Photosynthesis: Using light to make food Chapter 7

Photosynthesis: Using light to make food Chapter 7

Introduction Plants, algae, and certain prokaryotes
convert light energy to chemical energy and Store the chemical energy in sugar, made from carbon dioxide and water 6 CO2 + 6 H2O C6H12O6 + 6 O equation © 2012 Pearson Education, Inc. 2

The Light Reactions: Converting Solar Energy to Chemical Energy
Figure 7.0_1 Chapter 7: Big Ideas The Light Reactions: Converting Solar Energy to Chemical Energy An Overview of Photosynthesis Figure 7.0_1 Chapter 7: Big Ideas The Calvin Cycle: Reducing CO2 to Sugar Photosynthesis Reviewed and Extended 3

AN OVERVIEW OF PHOTOSYNTHESIS
© 2012 Pearson Education, Inc. 4

7.1 Autotrophs are the producers of the biosphere
make their own food through the process of photosynthesis, do not usually consume organic molecules made from other organisms. Teaching Tips 1. When introducing the diverse ways that plants impact our lives, consider challenging your students to come up with a list of products made from plants that they come across on a regular basis. The collective lists from your students can be surprisingly long and might help to build up your catalog of examples. 2. The evolution of chloroplasts from photosynthetic prokaryotes living inside of eukaryotic cells is discussed in Module If your students have not already read Chapter 4, consider discussing this theory of endosymbiosis. 3. Some students might think that the term producers applies to the production of oxygen by plants. In turn, they might think that consumers are organisms that use oxygen (which would include all aerobic organisms). Extra care may be needed to clarify the definitions of these frequently used terms. © 2012 Pearson Education, Inc. 5

7.1 Autotrophs are the producers of the biosphere
Photoautotrophs use the energy of light to produce organic molecules. Chemoautotrophs are prokaryotes that use inorganic chemicals as their energy source. Heterotrophs are consumers that feed on plants or animals, or decompose organic material. Teaching Tips 1. When introducing the diverse ways that plants impact our lives, consider challenging your students to come up with a list of products made from plants that they come across on a regular basis. The collective lists from your students can be surprisingly long and might help to build up your catalog of examples. 2. The evolution of chloroplasts from photosynthetic prokaryotes living inside of eukaryotic cells is discussed in Module If your students have not already read Chapter 4, consider discussing this theory of endosymbiosis. 3. Some students might think that the term producers applies to the production of oxygen by plants. In turn, they might think that consumers are organisms that use oxygen (which would include all aerobic organisms). Extra care may be needed to clarify the definitions of these frequently used terms. © 2012 Pearson Education, Inc. 6

Diversity of autotrophs
Figure 7.1A-D Photoautotroph diversity 7

7.2 Photosynthesis occurs in chloroplasts in plant cells
Chloroplasts are the major sites of photosynthesis in green plants. Chlorophyll is an important light-absorbing pigment in chloroplasts, is responsible for the green color of plants Teaching Tips 1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. 2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. © 2012 Pearson Education, Inc. 8

Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf. Sunlight penetrates cuticle-& epidermal cells Cuticle is waxy cover over leaf-CO2 can’t enter Stomata are tiny pores in the leaf that allow carbon dioxide to enter and oxygen & water to exit. Close hottest part of day, open when cool Veins in the leaf deliver water absorbed by roots. Teaching Tips 1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. 2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. © 2012 Pearson Education, Inc. 9

Figure 7.2 Zooming in on the location and structure of chloroplasts
Leaf Leaf Cross Section Mesophyll Vein CO2 O2 Stoma Mesophyll Cell Chloroplast Figure 7.2 Zooming in on the location and structure of chloroplasts Inner and outer membranes Granum Thylakoid Thylakoid space Stroma 10

Chloroplasts consist of an envelope of two membranes, which enclose an inner compartment filled with a thick fluid called stroma and contain a system of interconnected membranous sacs called thylakoids. Teaching Tips 1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. 2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. © 2012 Pearson Education, Inc. 11

Thylakoids are often concentrated in stacks called grana and have an internal compartment called the thylakoid space, similar to the intermembrane space of a mitochondrion. Thylakoid membranes are the places that convert light energy to chemical energy. Chlorophyll molecules are built into the thylakoid membrane and capture light energy. Teaching Tips 1. The authors note the analogous roles of the thylakoid space and the intermembrane space of a mitochondrion. Students might be encouraged to create a list of the similarities in structure and function of mitochondria and chloroplasts through these related chapters. 2. The living world contains many examples of adaptations to increase surface area. Some examples are the many folds of the inner mitochondrial membrane, the highly branched surfaces of plant roots, fish gills, and human lungs, and the highly branched system of capillaries in the tissues of our bodies. Consider relating this broad principle to the extensive folding of the thylakoid membranes. © 2012 Pearson Education, Inc. 12

Inner and outer membranes
Figure 7.2_2 Chloroplast Inner and outer membranes Granum Thylakoid Thylakoid space Figure 7.2_2 Zooming in on the location and structure of chloroplasts (part 2) Stroma 13

7.4 Photosynthesis is a redox process, as is cellular respiration
Photosynthesis, like respiration, is a redox (oxidation- reduction) process. CO2 becomes reduced to sugar as H- along with hydrogen+ from water are added to it. Water molecules are oxidized when they lose electrons along with hydrogen ions. Teaching Tips In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. © 2012 Pearson Education, Inc. 14

Becomes reduced Becomes oxidized Figure 7.4A
Figure 7.4A Photosynthesis (uses light energy) 15

7.4 Photosynthesis is a redox process, as is cellular respiration
In photosynthesis, light energy is captured by chlorophyll molecules to boost the energy of electrons, light energy is converted to chemical energy, and chemical energy is stored in the chemical bonds of sugars. Teaching Tips In our world, energy is frequently converted to a usable form in one place and used in another. For example, electricity is generated by power plants, transferred to our homes, and used to run computers, create light, and help us prepare foods. Consider relating this common energy transfer to the two-stage process of photosynthesis. © 2012 Pearson Education, Inc. 16

Becomes oxidized Becomes reduced Figure 7.4B
Figure 7.4B Cellular respiration (releases chemical energy) 17

7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH
Photosynthesis occurs in two stages. The light reactions occur in the thylakoid membranes In these reactions water is split, providing a source of electrons and giving off oxygen as a by-product, ATP is generated light energy is absorbed by the chlorophyll molecules to drive the transfer of H –(electrons) and H+ from water to the electron acceptor NADP+ reducing it to NADPH. NADPH produced by the light reactions provides the electrons for reducing carbon in the Calvin cycle. Student Misconceptions and Concerns Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange. Teaching Tips 1. 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. 2. Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. © 2012 Pearson Education, Inc. 18

7.5 Overview: The two stages of photosynthesis are linked by ATP and NADPH
The second stage is the Calvin cycle, which occurs in the stroma of the chloroplast. The Calvin cycle assembles sugar molecules using CO2 and the energy-rich products of the light reactions. During the Calvin cycle, CO2 is incorporated into organic compounds in a process called carbon fixation. After carbon fixation, enzymes of the cycle make sugars by further reducing the carbon compounds. The Calvin cycle is often called the dark reactions or light- independent reactions, because no light needed Student Misconceptions and Concerns Students may understand the overall chemical relationships between photosynthesis and cellular respiration, but many struggle to understand the use of carbon dioxide in the Calvin cycle. Photosynthesis is much more than gas exchange. Teaching Tips 1. 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. 2. Figure 7.5 is an important visual organizer, which notes the key structures and functions of the two stages of photosynthesis. This figure demonstrates that water and sunlight are used in the thylakoid membranes to generate oxygen, ATP, and NADPH. The second step, in the stroma, reveals the use of carbon dioxide, ATP, and NADPH to ultimately generate carbohydrates. © 2012 Pearson Education, Inc. 19

Chloroplast H2O Light NADP+ ADP P Light Reactions (in thylakoids)
Figure 7.5_s1 H2O Light NADP+ ADP P Light Reactions (in thylakoids) Figure 7.5_s1 An overview of the two stages of photosynthesis in a chloroplast (step 1) Chloroplast 20

Chloroplast H2O Light NADP+ ADP P Light Reactions (in thylakoids) ATP
Figure 7.5_s2 H2O Light NADP+ ADP P Light Reactions (in thylakoids) ATP Figure 7.5_s2 An overview of the two stages of photosynthesis in a chloroplast (step 2) NADPH Chloroplast O2 21

Chloroplast H2O CO2 Light NADP+ ADP P Calvin Cycle Light Reactions
Figure 7.5_s3 H2O CO2 Light NADP+ ADP P Calvin Cycle Light Reactions (in stroma) (in thylakoids) ATP Figure 7.5_s3 An overview of the two stages of photosynthesis in a chloroplast (step 3) NADPH Chloroplast O2 Sugar 22

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY

7.7 Photosystems capture solar energy
Two types of photosystems cooperate in the light reactions. Each type of photosystem has a characteristic reaction center. Photosystem II, which functions first, is called P680 because its pigment absorbs light with a wavelength of 680 nm. Photosystem I, which functions second, is called P700 because it absorbs light with a wavelength of 700 nm. Student Misconceptions and Concerns 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 The authors discuss a phenomenon that most students have noticed: dark surfaces heat up faster in the sun than do 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. © 2012 Pearson Education, Inc. 24

7.8 Two photosystems connected by an electron transport chain generate ATP and NADPH
In the light reactions, light energy is transformed into the chemical energy of ATP and NADPH. To accomplish this, H electrons are removed from water, passed from photosystem II to photosystem I, and H - accepted by NADP+, reducing it to NADPH. Between the two photosystems, the electrons move down an electron transport chain and provide energy for the synthesis of ATP. From photosystem p700, etc too short to make ATP so NADP+ grabs H- -> NADPH Teaching Tips The authors develop a mechanical analogy for the energy levels and movement of electrons in the light reaction. Figure 7.8B 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. © 2012 Pearson Education, Inc. 25

Figure 7.8A Electron transport chain Provides energy for synthesis of ATP by chemiosmosis NADP  H NADPH Light Light Photosystem I 6 Photosystem II Stroma 1 Primary acceptor Primary acceptor 2 Thylakoid membrane 4 5 P680 P700 Figure 7.8A Electron flow in the light reactions: light energy driving electrons from water to NADPH Thylakoid space 3 H2O 2 1 O2 H  2 26

Figure 7.8A_1 Electron transport chain Provides energy for synthesis of ATP by chemiosmosis Light Photosystem II Stroma 1 Primary acceptor 2 Thylakoid membrane 4 P680 Figure 7.8A_1 Electron flow in the light reactions: light energy driving electrons from water to NADPH (part 1) Thylakoid space 3 H2O 2 1 O2  2 H 27

Figure 7.8A_2 Electron transport chain Provides energy for synthesis of ATP by chemiosmosis NADP  H+ NADPH Light Photosystem I 6 Primary acceptor 4 5 Figure 7.8A_2 Electron flow in the light reactions: light energy driving electrons from water to NADPH (part 2) P700 28

7.8 Two photosystems connected by an electron transport chain generate ATP and NADPH
The products of the light reactions are NADPH & ATP used to run Calvin cycle Oxygen –a waste product Teaching Tips The authors develop a mechanical analogy for the energy levels and movement of electrons in the light reaction. Figure 7.8B 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. © 2012 Pearson Education, Inc. 29

7.9 Chemiosmosis powers ATP synthesis in the light reactions
In photophosphorylation, using the initial energy input from light, the electron transport chain pumps H+ into the thylakoid space against the gradient the resulting concentration gradient drives H+ back through ATP synthase, producing ATP. Teaching Tips Module 7.9 notes the similarities between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts. If your students have not already read or discussed chemiosmosis in mitochondria, consider assigning Modules 6.6 and 6.10 to show the similarities of these processes. (As noted in Module 7.2, the thylakoid space is analogous to the intermembrane space of mitochondria.) © 2012 Pearson Education, Inc. 30

Electron transport chain
Figure 7.9 Chloroplast To Calvin Cycle H+ ATP Light Light ADP P Stroma (low H+ concentration) H+ NADP+ H+ NADPH H+ H+ Thylakoid membrane Figure 7.9 The production of ATP by chemiosmosis H+ H+ H+ H+ H2O H+ 1 2 H+ Thylakoid space (high H+ concentration) O H+ H+ H+ H+ H+ H+ Electron transport chain H+ H+ Photosystem II Photosystem I ATP synthase 31

Electron transport chain
Figure 7.9_1 To Calvin Cycle H+ ATP Light Light ADP P H+ NADPH NADP+ H+ H+ H+ H+ H+ H+ H+ H2O H+ H+ Figure 7.9_1 The production of ATP by chemiosmosis (partial) 1 2 O2 2 H+ H+ H+ H+ H+ H+ Electron transport chain H+ H+ Photosystem II Photosystem I ATP synthase 32

THE CALVIN CYCLE: REDUCING CO2TO SUGAR

7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
The Calvin cycle makes sugar within a chloroplast. To produce sugar, the necessary ingredients are CO2 and ATP and NADPH generated by the light reactions. The Calvin cycle uses these three ingredients to produce an energy-rich, three-carbon sugar called glyceraldehyde-3-phosphate (G3P). A plant cell may then use G3P to make glucose and other organic molecules. Student Misconceptions and Concerns The terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at different times of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available. Teaching Tips 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. © 2012 Pearson Education, Inc. 34

CO2 ATP NADPH Input Calvin Cycle Output: G3P Figure 7.10A
Figure 7.10A An overview of the Calvin cycle Output: G3P 35

7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
The steps of the Calvin cycle include 1. carbon fixation-uses enzyme RuBP (rubisco) adds 3 CO2- makes PGA 2. Carbon Reduction- PGA reduced to make 1 G3P- a 3 Carbon sugar 3. Regeneration of the starting molecule ribulose bisphosphate (RuBP). Student Misconceptions and Concerns The terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at different times of the day. However, the Calvin cycle in most plants occurs during daylight, when NADPH and ATP from the light reactions are readily available. Teaching Tips 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. © 2012 Pearson Education, Inc. 36

Step Carbon fixation Input: 3 CO2 Rubisco 3 P P 6 P RuBP 3-PGA
Figure 7.10B_s1 Step Carbon fixation 1 Input: 3 CO2 Rubisco 1 3 P P 6 P RuBP 3-PGA Calvin Cycle Figure 7.10B_s1 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 1) 37

Step Carbon fixation Input: 3 CO2 Rubisco 3 P P 6 P RuBP 3-PGA
Figure 7.10B_s2 Step Carbon fixation 1 Input: 3 CO2 Rubisco 1 3 P P 6 P RuBP 3-PGA Step Reduction 2 6 ATP 6 ADP P Calvin Cycle 2 6 NADPH 6 NADP Figure 7.10B_s2 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 2) 6 P G3P 38

Step Release of one molecule of G3P 6 NADP 6 P 5 P G3P G3P
Figure 7.10B_s3 Step Carbon fixation 1 Input: 3 CO2 Rubisco 1 3 P P 6 P RuBP 3-PGA Step Reduction 2 6 ATP 6 ADP P Calvin Cycle 2 6 NADPH Step Release of one molecule of G3P 3 6 NADP Figure 7.10B_s3 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 3) 6 P 5 P G3P G3P 3 Glucose and other compounds Output: 1 P G3P 39

Step Release of one molecule of G3P 6 NADP 6 P 5 P G3P G3P
Figure 7.10B_s4 Step Carbon fixation 1 Input: 3 CO2 Rubisco 1 3 P P 6 P RuBP 3-PGA Step Reduction 2 6 ATP 3 ADP 6 ADP P Calvin Cycle 4 2 3 ATP 6 NADPH Step Release of one molecule of G3P 3 6 NADP Figure 7.10B_s4 Details of the Calvin cycle, which takes place in the stroma of a chloroplast (step 4) 6 P 5 P G3P G3P 3 Glucose and other compounds Step Regeneration of RuBP 4 Output: 1 P G3P 40

7.11 EVOLUTION CONNECTION: Other methods of carbon fixation have evolved in hot, dry climates
Most plants use CO2 directly from the air, and carbon fixation occurs when the enzyme rubisco adds CO2 to RuBP. Such plants are called C3 plants because the first product of carbon fixation is a three-carbon compound, 3-PGA. Teaching Tips 1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute. 2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. © 2012 Pearson Education, Inc. 42

In hot and dry weather, C3 plants close their stomata to reduce water loss but prevent CO2 from entering the leaf and O2 from leaving. As O2 builds up in a leaf, rubisco adds O2 instead of CO2 to RuBP, and a two-carbon product of this reaction is then broken down in the cell. This process is called photorespiration because it occurs in the light, consumes O2, and releases CO2. But unlike cellular respiration, it uses ATP instead of producing it. Teaching Tips 1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute. 2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. © 2012 Pearson Education, Inc. 43

C4 plants have evolved a means of carbon fixation that saves water during photosynthesis while optimizing the Calvin cycle. C4 plants are so named because they first fix CO2 into a four-carbon compound. When the weather is hot and dry, C4 plants keep their stomata mostly closed, thus conserving water. Teaching Tips 1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute. 2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. © 2012 Pearson Education, Inc. 44

Another adaptation to hot and dry environments has evolved in the CAM plants, such as pineapples and cacti. CAM plants conserve water by opening their stomata and admitting CO2 only at night. CO2 is fixed into a four-carbon compound, which banks CO2 at night and releases it to the Calvin cycle during the day. Teaching Tips 1. If you can find examples of C3, C4, and CAM plants, consider bringing them to class. Referring to living plants helps students understand these abstract concepts. Nice photographs can serve as a substitute. 2. Relate the properties of C3 and C4 plants to the regions of the country where each is grown. Students might generally understand that crops have specific requirements, but may not specifically relate these physiological differences to their geographic sites of production or specific evolutionary histories. © 2012 Pearson Education, Inc. 45

Figure 7.11 Mesophyll cell CO2 CO2 Night 4-C compound 4-C compound Bundle- sheath cell CO2 CO2 Calvin Cycle Calvin Cycle Figure 7.11 Comparison of C4 and CAM photosynthesis 3-C sugar 3-C sugar Day C4 plant CAM plant Sugarcane Pineapple 46

7.13 CONNECTION: Photosynthesis may moderate global climate change
Increasing concentrations of greenhouse gases have been linked to global climate change (also called global warming), a slow but steady rise in Earth’s surface temperature. Since 1850, the atmospheric concentration of CO2 has increased by about 40%, mostly due to the combustion of fossil fuels including coal, oil, and gasoline. 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. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! © 2012 Pearson Education, Inc. 47

The predicted consequences of continued warming include melting of polar ice, rising sea levels, extreme weather patterns, droughts, increased extinction rates, and the spread of tropical diseases. 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. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! © 2012 Pearson Education, Inc. 48

Widespread deforestation has aggravated the global warming problem by reducing an effective CO2 sink. Global warming caused by increasing CO2 levels may be reduced by limiting deforestation, reducing fossil fuel consumption, and growing biofuel crops that remove CO2 from the atmosphere. 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. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. Teaching Tips Some students might better relate the greenhouse effect to what happens inside their closed car on a sunny day. The glass in our automobiles functions like the glass of a greenhouse, trapping heat inside our car. This can be an advantage during the winter but is usually not welcome on a hot summer day! © 2012 Pearson Education, Inc. 49

Photosynthesis: Using light to make food Chapter 7

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