High School Biology Textbooks: A Benchmarks-Based Evaluation

BSCS Biology: An Ecological Approach. Kendall/Hunt, 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:

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Alignment

The topic of matter and energy transformations brings together a number of key ideas from both the biological and physical sciences. BSCS Biology: An Ecological Approach treats most of these ideas and distributes them over several chapters: Chapter 1: The Web of Life, Chapter 4: Matter and Energy in the Web of Life, Chapter 15: The Human Animal: Food and Energy, Chapter 18: The Flowering Plant: Form and Function, and Chapter 19: The Flowering Plant: Maintenance and Coordination. The ideas are treated most simply in chapters 1 and 4. In the later chapters, the level of sophistication presented greatly exceeds requirements for science literacy. 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 in text and investigations. The text first presents the idea in Chapter 1: The Web of Life in the context of describing matter transformation in ecosystems:

[P]lants use the simple compounds of carbon dioxide and water in photosynthesis, but only small amounts of chemical energy are present in these compounds. During photosynthesis, the plants build complex compounds. Using light energy, they link together the atoms from carbon dioxide and water to make sugars.

p. 12s

The idea is elaborated in Chapter 19: The Flowering Plant: Maintenance and Coordination, although it is imbedded in details of the photosynthesis reactions:

In the first group, the light reactions, light energy is absorbed and converted into chemical energy as short-lived, energy-rich molecules are formed. These molecules then are used to make 3-carbon sugars from carbon dioxide in...the series of reactions known as the Calvin cycle. In this cycle, chemical energy is stored in the sugars, and new carbon is incorporated into the plant for future growth.

p. 491s

Chapter 19 also includes two relevant investigations: one, in which students are to observe that plant leaves produce more starch when their stomates are open to (versus closed to) carbon dioxide (pp. 506–508s, Investigation 19.1) and another, in which students observe that photosynthesizing Elodea plants remove carbon dioxide from the water (pp. 508–510s, Investigation 19.2). However, the latter investigation focuses only on the disappearance of carbon dioxide rather than on its transformation to sugar or starch.

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 content match to this idea. The text makes explicit the idea that atoms are rearranged in Chapter 1: The Web of Life in the context of describing matter transformation in ecosystems:

Both energy and matter are stored in sugars....the plant can use the sugar molecules to make other molecules that it needs to build its body. To do this, a plant rearranges the atoms in the sugar molecules and adds new atoms.

pp. 12–13s

Chapter 4: Matter and Energy in the Web of Life describes the alternative fates of sugar molecules synthesized during photosynthesis:

The sugars created during photosynthesis can be used in four ways by the plant, as shown in Figure 4.24 on page 86. First, the plant may break down the sugar molecules immediately to release the stored energy. This happens during respiration. The energy that is released from the sugars during respiration may be used by plant cells to continue the activities of life. Second, a plant may use the sugar molecules for growth. In this case, many sugar molecules are joined together to make the building materials necessary for more cells....Third, the plant may store sugars for future use....Fourth, sugar molecules may be converted into the other biological molecules needed for life....

A plant also returns carbon dioxide to the air when it uses its own sugars as a source of energy.

pp. 84s and 86s

And Chapter 19: The Flowering Plant: Maintenance and Coordination describes these fates more precisely (and represents them in Figure 19.8), though it is embedded in details of the photosynthesis reactions:

Several things can happen to the 3-carbon sugar that leaves the Calvin cycle. In the stroma of the chloroplast, the sugar can be converted into starch and stored...or it can be used to synthesize...compounds needed in the plant cell....The 3-carbon sugar also may enter the pathway of glycolysis and cellular respiration, providing energy for all plant cells.

pp. 493–494s

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. In the context of describing how carbon cycles in an ecosystem, the text states most of the idea but does not get at the idea that carbon atoms are recombined with others to form new molecules:

As a plant grows, its body becomes larger. If the plant is eaten, the carbon in the plant is passed from producer to consumer. For the consumer to use the food, it must break down the plant body. As this happens, the carbon containing molecules are broken apart, releasing both carbon atoms and energy....Some of the carbon from the body of the plant is added to the body of the consumer....

[A] decomposer uses...the carbon from the bodies [of dead organisms] to build its own body.

p. 86s

The term “consumer” (which the material substitutes for “other organisms”) has been defined previously (p. 8s).

The idea that carbon atoms are rearranged to form new molecules is expressed most directly in the suggested response to an Applications question for Chapter 1: The Web of Life:

Someone once said, “You are what you eat.” If this is true, some people would say that your body is really rearranged plant fruits, roots, stems, and leaves. Would you agree or disagree? Explain.

p. 23s, question 6

Because we get all of our food from plants, either directly as in salads or indirectly as in hamburgers, our bodies may be said to be rearranged plant molecules.

p. T37, suggested answer to question 6

Chapter 15: The Human Animal: Food and Energy includes questions that are relevant to the concept of rearrangement of atoms:

How can your body use the protein in hamburger and the potato starch in french fries to grow and provide your muscles with energy? How do the plant and animal tissues you eat become human cells and tissues?

p. 373s

However, the text treats matter transformation in terms of substances only: “Contrary to popular claims, consuming excess protein does not result in ‘muscle building.’ Instead, the protein is respired to provide energy or converted to fat and stored” (p. 392s).

An investigation in Chapter 16: The Human Animal: Maintenance of Internal Environment demonstrates that carbon dioxide production increases with exercise (pp. 427–428s, Investigation 16.3), but the investigation is not related to the transformation of matter.

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: An Ecological Approach: The chemical elements [Carbon and nitrogen] that make up [in] the molecules of living things pass repeatedly through food webs and the environment, and are combined and recombined in different ways.

The text presents the idea that matter cycles repeatedly but does not present the idea in terms of the recombination of atoms in molecules. The less sophisticated idea that substances repeatedly cycle through ecosystems is presented in Chapter 1: The Web of Life:

When an animal eats a plant as food, both energy and matter are passed from one organism to another in a food web. Unlike the flow of energy in a food web, however, the flow of matter is not one way. Matter cycles within a community. Plants use carbon dioxide, water, and other substances during photosynthesis. These same substances are given off by organisms after they have used a plant as food. Other plants then can use these materials again to continue the process of photosynthesis.

In this manner, the same matter is used over and over again in a community. Matter travels in cycles from the nonliving environment into food webs and back to the nonliving environment. It then enters the food webs once again in photosynthesis.

p. 13s

The idea that carbon recycles is presented in the context of describing how carbon cycles through ecosystems, but its recycling is described only in terms of substances. Although the text indicates that “carbon containing molecules are broken apart,” it does not make clear that the atoms are recombined into different molecules during the cycle:

As a plant grows, its body becomes larger. If the plant is eaten, the carbon in the plant is passed from producer to consumer. For the consumer to use the food, it must break down the plant body. As this happens, the carbon containing molecules are broken apart, releasing both carbon atoms and energy....Some of the carbon from the body of the plant is added to the body of the consumer. The rest of the carbon is exhaled into the air as carbon dioxide....When another plant takes in this carbon dioxide during photosynthesis, the cycle of carbon through the community is complete.

Carbon dioxide also is returned to the air by decomposers....As its source of energy, a decomposer uses the energy locked in the bodies of dead organisms, and it uses the carbon from the bodies to build its own body. Carbon that is not used is returned to the air as carbon dioxide. Eventually, almost all the carbon that is taken in by plants during photosynthesis is returned to the air by the activity of decomposers.

p. 86s; see also Figure 4.25 on page 87s

Similarly, the text describes the recycling of nitrogen but is not explicit about the nitrogen atoms being recombined into new molecules. In Chapter 11: Prokaryotes and Viruses, the role of eubacteria in the nitrogen cycle is described:

Although nitrogen gas (N2) makes up about 78 percent of the atmosphere, neither plants nor animals can use that form of nitrogen. Instead, all consumers get nitrogen-containing compounds in the things they eat, which, of course, can be traced to producers. Producers get their nitrogen bearing compounds from the soil (or water) in which they grow. Nitrogen gas dissolved in water is present in the soil. Also living in the soil or in the roots of certain plants are nitrogen-fixing eubacteria. These chemosynthetic eubacteria can “fix” nitrogen, converting it to a form they or other organisms can use. Nitrogen fixers convert nitrogen gas to ammonia (NH3), which can be used to synthesize proteins and other nitrogen-containing compounds.

p. 268s

Decomposer eubacteria in the soil break down the complex organic compounds in dead plants and animals. They use the energy in these compounds and convert the compounds to simpler substances, including the gas ammonia. Some of the ammonia escapes into the atmosphere, but much of it dissolves in soil water, where it reacts chemically with hydrogen ions to form ammonium ions (NH4+). In the form of ammonium ions, nitrogen may be absorbed by the roots of plants. It then is built into living material again by the plants.

p. 269s

The text mentions iron, sodium, and calcium in the context of describing the nutrients in pizza (p. 373s), but does not note that the pizza is but one step in their being recycled.

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 the idea. The idea that plants transform light energy into chemical energy is stated in Chapter 1: The Web of Life, in an introduction to photosynthesis: “In the process of photosynthesis, plants absorb light energy and convert it to the chemical energy found in sugars” (p. 11s).

Chapter 4: Matter and Energy in the Web of Life restates the idea and represents it in Figure 4.9 (p. 76s):

Consumer organisms get their energy from the food they eat, but where do the producers get their energy? Usually, their energy comes from the sun. Because no organism can use light energy directly from the sun as a source of food energy, the energy must be converted to chemical energy.

In the process of photosynthesis, green plants (and some other organisms) convert light energy from the sun into chemical energy that is stored in complex food molecules.

p. 75s

The first step in photosynthesis is the absorption of light energy by a green plant....some of the light energy absorbed by the plant is stored in the sugar molecules as chemical energy.

p. 76s

Chapter 19: The Flowering Plant: Maintenance and Coordination presents the idea again in introducing the reactions of photosynthesis: “In...the light reactions, light energy is absorbed and converted into chemical energy as short-lived, energy-rich molecules are formed” (p. 491s). An Applications question at the end of the chapter asks students to “Trace the flow of energy in photosynthesis, beginning with the sun and ending with a sugar molecule” (p. 512s, question 9).

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. However, the most explicit statement is presented in the teacher's guide, which students may not see. Chapter 4: Matter and Energy in the Web of Life states the idea that plants get energy from breaking down (but not oxidizing) sugar molecules:

[T]he plant may break down the sugar molecules immediately to release the stored energy. This happens during respiration. The energy that is released from the sugars during respiration may be used by plant cells to continue the activities of life.

pp. 84s and 86s

Admittedly, the idea that plants do something with the energy is only vaguely conveyed in the phrase “to continue the activities of life.”

The idea that respiration is related to oxidation is presented later, in the context of cellular respiration, but is not explicitly related to plants:

Cells release energy from the basic molecules of food through the process of cellular respiration—a type of controlled burning. When something is burned, a great deal of energy is liberated all at once in the form of heat and light. Cells release the same amount of energy gradually in a stepwise series of reactions....the energy present in these basic molecules is freed in small amounts....

p. 378s

The student text mentions the idea that “Some of the energy is released as heat,” but does not specifically refer to plants: “Whenever an organism breaks down its food, some of the energy escapes as heat” (p. 11s). However, the teacher’s guide explicitly mentions plants in a suggested response to one of the Applications in Chapter 19: The Flowering Plant: Maintenance and Coordination:

Question: Energy can be changed from one form to another, but it cannot be created or destroyed. Give several examples from this chapter, or any part of the text, in which energy is changed from one form to another.

Suggested Response: Plants convert light energy into chemical energy during the process of photosynthesis, and some of this chemical energy is lost as heat energy during cellular respiration. Also, when an organism moves, chemical energy is converted into kinetic energy.

pp. 512s and T106, Applications, item 7

However, without explicit treatment of energy transformation in the student text, students may not be able to correctly respond to the question.

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 a content match to this idea but different parts of the idea are presented in widely separated parts of the textbook. In the context of presenting the carbon cycle in ecosystems, the text describes how energy is released as food is broken down in other organisms, but does not mention oxidation:

As a plant grows, its body becomes larger. If the plant is eaten, the carbon in the plant is passed from producer to consumer. For the consumer to use the food, it must break down the plant body. As this happens, the carbon containing molecules are broken apart, releasing both carbon atoms and energy. Much of the energy released is used for the activities of the consumer....

p. 86s

The idea that respiration is related to oxidation is presented much later, in the context of cellular respiration:

Cells release energy from the basic molecules of food through the process of cellular respiration—a type of controlled burning. When something is burned, a great deal of energy is liberated all at once in the form of heat and light. Cells release the same amount of energy gradually in a stepwise series of reactions....the energy present in these basic molecules is freed in small amounts....

p. 378s

In the context of describing energy flow in Chapter 1: The Web of Life, the text notes that heat is always a product of energy transformations:

The conversion of chemical energy to the energy used by living organisms is not efficient. Whenever an organism breaks down its food, some of the energy escapes as heat. If you touch your arm, for example, it feels warm. This is because some of the chemical energy stored in the fries and hamburger you ate is converted to heat energy. Your body uses the rest of the chemical energy to keep you alive and growing. Although some heat energy keeps the body warm, which allows biological activities to continue, most of it is lost to the air.

p. 11s

Much later, in an investigation in Chapter 15: The Human Animal: Food and Energy, students observe that energy is released as a peanut burns in a calorimeter (pp. 393–395s, Investigation 15.1), and a discussion question for this investigation relates this energy to the energy released as food is completely burned in human cells (p. 396s, question 4).

An investigation at the end of Chapter 16: The Human Animal: Maintenance of Internal Environment demonstrates that carbon dioxide production increases with exercise (pp. 427–428s, Investigation 16.3), but the investigation is not related to the transformation of energy.

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 a content match to this idea. In Chapter 1: The Web of Life, the text states and a diagram shows that as energy flows from producers to consumers to decomposers, energy is given off as heat:

Why is it impossible for organisms to recycle energy?

Their activities change it into heat, which cannot be used to do work.

p. 11st, Figure 1.10

After grass makes its own food in photosynthesis, it uses some of that food to grow. Thus, some of the energy that is captured from sunlight is used before it reaches the cow, even if the cow eats the whole plant....

No matter where energy comes from, all the energy that enters a food web eventually is lost from the community in the form of heat (see Figure 1.10 above). No organism can use heat energy for growth. Therefore, energy must enter a community continually, beginning with photosynthesis, or the community will die. The source of chemical energy for almost all communities in the world is light energy from the sun. If the sun were to burn out, life on earth would cease.

p. 11s

Less emphasis is given here to the idea that some energy is stored in newly made structures in the context of the carbon cycle, but this notion is presented later in the context of individual organisms (see reference to page 86s in the above discussion of alignment to Idea c1).

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.

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Building a Case

Although the material aligns with most of the key ideas, it does not build a case for them. While students experience a few relevant phenomena, the phenomena are neither connected to the key ideas nor used as evidence in building an argument to make them plausible. For example, students observe that blocking stomates reduces starch production in leaves (pp. 506–508st, Investigation 19.1), but the observation is not used to support the key idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1). Similarly, students observe that a burning peanut gives off heat (pp. 393–396st, Investigation 15.1), but this observation is not used to support the idea that “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” (Idea c2).

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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).

BSCS Biology: An Ecological Approach presents all but one of the key ideas and treats all parts of the ideas presented, except for Idea d1. The one idea not presented is the unifying concept that relates matter and energy transformation to their conservation in both living and physical systems (Idea e). The text presents key ideas first in the context of ecosystems (pp. 10–13s) and revisits them (pp. 75–77s) after presenting information about atoms and molecules (pp. 71–74s). Ideas related to cellular respiration are elaborated (pp. 377–384s) after describing human digestion (pp. 373–376s), and ideas related to photosynthesis are further developed (pp. 489–495s) after describing plant structure and function (pp. 463–473s).

However, most of the text in these elaborated presentations goes well beyond the sophistication of the key ideas. Teachers are not alerted to these different places where matter and energy ideas are treated nor is a rationale for this sequence conveyed. Furthermore, as described below, many of the connections among key ideas are made in the first chapter. Without the information that follows in subsequent chapters, the connections are not likely to be helpful.

Energy. Connections among key ideas. The text makes connections among key ideas about energy transformation in Chapter 1: The Web of Life by sequencing them in a description of a food web. First, the text states Idea a2 and connects it to Idea b2 (and, in the last sentence, to Idea c2):

In the process of photosynthesis, plants absorb light energy and convert it to the chemical energy found in sugars. The sugars formed by photosynthesis provide food for the plant. The plant then can use the energy in the sugars to grow and reproduce. Energy that is not used may be stored in the form of starch to be used at a later time. The potato plant, for example, stores energy as starch. When you eat the potato, you benefit from the chemical energy stored in it.

p. 11s

Next, the text connects Idea b2 to Idea d2:

Photosynthesis is the basis for almost all of the food energy in the world. After grass makes its own food in photosynthesis, it uses some of that food to grow. Thus, some of the energy that is captured from sunlight is used before it reaches the cow, even if the cow eats the whole plant.

p. 11s

Then the text connects Idea a2 to Idea c2 and states Idea c2 in the context of both herbivores and decomposers:

Because no animal can make its own food, it must get its energy from plants or other animals. The cow eats the grasses and uses the chemical energy in them to grow, to produce milk, and to move across the pasture. The energy not used by the cow remains in the waste products dropped in the pasture. This energy is not completely lost to all organisms. Decomposers break down the cow dung and use the energy from it for their own growth and reproduction. Decomposers also get energy from the bodies of the cows and plants that die. This series of steps is referred to as the flow of energy through a system.

p. 11s

Finally, the text connects Ideas a2, b2 and c2 to Idea d2 and states Idea d2:

The conversion of chemical energy to the energy used by living organisms is not efficient. Whenever an organism breaks down its food, some of the energy escapes as heat. If you touch your arm, for example, it feels warm. This is because some of the chemical energy stored in the fries and hamburger you ate is converted to heat energy. Your body uses the rest of the chemical energy to keep you alive and growing. Although some heat energy keeps the body warm, which allows biological activities to continue, most of it is lost to the air. No matter where energy comes from, all the energy that enters a food web eventually is lost from the community in the form of heat (see Figure 1.10 above). No organism can use heat energy for growth. Therefore, energy must enter a community continually, beginning with photosynthesis, or the community will die. The source of chemical energy for almost all communities in the world is light energy from the sun. If the sun were to burn out, life on earth would cease.

pp. 11–12s

The text also relates photosynthesis (Idea a2) to respiration in plants (Idea b2) in the context of describing the roles of various cell organelles. After characterizing mitochondria as powerhouses that “help to release energy from food molecules” (p. 106s) and chloroplasts as organelles that “contain chlorophyll, a pigment that is essential for capturing the energy in sunlight” (p. 107s), the text relates the two processes to one another through the sites where they occur: “The energy captured from the sun and stored in the structure of biological molecules during photosynthesis is released later in the mitochondria” (p. 107s). This same section relates respiration in plants (Idea b2) to respiration in animals (Idea c2) by noting that, “Mitochondria are especially abundant in the parts of an organism that have high energy requirements, such as a muscle in an animal or a growing root tip of a plant” (p. 107s).

Much later in the book, after the key ideas have been presented, students are asked to relate ideas about photosynthesis (Idea a2) and respiration (Ideas b2 and c2) in one of the Applications, and the suggested answer makes the connection:

Question: In what ways are photosynthesis and cellular respiration opposite sets of reactions?

Suggested Response: Photosynthesis is an energy-storing reaction; respiration is an energy-releasing reaction. The products of photosynthesis are the raw materials for respiration, and vice versa.

pp. 512s and T106, Applications, item 1

However, students could correctly respond to the question using ideas about matter transformation only.

Connections between key ideas and their prerequisites. The text implicitly relates the prerequisite idea that “Food provides the molecules that serve as fuel...for all organisms” to key ideas about photosynthesis and respiration. Just before introducing ideas about energy transformations in photosynthesis and respiration (see quoted text above from page 11s), the text notes that the activities of an organism require energy, asks where the energy comes from, notes that “[c]hemical energy is found in the structure of the molecules that make up the meat and the potatoes,” and then frames its presentation of the key ideas with a question: “The hamburger that contains chemical energy came from a cow; cows eat only grasses and grains. A grass plant and a potato do not eat other organisms, so where do they get their energy?” (p. 10s). The connections are made through the use of the same examples—hamburgers and potatoes. However, the material does not go beyond these two examples to food in general.

One of the Applications at the end of Chapter 19: The Flowering Plant: Maintenance and Coordination involves students in making a connection between the prerequisite idea that “Energy can only change from one form into another” and key ideas about energy transformation, but the key ideas about energy transformation in plants were presented more than 400 pages before the prerequisite was mentioned:

Question: Energy can be changed from one form to another, but it cannot be created or destroyed. Give several examples from this chapter, or any part of the text, in which energy is changed from one form to another.

Suggested Response: Plants convert light energy into chemical energy during the process of photosynthesis, and some of this chemical energy is lost as heat energy during cellular respiration....

pp. 512s and T106, Applications, item 7

A couple of opportunities were missed to make connections between key ideas about energy transformation and their prerequisites. For example, the text could have connected the prerequisite idea that “Arrangements of atoms have chemical energy” to energy transformation in photosynthesis (Idea a2) but failed to do so. The text states that “Chemical energy is found in the structure of the molecules that make up the meat and the potatoes” (p. 10s), but does not state the prerequisite itself or explain that the energy to arrange the atoms in the molecules of meat and potatoes came from the sun's energy. Similarly, a figure that compares burning and cellular respiration (p. 77s, Figure 4.10) could have been used to connect the prerequisite that “An especially important kind of reaction between substances involves combination of oxygen with something else—as in burning or rusting” and cellular respiration (Idea c2). However, the prerequisite idea is not presented.

Connections between key ideas and related ideas. The text connects ideas about energy transformations in plant respiration (Idea b2) and animal respiration (Idea c2) to the related idea that “Within cells are specialized parts for the...release of energy” by relating the number of these specialized parts in various types of cells to their energy needs: “Mitochondria are especially abundant in the parts of an organism that have high energy requirements, such as a muscle in an animal or a growing root tip of a plant” (p. 107s). The connection is made again in Section 5.6: Cell Activities Require Energy: “The more active a cell is, the more mitochondria it is likely to contain” (p. 108s).

Matter. Connections among key ideas. The material makes fewer connections among key ideas about matter transformation because it does not consistently relate matter transformation at the various levels of biological organization in terms of the combination and recombination of atoms in molecules. For example, the text in Chapter 1: The Web of Life that connects key ideas about energy transformation relates ideas about matter transformation in ecosystems in terms of substances or materials but not in terms of the combination and recombination of atoms:

When an animal eats a plant as food, both energy and matter are passed from one organism to another in a food web. Unlike the flow of energy in a food web, however, the flow of matter is not one way. Matter cycles within a community. Plants use carbon dioxide, water, and other substances during photosynthesis. These same substances are given off by organisms after they have used a plant as food. Other plants then can use these materials again to continue the process of photosynthesis.

p. 13s

Earlier in the same section, the text does a nice job of relating food making (Idea a1) to food use by plants (Idea b1) in terms of the recombination of atoms:

Plants and animals are made up of many different compounds, but the atoms used to make up these compounds occur all around you in the non-living world. For example, plants use the simple compounds of carbon dioxide and water in photosynthesis....During photosynthesis, the plants build complex compounds. Using light energy, they link together the atoms from carbon dioxide and water to make sugars....the plant can use the sugar molecules to make other molecules that it needs to build its body. To do this, a plant rearranges the atoms in the sugar molecules and adds new atoms.

pp. 12–13s

However, the text does not extend this molecular treatment to its discussion of ecosystems.

The text in Chapter 4: Matter and Energy in the Web of Life relates matter transformation in plants (Idea b1) to matter transformation in other organisms (Idea c1) in terms of atoms and molecules:

As a plant grows, its body becomes larger. If the plant is eaten, the carbon in the plant is passed from producer to consumer. For the consumer to use the food, it must break down the plant body. As this happens, the carbon containing molecules are broken apart, releasing both carbon atoms and energy. Much of the energy released is used for the activities of the consumer. Some of the carbon from the body of the plant is added to the body of the consumer. The rest of the carbon is exhaled into the air as carbon dioxide....When another plant takes in this carbon dioxide during photosynthesis, the cycle of carbon through the community is complete.

Carbon dioxide is also returned to the air by decomposers....As its source of energy, a decomposer uses the energy locked in the bodies of dead organisms, and it uses the carbon from the bodies to build its own body. Carbon that is not used is returned to the air as carbon dioxide. Eventually, almost all the carbon that is taken in by plants during photosynthesis is returned to the air by the activity of decomposers.

p. 86s

But its discussion of the carbon cycle is at the substance level, thus missing the opportunity to make explicit that the combination and recombination of atoms that occurs in organisms ultimately accounts for the conservation of atoms in ecosystems.

Connections between key ideas and their prerequisites. The text makes connections between key ideas about matter transformation and some of their prerequisites. Section 1.5: Matter Is Used to Build Living Things makes a connection between matter transformation in photosynthesis (Idea a1) and the prerequisite idea that “Carbon and hydrogen are common elements of living matter.” The text first states the prerequisite and represents it on a pie chart (Figure 1.12) and then states the key idea:

Of the more than 100 different elements found on the earth, only about 30 are used in the makeup of organisms. Most of these elements, such as the hydrogen found in a water molecule and the carbon found in the carbon dioxide of the air, are very common. Figure 1.12 shows the proportions of elements in humans.

Plants and animals are made up of many different compounds, but the atoms used to make up these compounds occur all around you in the non-living world. For example, plants use the simple compounds of carbon dioxide and water in photosynthesis, but only small amounts of chemical energy are present in these compounds. During photosynthesis, the plants build complex compounds. Using light energy, they link together the atoms from carbon dioxide and water to make sugars.

p. 12s

The text then goes on to define food, making the connection between plant food making (Idea b1) and the prerequisite idea that “Food provides the molecules that serve as...building materials for all organisms.” Although the prerequisite is stated in terms of substances, it follows a sentence that is explicit about the rearrangement of atoms:

...[T]he plant can use the sugar molecules to make other molecules that it needs to build its body. To do this, a plant rearranges the atoms in the sugar molecules and adds new atoms. Sugars, therefore, are a food—a substance that an organism can break down to get energy for growth, body maintenance, and repair. Food is also matter that can be used to build the structure of the body.

p. 13s

The breakdown and reassembly of food molecules by other organisms (Idea c1) is connected to the same prerequisite in the context of describing human digestion. The text states the prerequisite and explains why breakdown and reassembly are needed:

Three types of molecules are used in all living cells as building materials and as sources of energy—carbohydrates, proteins, and fats (lipids). Although the food you eat must supply these molecules, your body cannot use the molecules directly from the food. Just as an old brick building can be demolished and the bricks used to construct a patio or a fireplace, so the human body tears food molecules apart and forms useful building blocks.

p. 375s

However, the prerequisite idea on the conservation of matter is neither treated nor connected to the repeated cycling of elements between ecosystems and the physical environment (Idea e).

Connections between key ideas and related ideas. The text connects plant food making (Idea a1) to the related idea that “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus” in Section 1.5: Matter Is Used to Build Living Things:

Of the more than 100 different elements found on the earth, only about 30 are used in the makeup of organisms. Most of these elements, such as the hydrogen found in a water molecule and the carbon found in the carbon dioxide of the air, are very common. Figure 1.12 shows the proportions of elements in humans.

Plants and animals are made of many different compounds, but the atoms used to make up these compounds occur all around you in the non-living world. For example, plants use the simple compounds of carbon dioxide and water in photosynthesis....During photosynthesis, the plants build complex compounds. Using light energy, they link together the atoms from carbon dioxide and water to make sugars.

p. 12s

In Chapter 4: Matter and Energy in the Web of Life, the text connects the related idea that “Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules” to the ability of other organisms to build their body structures (Idea c1):

Carbon Is Found in All Living Things
Although organisms are composed of many different chemical elements, carbon is the central element for all living systems. Carbon atoms can join together to form chains or rings, as shown in Figure 4.14. Furthermore, carbon atoms can combine with hydrogen, oxygen, nitrogen, sulfur, and phosphorus to form a vast number of organic compounds. In fact, the atoms of the elements present in organic compounds can be arranged in so many ways that the variety of organic compounds is almost limitless....

Because all living organisms contain the same types of biological molecules, you can get the molecules you need for life from another organism. In fact, that is the only way you can get the molecules you need. To live, you must eat a plant or animal and rearrange its molecules and atoms into your own molecules and atoms.

pp. 78–79s

Matter and Energy. Connections among key ideas. The text connects ideas about matter and energy transformations in photosynthesis (Ideas a1 and a2) in several places by clearly stating what happens to both matter and energy during the process:

[P]lants use the simple compounds of carbon dioxide and water in photosynthesis, but only small amounts of chemical energy are present in these compounds. During photosynthesis, the plants build complex compounds. Using light energy, they link together the atoms from carbon dioxide and water to make sugars. Both energy and matter are stored in sugars.

p. 12s

Recall from Section 4.4 that plants take up carbon atoms in the form of carbon dioxide from the air. During photosynthesis, they use the energy in sunlight to make sugars from carbon dioxide and water. In this way, the energy from sunlight and the carbon from carbon dioxide are stored in the sugars.

p. 84s

The text then goes on to connect these ideas to the possible fates in plants of the sugars they produce (Ideas b1 and b2):

The sugars created during photosynthesis can be used in four ways by the plant, as shown in Figure 4.24 on page 86. First, the plant may break down the sugar molecules immediately to release the stored energy. This happens during respiration. The energy that is released from the sugars during respiration may be used by plant cells to continue the activities of life. Second, a plant may use the sugar molecules for growth. In this case, many sugar molecules are joined together to make the building materials necessary for more cells....Third, the plant may store sugars for future use....Fourth, sugar molecules may be converted into the other biological molecules needed for life.

pp. 84s and 86s

Next, the text connects these ideas to key ideas about matter and energy transformation in other organisms (Ideas c1 and c2) and connects them to one another:

If the plant is eaten, the carbon in the plant is passed from producer to consumer. For the consumer to use the food, it must break down the plant body. As this happens, the carbon containing molecules are broken apart, releasing both carbon atoms and energy. Much of the energy released is used for the activities of the consumer. Some of the carbon from the body of the plant is added to the body of the consumer. The rest of the carbon is exhaled into the air as carbon dioxide.

p. 86s

A figure relates matter and energy changes in a community (p. 13s, Figure 1.13), but it does not relate key ideas about matter and energy transformation in ecosystems (Ideas d1 and d2). For example, neither the figure nor accompanying text characterizes the repeated combination and recombination of atoms into molecules that vary in the amount of energy stored in their configurations.

And, as noted above, the text does not present the key idea that could tie together key ideas about matter and energy transformation and conservation in living and physical systems (Idea e).

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Beyond Literacy

While the text includes chapters and sections that go well beyond science literacy recommendations in Benchmarks for Science Literacy (AAAS, 1993) and the National Science Education Standards (NRC, 1996), it presents most of the more sophisticated material in the later chapters. For example, after describing how food is digested in humans, Chapter 15: The Human Animal: Food and Energy presents details of glycolysis, the Krebs cycle, and the electron transport chain (pp. 378–384s). And Chapter 19: The Flowering Plant: Maintenance and Coordination includes details on the light reactions and the Calvin cycle (pp. 491–495s). It is not clear whether the material intends these sections for all students. The section in the teacher’s guide entitled “Scheduling for the Year” indicates that the earlier chapters on matter and energy transformations (chapters 1 and 4) “are considered essential, basic biology, and you should include as much of these as possible” (p. T5). Though not explicit, the statement implies that the more advanced material in chapters 15 and 19 is not essential, core biology. However, each of the yearly plans provided include at least 4 days for chapter 15 and 3 days for chapter 19 (see page T6), and the yearly schedules do not indicate which sections can be omitted if these minimum number of days are devoted to the more advanced chapters.

In principle, the later chapters could be omitted from a course designed for science literacy (since most of the key ideas, prerequisites, and related ideas and the connections noted among them do not rely on what is presented in these chapters). This would allow the textbook to increase the instructional support provided for the science literacy ideas.

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