Biology: A Community Context. South-Western Educational Publishing, 1998
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 topic of matter and energy transformations brings together a number of key ideas from both the biological and physical sciences. Biology: A Community Context treats most of these key ideas in Unit 1: Matter and Energy for Life, Unit 2: Ecosystems, and Unit 8: The Biosphere. However, the key ideas are treated mainly as fragments rather than as complete ideas. Furthermore, many of the key ideas are more explicitly treated in the Teacher’s Guide—as background information to student inquiries or as suggested responses to discussion or review questions—than in the student edition. This may unfairly hold students responsible for knowing information that they have not been presented with in the student text. Similarly, many of the connections made among key ideas appear only in the Teacher’s Guide, in suggested responses to questions. Also, this textbook attempts to embed its presentation of science ideas in the context of societal issues. As a result, many of the key science ideas remain in the background. 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 treated in text and activities. In the context of describing how living things obtain and use energy, students use gumdrops and toothpicks to model the process of photosynthesis (Guided Inquiry 1.5, p. 37s). They are asked where the atoms that are used to produce glucose molecules come from and are expected to respond with the idea (pp. 37s, 63t). The text presents the symbolic equation and translates it into words:
[S]ix molecules of water and six molecules of carbon dioxide are used to form a six-carbon sugar molecule (glucose) and six molecules of oxygen gas...energy stored as ATP, the hydrogen atoms from water, and carbon dioxide (CO2) from the air are used to make organic molecules...the simple sugar, glucose (C6H12O6), is one product of photosynthesis.
pp. 38–39s
Later, in the context of contrasting the sources of plant versus animal biomass, the text again states the idea: “Plants get most of their water from the soil....Carbon dioxide (CO2) from the atmosphere provides the carbon atoms that plants use to make sugars during photosynthesis” (p. 81s).
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 a nearly complete content match to this idea, which is treated mainly in text. The following presentation of Idea b1 shows which parts of the idea are treated (in bold) in Biology: A Community Context: 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.
In the context of describing the process of respiration, the text states that respiration is the primary energy-using process in all organisms and gives the symbolic equation for the breakdown of sugar (p. 39s). A diagram of the carbon cycle indicates that respiration is carried out by animals and plants (p. 40s). Later, in the context of describing the energy transformations in photosynthesis, the text states most of the rest of the idea (but does not indicate that the food plants store can be used later by the plants):
[P]lants convert light energy (sunlight) to chemical energy (sugars). Plants use these sugars for growth, the production of biomass, and metabolism. Plants store within their cells any sugars that they do not need for growth. Usually, these are stored in the form of starch.
p. 88s
The suggested response to the question “How does photosynthesis cause mass to increase in plants?” (p. 117s, question 6) indicates that students are expected to know the idea:
The mass of plants increases as a result of photosynthesis because only about 50 percent of the sugar (carbohydrates) made from photosynthesis is consumed as fuel....Some of the remaining sugars are linked together to make...cellulose. Cellulose is a major component of cell walls....The remaining sugars are made into starch, which can be stored more easily than can the sugars....Cellulose and stored starch make up a large portion of a plant’s mass.
p. 141t
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 an incomplete content match to this idea. The following presentation of Idea c1 shows which parts of the idea are treated (in bold) in Biology: A Community Context: 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.
The text describes sugar breakdown but not its use in making more complex molecules or body structures. In the context of cellular respiration, students use gumdrops and toothpicks to model the processes of aerobic and anaerobic respiration (p. 37s). The text lists energy, CO2, and H2O as outputs of aerobic respiration (p. 31s); and a diagram of the carbon cycle indicates that respiration by plants and animals converts C6H12O6 + O2 into CO2 + H2O (p. 40s). Similarly, the suggested answer to the question “Describe an example of the carbon cycle in your community” (p. 37s, Applications, question 1) indicates that students are expected to understand that humans break down sugar but not that it can be incorporated into their own body structures:
[G]lucose...may be stored in the plant’s fruit as glucose or starch. When we eat the fruits and vegetables of the garden, we start the decomposition process by breaking down the biomass into smaller molecules.
p. 64t
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 Biology: A Community Context: The chemical elements [Carbon and nitrogen] that make up the molecules of living things pass repeatedly through food webs and the environment, and are combined and recombined in different ways.
The text presents two examples of the idea that elements pass through food webs but never states the generalization. In the context of describing how plants get nitrogen to build proteins and chlorophyll, the text describes how nitrogen cycles through ecosystems:
Plants need nitrogen to produce essential molecules such as proteins and chlorophyll. But where do plants get their nitrogen? Air contains much more molecular nitrogen (N2) than any other gas. However, plant cells cannot use this form of nitrogen. If nitrogen is combined with oxygen in the form of nitrates (NO3) and nitrites (NO2), it can be used by plants. How, then, are these forms of nitrogen produced?
Plants depend on nitrogen-fixing organisms...to change nitrogen from gaseous form into nitrates and nitrites (Figure 2.16). These molecules are used by plants to produce biomass, which is then consumed by animals or broken down by decomposers. Another nitrogen-containing molecule, ammonia (NH3), is produced. Other bacteria in the soil convert ammonia to nitrites and nitrates. Still other bacteria break down these molecules to liberate nitrogen gas to the atmosphere.
pp. 92–93s
In the context of presenting photosynthesis and respiration, the text describes the carbon cycle and provides a diagram to represent it:
Together the processes of photosynthesis and respiration form the basis of the biological carbon cycle (see Figure 1.29 on page 40). Photosynthesis removes carbon dioxide from the atmosphere and makes organic compounds. Through respiration, these organic compounds are broken down, and carbon dioxide is expelled as a waste product.
p. 39s
The cycle is described in more detail in the suggested response to the question “Describe an example of the carbon cycle in your community” (p. 37s, Applications, question 1):
[P]lants...use photosynthesis to remove carbon from the air (as CO2) and use it to make glucose. This glucose may be used, via cellular respiration, as an energy source to help plants grow or may be stored....When we eat the fruits and vegetables of the garden, we start...breaking down the biomass into smaller molecules. The part of the plant that we do not eat may then be composted, allowing traditional decomposers to use it as a food source and return CO2 to the air as a waste product.
p. 64t
Diagrams of both the carbon cycle (p. 40s) and the nitrogen cycle (p. 92s) show molecular formulas of substances undergoing transformation, which helps to convey the idea that matter transformations occur at the molecular level. Text accompanying the nitrogen cycle diagram (pp. 92–93s) conveys the idea that nitrogen is combined and recombined in different ways in the nitrogen cycle. And a suggested response in the Teacher’s Guide to the question “Why is the carbon cycle in nature called a cycle?” (p. 37s, Interpretations, question 5) conveys the idea that carbon is combined and recombined in the carbon cycle:
The carbon cycle is called a cycle because we can follow the movement of molecules through a continuous path, which has no clear beginning or end. A carbon atom that starts as a part of a carbon dioxide molecule can go through photosynthesis to become part of a glucose molecule, which can then be broken down during respiration to form CO2 again.
p. 64t
However, this response does not make explicit the idea that this process repeats itself, and this part of the idea is not treated elsewhere in the material.
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 presented in text and in a question. The text first states the idea in the context of its presentation of matter and energy:
[T]hrough the process of photosynthesis, plants and some other organisms capture energy from sunlight and use it to make organic molecules....This is how plants get their energy....
The process of photosynthesis has two major stages....In Stage 1, the light reactions, light energy is converted to energy stored in chemical bonds. A specialized molecule, called ATP..., stores this energy....In Stage 2...energy stored as ATP, the hydrogen atoms from water, and carbon dioxide from the air are used to make organic molecules...the simple sugar, glucose (C6H12O6) is one product of photosynthesis.
pp. 38–39s
The text states the idea again in its treatment of ecosystems:
In the process of photosynthesis, plants convert light energy (sunlight) to chemical energy (sugars)...plants absorb light energy and convert it to stored sugars and energy storage molecules. The stored energy is then used to make carbohydrate (sugar) molecules from carbon dioxide.
p. 88s
An accompanying figure represents the transformation of energy from light to metabolic energy in plant cells.
The idea is assessed in the Self-Check questions “What is the relationship between light and chemical energy?” and “What happens to the energy that is transformed in photosynthesis?” (p. 117s, questions 3 and 4), and the suggested responses indicate that students are expected to know the idea:
Light...provides the initial energy that plants use to change carbon dioxide and water into sugars and complex carbohydrates....Light energy is transformed into chemical energy in the process of photosynthesis. The light energy that strikes the pigments in the chloroplasts is the same energy that ends up stored in high-energy chemical bonds of sugar products (carbohydrates) after photosynthesis....The energy that is transformed in photosynthesis is harnessed into molecules of carbohydrates; it becomes stored as chemical energy in the bonds of sugar molecules.
p. 141t
Idea b2: Plants get energy to grow and function by oxidizing the sugar molecules. Some of the energy is released as heat.
There is a content match to this idea. In the context of presenting photosynthesis and respiration, the text states the generalization that “Respiration is the primary energy-using process in all organisms” (p. 39s). The diagram of the carbon cycle on the next page shows heat energy released as a by-product of respiration by plants and animals (p. 40s).
In the context of its treatment of ecosystems, the Teacher Background Information presents the idea that plants get energy by breaking down sugar molecules:
All organisms function by using energy. Autotrophs can make their own energy-rich molecules, while heterotrophs must ingest such molecules from other environments. Both use cellular respiration to break down the molecules and release the energy they need for their activities.
p. 129t
However, there is no indication that this information will be presented to students.
Nonetheless, students are expected to know the complete idea, as indicated by the suggested response to the question “What happens to the energy that is transformed in photosynthesis?” (p. 117s, question 4):
The plant can burn the sugars during cellular respiration to release the energy when it is needed. The plant can use this energy to build other organic materials it needs....This energy transformation is not 100 percent efficient as much of the original energy is lost as heat.
p. 141t
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) and what alternative vocabulary is used (in brackets) in Biology: A Community Context: Other organisms break down the consumed body structures to sugars and get energy to grow and function by oxidizing their food [breaking down these sugars], releasing some of the energy as heat.
The content is presented mainly in text and suggested responses in the Teacher’s Guide to discussion or review questions. In the context of describing photosynthesis and respiration, the text presents the idea that organisms get energy to function (but not to grow) by breaking down sugars (but not body structures):
Other organisms, such as animals, consume glucose or other molecules manufactured by photosynthetic organisms to acquire their energy. The chemical energy stored in glucose is released to cells through the process of cellular respiration (Figure 1.28). This multistep process involves: first, breakdown of glucose molecules to smaller (3 carbon) molecules; second, production of energy transport molecules and CO2 in the Krebs cycle; and third, use of the energy transport molecules—in the electron transport system—to make ATP....This process takes place as organisms use sugars for energy during everyday activities. Respiration is the primary energy-using process in all organisms.
p. 39s
Although an answer to an Applications question states that “we eat the fruit and vegetables of the garden,” it does not make explicit that these are plant body structures:
Question: Describe an example of the carbon cycle in your community.
Suggested Response: Evidence of the carbon cycle can be found in many homes in any city. An outdoor garden has plants that use photosynthesis to remove carbon from the air (as CO2) and use it to make glucose. This glucose may be used, via cellular respiration, as an energy source to help plants grow or may be stored in the plant’s fruit as glucose or starch. When we eat the fruits and vegetables of the garden, we start the decomposition process by breaking down the biomass into smaller molecules. The part of the plant that we do not eat may then be composted, allowing traditional decomposers to use it as a food source and return CO2 to the air as a waste product.
pp. 37s and 64t, Applications, item 1
Students are expected to know that energy from respiration is also used for growth. In response to a question about why the mass of solid material entering a sewage disposal plant is greater than the mass flowing out of the plant (p. 42s, Applications, question 2), the Teacher’s Guide provides the following answer: “The decomposers...use the material and produce less in waste than they take in because some of what they eat is burned up as energy for their growth and movement” (p. 68t). However, this information is not presented in the student text or activities.
The release of energy as heat is shown in two diagrams in the student text—one on the carbon cycle (p. 40s) and another on energy flow in an ecosystem (p. 107s). However, neither diagram is accompanied by further explanation of the source of the heat. Yet students are expected to know this idea, as evidenced by suggested responses in the Teacher’s Guide to discussion and review questions. For example, in the suggested response to the question “What happens to the energy that is transformed in photosynthesis?” (p. 117s, question 4), the Teacher’s Guide presents the idea:
The plant can burn the sugars during cellular respiration to release the energy when it is needed. The plant can use this energy to build other organic materials it needs....Animals may eat plants and use the energy that is stored in plant sugars in a similar manner. This energy transformation is not 100 percent efficient as much of the original energy is lost as heat.
p. 141t
Two activities might have been used to illustrate heat production that accompanies the breakdown of sugar: an investigation of a decomposing compost pile (pp. 14–15s) and an investigation on the fermentation of sugar water by yeast (pp. 29–31s). However, both investigations focus on experimental design and matter transformation rather than heat production.
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 incomplete content match to this idea, which is presented more explicitly in the teacher’s edition than in the student book. The following presentation of Idea d2 shows which parts of the idea are treated (in bold) in Biology: A Community Context: At each link in a food web, some energy is stored in newly made structures but much [energy] is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.
In the context of introducing the transfer of energy within ecosystems, the student book includes two diagrams that show energy loss: an energy pyramid shows the decrease of energy at each trophic level (p. 103s) and an energy flow diagram shows heat energy given off by members of a food chain (p. 107s). However, the text offers no explanation for the loss. Explanations are found only in the Teacher’s Guide, in suggested responses to discussion and review questions. For example, the explanation of heat loss is found in the suggested response to a question asking students to predict (but not explain) the fractional decrease in the number of organisms from one trophic level to the next:
From one level of the food pyramid to the next, there is a loss of energy from the system. This loss, which averages about 90 percent, is due mostly to respiration. This means that there is only 10 percent of the energy available for the next higher trophic level....
p. 128t
Similarly, answers to Self-Check questions provide explanations not found in the student text:
Question: What happens to the energy that is transformed in photosynthesis?
Suggested Response: ....Animals may eat plants and use the energy that is stored in plant sugars....This energy transformation is not 100 percent efficient as much of the original energy is lost as heat.
pp. 117s and 141t, Self-Check 1, question 4
Question: State the first and second laws of thermodynamics, and describe an example of how they are applied to living systems.
Suggested Response: ...much of the original energy in the sunlight striking a plant is lost as heat rather than being stored as chemical energy, and much of the original energy in the foods organisms consume is lost as heat rather than being converted to ATP energy.
pp. 117s and 142t, Self-Check 1, question 7
Neither the student book nor the teacher’s edition explains that the energy not lost is stored in newly made structures. And neither mentions that because of the continual loss of heat, a continual input of energy is required (from the sun).
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. Unit 1 presents the idea that “Living things transform energy and matter to other forms” (p. 27s), and unit 2 elaborates on this idea by describing interactions among organisms in an ecosystem:
A food web or food chain shows you how energy moves from the sun, to be transformed step by step, first by producers, then by primary consumers, then by secondary consumers, and so on.... The organisms in a food web interact with each other and with the environment. Energy and matter are passed from one organism to another and used for metabolic processes and growth.
p. 102s
Unit 2 states the “First Law of Thermodynamics: Energy is not created nor is it destroyed during conversion to another form” (p. 88s) and includes a review question that asks students to give an example that illustrates it (p. 117s, question 7).
However, the material does not present any of the following essential parts of this key idea in their entirety:
- Living organisms obey the laws/principles of conservation and transformation of matter and energy that apply to all natural systems.
- Matter and energy are transformed among living things and between them and the physical environment.
- The total amount of matter and energy remains constant.
- The previous ideas hold (even) over long spans of time.
Building a Case
While Biology: A Community Context presents most of the key ideas, it does not build a case for any of them. Students observe only a few phenomena relevant to the key ideas (see pages 28–31s, 223–224s, and 226–227s) and none of these are used to make an argument for the plausibility of the key ideas.
Connections
The set of key ideas on matter and energy transformations is highly complex, spanning four levels of biological organization (molecular, cellular, organism, and ecosystem) and depending heavily on knowledge in physical science (e.g., energy forms and transformations among them, and recombination of atoms in chemical reactions).
Biology: A Community Context treats key ideas about matter and energy transformation at two levels of biological organization: Unit 1: Matter and Energy for Life presents the chemistry of photosynthesis and respiration, and Unit 2: Ecosystems presents some of the same ideas in the context of ecosystems. These key ideas are not treated when cell parts and their functions are presented (pp. 207–211s) or when human digestion is presented (pp. 224–225s). Teachers are not alerted to the different places where matter and energy ideas are treated, nor is a rationale provided for the order in which they are presented.
Matter. Connections among key ideas. Out of the four key ideas about matter transformation, only one—the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1)—is fully presented in the student text. The idea that “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” (Idea b1) is presented nearly completely but only in the Teacher's Guide. The other two ideas are presented incompletely. Key ideas about matter transformation are presented briefly in two sections, How Do Living Things Obtain and Use Energy? (p. 38s) and Photosynthesis and Energy Transformations (p. 88s), so the matter part of the story may be lost entirely.
Furthermore, in some cases isolated phenomena are presented but are not identified as being examples of a general pattern in nature. For example, while the text presents the carbon cycle (p. 39s) and the nitrogen cycle (p. 93s), it does not state the more general idea that all the chemical elements that make up the molecules of living things are repeatedly recycled. And the text does not indicate that both the carbon and the nitrogen cycles are instances of this general idea.
The material makes connections within and between some of the key ideas but not others. Furthermore, some of the connections that are made are made only in the Teacher’s Guide. For example, though the text presents the idea that “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” (Idea b1) in two separate pieces—one dealing with breakdown and synthesis (pp. 39–40s) and the other with storage (p. 88s)—only the suggested response in the Teacher’s Guide puts the pieces together and the focus is on energy, not matter:
Question: What happens to the energy that is transformed in photosynthesis?
Suggested Response: The energy that is transformed in photosynthesis is harnessed into molecules of carbohydrates; it becomes stored as chemical energy in the bonds of sugar molecules. The plant can burn the sugars during cellular respiration to release the energy when it is needed. The plant can use this energy to build other organic materials it needs, such as lipids or proteins. Animals may eat plants and use the energy that is stored in plant sugars in a similar manner. This energy transformation is not 100 percent efficient as much of the original energy is lost as heat.
pp. 117s and 141t, Self-Check 1, question 4
A model-building activity helps students make the connection between the matter transformations involved in photosynthesis (Idea a1) and respiration (Ideas b1 and c1) (pp. 35–38s). Students prepare molecules of glucose and oxygen and use them to model aerobic respiration (p. 37s, step 5a in the procedure). Then they use the molecules that they have created to model the process of photosynthesis (step 5c in the procedure). The Interpretations questions focus students on the relationship between the two processes (p. 37s, questions 1–5). However, the connection between these ideas and matter transformation in ecosystems (Idea d1) is weak at best. The text notes that “Together the processes of photosynthesis and respiration form the basis of the biological carbon cycle” (p. 39s) and refers students to a diagram showing the cycling of carbon between CO2 and C6H12O6 (p. 40s). However, the emphasis appears to be on maintaining a balanced level of CO2, rather than on making the connection between the processes occurring in organisms and the repeated cycling of chemical elements in food webs and between organisms and the environment. While two questions ask students about carbon cycles, neither the questions nor the suggested responses are explicit about ecosystems:
Question: Why is the carbon cycle in nature called a cycle?
Suggested Response: The carbon cycle is called a cycle because we can follow the movement of molecules through a continuous path, which has no clear beginning or end. A carbon atom that starts as a part of a carbon dioxide molecule can go through photosynthesis to become part of a glucose molecule, which can then be broken down during respiration to form CO2 again.
pp. 37s and 64t, Interpretations, question 5
Question: Describe an example of the carbon cycle in your community.
Suggested Response: Evidence of the carbon cycle can be found in many homes in any city: An outdoor garden has plants that use photosynthesis to remove carbon from the air (as CO2) and use it to make glucose. This glucose may be used, via cellular respiration, as an energy source to help plants grow or may be stored in the plant’s fruit as glucose or starch. When we eat the fruits and vegetables of the garden, we start the decomposition process by breaking down the biomass into smaller molecules. The part of the plant that we do not eat may then be composted, allowing traditional decomposers to use it as a food source and return CO2 to the air as a waste product.
pp. 37s and 64t, Applications, question 1
A subsequent Guided Inquiry involves students in investigating what organisms are found in a compost pile (pp. 40–42s) and shows a food web of those organisms. However, none of the Interpretations or Applications questions focus students’ attention on the carbon cycle or on the combination and recombination of atoms in the compost food web.
Connections between key ideas and their prerequisites. The text does not make connections between the key ideas about matter transformation and their prerequisites. In the section Chemical Reactions, the text states that “All living things contain carbon” (p. 34s) and notes about a chemical equation that “the total number of each type of atom remains the same on either side of the arrow” (p. 34s). However, these ideas are not connected to key ideas about matter transformation in plants (Idea a1) or ecosystems (Idea d1). While the student text mentions that “Animals get the organic materials that they need for growth and metabolism from the foods they eat” (p. 81s), this is less sophisticated than the prerequisite idea that “Food provides molecules that serve as...building materials for all organisms.”
Connections between key ideas and related ideas. The text does not make connections between key ideas about matter transformation and other, related ideas that could reinforce them. Though a table showing the number of bonds formed by common atoms indicates that carbon can form four possible bonds (p. 35s) and students use gumdrops and toothpicks to model the combination and recombination of atoms in photosynthesis and respiration (pp. 35–37s), a connection is not made between the ideas. For example, the text doesn’t point out that life as we know it is possible because of the ability of carbon atoms to form four bonds. And the text neither presents the idea that “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen....” nor relates it to the key idea about the cycling of all these chemical elements in ecosystems (Idea d1).
Energy. Connections among key ideas. Two of the four key ideas on energy transformation are treated completely, a third is mostly presented, but the fourth is so marginally presented as to miss much of its meaning. Connections are made among key ideas about energy transformation in organisms (Ideas a2, b2, and c2) but not between them and energy transformation in ecosystems (Idea d2). Moreover, the connections made are usually found only in the Teacher’s Guide in suggested responses to Self-Check questions. For example, connections between key ideas (or parts of key ideas) about energy transformation in photosynthesis and in respiration in plants and animals are made only in the suggested response to the following Self-Check question:
Question: What happens to the energy that is transformed in photosynthesis?
Suggested Response: The energy that is transformed in photosynthesis is harnessed into molecules of carbohydrates; it becomes stored as chemical energy in the bonds of sugar molecules. The plant can burn the sugars during cellular respiration to release the energy when it is needed. The plant can use this energy to build other organic materials it needs, such as lipids or proteins. Animals may eat plants and use the energy that is stored in plant sugars in a similar manner. This energy transformation is not 100 percent efficient as much of the original energy is lost as heat.
pp. 117s and 141t, Self-Check 1, question 4
The student text could have connected these ideas when presenting the carbon cycle diagram (p. 40s), but neither the figure legend nor the surrounding text does so. For example, neither the diagram nor accompanying text relates the idea that energy is lost as heat in individual organisms (part of Ideas b2 and c2) to the idea in ecosystems that “at each link in a food web” energy is lost as heat (part of Idea d2). Using the phrase “living system” is not the same as being explicit about a food web or ecosystem, and simply labeling a diagram with the term “carbon cycle” does not count as making a connection.
The text does connect photosynthesis to respiration in animals:
Looking at the photosynthesis equation, you see that the simple sugar, glucose, is one product of photosynthesis. Other organisms, such as animals, consume glucose or other molecules manufactured by photosynthetic organisms to acquire their energy.
p. 39s
However, the text does not make the connection to respiration in plants, such as by stating that plants also use glucose molecules as an energy source. This connection is only made in the Teacher’s Guide in a suggested response to a Self-Check question (p. 141t, question 4).
Connections between key ideas and their prerequisites. As with the material’s presentation of connections among key ideas, connections to prerequisite ideas are presented only in suggested responses in the Teacher’s Guide. The two prerequisites treated—“Energy can only change from one form into another” and “Energy in the form of heat is almost always one of the products of an energy transformation”—are mentioned in the suggested response to a Self-Check question (p. 142t, question 7) and connected to key Ideas a2 and c2:
Question: State the first and second laws of thermodynamics, and describe an example of how they are applied to living systems.
Suggested Response: First law of thermodynamics: In all chemical and physical changes, energy is neither created nor destroyed but is only transformed from one form to another. (An alternative: In any process, the total energy of the system plus its surroundings remain[s] constant.)
In a living system, light energy is transformed into chemical energy by plants during photosynthesis. Herbivores then eat the plants and take up the chemical energy that is stored in the plants. This energy may be maintained in a chemical form or changed and used to do work. Carnivores or saprobes then eat the herbivores, and the energy is transferred and perhaps transformed again. No energy has been created or destroyed, only transformed.
Second law of thermodynamics: Any system plus its surroundings tends spontaneously toward increasing disorder. (Alternatives: [1] No real process can be 100% efficient. [2] In any energy conversion, some energy is transferred to the surroundings as heat.)
The second law states that...[s]ome of the energy that drives any process will be converted to or remain as heat. Therefore processes such as photosynthesis or cellular respiration are never 100 percent efficient. In other words, much of the original energy in the sunlight striking a plant is lost as heat rather than being stored as chemical energy, and much of the original energy in the foods organisms consume is lost as heat rather than being converted to ATP energy.
pp. 117s and 142t, Self-Check 1, question 7
However, the suggested response does not make a connection to energy loss in plants (Idea b2) or to the continual loss of energy in ecosystems (part of Idea d2). Nor does it relate the loss of energy in ecosystems to the prerequisite “Energy in the form of heat is almost always one of the products of an energy transformation.”
No other prerequisites are presented or connected to key ideas about energy transformation.
Connections between key ideas and related ideas. The material makes no connections between key ideas about energy transformation and related ideas. The text section Eukaryotic Cells fails to clearly make the point that “Within cells are specialized parts for the capture and release of energy.” Instead, it uses technical terms that are likely to convey little meaning: “Mitochondria are the cell’s powerhouses where cellular respiration takes place and ATP (adenosine triphosphate) is produced” (p. 209s). And no attempt is made to connect the function of these organelles in cells to the energy transformations that occur in organisms.
Matter and Energy. The material makes some connections between key ideas about matter transformation and those about energy transformation. However, the connections made are at the level of organisms but not of ecosystems. For example, the text description of the light and dark reactions of photosynthesis indicates that both matter and energy transformations occur (pp. 38–39s), making a connection between key Ideas a1 and a2. This connection is made again in Unit 2: Ecosystems in the Summary of Major Concepts:
Light energy from the sun is captured by plants during photosynthesis, transformed to chemical energy, and stored as carbohydrates. Photosynthesis uses carbon dioxide and water, releases oxygen, and produces sugars. As plants grow, they increase in mass primarily because of the carbon dioxide taken from the air and water taken from the ground, both of which have been reconfigured into carbohydrates.
p. 135s, item 3
And text and an accompanying diagram of cellular respiration showing the inputs and outputs of matter and the production of energy in the form of ATP (p. 39s) make a connection between Ideas b1 and b2 and c1 and c2.
The culminating idea about transformation and conservation is treated in terms of energy only, so there is no corresponding treatment of matter that could be linked to the energy story. Furthermore, the idea that energy is conserved is presented separately from the idea that energy is transferred, and is never connected to it. Energy conservation is presented by stating the first law of thermodynamics (p. 88s) and successive transfer of energy is presented through trophic levels and pyramids (pp. 102–103s). Neither is the connection made to the loss of transferable energy in the form of heat (which could tie together ideas about energy conservation and transformation).
Beyond Literacy
Unlike most other biology textbooks, Biology: A Community Context avoids use of details of metabolism. For example, diagrams of metabolic pathways show only the names of stages in the pathways—such as Calvin cycle and glycolysis—rather than also including the names and structures of intermediates. However, the material does include a lot of contextual material that is outside the scope of science literacy and frequently substitutes context for conceptual development. While the problems and issues presented may be interesting to students, they are not well connected to the key ideas and often seem incidental to them. At least on the topic of matter and energy transformations, the key ideas remain in the background.
Accuracy
While glaring inaccuracies were not noted, a few statements in the student text and Teacher’s Guide will likely be confusing to students. For example, the statements below seem irreconcilable. The text statement indicates that energy stored in glucose is released during respiration (breakdown of glucose molecules). But the suggested response to a related Self-Check question indicates that energy is released when molecules are built. No attempt is made to clarify and resolve these statements:
Text: Other organisms, such as animals, consume glucose or other molecules manufactured by photosynthetic organisms to acquire their energy. The chemical energy stored in glucose is released to cells through the process of cellular respiration (Figure 1.28). This multistep process involves: first, breakdown of glucose molecules to smaller (3 carbon) molecules; second, production of energy transport molecules and CO2 in the Krebs cycle; and third, use of the energy transport molecules—in the electron transport system—to make ATP.
Question: What are chemical bonds? What happens to the energy in chemical bonds when molecules are built? What happens when molecules are broken down?
Suggested Response: Chemical bonds are forces that act strongly enough between two atoms or groups of atoms to hold them together in a stable arrangement. Energy is released when molecules are built (i.e., bonds are formed), and energy is required to break apart the bonds that hold groups of atoms together.
p. 39s; p. 44s, question 12; p. 73t
In addition, the following muddled presentations of matter and energy may lead students to think that matter and energy are interconvertible in everyday reactions:
In the process of photosynthesis, plants convert light energy (sunlight) to chemical energy (sugars). Plants use these sugars for growth, the production of biomass, and metabolism.
p. 88s
This demonstration is intended to emphasize that burning does not absolutely get rid of waste, but rather converts it into different forms. Remind students of the first law of thermodynamics—that energy can be converted from one form to another but cannot be created or destroyed.
p. 44t
