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
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 6 CO 2 + 6 H 2 O Light energy C 6 H 12 O 6 + 6 O 2 Carbon dioxide Water Glucose Oxygen gas
Producers of the ecosystem Autotrophs Produce their own food and sustain themselves without eating other organisms Bacteria Algae Plants
Types of autotrophs based on energy source Photoautot rophs 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 O 2, and are then used to turn CO 2 into carbon skeletons Several bacterial species with varied mechanisms are found in more common places (mud)
Geothermal Vents https://www.youtube.com/watch?v=d69hgvcswga Electric bacteria http://www.extremetech.com/extreme/186537-biologists-discover-electricbacteria-that-eat-pure-electrons-rather-than-sugar-redefining-thetenacity-of-life https://www.newscientist.com/article/dn25894-meet-the-electric-lifeforms-that-live-on-pure-energy/
Het erot rophs consumers and decomposers of the biosphere. completely dependent on autotrophs
In plants, photosynthesis takes place in green leaves Mesophyll Stoma Leaf Cross Section Mesophyll Cell Leaf Mesophyll Chloroplast LM 2,600 Vein CO 2 O 2 Stoma TEM 9,750 Grana Stroma Chloroplast Stroma Granum ThylakoidThylakoid space Outer membrane Inner membrane Intermembrane space
Necessary components for Photosynthesis 1.Light 2.Chloroplast Thylakoids (stacked as grana) The light Reactions Stroma The Calvin Cycle Chloroplast TEM 9,750 Stroma Outer membrane Inner membrane Grana Stroma Granum Thylakoid Thylakoid space Intermembrane space
Light as a source of energy - Solar radiation received by Earth. - Visible light consists of photons of different wavelengths making up the colors of the rainbow. Increasing energy 10 5 nm 10 3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m Gamma rays X-rays UV Infrared Microwaves Radio waves Visible light http://science.hq.nasa. gov/kids/imagers/ems/ index.html 380 400 500 600 700 750 Wavelength (nm) 650 nm
An Overview of Photosynthesis H 2 O Chloroplast CO 2 Light LIGHT REACTIONS (in thylakoids) NADP + ADP + Pi ATP CALVIN CYCLE (in stroma) NADPH O 2 Sugar
The Light reactions - Converts light energy to chemical energy (ATP & NADPH) - Produces O 2 from breakdown of water The Calvin cycle - uses ATP & NADPH from light reaction to assemble sugar molecules from CO 2
Chloroplasts split water into hydrogen and oxygen, incorporating the electrons of hydrogen into sugar molecules during the light reaction
Specific details of the Light reactions: The Light Receptors Photosynthetic Pigments Different pigments absorb different wavelengths Wavelengths that are not absorbed are reflected or transmitted Pigments are present within photosystems
Light Reflected light Chloroplast Absorbed light Granum
Light-capturing Pigments: Chlorophyll CH 3 in chlorophyll a CHO in chlorophyll b Porphyrin ring: light-absorbing head of molecule; note magnesium atom at center In chlorophyll an electron from magnesium in the porphyrin ring that is excited. Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
Photosynthetic Pigments I. Chlorophyll a participates directly in the light reactions II. Accessory photosynthetic pigments.
II. Accessory Pigments 1. Chlorophyll b different absorption spectrum funnels the energy from these wavelengths to chlorophyll a. 2. Carotenoids funnel the energy from other wavelengths to chlorophyll a participate in photoprotection against excessive light. Chemistry of autumn leaf color http://chemistry.about.com/library/weekly/aa082602a.htm
Leaf Cross Section Leaf Mesophyll Light H 2 O CO 2 Vein CO 2 O 2 Chloroplast Stoma LIGHT REACTIONS NADP + ADP + P i ATP NADPH CALVIN CYCLE Chloroplast O 2 [CH 2 O] (sugar)
Chloroplast Components Light reactions: - Structures: Thylakoid membrane - Photosystems II & I - Photosynthetic pigments - Electron acceptor - Electron transport chain - ATP Synthase - Electron transport chain - NADP + Reductase - Energy and chemical factors: light, Water, ADP +P i, NADP + http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter10/animations.html#
Light-capturing Pigments: Chlorophyll CH 3 in chlorophyll a CHO in chlorophyll b Porphyrin ring: light-absorbing head of molecule; note magnesium atom at center In chlorophyll, an electron from magnesium in the porphyrin ring that is excited. Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown
Thylakoid Photon Photosystem STROMA Light-harvesting complexes Reaction center Primary electron acceptor Photosystem consists of a reaction center surrounded by light-harvesting complexes Thylakoid membrane Transfer of energy e Special chlorophyll a molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Two types of photosystems that work together to use light energy to generate ATP and NADPH. Photosystem II Photosystem I
Splitting of water http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter10/animations.html# ATP e e e NADPH e e e Mill makes ATP e Photosystem II Photosystem I
Light H 2 O CO 2 NADP + ADP LIGHT CALVIN REACTIONS CYCLE ATP NADPH STROMA (Low H + concentration) Light O 2 Photosystem II C ytochrome [CH 2 O] (sugar) Photosystem I complex Light NADP + 2 H + reductase Fd NADP + + 2H + Pq Pc NADPH+ H + H 2 O THYLAKOID SPACE (High H + concentration) 1/2O 2 +2 H + 2 H + To Calvin cycle STROMA (Low H + concentration) Thylakoid membrane ATP synthase ADP + P i H + ATP
Electron Flow during the light reaction Light H 2 O CO 2 NADP + ADP LIGHT REACTIONS ATP NADPH CALVIN CYCLE O 2 [CH 2 O] (sugar) Energy of electrons Light 2 H + + 1 /2 O 2 H 2 O e e Primary acceptor e P680 Pq Cytochrome complex Pc Primary acceptor e P700 Fd e e NADP + reductase Light NADP + + 2 H + NADPH + H + ATP Photosystem II (PS II) Photosystem I (PS I)
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 Chloroplast MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Intermembrane space H + Diffusion Thylakoid space Membrane Electron transport chain Key Higher [H + ] Lower [H + ] Matrix ATP synthase ADP + P i H + ATP Stroma
O2
The Calvin Cycle Uses ATP and NADPH CO 2 enters the cycle and leaves as a 3C sugar, glyceraldehyde-3-phosphate (G3P). Regenerates RuBP
The Calvin Cycle
Light reactions H 2 O Calvin cycle CO 2 Light NADP + ADP + P i Photosystem II Electron transport chain Photosystem I RuBP 3-Phosphoglycerate ATP NADPH G3P Starch (storage) Chloroplast Amino acids Fatty acids O 2 Sucrose (export)
Challenge to plants in hot and dry area Terrestrial plants face dehydration. The stomata close to limit loss of water. This limits amount of CO 2 while O 2 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. Leaf Leaf Cross Section Mesophyll Vein CO 2 O 2 Chloroplast Stoma
Photorespiration Rubisco can use both O 2 and CO 2 as substrates and can catalyze a wasteful reaction known as photorespiration when O 2 is the substrate. O 2 and organic fuel are consumed without producing sugar Photorespiration is an evolutionary relic
In most plants (C 3 plants), initial fixation of CO 2, via rubisco, forms a three-carbon compound In C 3 plants, a drop in CO 2 and rise in O 2 when stomata close on hot dry days divert the Calvin cycle to photorespiration C3 leaf anatomy Leaf Cross Section Leaf Mesophyll Vein CO 2 O 2 Chloroplast Stoma
Some plants have special adaptations to save water and limit Photorespiration by separating CO2 fixation from sugar formation 1. C 4 plants (spatial separation) corn, sugar cane 2. CAM plants (temporal separation) succulents (cacti and pineapple)
C 4 leaf anatomy and the C 4 pathway Photosynthetic cells of C 4 plant leaf Mesophyll cell Bundlesheath cell Vein (vascular tissue) C 4 leaf anatomy Mesophyll cell PEP carboxylase Oxaloacetate (4 CP)EP (3 C) ADP Malate (4 C) ATP CO 2 Stoma Bundlesheath cell CO 2 Pyruvate (3 C) CALVIN CYCLE Sugar Vascular tissue
C4 Plants C4 plants minimize the cost of photorespiration by incorporating CO 2 into four-carbon compounds in mesophyll cells These four-carbon compounds are exported to bundle-sheath cells, where they release CO 2 for use in the Calvin cycle Sugarcane Mesophyll cell Bundle-sheath cell 4-C compound CO 2 CALVIN CYCLE 3-C sugar C 4 plant CO 2
CAM Plants CAM plants open their stomata at night, incorporating CO 2 into organic acids. Stomata close during the day, and CO 2 is released from organic acids are used in the Calvin cycle CO 2 CALVIN CYCLE CO 2 4-C compound Night 3-C sugar CAM plant Day Pineapple