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Photosynthesis
Biology Unit 3
| Question | Answer |
|---|---|
| photosynthesis equation | 6CO2 + 12H2O(l) + light E --> C6H12O6 + 6O2 -note: light is often written on top of the arrow & it is VISABLE light that drives photosynthesis |
| Types of organisms that undergo photosynthesis | plants, algae, bacteria, certain other protists, and some prokaryotes |
| how does pigment (light-capturing mcs) in plants capture light for photosynthesis | -light has diff. wavelengths, each w/ their own color -different pigments absorb & reflect different wavelengths of light EX: chlorophyll absorbs red & blue light but reflects green light |
| what are the reactions that occur in chloroplasts that make up photosynthesis | -light dependent reactions -light independent reactions (Calvin cycle/"dark rxn") -these happen at the same time! |
| thylakoid membranes | -compartments in chloroplast that contain light-capturing pigments -facilitate light-dependent reactions -connected sacs in the chloroplast (stacked into granum) |
| Calvin Cycle stages & products (assuming in input of 3 CO2 mcs) | 1. Carbon fixation (6 PGA) - takes inorganic C & makes it usable) 2. Reduction (6PGAL, AKA 6G3P) 3. regeneration (3 RuBP) |
| stroma | fluid-filled space inside the chloroplast that surrounds the thylakoid -site of the calvin cycle |
| formula of light dependent rxn | 12H2O + 12NADP+ + 18ADP + 18Pi + light energy → 6O2 + 12NADPH + 18ATP -water from the soil (capillary action) -NADP+, ADP, and Pi from the Calvin cycle -light from the sun -O2 released into air -NADPH & ATP goes to Calvin cycle |
| formula of light independent reaction | 12 NADPH + 18 ATP + 6 CO2 → C6H12O6 + 12 NADP+ + 18 ADP + 18 Pi + 6 H2O -NADPH & ATP from the light-dep. -CO2 from the air -produces G3P to make glucose -ADP & Pi to light-dep -H2O released in air as gas |
| what are all the pigments found the chloroplasts and where are they in the chloroplast? | carotenoids (like carotenes & xanthophylls), chlorophyll A, chlorophyll B -they are in the light-harvesting complexes (part of the photosystems) |
| light dependent reactions summary | -in the thylakoids: Split H2O Release O2 Reduce NADP+ to NADPH Generate ATP from ADP by photophosphorylation |
| How are ATP and NADPH used? | ATP provides the E needed to drive rxns NADPH = reducing power - provides high E e- (& H) needed to reduce carbon compounds and help form G3P (a sugar) |
| G3P | -AKA PGAL (phosphoglyceraldehyde) -a 3-C sugar produced from CO2 in Calvin cycle -building block of glucose (2 G3P = 1 glucose) -final assembly of glucose takes place in the cytoplasm where the exported G3P undergoes a series of enzymatic reactions |
| Calvin cycle summary | -forms sugar from CO2, using ATP and NADPH -in the stroma -regenerates its starting material after mcs enter & leave the cycle |
| heterotroph | animals, fungi, some bacteria -glucose is supplied by indigestion or absorption rather than photosynthesis -depend on organic mcs (food) to provide glucose |
| Photoautotroph | -plants -produce E through photosynthesis -they get their energy from light |
| phosphorylation | the addition of a phosphate group (PO₄³⁻) to an organic molecule, which alters its activity, stability, or energy state. EX: attaching an inorganic phosphate group (free P ion in solution w/ central P atom surrounded by four O) to ADP to form ATP |
| which process provides the E for metabolic rxns | hydrolysis of ATP -some E is stored in chemical bonds while some is lost as heat |
| it takes E to break bonds, so how does the hydrolysis of ATP provide E for metabolic rxns? | -there's a reactive intermediate (which can be used to do work) - rxns that make the E in ATP available occur simultaneously, so the rxn is simplified to omit the intermediates |
| What colors of light are best absorbed by the pigments? What colors are least absorbed? | they absorb blue & red while reflecting green light |
| absorption spectrum | a graph plotting a pigment’s light absorption (y-axis) versus wavelength (x-axis) -spectrum of chlorophyll A suggests that violet-blue & red light work best for photosynthesis |
| How is cellulose produced | |
| photosystem | -light dependent rxn - protein in the thylakoid membrane w/ chlorophyll A on the inside-light hits it and gives its e- E -the e- then leave it, so it needs new e- which are supplied by water |
| lumen | the inside space of a membrane bound structure EX: thylakoid lumen = space inside the thylakoid where H+ ions build up during light rxns, H+ then flows through ATP synthase helping make ATP |
| light goes into the photosystem to power the movement of e- through the e- transport chain (goes through proteins, carrier proteins, etc) and it eventually goes to NADPH -everytime it goes through a protein, it pumps H+ into the inside | -occur in thylakoids -light E is absorbed by chlorophyll, water from the soil is split producing O2, H+ & e-, the light E is converted into chemical E (produces ATP & NADPH) |
| water in light dependent reactions | it's split in photosynthesis produces O2 and H+ |
| water's role in photosynthesis | -light dependent rxn -water from the soil gives the replaces the lost e- in the photosystem -water is split into H+, O2, and e- -O2 is released as waste -H+ is put into the lumen |
| electron transport chain | -light dependent rxn -e- move through several proteins in the thylacoid membrane (this is called the chain) -as e- move, they give off E (used to pump H+ into lumen) -creates H+ gradient -moving e- from H2O to NADPH ⬆ potential E |
| thylakoid lumen | continuous inner aqueous space enclosed by the thylakoid membrane inside chloroplasts and cyanobacteria |
| how is water used in the light dependent reactions of photosynthesis | -H2O from the soil is split inside the lumen by photosystem II into e-, H+ & O2 -the O2 is a waste product, the H+ remains inside the lumen (until it moves through ATP synthase), while the e- resupplied chloroplast with e- |
| Photosystem II | -light-dep. rxn -a protein embedded in thylakoid membrane -part of ETC -has pigments to absorb photons from light, exciting e- in pigment which begin traveling through the ETC -it splits H2O to resupply pigment's e- 2H2O = 4H+ + 4e- + O2 |
| Photosystem I | -light-dep. rxn -contains pigments that capture the light, replenishing the E that the e-s lost to the proton pump -the e- are then released & combine with an electron carrier to make NADPH (which is used in calvin ) -4 e- + NADP+ + 2H+ = 2NADPH |
| proton pump | -light-dep rxns -uses E from the moving e- in the ETC to move H+ against its [] gradient (from outside the thylacoid in the stroma into the thylacoid lumen) -maintains H+ [] inside the thylacoid |
| ATP synthase | -both an enzyme & channel protein -facilitated diffusion of H+ out of the cell (chemiosmosis) -The flow of H+ provides the E needed for the phsophorylation of ADP 3ADP + 3Pi = 3ATP |
| Chemiosmosis | the movement of ions across a semipermeable membrane down their electrochemical gradient to make ATP -consists of the ETC & ATP synthase |
| electrochemical gradient VS concentration gradient | A concentration gradient is a difference in particle concentration across a space, while an electrochemical gradient combines that concentration difference with an electrical charge difference across a membrane |
| Which products are exchanged between both the light independent and dependent stages of photosynthesis? | |
| Carbon fixation | -3 CO2s enter the stroma -1 rubisco attaches to each CO2 to 1 RuBP (ribulose biphosphate) to make a six carbon intermediate -the intermediate is unstable & immediately splits into 2 three carbons mcs called 3-PGA/GP |
| rubisco | an enzyme that starts carbon fixation (converts CO2 into an organic mc) -it combines RuBP (5-carbon mc synthesized in the regeneration step in the calvin cycle) with CO2 to make an unstable 6-carbon mc -located in the stroma |
| 3-PGA | AKA GP 3-phosphoglycerate -3 carbon mc -first stable product of the Calvin cycle (carbon fixation) |
| reduction phase | ATP (from ATP synthase) transfers Pi to 3-PGA , producing intermediate 1,3-BPG & ADP (goes to ATP synthase in light-dep) -1,3 -BPG recieves e- (reduction) & H+ (turns it into G3P) from NADPH to make G3P & NADP+(goes to photosystem I), H2O (g) & Pi - |
| regeneration | -releases 1 PGAL/TP/G3P (the net product used to produce glucose and other carbs) per turn (1 out of 6 TP) -5 TP rearrange into three ribulose 5- phosphates -those react w/ ATP to make 3RuBP (used in 1st step), 3ADP & 3Pi (goes to ATP synthase) |
| memorize the lewis structure of CO2, PGA, PGAL, & RuBP | |
| Pi | |
| NADPH | |
| leaf sun-catcher😝 | -water vapor is released through the stomata (transpiration causes H2O to evaporate through leaf) -O2 released through stomata (diffusion) -areas between veins capture sunlight & have stomata (air spaces) where CO2 diffuses through -water from soil |
| explain how water from the soil spread through a plant | roots absorb (osmosis- water [] is higher in the soil) -capillary action - water moves upward through narrow tube (adhesion > cohesion) -transpiration - water evaporates from the leaf) |
| transpiration | -the loss of water vapor from a plant (through the stomata in the leaves) -cools the plant cause when water evaporates after reaching the leaf, it takes heat E from the plant with it -cohesion-tension mechanism |
| adhesion | -water is attracted to other mcs because of its polarity -enables capillary action (ability of a liquid to flow against gravity in a narrow space) -meniscus of liquid in a tube -helps h2O mcs stick to xylem walls in capillary action |
| cohesion | -water mcs stick to each other because HBs form between them -allows water to form droplets -SURFACE TENSION -cohesion allows water to form an unbroken column while moving through the xylem of plants (water uptake from soil) |
| why might water be able to flow against gravity | -if adhesive forces (H2O & surface) are stronger than cohesive forces, H2O spreads along & climbs the surface -adhesion pulls H2O up the sides while cohesion carries other water mcs along -only in narrow spaces (more surface area compared to water) |
| How does the chloroplast and mitochondria interact? | -Chloroplasts produce the glucose & O2 used by the mitochonrai while cellular respiration produces the H2O and CO2 used in photosynthesis |
| Photosynthesis summary | -converts solar energy from the sun into chemical energy in the form of glucose |
| autotrophs | organisms that sustain themselves without eating anything derived from other organisms -produce organic mcs from CO2 from other inorganic mcs like H2O or CO2 |
| fossil fuels origin | -plants/photoautotrophic organisms created organic matter -the organisms died and were barried for millions of yrs -when we burn coal or oil, we are releasing the chem E that originally came form sunlight captured by ancient organisms |
| Mesophyll cells | plant cell inside the leaf where photosynthesis occurs -Leaves are the major locations of photosynthesis -chloroplasts are mainly found here (each cell has about 30-40) |
| Stomata | -tiny pores/opening on the surface of a leaf that control gas exchange -CO2 enters -O2 & water vapor exit |
| What does a photosystem consist of | reaction center complex surrounded by light-harvesting complexes 1. contains chlorophyll A & uses E from #2 to excite e-. Then, transfers e- to e- acceptor to begin ETC 2. contains many pigment mcs that transfer E from photons to reaction center |
| Chlorophyll A | main photosynthetic pigment- directly involved in the rxn center's e- transfer (inside the both the rxn center & light harvesting complex, loses e-) -reflects blue/green light |
| Chlorophyll B | accessory pigment that broadens the spectrum used for photosynthesis -not directly involved in e- transfer but still in photosystems -absorbs wavelengths that A doesn't absorb as well & transfers the E to chlorophyll A -reflects yellow/green light |
| carotenoids | accessory pigment that absorbs excessive light that would damage chlorophyll - absorb & safely dissipate excess E as heat -reflects yellow, orange & red (absorb blue/green light) |
| action spectrum | -shows how effective different wavelengths of light are at driving photosynthesis -wavelength of light (x-axis) VS rate of photosynthesis (y-axis) (measured by O2 release) -Blue = high, Red = high, Green = low |
| What determines the seasons? | -maximum intensity of Sun's rays over a given area (which changes as the subsolar pt moves north & south) -subsolar pt: exact point on Earth where the sun is directly overhead (sun's rays always hit it at a 90 deg angle) & it changes as the Earth tilts |
| xylem | -transports water and minerals from roots to shoots (above-ground parts of the plant, stems, leaves, flower, buds, etc) during photosynthesis -water up |
| phloem | transports photosynthetic products (sucrose - plants converts glucose into sucrose in the cytoplasm) from sources to sinks -food flow |
| sinks | a sink is a part of the plant that uses or stores sugars, growing roots, young leaves, flowers, developing fruits, seeds, storage organs - once a leaf matures its a source cause it produces more sugar than it needs & can export it through the phloem |
| explain how the stomata can be both beneficial to the plant's heath and inefficient | -when the stomata opens to allow CO2 to enter, it lets some water vapor escape -the water coming from the xylem is eventually lost through transpiration -plants adapt to balance both their need for H2O & photosynthesis |
| cohesion-tension mechanism | -describes how transpiration pulls water from the roots to the leaves -when water evaporates from the top of the xylem, it creates an upward pull on H2O column (water mcs are connected to each other through cohesion) - |
| epidermis | -outermost, waxy layers of cells covering a whole plant (roots, leaves, stem, etc) -protects the inside of leaf -reduces H2O loss (it's hydrophobic, so H2O can't evaporate through it- therefore, H2O only leaves through stomata) -contains stomata |
| guard cells | -specialized cells in the epidermis of a leaf that surround each stoma -when they swell, the stoma opens, and when they shrink, stoma closes -help balance water conservation with gas exchange |
| How does the guard cell operate | -open & closes by changes in turgor P -turgid (central vacuole takes in water, causing them to become more firm) = guard cells swell or BOW OUTWARD & stomata opens -flaccid (lose water) = guard cells shrink or become LESS BOWED & stomata closes |
| stomata density | -the # of stomata per unit of area of a leaf -it is controlled by genetics & environmental conditions |
| conditions that influence stomata density | high T = greater water loss risk = lower high water availability = less pressure to conserve water = plants can support more stomata higher Co2 [] = lower density more light = more E for photosynthesis = needs for CO2 = higher density |
| When do stoma open or close | open during the day & close at night to minimize water loss (hotter daytime weather increases water loss through the stoma - more water evaporates) |
| What are stomatal openings triggered by? | Light (light activates guard cells - cell takes up solutes & water enters) CO2 depletion (photosynthesis occurs faster at night = CO2 used up faster = CO2 inside leaf decreases = stoma opens to let in more) An internal “clock” in guard cells |
| circadian rhythms | a biological clock in ALL EUKARYOTES that help an organism keep track of roughly 24-hr cycles (circadian rhythms) -Plants: coordinates when guard cells open & close |
| what causes stomata to close during the daytime? | 1. Drought (less water = need to conserve more water) 2. high temperature (more evaporation), 3. wind (blows across leaf & removes humid air around the stomata = increases water-vapor gradient, transpiration increases) |
| abscisic acid | a hormone produced in response to water deficiency and causes the closure of stomata |
| why does a plant need alternative mechanisms of carbon fixation | - hot, arid climates cause dehydration plants close stomata, which conserves H2O but also limits photosynthesis, reducing access to CO2 and causes O2 to build up -these conditions favor photorespiration |
| photorespiration | -wasteful process -alternative to carbon fixation in hot climates |
| C3 plants | -most plants -initial fixation of CO2, via rubisco, forms a three-carbon compound (3-phosphoglycerate) |
| photorespiration | enzyme RuBisCO mistakenly binds O2 (instead of CO2 )to RuBP in the Calvin cycle, Plant makes a toxic byproduct (2-C compound) & has to spend E to clean it up (Wasteful) -consumes O2 and organic fuel and releases CO2 without producing ATP or sugar |
| is Photorespiration light dependent or light independent? | light-dependent -light-dependent rxn breaks down H2O & releases O2, When stomata close, O2 builds up & RuBisCo grabs it instead of CO2 -only occurs when light is present (active sunlight casues stomata to close) |
| Why is photorespiration so wasteful? | Instead of making sugars, it breaks down previously fixed C compounds (RuBP that is already inside the plant), releases CO2, & consumes E (ATP/NADPH) without making sugar. -drains up to 50% of the net C gain achieved by Calvin cycle in C3 plants |
| What causes photorespiration? | When plants close their leaf pores (stomata) to conserve water on hot or dry days, CO₂ cannot enter the leaf, while oxygen produced by photosynthesis builds up inside -O2-CO2 ratio increases |
| evolutionary significance of Rubisco | Rubisco evolved long before the Great Oxidation Event, when atmospheric O2 was scarce, meaning the enzyme did not need a strict way to tell O2 and CO2 apart. |
| How does photorespiration protect the cell? | When Calvin cycle slows (less CO2 becuase stomata closes), light rxn keeps absorbing solar E, creating excess ATP & NADPH. Photorespiration consumes this excess E, preventing it from damaging cell (specifically the photosystem proteins) |
| C4 plants steps | PEP carboxylase binds w/ CO2 to produce a 4-C compound -the compound is exported from the mesophyll cells to bundle-sheath cells -they release CO2 that is then used in the Calvin cycle -This creates a high CO2 concentration right around Rubisco |
| PEP carboxylase | -an enzyme that binds CO2 effectively, even when CO2 levels are low. Unlike Rubisco, it does not bind to oxygen & has no competing oxygenase activity -used by C4 plants |
| mesophyll cells | -initially capture CO2 using PEP carboxylase & turn it into a 4-C compound -C4 plant: delivers extra CO2 to the bundle-sheath cells (has PEP carboxylase to capture CO2) -C3: calvin cycle occurs here (rubisco fixes CO2) |
| bundle-sheath cells | -receive the 4-C compound from mesophyll cells & release concentrated CO2 -C4: calvin cycle occurs here, CO2 is concentrated around rubisco |
| How do plants in hot climates limit photorespiration? | 1. C4 plants (separate carbon fixation & Calvin cycle spatially-separate steps by time) 2. CAM plants (open their stomata at night - separate steps by location) |
| CAM plants steps | -plant opens stomata @ night (cooler = less H2O evaporation) -PEP carboxylase captures CO2 & incorporates it into organic acids (like maltic acid) -plant stores acids until daytime -DAY: the acids release CO2 inside plant's cells -succulents |
| What does CAM stand for | crassulacean acid metabolism |
| non-cyclic electron flow | -ordinary/main pathway -electrons travel in 1 direction through the photosystems & end up in NADPH -produces ATP, NADPH, and O2 -uses photosystems I & II |
| cyclic electron flow | -electrons cycle through ETC instead of being accepted by NADP+ -e- are excited in PS I & e- is passed to a carrier, then through H+ pump, & back to PS I -no NADPH or O2 produced (water is not split to produce e-) -only uses Photosystem I |
| NADP+/NADPH VS NADH/NAD+ | NAD = cellular respiration - delivers e- for the ETC NADP = photosynthesis - delivers the e- for the calvin cycle |
| Why do plants need cyclic electron flow? | -they need more ATP relative to NADPH, so if NADPH builds up, cyclic is activated - allows for extra ATP without making NADPH -all plants use it to boost ATP production (both occur simultaneously, but their rxn rates change based on plant's needs) |
| H2S | -hydrogen sulfide -some photosynthetic bacterial use them as electron donors instead of water - |
| Cyanobacteria | bacteria that get their energy through photosynthesis and are the only photosynthetic prokaryotes able to produce oxygen (they split water rather than H2S) -these caused the Great Oxygenation Event! |
| Stromatolites | layered structures formed by cynobacteria -contributed to the formation of oxygen of earth's atmosphere (transformed earth's atmosphere) -earliest known organisms to perform oxygenic photosynthesis |
| How do scientists know when the first oxygen first appeared in the atmosphere | oxygen produced from the cyanobacteria was used to make rust (iron + oxygen) -Rust in rock layers begins to form about 2.7 billion years ago -This is after the first stromatolite fossil appears in our fossil record |
| Oxygenic photosynthesis | photosynthesis that uses water as the electron donor and releases oxygen as a byproduct |
| anoxygenic photosynthesis | bacterial photosynthesis that occurs under anaerobic coniditions and produces no oxygen -use H2P as the electron donor |
| the Great Oxygenation Event | increased O2 in atmosphere & ocean (shifted them from being weakly reducing - has more substances that donate e- - to being oxidizing - O2 accepts e-) -led to evolution of multicellular eukaryotes |
| origins of chloroplasts | -cynobacteria are their ancestors (similarities in ribosomes & membrane organization) -endosymbiosis |
| Anoxygenic photosynthesis equation | CO2 + 2H2A + light --> CH2O (carb) + 2A + H2O -water is a product! just note! |
| Each mole of ATP hydrolyzed produces how much E | 30.7 kJ of E |
| Does breaking bonds or forming bonds require E | -breaking bonds requires energy -forming bonds released energy |
| Why does ATP hydrolysis release E | -E is required to break the bonds in ATP & water -new bonds form in ADP & Pi -forming the products releases E than was required to break the og bonds (net release) -overall rxn has neg change in free energy (products have lower G than reactants) |
| ATP hydrolysis | using water to break the bond connecting the last phosphate group to the rest in ATP -THEN, the atoms rearrange 7 new bonds form in ADP & inorganic phosphate |
| If a plant, for example, does not have access to light, how can it still produce glucose | -it uses E from chem rxns (often involving H2S) instead of light -H2S can supply E through oxidation |
| intermediate in hydrolysis of ATP | after ATP loses its terminal phosphate group, the phosphate group is transferred to a diff mc -that mc becomes the phosphorylated intermediate -this rxn allows cells to couple that E-releasing rxn to metabolic work |
| triose phosphates | 3-carbon phosphates produced in the Calvin cycle -used to build sugars and other organic mcs -the main one is G3P /PGAL -formed when electrons & hydrogen ions from the splitting of water are transferred to CO2 |
| Why is RuBisCo so abundant | -it works slowly -plants need large quantities to make enough food |
| Pathway of an electron in Photosynthesis | |
| pathway of hydrogen in photosynthesis | @ photosystem I, e-, H+, & NADP+ combine to form NADPH -then the H+ is carried to the Calvin cycle (transfers the H+ to convert the mc into the correct chemical form of G3P) |
| electromagnetic radiation | -a form of energy (light!) -they travel in waves & the greater the wavelength, the lower E of the photons in that radiation |
| Why does photosynthesis involving the photolysis of water | water splits into e-, H+ & O2 -O2 is released as waste -e- & H+ are transfered to CO2, reducing it to sugar -e- increase in potential E when they move form water to sugar |
| final electron acceptor in photosynthesis | NADP+ |
| How many turns in the calvin cycle are required to form hexose sugar (EX: glucose) | six turns! |
| explain the ratios of the calvin cycle needed to produce 6 RuBP | 6 CO2 + 6RuBP = 12 GP 12 GP+ 12 ATP = 12 ADP & 12 1,3 Bisphosphaglycerate 12 1,3 Bi. + 12 NADPH = 12 NADP+ & TP 2 triose phosphate leave cycle to make 1 hexose sugar remaining 10 TP becomes 6 ribulose-5-phosphate 6 R5P + 6 ATP = 6 ADP & 6 RuBP |
| What is the actual end product of the calvin cycle | triose phosphate (G3P is a type of TP) |
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