Photosynthesis: Using Light to Make Food

Photosynthesis: Using Light to Make Food
Chapter 7 Photosynthesis: Using Light to Make Food © 2016 Pearson Education, Inc.

The Basics of Photosynthesis
is used by plants, algae (protists), and certain bacteria, transforms light energy into chemical energy, uses carbon dioxide and water as starting materials, and releases oxygen gas as a by-product. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 2

The Basics of Photosynthesis
The chemical energy produced via photosynthesis is stored in the bonds of sugar molecules. Organisms that generate their own organic matter from inorganic ingredients are called autotrophs. Plants and other organisms that do this by photosynthesis—photoautotrophs—are the producers for most ecosystems. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 3

PHOTOSYNTHETIC AUTOTROPHS
Figure 7.1 PHOTOSYNTHETIC AUTOTROPHS Plants (mostly on land) Photosynthetic Protists (aquatic) Photosynthetic Bacteria (aquatic) LM Forest plants Kelp, a large, multicellular alga Micrograph of cyanobacteria Figure 7.1 A diversity of photoautotrophs

Chloroplasts: Sites of Photosynthesis
Chloroplasts are light-absorbing organelles, the site of photosynthesis, and found mostly in the interior cells of leaves. Their green color is from chlorophyll, a pigment (light-absorbing molecule) in the chloroplasts that plays a central role in converting solar energy to chemical energy. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 5

Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits. Membranes within the chloroplast form the framework where many of the reactions of photosynthesis occur. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 6

Photosynthetic cells Vein Stomata Leaf cross section
Figure 7.2-s1 Photosynthetic cells Vein CO2 O2 Stomata Leaf cross section Figure 7.2-s1 Journey into a leaf (step 1)

Photosynthetic cells Vein Stomata Leaf cross section
Figure 7.2-s2 LM Photosynthetic cells Vein Interior cell Chloroplast CO2 O2 Stomata Leaf cross section Figure 7.2-s2 Journey into a leaf (step 2)

Photosynthetic cells Vein Thylakoid Stomata Leaf cross section
Figure 7.2-s3 Inner and outer membranes LM Photosynthetic cells Vein Stroma Thylakoid Interior cell Thylakoid space Chloroplast Granum CO2 O2 Stomata Colorized TEM Leaf cross section Figure 7.2-s3 Journey into a leaf (step 3)

Vein (transports water and nutrients) Photosynthetic cells CO2 O2
Figure 7.2-1 Vein (transports water and nutrients) Photosynthetic cells CO2 O2 Stomata Leaf cross section Figure Journey into a leaf (part 1: leaf cross section)

Inner and outer membranes
Figure 7.2-2 Inner and outer membranes LM Stroma Thylakoid Interior cell Thylakoid space Chloroplast Granum Colorized TEM Figure Journey into a leaf (part 2: chloroplast)

Interior cell Chloroplast LM Figure 7.2-2a
Figure 7.2-2a Journey into a leaf (part 2a: chloroplast, LM)

Chloroplast Granum Colorized TEM Figure 7.2-2b
Figure 7.2-2b Journey into a leaf (part 2b: chloroplast, TEM)

Like a mitochondrion, a chloroplast has a double- membrane envelope. The inner membrane encloses a compartment filled with stroma, a thick fluid. Suspended in the stroma are interconnected membranous sacs called thylakoids. The thylakoids are concentrated in stacks called grana (singular, granum). The chlorophyll molecules that capture light energy are built into the thylakoid membranes. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 14

Energy Transformations: An Overview of Photosynthesis
In the overall equation for photosynthesis, notice that the reactants of photosynthesis, carbon dioxide (CO2) and water (H2O), are the same as the waste products of cellular respiration, and photosynthesis produces what respiration uses— glucose (C6H12O6) and oxygen (O2). © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 15

Light energy 6 CO2 6 H2O C6H12O6 6 O2 Photosynthesis Carbon dioxide
Figure 7.UN03 Light energy 6 CO2 6 H2O C6H12O6 6 O2 Photosynthesis Carbon dioxide Water Glucose Oxygen gas Figure 7.UN03 Summary of key concepts: photosynthesis equation

Photosynthesis is a chemical transformation that requires a lot of energy, and sunlight absorbed by chlorophyll provides that energy. Recall that cellular respiration is a process of electron transfer. A “fall” of electrons from food molecules to oxygen to form water releases the energy that mitochondria can use to make ATP. The opposite occurs in photosynthesis: Electrons are boosted “uphill” and added to carbon dioxide to produce sugar. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 17

e e Electrons from food NAD+ e– e– NAD+ NADH Stepwise release
Figure 6.9 e e Electrons from food NAD+ e– e– NAD+ NADH Stepwise release of energy used to make ATP ATP 2 e   Electron transport chain 2 e 1 O2 2 H2O Hydrogens, electrons, and oxygen combine to form water 2 H+ Figure 6.9 The role of oxygen in harvesting food energy

Figure 6.9-1 Figure The role of oxygen in harvesting food energy (part 1: lifeguard)

The overall equation for photosynthesis is a simple summary of a complex process. Like many energy-producing processes within cells, photosynthesis is a multistep chemical pathway, with each step in the path producing products that are used as reactants in the next step. This is a clear example of one of biology’s major themes: the use of metabolic pathways to obtain, process, and store energy. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 20

  H2O Chloroplast Light NADP+ ADP  P Light reactions ATP NADPH O2
Figure 7.3-s1 H2O Chloroplast Light NADP+ ADP  P Light reactions ATP   NADPH O2 Figure 7.3-s1 A road map for photosynthesis (step 1)

  H2O CO2 Chloroplast Light NADP+ ADP  P Calvin Light cycle
Figure 7.3-s2 H2O Chloroplast CO2 Light NADP+ ADP  P Light reactions Calvin cycle ATP   NADPH O2 Sugar Figure 7.3-s2 A road map for photosynthesis (step 2)

Photosynthesis occurs in two stages. In the light reactions, chlorophyll in the thylakoid membranes absorbs solar energy, which is then converted to the chemical energy of ATP and NADPH, and water is split, providing a source of electrons and giving off O2 gas as a by-product. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 23

The Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide. ATP generated by the light reactions provides the energy for sugar synthesis. The NADPH produced by the light reactions provides the high-energy electrons that drive the synthesis of glucose from carbon dioxide. Thus, the Calvin cycle indirectly depends on light to produce sugar because it requires the supply of ATP and NADPH produced by the light reactions. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 24

The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation. This can help reduce the concentration of carbon dioxide in the atmosphere. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 25

Deforestation, which removes a lot of photosynthetic plant life, thereby reduces the ability of the biosphere to absorb carbon. Planting new forests can have the opposite effect of fixing carbon from the atmosphere, potentially reducing the effect of the gases that contribute to global climate change. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. 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. 2. 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. But nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 3. Students may not connect the growth in plant mass to the fixation of carbon during the Calvin cycle. It can be difficult for many students to appreciate that molecules in air can contribute significantly to the mass of plants. 4. 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. 5. Students who have not read all of Chapter 7 may not realize that glucose is not the direct product of photosynthesis. Although glucose is shown as a product of photosynthesis, a three-carbon sugar is directly produced (G3P). A plant can use G3P to make many types of organic molecules, including glucose. (The authors address the production of G3P under the section “The Calvin Cycle” later in this chapter.) Teaching Tips 1. 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 fish gills and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle seen elsewhere to the extensive folding of the thylakoid membranes. 2. 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. 3. You might wish to discuss the evolution of chloroplasts from photosynthetic prokaryotes if you will not address this subject elsewhere in your course. 4. Figure 7.3 is an important visual organizer that notes the key structures and functions of the two stages of photosynthesis. This figure reminds students where 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 generate sugar. 5. The thylakoid space and the intermembrane space of a mitochondrion have analogous roles. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. Active Lecture Tips 1. When introducing the diverse ways that plants impact our lives, challenge your students to work with others seated nearby to come up with a list of products made from plants that they encounter on a regular basis. The collective lists from your students can be surprisingly long and might help you build your own catalog of examples. 2. 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. 3. 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. 26

The Light Reactions: Converting Solar Energy to Chemical Energy
Chloroplasts are solar-powered sugar factories. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 27

CO2 Calvin cycle Light reactions Sugar
Figure 7.UN01 CO2 Light H2O NADP+ ADP + P Calvin cycle Light reactions ATP   NADPH O2 Sugar Figure 7.UN01 In-text figure, light reactions, p. 110

The Nature of Sunlight Sunlight is a type of energy called radiation, or electromagnetic energy. The distance between the crests of two adjacent waves is called a wavelength. The full range of radiation is called the electromagnetic spectrum. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 29

Micro- waves Radio waves X-rays UV Infrared energy
Figure 7.4 Increasing wavelength 105 nm 103 nm 1 nm 103 nm 106 nm 1 m 103 m Gamma rays Micro- waves Radio waves X-rays UV Infrared Highest energy Lowest energy Visible light 380 400 500 600 700 750 Wavelength (nm) Wavelength = 580 nm Figure 7.4 The electromagnetic spectrum

The Nature of Sunlight When sunlight shines on a pigmented material, certain wavelengths (colors) of the visible light are absorbed and disappear from the light that is reflected by the material. In the 19th century, botanists discovered that only certain wavelengths of light are used by plants. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 31

The Process of Science: What Colors of Light Drive Photosynthesis?
Observation: In 1883, German biologist Theodor Engelmann saw that certain bacteria living in water 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. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 32

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, and used a prism to create a spectrum of light shining on the slide. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 33

Results: Most bacteria congregated around algae exposed to red-orange and blue-violet light. Very few moved to areas of green light. Other experiments have since verified that chloroplasts absorb light mainly in the blue-violet and red-orange part of the spectrum and those wavelengths of light are the ones mainly responsible for photosynthesis. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 34

Animation: Light and Pigments
© 2016 Pearson Education, Inc.

Wavelength of light (nm)
Figure 7.5 Light Prism Microscope slide Bacteria Bacteria Number of bacteria Algal cells 400 500 600 700 Wavelength of light (nm) Figure 7.5 Investigating how light wavelength affects photosynthesis

Chloroplast Pigments The selective absorption of light by leaves explains why they appear green to us. Light of that color is poorly absorbed by chloroplasts and is thus reflected or transmitted toward the observer. Energy cannot be destroyed, so the absorbed energy must be converted to other forms. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 37

Light Reflected light Chloroplast Absorbed light Transmitted
Figure 7.6 Light Reflected light Chloroplast Absorbed light Transmitted light (detected by your eye) Figure 7.6 Why are leaves green?

Light Reflected light Chloroplast Absorbed light Transmitted
Figure 7.6-1 Light Reflected light Chloroplast Absorbed light Transmitted light (detected by your eye) Figure Why are leaves green? (part 1: chloroplast)

Figure 7.6-2 Figure Why are leaves green? (part 2: leaves)

Chloroplast Pigments Chloroplasts contain several different pigments that absorb light of different wavelengths. Chlorophyll a participates directly in the light reactions and absorbs mainly blue-violet and red light. Chlorophyll b is very similar to chlorophyll a, absorbs mainly blue and orange light, and conveys absorbed energy to chlorophyll a. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 41

Chloroplast Pigments Carotenoids absorb mainly blue-green light and
absorb and dissipate excessive light energy that might damage chlorophyll. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 42

Chloroplast Pigments Some carotenoids are human nutrients.
Beta-carotene is a bright orange/red pigment found in pumpkins, sweet potatoes, and carrots and is converted to vitamin A in the body. Lycopene is a bright red pigment found in tomatoes, watermelon, and red peppers and is an antioxidant that is being studied for potential anti-cancer properties. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 43

Chloroplast Pigments The spectacular colors of fall foliage are due partly to the yellow-orange light reflected from carotenoids. The decreasing temperatures in autumn cause a decrease in the levels of chlorophyll. This allows the colors of the longer-lasting carotenoids to be seen in all their fall glory. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 44

Figure 7.7 Figure 7.7 Photosynthetic pigments

How Photosystems Harvest Light Energy
Light behaves as waves and discrete packets of energy called photons, fixed quantities of light energy. The shorter the wavelength of light, the greater the energy of a photon. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 46

When a pigment molecule absorbs a photon, one of the pigment’s electrons gains energy. This electron is now said to be “excited.” The excited state is highly unstable. An excited electron usually loses its excess energy and falls back to its ground state almost immediately. Most pigments release heat energy as their light- excited electrons fall back to their ground state. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 47

(a) Absorption of a photon
Figure 7.8-1 Excited state The electron falls to its ground state. Absorption of a photon excites an electron. e Heat Light Light (fluorescence) Photon Ground state Chlorophyll molecule (a) Absorption of a photon Figure Excited electrons in pigments (part 1: absorption)

Some pigments emit light as well as heat after absorbing photons. The fluorescent light emitted by a glow stick is caused by a chemical reaction that excites electrons of a fluorescent dye. The excited electrons quickly fall back down to their ground state, releasing energy in the form of fluorescent light. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 49

(b) Fluorescence of a glow stick
Figure 7.8-2 (b) Fluorescence of a glow stick Figure Excited electrons in pigments (part 2: fluorescence)

In the thylakoid membrane, chlorophyll molecules are organized with other molecules into photosystems. Each photosystem has a cluster of a few hundred pigment molecules, including chlorophylls a and b and some carotenoids. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 51

Chloroplast Cluster of pigment molecules Photon Primary electron
Figure 7.9 Chloroplast Cluster of pigment molecules Photon Primary electron acceptor Electron transfer e Reaction center Reaction- center chlorophyll a Pigment molecules Transfer of energy Thylakoid membrane Photosystem Figure 7.9 A photosystem: light-gathering molecules that focus light energy onto a reaction center

Chloroplast Cluster of pigment molecules Thylakoid membrane
Figure 7.9-1 Chloroplast Cluster of pigment molecules Thylakoid membrane Figure A photosystem: light-gathering molecules that focus light energy onto a reaction center (part 1: thylakoid membrane)

Photon Primary electron acceptor Electron transfer Reaction center
Figure 7.9-2 Photon Primary electron acceptor Electron transfer Reaction center e Reaction- center chlorophyll a Pigment molecules Transfer of energy Photosystem Figure A photosystem: light-gathering molecules that focus light energy onto a reaction center (part 2: photosystem)

This cluster of pigment molecules functions as a light-gathering antenna. When a photon strikes one of the pigment molecules, the energy jumps from molecule to molecule until it arrives at the reaction center of the photosystem. The reaction center consists of chlorophyll a molecules that sit next to a primary electron acceptor, which traps the light-excited electron from the chlorophyll a in the reaction center. Another team of molecules built into the thylakoid membrane then uses that trapped energy to make ATP and NADPH. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 55

How the Light Reactions Generate ATP and NADPH
Two photosystems cooperate in the light reactions: Photons excite electrons in the chlorophyll of the first photosystem. These photons are then trapped by the primary electron acceptor. This photosystem then replaces the lost electrons by extracting new ones from water. This is the step that releases O2 during photosynthesis. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 56

Reaction- center chlorophyll Reaction- center chlorophyll
Figure 7.10 Primary electron acceptor NADP+ 2e Energy to make ATP 3 Primary electron acceptor 2e 2   NADPH 2e Light Light Electron transport chain Reaction- center chlorophyll 1 1 Reaction- center chlorophyll Second photosystem H2O 2e First photosystem 2 H+ + 1 2 O2 Figure 7.10 The light reactions of photosynthesis

Reaction- center chlorophyll
Figure Primary electron acceptor 2e Light 1 Reaction- center chlorophyll H2O 2e First photosystem 2 H+ + 1 2 O2 Figure The light reactions of photosynthesis (part 1: first photosystem)

Reaction- center chlorophyll Reaction- center chlorophyll
Figure Primary electron acceptor Energy to make ATP Primary electron acceptor 2e 2 2e Electron transport chain Reaction- center chlorophyll Reaction- center chlorophyll Second photosystem First photosystem Figure The light reactions of photosynthesis (part 2: electron transport chain)

Reaction- center chlorophyll
Figure Primary electron acceptor NADP+ 2e 3 2e   NADPH Light Reaction- center chlorophyll Second photosystem Figure The light reactions of photosynthesis (part 3: second photosystem)

Energized electrons from the first photosystem pass down an electron transport chain to the second photosystem. The chloroplast uses the energy released by this electron “fall” to make ATP. The second photosystem transfers its light-excited electrons to NADP+, reducing it to NADPH. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 61

The light reactions are located in the thylakoid membrane. The two photosystems and the electron transport chain that connects them transfer electrons from H2O to NADP+, producing NADPH. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 62

  Calvin cycle Light Light H+ H+ Stroma Electron transport chain
Figure 7.11 Calvin cycle Light Light   H+ NADPH ATP ADP  P NADP+ H+ Stroma Electron transport chain Thylakoid membrane Photosystem Photosystem ATP synthase Inside thylakoid Electron flow 2e H+ H+ H2O H+ H+ H+ 1 2 O2 Thylakoid membrane Figure 7.11 How the thylakoid membrane converts light energy to the chemical energy of NADPH and ATP

Electron transport chain
Figure Light H+ Stroma Electron transport chain Thylakoid membrane Photosystem Inside thylakoid 2e H2O H+ 1 2 O2 Thylakoid membrane Figure How the thylakoid membrane converts light energy to the chemical energy of NADPH and ATP (part 1: first photosystem)

Calvin cycle Light Electron transport chain Photosystem Electron flow
Figure Calvin cycle Light   H+ NADPH ATP ADP + P NADP+ H+ Electron transport chain Photosystem ATP synthase Electron flow H+ H+ H+ H+ H+ Figure How the thylakoid membrane converts light energy to the chemical energy of NADPH and ATP (part 2: second photosystem)

The mechanism of ATP production during the light reactions is very similar to the mechanism we saw in cellular respiration. In both cases, an electron transport chain pumps hydrogen ions across a membrane and ATP synthases use the energy stored by the H+ gradient to make ATP. The main difference is that food provides the high- energy electrons in cellular respiration, whereas light-excited electrons flow down the transport chain during photosynthesis. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. The authors note that sunlight is a type of radiation. Many students think of radiation as a result of radioactive decay, a serious threat to health. The diverse types of radiation and the varying energy associated with each might need to be explained. 2. The authors note that electromagnetic energy travels through space in waves that are like those made by a pebble dropped in a pond. This wave imagery is helpful, but can confuse students when energy is also thought of as discrete packets called photons. The dual nature of light as a wave and particle may need to be discussed further if students are to do more than just accept the definitions. 3. The light reactions are not solely responsible for all of the products in the general chemical equation of photosynthesis. Point out that oxygen is generated in the light reactions but that glucose results from products of the Calvin cycle. 4. Even at the college level, students struggle to understand why we perceive certain colors. The authors discuss the specific absorption and reflection of certain wavelengths of light, noting which colors are absorbed and which are reflected (and thus available for our eyes to detect). Consider spending time to make sure that your students understand how photosynthetic pigments absorb and reflect certain wavelengths. Teaching Tips 1. Consider bringing a prism to class and demonstrating the spectrum of visible light. Depending on what you have available, it can be a dramatic reinforcement of this key concept. You might show an image of a rainbow if you are willing to explain how it is produced. 2. Consider bringing a glow stick to class just to help illustrate the authors’ note about the light-generating reactions in glow sticks. Small demonstrations break up lectures and stir attention. 3. The authors discuss a phenomenon that most students have noticed: Dark surfaces heat up faster in the sun than lighter-colored surfaces. This is an opportunity to demonstrate to your students the various depths of scientific explanations and help them appreciate their own educational progress. In elementary school, they might have learned that the sun heats darker surfaces faster than lighter surfaces. In high school, they may have learned about light energy and the fact that dark surfaces absorb more of this energy than lighter surfaces. Now, in college, they are learning that at the atomic level, darker surfaces absorb the energy of more photons, exciting more electrons, which then fall back to a lower state, releasing more heat. 4. The authors develop a mechanical analogy to the energy levels and movement of electrons in the light reaction. Figure 7.12 equates the height of an electron with its energy state. Thus, electrons captured at high levels carry more energy than electrons in lower positions. Although this figure can be very effective, students might need to be carefully led through the analogy to understand precisely what is represented. Active Lecture Tips 1. 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. 2. See the activity Satellite TV and Photosystems on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 66

Electron transport chain ATP synthase Matrix
Figure 6.10 Space between membranes H+ H+ H+ H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ H+ 3 H+ 5 H+ Protein complex Inner mitochondrial membrane   FADH2 FAD H+ Electron flow 2 1 O2 2 H+ H2O 6 2   4 NADH NAD+ ADP + P ATP 1 H+ H+ H+ H+ H+ Electron transport chain ATP synthase Matrix Figure 6.10 How electron transport drives ATP synthase machines

Electron transport chain ATP synthase Matrix
Figure Space between membranes H+ H+ H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ H+ 3 H+ 5 H+ Protein complex Inner mitochondrial membrane   FADH2 FAD H+ Electron flow 2 1 O2 + 2 H+ H2O 6 2   4 NADH NAD+ ADP + P ATP 1 H+ H+ H+ H+ H+ Electron transport chain ATP synthase Matrix Figure How electron transport drives ATP synthase machines (part 1: detail)

Electron transport chain
Figure a Space between membranes H H+ H+ H+ H+ H+ H+ Electron carrier H+ H+ H+ 3 H+ Protein complex Inner mitochondrial membrane   FADH2 FAD H+ Electron flow 2 1 O2 + 2 H+ 2   4 NADH NAD+ 1 H+ H+ H+ H+ Matrix Electron transport chain Figure a How electron transport drives ATP synthase machines (part 1a: detail, electron transport chain)

5 + 6 4 ATP synthase H+ H+ + H+ H+ H+ H+ O2 2 H+ H2O ADP + P ATP H+ H+
Figure b H+ H+ + H+ H+ H+ 5 H+ 1 O2 + 2 H+ H2O 6 2 4 ADP + P ATP H+ H+ ATP synthase Figure b How electron transport drives ATP synthase machines (part 1b: detail, ATP synthase)

Figure Figure How electron transport drives ATP synthase machines (part 2: dam)

First photosystem Second photosystem
Figure 7.12 e ATP e e   NADPH e e e Photon Electron transport chain e Photon First photosystem Second photosystem Figure 7.12 The light reactions illustrated using a hard-hat analogy

The Calvin Cycle: Making Sugar from Carbon Dioxide
functions like a sugar factory within a chloroplast and regenerates the starting material with each turn. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 73

With each turn of the cycle, there are chemical inputs and outputs. The inputs are CO2 from the air and ATP and NADPH produced by the light reactions. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 74

The Calvin cycle constructs an energy-rich sugar molecule called glyceraldehyde 3-phosphate (G3P) using carbon from CO2, energy from ATP, and high-energy electrons from NADPH. The plant cell can then use G3P as the raw material to make glucose and other organic compounds. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 75

1 CO2 (from air) RuBP sugar Three-carbon molecule Calvin cycle 1 1 P P
Figure 7.13-s1 CO2 (from air) 1 1 1 P RuBP sugar Three-carbon molecule P P Calvin cycle Figure 7.13-s1 The Calvin cycle (step 1)

1 2 CO2 (from air) RuBP sugar Three-carbon molecule Calvin cycle
Figure 7.13-s2 CO2 (from air) 1 1 P RuBP sugar Three-carbon molecule ATP P P ADP + Calvin cycle P   NADPH NADP+ G3P sugar 2 2 P Figure 7.13-s2 The Calvin cycle (step 2)

1 3 2 CO2 (from air) RuBP sugar Three-carbon molecule Calvin cycle
Figure 7.13-s3 CO2 (from air) 1 1 P RuBP sugar Three-carbon molecule ATP P P ADP + Calvin cycle P   NADPH NADP+ G3P sugar G3P sugar 3 3 P 2 2 P G3P sugar Glucose (and other organic compounds) P Figure 7.13-s3 The Calvin cycle (step 3)

1 3 2 CO2 (from air) RuBP sugar Three-carbon molecule Calvin cycle
Figure 7.13-s4 CO2 (from air) 1 1 P RuBP sugar Three-carbon molecule 4 ATP P P ADP + + Calvin cycle P ADP P   NADPH ATP NADP+ G3P sugar G3P sugar 3 3 P 2 P 2 G3P sugar Glucose (and other organic compounds) P Figure 7.13-s4 The Calvin cycle (step 4)

Evolution Connection: Creating a Better Biofuel Factory
The production of biofuels is highly inefficient. It is usually far more costly to produce biofuels than to extract the equivalent amount of fossil fuels. We must convert to “green-energy” resources (solar, wind, geothermal, etc.) in the future… © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 80

Biomechanical engineers are working to solve this dilemma by turning to an obvious example: evolution by natural selection. In nature, organisms with genes that make them better suited to their local environment will, on average, more often survive and pass those genes to the next generation. Repeated over many generations, genes that enhance survival within that environment will become more common, and the species evolves. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 81

When trying to solve an engineering problem, scientists can impose their own desired outcomes using a process called directed evolution, in which scientists in the laboratory determine which organisms are the fittest. Directed evolution of biofuel production often involves microscopic algae rather than plants because algae are easier to manipulate and maintain within the laboratory. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 82

Figure 7.14 Figure 7.14 Microscopic biofuel factories

In a typical directed evolution experiment, the researcher starts with a large collection of individual alga, sometimes naturally occurring species and sometimes transgenic algae that have been engineered to carry useful genes, such as fungal genes for enzymes that break down cellulose. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 84

The algae are exposed to mutation-promoting chemicals. This produces a highly varied collection of algae that can be screened for the desired outcome: the ability to produce the most useful biofuel in the largest quantity. The tiny fraction of total algae that can best perform this task is grown and subjected to another round of mutation and selection. Repeated many times, the algae may slowly improve their ability to efficiently produce biofuels. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, as noted in the text, G3P is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Teaching Tips 1. 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. Nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). 85

(a) Absorption of a photon (b) Fluorescence of a glow stick
Figure 7.8 Excited state The electron falls to its ground state. Absorption of a photon excites an electron. e Heat Light Light (fluorescence) Photon Ground state Chlorophyll molecule (a) Absorption of a photon (b) Fluorescence of a glow stick Figure 7.8 Excited electrons in pigments

CO2 Calvin cycle Light reactions Sugar
Figure 7.UN02 CO2 Light H2O NADP+ ADP + P Calvin cycle Light reactions ATP   NADPH O2 Sugar Figure 7.UN02 In-text figure, Calvin cycle, p. 115

Calvin cycle Light reactions
Figure 7.UN04 Chloroplast CO2 Light H2O Stack of thylakoids NADP+ Stroma ADP + P Calvin cycle Light reactions ATP   NADPH Sugar used for • cellular respiration • cellulose • starch • other organic compounds O2 Sugar Figure 7.UN04 Summary of key concepts: photosynthesis overview

  2e 2e 2e 2e NADP+ e acceptor ADP ATP e acceptor NADPH
Figure 7.UN05 NADP+ e acceptor 2e ADP ATP e acceptor 2e   2e NADPH Photon Electron transport chain Photon Chlorophyll H2O Chlorophyll Second photosystem 2e First photosystem 1 2 2 H+ + O2 Figure 7.UN05 Summary of key concepts: photosystems

+ CO2 ATP ADP P Calvin cycle   NADPH NADP+ G3P Glucose and
Figure 7.UN06 CO2 ATP ADP + P Calvin cycle   NADPH NADP+ G3P Glucose and other compounds (such as cellulose and starch) P Figure 7.UN06 Summary of key concepts: Calvin cycle

Absorption of light by chloroplast pigments
Figure 7.UN07 Chloro- phyll a Chlorophyll b Absorption of light by chloroplast pigments Carotenoids 400 500 600 700 Wavelength of light (nm) Figure 7.UN07 Process of science, question 12 (absorption spectrum)

Photosynthesis: Using Light to Make Food

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