Ch.10 PhotosynthesisCh.10 PhotosynthesisSarah Burton and Lauren Thompson Sarah Burton and Lauren Thompson

Plants and other Plants and other autotrophs are autotrophs are

the producers of the producers of the biospherethe biosphere

•Autotrophs- organisms that Autotrophs- organisms that obtain organic matter without obtain organic matter without

eating other organisms or eating other organisms or substances derived from substances derived from

organisms.organisms.•Photoautotrophs- organism that Photoautotrophs- organism that harnesses light energy to drive the harnesses light energy to drive the synthesis of organic compounds from synthesis of organic compounds from carbon dioxide.carbon dioxide.

•Chemoautotrophs- organism that Chemoautotrophs- organism that needs only carbon dioxide as a carbon needs only carbon dioxide as a carbon source but that obtains energy from source but that obtains energy from oxidizing inorganic substances.oxidizing inorganic substances.

•Hertotrophs- organism that Hertotrophs- organism that obtains organic food obtains organic food

molecules by eating other molecules by eating other organisms or their by-organisms or their by-

products.products.

Chloroplasts are Chloroplasts are the sites of the sites of

photosynthesis photosynthesis in plantsin plants

Chlorophyll- green Chlorophyll- green pigment located within pigment located within chloroplasts of plants.chloroplasts of plants.

Parts of the LeafParts of the Leaf•Mesophyll- ground tissue of a Mesophyll- ground tissue of a

leaf, sandwiched between upper leaf, sandwiched between upper & lower epidermis & specialized & lower epidermis & specialized

for photosynthesis.for photosynthesis.•Vascular bundle- part of the Vascular bundle- part of the transport system which exists transport system which exists

and either the xylem and phloem.and either the xylem and phloem.•Stomata- microscopic pore Stomata- microscopic pore

surrounded by guard cells in the surrounded by guard cells in the epidermis of leaves and stems epidermis of leaves and stems

that allows gas exchange.that allows gas exchange.

Chloroplasts- organelle Chloroplasts- organelle found only in plants & found only in plants & photosynthetic protists photosynthetic protists that absorbs sunlight & that absorbs sunlight &

uses it to drive the uses it to drive the synthesis of organic synthesis of organic

compounds from compounds from carbon dioxide & water.carbon dioxide & water.

•Stroma- fluid in the Stroma- fluid in the chloroplast surrounding the chloroplast surrounding the

thylakoid membrane; thylakoid membrane; involved in synthesis of involved in synthesis of organic molecules from organic molecules from

carbon dioxide and water.carbon dioxide and water.•Thylakoids- flattened Thylakoids- flattened

membrane sac inside the membrane sac inside the chloroplasts, used to convert chloroplasts, used to convert

light energy to chemical light energy to chemical energy.energy.

•Grana- stacked proton of the Grana- stacked proton of the thylakoid membrane in the thylakoid membrane in the

chloroplastchloroplast

Photosynthesis Photosynthesis EquationEquation

Photophosphorylation- process of generating Photophosphorylation- process of generating ATP from ADP and phosphate by means of ATP from ADP and phosphate by means of proton motive force motivated by the proton motive force motivated by the thylakoid membrane of chloroplast during thylakoid membrane of chloroplast during light reactions of photosythesis.light reactions of photosythesis.

NADPHNADPH22- acceptor that temporarily stores - acceptor that temporarily stores energized electrons produced during the light energized electrons produced during the light reactions.reactions.

Carbon fixation- incorporation of carbon from Carbon fixation- incorporation of carbon from COCO22 into an organic compound by an into an organic compound by an autotrophic organism.autotrophic organism.

Calvin CycleCalvin Cycle

The Calvin cycle uses ATP and NADPH from the light-The Calvin cycle uses ATP and NADPH from the light-dependent reactions to convert COdependent reactions to convert CO22 into sugar that the into sugar that the plant can use. COplant can use. CO22 is obtained from the outside is obtained from the outside environment though gas- exchanging organs on the plant’s environment though gas- exchanging organs on the plant’s surface known as stomata. The process of carbon fixation surface known as stomata. The process of carbon fixation incorporates the COincorporates the CO22 into organic molecules. The into organic molecules. The incorporation of COincorporation of CO22 is possible because of the energy-rich is possible because of the energy-rich enzyme rubisco (ribulosebiphosphatecarboxylase, or RuBP), enzyme rubisco (ribulosebiphosphatecarboxylase, or RuBP), a protein made during the light-dependent reactions of a protein made during the light-dependent reactions of photosynthesis and abundant in plant leaves. A COphotosynthesis and abundant in plant leaves. A CO22 molecule binds to RuBP. The molecule then splits into two molecule binds to RuBP. The molecule then splits into two 3-carbon molecules of PGA (3-phosphoglycerate). A series 3-carbon molecules of PGA (3-phosphoglycerate). A series of reactions occur to convert the PGA into the 3-carbon of reactions occur to convert the PGA into the 3-carbon sugar molecule glyceraldehyde 3-phosphate. This 3-carbon sugar molecule glyceraldehyde 3-phosphate. This 3-carbon sugar molecule can then be used to make other sugars, sugar molecule can then be used to make other sugars, including glucose and sucrose. The production of a single 3-including glucose and sucrose. The production of a single 3-carbon sugar molecule requires 3 COcarbon sugar molecule requires 3 CO22, 9 ATP, and 6 NADPH., 9 ATP, and 6 NADPH.

Wavelike properties of Wavelike properties of lightlight

Electromagnetic spectrum- entire spectrum of Electromagnetic spectrum- entire spectrum of radiation ranging in wavelength for less than radiation ranging in wavelength for less than a nanometer to more than a kilometer.a nanometer to more than a kilometer.

Visible light- portion of electromagnetic Visible light- portion of electromagnetic spectrum detected as various colors by the spectrum detected as various colors by the human eye, ranging in wavelength from human eye, ranging in wavelength from about 380 nm to about 750 nm.about 380 nm to about 750 nm.

Photosynthetic Photosynthetic Pigments: Light Pigments: Light

ReceptorsReceptors Pigments- material that changes the color of Pigments- material that changes the color of

light it reflects as the result of selective color light it reflects as the result of selective color absorptionabsorption

Absorption spectrum- shows the fraction of Absorption spectrum- shows the fraction of incident electromagnetic radiation absorbed incident electromagnetic radiation absorbed by the material over a range of frequencies.by the material over a range of frequencies.

Action spectrum- rate of a physiological Action spectrum- rate of a physiological activity plotted against wavelength of light.activity plotted against wavelength of light.

Chlorophyll a- type of Chlorophyll a- type of blue green blue green photosynthetic pigment photosynthetic pigment that participates that participates directly in light directly in light reactionsreactions

Accessory PigmentsAccessory Pigments

Chlorophyll b- type of Chlorophyll b- type of yellow green accessory yellow green accessory photosynthetic pigment photosynthetic pigment that transfers energy to that transfers energy to chlorophyll a.chlorophyll a.

Carotenoids- either Carotenoids- either yellow or orange; in the yellow or orange; in the chloroplast of plants; chloroplast of plants; broaden the spectrum broaden the spectrum of colors that can drive of colors that can drive photosynthesis.photosynthesis.

Photosystems: Light-Photosystems: Light-Harvesting Complexes of the Harvesting Complexes of the

Thylakoid MembraneThylakoid Membrane The light-harvesting (or antenna) complex of plants is an The light-harvesting (or antenna) complex of plants is an

array of protein and chlorophyll molecules embedded in array of protein and chlorophyll molecules embedded in the thylakoid membrane which transfer light energy to the thylakoid membrane which transfer light energy to one chlorophyll one chlorophyll aa molecule at the reaction center of  molecule at the reaction center of a photosystem.a photosystem.

The function of the reaction center chlorophyll is to use The function of the reaction center chlorophyll is to use the energy absorbed by and transferred to it from the the energy absorbed by and transferred to it from the other chlorophyll pigments in the photosystemto undergo other chlorophyll pigments in the photosystemto undergo a charge separation, a specific redox reaction in which the a charge separation, a specific redox reaction in which the chlorophyll donates an electron into a series of molecular chlorophyll donates an electron into a series of molecular intermediates called an electron transport chain.intermediates called an electron transport chain.

Primary electron acceptor – a specialized molecule sharing Primary electron acceptor – a specialized molecule sharing the reaction center with chlorophyll a molecule; it accepts the reaction center with chlorophyll a molecule; it accepts an electron from chlorophyll a molecule.an electron from chlorophyll a molecule.

Photosystem I- one of the two light harvesting Photosystem I- one of the two light harvesting units of a chloroplast’s thylakoid membrane; units of a chloroplast’s thylakoid membrane; used the P700 reaction center chlorophyll.used the P700 reaction center chlorophyll.

Photosystem II- one of the two light Photosystem II- one of the two light harvesting units of a chloroplast’s thylakoid harvesting units of a chloroplast’s thylakoid membrane; used P680 reaction center membrane; used P680 reaction center chlorophyll.chlorophyll.

How a photosystem How a photosystem harvests lightharvests light

When a photon strikes a When a photon strikes a pigment molecule, the pigment molecule, the energy is passed from energy is passed from molecule to molecule molecule to molecule until it reaches the until it reaches the reaction center.reaction center.

At the reaction center, an At the reaction center, an excited electron from the excited electron from the reaction-center reaction-center chlorophyll is captured chlorophyll is captured by a specialized molecule by a specialized molecule called the primary called the primary electron acceptor.electron acceptor.

Steps in creating Steps in creating NADPHNADPH

Photosystem II absorbs solar energy in the form of light.Photosystem II absorbs solar energy in the form of light.

The solar energy excites electrons in the reaction center The solar energy excites electrons in the reaction center of photosystem II, which then enter an electron transport of photosystem II, which then enter an electron transport chain. These electrons originate from the splitting of chain. These electrons originate from the splitting of water, which produces free electrons and Owater, which produces free electrons and O22..

As electrons pass down the electron transport chain, As electrons pass down the electron transport chain, protons are pumped into the thylakoid membrane space protons are pumped into the thylakoid membrane space of the chloroplast. Protons diffuse out of the thylakoid of the chloroplast. Protons diffuse out of the thylakoid membrane space through an ATP synthase protein, membrane space through an ATP synthase protein, creating ATP.creating ATP.

PhotosystemI accepts electrons from the electron PhotosystemI accepts electrons from the electron transport chain and uses light energy to excite the transport chain and uses light energy to excite the electrons further.electrons further.

Noncyclic Electron FlowNoncyclic Electron Flow

Noncyclic electron flow – a route of electron Noncyclic electron flow – a route of electron flow during the light reactions of flow during the light reactions of photosynthesis that involves both photosynthesis that involves both photosystems and produces ATP, NADPH, and photosystems and produces ATP, NADPH, and oxygen. The net electron flow is from water to oxygen. The net electron flow is from water to NADP+NADP+

Noncyclicphotophosphorolation – the Noncyclicphotophosphorolation – the production of ATP by noncyclic electron flowproduction of ATP by noncyclic electron flow

Cyclic Electron FlowCyclic Electron Flow

Cyclic electron flow - a route of electron flow Cyclic electron flow - a route of electron flow during the light reactions of photosynthesis during the light reactions of photosynthesis that involves that involves onlyonlyphotosystem I and that photosystem I and that produces ATP but not NADPH or oxygenproduces ATP but not NADPH or oxygen

Cyclic photophosphorolation - the generation Cyclic photophosphorolation - the generation of ATP by cyclic electron flowof ATP by cyclic electron flow

Alternative Mechanisms of Alternative Mechanisms of Carbon Fixation Have Evolved Carbon Fixation Have Evolved

in Hot, Arid Climatesin Hot, Arid Climates

Plants are divided into three different Plants are divided into three different categories depending on their method of categories depending on their method of carrying out photosynthesis: the Ccarrying out photosynthesis: the C33 pathway, pathway, the CAM pathway, and the Cthe CAM pathway, and the C44 pathway. pathway.

CC3 3 PlantsPlants

Photorespiration presents a Photorespiration presents a major problem for C3 plants major problem for C3 plants because they have no because they have no special adaptations to special adaptations to reduce the process. The reduce the process. The problem is exacerbated in problem is exacerbated in hot, arid climates, where hot, arid climates, where the rate of photorespiration the rate of photorespiration increases as the increases as the temperature goes up. temperature goes up. Consequently, CConsequently, C33 plants are plants are rarely found in these rarely found in these climates. Most plants, climates. Most plants, including wheat, barley, and including wheat, barley, and sugar beet, are Csugar beet, are C33 plants. plants.

CAM PlantsCAM Plants

CAM (crassulacean acid metabolism) plants CAM (crassulacean acid metabolism) plants reduce photorespiration and conserve water by reduce photorespiration and conserve water by opening their stomata only at night. COopening their stomata only at night. CO22 enters enters through the stomata and is fixed into organic through the stomata and is fixed into organic acids, which are then stored in the cell’s vacuole. acids, which are then stored in the cell’s vacuole. During the day, the acids break down to yield During the day, the acids break down to yield high levels of COhigh levels of CO22 for use in the Calvin cycle. for use in the Calvin cycle. Through the periodic opening and closing of the Through the periodic opening and closing of the stomata, CAM plants maintain a high COstomata, CAM plants maintain a high CO22 to O to O22 ratio, minimizing the rate of photorespiration. ratio, minimizing the rate of photorespiration. CAM plants, such as cacti and pineapple, are most CAM plants, such as cacti and pineapple, are most common in dry environments.common in dry environments.

CC44 Plants Plants

C4 plants use the enzyme C4 plants use the enzyme PEP carboxylase to fix COPEP carboxylase to fix CO22 in in the mesophyll cells of their the mesophyll cells of their chloroplasts. The fixed COchloroplasts. The fixed CO22 is is then shuttled to specialized then shuttled to specialized structures known as the structures known as the bundle-sheath cells, where it bundle-sheath cells, where it is released and incorporated is released and incorporated into the Calvin cycle. This into the Calvin cycle. This process is energetically process is energetically expensive, but it limits expensive, but it limits photorespiration by allowing photorespiration by allowing high concentrations of COhigh concentrations of CO22 to build up in the bundle-to build up in the bundle-sheath cells. Csheath cells. C44 plants, such plants, such as corn and sugar cane, are as corn and sugar cane, are common in warm common in warm environments.environments.

In C4 plants, carbon fixation and the Calvin cycle occur in different types of cells.

In CAM plants, carbon fixation and the Calvin cycle occur in the same cells at different times.

Light Reactions:Light Reactions:

Are carried out by molecules in the Are carried out by molecules in the thylakoid membranes.thylakoid membranes.

Convert light energy to the chemical Convert light energy to the chemical energy of ATP and NADPH.energy of ATP and NADPH.

Split HSplit H22O and release OO and release O22 to the to the atmosphereatmosphere

Calvin Cycle Reactions:Calvin Cycle Reactions:

Take place in the stromaTake place in the stroma

Use ATP and NADPH to convert COUse ATP and NADPH to convert CO22 to to the sugar G3Pthe sugar G3P

Return ADP, inorganic phosphate, and Return ADP, inorganic phosphate, and NADPNADP++ to the light reactions to the light reactions