Photosynthesis Notes PDF

 Photosynthesis Photosynthesis: the conversion of light energy to chemical energy ○ Plants are autotrophs (more specifically photoautotrophs) © Getting Down With Science Autotroph vs Heterotroph Autotrophs Heterotrophs...

 Photosynthesis Photosynthesis: the conversion of light energy to chemical energy ○ Plants are autotrophs (more specifically photoautotrophs) © Getting Down With Science Autotroph vs Heterotroph Autotrophs Heterotrophs Organisms that Organisms unable to produce their own make their own food food (organic so they live off of other molecules) from organisms simple substances in their surroundings © Getting Down With Science Evolution of Photosynthesis Photosynthesis first evolved in prokaryotic organisms ○ Cyanobacteria: early prokaryotes capable of photosynthesis Oxygenated the atmosphere of early Earth Prokaryotic photosynthetic pathways were the foundation of Eukaryotic photosynthesis © Getting Down With Science  Site of Photosynthesis Leaves are the primary location of photosynthesis in most plants Chloroplast: organelle for the location of photosynthesis ○ Found in the mesophyll, the cells that make up the interior tissue of the leaf ○ Stomata: pores in leaves that allow CO2 in and O2 out © Getting Down With Science  Structures of a Chloroplast Chloroplasts are surrounded by a double membrane Stroma: aqueous internal fluid Thylakoids form stacks known as grana Chlorophyll: green pigment in thylakoid membranes © Getting Down With Science  Photosynthesis Simplified Formula: 6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2 Reactants 6 CO2 12 H2O Products C6H12O6 6 H2O 6 O2 Tracking atoms in photosynthesis using the non-simplified formula © Getting Down With Science  Photosynthesis Photosynthesis splits H2O into H and O ○ Redox reaction: reaction involving complete or partial transfer of one or more electrons from one reactant to another In photosynthesis: the electrons are transferred with H+ (from split H2O) to CO2 reducing it to sugar © Getting Down With Science  Photosynthesis Remember: OIL RIG or LEO goes GER Oxidation is loss of e- Reduction is gain of e- 6 CO2 + 6 H2O + light energy C6H12O6 + 6 O2 Reduction Oxidation © Getting Down With Science  Stages of Photosynthesis There are two stages to photosynthesis: the light reactions and the calvin cycle “Photo” “Synthesis” light reactions calvin cycle © Getting Down With Science  Understanding Light Light: electromagnetic energy ○ Made up of particles of energy called photons ○ Travel in waves ○ Wavelength: the distance from the crest of one wave to the crest of the next The entire range is known as the electromagnetic spectrum 380 nm to 750 nm is visible light © Getting Down With Science  Understanding Light Short wavelengths = higher energy Long wavelengths = lower energy When light interacts with matter it can be: ○ Reflected ○ Transmitted ○ Absorbed Pigments are able to absorb visible light The color we see is the reflected wavelengths Example: leaves are green because chlorophyll absorbs violet-blue and red light, so it reflects green © Getting Down With Science  Photosynthetic Pigments Chlorophyll a: Primary pigment Involved in the light reactions Blue/green pigment Chlorophyll b: Accessory pigment Yellow/green pigment © Getting Down With Science  Photosynthetic Pigments Carotenoids: Broaden the spectrum of colors that drive photosynthesis Yellow/orange pigment Photoprotection: carotenoids absorb and dissipate excessive light energy that could damage chlorophyll or interact with oxygen © Getting Down With Science  Quick Check 1. A photon of which color of light would contain more energy: yellow (590 nm) or purple ( 410 nm)? a. Answer: purple (410 nm); the shorter the wavelength the higher the energy 2. Contrast heterotrophs and autotrophs a. Answer: autotrophs produce their own food from their surroundings, while heterotrophs rely on other organisms for food. © Getting Down With Science The Light Reactions © Getting Down With Science  Overview Light H2O Occur in the thylakoid membrane in the photosystems Converts solar energy to chemical energy O2 ATP and NADPH © Getting Down With Science  Light Reactions Chemical energy is in two forms: NADPH and ATP The cell accomplishes this conversion by using light energy (photons) to excite electrons © Getting Down With Science  How is Light Important to Chlorophyll? Chlorophyll absorbs a photon of light Excited state e- is boosted from a ground state to an excited state heat ○ e- is unstable ○ Falls back to ground Ph e- ot state on photons Releases energy as heat Ground state Emits photons as fluorescence Chlorophyll molecule © Getting Down With Science  Photosystems Photosystems: reaction center and light capturing complexes Reaction center: a complex of proteins associated with chlorophyll a and an electron acceptor Light capturing complexes: pigments associated with proteins ○ Think: antenna for the reaction centers © Getting Down With Science  Photosystems In the thylakoid membrane there are two photosystems Photosystem 2: reaction center P680 Named in ○ Absorbs light at 680 nm order of their Photosystem 1: reaction center P700 discovery ○ Absorbs light at 700 nm Photosystem 2 Photosystem 1 © Getting Down With Science  Looking in Photosystems In the next few slides, electron flow through the thylakoid membrane will be examined The picture above will be broken down into steps. We will start at photosystem II © Getting Down With Science  Inside Photosystem II Light energy (photon) causes Primary an e- to go from an acceptor excited state back to a ground state. Light This repeats until it reaches the P680 pair of chlorophyll a P680 molecules Pigment molecules Photosystem II © Getting Down With Science  Inside Photosystem II The e- is Primary transferred to a acceptor primary e- acceptor, forming e- P680+ Light P680+ © Getting Down With Science  Inside Photosystem II H2O is split into: H2O 2 e- Primary ○ Reduce 2 H+ acceptor P680+ + e- 2 H+ ½ O2 e- e- ○ Released Light into thylakoid space 1 oxygen atom P680+ (which immediately bonds to another oxygen atom) © Getting Down With Science  Inside Photosystem II Linear electron H2O flow: each Primary excited electron 2 H+ acceptor e- will pass from PS + e- II to PS I via the ½ O2 e- e- electron transport Light chain PQ P680+ cytochrome © Getting Down With Science PC  Generation of ATP The “fall” of electrons from PS II to PS I provides energy to form ATP The H+ gradient is a form of potential energy ATP synthase couples the diffusion of H+ to the formation of ATP © Getting Down With Science  e- Inside Photosystem I PQ cytochrome Primary acceptor PC e- Light Light energy excites electrons in the P700 P700+ chlorophyll molecules Become P700+ © Getting Down With Science  Inside Photosystem I Electrons go down a second transport Primary e- chain acceptor e- Fd Light e- e- P700+ NADP+ reductase © Getting Down With Science  Inside Photosystem I NADP+ reductase catalyzes the Primary e- transfer of e- from acceptor Fd to NADP+ e- Fd Light e- e- P700+ NADP+ reductase + NADP + H + NADPH © Getting Down With Science Light Reactions:Putting it all Together © Getting Down With Science  Inputs and Outputs Inputs H2O ADP Light Reactions NADP+ Outputs O2 ATP NADPH © Getting Down With Science  Light Reactions Summary Converts solar energy to chemical energy ○ Chemical energy is in 2 forms: NADPH and ATP Water is split ○ Provides a source of electrons and protons (H+) ○ Releases O2 as a by-product Light absorbed by chlorophyll drives the transfer of electrons and hydrogen ions from H2O to an electron acceptor called NADP+ ○ NADP+ is reduced to NADPH Generates ATP by phosphorylating ADP © Getting Down With Science Calvin Cycle © Getting Down With Science  Calvin Cycle The calvin cycle is cyclic electron flow Uses ATP and NADH to reduce CO2 to sugar (G3P) For net synthesis of 1 G3P molecule, the cycle must take place 3 times © Getting Down With Science  Calvin Cycle Three phases: 1. Carbon fixation 2. Reduction 3. Regeneration of RuBP © Getting Down With Science  Phase 1: Carbon Fixation CO2 is incorporated into the calvin cycle one at a time ○ Each CO2 attaches to a molecule of RuBP Catalyzed by the enzyme rubisco ○ Forms 3-phosphoglycerate © Getting Down With Science  Phase 2: Reduction Each molecule of 3-phosphoglycerate is phosphorylated by ATP (uses 6 total) ○ Becomes 1,3-bisphosphoglycerate 6 NADPH molecules donate electrons to 1,3-bisphosphoglycerate Reduces to G3P 6 molecules of G3P are formed, but only one is counted as a net gain ○ The other 5 G3P molecules are used to regenerate RuBP © Getting Down With Science Phase 3: Regeneration of RuBP 5 G3P molecules are used to regenerate 3 molecules of RuBP ○ Uses 3 ATP for regeneration Cycle is now ready to take in CO2 again © Getting Down With Science Calvin Cycle: Putting it all Together © Getting Down With Science  Inputs and Outputs Inputs 3 CO2 9 ATP Calvin Cycle 6 NADPH Outputs 1 G3P 9 ADP 6 NADP+ © Getting Down With Science  Calvin Cycle Summary Uses NADPH, ATP, and CO2 Produces a 3-C sugar G3P Three phases: 1. Carbon fixation 2. Reduction 3. Regeneration of RuBP © Getting Down With Science  Problem for C3 Plants Photorespiration: ○ On very hot days plants close their stomata to stop water loss ○ Causes less CO2 to be present, and more O2 ○ Rubisco binds to O2 and uses ATP The process produces CO2 NO sugar is produced BAD for the plant © Getting Down With Science  Adaptations Plants that live in hot, dry climates have evolved to have alternative mechanisms of carbon fixation © Getting Down With Science  Adaptations C4 Plants ○ Spatial separation of steps ○ Stomata partially close to conserve water ○ Mesophyll cells fix CO2 into a 4-C molecule Transferred to bundle sheath cells Releases CO2 to be used in the Calvin cycle ○ Examples: maize (corn), grasses, sugarcane © Getting Down With Science  Adaptations CAM plants ○ Open stomata at night and close during the day ○ CO2 is incorporated into organic acids and stored in vacuoles ○ During the day, light reactions occur and CO2 is released from the organic acids and incorporated into the Calvin cycle ○ Examples: pineapples, cacti, succulents, jade © Getting Down With Science  Practice FRQ A student wanted to study the effect of varying colors of light on the growth of plants. The student exposed tomato plants to 3 different wavelengths of light for the course of one week and measured the overall height each plant each day. All other conditions were kept consistent between the plants. The results are below: a) Identify the wavelength that caused the least amount of growth. b) Explain why the wavelength identified in part a was ineffective. © Getting Down With Science  Practice FRQ Rubisco can bind to CO2 or O2 in the Calvin cycle. After learning this, a student was interested in photorespiration. After doing research she claimed that it is simply a metabolic relic; early atmospheric conditions did not have oxygen, therefore it never posed a problem early on. Would you support or reject this claim? Justify your response. © Getting Down With Science