© 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

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.

Figure 7.0

© 2010 Pearson Education, Inc. 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.

© 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

© 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.

© 2010 Pearson Education, Inc. 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

Plants (mostly on land) Forest plants Figure 7.1a

Photosynthetic Protists (aquatic) Kelp, a large alga Figure 7.1b

Photosynthetic Bacteria (aquatic) Micrograph of cyanobacteria LM Figure 7.1c

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

© 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.

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

Leaf cross section Stomata Vein CO 2 O2O2 Figure 7.2-1

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

Leaf cross section Stomata Vein CO 2 O2O2 Figure 7.2a

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

© 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.

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

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

© 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.

© 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 Blast Animation: Photosynthesis: Light-Independent Reaction

Light H2OH2O O2O2 Chloroplast Light reactions NADPH ATP Figure 7.3-1

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

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.

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.

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

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.

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

© 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. Animation: Light and Pigments

Bacterium Wavelength of light (nm) Light Number of bacteria Algal cells Prism Microscope slide Figure 7.5

Light Chloroplast Reflected light Absorbed light Transmitted light Figure 7.6

Light Chloroplast Reflected light Absorbed light Transmitted light Figure 7.6a

Figure 7.6b

© 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

© 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.

Figure 7.7

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

© 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.

Light (b) Fluorescence of a glow stick Photon Heat Light (fluorescence) Ground state Chlorophyll molecule Excited state e–e– (a) Absorption of a photon Figure 7.8

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

(b) Fluorescence of a glow stick Figure 7.8b

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

Chloroplast Figure 7.9-1

Chloroplast Thylakoid membrane Pigment molecules Figure 7.9-2

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

© 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

Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H Reaction- center chlorophyll 2e – – O2O2 + + Figure

Primary electron acceptor Water-splitting photosystem Light H2OH2O 2 H Reaction- center chlorophyll 2e – – O2O2 + + Electron transport chain Energy to make ATP Figure

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

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

© 2010 Pearson Education, Inc. 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

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

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

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.

Calvin cycle P P P Three-carbon molecule RuBP sugar CO 2 (from air) Figure

ATP NADPH Calvin cycle ADP  P NADP  P P P P G3P sugar Three-carbon molecule RuBP sugar CO 2 (from air) Figure

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

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 © 2010 Pearson Education, Inc.

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

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

Sugar C 4 Pathway (example: sugarcane) C 4 plant Calvin cycle Cell type 1 Four-carbon compound Cell type 2 CO 2 Figure 7.14a

CAM plant Sugar Calvin cycle Day Four-carbon compound Night CAM Pathway (example: pineapple) CO 2 Figure 7.14b

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

Light reactions CO 2 O2O2 H2OH2O (C 6 H 12 O 6 ) NADPH Light Sugar ATP ADP P NADP  Calvin cycle Figure 7.UN2

Light reactions CO 2 O2O2 H2OH2O (C 6 H 12 O 6 ) NADPH Light Sugar ATP ADP P NADP  Calvin cycle Figure 7.UN3

Carbon dioxide 6 O 2 6 CO 2 6 H 2 O C 6 H 12 O 6 Water Glucose Photosynthesis Oxygen gas Light energy Figure 7.UN4

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

acceptor Water-splitting photosystem Photon H2OH2O 2 H Chlorophyll 2e – O2O2 + + Electron transport chain ATP NADPH-producing photosystem Chlorophyll NADPH NADP + e – 2e – – – e – acceptor ADP Photon 2 1 Figure 7.UN6

NADPH Calvin cycle ADPP NADP  P ATP G3P CO 2 Glucose and other compounds Figure 7.UN7