1. Photosynthesis Chapter 8 Section 8.2 Overview of photosynthesis

2. Review PhotosynthesisPhotosynthesis = the process where light energy is converted into chemical energy AutotrophsAutotrophs= “self feeders” Organisms that use energy from sunlight or chemical bonds to make organic compounds Majority are photosynthetic

3. Photosynthesis equation: Reactants products

4. ATP is essential for life –What is ATP? Adenosine triphosphate ENERGY Why do cells need energy? ATP

5. How do cells release their stored energy? By breaking the high energy bond between the last two phosphates in ATP

6. ATP synthaseATP synthase makes ATP from ADP –Puts a phosphate back on the inactive ADP so it can then store energy again like a compacted spring.

7. Almost all plants are photosynthetic autotrophs, as are some bacteria and protists –Autotrophs generate their own organic matter through photosynthesis –Sunlight energy is transformed to energy stored in the form of chemical bonds (a) Mosses, ferns, and flowering plants (b) Kelp (c) Euglena (d) Cyanobacteria An Overview of Photosynthesis How do they capture energy and change it into a useful form?

8. Chlorophyll and Chloroplasts In order for photosynthesis to occur, light from the sun must be captured Our eyes see the different wavelengths of the visible spectrum as different colors: red, orange, yellow, green, blue, indigo, and violet.

9. Remember The Electromagnetic Spectrum?

10. pigmentsPlants gather the energy from the sun with light absorbing molecules called pigments PigmentsPigments: light absorbing substances that absorb certain wavelengths. PhotonPhoton: Particles of light energy Chlorophyll is the primary pigment involved in photosynthesis –Chlorophyll a and chlorophyll b –Located in the chloroplast!

11. The difference between chlorophyll a and b are the structure shown here This determines what wavelengths of light they can absorb

12. Carotenoids and xanthophylls give trees their fall colors are pigments that produce the orange and yellow colors on the leaves in the fall. These pigments are called accessory pigments

14. Chloroplasts absorb light energy and convert it to chemical energy Light Reflected light Absorbed light Transmitted light Chloroplast The color seen is the color not absorbed.

15. The Chloroplast Membrane bound organelle that contains chlorophyll Site of photosynthesis

16. thylakoids – membranes in flattened coin- shaped stacks, the stacks are called grana. The light dependent reactions happen in these thylakoids.

17. stroma – the fluid-filled spaces around the grana/thylakoids, the light independent reactions of photosynthesis take place in the stroma.

18. What’s so special about chlorophyll that makes it important for photosynthesis? When light strikes the thylakoid in a chloroplast the energy is transferred to electrons. Electrons get “excited” and their energy level is raised. Raising this level produces high-energy electrons which make photosynthesis work.

19. High energy electrons ATP – adenosine triphosphate, carries energy NADPH – nicotinamide adenine dinucleotide phosphate, a molecule that carries hydrogen and excited electrons; this will transfer energy NADP + is converted to an active form to be used by the cell to make glucose.

20. Photosynthesis Overview Occurs in two main phases. Light reactions –the “photo” part of photosynthesis. – Light is absorbed by pigments. –Takes place in the thylakoid. – Produce energy rich compounds (ATP and NADPH) Light independent reactions (Calvin Cycle) – the “synthesis” part of photosynthesis. – Take place in the stroma –Uses carbon dioxide, ATP and NADPH to produce high energy sugars

21. What are the reactants in the light independent reactions? What are the products in the light independent reactions?

22. Section 8.3 The Process of Photosynthesis

23. Why do chloroplasts contain so many membranes? When most pigments absorb light, they eventually lose most of that energy as heat. Chloroplasts avoid such losses. Membranes are the key to capturing light energy in the form of high-energy electrons Where do the light dependent reactions occur?

24. Light Dependent Reactions photosystems.Thylakoids contain clusters of chlorophyll and proteins known as photosystems. These photosystems absorb sunlight and generate the high-energy electrons that are passed down a series of electron carriers embedded in the membrane of the thylakoid. Photosystem II and photosystem I

25. Primary electron acceptor Photon Reaction center PHOTOSYSTEM Pigment molecules on the thylakoid Molecular Game of “Hot Potato”

26. The Light Dependent Reactions of Photosynthesis 1.Photons of light are absorbed by photosystem II 2. An enzyme splits water into H+, which is put into the thylakoid space (compartment), oxygen, and electrons 3. Oxygen from the water is given off as waste O HH

27. 4. Electrons are excited when light hits photosystem II; electrons go from a ground state to an excited state electron transport chain 5.High energy level electrons are then transported down the electron transport chain (etc) embedded in the thylakoid membrane –A series of electron carrier proteins that carry electrons

29. The thylakoid membrane provides new electrons to chlorophyll from water molecules. Enzymes of the inner surface of the thylakoid break up water molecules into 2 electrons, 2 H + ions, and 1 oxygen atom.

30. The O 2 liberated by photosynthesis is made from the oxygen in water (H + and e - ) Plants produce O 2 gas by splitting H 2 O

31. What happens to the energy of the excited electron? Some of the energy that is released by the electrons is used to pump protons (H+ ions) into the thylakoid space

32. Outside Thylakoid Inside thylakoid H2OH2O H+ An electron from water replaces the electron in chlorophyll-a that goes down the electron transport chain. e ½ O

33. As more and more electrons are transported down the electron transport chain, more and more hydrogen ions are pumped inside the thylakoid. Inside thylakoid e H+

34. At the end of the electron transport chain, the electrons pass to photosystem I. Pigments from photosystem I reenergize the electron and they travel down a second ETC. At the end of the ETC, NADP+ picks up the electron and a H+ ion to become NADPH

36. ATP synthaseAs more H+ ions are being pumped into the thylakoid space, they begin to diffuse down their concentration gradient out into the stroma through ATP synthase the specific protein channel that will only let H+ ions out. –This process is called chemiosmosis As the protons flow down their concentration gradient, the energy is used to add a phosphate to ADP to make ATP.

37. Outside Thylakoid Inside thylakoid H+ ADP ATP P

38. Chemiosmosis

39. Notice that water has been used and oxygen wastes have been released from the light dependent reactions. No carbon dioxide has been used and no glucose has been made yet. These will occur in the Calvin cycle (the light independent reactions)

40. Products from the light reactions Oxygen ATP NADPH ATP and NADPH are used for the second stage of photosynthesis…

41. Role of the Calvin Cycle The Calvin cycle uses ATP and NADPH to make sugar from CO 2. –anabolic Where do these reactions occur?

42. Uses ATP as an energy source Consumes NADPH as reducing power to add high-energy electrons to make carbohydrates The carbohydrate produced is a 3-C sugar called glyceraldehyde-3-phosphate (G3P) –Two G3P can be made into glucose (6 carbons)

43. Phase 1: Carbon fixation: –The initial incorporation of CO 2 into organic compounds Rubisco is the enzyme that incorporates carbon from CO 2 into a 5 carbon sugar Phase 2: Reduction: –ATP is used –High energy electrons are donated from NADPH (where does this come from?) –this is reducing power –A 3-carbon sugar (G3P) is made and exits the cycle

44. Phase 3: Regeneration: –The 5-carbon compound is regenerated so that the cycle can continue –More ATP is used to accomplish this

46. How many ATP are used to make 1 molecule of glucose? How many NADPH are used to make one molecule of glucose?

47. Factors Affecting Photosynthesis factors that affect photosynthesis are temperature, light intensity, and the availability of water. Temperature: –enzymes that function best between 0°C and 35°C – what is temperature is too high or low?

48. Light intensity –high light intensity increases the rate of photosynthesis…why? –When light intensity reaches a certain level, the plant will reach its maximum rate of photosynthesis

49. Available Water What does water do in photosynthesis? Water loss can also damage tissues…how? waxy cuticlePlants that live in dry conditions have a waxy cuticle on their leaves to prevent water loss.

50. Gas Exchange in Plant Leaves stomataOccurs through small openings called stomata guard cellsOpenings surrounded by guard cells CO 2 travels in O 2 and H 2 O vapor travels out

51. Plants that survive under extreme conditions Some plants have evolved special metabolic pathways to allow them to continue photosynthesis at a high rate even when it is very hot and dry outside These include C4 plants and CAM plants.

52. Plants that live in hot, dry conditions may close their stomata to prevent water loss This can reduce photosynthesis…why Two alternative pathways have evolved in some plant groups that allow PS rate to be high even under hot, dry conditions: C4 & CAM pathways

53. C 4 Plants 1. A special enzyme called PEP- carboxylase initially fixes carbon dioxide into 4-carbon compounds (the normal Calvin cycle fixes them into 3-carbon molecules with rubisco) 2. CO 2 is incorporated in mesophyll cells 3. The Calvin cycle occurs in the bundle sheath cells

54. C 4 plants have bundle sheath cells and mesophyll cells

55. CAM Plants undergo Crassulacean Acid Metabolism 1. The CAM pathway is found in many desert plants (hot, arid environments) 2. Plants assimilate CO 2 at night, when their stomata are open; stomata are closed during the day 3. Plants store organic acids in vacuoles 4. In the morning, the organic acids are broken down, CO 2 is released, and the Calvin cycle occurs

56. CAM plants