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31 Cards in this Set
- Front
- Back
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Who does photosynthesis? Autotrophs and photoautotrophs |
Autotrophs: Producers > CO2> organic molecules(sustain life without eating other organisms)- bacteria Photoautotrophs: use energy of sunlight to make organic molecules from H2O and CO2 (plants, algae, certain protists and prokaryotes) |
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Photosynthesis |
the process that converts solar energy into chemical energy - directly or indirectly, photosynthesis nourishes almost the entire living world |
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Overview: The Process That Feeds the Biosphere
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Energy within light is captured and used to synthesize carbohydrates (mainly glucose) and O2Nearly all living organisms rely on this process CO2 + H2O + light energy → C6H12O6 + O2 + H2OΔG = 686 kcal/mol CO2 is reduced H2O is oxidized Energy from light drives this endergonic reaction |
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What is the difference between photosynthesis and respiration in terms of energy and oxidation/reduction of Electrons
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Photosynthesis: requires energy and reduces the carbon molecules: endergonic Respiration: releases energy and oxidizes the carbon molecules |
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Heterotrophs |
obtain their organic material from other organisms - they are consumers of the biosphere - Humans: we depend on photoautotrophs for food and O2 |
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Location of Chloroplasts?
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Mesophyll: inner tissue of the leaf - a typical , mesophyll cell has 30 to 40 chloroplasts |
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Microscopic pores on the leaf:
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Stroma -CO2 enters -Oxygen leaves |
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structure of chloroplasts |
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Thylakoids
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connected stacks of chloroplasts -stacked in columns called grana |
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Stroma |
dense fluid inside the chloroplast
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Photosynthesis contrasts with cellular respiration
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- photosynthesis is endergonic reduces CO2 to sugar - Cellular respiration is exergonic Oxidizes sugar to CO2 |
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Importance of water as the electron source
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splits H2O into H2 and O2 incorporating the electrons of hydrogen into sugar molecules Photosynthesis is a REDOX process: H2O is the source of electrons |
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Two stages of Photosynthesis
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1. Light reactions (the photo part) 2. Calvin Cycle (the synthesis part) |
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the light reactions in the thylakoids...
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- split H2O - reduce NADP+ to NADPH - generate ATP from ADP by photophosphorylation - Release O2 |
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The calvin cycle in the stroma....
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-forms sugar from CO2 using ATP and NADPH - the Calvin cycle begins with carbon fixation, incorporating CO2 into organic molecules - the reactions are linked by electrons *released from water in the light reactions *transferred to electron carrier NADP+, forming NADPH *Happens in the stroma |
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Where is the green color from?
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pigment within chloroplasts - in the membrane of the thylakoids - light energy is absorbed by chlorophyll |
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Photosynthetic Pigments: The Light Receptors
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Pigments -Substances that absorb visible light Different pigments absorb different wavelengths-Wavelengths that are not absorbed are reflected (or transmitted) = what you see Leaves appear green because chlorophyll reflects and transmits green light |
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Engelmann experiment and what it showed
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which of the pigments found in white light are responsible for driving photosynthesis? - expose algal cells to all the wavelengths of visible light in the presence oxygen-seeking bacteria - record the number of bacteria swarming near sigal cells exposed to different wavelengths - bacteira conjegates around the waveltegths of light where the alga is producing the most oxygen - pigments that absorb violet to blue and red wavelengths are most effective at triggering photosynthesis |
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Absorption Spectrum |
is a graph plotting a pigments light absorption versus wavelengths - the absorption spectrum of Chlorophyll a suggests that violet-blue and red light work best for photosynthesis |
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What are accessory pigments good for?
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broaden spectrum, absorb excessive light that would damage chlyophyll Examples are : Chlorophyll B and Carotenoids |
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When a pigment absorbs light....
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e- moves from ground state > excited state (unstable) - Excited electrons need to fall back to the ground state -Usually heat is given off -Sometimes photons are given off (afterglow = fluorescence) |
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What happens in photosystem II?
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best at absorbing wavelengths of 680 - light come in (photon) and excites accessory molecules (680) -H20 is split goes up to 680- primary electron chain - P680+ (missing an electron) but when H2O splits the adds an electron -O2 is released as a by-product - after it shoots up an electron it then splits H2O |
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Photosystem 1 |
- transferred light energy excites P700 which loses an electron to an electron acceptor - accepts electron from PS1 via electron transport chain - the electrons are then transferred to NADP+ and reduce it to NADPH and these are available for the reactions of the Calvin Cycle -ATP and NADPH are produced on the side facing the stroma, where the Calvin Cycle takes place - Light reactions generate ATP increasing the potential energy of electrons by moving them from H2O to NADPH |
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The Calvin Cycle: |
-uses ATP and NADPH to convert CO2 to Sugar - regenerates its starting materials after molecules enter and leave the cycle - The cycle buils sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH |
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The sugar that leaves the Calvin Cycle
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glyceraldehyde-3-phospate (G3P) - for net synthesis of 1G3P, the cycle must take place 3 times fixing 3 molecules of CO2 |
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Three Phases of the Calvin Cycle: |
1. Carbon Fixation catalyzed by RUBISCO 2. Reduction 3. Regeneration of the CO2 acceptor (RuBP) |
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Photorespiration |
in most plants (C2, plants) initial fixation of CO2, via rubisco, forms a three carbon compound - On Photorespiration, rubisco adds O2 instead of CO2 in the Calvin Cycle - Photorespiration comsumes O2 and organic fuel and releases CO2 without producing ATP or sugar |
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Photorespiration may be an evolutionary relic...
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-because rubisco 1st eveolved at a time when the atmosphere had far less O2 and more CO2 - PR limits damaging products of light reactions that build up in the absence of the Calvin Cycle |
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C4 plants Another Pathway |
minimize the cost of photorespiration by incorporating CO2 into 4-carbon compounds in mesophyll cells - this step requires the enzyme PEP which has a higher affinity for CO2 than rubisco does: it can fix CO2 even when CO2 concentraions are low - These 4 Carbon compounds are exported to the bundle sheath cells, where they release CO2 that is then used in the Calvin Cycle !Releases CO2 to the Calvin Cycle in an interier cell tissue |
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CAM Plants Another Pathway |
Some plants use CAM- crassulacean acid metabolism- to fix carbon - CAM plants open their stroma at night incorporating CO2 into organic acids - Stromata closes during the day and CO2 is released from organic acids and used in the Calvin Cycle ! releases CO2 to the Calvin Cycle at a later time |
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the importance of Photosynthesis: an overview
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-The energy entering chloroplasts as sunlight gets stored as chemical energy in organic compounds -Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells -Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits -In addition to food production, photosynthesis produces the O2 in our atmosphere |
