Plant Power Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain.

Plant Power Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain themselves without eating anything derived from other living beings. Plants produce oxygen, a by-product of photosynthesis, that is used in respiration. The solar energy used in photosynthesis traveled 150 million kilometers from the sun to Earth to be converted into chemical energy. You may want to reintroduce the terms producers and consumers within the context of this chapter.

Plant Power Photosynthesis: Plants use water and atmospheric carbon dioxide to produce a simple sugar and liberate oxygen Earth’s plants produce 160 billion metric tons of sugar each year Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain themselves without eating anything derived from other living beings. Plants produce oxygen, a by-product of photosynthesis, that is used in respiration. The solar energy used in photosynthesis traveled 150 million kilometers from the sun to Earth to be converted into chemical energy. You may want to reintroduce the terms producers and consumers within the context of this chapter. Carbon dioxide C6H12O6 Photosynthesis H2O CO2 O2 Water + 6 6 Light energy Oxygen gas Glucose + 6 Copyright © 2009 Pearson Education, Inc.

Autotrophs are the primary producers of the biosphere
Autotrophs are living things that are able to make their own food without using organic molecules derived from any other living thing Photoautotrophs: autotrophs that use the energy of light to produce organic molecules A very interesting class of autotrophs are the autotrophic bacteria that use carbon dioxide to synthesize organic molecules without solar energy. 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 briefly noted in a reference to Module If your students have not already read Chapter 4, consider discussing the evidence that suggests this endosymbiotic origin. 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. Copyright © 2009 Pearson Education, Inc.

Photosynthesis occurs in chloroplasts in plant cells
CO2 O2 Stoma Mesophyll Cell Vein Chloroplast Mesophyll Leaf Cross Section Leaf Outer and inner membranes Intermembrane space Granum Stroma Thylakoid Chloroplasts are the major sites of photosynthesis in green plants Chloroplasts are concentrated in the cells of the mesophyll, the green tissue in the interior of the leaf Stomata are tiny pores in the leaf that allow carbon dioxide to enter and oxygen to exit Chlorophyll absorbs light energy and drives the synthesis of organic molecules. 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 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. Copyright © 2009 Pearson Education, Inc.

Chloroplast structure
CO2 O2 Stoma Mesophyll Cell Vein Chloroplast Mesophyll Leaf Cross Section Leaf Outer and inner membranes Intermembrane space Granum Stroma Thylakoid An envelope of two membranes encloses the stroma, the dense fluid within the chloroplast A system of interconnected membranous sacs called thylakoids segregates the stroma from another compartment, the thylakoid space Chlorophyll resides in the thylakoid membranes. 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 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. Copyright © 2009 Pearson Education, Inc.

Where does O2 gas come from in photosynthesis?
Scientists have known for a long time that plants produce O2  where does it come from? C. B. van Niel of Stanford University hypothesized that plants split water into hydrogen and oxygen. His hypothesis was confirmed 20 years later. A significant result of photosynthesis is the extraction of hydrogen from water and its incorporation into sugar. Oxygen is a waste product of photosynthesis. The chloroplast is the site where water is split into hydrogen and oxygen. Student Misconceptions and Concerns 1. 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. Teaching Tips 1. Many students do not realize that glucose is not the direct product of photosynthesis. The authors note that 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. Copyright © 2009 Pearson Education, Inc.

O2 gas comes from splitting of water
6 CO H2O Experiment 1 C6H12O H2O O2 Not labeled 6 CO H2O Experiment 2 C6H12O H2O O2 Labeled C. B. van Niel of Stanford University hypothesized that plants split water into hydrogen and oxygen. His hypothesis was confirmed 20 years later. A significant result of photosynthesis is the extraction of hydrogen from water and its incorporation into sugar. Oxygen is a waste product of photosynthesis. The chloroplast is the site where water is split into hydrogen and oxygen. Student Misconceptions and Concerns 1. 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. Teaching Tips 1. Many students do not realize that glucose is not the direct product of photosynthesis. The authors note that 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. Reactants: 6 CO2 Products: 12 H2O C6H12O6 6 H2O 6 O2 Copyright © 2009 Pearson Education, Inc.

Photosynthesis is a redox process, as is cellular respiration
Oxidation: Water molecules are split apart by oxidation, which means that they lose electrons along with hydrogen ions (H+) Reduction: CO2 is reduced to sugar as electrons and hydrogen ions are added to it The simple sugar produced in photosynthesis is glucose, using a number of energy-releasing redox reactions. 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. 6 CO H2O C6H12O O2 Reduction Oxidation Copyright © 2009 Pearson Education, Inc.

H2O ADP P LIGHT REACTIONS (in thylakoids) Light Chloroplast NADPH ATP
Electrons CALVIN CYCLE (in stroma) Sugar CO2  NADP+

THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
Copyright © 2009 Pearson Education, Inc.

Visible radiation drives the light reactions
Sunlight contains energy called electromagnetic energy or radiation Visible light is only a small part of the electromagnetic spectrum Electromagnetic energy travels in waves, and the wavelength is the distance between the crests of two adjacent waves Student Misconceptions and Concerns 1. The authors note that electromagnetic energy travels through space in waves that are like ripples 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, which exhibits the properties of both waves and particles, may need to be discussed further, if students are to do more than just accept the definitions. 2. 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. 3. 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 light. Depending on what you have available, it can be a dramatic reinforcement. Copyright © 2009 Pearson Education, Inc.

Chlorophyll absorbs some wavelengths of light and transmit others Light Chloroplast Thylakoid Absorbed light Transmitted Reflected Each type of pigment absorbs certain wavelengths of light because it is able to absorb the specific amount of energy in those photons. Student Misconceptions and Concerns 1. The authors note that electromagnetic energy travels through space in waves that are like ripples 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, which exhibits the properties of both waves and particles, may need to be discussed further, if students are to do more than just accept the definitions. 2. 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. 3. 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 light. Depending on what you have available, it can be a dramatic reinforcement. Copyright © 2009 Pearson Education, Inc.

Chloroplasts contain several different pigments and all absorb light of different wavelengths Chlorophyll a absorbs blue violet and red light and reflects green Chlorophyll b absorbs blue and orange and reflects yellow-green Carotenoids absorb mainly blue-green light and reflect yellow and orange So why are plants usually green? The colors of fall foliage in certain parts of the world are due partly to the yellow-orange hues of longer lasting carotenoids that show through once the green chlorophyll breaks down. Student Misconceptions and Concerns 1. The authors note that electromagnetic energy travels through space in waves that are like ripples 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, which exhibits the properties of both waves and particles, may need to be discussed further, if students are to do more than just accept the definitions. 2. 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. 3. 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 light. Depending on what you have available, it can be a dramatic reinforcement. Copyright © 2009 Pearson Education, Inc.

Photosystems capture solar power
Chlorophyll absorbs light energy (photons)- cause electrons to jump to higher energy level The electrons drop back down to their “ground state,” and, as they do, release their excess energy Chlorophyll molecule Excited state Ground state Heat Photon (fluorescence) e– Student Misconceptions and Concerns 1. 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. 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. Copyright © 2009 Pearson Education, Inc.

P 700 P 680 NADPH Mill makes ATP Photosystem II Photosystem I e–
Photon Photosystem I P 700 P 680

Photosystems capture solar power
The energy released could be lost as heat or light, but rather it is conserved as it is passed from one molecule to another molecule Photosystems are light-harvesting complexes surrounding a reaction center complex Photosystem I absorbs wavelenghts of 700 nm Photosystem II absorbs wavelengths of 680 nm Because of their functions, you can think of photosystems as light-gathering antennae. Student Misconceptions and Concerns 1. 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. 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. Copyright © 2009 Pearson Education, Inc.

Summary of two photosystems
During the light reactions, light energy is transformed into the chemical energy of ATP and NADPH To accomplish this, electrons removed from water pass from photosystem II to photosystem I and are accepted by NADP+ The bridge between photosystems II and I is an electron transport chain that provides energy for the synthesis of ATP through chemiosmosis Teaching Tips 1. 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. Copyright © 2009 Pearson Education, Inc.

Electron transport chain
Stroma O2 H2O 2  1 H+ NADP+ NADPH Photon Photosystem II Electron transport chain Provides energy for synthesis of by chemiosmosis + 2 Primary acceptor Thylakoid membrane P680 4 3 space e– 5 P700 6 Photosystem I ATP +

Electron transport chain
Chloroplast Stroma (low H+ concentration) H+ Light Light H+ ADP + P ATP H+ NADP+ + H+ NADPH H+ Thylakoid membrane H2O H+ H+ 1  2 O2 + 2 H+ H+ H+ H+ H+ H+ H+ Photosystem II Electron transport chain Photosystem I H+ ATP synthase H+ Thylakoid space (high H+ concentration)

TOTAL OUTCOME OF LIGHT REACTIONS: PHOTOPHOSPHORYLATION
Light energy is converted to chemical energy and O2 1. Water is split to provide the O2 , H+ ions and electrons 2. H+ ions and electrons reduce NADP+ to NADPH, 3. Generation of ATP through chemiosmosis  PHOTOPHOSPHORYLATION

ATP and NADPH are used to make sugar in the Calvin cycle
The Calvin cycle makes sugar within a chloroplast CO2, ATP, and NADPH  glyceraldehyde-3-phosphate (G3P) Process called carbon fixation G3P makes other sugars CO2 ATP NADPH Input CALVIN CYCLE G3P Output: The Calvin cycle is called a “cycle” because the starting material is regenerated as the process occurs. Student Misconceptions and Concerns 1. As noted in Module 7.5, the terms light reactions and dark reactions can lead students to conclude that each set of reactions occurs at a different time 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 1. Glucose is not the direct product of the Calvin cycle, as might be expected from the general equation for photosynthesis. Instead, G3P, as noted in the text, is the main product. Clarify the diverse uses of G3P in the production of many important plant molecules for students. Copyright © 2009 Pearson Education, Inc.

Why are photosynthetic organisms producers?
Although photosynthesizers produce sugar for self-consumption, their sugar is a source for virtually all other organisms on Earth. Student Misconceptions and Concerns 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. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). Teaching Tips 1. Challenge students to explain how the energy in beef is ultimately derived from the sun. 2. The authors note that G3P is also used to produce cellulose, the most abundant compound on Earth. Each year, plants produce about 100 billion tons of cellulose! Copyright © 2009 Pearson Education, Inc.

Why are photosynthetic organisms producers?
Plants make more food than they actually need and stockpile it as starch in roots, tubers, and fruit Together with photosynthetic algae and bacteria they are primary producers We are defined as _________________ NADP+ NADPH ATP CO2 + H2O ADP P Electron transport chains Thylakoid membranes Light Chloroplast O2 CALVIN CYCLE (in stroma) Sugars Photosystem II Photosystem I LIGHT REACTIONS RuBP 3-PGA CALVIN CYCLE Stroma G3P Cellular respiration Cellulose Starch Other organic compounds Although photosynthesizers produce sugar for self-consumption, their sugar is a source for virtually all other organisms on Earth. Student Misconceptions and Concerns 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. As noted in the text, nearly 50% of the carbohydrates produced by plant cells are used for cellular respiration (involving mitochondria). Teaching Tips 1. Challenge students to explain how the energy in beef is ultimately derived from the sun. 2. The authors note that G3P is also used to produce cellulose, the most abundant compound on Earth. Each year, plants produce about 100 billion tons of cellulose! Copyright © 2009 Pearson Education, Inc.

The greenhouse effect Gases in the atmosphere (often called greenhouse gases), including CO2, reflect heat back to Earth, keeping the planet warm and supporting life As we increase the level of greenhouse gases, Earth’s temperature rises above normal (question: correlative or causative?) Atmosphere Sunlight Some heat energy escapes into space Radiant heat trapped by CO2 and other gases Student Misconceptions and Concerns 1. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. 2. 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. Teaching Tips 1. 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 just 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! Copyright © 2009 Pearson Education, Inc.

Global warming… hypothesis or theory?
Increasing concentrations of greenhouse gases could be leading to global warming, a slow but steady rise in Earth’s surface temperature The consequences of continued rise will be melting of polar ice, changing weather patterns, and spread of tropical disease But is this happening? Is it part of the normal cyclical pattern of the earth? Student Misconceptions and Concerns 1. Students may confuse global warming with the breakdown of the ozone layer. Be prepared to explain both phenomena and the impact of human activities. 2. 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. Teaching Tips 1. 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 just 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! Copyright © 2009 Pearson Education, Inc.

Plant Power Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain.

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Plant Power Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain.

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Presentation on theme: "Plant Power Photosynthesis nourishes almost the entire living world directly or indirectly. Almost all plants are autotrophs, meaning that they sustain."— Presentation transcript:

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