© 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

© 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. Organisms that use photosynthesis are: –Photosynthetic autotrophs –The producers for most ecosystems

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

© 2010 Pearson Education, Inc. Chloroplasts: Sites of Photosynthesis Chloroplasts are: –The site of photosynthesis –Found mostly in the interior cells of leaves 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. Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.

Leaf cross section Stomata Vein CO 2 O2O2 Figure 7.2a

Stroma Granum Thylakoid Chloroplast Outer membrane Inner membrane TEM Figure 7.2b

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 In the overall equation for photosynthesis, notice that: The reactants of photosynthesis are the waste products of cellular respiration.

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

© 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

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

Visible light Wavelength (nm) Radio waves 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

© 2010 Pearson Education, Inc. The light reactions are located in the thylakoid membrane. An electron transport chain: –Connects the two photosystems –Releases energy that the chloroplast uses to make ATP

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

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.

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

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

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

Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP Calvin cycle CO 2 NADP + ADP P Sugar (C 6 H 12 O 6 ) Stack of thylakoids Stroma Figure 7.UN5