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2. Introduction Autotrophs: any organism that can make their own food. Photoautotrophs : use light energy Chemoautotrophs change inorganic chemicals such as hydrogen sulfate into chemical energy 2

3. Important structures Chloroplast: Site of photosynthesis in eukaryotic cells. Thylakoids: Disk shaped membranes containing photosynthetic pigments. Site of light dependent reactions. Grana: Stacks of thylakoids. Stroma: Fluid filled space surrounding grana. Site of light independent reactions. 3

4. Properties of Light White light from the sun is composed of a range of wavelengths. Chlorophyll is the main pigment that absorbs sunlight. Chlorophyll absorbs blue light and to a lesser extent, red light. It reflects green light hence its intense green color. 4

5. What do chlorophyll and fireworks have in common? Fireworks are made up of various metal salts that go through oxidation and reduction reactions, producing great heat that causes electrons to move from their usual level around the nucleus (ground state) up to a higher position further away from the nucleus (excited state). The energy from heat has been imparted to the electron(s), which now has more potential energy. These excited electrons move almost instantaneously back down to their ground state, releasing their stored potential energy in the form of light. The greater the electrons movement away from the nucleus to the excited state, the more potential energy it has and the more energy it will release. It should be pointed out that chlorophyll absorbs light energy, specifically its electrons, and this energy is used to pump protons instead of producing light. This proton gradient in turn is used to produce ATP, which along with other energized electrons are transferred to the Calvin cycle. 5

6. Suppose a large meteor hit the earth. How could smoke and soot in the atmosphere wipe out life far beyond the area of direct impact? Because any particles in the atmosphere can block the light from the sun and reduce the excitation of electrons in chlorophyll molecules, photosynthesis depends on a relatively clean atmosphere. Any reduction in the available sunlight can have serious effects on plants. Scientists believe that if a large meteor hit the earth—as one did when the dinosaurs were wiped out 65 million years ago—smoke, soot, and dust in the atmosphere could block sunlight to such an extent that plants in the region, or even possibly all of the plants on earth, could not conduct photosynthesis at high enough levels to survive. And when plants die off, all of the animals and other species that rely on them for energy die as well. As dire as it sounds, all life on earth is completely dependent on the continued excitation of electrons by sunlight. 6

7. stroma thylakoid compartment thylakoid membrane system two outer membranes Chloroplast Organelle of photosynthesis in plants and algae 7

8. a A look inside the leaf b One of the photosynthetic cells inside leaf leaf’s upper epidermis photosynthetic cell in leaf leaf vein leaf’s lower epidermis Leaf Structure 8

9. Photosynthesis Equation 6H 2 O + 6CO 2 6O 2 + C 6 H 12 O 6 watercarbon dioxide oxygenglucose LIGHT ENERGY 9

10. Photosynthesis Two stages: light-dependent reactions require light to work light-independent reactions do not require light 10

11. sunlight Where the two stages of photosynthesis occur inside the chloroplast light- dependent reactions light- independent reactions CO 2 sugars NADPH, ATP NADP +, ADP O2O2 H2OH2O Two Steps in Photosynthesis 11

12. Photosynthesis: Light- Dependent Photosystems - pigments surrounding a central chlorophyll a molecule....the reaction center Each pigment absorbs a different wavelength of light & transfers its energy to the reaction center which in turns energizes an electron. Only the chlorophyll that is the reaction center can give the energized electrons to the electron acceptors! The energized electron is then used elsewhere to make ATP or NADPH 12

13. Two Potential Fates of Excited Electrons 1. Electron returns to resting, unexcited state. 2. Excited electrons are passed to other atoms. 13

14. 14 Photosynthesis: Light-Dependent

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17. The Passing of Electrons in Their Excited State Chief way energy moves through cells Molecules that gain electrons always carry greater energy than before receiving them Can view this as passing of potential energy from molecule to molecule 17

18. Photosynthesis: Light- Dependent 18

19. Photosynthesis: Light- Dependent As these pigments absorb photons from the sunlight that hits the leaves, electrons in the pigments become excited and then return to their resting state. As the electrons return to their resting state, energy (but not the electrons) is transferred to neighboring pigment molecules. This process continues until the transferred energy from many pigment molecules excites the electrons in a chlorophyll a molecule at the center of the photosystem. 19

20. Photosynthesis: Light- Dependent This is where the electron journey begins. The special chlorophyll a continually loses its excited electrons to a nearby molecule, called the primary electron acceptor, which acts like an electron vacuum. Why must plants get water for photosynthesis to occur? As electrons keep getting taken away from the special chlorophyll a molecule, the electrons must be replaced. The replacement electrons come from water. 20

21. Photosynthesis: Light- Dependent 21

22. Photosynthesis: Light- Dependent Think of a pump pushing water into an elevated tank, creating a store of potential energy that can run out of the tank with great force and kinetic energy, which can be harnessed to do work, such as moving a large paddle wheel. Similarly, the protons eventually rush out of the thylakoid sacs with great force—and that force is harnessed to build energy-storing ATP molecules, one of the two products of the “photo” portion of photosynthesis. 22

23. Photosynthesis: Light- Dependent Product #1 of the “Photo” Portion of Photosynthesis: ATP Product #2: NADPH Product #3 (waste): O 2 23

24. Also known as the Calvin Cycle They occur whether or not light is present. Occur in the stroma of the chloroplast. The purpose of the reactions is to take the energy from ATP and energized ions from NADPH and add them to carbon dioxide to make glucose or sugar. The reactions reduce carbon dioxide by adding energize electrons and protons to it and removing one oxygen atom. This effectively converts the carbon dioxide into CH 2 O. 24 Photosynthesis: Light- inDependent

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26. Photosynthesis: Light- inDependent 26

27. Factors that Affect Rates 3 factors can limit the speed of photosynthesis: light intensity, CO 2 concentration, temperature Without enough light, a plant cannot photosynthesize very quickly, even if there is plenty of water and CO 2. 27

28. Factors that Affect Rates 28 Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesize if there is insufficient carbon dioxide.

29. Factors that Affect Rates If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesize if it gets too hot. 29

30. Summary of Photosynthesis 12H 2 O sunlight Calvin- Benson cycle 6O 2 Light Dependent Reactions Light Independent Reactions NADP + ADP + P i 6 RuBP 12 PGAL P end products (e.g., sucrose, starch, cellulose) phosphorylated glucose 6H 2 O 6CO 2 ATP NADPH

31. Linked Processes Photosynthesis Energy-storing pathway Releases oxygen Requires carbon dioxide Aerobic Respiration Energy-releasing pathway Requires oxygen Releases carbon dioxide

32. Photosynthesis: The Movie Animation 32

33. The battle against world hunger can use plants adapted to water scarcity.

34. Stomata Pores for gas exchange

35. How to get CO 2 when stomata are shut? Primary sites for gas exchange in plants CO 2 for photosynthesis O 2 generated as a by-product in photosynthesis exits water vapor evaporates Closed stomata: prevents water evaporation O 2 cannot be released from the chloroplasts  CO 2 cannot enter them  No carbon = no Calvin cycle plant growth comes to a standstill; crops fail 35

36. Evolutionary Adaptations Some plants are able to thrive in hot, dry conditions. Evolutionary adaptations – along with recent agricultural (technological) advances – help battle world hunger plants close their stomata to combat water loss through evaporation 36

38. C4 Photosynthesis C4 plants produce an enzyme that is better at attracting carbon (in addition to RUBISCO) called PEP Carboxylase allows CO 2 to be taken into the plant very quickly "delivers" the CO 2 directly to RUBISCO Called C4 because the CO 2 is first incorporated into a 4-carbon compound Stomata are open during the day

39. C4 Photosynthesis Adaptive Value: photosynthesizes faster than C3 plants under high light intensity and high temperatures better water use efficiency because PEP Carboxylase brings in CO 2 faster  doesn’t need to keep stomata open as much C4 plants include several thousand species in at least 19 plant families, including corn & sugarcane C4 photosynthesis also adds additional energy expense; outcompeted in mild climates by C3 plants.

40. C4 Photosynthesis

42. CAM Photosynthesis CAM = Crassulacean Acid Metabolism after plant family in which it was first found (Crassulaceae) because CO 2 is stored as an acid before use in photosynthesis Stomata open at night (evaporation rates usually lower), closed during day CO 2 converted to acid, stored @ night daytime: acid broken down CO 2 released to RUBISCO for photosynthesis

43. CAM Photosynthesis Adaptive Value: better water use efficiency than C3s under arid conditions open stomata @ night when transpiration rates are lower no sunlight, lower temperatures, lower wind speeds, etc. May CAM-idle under extremely arid conditions leave stomata closed night and day O 2 given off in photosynthesis is used for respiration CO 2 given off in respiration is used for photosynthesis kind of like a perpetual energy machine, but plant cannot CAM- idle forever allows plant to survive dry spells, recover very quickly when water is available again (unlike plants that drop their leaves and twigs and go dormant during dry spells)

44. 44 CAM Photosynthesis

45. All Three Photosynthetic Pathways

46. Evolutionary Adaptations & World Hunger C4 and CAM photosynthesis originally evolved as successful adaptations to hot/dry regions Researchers are now using these adaptations to fight world hunger. several genes that code for the C4 photosynthesis enzymes have been introduced from corn into rice once in rice, genes increase rice plant’s ability to photosynthesize  higher growth rates and food yields