Photosynthesis (Outline) 1. Overview of photosynthesis 2. Producers, consumers, and decomposers of the ecosystem (source of carbon and energy) (Autotrophs: photo-autotrophs, chemo-autotrophs, electro-autotrophs, and heterotrophs) 3. Plant structures: organ, tissue, cells, sub-cellular organelle, and molecules. 4. Visible Light and its wavelengths 5. Overview of the two pathways of photosynthesis Light reactions: Substrates, products, cellular components and their location Calvin cycle: Substrates, products, cellular components and their location 6. Specifics of the Light reactions and the Calvin Cycle -Light Reactions: The light receptors (Pigments), Photosystems, Location within chloroplast, Photophosphorylation, Flow of energy -The Calvin cycle: Energy molecules, Carbon source, RuBp, G3P 7. Comparison of chemiosmosis in respiration and photosynthesis 8. Photorespiration Role of Rubisco Challenge to plants on hot dry days Adaptations of C4 and CAM plants
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Photosynthesis (Outline)1. Overview of photosynthesis2. Producers, consumers, and decomposers of the ecosystem (source of carbon and
energy) (Autotrophs: photo-autotrophs, chemo-autotrophs, electro-autotrophs, and heterotrophs)
3. Plant structures: organ, tissue, cells, sub-cellular organelle, and molecules.4. Visible Light and its wavelengths5. Overview of the two pathways of photosynthesis
Light reactions: Substrates, products, cellular components and their location Calvin cycle: Substrates, products, cellular components and their location
6. Specifics of the Light reactions and the Calvin Cycle-Light Reactions: The light receptors (Pigments), Photosystems, Location withinchloroplast, Photophosphorylation, Flow of energy-The Calvin cycle: Energy molecules, Carbon source, RuBp, G3P
7. Comparison of chemiosmosis in respiration and photosynthesis8. Photorespiration
Role of RubiscoChallenge to plants on hot dry days Adaptations of C4 and CAM plants
Photosynthesis
Life on the surface of Earth is powered by solar energy that is converted into chemical energy in organic molecules, for use in cellular respiration
Light energy
6 CO2 + 6 H2O
Carbon dioxide Water
C6H12O6+
Glucose6 O2
Oxygen gas
Producers of the ecosystemAutotrophs
Produce their own food and sustain themselves without eating other organisms
Bacteria Algae Plants
Types of autotrophs based on energy source • Photoautotrophs solar energy• Chemoautotrophs chemical energy of inorganic substances.
Bacteria can uniquely oxidize sulfur and ammonia• Electrolithoautotrophs (newly discovered bacteria)
• electrons directly from electric currents are passed through biologic nanowires to heavy metals, not to O2, and are then used to turn CO2 into carbon skeletons
• Several bacterial species with varied mechanisms are found in more common places (mud)
Electric bacteriahttp://www.extremetech.com/extreme/186537-biologists-discover-electric-bacteria-that-eat-pure-electrons-rather-than-sugar-redefining-the-tenacity-of-life
A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
• Chloroplasts and mitochondria generate ATP by chemiosmosis, using different sources of energy
• Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP
MITOCHONDRION STRUCTURE
Intermembranespace
MembraneElectron transport
chain
Mitochondrion Chloroplast
CHLOROPLAST STRUCTURE
Thylakoid space
Stroma
ATP
Matrix
ATPsynthase
Key
H+ Diffusion
ADP + P
H+
i
Higher [H+] Lower [H+]
O2
The Calvin Cycle• Uses ATP and NADPH• CO2 enters the cycle and leaves as a 3C
sugar, glyceraldehyde-3-phosphate (G3P).
• Regenerates RuBP
The Calvin Cycle
LightNADP+
ADP+ P i
CO2H2O
Light reactions Calvin cycle
RuBP
G3PATP
Photosystem II Electron transport
chain Photosystem I
O2
Chloroplast
NADPH
3-Phosphoglycerate
Starch (storage)
Amino acids Fatty acids
Sucrose (export)
Leaf Cross Section
Leaf
Mesophyll
VeinStoma
CO2 O2
Chloroplast
• Terrestrial plants face dehydration.• The stomata close to limit loss of water.• This limits amount of CO2 while O2 production continues• A wasteful process called photorespiration• On a hot dry day photorespiration drains 50% of the carbon
that could be fixed by the Calvin Cycle.
Challenge to plants in hot and dry area
Photorespiration
Rubisco can use both O2 and CO2 as substrates and can catalyze a wasteful reaction known as photorespiration when O2is the substrate.
O2 and organic fuel are consumed without producing sugar
Photorespiration is an evolutionary relic
• In most plants (C3 plants), initial fixation of CO2, via rubisco, forms a three-carbon compound
• In C3 plants, a drop in CO2 and rise in O2 whenstomata close on hot dry days divert the Calvincycle to photorespiration
• C3 leaf anatomyLeaf Cross Section
Leaf
Mesophyll
VeinStoma
CO2 O2
Chloroplast
Some plants have special adaptationsto save water and limit “Photorespiration” by separating CO2 fixation from sugar formation
1. C4 plants (spatial separation) corn,sugar cane
2. CAM plants (temporal separation) succulents (cacti and pineapple)
Photosyntheticcells of C4 plantleaf
Mesophyll cell
Bundle-sheath cell
Vein(vascular tissue)
C4 leaf anatomy
StomaBundle-sheath cell
Pyruvate (3 C) CO2
Sugar
Vascular tissue
CALVIN CYCLE
Oxaloacetate (4 CP)EP (3 C)ADPATPMalate (4 C)
CO2PEP carboxylaseMesophyllcell
C4 leaf anatomy and the C4 pathway
• C4 plants minimize the cost of photorespiration by incorporating CO2 into four-carbon compounds in mesophyll cells
• These four-carbon compounds are exported tobundle-sheath cells, where they release CO2 for use in the Calvin cycle
C4 Plants
Sugarcane
C4 plant
CALVIN CYCLE
3-C sugar
CO2
4-C compound
CO2Mesophyll cell
Bundle-sheath cell
• CAM plants open their stomata at night, incorporating CO2 into organic acids.
Stomata close during the day, and CO2 is released from organic acids are used in the Calvin cycle