© 2015 Pearson Education, Inc.

Figure 7.0-2 Chapter 7: Big Ideas The Light Reactions: Converting Solar Energy to Chemical Energy An Introduction to Photosynthesis Figure 7.0-2 Chapter 7: Big Ideas The Calvin Cycle: Reducing CO2 to Sugar The Global Significance of Photosynthesis

AN INTRODUCTION TO PHOTOSYNTHESIS 7.1 -7.5 AN INTRODUCTION TO PHOTOSYNTHESIS © 2015 Pearson Education, Inc.

7.1 Photosynthesis fuels the biosphere Plants are autotrophs, which make their own food through the process of photosynthesis. Photoautotrophs use the energy of light to produce organic molecules. Chemoautotrophs are prokaryotes that use inorganic chemicals as their energy source. Heterotrophs are consumers that feed on plants or animals or decompose organic material. Teaching Tips  The evolution of chloroplasts from photosynthetic prokaryotes living inside of eukaryotic cells is discussed in Module 4.15. If your students have not already read Chapter 4, consider discussing this theory of endosymbiosis. Some students might think that the term “producers” applies to the production of oxygen by plants. In turn, they might think that consumers are organisms that use oxygen (which would include all aerobic organisms). Extra care may be needed to clarify the definitions of these frequently used terms. Active Lecture Tips  When introducing the diverse ways that plants impact our lives, challenge your students to work with students seated nearby to come up with a list of products made from plants that they come across on a regular basis. The collective lists from your students can be surprisingly long and might help to build up your catalog of examples. © 2015 Pearson Education, Inc.

7.1 Photosynthesis fuels the biosphere Photoautotrophs feed us, clothe us (think cotton), house us (think wood), and provide energy for warmth, light, transport, and manufacturing. Teaching Tips  The evolution of chloroplasts from photosynthetic prokaryotes living inside of eukaryotic cells is discussed in Module 4.15. If your students have not already read Chapter 4, consider discussing this theory of endosymbiosis. Some students might think that the term “producers” applies to the production of oxygen by plants. In turn, they might think that consumers are organisms that use oxygen (which would include all aerobic organisms). Extra care may be needed to clarify the definitions of these frequently used terms. Active Lecture Tips  When introducing the diverse ways that plants impact our lives, challenge your students to work with students seated nearby to come up with a list of products made from plants that they come across on a regular basis. The collective lists from your students can be surprisingly long and might help to build up your catalog of examples. © 2015 Pearson Education, Inc.

7.2 Photosynthesis occurs in chloroplasts in plant cells Chlorophyll is a light-absorbing pigment in chloroplasts is responsible for the green color converts solar energy to chemical energy. Teaching Tips  The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.  The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane; the highly branched surfaces of plant roots, fish gills, and human lungs; and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. © 2015 Pearson Education, Inc.

7.2 Photosynthesis occurs in chloroplasts in plant cells Chloroplasts are in the cells of the mesophyll. Stomata are tiny pores in the leaf that allow CO2 to enter and O2 to exit. Veins in the leaf deliver water absorbed by roots. Teaching Tips  The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.  The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane; the highly branched surfaces of plant roots, fish gills, and human lungs; and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes.

7.2 Photosynthesis occurs in chloroplasts in plant cells Chloroplasts consist of an Double membrane Stroma Fluid filled interior Thylakoids Grana stacks Thylakoid membrane contains Chlorophyll molecules Electron transport chain ATP synthase H+ gradient built up within thylakoid space Teaching Tips  The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters.  The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane; the highly branched surfaces of plant roots, fish gills, and human lungs; and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes.

7.4 Photosynthesis is a redox process, as is cellular respiration Photosynthesis, like respiration, is a redox (oxidation-reduction) process. CO2 becomes reduced to sugar as electrons, along with hydrogen ions (H+) from water, are added to it. Water molecules are oxidized when they lose electrons along with hydrogen ions. Teaching Tips  In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. Active Lecture Tips  See the activity Photosynthesis and Respiration: Are They Similar on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

7.4 Photosynthesis is a redox process, as is cellular respiration In photosynthesis, light energy is captured by chlorophyll molecules and converted to chemical energy chemical energy is stored in the chemical bonds of sugars. Teaching Tips  In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. Active Lecture Tips  See the activity Photosynthesis and Respiration: Are They Similar on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

7.5 The two stages of photosynthesis are linked by ATP and NADPH Stage 1: 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 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 “reducing power” to the Calvin cycle. Student Misconceptions and Concerns  Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange. Teaching Tips  In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.  Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. Active Lecture Tips  See the activity Photosynthesis and Respiration: Are They Similar on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the activity Demonstration of the Light Dependent Reactions of Photosynthesis Using Students as Molecules on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Light Reactions (energy building reactions) H2O ATP O2 light energy  + NADPH H2O sunlight produces ATP produces NADPH releases O2 as a waste product Energy Building Reactions NADPH ATP O2

7.5 The two stages of photosynthesis are linked by ATP and NADPH Stage 2: The Calvin cycle occurs in the stroma of the chloroplast. The Calvin cycle is a cyclic series of reactions that assembles sugar molecules using CO2 and the energy- rich products (ATP and NADPH) of the light reactions. During the Calvin cycle, CO2 is incorporated into organic compounds in a process called carbon fixation. After carbon fixation, the carbon compounds are reduced to sugars. The Calvin cycle is often called the dark reactions, or light-independent reactions, because none of the steps requires light directly. Student Misconceptions and Concerns  Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange. Teaching Tips  In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis.  Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. Active Lecture Tips  See the activity Photosynthesis and Respiration: Are They Similar on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the activity Demonstration of the Light Dependent Reactions of Photosynthesis Using Students as Molecules on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Calvin Cycle (sugar building reactions) CO2 C6H12O6  + NADP ATP NADPH ADP CO2 builds sugars uses ATP & NADPH recycles ADP & NADP back to make more ATP & NADPH ADP NADP Sugar Building Reactions NADPH ATP sugars

Putting it all together CO2 H2O C6H12O6 O2 light energy  + H2O CO2 Plants make both: energy ATP & NADPH sugars sunlight ADP NADP Energy Building Reactions Sugar Building Reactions NADPH ATP O2 sugars

ATP Energy cycle Photosynthesis Cellular Respiration sun CO2 O2 H2O C6H12O6 O2 light energy  + H2O plants CO2 glucose O2 animals, plants CO2 H2O C6H12O6 O2 ATP energy  + Cellular Respiration ATP

THE GLOBAL SIGNIFICANCE OF PHOTOSYNTHESIS 7.12-7.15 THE GLOBAL SIGNIFICANCE OF PHOTOSYNTHESIS © 2015 Pearson Education, Inc.

roots, tubers, seeds, and fruits. 7.12 Photosynthesis makes sugar from CO2 and H2O, providing food and O2 for almost all living organisms About 50% of the carbohydrates made by photosynthesis is 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. Many glucose molecules are linked together to make cellulose, the main component of cell walls. Most plants make much more food each day than they need. They store the excess in roots, tubers, seeds, and fruits. Plants (and other photosynthesizers) are the ultimate source of food for virtually all other organisms. Student Misconceptions and Concerns  Some students do not realize that plant cells also have mitochondria. Instead, they assume that the chloroplasts are sufficient for the plant cell’s needs. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). Teaching Tips  The authors note that G3P is also used to produce cellulose, the most abundant organic molecule in a plant and probably on the surface of the Earth! Active Lecture Tips  Have your students work together in small groups to explain how the energy in beef is ultimately derived from the sun. Perhaps have them turn in a single diagram linking the steps of energy transfer from the sun to their cells. © 2015 Pearson Education, Inc.

7.13 SCIENTIFIC THINKING: Rising atmospheric levels of carbon dioxide and global climate change will affect plants in various ways The greenhouse effect operates on a global scale. Solar radiation passes through the atmosphere and warms Earth’s surface. Heat radiating from the warmed planet is absorbed by greenhouse gases, such as CO2, water vapor, and methane, which then reflect some of the heat back to Earth. Without this natural heating effect, the average air temperature would be a frigid –18C (–0.4F), and most life as we know it could not exist. Increasing concentrations of greenhouse gases have been linked to global climate change, of which one major aspect is global warming. Student Misconceptions and Concerns  Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.  Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips  Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day!

The predicted consequences of global climate change include 7.13 SCIENTIFIC THINKING: Rising atmospheric levels of carbon dioxide and global climate change will affect plants in various ways The predicted consequences of global climate change include melting of polar ice, rising sea levels, extreme weather patterns, droughts, increased extinction rates, and the spread of tropical diseases. Many of these effects are already being documented. Student Misconceptions and Concerns  Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.  Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips  Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! © 2015 Pearson Education, Inc.

How may global climate change affect plants? 7.13 SCIENTIFIC THINKING: Rising atmospheric levels of carbon dioxide and global climate change will affect plants in various ways How may global climate change affect plants? Increasing CO2 levels can increase plant productivity. Research has documented such an increase, although results often indicate that the growth rates of weeds, such as poison ivy, increase more than those of crop plants and trees. Student Misconceptions and Concerns  Students often do not fully understand how the burning of fossil fuels contributes to global warming. They might wonder, “How does the burning of fossil fuels differ from the burning of ethanol produced from crops?” Students might not realize that the carbon in fossil fuels was removed from the atmosphere hundreds of millions of years ago, while the carbon in crops was removed much more recently, when the crops were grown. The use of ethanol as an alternative is complicated by the typical reliance upon fossil fuels for ethanol production.  Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips  Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day!

7.14 Scientific research and international treaties have helped slow the depletion of Earth’s ozone layer Solar radiation converts O2 high in the atmosphere to ozone (O3), which shields organisms from damaging UV radiation. A gigantic hole in the ozone layer has appeared every spring over Antarctica since the late 1970s and continues today. Industrial chemicals called CFCs have caused dangerous thinning of the ozone layer. Student Misconceptions and Concerns  Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips  Consider an analogy between the ozone layer and sunscreen applied to the skin. The thinning of the ozone layer is like putting on less and less sunscreen. In both situations, more harmful UV light penetrates the layers and causes damage.  Frustration can overwhelm concerned students alarmed by the many problems addressed in this chapter. One way to address this is to provide meaningful ways for students to respond to this information (for example, changes in personal choices and voting). The Earth Day Network, www.earthday.org, is just one of many Internet sites devoted to positive action.

7.14 Scientific research and international treaties have helped slow the depletion of Earth’s ozone layer Global emissions of CFCs are near zero now, but because these compounds are so stable, recovery of the ozone layer is not expected until around 2060. Meanwhile, unblocked UV radiation is predicted to increase skin cancer and cataracts and damage crops and phytoplankton in the oceans. Student Misconceptions and Concerns  Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips  Consider an analogy between the ozone layer and sunscreen applied to the skin. The thinning of the ozone layer is like putting on less and less sunscreen. In both situations, more harmful UV light penetrates the layers and causes damage.  Frustration can overwhelm concerned students alarmed by the many problems addressed in this chapter. One way to address this is to provide meaningful ways for students to respond to this information (for example, changes in personal choices and voting). The Earth Day Network, www.earthday.org, is just one of many Internet sites devoted to positive action. © 2015 Pearson Education, Inc.

You should now be able to Define autotrophs, heterotrophs, producers, and photoautotrophs. Describe the structure of chloroplasts and their location in a leaf. Explain how plants produce oxygen. Describe the role of redox reactions in photosynthesis and cellular respiration. Compare the reactants and products of the light reactions and the Calvin cycle. © 2015 Pearson Education, Inc.

You should now be able to Describe the properties and functions of the different photosynthetic pigments. Explain how photosystems capture solar energy. Explain how the electron transport chain and chemiosmosis generate ATP, NADPH, and oxygen in the light reactions. Compare photophosphorylation and oxidative phosphorylation. Describe the reactants and products of the Calvin cycle. © 2015 Pearson Education, Inc.

You should now be able to Compare the mechanisms that C3, C4, and CAM plants use to obtain and use carbon dioxide. Review the overall process of the light reactions and the Calvin cycle, noting the products, reactants, and locations of every major step. Describe the greenhouse effect. Explain how the ozone layer forms, how human activities have damaged it, and the consequences of the destruction of the ozone layer. © 2015 Pearson Education, Inc.

Photosynthesis 6 CO2 6 H2O C6H12O6 6 O2 Carbon dioxide Water Figure 7.UN01 Light energy 6 CO2 6 H2O C6H12O6 6 O2 Carbon dioxide Water Oxygen gas Photosynthesis Glucose Figure 7.UN01 Reviewing the concepts, 7.3

Light Reactions Calvin Cycle Figure 7.UN02 Chloroplast H2O CO2 Light NADP+ Stroma Thylakoids ADP + P Light Reactions Calvin Cycle ATP NADPH Figure 7.UN02 Reviewing the concepts, 7.12 O2 Sugar

light-excited electrons of chlorophyll Figure 7.UN03 Photosynthesis converts includes both (a) (b) (c) to in which in which chemical energy light-excited electrons of chlorophyll CO2 is fixed to RuBP H2O is split and and then 3-PGA is reduced (d) are passed down Reduce NADP+ to Figure 7.UN03 Connecting the concepts, question 1 using (e) (f) to produce producing chemiosmosis by (g) (h)

Mitochondrion Chloroplast Intermembrane space c. Membrane Matrix d. a. Figure 7.UN04 Mitochondrion Chloroplast Intermembrane space H+ c. Membrane Matrix d. Figure 7.UN04 Testing your knowledge, question 12 a. b. e.