1. © 2010 Pearson Education, Inc. Lectures by Chris C. Romero, updated by Edward J. Zalisko PowerPoint ® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Chapter 7 Photosynthesis: Using Light to Make Food

2. Biology and Society: Green Energy Wood has historically been the main fuel used to: –Cook –Warm homes –Provide light at night © 2010 Pearson Education, Inc.

3. Industrialized societies replaced wood with fossil fuels. To limit the damaging effects of fossil fuels, researchers are investigating the use of biomass (living material) as efficient and renewable energy sources.

4. © 2010 Pearson Education, Inc. Fast-growing trees, such as willows: –Can be cut every three years –Do not need to be replanted –Are a renewable energy source –Produce fewer sulfur compounds –Reduce erosion –Provide habitat for wildlife

5. © 2010 Pearson Education, Inc. THE BASICS OF PHOTOSYNTHESIS Photosynthesis: –Is used by plants, some protists, and some bacteria –Transforms light energy into chemical energy –Uses carbon dioxide and water as starting materials The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules.

6. © 2010 Pearson Education, Inc. Organisms that use photosynthesis are: –Photosynthetic autotrophs –The producers for most ecosystems

7. Plants (mostly on land) Photosynthetic Protists (aquatic) PHOTOSYNTHETIC AUTOTROPHS Photosynthetic Bacteria (aquatic) Micrograph of cyanobacteriaKelp, a large alga Forest plants LM Figure 7.1

8. © 2010 Pearson Education, Inc. Chloroplasts: Sites of Photosynthesis Chloroplasts are: –The site of photosynthesis –Found mostly in the interior cells of leaves

9. © 2010 Pearson Education, Inc. Inside chloroplasts are membranous sacs called thylakoids, which are suspended in a thick fluid, called stroma. Thylakoids are concentrated in stacks called grana. The green color of chloroplasts is from chlorophyll, a light- absorbing pigment.

10. © 2010 Pearson Education, Inc. Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.

11. Leaf cross section Stomata Vein CO 2 O2O2 Interior cell LM Stroma Granum Thylakoid Chloroplast Outer membrane Inner membrane TEM Figure 7.2-2

12. © 2010 Pearson Education, Inc. The Overall Equation for Photosynthesis In the overall equation for photosynthesis, notice that: –The reactants of photosynthesis are the waste products of cellular respiration.

13. Carbon dioxide 6 O 2 6 CO 2 6 H 2 O C 6 H 12 O 6 Water Glucose Photo- synthesis Oxygen gas Light energy Figure 7.UN1

14. © 2010 Pearson Education, Inc. In photosynthesis: –Sunlight provides the energy –Electrons are boosted “uphill” and added to carbon dioxide –Sugar is produced

15. © 2010 Pearson Education, Inc. During photosynthesis, water is split into: –Hydrogen –Oxygen Hydrogen is transferred along with electrons and added to carbon dioxide to produce sugar. Oxygen escapes through stomata into the atmosphere.

16. © 2010 Pearson Education, Inc. A Photosynthesis Road Map Photosynthesis occurs in two stages: –The light reactions convert solar energy to chemical energy –The Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide

17. Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP Calvin cycle CO 2 NADP + ADP P Sugar (C 6 H 12 O 6 ) Figure 7.3-2

18. THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Chloroplasts: –Are chemical factories powered by the sun –Convert solar energy into chemical energy © 2010 Pearson Education, Inc.

19. The Nature of Sunlight Sunlight is a type of energy called radiation, or electromagnetic energy. The full range of radiation is called the electromagnetic spectrum.

20. Visible light Wavelength (nm) Radio waves 380 400 500 600 750 700 Wavelength = 580 nm Micro- waves Gamma rays Infrared UV X-rays 10 –5 nm 10 –3 nm10 3 nm 1 nm 10 6 nm 1 m1 m 10 3 m Increasing wavelength Figure 7.4

21. The Process of Science: What Colors of Light Drive Photosynthesis? Observation: In 1883, German biologist Theodor Engelmann saw that certain bacteria tend to cluster in areas with higher oxygen concentrations. Question: Could this information determine which wavelengths of light work best for photosynthesis? Hypothesis: Oxygen-seeking bacteria will congregate near regions of algae performing the most photosynthesis. © 2010 Pearson Education, Inc.

22. Experiment: Engelmann: –Laid a string of freshwater algal cells in a drop of water on a microscope slide –Added oxygen-sensitive bacteria to the drop –Used a prism to create a spectrum of light shining on the slide

23. © 2010 Pearson Education, Inc. Results: Bacteria: –Mostly congregated around algae exposed to red-orange and blue-violet light –Rarely moved to areas of green light Conclusion: Chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum.

24. Bacterium Wavelength of light (nm) 400 500 600 700 Light Number of bacteria Algal cells Prism Microscope slide Figure 7.5

25. Light Chloroplast Reflected light Absorbed light Transmitted light Figure 7.6

26. Light Chloroplast Reflected light Absorbed light Transmitted light Figure 7.6a

27. © 2010 Pearson Education, Inc. Chloroplast Pigments Chloroplasts contain several pigments: –Chlorophyll a: –Absorbs mostly blue-violet and red light –Participates directly in the light reactions –Chlorophyll b: –Absorbs mostly blue and orange light –Participates indirectly in the light reactions

28. © 2010 Pearson Education, Inc. –Carotenoids: –Absorb mainly blue-green light –Participate indirectly in the light reactions –Absorb and dissipate excessive light energy that might damage chlorophyll –The spectacular colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids.

29. Figure 7.7

30. © 2010 Pearson Education, Inc. How Photosystems Harvest Light Energy Light behaves as photons, discrete packets of energy.

31. © 2010 Pearson Education, Inc. Chlorophyll molecules absorb photons. –Electrons in the pigment gain energy. –As the electrons fall back to their ground state, energy is released as heat or light.

32. Light Photon Heat Light (fluorescence) Ground state Chlorophyll molecule Excited state e–e– (a) Absorption of a photon Figure 7.8a

33. © 2010 Pearson Education, Inc. A photosystem is a group of chlorophyll and other molecules that function as a light-gathering antenna.

34. Chloroplast Thylakoid membrane Pigment molecules Antenna pigment molecules Primary electron acceptor Reaction- center chlorophyll a Photon Electron transfer Reaction center Photosystem Transfer of energy Figure 7.9-3

35. © 2010 Pearson Education, Inc. How the Light Reactions Generate ATP and NADPH Two types of photosystems cooperate in the light reactions: –The water-splitting photosystem –The NADPH-producing photosystem

36. Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H Reaction- center chlorophyll 2e – – O2O2 + + Electron transport chain Energy to make ATP Primary electron acceptor 2e – Light NADPH-producing photosystem Reaction- center chlorophyll 2e – NADPH NADP  Figure 7.10-3

37. © 2010 Pearson Education, Inc. The light reactions are located in the thylakoid membrane.

38. © 2010 Pearson Education, Inc. An electron transport chain: –Connects the two photosystems –Releases energy that the chloroplast uses to make ATP

39. Light H2OH2O Thylakoid membrane 2e – O2O2 ATP NADP  Light Stroma Inside thylakoid Photosystem Electron transport chain NADPH ADP  P H+H+ ATP synthase To Calvin cycle HH Electron flow H+H+ HH HH HH HH Figure 7.11

40. Light H2OH2O Thylakoid membrane 2e – O2O2 ATP NADP  Light Stroma Inside thylakoid Photosystem Electron transport chain NADPH ADP  P ATP synthase To Calvin cycle Electron flow HH HH HH HH HH HH HH Figure 7.11a

41. Water-splitting photosystem e – Photon ATP NADPH e – e – e – e – e – Photon e – NADPH-producing photosystem Figure 7.12

42. THE CALVIN CYCLE: MAKING SUGAR FROM CARBON DIOXIDE The Calvin cycle: –Functions like a sugar factory within the stroma of a chloroplast –Regenerates the starting material with each turn © 2010 Pearson Education, Inc.

43. ATP NADPH Calvin cycle ADP  P NADP  P P P P P P ADP  P ATP G3P sugar Three-carbon molecule G3P sugar RuBP sugar CO 2 (from air) Glucose (and other organic compounds) Figure 7.13-4

44. Evolution Connection: Solar-Driven Evolution C 3 plants: –Use CO 2 directly from the air –Are very common and widely distributed © 2010 Pearson Education, Inc.

45. C 4 plants: –Close their stomata to save water during hot and dry weather –Can still carry out photosynthesis CAM plants: –Are adapted to very dry climates –Open their stomata only at night to conserve water

46. Sugar C 4 Pathway (example: sugarcane) C 4 plant CAM plant Sugar Calvin cycle Calvin cycle Day Cell type 1 Four-carbon compound Night Four-carbon compound Cell type 2 CAM Pathway (example: pineapple) ALTERNATIVE PHOTOSYNTHETIC PATHWAYS CO 2 Figure 7.14