PHOTOSYNTHESIS
Fundamental biological processes for making and using energy Photosynthesis : process by which plants convert radiant energy to chemical energy Respiration : process by which glucose molecules are broken down and stored energy is released Photosynthesis - autotrophs make glucose Respiration – organisms break down glucose
TYPES OF ORGANISMS BY ENERGY PRODUCTION Autotrophs Heterotrophs - organisms that produce organic - organisms that obtain energy molecules from inorganic from other organisms substances (photosynthesis) (heterotrophs or autotrophs) - Photoautotrophs - use - do not make own food light energy to make food (plants, algae, cyanobacteria) - Chemiautotrophs - oxidize inorganic chemicals to drive food making reactions (bacteria, fungi)
Location of photosynthesis Chloroplast- double membrane organelle Thylakoid discs (photosystem: 200-300 thylakoids) - Harvest sunlight - Contains chlorophyll and accessory pigments - Photosystem I and II are linked structurally and functionally Grana (stacks of thylakoid discs) location of light reactions Stroma (protein rich solution, outside grana) location of Calvin Cycle Mesophyll: location of chloroplasts Stomata: pores in leaf CO2 enters/ O2 exits Chlorophyl l: pigiment in thylakoids
PHOTOSYNTHESIS 6 CO 2 + 6 H 2 O + light energy → C 6 H 12 O 6 + 6 O 2 process whereby autotrophs (plants) take in light energy and convert it to chemical energy (sugar) Redox Reactions water is split → e - transferred with H + to CO 2 → sugar biochemical pathway- series of linked redox reactions where product of one reaction is consumed by the next reaction Endergonic- absorbs solar energy Exergonic- releases energy for organism
Tracking Atoms through Photosynthesis Evidence that chloroplasts split water molecules enabled researchers to track atoms through photosynthesis (C.B. van Niel) 6 CO 2 6 CO 2 12 H 2 O Reactants: C 6 H 12 O 6 6 H 2 O 6 O 2 Products:
Photosynthesis = Light Reactions + Calvin Cycle “photo” “synthesis” energy building sugar building reactions reactions
Light Energy and Pigments Comes from radiation (energy that travels in waves) from the sun photon - particles which have energy wavelength- crest to crest of wave sunlight- mixture of all visible wavelengths white light- all wavelengths reflected equally so looks white visible spectrum- all colors of white light
Pigment : substance that absorbs light - photosynthesis: absorbed light energy is used to make chemical bond energy - wavelengths not absorbed are reflected (color we see) Absorption spectrum graph plotting pigment light absorption vs wavelength representation of how well particular pigment absorbs different wavelengths of white light
Photosynthetic pigments chlorophyll a (blue green) - primary photosynthetic pigment - directly involved in converting light → chemical energy - hides other pigments chlorophyll b (yellow green) - accessory pigment - absorbs light and transfers energy to chlorophyll a carotenoids (orange, yellow) - xanthophylls (yellow) / carotenes (orange) - accessory pigments - converts energy to chloro. a - seen in autumn when chloro. breaks down - photoprotection for chlorophyll anthocyanin (red, purple, blue): antioxidants - non photosynthetic parts of plant (flowers/fruits) - absorb different pigments so we see other colors
Determining Absorption Spectrum
Action Spectrum Action spectrum plots rate of photosynthesis of different wavelengths, i.e. CO2 consumption , O2 release (different than absorption spectrum) Englemann’s experiment: Used alga and bacteria Measured O2 output Result: violet-blue and red wavelengths caused most photosynthesis
Electron Excitement -light is made of photons (particles which carry fixed amount of energy) -when light strikes chlorophyll , some of its atoms absorb the photons -energy is transferred to the atoms electrons and excites them to jump to next level * *Move from ground state to excited state** - excess energy is released as light or heat
Photosystems Photosystem: reaction center (proteins that hold special pair of chlorophyll a molecules) + light harvesting complexes (cloro. a & b, carotenoids bound to proteins) - located in thylakoid discs - absorb light energy Primary electron acceptor: accepts electrons and becomes reduced (electrons move to higher energy level) Photosystem I: chlorophyll a absorbs at 700 nm- far red (p700) Photosystem II: chlorophyll a absorbs at 680 nm- red (p680)
Overview of Stages of Photosynthesis 2 Stage Process 1. light reactions (needs light) - occurs in thylakoid membranes 4 basic steps - sun’s energy is trapped by chlorophyll - electron transport (linear/cyclical) - water is split and oxygen is released (O 2 production) - ATP and NADPH are formed and released into stroma - purpose: to make ATP and NADPH (energy carrier molecule)
2. Calvin Cycle : - occurs after light reactions - can occur in light or dark 3 basic steps - carbon fixation to glucose - reduction of NADP to NADPH - regeneration of RuBP to start cycle over again
Light Reactions Electron Flow Two routes for electron flow: A. Non-cyclic (linear) electron flow B. Cyclic electron flow animation
STEPS OF LIGHT REACTION 1. photosystem II absorbs light and excites electrons of chlorophyll a - molecules and electrons are forced to higher energy level (reaction center) ***purpose of photosystem II is to generate ATP and supply electrons to photosystem I *** 2. excited electrons leave chlorophyll a molecule (oxidation reaction)
3. primary electron acceptor sends electrons into ETC - reduction reaction - chain uses energy of electrons to make ATP - water is split ( photolysis ) and O2 is released into atmosphere - electrons from water replace those lost in Photosystem II - pumps H+ ions (from splitting of water) to interior of grana (lumen) - inside grana , there is a high concentration ( proton gradient) of H+ ions - chemiosmosis occurs (making of ATP) - H+ ions back move across grana membranes ( ATPsynthase) LINEAR ELECTRON FLOW NON-CYCLICAL PHOTOPHOYPHORYLATION animation
4. at end of ETC, electrons are passed to photosystem I thru the ( cytochrome complex = plastiquinone Pq (e- carrier) and plastocyanin Pc (protein) - photosystem also absorbs light to excite electrons in chloro. A - electrons go thru separate electron transport chain in photosystem I to a different primary electron acceptor ferradoxin Fd (protein) facilitates movement of e- - purpose of photosystem I is to generate NADPH 5. NADP+ - accepts electrons and H+ ions (reduces it to NADPH ) - NADPH and ATP move into stroma LINEAR ELECTRON FLOW NON-CYCLICAL PHOTOPHOYPHORYLATION
Cyclic Electron Flow: • uses PSI only • produces ATP for Calvin Cycle animation
Cyclic • PS I only • Reaction center is P700 • Electrons travel back to PS I • Only ATP is produced • No photolysis of water • No O2 involved • Predominant in bacteria Non cyclic • PS II and I • Reaction center is P680 • Both ATP and NADPH are produced • Photolysis (splitting) of water occurs • O2 is by-product • Predominant in green plants
End products of light reactions 1. ATP and NADPH: needed to power dark reactions 2 . O2: by product released into atmosphere
Chemiosmosis in Chloroplasts and Mitochondria Respiration and photosynthesis use chemiosmosis to generate ATP ETCs pump protons (H+) across membrane from areas of low concentration to high concentration Protons then diffuse back across membrane thru ATPsynthase to make ATP H+ reserviors for each organelle mitochondria- matrix chloroplast – lumen Mitochondria :high energy e- come from organic molecules Chloroplasts: high energy e- come from water
Thylakoid Membrane Organization Proton motive force (H+ gradient) generated by: (1) H + from water (2) H + pumped across by cytochrome (3) Removal of H + from stroma when NADP + is reduced animation
Calvin Cycle - light independent: can occur in light or darkness, always after light rxns - occurs in stroma - purpose: Carbon fixation to glucose molecule (from CO2 in atmosphere) - Uses ATP and NADPH - 3 Phases 1. carbon fixation 2. reduction 3. regeneration of RuBP (CO2 acceptor) calvin cycle animation
Steps of Calvin Cycle 1. Carbon fixation - 3 CO2 enters plant from atmosphere and binds with RuBP ribulose biphosphate (5 C sugar) - catalyzed by rubisco enzyme ( RuBP carboxylase) - forms unstable 6 C intermediate sugar - this splits into 2 PGA per CO2 net: 6 PGA
2. Reduction (PGA to G3P) 2 steps - each PGA gets phosphate from ATP - then each molecule reacts with H from NADPH and breaks phosphate bond - net gain: 1 molecule of G3P/PGAL (glyceraldehydre 3 phosphate) - 6 G3P formed, but - 1 molecule used to make sugar - 5 molecules used to regenerate RuBP 6 ATP and 6 NADPH needed to produce 1 net G3P/PGAL
3. Regeneration of RuBP from G3P - 1 G3P/PGAL placed on glucose - 5 G3P/PGAL used to regenerate RuBP (cyclical – continues over and over again) 3 ATP needed to regenerate RuBP
End product of Calvin Cycle Glucose *6 turns of cycle needed to make 1 molecule of glucose* Calvin Cycle uses: 3 CO2, 9 ATP, 6 NADPH animation 1 C6H12O6 molecule = 6 CO2, 18 ATP, 12 NADPH
Vcell photosynthesis video
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