botit.botany.wisc

1. PhotosynthesisLecture 7 http://botit.botany.wisc.edu

2. Much of the text material in the lecture notes is from our textbook, “Essential Biology with Physiology” by Neil A. Campbell, Jane B. Reece, and Eric J. Simon (2004 and 2008). I don’t claim authorship. Other sources were sometimes used, and are noted.

3. Outline • Our Sun • Energy production from biomass • Chloroplasts • The nature of light • Photosynthesis • Water-saving plant adaptations • Global warming • Ozone effects • The oxygen revolution • Words and terms to know • Possible test items

4. Morning Vincent Van Gogh, “Olive Trees and Yellow Sun” http:/www.vin.bg.yu The Sun, trees, and grass are part of a fascinating story…

5. Our Sun • Our Sun accounts for 99.8 percent of the total mass of the solar system. • The Sun is a third-generation star composed of hydrogen, helium, and small quantities of other elements formed in earlier stars. • Energy is generated through the nuclear fusion of hydrogen into helium. • The Sun formed about five billion years ago—it has enough hydrogen fuel for another five billion years.

6. Solar Image http://students.utsi.edu Sunlight enables life on earth through photosynthesis. It also drives the Earth’s climate and weather patterns.

7. A Few Statistics • Earth is about 93 million miles from the Sun depending upon where we are in the elliptical orbit. • Sunlight reaches us in 500 seconds. • The light from the next nearest star, Alpha Centauri, takes four years at the speed of light, 186,000 miles per second.

8. Mt. Wilson Solar Observatory http://www.starimager.com Check-out the skycam at http://www.astro.ucla.edu/~obs/towercam.htm Daily records of solar activity have been kept for over 100 years.

9. Vegetation Aspen grove and ferns http://www.nbil.gov An aspen grove has a common root system.

10. Photosynthetic Organisms • Plants and other photosynthetic organisms produce about 1.5 x 1011 tons of organic material each year by converting sunlight to chemical energy. • All food consumed by humans can be traced to the process of photo-synthesis. • Plants also produce other raw materials we use including wood, cotton, and paper. • Coal and hydrocarbon fuels that power our automobiles, airplanes, and trains can be traced to early plant life.

11. Energy from Biomass • Energy plantations provide a source of renewable energy—tree species include willow, sycamore, eucalyptus, and black locust. • The trees are cut every few years and used in power plants to produce electricity. • Wood burned for energy has few of the sulfur impurities found in coal that produces acid rain in the northeastern United States and Canada. • Tree plantations provide habitat for wildlife, reduce erosion, renew soil, and help farmers diversify. • The rapidly growing young trees also remove CO2from the atmosphere.

12. Biomass Energy Cycle http://www.repp.org Energy produced from biomass currently accounts for about four percent of all energy consumed today in the United States.

13. Forms of Biomass http://www.eia.doe.gov All forms of biomass ultimately derive their energy content from sunlight.

14. Photosynthesis • All green parts of plants can perform photosynthesis. • The green color of plants is from the chlorophyll pigments contained in chloroplasts. • Chlorophyll absorbs the light energy that chloroplasts use for producing chemical energy.

15. Chloroplasts • Since leaves typically have the most chloroplasts, they are the major sites of photosynthesis. • Chloroplasts are concentrated in the cells of the mesophyll, the tissue in the interior of the leaf. • Carbon dioxide enters and oxygen exits by way of stomata found on the undersurface of leaves. • Roots provide the water, which travels to the leaves via veins, needed for photosynthesis.

16. Internal Structure http://micro.magnet.fsu.edu Photosynthesis occurs in chloroplasts.

17. Internal Structure • Chloroplasts, like the mitochondria, have a double-membrane envelope. • The inner membrane encloses a compartment containing stroma, a thick fluid. • Thylakoids are suspended in the stroma, and the chlorophyll molecules are contained in their membranes. • The thylakoids are organized in elaborate stacked systems known as grana.

18. Microscopic View Electron micrograph http://botany.wisc.edu The stroma, grana, and individual thylakoids are visible.

19. Stomata Stomata are found primarily on the undersurface of leaves. The word means ‘mouth’ in Greek. http://www.eoearth.org Microscopic views http://www.agr.gc.ca

20. Chemical Cycle in Ecosystems Sunlight http://img.dailymail.co.uk Photosynthesis Chloroplasts in plants http://pws.byu.edu C6H12O6 (glucose) + O2(oxygen) CO2 (carbon dioxide) + H2O (water) Cellular Respiration Mitochondria in animals and plants http://www.soquel.org ATP Cellular Work

21. Cellular Respiration + + + C6H12O6 (glucose) 6O2 6CO2 6H2O ATP (chemical energy) Cellular Respiration ATP molecule Glucose molecule http://biology.clc.uc.edu http://eurekalert.org

22. Photosynthesis http://www.kidsforsavingearth.org + + 6CO2 C6H12O6 (glucose) 6O2 6H2O Chloroplasts

23. Light Reaction and Calvin Cycle • Photosynthesis is not one process, but two closely-related processes that each have many steps. • The processes are the light reaction and Calvin cycle (also known as the dark reaction).

24. Light Reaction and Calvin Cycle H2O CO2 Chloroplast NADP+ and ADP plus phosphorous Sunlight Calvin Cycle Light Reaction ATP and NADPH Oxygen (waste product) Glucose O2 http://eurekalert.org

25. Light and Dark Reactions • The light reaction process converts sunlight to chemical energy by splitting the covalent bonds in H2O. • The chemical energy is stored in ATP and NADPH molecules—NADPH is related to NADH in cellular respiration. • The Calvin cycle uses the energy-rich molecules from the light reaction to produce glucose from CO2.

26. Other Photosynthetic Organisms http://user.uni-frankfurt.de http://www.scribemedia.org Cyanobacteria Algae http://www.dtplankton.com Phytoplankton

27. The Nature of Light • Light is a type of radiation, or electromagnetic energy, consisting of particles and waves. • Photons are particles, and waves are measured by their wavelength. • A photon behaves as a discrete package of energy called a quantum. • Photons have greater energy in the shorter wavelengths of visible light (blue, purple, and violet) than they do in the longer wavelengths (red and orange).

28. Electromagnetic Spectrum Increasing energy Wavelength 10-5 nm 10-3 nm 1 nm 103 nm 106 nm 1 m 103 m Electromagnetic spectrum Gamma rays Ultra- violet X-rays Infrared Microwaves Radio waves 380 nm 750 nm Visible light VioletIndigoBlueGreenYellowOrangeRed ‘ROY G BIV’ R—Red O—Orange Y—Yellow G—Green B—Blue I—Indigo V—Violet The light we see is a small slice of the electromagnetic spectrum. Sunlight consists of 45 percent visible light, 46 percent infrared, and 9 percent ultraviolet.

29. http://www.missouriskies.org Rainbow

30. The Nature of Color • The light shining on a pigmented material absorbs all wavelengths except those reflected from the object. • The reflected light gives the object its color. • Plant leaves appear green because the pigments contained in chlorophyll absorb the blue-violet and red-orange wavelengths. • Color is the brain’s processing and interpretation of wavelengths of light. http://www.cg.tuwien.ac.at

31. Other Animals • Some animals can sense somewhat different wavelengths than humans. • Honeybees sense ultraviolet light, which is used in communicating the path to nectar-bearing flowers to other hive members. • Pit vipers, including rattlesnakes, use infrared radiation to find prey in the night. http://joeorman.shutterace.com

32. Chloroplast Pigments • The pigment in chlorophyll a absorbs blue-violet and red wavelengths. • Chlorophyll a participates in the light reaction process. • Chlorophyll b is sensitive to other wavelengths,and conveys energy to chlorophyll a.

33. Carotenoids • Carotenoids in chloroplasts contain yellow-orange pigments that absorb blue-green light—their energy is also conveyed to chlorophyll a. • The carotenoids in carrots and other vegetables can absorb excessive light energy to prevent damage to chlorophyll. http://www.worldcommunitycookbook.org

34. Autumn Color Fuji-Hakone-Izu National Park, Japan http://www.tropicalislands.de Color changes are partly due to decreases in green chlorophyll, allowing the red-orange hues of the carotenoids to show through the epidermis of the leaves.

35. Photosystem • The pigments in thylakoids are organized into complex photosystems. • Each photosystem has several hundred elements of chlorophyll a, chlorophyll b, and carotenoids. • The photosystem acts as a light gathering antenna—when a photon strikes a pigment molecule, an electron in the molecule gains energy.

36. Photosystem http://fig.cox.miami.edu

37. Harvesting of Light Energy • The electron jumps from element to element in the photosystem until it arrives at the reaction center of the photosystem. • The reaction center of chlorophyll a, is located adjacent to a primary electron acceptor. • This acceptor traps the electron, and passes it to molecules in the thylakoid membrane to produce ATP from ADP, and NADPH from NADP+.

38. Calvin Cycle • The Calvin cycle produces sugar molecules in the stroma of the chloro-plasts. • As with the Krebs cycle, materials are regenerated with each turn of the cycle. • Inputs are CO2 from the atmosphere, and ATP and NADPH produced by the light reaction process.

39. G3P Molecule • The output of the Calvin cycle is the sugar molecule, glyceraldehyde 3-phosphate, or G3P. • Plant cells use the energy-rich molecule as material to produce glucose and other organic molecules, including starches.

40. Biochemistry of the Calvin Cycle http://fig.cox.miami.edu

41. Afternoon http://users.tk.fi/jsreunan Sunflowers offer a reminder of the importance of the Sun in the formation and sustainment of life.

42. Varieties of Sunflowers Many varieties of sunflowers exist. http://gmushrooms.com

43. Water-Saving Plant Adaptations • Like animals, plants have adapted to their unique environments to help assure their survival. • Different biological processes are employed, but with the same purpose of retaining water.

44. Wheatfield Eastern Montana http://dnrc.mt.gov Wheat is a C3 plant.

45. C3 Plants • Some plants are able to thrive in dry or arid conditions due to adapta-tions of the photosynthesis process. • Water-saving plants that use CO2 directly from the atmosphere are called C3 plants. • C3 plants found in agriculture include wheat, soybeans, oats, and rice.

46. C3 Plants • C3 plants close their stomata on hot, dry days to reduce water loss to the atmosphere. • The stomata closing prevents CO2 from entering the leaf, which slows or stops the Calvin cycle.

47. Cornfield Corn is a C4 plant. Kansas http://www.oznet.ksu.edu

48. C4 Plants • C4 plants can retain water in dry conditions without the photosynthesis process shutting-down. • In hot, dry weather the stomata are closed most of the time although photosynthesis continues. • C4 plants found in agriculture include corn, sorghum, and sugarcane. • These plants evolved in hot regions where frequent dry spells occur.

49. C4 Plants • C4 plants have an enzyme that incorporates an additional carbon from CO2 to form a four-carbon molecule in the Calvin cycle. • This enzyme has an intense affinity (attraction) for CO2, to mine carbon dioxide from the air spaces of leaves even when the stomata are closed.

50. Jade Crassula Argentea http://www.botany.wisc.edu Jade is a CAM plant.