Photosynthesis
Sunlight and Survival Plants are photoautotrophs; they use sunlight and CO2 to produce sugar in the process of photosynthesis
Energy From The Sun Many kinds of energy Wavelengths of visible light
Visible Light Wavelengths humans perceive as different colors Violet (380 nm) to red (750 nm) Longer wavelengths, lower energy
Visible Light 400 500 600 700 Wavelengths of visible light (in nanometers)
Pigments Visible color is from wavelengths not absorbed (they reflect the color we see) Pigments capture light energy from absorbed wavelengths Light energy destabilizes bonds and boosts electrons to higher energy levels
Variety of Pigments Chlorophylls ; green, yellow CH 3 Carotenoids; red, orange, yellow Xanthophylls; yellow, brown, purple, blue Anthocyanins, red, purple, blue Phycobilins; red or blue-green chlorophyll a
Fig. 5-2, p.74
Light Receptors Pigments capture light energy photon Light-Harvesting Complex
Photosynthesis Equation 12H 2 O + 6CO 2 water carbon dioxide LIGHT ENERGY 6O 2 + C 6 H 12 O 6 + 6H 2 O oxygen glucose water
The Cell s Energy Currency ATP couples energy inputs and outputs ATP/ADP cycle regenerates ATP ATP energy input ADP + P i energy output
ATP nucleotide base (adenine) Main energy carrier in cells sugar (ribose) 3 phosphate groups Can give up phosphate group to another molecule Phosphorylation energizes molecules to react
base ATP three phosphate groups cellular work reactions that release energy ATP sugar reactions that require energy (e.g., synthesis, breakdown, or rearrangement of substances; contraction of muscle cells; active transport across a cell membrane) ADP + Pi Fig. 4-2, p.59
Two Steps in Photosynthesis Light-dependent reactions Light-independent reactions
Two Steps in Photosynthesis sunlight H 2 O O 2 CO 2 Both stages of photosynthesis occur inside the chloroplast lightdependent reactions NADPH, ATP NADP +, ADP sugars lightindependent reactions Fig. 5-4d, p.75
a A look inside the leaf b One of the photosynthetic cells inside leaf leaf s upper epidermis photosynthetic cell in leaf leaf vein leaf s lower epidermis Leaf Structure
Chloroplast two outer membranes thylakoid membrane system Organelle of photosynthesis in plants and algae stroma thylakoid compartment
Light-Dependent Reactions Cyclic pathway ATP forms Requires one type of photosystem Noncyclic pathway ATP and NADPH form Water is split and oxygen released Requires two types of photosystems
Chloroplast two outer membranes thylakoid membrane system Organelle of photosynthesis in plants and algae stroma thylakoid compartment
Thylakoid Membrane Section stroma thylakoid membrane thylakoid compartment ATP SYNTHASE PHOTOSYSTEM II reaction center PHOTOSYSTEM I reaction center electron acceptor first electron transfer chain electron acceptor second electron transfer chain
Role of Electron Transfer Chains Adjacent to photosystems Acceptor molecule accepts electrons from reaction center As electrons pass along chain, energy released drives synthesis of ATP
Cyclic Electron Flow Electrons are donated by chlorophyll a in photosystem I to an acceptor molecule flow through electron transfer chain and back to photosystem Electron flow drives ATP formation No NADPH is formed
energy The Cyclic Pathway e Occurs in some organisms when ratio of NADPH & H to NADP is high (i.e. plenty of NADPH, just need more ATP) b light Photosystem I
Noncyclic Electron Flow Two-step pathway for light absorption and electron excitation Uses type I and type II photosystems Produces ATP and NADPH Involves photolysis (splitting of water) and releases oxygen as a byproduct
energy The Noncyclic Pathway e NADP + e light light Photosystem I a H 2 O 1/2 O 2 + 2H + Photosystem II Fig. 5-6a, p.76
ATP Formation in the Noncyclic Pathway Photolysis and electron transfer chains create electrical and H + concentration gradients across thylakoid membrane H + flows down gradients into stroma through ATP synthases Flow of ions drives formation of ATP from ADP and phosphate
Light- Harvesting Complex Photosystem II sunlight Photosystem I H + e e e e e e NADPH H 2 O e O 2 H + H + H + H+H+ H + H + H + H + H + H + NADP + + H + thylakoid compartment thylakoid membrane cross-section through a diskshaped fold in the thylakoid membrane ADP + P i H + ATP stroma Fig. 5-7, p.77
Light-Independent Reactions Synthesis part of photosynthesis Can proceed in the dark using energy stored in light reactions Take place in stroma Calvin-Benson cycle
Calvin-Benson Cycle Reactants Carbon dioxide ATP NADPH Products Glucose ADP NADP + Reaction pathway is cyclic RuBP (ribulose bisphosphate) is regenerated
Calvin-Benson Cycle REACTIONS PROCEED IN CHLOROPLAST S STROMA 6CO 2 6 RuBP 12 PGA ATP ATP Calvin-Benson cycle NADPH 12 PGAL 1 glucose Fig. 5-8, p.78
The C3 Pathway In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA Because the first intermediate has three carbons, the pathway is called the C3 pathway
Leaves of a C3 Plant Basswood, a typical C3 plant upper epidermis palisade mesophyll spongy mesophyll lower epidermis stoma vein air space
Photorespiration in C3 Plants On hot, dry days stomata close Inside leaf Oxygen levels rise Carbon dioxide levels drop Rubisco attaches RuBP to oxygen instead of carbon dioxide Only one PGAL forms instead of two
C4 Plants Carbon dioxide is fixed twice In mesophyll cells, carbon dioxide is fixed to form 4-carbon oxaloacetate Oxaloacetate is transferred to bundlesheath cells Carbon dioxide is released and fixed again in Calvin-Benson cycle
The C4 Cycle stomata closed, no CO 2 uptake C4 cycle oxaloacetate mesophyll cell CO 2 RuBP Calvin- Benson cycle PGA bundlesheath cell sugar
Leaves of a C4 Plant upper epidermis mesophyll cell bundlesheath cell lower epidermis vein stoma Corn leaf, cross-section
CAM Plants Carbon is fixed twice (in same cells) Night Carbon dioxide is fixed by repeated turns of a type of C4 cycle Day Carbon dioxide is released and fixed in Calvin-Benson cycle
CAM Plants
Summary of Photosynthesis Light Dependent Reactions sunlight 12H 2 O 6O 2 ADP + P i ATP NADPH NADP + Light Independent Reactions 6CO 2 Calvin- Benson cycle 6 RuBP 12 PGAL 6H 2 O P phosphorylated glucose end products (e.g., sucrose, starch, cellulose)
sunlight energy photosynthesis carbon dioxide, water organic compounds, oxygen aerobic respiration p.92
Main Types of Energy-Releasing Pathways Anaerobic pathways Aerobic pathways Evolved first Don t require oxygen Start with glycolysis in cytoplasm Completed in cytoplasm Evolved later Require oxygen Start with glycolysis in cytoplasm Completed in mitochondria
Linked Processes Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide
Photosynthesis and Ecological Applications We can use photosynthesis measurements to asses ecosystem health. Why? Because photosynthetic organisms are the fundamental carbon source: no plants = no food Also, some plants and algae are habitat engineers: plant roots and algal films stabilize sediments or provide habitat CO 2 + H 2 O + Photosynthetic Organisms Herbivores Carnivores
Study Site: Stege Marsh, Richmond
Photosynthesis and Ecological Applications We can use photosynthesis measurements to asses ecosystem health. How? Destructive Methods Measure Stress proteins Measure chlorophyll content directly Time consuming and often involve using toxic chemicals Non-destructive Spectral Reflectance Chlorophyll Fluorescence Provide instantaneous information about photosynthetic efficiency and plant health Measurements can be repeated on the same plant to track physiological changes
Spectral Reflectance Light is absorbed, reflected, or transmitted by plants Reflectance spectroradiometry utilizes light reflected from leaves to measure chlorophyll and other pigments Absorbed Light Chlorophyll absorbs blue and red wavelengths, but reflects the green
Copyright 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Reflectance Spectral Reflectance 0.6 0.5 0.4 0.3 0.2 0.1 Absorbed Light Reflected light 400 600 800 Wavelength Spectroradiometer Transmitted light Fiber optic cable
Reflectance Spectra and Vegetation Indices Reflectance spectra can be reduced to useful indices that are indicative of pigment content and plant condition from Ponciano et al. 1998
Reflectance NDVI (Normalized Difference Vegetation Index) 0.6 Reflectance at 750nm 0.5 NDVI = R 750 -R 705 / R 750 + R705 0.4 0.3 Reflectance at 705nm 0.2 0.1 400 450 500 550 600 650 700 750 800 Wavelength
NDVI NDVI (Normalized Difference Vegetation Index) NDVI is normalized for variability in overall reflectance due to leaf structural characteristics such as thickness. Reflectance in the infrared region of a spectrum (e.g. at 750nm) are sensitive to leaf structure 0.55 0.50 0.45 0.40 0.35 Sta. Q Sta. R Sta. S 0.6 0.5 NDVI vs Leaf Chloropyll R 2 = 0.8114 0.30 0.25 0.20 0.15 0.10 0.05 0.00 400 500 600 700 800 900 1000 0.4 0.3 0.2 0.1 0 0 20 40 60 80 100 120 Chlorophyll g/cm 2 NDVI provides an excellent estimate of chlorophyll content
Reflectance NDVI NDVI as an indicator of contamination in salt marshes 0.45 0.45 0.50 0.45 0.40 China Camp Stege BCD Stege NOP Stege QRS 0.40 0.35 0.40 0.35 0.35 0.30 0.25 0.30 0.25 0.30 0.25 0.20 0.20 0.20 0.15 0.10 0.15 0.15 0.05 0.10 0.10 0.00 400 500 600 700 800 900 1000 0.05 0.05 Wavelength (nm) 0.00 A B C 0.00 B C D Q R S N O P
Anthocyanin Index (NARI) is also good indicator of contamination Salicornia NARI 0.6 0.4 0.2 0.0-0.2-0.4 R 2 0. 829, p CCB CCC CCA 0. 001 SMC SMB SMD SMN SMQ SMS SMO SMR SMP Salicornia NARI 0.6 0.4 0.2 0.0-0.2-0.4 2 R 0. 645, p CCA CCB CCC. 0017 SMC SMD SMB SMN SMQ SMSSMO SMR SMP Spartina NARI 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 2 R 0. 535, p CCC CCB CCA 0. 007 SMN SMB SMS SMO SMD SMC SMR SMQ SMP Spartina NARI 0.6 0.4 0.2 0.0 2 R 0. 567,p 0. 0047 CCC CCB CCA SMC SMD SMN SMB SMS SMO SMR SMQ SMP 0 2 4 6 8 10 12 14 Number of pesticides reported 0 5 10 15 20 Number of organic compounds reported
Spectral Reflectance and Remote Sensing The current challenge: Linking ground, airborne and satellite borne platforms to detect ecosystem health at the landscape level Satellite Airborne Ground based instruments