© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 7 Photosynthesis: Using Light to Make Food

Introduction  Plants, algae, and certain prokaryotes –convert light energy to chemical energy –by the process of photosynthesis and –store the chemical energy in sugar, made from –carbon dioxide and –water. © 2012 Pearson Education, Inc.

Figure 7.0_2 Unicellular algae

Introduction  Algae farms can be used to produce –oils for biodiesel or –carbohydrates to generate ethanol. –Unlike biofuel crops such as corn, algae don’t require large areas of fertile land, and they grow fast. © 2012 Pearson Education, Inc.

Figure 7.0_1 Chapter 7: Big Ideas An Overview of Photosynthesis The Light Reactions: Converting Solar Energy to Chemical Energy The Calvin Cycle: Reducing CO 2 to Sugar Photosynthesis Reviewed and Extended

AN OVERVIEW OF PHOTOSYNTHESIS © 2012 Pearson Education, Inc.

7.1 Autotrophs are the producers of the biosphere  Autotrophs –make their own food through the process of photosynthesis, and do not usually consume organic molecules derived from other organisms. –There are two kinds of autotrophs –Photoautotrophs- use the energy of light to produce organic molecules. Eg: Plants, algae, some protists & cyanobacteria –Chemoautotrophs- are prokaryotes that use energy in inorganic chemicals as their energy source. Eg: Sulfur bacteria that live in deep-ocean vents © 2012 Pearson Education, Inc.

Figure 7.1A-D Photoautotroph diversity Plants Photosynthetic protists Kelp, a multicellular alga Cyanobacteria

7.1 Autotrophs are the producers of the biosphere  Heterotrophs –are consumers that feed on other organisms (such as plants, animals, or decomposing organic material) –All animals –Humans –Fungi –Protists (that are not autotrophs) –Bacteria (except cyanobacteria) © 2012 Pearson Education, Inc.

7.1 Autotrophs are the producers of the biosphere  Photosynthesis –converts carbon dioxide and water –into organic molecules, and releases oxygen. © 2012 Pearson Education, Inc. Light energy C 6 H 12 O 6 CO 2 H2OH2O O2O2

Figure 7.2_1 Leaf Cross Section Mesophyll CO 2 O2O2 Vein Leaf Stoma Mesophyll Cell Chloroplast Cross section of a Leaf

7.2 Photosynthesis occurs in chloroplasts in plant cells  Mesophyll is the green tissue in the interior of the leaf. Chloroplasts are concentrated in mesophyll cells  Stomata are tiny pores in the leaf that allow –carbon dioxide to enter and –oxygen to exit.  Veins in the leaf deliver water absorbed by roots. © 2012 Pearson Education, Inc.

Figure 7.2_2 Chloroplast Thylakoid Thylakoid space Stroma Granum Inner and outer membranes Structure of Chloroplasts

7.2 Photosynthesis occurs in chloroplasts in plant cells  Chloroplasts –are the major sites of photosynthesis in green plants. –Chloroplasts consist of photosynthetic pigments, enzymes, and other molecules grouped together in membranes –There are about half a million chloroplasts per square millimeter of leaf surface. © 2012 Pearson Education, Inc.

7.2 Photosynthesis occurs in chloroplasts in plant cells  Chloroplasts –Consist of an envelope of two membranes, inner & outer membrane –Inner compartment is filled with a thick fluid called stroma –Contain a system of interconnected membranous sacs called thylakoids. –Stacks of thylakoides are called grana and © 2012 Pearson Education, Inc.

7.2 Photosynthesis occurs in chloroplasts in plant cells  Chlorophyll –molecules are built into the thylakoid membrane and –is an important light-absorbing pigment in chloroplasts, –is responsible for the green color of plants, and –plays a pivotal role in converting solar energy to chemical energy. © 2012 Pearson Education, Inc.

Figure 7.3A Bubbles on the leaves of an aquatic plant Q: Which gas is in the bubbles?

7.3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes  Scientists have known since the 1800s that plants produce O 2. But does this oxygen come from carbon dioxide or water? –For many years, it was assumed that oxygen was extracted from CO 2 taken into the plant. –However, later research using a heavy isotope of oxygen, 18 O, confirmed that oxygen produced by photosynthesis comes from H 2 O. © 2012 Pearson Education, Inc.

Figure 7.UN01 Photosynthesis Carbon dioxide Water Glucose Oxygen gas Light energy C 6 H 12 O 6 CO 2 H2OH2O O2O2 Photosynthesis

7.3 SCIENTIFIC DISCOVERY: Scientists traced the process of photosynthesis using isotopes Experiment 1: 6 CO 2  12 H 2 O → C 6 H 12 O 6  6 H 2 O  6 O 2 © 2012 Pearson Education, Inc. Experiment 2: 6 CO 2  12 H 2 O → C 6 H 12 O 6  6 H 2 O  6 O 2

Figure 7.3B Reactants: Products: Q: Photosynthesis produces billions of tons of carbohydrates a year. Where does most of the mass of this huge amount of organic matter come from?

7.4 Photosynthesis is a redox process, as is cellular respiration  Photosynthesis, –like respiration, is a redox (oxidation-reduction) process. –CO 2 becomes reduced to sugar as electrons along with hydrogen ions from water are added to it. –Water molecules are oxidized when they lose electrons along with hydrogen ions. © 2012 Pearson Education, Inc.

Figure 7.4A Becomes reduced Becomes oxidized Photosynthesis is a redox (reduction & oxidation) process

Figure 7.4A Becomes reduced Becomes oxidized Photosynthesis (uses light energy) Becomes reduced Becomes oxidized Cellular respiration (releases chemical energy)

7.4 Photosynthesis is a redox process, as is cellular respiration  Cellular respiration –The electrons lose potential as they travel down the electron transport chain to O 2. –Harvests chemical energy from food molecules.  Photosynthesis –Light energy is captured by chlorophyll molecules to boost the energy of electrons, –The electrons gain energy as they travel climb uphill. –Light energy is converted to chemical energy, and –Chemical energy is stored in the chemical bonds of sugars. © 2012 Pearson Education, Inc.

7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH  Photosynthesis occurs in two metabolic stages –Light reactions: Light energy is converted in the to chemical energy and O 2 in the thylakoid membranes –Calvin cycle: CO 2 is incorporated into organic compounds in the stroma –Calvin cycle is sometimes referred to as dark reactions because it does not need light directly Copyright © 2009 Pearson Education, Inc.

7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH  Light reactions –Occur in the thylakoid membranes. –In these reactions, water is split, providing a source of electrons and giving off oxygen as a by-product, –ATP is generated from ADP and a phosphate group, and –Light energy is absorbed by the chlorophyll molecules to drive the transfer of electrons and H + from water to the electron acceptor NADP + reducing it to NADPH. –NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle. © 2012 Pearson Education, Inc.

7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH  Calvin cycle, – Occurs in the stroma of the chloroplasts –During the Calvin cycle, CO 2 is incorporated into organic compounds in a process called carbon fixation. –After carbon fixation, enzymes of the cycle make sugars by further reducing the carbon compounds. –The Calvin cycle is often called the dark reactions or light- independent reactions, because none of the steps requires light directly. © 2012 Pearson Education, Inc.

Figure 7.5_s1 Light Reactions (in thylakoids) NADP + ADP P H2OH2O Light Chloroplast

Figure 7.5_s2 Light Reactions (in thylakoids) O2O2 NADPH ATP NADP + ADP P H2OH2O Light Chloroplast

Figure 7.5_s3 Light Reactions (in thylakoids) Calvin Cycle (in stroma) Sugar O2O2 NADPH ATP NADP + ADP P H2OH2O CO 2 Light Chloroplast

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY © 2012 Pearson Education, Inc.

7.6 Visible radiation absorbed by pigments drives the light reactions  Sunlight –Contains energy called electromagnetic energy or electromagnetic radiation. –Visible light is only a small part of the electromagnetic spectrum, the full range of electromagnetic wavelengths. –Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves. –The shorter the wavelength, the greater the energy. © 2012 Pearson Education, Inc.

Figure 7.6A Increasing energy 10  5 nm 10  3 nm 1 nm 10 3 nm 10 6 nm 1 m 10 3 m 650 nm Wavelength (nm) Visible light Gamma rays Micro- waves Radio waves X-rays UVInfrared The electromagnetic spectrum

7.6 Visible radiation absorbed by pigments drives the light reactions  Light –Behaves as discrete packets of energy called photons. –A photon is a fixed quantity of light energy. –The shorter the wavelength, the greater the energy in photons. © 2012 Pearson Education, Inc.

7.6 Visible radiation absorbed by pigments drives the light reactions  Pigments –absorb light and –are built into the thylakoid membrane. –Plant pigments absorb some wavelengths of light and –reflect or transmit other wavelengths.  We see the color of the wavelengths that are transmitted. For example, chlorophyll transmits green wavelengths. © 2012 Pearson Education, Inc.

Animation: Light and Pigments Right click on animation / Click play

Figure 7.6B Light Reflected light Absorbed light Transmitted light Chloroplast Thylakoid

7.6 Visible radiation absorbed by pigments drives the light reactions  Different pigments, which absorb light of different wavelengths. –Chlorophyll a absorbs blue-violet and red light and reflects green. –Chlorophyll b absorbs blue and orange and reflects yellow-green. –Carotenoids – (accessory pigments) Their role is to capture sunlight and transfer to chlorophyll. Yellow –Eg: Carotene (Orange) ; Xanthophyll (Yellow) © 2012 Pearson Education, Inc.

7.7 Photosystems capture solar energy  Pigments in chloroplasts absorb photons, which –increases the potential energy of the pigment’s electrons and –sends the electrons into an unstable state. –These unstable electrons drop back down to their “ground state,” and –as they drop down, they release their energy as heat and light. © 2012 Pearson Education, Inc.

Figure 7.7A Excited state Heat Ground state Photon of light Photon (fluorescence) Chlorophyll molecule A solution of chlorophyll glowing red when illuminated

7.7 Photosystems capture solar energy  Photosystems –In the thylakoid membrane, chlorophyll molecules are organized along with other pigments and proteins into photosystems. –A photosystem consists of a number of light-harvesting complexes surrounding a reaction-center complex. –A light-harvesting complex contains various pigment molecules bound to proteins. –Collectively, the light-harvesting complexes function as a light-gathering antenna. © 2012 Pearson Education, Inc.

Figure 7.7B Photosystem Light Light-harvesting complexes Reaction-center complex Primary electron acceptor Pigment molecules Pair of chlorophyll a molecules Transfer of energy Thylakoid membrane

7.7 Photosystems capture solar energy  Photosystems –The light energy is passed from molecule to molecule within the photosystem. –Finally it reaches the reaction center where a primary electron acceptor accepts these electrons and consequently becomes reduced. –This solar-powered transfer of an electron from the reaction-center pigment to the primary electron acceptor is the first step in the transformation of light energy to chemical energy in the light reactions. –There are two types of photosystems, I and II. © 2012 Pearson Education, Inc.

7.7 Photosystems capture solar energy  Photosystem I –This photosystem functions second, –It is called P700 because it absorbs light of 700 nm.  Photosystem II –This photosystem functions first, –It is called P680 because its absorbs light of 680 nm.  The two photosystems are connected by an electron transport chain © 2012 Pearson Education, Inc.

Figure 7.8A Light Stroma Photosystem II Thylakoid space Thylakoid membrane Primary acceptor P680 P700 Photosystem I Light NADP   NADPH Electron transport chain Provides energy for synthesis of ATP by chemiosmosis 2 1 H2OH2O HH O2O2 HH  2 Electron Flow in the Light Reactions

7.8 Two photosystems connected by an electron transport chain generate ATP and NADPH  Electron flow in the light reactions (from water to NADP) –Electrons removed from water –Gain energy passed from pigments and excited to a higher energy level –Photo excited high-energy electrons are captured by a primary electron acceptor –High energy electrons travel from photosystem II to photosystem I –Between the two photosystems, the electrons move down an electron transport chain. –. © 2012 Pearson Education, Inc.

Figure 7.8B Photosystem I Photosystem II NADPH ATP Mill makes ATP Photon A mechanical analogy of the light reactions

7.9 Chemiosmosis powers ATP synthesis in the light reactions  Generation of ATP in the light reactions –The energy released by the electrons “falling” in the electron transport chain is used to pump H + into the thylakoid space, and –This results in a concentration gradient of H + across the thylakoid membrane –The energy in the concentration gradient drives H + back to the stroma through ATP synthase, producing ATP. © 2012 Pearson Education, Inc.

Figure 7.9 H+H+ ATP synthasePhotosystem I Photosystem II Electron transport chain ATP P ADP NADPH NADP + Light Chloroplast To Calvin Cycle Stroma (low H + concentration) Thylakoid membrane Thylakoid space (high H + concentration) H2OH2O O H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ The production of ATP by Chemiosmosis

7.9 Chemiosmosis powers ATP synthesis in the light reactions  Photophosphorylation, –Production of ATP using the initial energy input from light © 2012 Pearson Education, Inc.

7.9 Chemiosmosis powers ATP synthesis in the light reactions  How does photophosphorylation compare with oxidative phosphorylation? –Mitochondria use oxidative phosphorylation to transfer chemical energy from food into the chemical energy of ATP. –Chloroplasts use photophosphorylation to transfer light energy into the chemical energy of ATP. © 2012 Pearson Education, Inc.

7.8 Two photosystems connected by an electron transport chain generate ATP and NADPH  The products of the light reactions are –NADPH, –ATP, and –Oxygen. © 2012 Pearson Education, Inc.

THE CALVIN CYCLE: REDUCING CO 2 TO SUGAR © 2012 Pearson Education, Inc.

7.10 ATP and NADPH power sugar synthesis in the Calvin cycle  Calvin cycle –Makes sugar within a chloroplast. –Using atmospheric CO 2 and –ATP and NADPH generated by the light reactions. –Produces an energy-rich, three-carbon sugar called glyceraldehyde-3-phosphate (G3P). –A plant cell may then use G3P to make glucose and other organic molecules. © 2012 Pearson Education, Inc.

Figure 7.10A Input Output: G3P Calvin Cycle CO 2 ATP NADPH An overview of the Calvin cycle

7.10 ATP and NADPH power sugar synthesis in the Calvin cycle  The steps of the Calvin cycle include 1.carbon fixation, 2.reduction, 3.release of G3P, and 4.regeneration of the starting molecule ribulose bisphosphate (RuBP). © 2012 Pearson Education, Inc.

Figure 7.10B_s1 11 P P P PGA RuBP CO 2 Rubisco Input: Step Carbon fixation Calvin Cycle

Figure 7.10B_s P P P P P ATP ADP NADPH NADP  G3P 3-PGA RuBP CO 2 Rubisco Input: Step Reduction Step Carbon fixation Calvin Cycle

Figure 7.10B_s Glucose and other compounds P P P P P P P ATP ADP NADPH NADP  G3P 3-PGA RuBP CO 2 Rubisco Input: Output: Step Release of one molecule of G3P Step Reduction Step Carbon fixation Calvin Cycle

Figure 7.10B_s Glucose and other compounds P P P P P P P ATP ADP NADPH NADP  G3P 3-PGA RuBP CO 2 Rubisco Input: Output: Step Regeneration of RuBP Step Release of one molecule of G3P Step Reduction Step Carbon fixation Calvin Cycle

7.11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates  Most plants use CO 2 directly from the air, and carbon fixation occurs when the enzyme Rubisco adds CO 2 to RuBP.  Such plants are called C 3 plants because the first product of carbon fixation is a three-carbon compound, 3-PGA.  Skip C 4 and CAM plants © 2012 Pearson Education, Inc.

PHOTOSYNTHESIS REVIEWED AND EXTENDED © 2012 Pearson Education, Inc.

7.12 Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules  Most of the living world depends on the food- making machinery of photosynthesis.  The chloroplast –integrates the two stages of photosynthesis and –makes sugar from CO 2. © 2012 Pearson Education, Inc.

7.12 Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules  About half of the carbohydrates made by photosynthesis are consumed as fuel for cellular respiration in the mitochondria of plant cells.  Sugars also serve as the starting material for making other organic molecules, such as proteins, lipids, and cellulose.  Excess food made by plants is stockpiled as starch in roots, tubers, seeds, and fruits. © 2012 Pearson Education, Inc.

Figure 7.12 Light Thylakoids H2OH2O CO 2 O2O2 NADP  ADP P ATP NADPH G3P 3-PGA RuBP Chloroplast Sugars Photosystem II Photosystem I Light Reactions Electron transport chain Calvin Cycle (in stroma) Stroma Cellular respiration Other organic compounds Cellulose Starch

7.13 CONNECTION: Photosynthesis may moderate global climate change  The greenhouse effect operates on a global scale. –Solar radiation includes visible light that penetrates the Earth’s atmosphere and warms the planet’s surface. –Heat radiating from the warmed planet is absorbed by gases in the atmosphere, which then reflects some of the heat back to Earth. –Without the warming of the greenhouse effect, the Earth would be much colder and most life as we know it could not exist. © 2012 Pearson Education, Inc.

Figure 7.13A

Figure 7.13B Sunlight Atmosphere Some heat energy escapes into space Radiant heat trapped by CO 2 and other gases CO 2 in the atmosphere and the greenhouse effect

7.13 CONNECTION: Photosynthesis may moderate global climate change  The gases in the atmosphere that absorb heat radiation are called greenhouse gases. These include –water vapor, –carbon dioxide, and –methane. © 2012 Pearson Education, Inc.

7.13 CONNECTION: Photosynthesis may moderate global climate change  Increasing concentrations of greenhouse gases have been linked to global climate change (also called global warming), a slow but steady rise in Earth’s surface temperature.  Since 1850, the atmospheric concentration of CO 2 has increased by about 40%, mostly due to the combustion of fossil fuels including –coal, –oil, and –gasoline. © 2012 Pearson Education, Inc.

7.13 CONNECTION: Photosynthesis may moderate global climate change  The predicted consequences of continued warming include –melting of polar ice, –rising sea levels, –extreme weather patterns, –droughts, –increased extinction rates, and –the spread of tropical diseases. © 2012 Pearson Education, Inc.

7.13 CONNECTION: Photosynthesis may moderate global climate change  Widespread deforestation has aggravated the global warming problem by reducing an effective CO 2 sink.  Global warming caused by increasing CO 2 levels may be reduced by –limiting deforestation, –reducing fossil fuel consumption, and –growing biofuel crops that remove CO 2 from the atmosphere. © 2012 Pearson Education, Inc.

7.14 SCIENTIFIC DISCOVERY: Scientific study of Earth’s ozone layer has global significance  Solar radiation converts O 2 high in the atmosphere to ozone (O 3 ), which shields organisms from damaging UV radiation.  Industrial chemicals called CFCs (Chloro-fluro- carbons) have caused dangerous thinning of the ozone layer, but international restrictions on CFC use are allowing a slow recovery. © 2012 Pearson Education, Inc.

Figure 7.14A Antarctica Southern tip of South America The ozone hole in the Southern Hemisphere, spring 2006

Learning from plants

Figure 7.UN02 P NADP  ADP NADPH