch Is a Long-Chain Polymer of many Glucose Molecules
Linked Together
Water-Soluble to Be Able to Be Mobilized Later by Plants if
Needed
Common Form of Stored Carbohydrates
» Mainly Starch: White Potato and Sweet Potato Tubers,
Seed Cotyledons, Endosperm
Photosynthesis Logistics
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
•
Sugar/Glucose Output
–
Fate of Glucose Produced by PS
3. Converted to Cellulose or other Structural Carbohydrate
•
•
•
Long-Chain Polymer of many Glucose Molecules Linked
Together
Linked with Different Bond than Starch, so Cellulose Is not
Water-Soluble
Formed by Cellulose and Related Compounds
» Cell Walls
» Plant Fibers (Cotton, Hemp, Jute)
» Wood (Lignin is the main Structural Carbohydrate in
Wood)
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Availability of CO2
– CO2 Supply Diminishes if Stomates Close
– Air Movement Replaces CO2 Taken up by
Plants
– On Still Days within Crop Leaf Canopy
• CO2 Levels may Drop Below Optimum, Slowing PS
Slightly
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Availability of CO2
– Normal [CO2] Is 400 ppm (0.04%)
– Increasing [CO2] can Increase Plant
Photosynthetic Rates
– Occurring due to Environmental Changes
– Artificial Enhancement usually not Practical
in Field Production
– Has Been Used Effectively in some
Greenhouse Production
Factors Affecting
Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Availability of Water
– Water (almost always) Is not a Limiting
Factor for PS
• So Little Is actually Used (Less than 1% of Water
Absorbed) and Plants Are Made up of so much
Water
– Water Stress that Causes Stomata to Close
can Slow or Stop PS due to Lack of CO2
http://www.dentalindia.com/CO2b.jpg
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Light Quality (Color)
– Chlorophyll Absorbs
Light in Red (660 nm)
and Blue (450 nm)
Wavelengths
– These Are the
Photosynthetic
Wavelengths of Light
– Called
Photosynthetically
Active Radiation (PAR)
http://www.firstrays.com/plants_and_light.htm
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Light Duration (Photoperiod)
– Plants Need Sufficient Length of Light Period to
Produce enough Carbs for Normal Growth
– Longest Days in Northern Hemisphere Occur in June
• December in Southern Hemisphere
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Light Intensity
(Brightness)
– As Light Intensity Increases, PS
Rates Increase
• Up to a Certain Level of Intensity
– Light Saturation Point
• PS Reaches Its Maximum Point
• Increasing Light Intensity no
Longer Increases PS Rate
http://aesop.rutgers.edu/~horteng/openroof.htm
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Leaf Chlorophyll Content
– Pigment that Captures Light
Energy and Begins the
Transformation of that
Energy to Chemical Energy
– Located in Chloroplasts
• About 20 to 100
Chloroplasts/Mesophyll Cell in
Leaves
http://content.answers.com/main/content/wp/en/thumb/3/34/250px-Leaf.jpg
Factors Affecting Photosynthesis
• Leaf Chlorophyll Content
– Chlorosis is Yellowing of Leaf from Lack of
Chlorophyll
• If Chlorophyll Is Reduced, PS Will Be Reduced
• Causes of Chlorosis
– Nutrient Deficiencies
» N and Mg Are Parts of the Chlorophyll Molecule
» K Needed for Enzyme Activation in Production of
Chlorophyll
» Any other Nutrient Deficiencies that Cause Chlorosis also
Reduce PS
– Diseases
http://toptropicals.com/pics/toptropicals/articles/cultivation/chlorosis/4061.jpg
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Temperature
– Increasing Temp will Increase
Rate of PS, within Normal
Ranges
– Below Normal Ranges, PS
Slows or Stops
• Cytoplasm (Liquid inside Cells)
Slows Moving
– Cells may Freeze
– Chilling can Change Protein
and Membrane Structure
» Causes Cell Content
Leakage and Death
http://www.semena.org/agro/diseases2/environmental-stresses-e.htm
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Temperature
– Above Normal Ranges
• Proteins may Change Shape
• Membranes may Become too Leaky
– Leads to PS Stoppage and Possible
Cell Death
• C3 Plants Have Optimum PS from
about 55-75°F
– Can Carry out PS from 32-95°F
http://www.bbc.co.uk/science/hottopics/obesity/fat.shtml
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Temperature
– Above Normal Ranges
• C4 Plants Optimum PS 75-95°F
– Can Carry out PS from 55-105°F
– PEP Enzyme Deactivates below 55°F
» Hatch-Slack Pathway and Dark Reactions (Calvin Cycle) of
PS no Longer Occur
» Extra Energy from the Light Reaction actually Destroys
Chlorophyll
Why Perennial Warm-Season Grasses Tend to Bleach
out when It Turns Cold
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Temperature
– C3 Plants Are Called Cool-Season Plants
– C4 Plants Are Called Warm-Season Plants
Factors Affecting Photosynthesis
•
6CO2 + 12H2O + Light → C6H12O6 + 6O2 + 6H2O
• Carbohydrate Translocation
– Sugars not Moved out of Mesophyll Cells can Inhibit
PS
• ‘Feedback Inhibition’
– Buildup of End Product of a Metabolic Process Reduces
Metabolic Production of that Product
– As more Sugars Are Needed by the Plant, It can
Increase the Rate of PS
• ‘Source-Sink Relationship’
– Source of Sugars (PS) Is Affected by the Demand for Sugars
» Meristems, Filling Seeds, etc.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/pressflo.jpg
Factors Affecting Photosynthesis
• Leaf Age
– Young, Mature Leaves Have Greatest Rate and
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
– Must Pull from Stored Carbs in Stems and Roots to
Regenerate enough Leaves to Provide needed Carbs
• Reduces Root Growth
• Usually Results in Y Losses in Crops
CAM Photosynthesis
• Crassulacean Acid
Metabolism
• Another Type of PS
Carried out only by
Xerophytes
• At Night
– Stomata Are Open
– Plants Fix CO2 into a 4Carbon Product
– 4-Carbon Product Stored
overnight in Vacuole
http://www.ualr.edu/~botany/c4andcam.jpg
CAM Photosynthesis
• During the Day
– Stomata Are Closed
– CO2 Is Released from the 4Carbon Produce
– Normal Light and Dark
Reactions occur without
Stomata Opening
– Allows the Plants to
Conserve Water during the
Day
• When Water Is Adequate,
these Plants usually Carry
out C3 PS
http://www.ualr.edu/~botany/c4andcam.jpg
CAM Photosynthesis
• CAM Plants
– Cacti, Succulents
– Crops include Pineapple,
Tequila Agave
http://www.ualr.edu/~botany/c4andcam.jpg
Respiration
• Free Energy Is
Released and
Incorporated into a
Form (ATP) that
can Be Readily
Used for the
Maintenance and
Development of
the Plant
http://www.biol.lu.se/cellorgbiol/dehydrogenase/pop_sv.html
Respiration
• Low-Temperature Oxidation of
Carbohydrates Carried out by Enzymes
and Living Systems
• Net Reaction Appears as the Reverse of PS
– The Individual Reactions that Occur to
Achieve the Net Effect Are Entirely Different
– Reactions Occur in Different Parts of Cells
Chemical Reaction
• Net Reaction
• C6H12O6 + 6O2 + 40 ADP + 40 Phosphates → 6 CO2 + 6 H2O + 40 ATP
Respiration
• Respiration Is the Means to Turn Carbs
into Usable Chemical energy (ATP) for
many other Plant Reactions including PS
• All Living Plant and Animal Cells Carry out
Respiration
• Respiration Occurs
–
–
–
–
At same Time as PS
During the Night
In Developing and Ripening Fruit
In Dormant Seeds
Mitochondria
• Occurs in Mitochondria
of Cells
• Mitochondria are
membrane-enclosed
organelles distributed
through the cytosol of
most eukaryotic cells.
Their main function is
the conversion of the
potential energy of food
molecules into ATP
http://www.science.siu.edu/plant-biology/PLB117/JPEGs%20CD/0077.JPG
Light Compensation Point
• Level of Light Intensity where the Rate of
Respiration (CO2 Produced) Equals the Rate of
PS (CO2 Consumed)
• Greater Light Intensity should Result in Net Dry
Matter (Carbohydrate Accumulation)
• Lower Light Intensity will Result in Net Dry
Matter Loss over Time
• Light Compensation Point Is generally Reached
for Plants Grown Outdoors
• May not Be Reached for Full Sun Plants Grown
in Shade or for Houseplants Grown Indoors in
Inadequate Light
Aerobic Respiration
• Requires Oxygen
• Main Type of Respiration that Occurs in most
Situations in Plants and Animals
• Involves Complete Breakdown of Glucose back
to CO2 and Water
• Not all of the Energy in Glucose Is Converted to
ATP Formation
– Only about 40% Efficient
– Extra Energy Is Given off as Heat
• In Plants, Heat Quickly Dissipates
• For Animals, Heat Is Retained to Hold Body Temperature
http://www.kathleensworld.com/mitochondria.jpg
3 Main Respiration Steps
1. Glycolysis
• Breakdown of Glucose to a 3-Carbon Compound
Called Pyruvate
• Occurs in Cytosol
• Some ATP and NADH Are also Formed
–
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
Respiration Steps
2. Krebs Cycle
•
•
•
•
•
‘Tricarboxylic acid Cycle (TCA Cycle)’
‘Citric Acid Cycle’
Occurs in Mitochondrial Matrix
A Cyclic Series of Rxs that Completely Break down
Pyruvate to CO2 and Various Carbon Skeletons
Skeletons Are Used in other Metabolic Pathways to Make
various Compounds
–
–
–
–
–
–
–
•
•
Proteins
Lipids
Cell Wall Carbohydrates
DNA
Plant Hormones
Plant Pigments
Many other Biochemical Compounds
The Step where CO2 Is Given off by the Plant
10 NADH Are Generated
http://www.sp.uconn.edu/~bi107vc/images/mol/krebs_cycle.gif
Respiration Steps
3. Electron Transport
Chain
–
–
‘Oxidative
Phosphorylation’
Series of Proteins in
the Mitochondria Helps
Transfer Electrons (e-)
from NADH to Oxygen
•
–
Releases a Lot of Energy
Occurs on
Mitochondrial Inner
Membrane (Proteins
Bound to Membrane)
http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter%205/ch05.htm
Respiration Steps
–
Released Energy Is
Used to Drive the
Reaction ADP + P
→ ATP
• Many ATP Are Made
–
–
Oxygen Is
Required for this
Step
Water Is Produced
http://www.uccs.edu/~rmelamed/MicroFall2002/Chapter%205/ch05.htm
Anaerobic Respiration
• ‘Fermentation’
• Occurs in Low-Oxygen
Environments
– Wet or Compacted Soils for
Plants
– After Strong Exertion for Animals
• ATP Is still Produced from
Glucose but not as Efficiently
as with Aerobic Respiration
http://www.jracademy.com/~vinjama/2003pics/fermentation%5B1%5D.jpg
Anaerobic Respiration
• C6H12O6 + O2 → 2 CH2O5 + 2 H2O + 2 ATP
or
• Glucose + Oxygen → 2 Ethanol + 2 Water + 2 ATP
• Same Rx Used to Produce Alcohol from
Corn or to Make Wine or other Consumed
Alcohol
Aerobic:
C6H12O6 + 6O2 + 40 ADP + 40 Phosphates → 6 CO2 + 6 H2O + 40 ATP
Anaerobic Respiration
• Only 2 ATP Are Formed instead of 40 from
Aerobic Respiration
– Plant Soon Runs out of Energy
– Can Begin to Suffer from Toxic Levels of
Ethanol and Related Compounds
• Extended Periods of Anaerobic
Respiration will Seriously Reduced Plant
Growth and Yields
Anaerobic:
C6H12O6 + O2 → 2 CH2O5 + 2 H2O + 2 ATP
Aerobic:
C6H12O6 + 6O2 + 40 ADP + 40 Phosphates → 6 CO2 + 6 H2O + 40 ATP
Photorespiration
•
•
•
•
•
•
In the "normal" reaction, CO2 is joined
with RUBP to form 2 molecules of 3PGA
In the process called photorespiration,
O2 replaces CO2 in a non-productive,
wasteful reaction
It is believed that photorespiration in
plants has increased over geologic time
and is the result of increasing levels of
O2 in the atmosphere--the byproduct of
photosynthetic organisms themselves
The appearance of C4-type plants
appears to be an evolutionary
mechanism by which photorespiration is
suppressed
It has long been the dream of biologists
to increase the production of certain
crop plants, such as wheat, that carry on
C3 PS by genetically re-engineer them to
perform C4 PS
It seems unlikely that this goal will be
accomplished in the near future due to
the complex anatomical and metabolic
differences that exist between C3- and
C4-type plants
http://www.marietta.edu/~spilatrs/biol103/photolab/photresp.html
Photorespiration
• Respiration Driven by Light Energy
• Discovered when Scientists Realized that some
Plants Have Faster Respiration Rate in Light
than in Dark
• Occurs in Chloroplasts and other Structures in a
Photosynthetic Cell
• Rubisco can React with Oxygen to Start a
slightly Different Series of Rxs
– Result in a Loss or no Net Gain of Dry Matter for the
Plant
– Less ATP Is Produced from the Photorespiration
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
Factors Influencing
Photorespiration
• O2 : CO2 Ratio
• If Cells Have Low O2 but Higher CO2,
Normal PS Calvin Cycle Dominates
• C4 Plants Have Little Photorespiration
because They Carry the CO2 to the bundle
Sheath Cells and can Build up High [CO2]
– Calvin Cycle Rxs always Favored over
Photorespiration
• If Cells Have Higher O2 and Lower CO2,
Photorespiration Dominates
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
Factors Influencing
Photorespiration
• Light Intensity
– Increasing Light Intensity will Increase Energy
for the Photorespiration Process and for PS
– C3 Plants Light-Saturate at Lower Light
Intensities than C4 Plants
• Reach Their ‘Break-Even Point’ at much Lower
Light Levels due to Increasing Photorespiration
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
Factors Influencing
Photorespiration
• Temperature
– Aerobic
Respiration and
Photorespiration
Increase with
Temp
– Plants Have
Optimum,
Minimum and
Maximum Temp
Ranges
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
Factors Influencing
Photorespiration
• Net Photosynthesis or Net Assimilation
Rate
– C4 Plants generally Have Net Assimilation
Rates about 2 to 3 Times that of C3 Plants
– C4 Plants Are often Called Efficient Plants
and C3 Plants Called Non-Efficient Plants
– A Few C3 Plants Have Low Respiration and
Similar Assimilation Rates as C4 Plants
• Sunflower
• Peanut
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
Factors Influencing
Photorespiration
• Net Photosynthesis or Net Assimilation
Rate
– Cooler Temps Are the only Time when C3
Plants Have Higher Net Assimilation Rates
than C4 Plants
• PEP Carboxylase Needed to Incorporate CO2 into
the 4-Carbon Structure no Longer Functions
• C4 PS Rates Drop Dramatically or Stop
http://www.botany.hawaii.edu/faculty/webb/BOT311/BOT311-00/PSyn/Image81.gif
C3 and C4 Plants Differ in Water Use
• C4 Plants Can Produce 3 Times as much
Dry Matter per Unit of Water as C3 Plants
Factors Affecting Respiration
• Kind of Cell or Tissue
– Young and Developing Cells (Meristematic
Areas) usually Have Higher Respiration Rates
– Developing and Ripening Fruit and Seeds, too
– Older Cells and Structural Cells Respire at
Lower Rates
Factors Affecting Respiration
• Temperature
– Respiration generally Has Higher Optimum
and Maximum Temps than PS Rxs
– Can Have Net Dry Matter Loss at High Temps
where Respiration Exceeds PS
– Temp Refers to Temp Inside Plant or Animal
Cell, not Air Temp
• Using Irrigation to Help Cool the Plant Can Keep
the Plant in Net Gain Range
Factors Affecting Respiration
• Oxygen
– Low O2 Can Reduce Aerobic Respiration and
Increase Anaerobic Respiration
– Low O2 Can Reduce Photorespiration
Factors Affecting Respiration
• Light
– Can Enhance Rate of Photorespiration
– Does not Directly Affect other Forms of
Respiration
Factors Affecting Respiration
• [Glucose]
– Adequate Glucose Needed to Carry out
Respiration
– Reductions can Occur
• Reduced PS
• Reduced Flow of Carbohydrates in Plant
– Insect Feeding
– Phloem Blockages
Factors Affecting Respiration
• [CO2]
– Higher CO2 Levels Reduce Rate of Respiration
• Feedback Inhibition
– Seldom Occurs except when O2 Levels Are
Limited
• Flooded, Compacted Soils
Factors Affecting Respiration
• [ATP]
– Higher [ATP] Reduces Rate of Respiration
• Feedback Inhibition
– Usually Occurs when other Metabolic
Processes Have Slowed or Stopped
Factors Affecting Respiration
• Plant Injury
– Injury will Increase Respiration
– Plant’s Growth Rate Increases in Attempt to Recover
• Mechanical Damage
• Hail
• Mowing, Grazing, Cultivation, Wind
– Plant Synthesizes Compounds to Fight Pests
• Insect Feeding
• Diseases
– Some Herbicides Kill Plants by Disrupting or Affecting
Respiration
• Generally an Indirect Effect
• Herbicide Disrupts Enzyme Activity or some other Metabolic
Process that will Affect Respiration
Plant Mitochondria and Chloroplasts
May Have Evolved from Bacteria
Many of the features of the
mitochondrial genetic system
resemble those found in
prokaryotes like bacteria. This has
strengthened the theory that
mitochondria are the evolutionary
descendants of a prokaryote that
established an endosymbiotic
relationship with the ancestors of
eukaryotic cells early in the
history of life on earth. However,
many of the genes needed for
mitochondrial function have since
moved to the nuclear genome.