BSCS Biology: A Human Approach. Kendall/Hunt, 1997
Matter and Energy Transformations: Content Analysis
Map: What the Reviewers Found
This map displays the Content Analysis findings for this textbook in graphical form, showing what the reviewers found in terms of the book’s content alignment and coherence for the set of key ideas on matter and energy transformations. You may find it helpful to print out this map and refer to it as you read the rest of the Content Analysis:
Also helpful for reference are the Matter and Energy Transformations topic maps, which contrast the coherent set of key ideas that the reviewers looked for with a composite of the treatment actually found in all nine evaluated textbooks:
Alignment
The organization of BSCS Biology: A Human Approach is different from that of many other textbooks. The first part of the student book consists of six instructional units that present different themes of biology, such as Unit Three: Energy, Matter, and Organization: Relationships in Living Systems. Chapters in these units present scientific ideas through explanatory text, scenarios, student investigations, analysis questions, and challenge activities. The latter part of the book consists of a series of illustrated essays that support and expand upon the ideas presented in the first section. It is unclear whether the essays are intended as required reading by students. References to the essays in text for the students may say a particular essay “contains information that you will find useful” (p. 169s) or will be “helpful in completing this task” (p. 174s). Information for the teacher is contained in a separate Teacher’s Guide. As its title indicates, the focus of the textbook is on human biology.
The topic of matter and energy transformations brings together a number of key ideas from both the biological and physical sciences. BSCS Biology: A Human Approach treats most of these ideas in Unit Three: Energy, Matter, and Organization: Relationships in Living Systems. The chapters in this unit are Chapter 7: Performance and Fitness; Chapter 8: The Cellular Basis of Activity; and Chapter 9: The Cycling of Matter and the Flow of Energy in Communities. The key ideas appear in student activities, text, and questions in chapters 7–9. They also appear in the relevant essays and illustrations in the latter part of the book. Matter and energy are usually discussed together. Perhaps in keeping with the textbook’s focus on human biology, the idea that plants break down the sugar molecules they have made in photosynthesis and use them as building materials or store them is not treated. The idea that plants also get the energy to grow and function by breaking down the sugar molecules they have made is treated minimally. Energy transformation and conservation are both presented. Matter transformation is treated at both the substance level and the molecular level, although the focus at the molecular level is primarily on the carbon atom. The conservation of matter is not presented at all. The following analysis provides details on how the textbook treats each of the specific key ideas.
Matter is transformed in living systems.
Idea a1: Plants make sugar molecules from carbon dioxide (in the air) and water.
There is a content match to this idea, which is presented in a diagram. Text introduces the definition of photosynthesis in the context of how light energy is used to build matter but does not explicitly treat the transformation of carbon dioxide and water into food:
Autotrophs are able to make all of their own macromolecules. Plants need only light, water, air, and a few essential elements that are available from the soil to grow. In other words, plants are able to make their own food—the carbon-containing molecules such as simple sugars and starch that are used to support their cellular activities. The process of making these carbon-containing molecules is called photosynthesis....
p. 176s
In the context of a student discussion about who discovered photosynthesis, the text is explicit about the transformation of carbon dioxide but not about transformation at the molecular level. Fernando, a participant in the discussion, refers to “...the guy who first figured out that plants use light and carbon dioxide from the air to make their own food” (p. E122s). Water is not mentioned in this discussion.
Transformation at the molecular level is presented in Figure E8.20 Summary of the reactions of photosynthesis (p. E124s). This diagram includes both water and carbon dioxide. However, the diagram is somewhat confusing (see Representing Ideas Effectively under Category IV in the Instructional Analysis) and is set in a five-page essay, Getting Energy and Matter into Biological Systems, which presents biochemical details that go well beyond the key idea.
Idea b1: Plants break down the sugar molecules that they have synthesized into carbon dioxide and water, use them as building materials, or store them for later use.
There is not a content match to this idea. The breakdown of sugars is mentioned in the essay Controlling the Release of Energy from Matter (pp. E116–E117s). But the point is not made that the breakdown of sugar molecules happens in plants, even though the essay begins with a reference to the grain storage explosion described on page 167s. The essay focuses entirely on cellular respiration in humans, which is in keeping with the stated “human approach” of the text, but which also means that one key idea related to the flow of matter and energy through all kinds of living things (including plants) is not addressed. Furthermore, only the production of carbon dioxide is mentioned, well hidden in the caption for Figure E8.11 with details that go way beyond key ideas. There is nothing about water or the use of these products for building materials or storage. Students are asked to diagram a possible path of radioactive carbon from carbon dioxide to human muscle protein (p. 182s). The Teacher’s Guide provides a fairly complete sequence that includes the statement, “The plant uses these labeled sugars to synthesize labeled macromolecules, including labeled starch and labeled proteins,” but indicates that student answers need not be this complete (p. 281t).
Idea c1: Other organisms break down the stored sugars or the body structures of the plants they eat (or animals they eat) into simpler substances, reassemble them into their own body structures, including some energy stores.
There is a content match to this idea, which is treated in text and a student-designed experiment. However, most instances treat the idea in the context of humans and do not generalize to other organisms. Under the title You Are What You Eat in chapter 7, the text introduces the idea that, to be useful in the human body, food must be broken down into smaller parts:
Now you know what is in the food you eat, but once this food is inside you, how does it become useful to your body? What does your body do to this matter so that you can use the energy it contains for performance? How does your body prepare this matter so that you will have the building blocks necessary for growth and repair? In this activity you will look at digestion to understand the role it plays in preparing to release the energy stored in the molecules of food and in providing a source of building blocks for biosynthesis.
p. 151s
As Step 1 in an experiment, students are told to read the following paragraph:
Starch is an energy storage molecule in plants, and it makes up a large part of the food of many organisms. Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules. Animals that eat plants can use starch in the same way. Starch is too large to be absorbed into the blood stream directly from the intestine, but many animals have enzymes that break down starch to small sugars. In humans the enzyme amylase, which is present in saliva, accomplishes the breakdown of starch.
p. 151s
Students are then asked to design and carry out an experiment to demonstrate that amylase breaks down starch to sugar (p. 151s). Students are asked to read the essay What Happens to the Food You Eat? to help them design the experiment. Here they read once again how foods need to be broken down if they are to be used by the body:
If your body is to use the proteins, it must break them down all the way to amino acids....If your body is to use such carbohydrates, your body must break them down to sugars. Starch is a molecule manufactured in plants that is made up of large numbers of sugars bonded together in a large branching molecule....
p. E97s
In the next section in chapter 7, students read about how the foods that have been broken down are reassembled into body structures:
Recall from the previous activity...that the food you eat is broken down by the digestive system. The raw materials that result from digestion, materials such as amino acids, sugars, and fatty acids, may serve as building blocks in the synthesis of various body structures. Muscle tissue is a good example. For instance, amino acids are the building blocks your body requires for the repair and growth of muscle tissue. Once these building blocks are synthesized into muscle protein, they become part of a larger structure, a muscle.
p. 153s
Idea c1 is presented again in chapter 8 in the context of a discussion of how living systems are built:
Food molecules can come from a variety of sources: plants, animals, or fungi. Not surprisingly, the molecules that make up these other organisms are not always the same molecules needed by your body. In this activity you will see how your body is capable of taking matter from an outside source, converting it into usable energy and matter, and rearranging the molecular structure of that matter to provide building materials for new molecules, cells, and tissues.
p. 180s
Students are then asked to consider how materials from a cow (a burger) can become part of their own bodies. Students are asked to read an essay, Metabolism Includes Synthesis and Breakdown, where text says:
For example, when you eat potatoes, your body breaks down the potato starch to the small glucose molecules of which it is made. The glucose then can be broken down further during cellular respiration to provide immediate energy in the form of ATP, or it can be transported to your liver or muscles and combined with other glucose molecules to form glycogen, which is a large, energy-storage molecule. Your body uses some of the energy that is released during cellular respiration to build, or synthesize, the glycogen.
p. E127s
The same essay further states:
That is why the protein that you consume in your diet, which has been made by a plant or animal of a different species, cannot be used directly as a prefabricated protein in your body. Instead, the dietary protein is broken down to its component amino acids, and your cells assemble the amino acids into the specific protein patterns that your body requires.
p. E128s
Idea d1: The chemical elements that make up the molecules of living things pass repeatedly through food webs and the environment, and are combined and recombined in different ways.
There is an incomplete content match to this idea. The following presentation of Idea d1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in BSCS Biology: A Human Approach: The chemical elements that make up the [Carbon] molecules of living things pass[es] repeatedly through food webs and the environment, and are [is] combined and recombined in different ways.
The idea that carbon atoms pass through food webs and the environment in different molecules is mentioned both in text and in student activities. After students have considered how materials from a cow can become part of their own bodies by being broken down and reassembled into new materials (pp. 180–181s), students are engaged in an activity that requires them to trace the path of a carbon atom from one organism to another:
The atom begins its journey as part of a carbon dioxide molecule and ends up as part of a muscle protein in a human arm. Your task is to use the knowledge that you have gained in this chapter to draw a diagram of what happens to the atom during its journey....
Construct a diagram or other visual aid to show a plausible set of events that could explain how a labeled carbon atom in a molecule of atmospheric carbon dioxide ends up in a human muscle protein.
p. 182s
The student text points out that there is more than one possible scenario. The Teacher’s Guide also points this out to the teacher and notes key points that the students should include:
- the trapping of energy and matter through the reactions of photosynthesis and carbon fixation and
- the transfer of matter and energy from one organism to another.
p. 281t
The Teacher’s Guide also gives a sample student response that presents eleven steps in the carbon atom’s possible path in considerable detail (pp. 281–282t) and notes that while student responses can be less complete, students should “understand that the muscle protein of humans is not deposited intact from the muscle protein of the cow” (p. 282t).
After constructing a diagram, students are asked to write an explanation of the sequence of events and then to discuss questions including the following:
Question: How will biosynthesis play a role in the fate of the carbon atom?
Suggested Response: Biosynthetic reactions are closely linked to photosynthesis because carbon becomes fixed into sugars and starch in plants. Biosynthetic reactions are necessary to convert simpler, intermediate compounds into amino acids and finally into a chain of amino acids—a protein.
p. 282t, question d
Question: Suggest a way in which the labeled carbon in the last step of your sequence could complete the cycle and find its way back into a labeled carbon dioxide molecule in the air.
Suggested Response: If the labeled protein in the human muscle is broken down to its component amino acids, then the amino acids could be metabolized into a carbon skeleton that can enter glycolysis and aerobic respiration....The labeled carbon could be part of the carbon dioxide given off as metabolic waste. The circulatory system would pick it up and carry it to the lungs, where it could be expelled from the body during exhalation.
pp. 282–283t, question e
The final step in this activity requires students, after participating in the discussion, to make appropriate changes in the sequences they devised.
Another activity requires students to reflect on earthworm habitats they set up several weeks previously (p. 188s). In connection with this activity, students are to read the essay Matter in Nature Is Going Around in Cycles...What Next? (p. E132s), which presents another example of how carbon can be part of many different molecules in food webs and the environment:
Consider, for example, a single atom of carbon. If you could follow a single atom of carbon in the riverbed community through time, you would see it cycle through many different molecules. At one point it may form part of a protein molecule in a floating leaf of duckweed. At another time the same carbon atom may become one of the atoms within a DNA molecule in the genetic material of a fish or a frog that ate the duckweed. At still another point it may remain for a long period within dead plant or animal material in the mud of the river until it is finally used by bacteria or fungi and rejoins the biotic community. Figure E9.7 illustrates some of these interactions and relationships in the carbon cycle.
p. E134s
The next activity engages students in devising “an experiment to provide evidence of the cyclical movements of matter in a community” (p. 189s) using snails and Anacharis. Afterwards, students create a diagram or concept map to represent their understanding of the cycling of matter through a community (p. 190s, number 3).
However, no other elements (besides carbon) are shown to cycle and the text does not generalize the idea of recycling or of combination and recombination to other elements. Furthermore, both instances of carbon cycling involve a single cycle rather than repeated cycling.
The cycling of water through food webs and the environment is presented in Figure E9.6 The water cycle (p. E133s), but it is not used to illustrate the combination and recombination of atoms. Rather, the diagram and accompanying text emphasize the recycling of water as a substance. The only indication that the water may change forms is in two arrows labeled “respiration”—one that goes from the bear toward the sky and another that goes from trees to the sky—but this is only implicit.
Energy is transformed in living systems.
Idea a2: Plants transfer the energy from light into “energy-rich” sugar molecules.
There is a content match to this idea, which is treated in text and a diagram. The essay Getting Energy and Matter into Biological Systems, while discussing how food supplies energy, says:
The main way is through photosynthesis, the series of reactions by which plants, algae, and some bacteria use the sun’s energy, in the form of light, to synthesize macromolecules from smaller, simpler molecules.
You might think of a plant as a solar-powered factory that converts the radiant energy of sunlight (solar energy) into potential energy stored in chemical form.
p. E123s
The caption for Figure E8.20 also addresses Idea a2:
Figure E8.20 Summary of the reactions of photosynthesis During photosynthesis light energy is absorbed and converted into chemical energy (ATP and hydrogen carriers). This step traps solar energy in the structure of matter. The chemical energy in these short-term storage molecules then powers the incorporation of carbon from carbon dioxide into carbohydrates, which are long-term energy storage molecules....
p. E124s
However, the essay accompanying this figure presents biochemical details that go well beyond the key idea.
Idea b2: Plants get energy to grow and function by oxidizing the sugar molecules. Some of the energy is released as heat.
There is an incomplete content match to this idea, which is treated briefly once in text and once in the answer to an analysis question. The following presentation of Idea b2 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in BSCS Biology: A Human Approach: Plants get energy to grow and function by oxidizing [breaking down] the sugar [starch] molecules. Some of the energy is released as heat.
The breakdown of sugar molecules in plants is not specifically mentioned. Before students explore digestion, they read:
Starch is an energy storage molecule in plants, and it makes up a large part of the food of many organisms. Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules.
p. 151s
In an activity to study factors that affect the rate of photosynthesis, students are asked, “Do plants carry out cellular respiration? Explain your response” (pp. 180s and 276t, question 3). The answer given in the Teacher’s Guide is, “Plants, like other organisms, must have a way to release and use the energy stored in macromolecules such as carbohydrates. Thus they do carry out cellular respiration...” (p. 276t).
Idea c2: Other organisms break down the consumed body structures to sugars and get energy to grow and function by oxidizing their food, releasing some of the energy as heat.
There is an incomplete content match to this idea. The following presentation of Idea c2 shows which parts of the idea are treated (in bold) in BSCS Biology: A Human Approach: Other organisms break down the consumed body structures to sugars and get energy to grow and function by oxidizing their food, releasing some of the energy as heat. Furthermore, the parts treated are presented in different parts of the textbook.
In an investigation of how food becomes useful in the human body, students read:
Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules. Animals that eat plants can use starch in the same way. Starch is too large to be absorbed into the blood stream directly from the intestine, but many animals have enzymes that break down starch to small sugars.
p. 151s
In the context of an exploration of energy in reactions, students read, “The essay Matter and Energy Are Related (page E108) contains information that you will find useful” (p. 169s). In this essay, students read:
Energy transfer also takes place in your body, where food is supplied to the digestive system, nutrients and energy are removed and supplied to muscles and other tissues, and heat is produced.
p. E112s
The essay, however, goes on to give details about how energy properties of molecules are determined by chemical bonds (p. E113s), information that goes beyond the key idea.
During experimentation to determine the calories in selected food samples, students are referred (p. 174s) to two essays, which address parts of the key idea:
When you eat flour made from grain, your body’s cells release the energy stored in this form of matter, but it takes place one small step at a time....The process by which enzymes convert the energy stored in macromolecules (such as starch and glycogen) or in the smaller molecules (such as glucose) that make up these macromolecules into readily available energy in the form of ATP is called cellular respiration.
p. E116s
The specific energy needs of organisms include mechanical work, such as the contraction of muscles; active transport; and the building of new molecules, cells, and higher structures, all of which are necessary for tissue repair and growth. Indirectly, the potential energy in molecules of food satisfies the energy needs of organisms, but the structure of these molecules does not store energy in a form that can be released and used directly for cellular work. Thus, some method of converting the energy of food into more usable energy seems essential.
p. E117s
However, most of the essays are devoted to biochemical details of cellular respiration that go well beyond the key idea (pp. E116–E120s).
Later, in the context of understanding how “energy that is stored in matter flows through a community and fuels the activities of its organisms” (p. 191s), students read:
When you eat various forms of matter, some of that energy is transformed and is available to you so that you can carry out the daily activities of life and the distinctive activities that make you who you are.
p. 191s
Idea d2: At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.
There is an almost complete content match to this idea, which is treated in student activities and text. The following presentation of Idea d2 shows which parts of the idea are treated (in bold) in BSCS Biology: A Human Approach: At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.
The text asks students to construct a food web in order to “develop a greater understanding of how the energy that is stored in matter flows through a community and fuels the activities of its organisms” (p. 191s). To help them in a discussion of their food webs, they are referred to the essays Let’s Ask Drs. Ricardo and Rita (p. E136s) and Losing Heat (p. E141s). Text in the first essay characterizes the sun as the ultimate source of energy but does not mention that the sun’s input of energy must be continual: “A food web helps us understand the flow of energy through a community. Ultimately the sun is the source of energy for nearly all earth communities” (p. E140s).
Text in the second essay presents the idea that, at each link in a food web, only some energy is stored in newly made structures, while some is released as heat:
Each time that an organism uses energy, it loses part of the energy in the form of released heat. This means that only a portion of the solar energy that producers take up is stored in biomass that herbivores can eat. In turn only a portion of the plant material that herbivores eat is converted into body parts that could become food for predators. Each transfer of energy from organisms at one trophic level to organisms at the next trophic level results in a decrease in the amount of energy that is available.
p. E141s
Figure E9.14 supports this idea. The caption reads, “Figure E9.14 Energy pyramid This idealized energy pyramid illustrates that only a portion of the energy available at one trophic level is available at the next higher trophic level” (p. E141s). The sun is shown outside the pyramid, delivering 1,000,000 kcal of solar energy. Grasses at the bottom of the pyramid are labeled 8000 kcals; the next higher level shows a grasshopper, 800 kcals. Above that is a mouse, 80 kcals, and at the top is an eagle, 8 kcal. The text elaborates on the examples in the figure:
If we begin with 1 million kcals of solar energy entering the ecosystem, producers convert only a small fraction (0.8 percent) of this solar energy into plant biomass (see Figure E9.13). This biomass represents 8000 kcals of stored chemical energy. The herbivores, such as the grasshoppers that feed on these plants, incorporate only 800 kcals into their biomass, which is only 10 percent of the 8000 kcals of plant energy available to them. Similarly, the predators, such as the mice that feed on the herbivores, incorporate only 80 kcals into their biomass, which is 10 percent of the 800 kcals available to them. Finally, the secondary predators, such as the hawk, that feed on the first level of predators, incorporate only 8 kcals into their biomass. Again, this is 10 percent of the 80 kcals available to them. This pattern of reduction in the amount of energy at successive trophic levels means that the secondary predators acquire only 8 kcals of the 8000 kcals of energy that became part of the food web at the producer level.
p. E141s
In the context of creating compost systems and looking particularly at the role of decomposers, students again encounter the dissipation of energy into the environment as heat as energy flows through links in a food web. Two analysis questions, particularly, focus on this idea:
Question: The heat that you noticed [from the compost systems] is a form of energy. In what form was this energy before it was released as heat? What happens to this energy after it is released as heat?
Suggested Response: Before the energy was released as heat, it was present in the molecular structures of the matter that the decomposers used as food. Heat energy that is generated by the decomposers goes into the environment and is no longer usable for energy in biological systems.
pp. 196s and 307t, question 3
Question: What does your answer to Question 3 reveal about the flow of energy in a community?
Suggested Response: This is the end of energy flow in the biological systems. Organisms can no longer capture the heat and use it in a way that provides energy to them. This is a graphic illustration of the end point in the flow of energy. It is not recycled. Solar energy enters the biosphere through photosynthesis, flows through the various trophic levels, energizing organisms at each level, flows through decomposers, and ends up as heat, which is no longer usable by biological systems.
pp. 196s and 307t, question 4
The textbook returns to the importance of the input of energy from the sun in the evaluation activity at the end of chapter 9, What Have I Learned about Energy and Matter in Communities? Among the questions asked are:
Question: What might be the effect if only 80–85 percent of the sunlight were blocked from the earth? What might be the effect on the following organisms: an earthworm, a shark, a maple tree, a saguaro cactus, and a teenager?
pp. 197s and 308t, question 2a
Question: Imagine that the trend described in the scenario continues and eventually all sunlight is blocked from reaching the earth’s surface.
- What might be the effect on the following organisms: the producers, the consumers, and the decomposers?
- Describe how the cycling of matter through a community would be affected.
pp. 197s and 309t, question 2b
The Teacher’s Guide offers detailed possible answers to these questions, concluding:
The students should realize that the cycling of matter will continue for a brief time until all the producers and ultimately the consumers die. At this point, the decomposers will continue to break down the remains of the producers and the consumers until all decomposition has occurred. The decomposers will then die and life on earth would almost cease to exist.
p. 309t
Again, the need for continual input of energy from the sun is not explicitly stated.
The total amount of matter and energy stays the same.
Idea e: However complex the workings of living organisms, they share with all other natural systems the same physical principles of the conservation and transformation of matter and energy. Over long spans of time, matter and energy are transformed among living things, and between them and the physical environment. In these grand-scale cycles, the total amount of matter and energy remains constant, even though their form and location undergo continual change.
There is not a content match to this idea. While the material implies one part of the idea and explicitly states another part of the idea, the complete idea (which is its essence) is never presented. A sentence in the introduction to chapter 8 relates matter and energy but does not make clear that “...living organisms...share with all other natural systems the same physical principles of the conservation and transformation of matter and energy” (first part of Idea e):
Gasoline, nuclear power, and electricity all are obvious forms of energy, but do you also think of energy when you see sunlight or green plants? In fact, energy is found wherever matter is organized, from the molecules of rocks to cells to entire living organisms.
p. 165s
In chapter 8 students encounter examples of living systems and non-living systems that transform or conserve energy but the text does not state the generalization that these systems share the same principles of conservation and transformation of matter and energy. For example, the essay Energy Is Converted and Conserved gives examples of how energy can be transformed from one form to another, including when gasoline powers machinery (chemical to mechanical energy), when grain dust explodes (energy stored in food molecules to heat), and when a boulder rolls downhill (potential to kinetic energy) (p. E111s). Subsequent text provides an example of the transfer and conservation of energy in the human body:
Energy transfer also takes place in your body, where food is supplied to the digestive system, nutrients and energy are removed and supplied to muscles and other tissues, and heat is produced. Even through all of the intermediate steps necessary for this transfer, no energy is lost or created. This phenomenon, called the conservation of energy, means that even though the amount of energy at one location can change, the total amount of energy in the universe remains the same.
In living organisms this phenomenon is important because energy is conserved at the level of molecules. For instance, if one large storage molecule contains eight units of energy and it is broken down into two smaller molecules, then the two smaller molecules together (plus any small amount of heat or side reactions) will contain eight units of energy as well.
p. E112s
In the final activity of chapter 8, Tracing Matter and Energy, students trace the path of a carbon atom from its position in a molecule of atmospheric carbon dioxide to a molecule in a human muscle protein. In discussion after the activity, students describe the conversions of energy during this passage. The expected answer, according to the Teacher’s Guide, is:
Energy is converted from solar into chemical energy. Energy stored in some molecules, such as sugars, starch, or proteins, later will be released, and some newly available energy, such as that stored in ATP, can be used to power other reactions. Some energy is converted into heat.
p. 282t
However, although examples of energy conservation and transformation in both living and non-living systems are given, the idea is never presented in its general form.
Several examples are given of how matter is changed (transformed) as atoms and molecules move from one substance to another in living systems. In the final activity of chapter 8, Tracing Matter and Energy, students trace the path of a carbon atom from its position in a molecule of atmospheric carbon dioxide to a molecule in a human muscle protein (pp. 182–183s). Also, the movement of carbon from carbon dioxide to glucose in plants is shown in an illustration (p. E124, Figure E8.20). A general statement is also made about transformation of matter in the human body:
[Y]our body is capable of taking matter from an outside source...and rearranging the molecular structure of that matter to provide building materials for new molecules, cells, and tissues.
p. 180s
However, the idea that transformation of matter occurs in both living and non-living systems is not presented.
Notably omitted is any discussion of the conservation of matter. At several points in unit three, the textbook could have presented the idea that atoms are conserved in chemical reactions. This idea could logically have been presented immediately before or after the essay on conservation of energy (pp. E110–E114s). Or it could have been presented in connection with chemical reactions such as photosynthesis (pp. E123–E127s) or respiration (pp. E117–E120s), although a clear and simple presentation of this central idea might necessitate omission of many of the biochemical details that are provided in these essays (but which are not essential for understanding the idea that matter is conserved). Another logical place to introduce the conservation of matter would be when the textbook points out, in the context of a discussion of how living systems are built, first why matter and energy are needed by the human body:
The cells of your body must receive a constant supply of usable energy and matter if you are to grow into an adult. Even after growth has stopped, your body must be able to make new cells to replace damaged or infected ones, a process that occurs whenever healing is necessary, such as at the site of a skin cut. Cells also must build small simple molecules, such as amino acids and simple sugars, into the more complex biological molecules, such as proteins and glycogen, that are important for your daily activities.
p. 180s
And then how this can happen:
Food molecules can come from a variety of sources: plants, animals, or fungi. Not surprisingly, the molecules that make up these other organisms are not always the same molecules needed by your body. In this activity you will see how your body is capable of taking matter from an outside source, converting it into usable energy and matter, and rearranging the molecular structure of that matter to provide building materials for new molecules, cells, and tissues.
p. 180s
It could be pointed out, in connection with the rearrangement of the molecular structure of matter, that matter is conserved.
Building a Case
BSCS Biology: A Human Approach does not build a case for any of the key ideas. Rather, the essays assert the key ideas but provide no evidence for their plausibility and no argument for why they are believable or why scientists have confidence in them.Connections
The set of key ideas on matter and energy transformations is highly complex, spanning four levels of biological organization (molecular, cellular, organism, ecosystems) and depending heavily on knowledge in physical science (e.g., energy forms and transformations among them, and recombination of atoms in chemical reactions).
BSCS Biology: A Human Approach presents ideas related to the transformation of matter and energy in a single unit: Unit Three: Energy, Matter, and Organization: Relationships in Living Systems. The key ideas appear first at the human organism level (chapter 7), then at the molecular and cellular level (chapter 8), and finally at the ecosystem level (chapter 9). As its title suggests, BSCS Biology: A Human Approach focuses its efforts on the biology of the human organism. With respect to the key ideas on matter and energy transformation, the material emphasizes transformations of matter and energy that occur in the human body and the cellular transformations needed to understand them. As is evident in the map showing what the reviewers found in this material for the matter and energy transformations topic, plants are given short shrift. While the material treats matter and energy transformation at the ecosystem level, it only briefly relates these transformations to those that occur at other levels of biological organization. Furthermore, the material does not present the transformations of matter and energy in humans as illustrating more general principles of transformation and conservation of matter and energy in living and physical systems.
In general, key ideas about energy transformations are given more treatment and connected more extensively to one another and to prerequisite ideas than are key ideas about matter transformations.
Energy. Connections among key ideas. The text makes some connections between key energy ideas. For example, Idea c2, “Other organisms break down the consumed body structures to sugars and get energy to grow and function...releasing some of the energy as heat,” is connected to the idea that plants make “energy-rich” sugar molecules, part of Idea a2. (In this text Idea c2 is, quite legitimately, introduced before Idea a2.) The connection is made in text introducing a student activity, Using Light Energy to Build Matter:
In the last activity you studied cellular respiration, a method for obtaining energy from matter in a form that is useful for cell activity....Humans, and all organisms that depend on previously assembled molecules for their carbon and energy, are called heterotrophs....This dependence on other sources raises some interesting questions about the original source of energy and matter. For instance, how did energy first come to be stored in these molecules on which we depend, and what is the original source of the energy contained in their structures?
The answer is green plants, which are quite different from heterotrophs. They are called autotrophs....plants are able to make their own food—the carbon-containing molecules such as simple sugars and starch that are used to support their cellular activities.
p. 176s
The connection between the energy transformations in Ideas a2 and c2 is made explicitly when text in the essay referenced for the activity Using Light Energy to Build Matter says:
[C]ellular respiration releases usable energy from storage molecules, but a certain amount of energy is needed to start this process. Likewise, food supplies the energy and matter requirements of many organisms, but the food itself usually is derived from other living systems. How, then, do energy and matter get into living systems in the first place? The main way is through photosynthesis, the series of reactions by which plants, algae, and some bacteria use the sun’s energy, in the form of light, to synthesize macromolecules from smaller, simpler molecules.
p. E123s
A connection is implied between Idea a2 and the idea that plants get energy by breaking down starch molecules (part of Idea b2) at the beginning of the activity You Are What You Eat. Students read a paragraph with the information, “Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules” (p. 151s). However, the text does not make clear that it is some of the energy from the sun that is stored in the starch molecules.
A connection is made between the idea that “Other organisms break down the consumed body structures to sugars and get energy to grow and function...releasing some of the energy as heat” (Idea c2), and the idea that “At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat....input of energy from sunlight keeps the process going” (Idea d2) in the essay Losing Heat:
Each time that an organism uses energy, it loses part of the energy in the form of released heat. This means that only a portion of the solar energy that producers take up is stored in biomass that herbivores can eat. In turn only a portion of the plant material that herbivores eat is converted into body parts that could become food for predators. Each transfer of energy from organisms at one trophic level to organisms at the next trophic level results in a decrease in the amount of energy that is available.
p. E141
Following this passage, detailed examples in text and a diagram of an energy pyramid showing particular organisms help to make it clear that the energy loss that occurs as energy flows through an ecosystem is the result of heat loss occurring within individual organisms.
Connections between key ideas and their prerequisites. The material presents three prerequisite ideas related to energy and connects them to key ideas about energy transformation. The text links the prerequisite idea that “Food provides the molecules that serve as fuel and building material for all organisms” to the idea that “Other organisms break down the consumed body structures to sugars and get energy to grow and function...[from] their food....” (Idea c2) in the introduction to the activity You Are What You Eat:
Now you know what is in the food you eat, but once this food is inside you, how does it become useful to your body? What does your body do to this matter so that you can use the energy it contains for performance? How does your body prepare this matter so that you will have the building blocks necessary for growth and repair? In this activity you will look at digestion to understand the role it plays in preparing to release the energy stored in the molecules of food and in providing a source of building blocks for biosynthesis.
p. 151s
The prerequisite idea that “Arrangements of atoms have chemical energy” is presented and connected to both the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2) and the idea that “...[Humans] get energy to grow and function...[from] their food....” (part of Idea c2) in the explanation of why food is a source of potential energy:
Stronger bonds result when the atoms that make up a molecule share their electrons. These bonds are called covalent bonds....The carbohydrate molecules glycogen (in muscles and liver) and starch (in plants) are complex molecules and rich sources of potential energy; each is a macromolecule with large numbers of covalent bonds....
Energy for cellular activity....The source of this energy is long-term storage molecules such as glycogen. These molecules are so large and inaccessible, however, that a cell cannot use the energy in storage molecules directly....cellular reactions convert some of the energy in large molecules into another form of chemical energy that can be used directly by cells....In these reactions the energy is used to help perform cellular work; the energy is not all wasted as heat.
pp. E113–E114s
The prerequisite idea that “...Energy can only change from one form into another” is presented in the essay Energy Is Converted and Conserved and implicitly linked to the idea that “Food provides the molecules that serve as fuel....” (another prerequisite) by illustrating that food contains potential energy:
When electricity flows through the metal coils on a stove burner, making the coils red hot, it does more than ready the teapot for tea. It illustrates an essential property of energy: energy can be converted from one form into another. In this case electrical energy is converted into heat energy....power-generating dams harness the mechanical energy of water by passing the water over turbines, which rotate and convert the movement of the water into electrical energy.
p. E110s
Exploding grain elevators are another example of the conversion of energy from a stored form (the molecules of grain dust) to heat (the energy of motion)....Grain dust contains a great deal of potential energy, but when this energy is released, it becomes active. Active energy is called kinetic energy.
p. E111s
However, the text does not make clear that grain dust is food. Unless students appreciate that grain elevators store food from the harvest to feed animals over the winter, the connection between food and energy transformation will not be made.
Finally, the essay makes the point that energy can only change from one form into another and relates it to the idea that “...[Humans] get energy to grow and function...[from] their food, releasing some of the energy as heat” (Idea c2):
Energy transfer also takes place in your body, where food is supplied to the digestive system, nutrients and energy are removed and supplied to muscles and other tissues, and heat is produced. Even through all of the intermediate steps necessary for this transfer, no energy is lost or created. This phenomenon, called the conservation of energy, means that even though the amount of energy at one location can change, the total amount of energy in the universe remains the same.
p. E112s
The connection is reinforced in the following question and suggested response:
Question: Explain how energy can be stored in a molecule yet not be destroyed when that molecule is broken down into smaller molecules.
Suggested Response: Energy is stored in the structure of bonds and atoms that make up all molecules, and any differences in energy are due to transfers with the surroundings. Energy is conserved; it is never destroyed. When one molecule (the reactant) is split into two (the products), the product molecules will contain a certain amount of energy. If they contain more energy than the starting molecule, the excess will have to come from other molecules involved in the reaction, such as ATP, or from surrounding heat. If the product molecules contain less energy than the starting molecule, the difference will have been lost as heat or transferred to other molecules.
pp. 170s and 262t, question 3
The prerequisite ideas relating chemical energy to the arrangement of atoms and different amounts of energy to different configurations of atoms are not explicitly presented, even though students observe endothermic and exothermic reactions (pp. 166–169s), make molecular models to represent the organization of matter (pp. 169–170s), and respond to questions that expect them to relate energy transfer to energy conservation:
Question: For the endothermic reaction, describe where the energy needed for the reaction came from. For the exothermic reaction, describe where the energy produced by the reaction went.
Suggested Response: The energy needed for the endothermic reaction came from the heat present in the water and flask before the ammonium nitrate was added. In other words, the small amount of room temperature heat energy present initially was transferred to the reaction that dissolved the solid, hence the water and flask became colder. The energy produced by the exothermic reaction was transferred to the surrounding water and glass, which caused the test tube to become warmer.
pp. 169s and 260t, question 6b
Furthermore, even the ideas about exothermic and endothermic reactions are not connected to ideas about energy transformation in organisms (Ideas a2, b2, and c2) or ecosystems (Idea d2).
The essay Energy is Converted and Conserved (pp. E110–E114s) describes the role of ATP in transferring energy but does not relate its ability to serve as an energy carrier to the arrangement of atoms or to changes in configurations of atoms:
[N]early all biological reactions require the input of some energy before they can proceed. The source of this energy is long-term storage molecules such as glycogen. These molecules are so large and inaccessible, however, that a cell cannot use the energy in storage molecules directly. To make this energy useful, cellular reactions convert some of the energy in large molecules into another form of chemical energy that can be used directly by cells. A special type of molecule called adenosine triphosphate, or ATP (see Figure E8.9), accomplishes this by carrying energy (in its molecular structure) between reactions within a cell. ATP is a carrier—a molecule that carries or transfers something (the way a mail carrier carries the mail). In fact, ATP also is an energy storage molecule, but it is a short-term storage molecule; it carries energy to places in the cell where the energy is used directly to fuel chemical reactions. In these reactions the energy is used to help perform cellular work; the energy is not all wasted as heat.
pp. E113–E114s
Two prerequisite ideas related to energy are not presented in this material. The first is the idea that “Most of what goes on in the universe...involves some form of energy being transformed into another. Energy in the form of heat is almost always one of the products of an energy transformation.” The student text provides examples in the essay Energy is Converted and Conserved (pp. E110–E114s), but the generalization is not made. While the examples may be adequate to build ideas about energy transformation in individual organisms, such as the key idea that “...[Humans] get energy to grow and function...[from] their food, releasing some of the energy as heat” (Idea c2), the generalization is needed for the idea that “At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going” (Idea d2) and for students to appreciate that this need for continual input of energy is a property of systems in general.
The other prerequisite idea not treated is that “An especially important kind of reaction between substances involves combination of oxygen with something else—as in burning or rusting.” However, since the material does not attempt to relate breakdown and energy release from glucose to its oxidation, this prerequisite is probably not needed.
Connections between key ideas and related ideas. BSCS Biology: A Human Approach presents the related idea that “Within cells are specialized parts for the capture and release of energy” in the essay Getting Energy and Matter into Biological Systems, when the text notes the existence of chloroplasts and their role in energy transformation:
The reactions of photosynthesis take place in chloroplasts, small compartments inside certain plant cells....The internal structure of the chloroplast is very important in the process of converting light into chemical energy.
p. E124s
However, it fails to bring home the connection between chloroplasts and energy transformation by not noting, for example, that more chloroplasts are found in the upper parts of leaves, which get more light than lower parts.
Similarly, the text notes the role of mitochondria in releasing energy in muscle fibers but fails to bring home the connection between mitochondria and energy release because it doesn’t note that muscle cells and others with high energy needs have more mitochondria than other cells:
Scattered among muscle fibers are many cylindrical mitochondria, subcellular compartments in which oxygen is used to release energy.
p. E104s
The reactions of aerobic respiration take place in this cellular organelle.
p. E118s
Matter. Connections among key ideas. Although ideas about matter are mentioned in this material, they are considerably less prominent than ideas related to energy. The idea that “Plants break down the sugar molecules that they have synthesized into carbon dioxide and water....” (Idea b1) is not treated at all. Some connections are made among the ideas about matter. For example, the text partially connects the idea that “...[Humans] break down the stored sugars...into simpler substances....” (part of Idea c1) to the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1) by explaining where the sugars humans need for respiration come from:
[C]ellular respiration....is dependent on glucose molecules, which can be derived from glycogen, starch, fats, and other macromolecules. In humans this glucose, and indeed all of the carbon in human macromolecules, originally came from molecules produced outside our bodies. Many of these molecules come from the plants we eat; the rest come from animals or other organisms that are dependent on plants....Autotrophs [plants] are able to make all of their own macromolecules. Plants need only light, water, air, and a few essential elements that are available from the soil to grow. In other words, plants are able to make their own food—the carbon-containing molecules such as simple sugars and starch that are used to support their cellular activities. The process of making these carbon-containing molecules is called photosynthesis....
p. 176s
However, the connection deals only with the output of one process being the input to another process and thus does not make explicit that the same atoms are simply rearranged. Similarly, the concept of rearrangement is not explicit in a passage in the essay What Happens to the Food You Eat?:
[B]read, like the finely powdered flour from which it is made, still has its carbohydrates intact, mainly in the form of long storage molecules known as starch. If your body is to use such carbohydrates, your body must break them down to sugars. Starch is a molecule manufactured in plants....
p. E97s
Students are expected to make a more thorough connection between the key ideas when they are asked to trace the path of a carbon atom from its place in a molecule of atmospheric carbon dioxide to its place in a muscle protein in a human arm (pp. 182–183s). However, while the suggested answer in the Teacher’s Guide (pp. 281–282t) clearly states the connection, it is questionable whether the information and support provided will enable students to come up with this response.
Connections between key ideas and their prerequisites. The text links the prerequisite idea that “Food provides the molecules that serve as fuel and building material for all organisms” to the idea that “Other organisms break down the stored sugars or the body structures of the plants they eat (or animals they eat) into simpler substances, reassemble them into their own body structures, including some energy stores” (Idea c1) in the introduction to the activity You Are What You Eat:
Now you know what is in the food you eat, but once this food is inside you, how does it become useful to your body? What does your body do to this matter so that you can use the energy it contains for performance? How does your body prepare this matter so that you will have the building blocks necessary for growth and repair? In this activity you will look at digestion to understand the role it plays in preparing to release the energy stored in the molecules of food and in providing a source of building blocks for biosynthesis.
p. 151s
The prerequisite idea that “Carbon and hydrogen are common elements of living matter” is mentioned in the Teacher’s Guide—“Emphasize carbon, oxygen, hydrogen, nitrogen, phosphorus, and sulfur as the principal building blocks of all organic matter” (p. 261t)—but it is not linked to key ideas about matter transformation in photosynthesis (Idea a1), respiration in plants and animals (Ideas b1 and c1) or about the cycling of elements in ecosystems (Idea d1). Notably absent is any treatment of the conservation of matter. The discussion in the essay Matter in Nature Is Going Around in Cycles...What Next? does not convey the important idea that the Earth consists of an essentially constant number of a few kinds of atoms that, like a kit of Legos or Tinkertoys, can combine and recombine (pp. E132–E135s).
Connections between key ideas and related ideas. The text presents the related idea “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus....” in a suggestion to the teacher (p. 261t) but does not relate it to the key idea “The chemical elements that make up the molecules of living things pass repeatedly through food webs and the environment, and are combined and recombined in different ways” (Idea d1). Moreover, the text does not present the related idea that “Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules.” The text shows one complex carbon molecule (p. E109s, Figure E8.2) but does not take the opportunity to make the point that this illustrates how carbon’s bonding capacity enables a variety of molecules to be made from it. And even though students build molecular models and observe a videodisc of molecular models (p. 170s and p. 261t), the emphasis is on common elements rather than on the ability of carbon to form large and complex molecules.
Matter and Energy. BSCS Biology: A Human Approach treats ideas about matter and energy together in the context of molecular interactions and in the context of the human organism. For example, ideas related to matter and energy are introduced together at the human organism level in the context of activities on fitness and the components of foods people eat (chapter 7, pp. 141–150s). Food is presented as the source of both matter and energy: “[T]he nutrients in food supply both the matter and the energy that your body requires for human performance” (p. 146s). An essay referenced in chapter 8 relates energy to the organization of matter and to the storage of energy in chemical bonds:
Because atoms are microscopic and cannot be observed directly through our senses, the importance of atomic interactions generally is not appreciated. As you will see, however, these interactions are critical to understanding the relationship between matter and energy.
Individual atoms may be hidden from our view because of their small size, but if many atoms are assembled together as an organized collection, they may form unique structures that are large enough to be clearly visible. It is in the organization [emphasis added] of many types of atoms that explains why skin is distinctly different from the gears of a watch. As Figure E8.2 shows, the source of this important atomic organization is chemical bonds. Chemical bonds hold atoms together in very predictable ways to form molecules; energy is stored within the structure of a molecule’s bonds and atoms.
p. E108s
Students are expected to deal with both matter and energy in responding to questions in the final activities of chapter 8. In the context of describing how matter from a cow can become matter in the human body, students are asked to list three biological processes involving biosynthesis and/or breakdown that are necessary for maintaining the human body and then choose one of these processes and answer questions about both matter and energy:
Question: What is a source of energy for this process? What is a source of matter for this process?
Suggestions to Teacher: Help them [students] think back to what they do know: that cells and tissues consist of macromolecules, that living systems require energy to organize matter, and so on. The essay Metabolism Includes Synthesis and Breakdown should help them with this step.
p. 181s, step 3; p. 278t, steps 2–3
The text next asks students how matter and energy are used to maintain the organization of an organism they have invented and notes:
You will know that you have addressed adequately the preceding question when your response
- indicates the organism’s source of energy and matter and how these are obtained from its surroundings,
- demonstrates how energy is stored and made available for its activities, and
- distinguishes the macromolecules that it is able to synthesize from the macromolecules that this organism must obtain from its external environment (through its diet or other means).
p. 181s
The scoring rubric provided in the Teacher’s Guide for this task says that an excellent response “Builds in connections between matter, energy, and organization,” and “Chooses a source of energy, identifies how it is stored and accessed by the organism, and provides several examples” (p. 279t).
Treating matter and energy together has the advantage that relationships between matter and energy can be presented, as in the previous examples (food is the source of both matter and energy [p. 146s] and “energy is stored within the structure of a molecule’s [matter’s] bonds and atoms” [p. E108]) and in the case of matter and energy both getting into living systems through photosynthesis (p. E123s). Furthermore, student understanding of these relationships can be checked by tasks such as the chapter 8 task on how matter from a cow can become matter in a human body, where questions about matter and energy can be asked together (pp. 180–181s).
However, treating matter and energy transformations together (rather than treating matter transformation first—in terms of the combination and recombination of atoms—and only then bringing in energy transformation—in terms of the changes in configuration of atoms) may lead to considerable student confusion. For example, the introduction to the activity Using Light Energy to Build Matter may lead students to conclude that matter and energy are interconvertible in biological systems:
In the last activity you studied cellular respiration, a method for obtaining energy from matter in a form that is useful for cell activity. This process is dependent upon glucose molecules, which can be derived from glycogen, starch, fats, and other macromolecules. In humans this glucose, and indeed all of the carbon in human macromolecules, originally came from molecules produced outside our bodies. Many of these molecules come from the plants we eat; the rest come from animals or other organisms that are dependent on plants. Humans, and all organisms that depend on previously assembled molecules for their carbon and energy, are called heterotrophs....This dependence on other sources raises some interesting questions about the original source of energy and matter. For instance, how did energy first come to be stored in these molecules on which we depend, and what is the original source of the energy contained in their structures?
The answer is green plants, which are quite different from heterotrophs. They are called autotrophs...which means that they do not have to rely on other organisms for the complex molecules necessary for life. Autotrophs are able to make all of their own macromolecules. Plants need only light, water, air, and a few essential elements that are available from the soil to grow. In other words, plants are able to make their own food—the carbon-containing molecules such as simple sugars and starch that are used to support their cellular activities. The process of making these carbon-containing molecules is called photosynthesis....
p. 176s
The text relates energy transformation in individual organisms to the flow of energy in ecosystems, but the link between matter and energy is vague and is not further clarified:
You already have explored how matter cycles through various communities, and you are aware that energy is stored in matter. When you eat various forms of matter, some of that energy is transformed and is available to you so that you can carry out the daily activities of life....Let’s examine the larger picture of matter and energy, of which you are a part. By relating the food that you eat for one day to the plants and animals from which it came, you can begin to develop a greater understanding of how the energy that is stored in matter flows through a community and fuels the activities of its organisms.
p. 191s
Beyond Literacy
The material attempts to restrict topics and terms to those needed for science literacy, as defined in Benchmarks for Science Literacy (AAAS, 1993) and the National Science Education Standards (NRC, 1996). Information on topics like exothermic and endothermic reactions and potential and kinetic energy is presented qualitatively and related to analogies (e.g., energy stored in molecular structures is likened to energy in stacked magnets [pp. E108–E109s]) or to real world examples (e.g., the explosive combustion of grain dust to illustrate an exothermic reaction [p. E109s] and the conversion of potential to kinetic energy [p. E111s]).
However, some essays include material that goes beyond that needed for science literacy and may even obscure the key ideas. For example, essays on cellular respiration refer to hydrogen carrier molecules (pp. E116–E117s) without attempting to explain what carrying hydrogen has to do with carrying energy. Similarly, it is not clear how diagrams of glycolysis, the Krebs cycle, and electron transport, which point out where NADH and ATP are produced from NAD+ and ADP (pp. E117–E119s), or an essay on photosynthesis, which presents details of ATP and NADPH production (pp. E125–E126s), contribute to a basic understanding of the matter and energy transformations in these processes. College curricula require courses in physics, general chemistry, and organic chemistry before students are expected to appreciate the logic of biochemical pathways. The information in these essays is inadequate to develop this appreciation and may even mislead students.
Accuracy
Some sightings were noted in which inaccurate or misleading statements were made. For example, in discussing the nature of food, the essay Food: Our Body’s Source of Energy and Structural Materials says:
In its most basic sense, food is any substance that your body can use as a raw material to sustain its growth, repair it, or provide energy to drive its vital processes....Water is an important nutrient that we often take for granted, but our bodies need enormous amounts of it in comparison to other nutrients.
p. E91s
This statement may reinforce the misconception that food is whatever nutrients organisms must take in if they are to grow and survive rather than those substances from which organisms derive the energy they need to grow and the material of which they are made.
In Chapter 8, the text asks, “How does the matter [emphasis added] in the food become usable energy [emphasis added] for the body? In particular, how does it help a marathon runner keep on running?” (p. 175s). Also, the Teacher’s Guide discusses how, in chapter 8, “[T]he learners develop a greater depth of understanding by examining how cellular processes convert energy into matter [emphasis added]....” (p. 205t). If students read the first example and if the teacher conveys the second idea to students, they might think that matter and energy are converted back and forth in everyday (non-nuclear) phenomena, even though this idea is stated correctly in the essay on photosynthesis:
...photosynthesis, the series of reactions by which plants, algae, and some bacteria use the sun’s energy, in the form of light, to synthesize macromolecules from smaller, simpler molecules [emphasis added].
p. E123s
A sentence in the essay Matter and Energy Are Related conveys the erroneous idea that atoms are microscopic in size: “Because atoms are microscopic and cannot be observed directly through our senses...” (p. E108s). Also misleading is the statement:
Starch is an energy storage molecule in plants, and it makes up a large part of the food of many organisms. Plants manufacture starch using energy from the sun and then break down the starch to its component sugars, releasing the energy that was stored in the starch molecules.
p. 151s
It is only when the sugar molecules are broken down that energy is released.
