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2.  Autotrophs produce organic molecules from CO 2 and other inorganic raw materials obtained from the environment.  Heterotrophs live on organic compounds produced by other organisms.  Autotrophs produce organic molecules from CO 2 and other inorganic raw materials obtained from the environment.  Heterotrophs live on organic compounds produced by other organisms. 2 The chloroplasts of plants use a process called photosynthesis to capture light energy from the sun and convert it to chemical energy stored in sugars and other organic molecules.

3. Plant cells have chloroplasts. The structure of a leaf is to the left. Structures to note: - Stoma (stomata) - Cuticle -Veins (xylem/ phloem) - Guard Cells - Epidermis -Mesophyll (in this pic it is called parenchyma – that is the type of cell) Plant cells have chloroplasts. The structure of a leaf is to the left. Structures to note: - Stoma (stomata) - Cuticle -Veins (xylem/ phloem) - Guard Cells - Epidermis -Mesophyll (in this pic it is called parenchyma – that is the type of cell) Photosynthesis mainly occurs in mesophyll cells 3

4. Chloroplasts are the organelles where photosynthesis takes place. Know the following structures: stroma, thylakoid, grana, lumen (inside thylakoid) 4 Stomata  microscopic pores in the bottom of the leaf; used for gas exchange Veins  run throughout the plant to deliver water from the roots and carry sugar from the leaves to the rest of the plant IN THE CHLOROPLAST…. Stroma  fluid in the chloroplast; Calvin cycle happens here Thylakoids  membrane sacs where the light reaction happens Thylakoid Space/ Lumen  inside the thylakoids Grana  stacks of thylakoids Stomata  microscopic pores in the bottom of the leaf; used for gas exchange Veins  run throughout the plant to deliver water from the roots and carry sugar from the leaves to the rest of the plant IN THE CHLOROPLAST…. Stroma  fluid in the chloroplast; Calvin cycle happens here Thylakoids  membrane sacs where the light reaction happens Thylakoid Space/ Lumen  inside the thylakoids Grana  stacks of thylakoids Chlorophyll, the green pigment in chloroplasts, is found in the thylakoid membranes.

5.  Process that converts sunlight (light energy) into food (chemical energy)  6CO 2 + 6 H 2 O + Light → C 6 H 12 O 6 + 6O 2  The oxygen given off by plants comes from WATER, not CARBON DIOXIDE Make sure you know this picture! 5

6. Cornelis B. Van Niel was a teacher and made great contributions to the world of science as we know it. He was a pioneer in the field of microbiology and he also discovered some of the chemistry behind photosynthesis. He did research with plants and figured out that water was split to give the ETC a source of hydrogen (and electrons) and that oxygen was given off as a byproduct. Thus, the oxygen that is released during PS is from water, not the CO 2 that is consumed. Twenty years later (in the 1950’s), this theory was confirmed by doing research using a heavy isotope of oxygen ( 18 O) as a tracer to follow the path of the oxygen. The radioactive label (isotope) was only found in the released oxygen if the source of the 18 O was originally in the water (not the CO 2 ). Cornelis B. Van Niel was a teacher and made great contributions to the world of science as we know it. He was a pioneer in the field of microbiology and he also discovered some of the chemistry behind photosynthesis. He did research with plants and figured out that water was split to give the ETC a source of hydrogen (and electrons) and that oxygen was given off as a byproduct. Thus, the oxygen that is released during PS is from water, not the CO 2 that is consumed. Twenty years later (in the 1950’s), this theory was confirmed by doing research using a heavy isotope of oxygen ( 18 O) as a tracer to follow the path of the oxygen. The radioactive label (isotope) was only found in the released oxygen if the source of the 18 O was originally in the water (not the CO 2 ). 6

7.  Both photosynthesis and aerobic respiration involve redox reactions.  Photosynthesis reverses the direction of electron flow.  Water is split and electrons are transferred with H + from water to CO 2, reducing it to sugar.  Oxidized = water  Reduced = CO 2  Both photosynthesis and aerobic respiration involve redox reactions.  Photosynthesis reverses the direction of electron flow.  Water is split and electrons are transferred with H + from water to CO 2, reducing it to sugar.  Oxidized = water  Reduced = CO 2 7

8.  The light reactions (photo) convert solar energy to chemical energy.  In the light reactions, water is split, providing a source of electrons and protons (H + ions) and giving off O 2 as a by-product.  Light absorbed by chlorophyll drives the transfer of electrons and hydrogen ions from water to NADP + (nicotinamide adenine dinucleotide phosphate), forming NADPH.  The light reactions also generate ATP using chemiosmosis, in a process called photophosphorylation (comparable to oxidative phosphorylation in cellular respiration.)  The light reactions (photo) convert solar energy to chemical energy.  In the light reactions, water is split, providing a source of electrons and protons (H + ions) and giving off O 2 as a by-product.  Light absorbed by chlorophyll drives the transfer of electrons and hydrogen ions from water to NADP + (nicotinamide adenine dinucleotide phosphate), forming NADPH.  The light reactions also generate ATP using chemiosmosis, in a process called photophosphorylation (comparable to oxidative phosphorylation in cellular respiration.) 8

9.  The Calvin cycle (synthesis) uses energy from the light reactions to incorporate CO 2 from the atmosphere into sugar (named for Melvin Calvin ~1940’s.)  The Calvin cycle begins with the incorporation of CO 2 into organic molecules, a process known as carbon fixation.  The fixed carbon is reduced with electrons provided by NADPH.  ATP from the light reactions also powers parts of the Calvin cycle.  Thus, it is the Calvin cycle that makes sugar (G3P), but only with the help of ATP and NADPH from the light reactions.  The Calvin cycle (synthesis) uses energy from the light reactions to incorporate CO 2 from the atmosphere into sugar (named for Melvin Calvin ~1940’s.)  The Calvin cycle begins with the incorporation of CO 2 into organic molecules, a process known as carbon fixation.  The fixed carbon is reduced with electrons provided by NADPH.  ATP from the light reactions also powers parts of the Calvin cycle.  Thus, it is the Calvin cycle that makes sugar (G3P), but only with the help of ATP and NADPH from the light reactions. 9

10.  Light is a form of electromagnetic energy or radiation.  Light travels in waves and the distance between crests of electromagnetic waves is called the wavelength.  The entire range of electromagnetic radiation is the electromagnetic spectrum.  The most important segment of the electromagnetic spectrum for life is a narrow band between 380 and 750 nm, the band of visible light detected as colors by the human eye. (ROY.G.BIV!)  Although light travels as a wave, many of its properties are those of a discrete particle, a photon.  Light is a form of electromagnetic energy or radiation.  Light travels in waves and the distance between crests of electromagnetic waves is called the wavelength.  The entire range of electromagnetic radiation is the electromagnetic spectrum.  The most important segment of the electromagnetic spectrum for life is a narrow band between 380 and 750 nm, the band of visible light detected as colors by the human eye. (ROY.G.BIV!)  Although light travels as a wave, many of its properties are those of a discrete particle, a photon. 10

11. Light can be transmitted, reflected, or absorbed. Substances that absorb visible light are called PIGMENTS. Whatever color wavelength is reflected is the color that the pigment appears to be. This color wavelength is NOT helpful in providing energy because none of it is absorbed (therefore green is NOT helpful for photosynthesis because chlorophyll reflects green light). This is the visible light spectrum. The shorter the wavelength (violet), the more energy it has. 11

12. The spectrophotometer is a machine that measures a pigments ability to absorb at different wavelengths of light. The more light that is absorbed, the less that gets through, so the lower the transmittance. Low Transmittance = High Absorption 12 An absorption spectrum plots a pigment’s light absorption versus wavelength. An overall action spectrum for photosynthesis profiles the relative effectiveness of different wavelengths of light in driving the process. An absorption spectrum plots a pigment’s light absorption versus wavelength. An overall action spectrum for photosynthesis profiles the relative effectiveness of different wavelengths of light in driving the process.

13. Engelmann’s Experiment → Engelmann shone light of different colors (wavelengths) of light onto filaments of Spirogyra (through a prism). Spirogyra is an alga made up of filaments (chains) of cells. He added motile bacteria (which could swim) and which needed oxygen and observed where they went. He found that the bacteria clustered around the blue and red colors of the spectrum, where the Spirogyra were producing the most oxygen. So he concluded that these two colors were the most important for photosynthesis. RESULT: Red and Blue are the most effective colors for photosynthesis! 13

14. Accessory Pigments: -Chlorophyll b → similar to chlorophyll a, but traps a slightly different wavelength of energy -Carotenoids → yellow/orange color; absorb and pass on energy; function in photoprotection Accessory Pigments: -Chlorophyll b → similar to chlorophyll a, but traps a slightly different wavelength of energy -Carotenoids → yellow/orange color; absorb and pass on energy; function in photoprotection Only Chlorophyll a can participate directly in the light reactions. However, it gets energy from other pigments called accessory pigments. These pigments absorb wavelengths of light that chlorophyll cannot, and then pass along that energy to the chlorophyll a. 14

15. Part 1 – Light Reactions 15

16.  Light Reaction makes ATP and NADPH and sends it to the Calvin Cycle  It occurs in the thylakoid  Makes ATP by Photophosphorylation (similar to oxidative phosphorylation with the ETC and chemiosmosis)  Energy carrier = NADPH (reduced from NADP+)  Gets electrons from H 2 O and gives off O 2  Light Reaction makes ATP and NADPH and sends it to the Calvin Cycle  It occurs in the thylakoid  Makes ATP by Photophosphorylation (similar to oxidative phosphorylation with the ETC and chemiosmosis)  Energy carrier = NADPH (reduced from NADP+)  Gets electrons from H 2 O and gives off O 2 16

17. Photosystems  composed of a reaction center complex and several light harvesting complexs that contain pigments that absorb light energy Reaction Center → made up of the special chlorophyll a molecule and a primary e- acceptor Photosystem II → comes first in the ETC, but was discovered second; called P680 because has an absorption peak at 680nm Photosystem I → comes second in the ETC, but was discovered first; gives e- to NADP+; called P700 because has an absorption peak at 700nm 17

18. There are two ways electrons can pass through the ETC: Cyclic e- Flow → this is when the e- go down PS II to the next photosystem, but then get passed from ferredoxin BACK to the cytochrome complex; this makes more ATP and makes NO NADPH Linear (Non-Cyclic) e- Flow → this passes through both electrons transport chains and makes both ATP and also NADPH There are two ways electrons can pass through the ETC: Cyclic e- Flow → this is when the e- go down PS II to the next photosystem, but then get passed from ferredoxin BACK to the cytochrome complex; this makes more ATP and makes NO NADPH Linear (Non-Cyclic) e- Flow → this passes through both electrons transport chains and makes both ATP and also NADPH Because the Calvin uses more ATP than NADPH, there is a way to make more ATP (and less NADPH) → cyclic e- flow! 18

19. Makes NADPH and ATP Discuss: -Water → donates e- to PSII, releases O 2 as waste, contributes H+ to concentration gradient -Electrons get energized by light and then get trapped by a primary e- acceptor and passed down the ETC (energy released pumps H+ INTO the lumen) -First ETC→ made up of Plastoquinone, Cytochromes, and Plastocyanin -Electrons from 1 st ETC supply e- to PSI where they get re- energzizd by light and passed down the second ETC (ferredoxin and NADP+ reductase) to NADP+ to make NADPH Discuss: -Water → donates e- to PSII, releases O 2 as waste, contributes H+ to concentration gradient -Electrons get energized by light and then get trapped by a primary e- acceptor and passed down the ETC (energy released pumps H+ INTO the lumen) -First ETC→ made up of Plastoquinone, Cytochromes, and Plastocyanin -Electrons from 1 st ETC supply e- to PSI where they get re- energzizd by light and passed down the second ETC (ferredoxin and NADP+ reductase) to NADP+ to make NADPH 19 Electron Flow: Water  PSII  primary e- acceptor  plastoquinone (Pq)  cytochromes  plastocyanin (Pc)  PSI  primary e- acceptor  Ferredoxin (Fd)  NADP+ reductase  NADPH Electron Flow: Water  PSII  primary e- acceptor  plastoquinone (Pq)  cytochromes  plastocyanin (Pc)  PSI  primary e- acceptor  Ferredoxin (Fd)  NADP+ reductase  NADPH

20. - Makes ATP only -Ferredoxin returns the electrons back to the cytochrome complex in the first ETC rather than passing them to NADP+ reductase; no NADPH is made here -Both cyclic and non-cyclic are used because the Calvin cycle uses more ATP than NADPH……so we need more ATP than NADPH 20

21. Makes both ATP (via ATP Synthase) and NADPH (via NADP+ reductase) Uses the proton gradient and ATP synthase to make ATP via photophosphorylation 21 During the Light Reactions, protons (H+) are pumped from the stroma into the lumen (thylakoid space) against their concentration gradient. The want to diffuse back out and the only way they can get out of the thylakoid is to go through ATP SYNTHASE. This is an enzyme that works like a water wheel and converts ADP to ATP. This is utilized in cellular respiration as well.

22. -Occurs in the stroma of the chloroplast -Carbon enters as CO 2 and leaves as sugar -Produces a sugar called glyceraldehyde-3-phosphate (G3P) -Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin -Occurs in the stroma of the chloroplast -Carbon enters as CO 2 and leaves as sugar -Produces a sugar called glyceraldehyde-3-phosphate (G3P) -Each turn “fixes” one molecule of carbon, so one G3P takes 3 turns of the Calvin 22

23. 23 Phase 1: Carbon fixing  Each CO2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP). This reaction is catalyzed by RuBP carboxylase-oxygenase, or rubisco. The six-carbon intermediate is unstable and splits in half to form two molecules of 3-phosphoglycerate for each CO 2 fixed. Phase 1: Carbon fixing  Each CO2 molecule is attached to a five-carbon sugar, ribulose bisphosphate (RuBP). This reaction is catalyzed by RuBP carboxylase-oxygenase, or rubisco. The six-carbon intermediate is unstable and splits in half to form two molecules of 3-phosphoglycerate for each CO 2 fixed. Phase 2: Reduction  During reduction, each 3- phosphoglycerate receives another phosphate group from ATP to form 1,3- bisphosphoglycerate. A pair of electrons from NADPH reduces each 1,3-bisphosphoglycerate to G3P. For every three molecules of CO 2 that enter the cycle, there are six molecules of G3P formed…but 5 have to be recycled so we only get net gain of one G3P. This molecule exits the cycle to be used by the plant cell, while the other five molecules are recycled to regenerate the three molecules of RuBP Phase 2: Reduction  During reduction, each 3- phosphoglycerate receives another phosphate group from ATP to form 1,3- bisphosphoglycerate. A pair of electrons from NADPH reduces each 1,3-bisphosphoglycerate to G3P. For every three molecules of CO 2 that enter the cycle, there are six molecules of G3P formed…but 5 have to be recycled so we only get net gain of one G3P. This molecule exits the cycle to be used by the plant cell, while the other five molecules are recycled to regenerate the three molecules of RuBP Phase 3: Regeneration of RuBP  In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle to regenerate three molecules of RuBP. Phase 3: Regeneration of RuBP  In a complex series of reactions, the carbon skeletons of five molecules of G3P are rearranged by the last steps of the Calvin cycle to regenerate three molecules of RuBP.

24. In hot and dry environments, plants close their stomata so that they don’t lose too much water (dehydrate). However, closed stomata lead to no gas exchange, which inhibits photosynthesis. This leads to….. Photorespiration → makes no ATP, makes no food, wastes the plants materials (takes away from the Calvin Cycle. In C3 plants, with the higher levels of O 2 (byproduct it can’t get rid of) and low levels of CO 2, rubisco (enz) actually adds OXYGEN to the Calvin instead of CO 2 …..it wastes all the raw materials. Evolutionary baggage  early environment didn’t have a lot of O 2 so the inability of rubisco to exclude O 2 wouldn’t have made a difference. In order to minimize photorespiration, plants have adapted a C4 pathway or a CAM pathway In hot and dry environments, plants close their stomata so that they don’t lose too much water (dehydrate). However, closed stomata lead to no gas exchange, which inhibits photosynthesis. This leads to….. Photorespiration → makes no ATP, makes no food, wastes the plants materials (takes away from the Calvin Cycle. In C3 plants, with the higher levels of O 2 (byproduct it can’t get rid of) and low levels of CO 2, rubisco (enz) actually adds OXYGEN to the Calvin instead of CO 2 …..it wastes all the raw materials. Evolutionary baggage  early environment didn’t have a lot of O 2 so the inability of rubisco to exclude O 2 wouldn’t have made a difference. In order to minimize photorespiration, plants have adapted a C4 pathway or a CAM pathway 24

25. C4 plants → the first product of carbon fixing is a 4C molecule (instead of a 3C molecule); it occurs in the mesophyll cells and sends the product to the bundle sheath cells and the calvin cycle happens there (Calvin cycle is confined to bundle sheath cells!) PEP Carboxylase (enzyme) has a high affinity for CO 2 so it can work when rubisco can’t 25 The key enzyme, phosphoenolpyruvate carboxylase, adds CO 2 to phosphoenolpyruvate ( PEP ) to form the four-carbon product oxaloacetate. PEP carboxylase has a very high affinity for CO 2 and no affinity for O 2. Therefore, PEP carboxylase can fix CO 2 efficiently when rubisco cannot (that is, on hot, dry days when the stomata are closed). In effect, the mesophyll cells pump CO 2 into the bundle-sheath cells, keeping CO 2 levels high enough for rubisco to accept CO 2 and not O 2. C 4 photosynthesis minimizes photorespiration and enhances sugar production. C 4 plants thrive in hot regions with intense sunlight. The key enzyme, phosphoenolpyruvate carboxylase, adds CO 2 to phosphoenolpyruvate ( PEP ) to form the four-carbon product oxaloacetate. PEP carboxylase has a very high affinity for CO 2 and no affinity for O 2. Therefore, PEP carboxylase can fix CO 2 efficiently when rubisco cannot (that is, on hot, dry days when the stomata are closed). In effect, the mesophyll cells pump CO 2 into the bundle-sheath cells, keeping CO 2 levels high enough for rubisco to accept CO 2 and not O 2. C 4 photosynthesis minimizes photorespiration and enhances sugar production. C 4 plants thrive in hot regions with intense sunlight.

26. CAM (crassulacean acid metabolism) Plants → They open their stomata at night and store the CO 2 in organic acids; then during the day they break those acids down to use the CO 2 26

27.  Both C 4 and CAM plants add CO 2 to organic intermediates before it enters the Calvin cycle.  In C 4 plants, carbon fixation and the Calvin cycle are structurally separated (bundle sheath cells vs. mesophyll cells)  In CAM plants, carbon fixation and the Calvin cycle are temporally separated (day vs. night)  Both C 4 and CAM plants add CO 2 to organic intermediates before it enters the Calvin cycle.  In C 4 plants, carbon fixation and the Calvin cycle are structurally separated (bundle sheath cells vs. mesophyll cells)  In CAM plants, carbon fixation and the Calvin cycle are temporally separated (day vs. night) 27