BIO 114: Photosynthesis

Chemiosmosis •Net accumulation of ____ in thylakoid ____ occurs from splitting of ____ molecules and ____ transport. •Proton gradient gives special proteins, ____ (= ATP Synthase), in thylakoid membrane potential to move ____ form ____ to ____. •Movement of protons across membrane = source of energy for synthesis of ____

Chemiosmosis •Net accumulation of protons in thylakoid lumen occurs from splitting of water molecules and electron transport. •Proton gradient gives special proteins, ATPase (= ATP Synthase), in thylakoid membrane potential to move protons form lumen to stroma. •Movement of protons across membrane = source of energy for synthesis of ATP

Photosynthesis

Converts light energy to a usable form is the process of transforming solar energy into chemical energy (in the form of carbohydrates).

There are two types of chlorophyll in plants: (1) Chlorophyll ____ - absorbs best around ____ nm (purple/blue) and at about ____ nm (red) of the light spectrum (10.2, 10.6, 10.7) (2) Chlorophyll ____ - absorbs best around ____ nm (blue) and at about ____ nm (orange/red) of the light spectrum (10.2, 10.6, 10.7)

There are two types of chlorophyll in plants: (1) Chlorophyll a - absorbs best around 430 nm (purple/blue) and at about 680 nm (red) of the light spectrum (10.2, 10.6, 10.7) (2) Chlorophyll b - absorbs best around 470 nm (blue) and at about 660 nm (orange/red) of the light spectrum (10.2, 10.6, 10.7)

Less than ____% of all water absorbed by plants used in ____. •Most of remainder ____ or incorporated into plant ____. ____ is the source* of electrons in photosynthesis and oxygen is released as by-____. If ____ is in ____ supply or ____ intensities too ____, stomata close and thus reduce supply of ____ ____ available for photosynthesis.

Less than 1% of all water absorbed by plants used in photosynthesis. •Most of remainder transpired or incorporated into plant materials. Water is the source* of electrons in photosynthesis and oxygen is released as by-product. If water is in short supply or light intensities too high, stomata close and thus reduce supply of carbon dioxide available for photosynthesis.

Pathway of electrons From photosystem II to photosystem I: PSII -> ____ -> ____ -> ____ ____ ____ -> ____ -> photosystem I From photosystem I to NADP reductase: Photosystem I -> ____ ____ -> ____ -> ____ ____ -> NADP reductase

Pathway of electrons From photosystem II to photosystem I: PSII -> pheophytin -> plastoquinone -> cytochrome b6f complex -> plastocyanin -> photosystem I From photosystem I to NADP reductase: Photosystem I -> Fe-S complex -> ferrodoxin -> FAD complex -> NADP reductase

Photosystem I = chlorophyll ____, small amount of chlorophyll ____, ____ pigment, and ____ •P700 = ____-____ molecule - Only one that actually can use ____ energy •Remaining pigments = ____ pigments -Gather and pass light energy to ____ center •Iron-sulfur proteins - ____ electron acceptors, ____ to receive electrons from P700

Photosystem I = chlorophyll a, small amount of chlorophyll b, carotenoid pigment, and P700 •P700 = reaction-center molecule - Only one that actually can use light energy •Remaining pigments = antenna pigments -Gather and pass light energy to reaction center •Iron-sulfur proteins - Primary electron acceptors, first to receive electrons from P700

Photosystem II = chlorophyll ____, B-____, small amounts of chlorophyll ____, and reaction-center molecule: ____ Pheophytin (Pheo) - ____ electron acceptor see image on slide 25, 26

Photosystem II = chlorophyll a, B-carotene, small amounts of chlorophyll b, and reaction-center molecule: P680 Pheophytin (Pheo) - Primary electron acceptor

Plants absorb VERY LITTLE light in the green portion (____-____ nm) of the light spectrum -> This is why plants are ____! The chlorophyll ____ the green light and, of course, that is what we ____ (10.2)

Plants absorb VERY LITTLE light in the green portion (500-600 nm) of the light spectrum -> This is why plants are green! The chlorophyll reflects the green light and, of course, that is what we see (10.2)

Several types of chlorophyll molecules •____ end captures ____. •____ tail anchors into ____ membrane. • •Most plants contain chlorophyll a (____-____ color) and chlorophyll b (____-____ color). -Chlorophyll b transfers ____ from ____ to chlorophyll a. oMakes it possible for ____ to occur over broader spectrum of light

Several types of chlorophyll molecules •Magnesium end captures light. •Lipid tail anchors into thylakoid membrane. • •Most plants contain chlorophyll a (blue-green color) and chlorophyll b (yellow-green color). -Chlorophyll b transfers energy from light to chlorophyll a. oMakes it possible for photosynthesis to occur over broader spectrum of light

Two types of photosynthetic units: photosystem I and photosystem II. •Events of photosystem ____ come before those of photosystem ____, in sequence. •Both can produce ____. •Only organisms with both photosystem I and photosystem II can produce ____ and ____ as a consequence of ____ flow.

Two types of photosynthetic units: photosystem I and photosystem II. •Events of photosystem II come before those of photosystem I, in sequence. •Both can produce ATP. •Only organisms with both photosystem I and photosystem II can produce NADPH and oxygen as a consequence of electron flow.

Reduction

gain of electrons

Oxidation

loss of electrons

Photosynthetically Active Pigment Absorption see image on slide 10

see image

Catabolism

•Breaking chemical bonds -Cellular respiration reactions - Release energy held in chemical bonds by breaking down carbohydrates, producing carbon dioxide and water

Anabolism

•Forming chemical bonds to build molecules -Photosynthesis reactions - Store energy by constructing carbohydrates by combining carbon dioxide and water

•____ of one compound usually ____ with ____ of another compound, catalyzed by same enzyme or enzyme complex. •____ atom is ____ during oxidation and ____ during reduction. •____ is usually final acceptor of electron.

•Oxidation of one compound usually coupled with reduction of another compound, catalyzed by same enzyme or enzyme complex. •Hydrogen atom is lost during oxidation and gained during reduction. •Oxygen is usually final acceptor of electron.

Carbon dioxide reaches chloroplasts in what and how? see image on slide 6

reaches chloroplasts in mesophyll cells by diffusing through stomata into leaf interior.

About ____% of radiant energy received on earth is in form of ____ light. •____ to ____ and ____-____ to ____ wavelengths are used more extensively. •Green light is ____. •Leaves commonly absorb about ____% of visible light reaching them. •Light intensity varies with time of ____, ____, ____, ____, and _____ composition. see image on slide 8 & 9

About 40% of radiant energy received on earth is in form of visible light. •Violet to blue and red-orange to red wavelengths are used more extensively. •Green light is reflected. •Leaves commonly absorb about 80% of visible light reaching them. •Light intensity varies with time of day, season, altitude, latitude, and atmospheric composition.

C4 Plants (10.12) (1) The first stable fixed carbon compound contains ____ (4) carbons, not three. (2) ____ is fixed in the mesophyll cell - into a four carbon molecule called malate; there is usually ____ RuBisCO located in the mesophyll cells (a) Carbon dioxide is fixed by being joined to a molecule called ____ (PEP) by the enzyme ____ ____ (= PEP carboxylase) (b) The molecule formed by this fixation step is a four-carbon compound called _____ (Mesophyll cells of C4 plants ____ PEP carboxylase but ____ RuBisCO) (b) Oxaloacetate is then converted to ____ (3) Malate is moved to the ____-____ cells where it enters into the Calvin Cycle (a) Please note that C3 plants also have bundle-sheath cells, but these are ____ used for carbon fixation at all (b) Furthermore, C4 plants exhibit ____ anatomy - the bundle-sheath cells have a ____ arrangement of chloroplasts (many ____ than in mesophyll cells) ("kranz" is a German word meaning "____" - cells look like they contain a "wreath" of chloroplasts) (c) Malate is broken down to release ____ ____ and ____ - which will then enter the normal Calvin Cycle (but only in the ____-____ cells) - The released ____ goes back to the ____ cells to be ____ in the fixation of carbon dioxide (d) ____ is found in abundance in the bundle-sheath cells Thus, carbon dioxide is highly _____ in the bundle-sheath cells where the RuBisCO is located. So, it is more likely that RuBisCO binds ____ ____ and NOT ____, greatly decreasing the chances of ____. (4) This process is found in many ____ angiosperms or angiosperms adapted to ____, ____ climates (especially members of the grass family and the sedge family) Most C4 plants are ____, including corn, sorghum, and sugarcane (three very economically important crop plants). (5) ____ ____ does not react with oxygen, so the initial carbon fixation always works; no need to "worry" about the enzyme combining with ____ and losing carbon as CO2 is always fixed (and NEVER oxygen) (6) Once carbon is ____, the organic compound moves to the ____-____cells where carbon dioxide is liberated and it can ____ the Calvin Cycle à à this is a way for the plant to maximize its carbon dioxide so as to saturate RuBisCO; thus, if there is lots of carbon dioxide in the bundle-sheath cells and very little oxygen, then RuBisCO is extremely likely to combine with ____ ____ In other words, NO photorespiration, which means no lost ____ and no wasted ____ (7) C4 plants can fix carbon dioxide until the internal concentrations of CO2 near ____; this enables them to thrive in ____, ____ climates where stomates may have to close during much of the day and carbon dioxide is not taken in (a) C4 photosynthesis is most likely an ____ that evolved in plants located in ____ climates; it may have evolved during the period of earth's history when carbon dioxide concentrations ____ considerably (____-____ million years ago) à this might have given ____ plants a selective advantage over ____ plants in hot, dry climates (b) In hot, dry climates, C4 plants can ____ C3 plants; in these types of climates, C4 plants can produce more ____ than C3 plants (that is, more ____ can be fixed) à this translates into higher yields for farmers (8) So, why don't all plants use C4 photosynthesis?? (a) if C3 plants are given adequate ____ and ____ temperatures, they can usually fix carbon at the same levels as ____ plants (this is normally an ideal ____ situation, though) At moderate temperatures (EX: ~ ____°C), RuBisCO preferentially binds to carbon dioxide EX: At these moderate temperatures, the carboxylase reaction occurs at a much ____ rate than the oxygenase reaction (carboxylase rxn is ____ times more likely to occur) (b) This is why C4 plants don't ____ our landscape à in ____ climates (such as we have here in Kentucky), with adequate ____ and more moderate ____, C4 plants ____ outcompete C3 plants (c) C4 photosynthesis is ____ expensive: it takes about ____ ATP for a C4 plant to fix carbon vs. approximately ____ ATP in a C3 plant; so, when conditions are not hot and dry, the C4 plants expend a ____ amount of energy to get the ____ amount of plant biomass that a C3 plant produces with about ____ the energy cost Thus, it is too energetically expensive for a plant to conduct C4 photosynthesis in a ____ climate (or any climate outside of tropical and subtropical regions) So, in temperate climates, which ____ the global terrestrial environment. RuBisCO will ____ fix carbon dioxide, and not oxygen, in most situations thus greatly reducing the occurrence of ____

C4 Plants (10.12) (1) The first stable fixed carbon compound contains four (4) carbons, not three. (2) Carbon is fixed in the mesophyll cell - into a four carbon molecule called malate; there is usually NO RuBisCO located in the mesophyll cells (a) Carbon dioxide is fixed by being joined to a molecule called phsosphoenolpyruvate (PEP) by the enzyme phosphoenolpyruvate carboxylase (= PEP carboxylase) (b) The molecule formed by this fixation step is a four-carbon compound called oxaloacetate (Mesophyll cells of C4 plants contain PEP carboxylase but NO RuBisCO) (b) Oxaloacetate is then converted to malate (3) Malate is moved to the bundle-sheath cells where it enters into the Calvin Cycle (a) Please note that C3 plants also have bundle-sheath cells, but these are NOT used for carbon fixation at all (b) Furthermore, C4 plants exhibit Kranz anatomy - the bundle-sheath cells have a dense arrangement of chloroplasts (many more than in mesophyll cells) ("kranz" is a German word meaning "wreath" - cells look like they contain a "wreath" of chloroplasts) (c) Malate is broken down to release carbon dioxide and PEP - which will then enter the normal Calvin Cycle (but only in the bundle-sheath cells) - The released PEP goes back to the mesophyll cells to be reused in the fixation of carbon dioxide (d) RuBisCO is found in abundance in the bundle-sheath cells Thus, carbon dioxide is highly concentrated in the bundle-sheath cells where the RuBisCO is located. So, it is more likely that RuBisCO binds carbon dioxide and NOT oxygen, greatly decreasing the chances of photorespiration. (4) This process is found in many tropical angiosperms or angiosperms adapted to hot, dry climates (especially members of the grass family and the sedge family) Most C4 plants are monocots, including corn, sorghum, and sugarcane (three very economically important crop plants). (5) PEP carboxylase does not react with oxygen, so the initial carbon fixation always works; no need to "worry" about the enzyme combining with oxygen and losing carbon as CO2 is always fixed (and NEVER oxygen) (6) Once carbon is fixed, the organic compound moves to the bundle-sheath cells where carbon dioxide is liberated and it can enter the Calvin Cycle à à this is a way for the plant to maximize its carbon dioxide so as to saturate RuBisCO; thus, if there is lots of carbon dioxide in the bundle-sheath cells and very little oxygen, then RuBisCO is extremely likely to combine with carbon dioxide In other words, NO photorespiration, which means no lost carbon and no wasted energy (7) C4 plants can fix carbon dioxide until the internal concentrations of CO2 near 0; this enables them to thrive in hot, dry climates where stomates may have to close during much of the day and carbon dioxide is not taken in (a) C4 photosynthesis is most likely an adaptation that evolved in plants located in tropical climates; it may have evolved during the period of earth's history when carbon dioxide concentrations dropped considerably (50-60 million years ago) à this might have given C4 plants a selective advantage over C3 plants in hot, dry climates (b) In hot, dry climates, C4 plants can outcompete C3 plants; in these types of climates, C4 plants can produce more biomass than C3 plants (that is, more carbon can be fixed) à this translates into higher yields for farmers (8) So, why don't all plants use C4 photosynthesis?? (a) if C3 plants are given adequate water and cooler temperatures, they can usually fix carbon at the same levels as C4 plants (this is normally an ideal laboratory situation, though) At moderate temperatures (EX: ~ 25°C), RuBisCO preferentially binds to carbon dioxide EX: At these moderate temperatures, the carboxylase reaction occurs at a much higher rate than the oxygenase reaction (carboxylase rxn is 4 times more likely to occur) (b) This is why C4 plants don't dominate our landscape à in temperate climates (such as we have here in Kentucky), with adequate rainfall and more moderate temperatures, C4 plants cannot outcompete C3 plants (c) C4 photosynthesis is energetically expensive: it takes about 60 ATP for a C4 plant to fix carbon vs. approximately 36 ATP in a C3 plant; so, when conditions are not hot and dry, the C4 plants expend a high amount of energy to get the same amount of plant biomass that a C3 plant produces with about half the energy cost Thus, it is too energetically expensive for a plant to conduct C4 photosynthesis in a temperate climate (or any climate outside of tropical and subtropical regions) So, in temperate climates, which dominate the global terrestrial environment. RuBisCO will preferentially fix carbon dioxide, and not oxygen, in most situations thus greatly reducing the occurrence of photorespiration

4-Carbon pathway - Produces ____-carbon compound instead of ____-carbon PGA during initial steps of light-independent reactions •C4 plants - ____ grasses and plants of ____ regions •Plants have ____ anatomy. -Mesophyll cells with ____ chloroplasts with well-developed ____ -Bundle sheath cells with ____ chloroplasts with numerous ____ grains •CO2 converted to organic acids in ____ cells. -PEP (phosphoenolpyruvate) and CO2 combine, with aid of ____ ____. -Form 4-carbon, ____ acid, instead of PGA -PEP carboxylase converts CO2 to carbohydrate at ____ CO2 concentrations than does ____. oNot ____ to O2, no ____ •CO2 is transported as organic acids to ____ ____ cells, is released and enters Calvin cycle. -CO2 concentration high in bundle sheath, thus ____ minimized. -C4 plants ____ at higher temperatures than C3 plants. -At low temperatures, C3 more ____ . oCosts about ____ ATP for C4 photosynthesis.

4-Carbon pathway - Produces 4-carbon compound instead of 3-carbon PGA during initial steps of light-independent reactions •C4 plants - Tropical grasses and plants of arid regions •Plants have Kranz anatomy. -Mesophyll cells with smaller chloroplasts with well-developed grana -Bundle sheath cells with large chloroplasts with numerous starch grains •CO2 converted to organic acids in mesophyll cells. -PEP (phosphoenolpyruvate) and CO2 combine, with aid of PEP carboxylase. -Form 4-carbon, oxaloacetic acid, instead of PGA -PEP carboxylase converts CO2 to carbohydrate at lower CO2 concentrations than does RuBisCO. oNot sensitive to O2, no photorespiration •CO2 is transported as organic acids to bundle sheath cells, is released and enters Calvin cycle. -CO2 concentration high in bundle sheath, thus photorespiration minimized. -C4 plants photosynthesize at higher temperatures than C3 plants. -At low temperatures, C3 more efficient . oCosts about 2x ATP for C4 photosynthesis.

Photosynthesis Equation!

6CO2+12H2O + light -> C6H12O6+6O2+6H2O -Many intermediate steps to process, and glucose is not immediate first product.

A closer look: light-dependent reactions ____ - Water-splitting, Photosystem II •Light ____ absorbed by P680, which boosts electrons to ____ energy level. •Electrons passed to acceptor molecule, ____, then to PQ (____), then along electron transport system to photosystem ____. •Electrons extracted from ____ ____ electrons lost by P680. •____ molecule of oxygen, 4 protons and 4 electrons produced from ___ water molecules. Electron flow and photophosphorylation •Electron transport system consists of ____, other electron transfer molecules and ____. •____ move across thylakoid membrane by ____. •____ - ATP is formed from ADP.

A closer look: light-dependent reactions Photolysis - Water-splitting, Photosystem II •Light photons absorbed by P680, which boosts electrons to higher energy level. •Electrons passed to acceptor molecule, pheophytin, then to PQ (plastoquinone), then along electron transport system to photosystem I. •Electrons extracted from water replace electrons lost by P680. •One molecule of oxygen, 4 protons and 4 electrons produced from two water molecules. Electron flow and photophosphorylation •Electron transport system consists of cytochromes, other electron transfer molecules and plastocyanin. •Photons move across thylakoid membrane by chemiosmosis. •Phosphorylation - ATP is formed from ADP.

A closer look: light-dependent reactions Photosystem I •____ absorbed by P700, which boosts electrons to ____ energy level. •Electrons passed to iron-sulfur acceptor molecule, Fd (____), then to FAD (flavin adenine dinucleotide). •NADP reduced to ____. •Electrons removed from P700 ____ by electrons from ____ ____.

A closer look: light-dependent reactions Photosystem I •Light absorbed by P700, which boosts electrons to higher energy level. •Electrons passed to iron-sulfur acceptor molecule, Fd (ferredoxin), then to FAD (flavin adenine dinucleotide). •NADP reduced to NADPH. •Electrons removed from P700 replaced by electrons from photosystem II.

All of the world's photosynthetic organisms produce between ____ and ____ ____ metric tons of sugars per year. -- 1 ton = ____ pounds -- 100,000,000,000 x 2,000 = 200,000,000,000,000 lbs. (= 200 ____ pounds of sugar per year) Or, 2 ____ railroad coal cars (which hold about 50 tons of coal)

All of the world's photosynthetic organisms produce between 100 and 200 billion metric tons of sugars per year. -- 1 ton = 2000 pounds -- 100,000,000,000 x 2,000 = 200,000,000,000,000 lbs. (= 200 trillion pounds of sugar per year) Or, 2 BILLION railroad coal cars (which hold about 50 tons of coal)

C3 Plants (1) These plants have the carbon fixation pathway that we have just discussed: carbon dioxide combines with ____ to form two molecules of ____ (PGA), each of which contains ____ (3) carbons (this is why it is referred to as C3 photosynthesis - the first ____ carbon compound formed after fixation contains three carbons) (2) This pathway occurs in the chloroplasts of ____ cells (primarily, the ____ ____); these mesophyll cells, of course, contain RuBisCO (3) We basically live in a C3 world: all ____, all ____ (= the ____ plants, such as mosses), all ____, and the majority of ____ (including all ____ angiosperms) have the C3 pathway App. ____% of known plant species are C3 plants.

C3 Plants (1) These plants have the carbon fixation pathway that we have just discussed: carbon dioxide combines with RuBP to form two molecules of 3-phosphoglycerate (PGA), each of which contains three (3) carbons (this is why it is referred to as C3 photosynthesis - the first stable carbon compound formed after fixation contains three carbons) (2) This pathway occurs in the chloroplasts of mesophyll cells (primarily, the palisade mesophyll); these mesophyll cells, of course, contain RuBisCO (3) We basically live in a C3 world: all gymnosperms, all bryophytes (= the nonvascular plants, such as mosses), all algae, and the majority of angiosperms (including all woody angiosperms) have the C3 pathway App. 85% of known plant species are C3 plants.

CAM (____ ____ Metabolism) (10.13) (1) CAM plants include mostly ____ (in our flora), such as species of ____, jade plants (Crassula spp.), Sedum, Kalanchoe, Agave, and ____; please be aware, though, that all CAM plants are ____ succulents (as in the case of ____ and Spanish moss, for example) (2) These plants take up carbon dioxide and fix it at ____; the carbon is then stored overnight and enters the Calvin Cycle the next ____ Why would these plants "want" to open their stomata at night and take up carbon dioxide then? To minimize ____ loss - if you are a plant living in a hot, dry climate, it is very disadvantageous to open your stomata during the day due to the potential for MAJOR water loss It would be much MORE advantageous to the plant to open stomata at ____ so that the amount of water loss is much, much less (3) CAM plants basically have the ____ pathway of carbon fixation; however, the separation of carbon fixation and reduction does not occur in ____ different cell types, but, rather, it is a ____ separation (a) the entire process occurs in one cell type: the ____ (CAM plant cells possess BOTH ____ and ____ ____) (b) carbon is initially fixed into ____ at night and stored in the plant overnight (stored in ____) (c) malate is split apart the next day and carbon dioxide is ____; this carbon dioxide then enters into the normal ____ ____ The plant "waits" until the next ____ to proceed with the Calvin Cycle since the cycle requires the products of the ____-____ reactions to function properly; the light-dependent reactions can only occur during the ____ so the plant holds on to its malate overnight, "waiting" for the light-independent reactions to resume the next day (d) CAM photosynthesis is more widespread than C4 photosynthesis; it occurs in ____, ____, and many ____ plant groups (e) CAM plants are typically very ____ growing due to a ____ carbon dioxide supply; however, in arid conditions, they have an enormous advantage in ____ conservation over other species

CAM (Crassulacean Acid Metabolism) (10.13) (1) CAM plants include mostly succulents (in our flora), such as species of cacti, jade plants (Crassula spp.), Sedum, Kalanchoe, Agave, and Aloe; please be aware, though, that all CAM plants are not succulents (as in the case of pineapple and Spanish moss, for example) (2) These plants take up carbon dioxide and fix it at night; the carbon is then stored overnight and enters the Calvin Cycle the next day Why would these plants "want" to open their stomata at night and take up carbon dioxide then? To minimize water loss - if you are a plant living in a hot, dry climate, it is very disadvantageous to open your stomata during the day due to the potential for MAJOR water loss It would be much MORE advantageous to the plant to open stomata at night so that the amount of water loss is much, much less (3) CAM plants basically have the C4 pathway of carbon fixation; however, the separation of carbon fixation and reduction does not occur in two different cell types, but, rather, it is a temporal separation (a) the entire process occurs in one cell type: the mesophyll (CAM plant cells possess BOTH RuBisCO and PEP carboxylase) (b) carbon is initially fixed into malate at night and stored in the plant overnight (stored in vacuole) (c) malate is split apart the next day and carbon dioxide is liberated; this carbon dioxide then enters into the normal Calvin Cycle The plant "waits" until the next day to proceed with the Calvin Cycle since the cycle requires the products of the light-dependent reactions to function properly; the light-dependent reactions can only occur during the daytime so the plant holds on to its malate overnight, "waiting" for the light-independent reactions to resume the next day (d) CAM photosynthesis is more widespread than C4 photosynthesis; it occurs in monocots, dicots, and many primitive plant groups (e) CAM plants are typically very slow growing due to a limited carbon dioxide supply; however, in arid conditions, they have an enormous advantage in water conservation over other species

CAM photosynthesis - Similar to C4 photosynthesis in that ____-carbon compounds produced during light-independent reactions, however: •Organic acids accumulate at ____ (____ open). •Converted back to CO2 during ____ for use in Calvin cycle (____ closed) -Allows plants to function well under limited ____ supply, as well as high ____ intensity.

CAM photosynthesis - Similar to C4 photosynthesis in that 4-carbon compounds produced during light-independent reactions, however: •Organic acids accumulate at night (stomata open). •Converted back to CO2 during day for use in Calvin cycle (stomata closed) -Allows plants to function well under limited water supply, as well as high light intensity.

Calvin cycle •Six molecules of ____ combine with six molecules of RuBP (____ ____) with aid of RuBisCO. •RuBisCO = ____ ____ ____/____ •Forms a highly unstable ____ that is rapidly hydrolyzed into two 3-carbon molecules à •Resulting in two 3-carbon molecules of 3PGA (____ ____), which is a chemically ____ molecule . •The enzyme ____ ____ converts PGA to ____ •NADPH and ATP supply energy and electrons that reduce ____ to GA3P (____ ____), or G3P or PGAL. Accomplished by the enzyme ____ ____ •Ten of the twelve PGAL molecules are restructured, using 6 ATP, into six ____-carbon ____ molecules. •Net gain of 2 PGAL, which can be converted to ____ or used to make ____ and ____ ____ (see images on 40, 41, 44, 45)

Calvin cycle •Six molecules of CO2 combine with six molecules of RuBP (ribulose 1,5-bisphosphate) with aid of RuBisCO. •RuBisCO = ribulose 1,5-bisphosphate carboxylase/oxygenase •Forms a highly unstable hexose that is rapidly hydrolyzed into two 3-carbon molecules à •Resulting in two 3-carbon molecules of 3PGA (3-phosphoglyceric acid), which is a chemically stable molecule . •The enzyme phosphoglycerate kinase converts PGA to 1,3-bisphosphoglycerate •NADPH and ATP supply energy and electrons that reduce 1,3-bisphosphoglycerate to GA3P (glyceraldehyde 3-phosphate), or G3P or PGAL. Accomplished by the enzyme glyceraldehye-3-phosphate dehydrogenase •Ten of the twelve PGAL molecules are restructured, using 6 ATP, into six 5-carbon RuBP molecules. •Net gain of 2 PGAL, which can be converted to carbohydrates or used to make lipids and amino acids

Cyclic Electron Flow (A) Plants also have an additional ATP-generating mechanism other than noncyclic electron flow: ____ ____ ____ (1) Sometimes, electrons that have left photosystem I do ____ move on to ____ ____ (2) Instead, ferrodoxin will transport the electron to the ____ ____ ____ (instead of moving it farther down the chain towards NADP reductase) (3) The cytochrome complex then gives the electron to ____, which returns the electron back to photosystem ____ In this way, the flow of electrons is "____" à the electron ends up at the same chlorophyll molecule from which it ____ (4) Cyclic electron flow generates some ____ (a) It does NOT produce any ____ or ____ So, a plant ____ use only cyclic electron flow (b) Provides additional ATP molecules to power ____ (especially the Calvin Cycle) (5) Cyclic flow is thought to be a left-over mechanism from the very ____ photosynthesizers (Some bacteria ____ photosynthesize using cyclic flow) (a) Remember, plants have to use noncyclic flow in addition to cyclic flow à ____ MUST be produced for sugars to be made, otherwise photosynthesis is ____ to the plant (b) Cyclic electron flow has ____ been observed in all plant species; for the species in which it does occur, it always does so along with ____ flow (again, NO plant ever does ____ cyclic flow - it did, it would NOT survive)

Cyclic Electron Flow (A) Plants also have an additional ATP-generating mechanism other than noncyclic electron flow: cyclic electron flow (1) Sometimes, electrons that have left photosystem I do NOT move on to NADP reductase (2) Instead, ferrodoxin will transport the electron to the cytochorme b6/f complex (instead of moving it farther down the chain towards NADP reductase) (3) The cytochrome complex then gives the electron to plastocyanin, which returns the electron back to photosystem I In this way, the flow of electrons is "cyclic" à the electron ends up at the same chlorophyll molecule from which it departed (4) Cyclic electron flow generates some ATP (a) It does NOT produce any NADPH or oxygen So, a plant cannot use only cyclic electron flow (b) Provides additional ATP molecules to power photosynthesis (especially the Calvin Cycle) (5) Cyclic flow is thought to be a left-over mechanism from the very earliest photosynthesizers (Some bacteria only photosynthesize using cyclic flow) (a) Remember, plants have to use noncyclic flow in addition to cyclic flow à NADPH MUST be produced for sugars to be made, otherwise photosynthesis is useless to the plant (b) Cyclic electron flow has not been observed in all plant species; for the species in which it does occur, it always does so along with noncyclic flow (again, NO plant ever does ONLY cyclic flow - it did, it would NOT survive)

Each pigment has its own distinctive pattern of light absorption = ____ ____ spectrum. •When pigments absorb ____, energy levels of electrons are ____. -Energy from an excited electron is ____ when it drops back to its ____ state. -In photosynthesis, energy is stored in ____ bonds. see image on slide 22

Each pigment has its own distinctive pattern of light absorption = pigment's absorption spectrum. •When pigments absorb light, energy levels of electrons are raised. -Energy from an excited electron is released when it drops back to its ground state. -In photosynthesis, energy is stored in chemical bonds.

Energy for most cellular activity involves ____ ____ (____) •Plants make ____ using ____ as an energy source. -Takes place in ____ and other ____ parts of the organisms

Energy for most cellular activity involves adenosine triphosphate (ATP) •Plants make ATP using light as an energy source. -Takes place in chloroplasts and other green parts of the organisms

If light and temperatures too ____- Ratio of carbon dioxide to oxygen inside leaves may ____. •Accelerates ____, which uses ____ and wastes ____ ____ -Carbon dioxide is wasted as it does not enter into the ____ ____ -Very ____ expensive for the plant to recover this lost ____

If light and temperatures too high - Ratio of carbon dioxide to oxygen inside leaves may change. •Accelerates photorespiration, which uses oxygen and wastes carbon dioxide -Carbon dioxide is wasted as it does not enter into the Calvin Cycle -Very energetically expensive for the plant to recover this lost carbon

If light intensity too ____- ____ occurs, which results in destruction of ____. If water in short ____ or light intensities too ____, stomata ____ and thus reduce supply of carbon dioxide available for ____.

If light intensity too high - photooxidation occurs, which results in destruction of chlorophyll. If water in short supply or light intensities too high, stomata close and thus reduce supply of carbon dioxide available for photosynthesis.

Light - Dependent Rxns ("Light" Rxns.) - occur in the membranes of the ____ in chloroplasts (10.8, 10.9) - most photosynthesis takes place in the ____ ____ cells of the leaves (app. 50 to 200 chloroplasts per cell, which averages out to ~ ____ chloroplasts per square ____ of leaf) (1) ____ energy is "captured" by ____ located on the thylakoid membranes. This "____" electrons by ____ them. (2) ____ move through an electron transport system, from one ____ to the next. (3) The movement of electrons drives the production of ____ and ____ (both of which are used in the next set of rxns) (4) ____ is released as a byproduct. Plants produce a tremendous amount of oxygen per year as a byproduct of photosynthesis. For example, a fully mature oak tree may produce enough oxygen to sustain a family of ____ for nearly a full ____.

Light - Dependent Rxns ("Light" Rxns.) - occur in the membranes of the thylakoids in chloroplasts (10.8, 10.9) - most photosynthesis takes place in the palisade mesophyll cells of the leaves (app. 50 to 200 chloroplasts per cell, which averages out to ~ 500,000 chloroplasts per square mm of leaf) (1) Solar energy is "captured" by photosystems located on the thylakoid membranes. This "excites" electrons by energizing them. (2) Electrons move through an electron transport system, from one carrier to the next. (3) The movement of electrons drives the production of ATP and NADPH (both of which are used in the next set of rxns) (4) Oxygen is released as a byproduct. Plants produce a tremendous amount of oxygen per year as a byproduct of photosynthesis. For example, a fully mature oak tree may produce enough oxygen to sustain a family of four for nearly a full year.

Light - Independent Rxns ("Dark" Rxns., or the Calvin Cycle) - occur in the ____ of the chloroplast (10.5, 10.9, 10.10) (1) ____ ____ is taken up by the plant (2) ATP and NADPH act on carbon dioxide (via the activity of numerous enzymes) to convert it to a ____ These carbohydrates are used by the plant for various functions, especially making more plant (that is, ____ = making more parts); of course, other organisms benefit from these compounds as well as they depend on them, primarily, for ____ (3) ____ and ____ cycle back to be used in the light-dependent rxns

Light - Independent Rxns ("Dark" Rxns., or the Calvin Cycle) - occur in the stroma of the chloroplast (10.5, 10.9, 10.10) (1) Carbon dioxide is taken up by the plant (2) ATP and NADPH act on carbon dioxide (via the activity of numerous enzymes) to convert it to a carbohydrate These carbohydrates are used by the plant for various functions, especially making more plant (that is, growth = making more parts); of course, other organisms benefit from these compounds as well as they depend on them, primarily, for FOOD (3) ADP and NADP cycle back to be used in the light-dependent rxns

Light-Independent Reactions (= Calvin Cycle) -- Three basic phases of the Calvin Cycle (10.10) (A) The first step of the Calvin Cycle is carbon dioxide ____ à converting carbon dioxide into a ____ multicarbon compound (1) Carbon dioxide combines with ____ ____ (RuBP), a ____ carbon molecule, to form a ____ carbon molecule. (a) The enzyme that accomplishes this task is called ____ ____ ____/____ (aka RuBisCO) (b) RuBisCO is the most ____ protein in the world; every person on earth is supported by ____ kg of RuBisCO (= ____ lbs. !!) (2) The six carbon molecule immediately splits into two 3-carbon molecules called ____, or phosphoglyceric acid (PGA). The PGA molecules continue on in the Calvin Cycle. (B) Carbon Dioxide ____ (1) The PGA molecules undergo reduction reactions in which they ____ electrons from ____; the NADP+ then returns to the thylakoid and is ____ in the light-dependent reactions (a) PGA is phosphorylated by the enzyme ____ ____ to produce ____ (in other words, PGA is reduced to 1,3-bisphosphoglycerate) (b) 1,3-bisphosphoglycerate is then reduced as the enzyme ____ ____ ____ adds electrons from NADPH (c) ATP provides the energy for these ____ reactions. ATP is oxidized to ____, and the ADP also returns to the thylakoids to be ____ in the light-dependent reactions. (2) During the reduction reactions, PGA is ultimately converted to ____ (PGAL), also known as G3P. (3) PGAL can be converted to numerous other ____ molecules. (a) PGAL can be converted to ____ (three carbon sugar with a phosphate attached), which is the starting point for the synthesis of ____ and ____ (b) Glucose-phosphate can also be joined to ____ to form ____ (mobile energy) (c) PGAL can also be used to synthesize ____ acids and ____ acids. (C) RuBP ____ (1) All PGAL is not converted to organic compounds; some is converted to ____ and then back to ____ (2) RuBP remains in the Calvin Cycle and will combine with ____ ____ once again to form PGA. (3) Note that conversion of PGAL to RuBP requires ____. VIII. RuBisCO (A) RuBisCO is actually a "____" enzyme and sometimes doesn't do a good job with respect to carbon fixation (1) The problem is that RuBisCO will bind to both ____ ____ and ____. (a) If carbon dioxide levels inside the leaves are ____ (what would cause this problem?), then the carbon dioxide/oxygen ratio is very ____. (b) In these conditions, RuBisCO will bind to oxygen and a process called ____ occurs. (c) This is a BIG problem for many of the crop plants (and for plants, in general) of the world as it wastes carbon - decreases yield resulting in ____, ____, and ____ (2) During photorespiration, oxygen combines with RuBP to form a compound called ____. (a) Phosphoglycolate does ____ stay in the Calvin cycle. The cell has to expend ____ to recover this carbon so that it can be used in the cycle; while some of the carbon dioxide may enter back into the Calvin cycle, for most plants, as much as ____% of the carbon previously fixed may escape from the plant (b) Photorespiration not only wastes carbon, but it also produces no ____; it squanders much of the carbon previously fixed by the plant, and, at the same time, at a great energy expense to the Calvin Cycle Thus, photorespiration is a very ____ process. (c) Photorespiration is thought to be a genetic relict from a time long ago when the earth's atmosphere contained much more ____ ____ (and much less oxygen) than it does now. At that time, plants did not need to "____" about photorespiration. (d) Some plants have a very interesting way to avoid the disadvantages posed by photorespiration. They have a method of fixing carbon that greatly minimizes the amount of carbon lost to photorespiration. These plants are called ____ plants

Light-Independent Reactions (= Calvin Cycle) -- Three basic phases of the Calvin Cycle (10.10) (A) The first step of the Calvin Cycle is carbon dioxide fixation à converting carbon dioxide into a non-gaseous multicarbon compound (1) Carbon dioxide combines with ribulose 1,5 -bisphosphate (RuBP), a five carbon molecule, to form a 6 carbon molecule. (a) The enzyme that accomplishes this task is called ribulose 1,5-bisphospate carboxylase- oxygenase (aka RuBisCO) (b) RuBisCO is the most abundant protein in the world; every person on earth is supported by 44 kg of RuBisCO (= 97 lbs. !!) (2) The six carbon molecule immediately splits into two 3-carbon molecules called 3-phosphoglycerate, or phosphoglyceric acid (PGA). The PGA molecules continue on in the Calvin Cycle. (B) Carbon Dioxide Reduction (1) The PGA molecules undergo reduction reactions in which they gain electrons from NADPH; the NADP+ then returns to the thylakoid and is reused in the light-dependent reactions (a) PGA is phosphorylated by the enzyme 3-phosphoglycerate kinase to produce 1,3 - bisphosphoglycerate (in other words, PGA is reduced to 1,3-bisphosphoglycerate) (b) 1,3-bisphosphoglycerate is then reduced as the enzyme glyceraldehyde 3-phosphate dehydrogenase adds electrons from NADPH (c) ATP provides the energy for these endergonic reactions. ATP is oxidized to ADP, and the ADP also returns to the thylakoids to be used in the light-dependent reactions. (2) During the reduction reactions, PGA is ultimately converted to glyceraldehyde-3-phosphate (PGAL), also known as G3P. (3) PGAL can be converted to numerous other organic molecules. (a) PGAL can be converted to triose-phosphate (three carbon sugar with a phosphate attached), which is the starting point for the synthesis of starch and cellulose (b) Glucose-phosphate can also be joined to fructose to form sucrose (mobile energy) (c) PGAL can also be used to synthesize fatty acids and amino acids. (C) RuBP Regeneration (1) All PGAL is not converted to organic compounds; some is converted to triose-phosphate and then back to RuBP (2) RuBP remains in the Calvin Cycle and will combine with carbon dioxide once again to form PGA. (3) Note that conversion of PGAL to RuBP requires ATP. VIII. RuBisCO (A) RuBisCO is actually a "sloppy" enzyme and sometimes doesn't do a good job with respect to carbon fixation (1) The problem is that RuBisCO will bind to both carbon dioxide and oxygen. (a) If carbon dioxide levels inside the leaves are low (what would cause this problem?), then the carbon dioxide/oxygen ratio is very low. (b) In these conditions, RuBisCO will bind to oxygen and a process called photorespiration occurs. (c) This is a BIG problem for many of the crop plants (and for plants, in general) of the world as it wastes carbon - decreases yield resulting in famine, starvation, and poverty (2) During photorespiration, oxygen combines with RuBP to form a compound called phosphoglycolate. (a) Phosphoglycolate does not stay in the Calvin cycle. The cell has to expend energy to recover this carbon so that it can be used in the cycle; while some of the carbon dioxide may enter back into the Calvin cycle, for most plants, as much as 50% of the carbon previously fixed may escape from the plant (b) Photorespiration not only wastes carbon, but it also produces no ATP; it squanders much of the carbon previously fixed by the plant, and, at the same time, at a great energy expense to the Calvin Cycle Thus, photorespiration is a very wasteful process. (c) Photorespiration is thought to be a genetic relict from a time long ago when the earth's atmosphere contained much more carbon dioxide (and much less oxygen) than it does now. At that time, plants did not need to "worry" about photorespiration. (d) Some plants have a very interesting way to avoid the disadvantages posed by photorespiration. They have a method of fixing carbon that greatly minimizes the amount of carbon lost to photorespiration. These plants are called C-4 plants

Light-dependent reactions: •In ____ membranes of ____ •Water molecules ____ apart, releasing ____ and ____ ions; ____ gas released. •____ pass along electron transport system. •____ produced. •____ is reduced, forming ____ (used in light-independent reactions).

Light-dependent reactions: •In thylakoid membranes of chloroplasts •Water molecules split apart, releasing electrons and hydrogen ions; oxygen gas released. •Electrons pass along electron transport system. •ATP produced. •NADP is reduced, forming NADPH (used in light-independent reactions).

Light-independent reactions: •In ____ of ____ •Utilize ____ and ____ to form sugars •____ cycle -____ ____ combines with ____ (ribulose bisphosphate) and then combined molecules are converted to ____ (glucose). -____ furnished from ATP and NADPH produced during light-dependent reactions. see image on slide 19, 20, 21

Light-independent reactions: •In stroma of chloroplasts •Utilize ATP and NADPH to form sugars •Calvin cycle -Carbon dioxide combines with RuBP (ribulose bisphosphate) and then combined molecules are converted to sugars (glucose). -Energy furnished from ATP and NADPH produced during light-dependent reactions.

Metabolism

Sum of all interrelated biochemical processes in living organisms

TRUE or FALSE: Animals rely on green plants for oxygen, food, shelter and other products.

TRUE

Note that chlorophylls absorb light best in the ____/____ AND ____/____ portions of the light spectrum; the carotenoids absorb best in the upper ____/____ regions; and the anthocyanins absorb best in the ____/____ regions see image on slide 12

Note that chlorophylls absorb light best in the violet/blue AND orange/red portions of the light spectrum; the carotenoids absorb best in the upper blue/green regions; and the anthocyanins absorb best in the yellow/orange regions

Other Significant Processes that Occur in Chloroplast Reduction of sulfate to ____ •Sulfides used to make ____-acids Nitrates converted to ____ •Ammonia used to make ____-acids, for ____ which is stored in ____ and specialized ____

Other Significant Processes that Occur in Chloroplast Reduction of sulfate to sulfide •Sulfides used to make amino-acids Nitrates converted to ammonia •Ammonia used to make amino-acids, for glutamine which is stored in roots and specialized stems

Other photosynthetic pigments include carotenoids (____ and ____), phycobilins (____ or ____, in cyanobacteria and red algae), and several other types of chlorophyll. Anthocyaninis are also present in plants but are not ____ in photosynthesis About 250-400 pigment molecules grouped in light-harvesting complex = ____. •Two types of photosynthetic ____ work together in light-dependent reactions. Two phases of photosynthesis: •Light-____ reactions •Light-____ reactions (AKA Calvin Cycle or "dark" rxns)

Other photosynthetic pigments include carotenoids (yellow and orange), phycobilins (blue or red, in cyanobacteria and red algae), and several other types of chlorophyll. Anthocyaninis are also present in plants but are not involved in photosynthesis About 250-400 pigment molecules grouped in light-harvesting complex = photosystems. •Two types of photosynthetic units work together in light-dependent reactions. Two phases of photosynthesis: •Light-dependent reactions •Light-independent reactions (AKA Calvin Cycle or "dark" rxns)

Photophosporylation (A) The flow of electrons from one protein to another, down the electron transport chain generates some ____ through a process called ____ ____ (1) "Noncyclic" because electron flow is from point A to point B, that is, from ____ to ____ ____; there is NO ____ of electrons (2) "- phosphorylation" refers to the phosphorylation of ____ to make ATP (3) "photo - " refers to the fact that this type of phosphorylation is driven by ____ (B) The cytochrome b6/f complex uses the energy of the electrons moving down the electron transport chain to pump ____ ions across the thylakoid membrane INTO the interior of the thylakoid (called the ____) (1) As the high energy electrons move from carrier to carrier, they lose a little bit of ____ from each move (2) The cytochrome complex uses the energy to pump hydrogen ions across the membrane into the ____. (C) A hydrogen ion ____ builds due to the pumping of hydrogen ions into the lumen (and also due to the splitting of ____ at photosystem ____ - recall that H+ ions are released into the lumen of the thylakoid as a result of the water-splitting process) (D) Hydrogen ions "want" to move down their concentration gradient but cannot ____ through the membrane (E) They flow through the channel found in the ____ ____ complex (1) The ATP synthase complex is formed by several different large ____ (a) Note that like the photosystems, there are ____ ATP synthase complexes found in each thylakoid membrane (2) Part of the complex utilizes the ____ created by the hydrogen ion gradient to form ____ (= part of the complex is an enzyme that can join ADP to inorganic ____) (a) There is a charge ____ across the plasma membrane of the thylakoid - ____ H+ ions inside of the thylakoid in the lumen and many ____ on the outside of the membrane (b) This major charge differential creates what is called an ____ ____, which is a form of ____ energy This gradient was primarily created due to the ____ of electrons down the electron transport chain à the ____ of the electrons are transferred to the electrochemical gradient The electrochemical gradient, in the form of the H+ gradient, is the energy source that the ATP synthase uses to form ATP (= ____ energy is converted to ____ energy) (F) As hydrogen ions flow down their concentration gradient through ATP synthase, ____ is produced (1) About ____ ATP molecules are produced per ____ of photons (One mole of photons can "excite" ____ pairs of electrons, so it takes 6 pairs of electrons to make 6 ATP molecules, and also 6 ____ molecules) (2) Though ATP is produced, plants cannot exist on ATP generated by ____ alone. Basically, photosynthesis generates enough ATP to power itself BUT not other cell ____ processes Thus, plant cells still need to undergo ____ to meet their ATP need.

Photophosporylation (A) The flow of electrons from one protein to another, down the electron transport chain generates some ATP through a process called noncyclic photophosphorylation (1) "Noncyclic" because electron flow is from point A to point B, that is, from photosystem to NADP reductase; there is NO cycling of electrons (2) "- phosphorylation" refers to the phosphorylation of ADP to make ATP (3) "photo - " refers to the fact that this type of phosphorylation is driven by light (B) The cytochrome b6/f complex uses the energy of the electrons moving down the electron transport chain to pump hydrogen ions across the thylakoid membrane INTO the interior of the thylakoid (called the lumen) (1) As the high energy electrons move from carrier to carrier, they lose a little bit of energy from each move (2) The cytochrome complex uses the energy to pump hydrogen ions across the membrane into the lumen. (C) A hydrogen ion concentration builds due to the pumping of hydrogen ions into the lumen (and also due to the splitting of water at photosystem II - recall that H+ ions are released into the lumen of the thylakoid as a result of the water-splitting process) (D) Hydrogen ions "want" to move down their concentration gradient but cannot diffuse through the membrane (E) They flow through the channel found in the ATP synthase complex (1) The ATP synthase complex is formed by several different large proteins (a) Note that like the photosystems, there are multiple ATP synthase complexes found in each thylakoid membrane (2) Part of the complex utilizes the energy created by the hydrogen ion gradient to form ATP (= part of the complex is an enzyme that can join ADP to inorganic phosphate) (a) There is a charge differential across the plasma membrane of the thylakoid - many H+ ions inside of the thylakoid in the lumen and many fewer on the outside of the membrane (b) This major charge differential creates what is called an electrochemical gradient, which is a form of potential energy This gradient was primarily created due to the flow of electrons down the electron transport chain à the energy of the electrons are transferred to the electrochemical gradient The electrochemical gradient, in the form of the H+ gradient, is the energy source that the ATP synthase uses to form ATP (= chemical energy is converted to mechanical energy) (F) As hydrogen ions flow down their concentration gradient through ATP synthase, ATP is produced (1) About 6 ATP molecules are produced per mole of photons (One mole of photons can "excite" 6 pairs of electrons, so it takes 6 pairs of electrons to make 6 ATP molecules, and also 6 NADPH molecules) (2) Though ATP is produced, plants cannot exist on ATP generated by photosynthesis alone. Basically, photosynthesis generates enough ATP to power itself BUT not other cell metabolic processes Thus, plant cells still need to undergo respiration to meet their ATP need.

Photorespiration - ____ with carbon-fixing role of photosynthesis •RubisCO fixes ____ instead of carbon dioxide. During photorespiration, oxygen combines with ____ to form a compound called phosphoglycolate. (a) _____ does not stay in the Calvin cycle. The cell has to ____ energy to recover this carbon so that it can be used in the cycle; v while some of the carbon dioxide may enter back into the Calvin cycle, for most plants, as much as ____% of the carbon previously fixed may escape from the plant (b) Photorespiration not only wastes carbon, but it also produces no ____; it squanders much of the carbon previously fixed by the plant, and, at the same time, at a great energy ____ to the Calvin Cycle Thus, photorespiration is a very ____ process. see image 52 on carbon recovery!!!! (chloroplast, peroxisome, mitochondrion)

Photorespiration - Competes with carbon-fixing role of photosynthesis •RubisCO fixes oxygen instead of carbon dioxide. During photorespiration, oxygen combines with RuBP to form a compound called phosphoglycolate. (a) Phosphoglycolate does not stay in the Calvin cycle. The cell has to expend energy to recover this carbon so that it can be used in the cycle; v while some of the carbon dioxide may enter back into the Calvin cycle, for most plants, as much as 50% of the carbon previously fixed may escape from the plant (b) Photorespiration not only wastes carbon, but it also produces no ATP; it squanders much of the carbon previously fixed by the plant, and, at the same time, at a great energy expense to the Calvin Cycle Thus, photorespiration is a very wasteful process.

Photosynthesis is possible, primarily, due to a pigment called ____ (10.4) (1) ____ are molecules that can absorb ____; there are lots of different pigments in plants, including not only ____, but also ____, ____, ____, etc. (2) In plants, ____ (= carotenes) are also involved, ____, in the photosynthesis process

Photosynthesis is possible, primarily, due to a pigment called CHLOROPHYLL (10.4) (1) Pigments are molecules that can absorb light; there are lots of different pigments in plants, including not only chlorophyll, but also xanthopylls, carotenoids, anthocyanins, etc. (2) In plants, carotenoids (= carotenes) are also involved, indirectly, in the photosynthesis process

Photosynthetic organisms are responsible for ____ nearly ALL life on earth (excluding a tiny group of ____). WHY? Almost every organism on the planet uses the ____ products of PS as ____ blocks for cell ____ and ____ AND as a source of ____ energy to do ____ Without PS, humans and all other animals on earth would eventually go ____. "Photosynthesis is undoubtedly the most important ____ to life on Earth as we know it." (Stern)

Photosynthetic organisms are responsible for sustaining nearly ALL life on earth (excluding a tiny group of bacteria). WHY? Almost every organism on the planet uses the organic products of PS as building blocks for cell growth and repair AND as a source of chemical energy to do work Without PS, humans and all other animals on earth would eventually go extinct. "Photosynthesis is undoubtedly the most important process to life on Earth as we know it." (Stern)

Photosynthetic organisms include: (1) ____ (2) ____ and other "____" (3) ____ ("____-____ ____") Most photosynthesis in the world takes place in the ____ by the ____ living there. Of course, on land, ____ perform the vast majority of PS.

Photosynthetic organisms include: (1) Plants (2) Algae and other "protists" (3) Cyanobacteria ("Blue-Green Algae") Most photosynthesis in the world takes place in the oceans by the protists living there. Of course, on land, plants perform the vast majority of PS.

Respiration

Releases stored energy •Facilitates growth, development and reproduction

The Light-Dependent Reactions - Introduction (10.8, 10.9) (A) Takes place in the ____ membranes (B) ____ energy is "captured" by photosystems (1) ____ photosystems are involved (2) Each photosytem is composed of about ____ - ____ pigment molecules (3) Each photosystem consists of two functional units: (a) ____ complex - pigments that serve to gather ____ energy and "funnel" it to the reaction center (7.10) (b) ____ center - the group of proteins and chlorophyll molecules that is responsible for the beginning of the conversion of ____ energy to ____ energy (7.10) (4) Photosystem II ( = P680) consists of (a) chlorophyll ____ molecules (b) ____-carotene (pigment) attached to a protein (c) a small amount of chlorophyll ____ molecules (d) chemically-unique and special chlorophyll a molecules referred to as ____ (e) transmembrane ____ that the pigment molecules are attached to (5) Photosystem I (= P700) consists of (a) chlorophyll ____ molecules (b) a small amount of chlorophyll ____ molecules (c) ____ pigment with a protein attached (d) special chlorophyll a molecules called ____ (e) transmembrane ____ that pigment molecules are attached to (6) Note that there are ____ photosystem I and photosystem II complexes in the membrane of each thylakoid (7.13) Is is NOT the case that there is only one of each photosystem in the membrane of every thylakoid; each thylakoid contains ____ photosystems (both I and II)

The Light-Dependent Reactions - Introduction (10.8, 10.9) (A) Takes place in the thylakoid membranes (B) Solar energy is "captured" by photosystems (1) TWO photosystems are involved (2) Each photosytem is composed of about 300 - 400 pigment molecules (3) Each photosystem consists of two functional units: (a) antenna complex - pigments that serve to gather light energy and "funnel" it to the reaction center (7.10) (b) reaction center - the group of proteins and chlorophyll molecules that is responsible for the beginning of the conversion of light energy to chemical energy (7.10) (4) Photosystem II ( = P680) consists of (a) chlorophyll a molecules (b) beta-carotene (pigment) attached to a protein (c) a small amount of chlorophyll b molecules (d) chemically-unique and special chlorophyll a molecules referred to as P680 (e) transmembrane proteins that the pigment molecules are attached to (5) Photosystem I (= P700) consists of (a) chlorophyll a molecules (b) a small amount of chlorophyll b molecules (c) carotenoid pigment with a protein attached (d) special chlorophyll a molecules called P700 (e) transmembrane proteins that pigment molecules are attached to (6) Note that there are multiple photosystem I and photosystem II complexes in the membrane of each thylakoid (7.13) Is is NOT the case that there is only one of each photosystem in the membrane of every thylakoid; each thylakoid contains multiple photosystems (both I and II)

The Light-Dependent Reactions - The Process (A) When solar energy strikes Photosystem ____, an electron within the ____ ____ is boosted to a ____ energy level, i.e., that electron becomes "excited". (1) This occurs because the chlorophylls and other pigment molecules of the ____ ____ direct the ____ energy towards the reaction center; energy flows "____" towards the reaction center (7.10, 7.11) (a) The chlorophyll a and b molecules of the antenna complex absorb very ____ of the solar energy that strikes them (b) The antenna complex pigments ____ the majority of the solar energy to the ____ ____ chlorophyll molecule (c) So, for any quanta of energy that strikes a photosystem, the vast ____ will end up being ____ by the reaction center chlorophyll (2) The reaction center ends up receiving the energy that has be redirectd by the ____ ____ (3) Electrons in the P680 reaction center chlorophyll molecules become very highly ____ If the energy is not harnessed, it will be lost as ____ (B) The highly energized electron is immediately captured by the primary electron acceptor, which is a protein known as ____. (1) Pheophytin is one of the ____ found in the photosystem II complex (7.12) (C) The electron lost from photosystem II must be ____ or the photosystem will not ____ properly (that is, it will stop absorbing ____). (7.12) (1) To accomplish this, an electron is removed from a ____ molecule by a special water-splitting enzyme that is part of the photosystem II complex à water splits into oxygen and hydrogen ions (H+). Thus, this is the point where ____ is produced during photosynthesis. (2) The electron is then transferred back to the ____ ____ chlorophyll molecule to fill the "____" left by the departed electron (3) For ____ electron that leaves a reaction center chlorophyll, a water molecule is split apart à one major reason that plants require so much water for ____ (= photosynthesis uses a LOT of water) (D) Pheophytin passes the electron to a ____ protein carrier called ____ (E) Plastoquinone passes the electron to the large ____ ____ ____ (F) The cytochrome b6/f complex passes the electron on to another ____ carrier called ____ (G) Plastocyanin passes the electron on to photosystem ____ (1) At the same time that electrons are being lost from P680, the reaction center (= ____) at photosystem I is also ____ high energy electrons (2) Electrons leaving photosystem I are passed to the ____ (iron-sulfur) complex (3) The electron is then passed to a ____ carrier called ____ (4) The electron is finally transferred to the ____ ____, which contains an enzyme involved in the reduction of ____ (more on that in a moment) (5) The electron lost by photosystem I is replaced by the electron coming down the "chain", carried by ____ (6) Plastocyanin gives its electron to the photosystem I reaction center to fill its electron "____" (H) The FAD complex transfers its electron to the final protein in the "chain": an enzyme called ____ ____ (which is part of the larger FAD complex) (I) The final electron acceptor is a molecule called ____. (1) The enzyme NADP reductase transfers the electron it received from ____ to the molecule NADP+ to form ____ (it actually transfers ____ electrons to NADP+, and adds a ____ ion to form NADPH) (2) The NADPH that is formed after the reduction then will move on to be used in the ____ ____.

The Light-Dependent Reactions - The Process (A) When solar energy strikes Photosystem II, an electron within the reaction center is boosted to a higher energy level, i.e., that electron becomes "excited". (1) This occurs because the chlorophylls and other pigment molecules of the antenna complex direct the light energy towards the reaction center; energy flows "downhill" towards the reaction center (7.10, 7.11) (a) The chlorophyll a and b molecules of the antenna complex absorb very little of the solar energy that strikes them (b) The antenna complex pigments deflect the majority of the solar energy to the reaction center chlorophyll molecule (c) So, for any quanta of energy that strikes a photosystem, the vast majority will end up being absorbed by the reaction center chlorophyll (2) The reaction center ends up receiving the energy that has be redirectd by the antenna complex (3) Electrons in the P680 reaction center chlorophyll molecules become very highly energized If the energy is not harnessed, it will be lost as heat (B) The highly energized electron is immediately captured by the primary electron acceptor, which is a protein known as pheophytin. (1) Pheophytin is one of the proteins found in the photosystem II complex (7.12) (C) The electron lost from photosystem II must be replaced or the photosystem will not function properly (that is, it will stop absorbing light). (7.12) (1) To accomplish this, an electron is removed from a water molecule by a special water-splitting enzyme that is part of the photosystem II complex à water splits into oxygen and hydrogen ions (H+). Thus, this is the point where Oxygen is produced during photosynthesis. (2) The electron is then transferred back to the reaction center chlorophyll molecule to fill the "hole" left by the departed electron (3) For every electron that leaves a reaction center chlorophyll, a water molecule is split apart à one major reason that plants require so much water for survival (= photosynthesis uses a LOT of water) (D) Pheophytin passes the electron to a mobile protein carrier called plastoquinone (E) Plastoquinone passes the electron to the large cytochrome b6/f complex (F) The cytochrome b6/f complex passes the electron on to another mobile carrier called plastocyanin (G) Plastocyanin passes the electron on to photosystem I (1) At the same time that electrons are being lost from P680, the reaction center (= P700) at photosystem I is also losing high energy electrons (2) Electrons leaving photosystem I are passed to the Fe-S (iron-sulfur) complex (3) The electron is then passed to a mobile carrier called ferrodoxin (4) The electron is finally transferred to the FAD complex, which contains an enzyme involved in the reduction of NADP+ (more on that in a moment) (5) The electron lost by photosystem I is replaced by the electron coming down the "chain", carried by plastocyanin (6) Plastocyanin gives its electron to the photosystem I reaction center to fill its electron "hole" (H) The FAD complex transfers its electron to the final protein in the "chain": an enzyme called NADP reductase (which is part of the larger FAD complex) (I) The final electron acceptor is a molecule called NADP+. (1) The enzyme NADP reductase transfers the electron it received from ferrodoxin to the molecule NADP+ to form NADPH (it actually transfers TWO electrons to NADP+, and adds a hydrogen ion to form NADPH) (2) The NADPH that is formed after the reduction then will move on to be used in the Calvin Cycle.

What is the function of enzymes?

to regulate metabolic activities

Photosynthesis-respiration cycle involves what?

transfer of energy via oxidation-reduction reactions.