Biology by Miller and Levine. Prentice Hall, 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 by Miller and Levine treats most of these ideas and distributes them over several chapters: Chapter 3: Introduction to Chemistry, Chapter 4: The Chemical Basis of Life, Chapter 5: Cell Structure and Function, Chapter 6: Cell Energy: Photosynthesis and Respiration, Chapter 39: Nutrition and Digestion, and Chapter 47: The Biosphere. The ideas usually appear as assertions in text and rarely in the list of section objectives, class discussions, investigations, or review questions. Energy transformation is treated more extensively than matter transformation, which is treated minimally and primarily in terms of transforming one substance into another. Although an introductory section on chemistry treats atoms, elements, molecules, and compounds, discussion of matter transformation is treated at the substance level rather than in terms of the combination and recombination of atoms. The ideas given least attention are those that relate to the conservation and cycling of matter and energy. 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. The student text describes Jan Van Helmont’s experiment (from which he concluded that water is responsible for the increase in mass of a growing tree) and explains the role of carbon dioxide:
Van Helmont carefully found the mass of a pot of dry soil and a small seedling. Then he planted the seedling in the pot of soil. He took care of it and watered it regularly for five years. At the end of five years, the seedling, which by then was a small tree, had gained about 75 kilograms. However, the mass of the soil was almost unchanged. Van Helmont concluded that most of the mass must have come from water because that was the only thing that he had added to the pot.
Van Helmont’s experiment accounts for the hydrate, or water, portion of the carbohydrate produced by photosynthesis. But where does the carbon of the carbo portion come from? Although Van Helmont did not realize it, carbon dioxide in the air made a major contribution to the mass of his tree. And it is the carbon in carbon dioxide that is used to make carbohydrates in photosynthesis. Even though Van Helmont had only part of the story, he had made a major contribution to science.
p. 114s
The text then states the idea and presents the symbolic and word equations for photosynthesis:
The experiments performed by Van Helmont, Priestley, Ingenhousz, and other scientists reveal that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen. This gives us the basic outline of the process of photosynthesis:
light CO2 + H2O → (CH2O)n + O2 light carbon dioxide + water → carbohydrate + oxygen p. 115s
Teacher notes provide the following questions for teachers to ask students:
- What one important ingredient in photosynthesis did none of these three scientists recognize? (Carbon dioxide.)
- Why is carbon dioxide essential in the process of photosynthesis? (It provides the carbon for carbohydrate.)
p. 114t
At the end of the book, in the context of describing the flow of energy in food webs, the text repeats the idea:
During photosynthesis, green plants and certain bacteria trap sunlight and use it to assemble carbon dioxide and water into carbohydrates. Because photosynthetic organisms are able to make their own food from inorganic substances, they are called producers.
p. 1021s
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 an incomplete content match to this idea. The following presentation of Idea b1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Biology by Miller and Levine: Plants [autotrophs] 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.
The ideas of breakdown and storage are presented as separate fragments in different chapters. The text states the idea that autotrophs break down sugars in its introduction to cellular respiration (although the emphasis is on transformation of energy rather than matter):
The ability of autotrophs to produce glucose and other food molecules reflects the fact that photosynthesis is able to trap some of the energy of sunlight in chemical bonds. In a way, the energy stored by photosynthesis is like money deposited in a savings account: It is available for future needs. But organisms—autotrophs and heterotrophs alike—must be capable of making “withdrawals” from that savings account; that is, they must be able to release energy by breaking down food molecules. In this section we will examine two processes used to release energy from glucose.
Glucose (C6H12O6) is a simple 6-carbon sugar. If glucose is broken down completely in the presence of oxygen, carbon dioxide and water are produced:
C6H12O6 + 6O2 → 6CO2 + 6H2O glucose + oxygen → carbon dioxide + water p. 123s
The idea that plants store sugars is mentioned in Chapter 4: The Chemical Basis of Life in the context of presenting information about carbohydrates:
One important polysaccharide is starch. Plants store excess sugar in the form of starch, which is present in potatoes and grains. Starch is a very large molecule formed by joining together hundreds of glucose molecules.
p. 71s
The idea is mentioned again in two chapters at the end of the book. In Chapter 39: Nutrition and Digestion, the text notes that “Plants and animals store sugars as polysaccharides, long chains of monosaccharides” (p. 858s). In Chapter 47: The Biosphere, the text introduces the flow of energy in ecosystems with a statement about energy storage: “Approximately one half of the energy plants absorb from the sun is used immediately. The rest is stored in plant tissues in the form of energy-containing compounds (carbohydrates)” (p. 1021s).
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) and what alternative vocabulary is used (in brackets) in Biology by Miller and Levine: Other organisms [heterotrophs] 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.
Fragments of the idea are presented in different parts of the textbook but the complete idea is never treated. The text states the idea that heterotrophs break down sugars in its introduction to cellular respiration (although the emphasis is on transformation of energy rather than matter):
The ability of autotrophs to produce glucose and other food molecules reflects the fact that photosynthesis is able to trap some of the energy of sunlight in chemical bonds. In a way, the energy stored by photosynthesis is like money deposited in a savings account: It is available for future needs. But organisms—autotrophs and heterotrophs alike—must be capable of making “withdrawals” from that savings account; that is, they must be able to release energy by breaking down food molecules. In this section we will examine two processes used to release energy from glucose.
Glucose (C6H12O6) is a simple 6-carbon sugar. If glucose is broken down completely in the presence of oxygen, carbon dioxide and water are produced:
C6H12O6 + 6O2 → 6CO2 + 6H2O glucose + oxygen → carbon dioxide + water p. 123s
The idea that animals store glucose is mentioned in Chapter 4: The Chemical Basis of Life. In the context of presenting information on carbohydrates, the text notes that “Animals store their excess sugar in the form of glycogen in the liver and muscles” (p. 71s). The idea that humans store extra energy as fat is presented in Chapter 39: Nutrition and Digestion (although the emphasis is on energy storage rather than on matter transformation):
Fats provide twice as many calories per gram as carbohydrates. For that reason, fats are an excellent way to store energy for future use. When a person eats more food than is needed, the body stores the extra energy by producing fat.
p. 862s
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 by Miller and Levine: 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.
The text illustrates the idea that elements are recycled in its presentation of the nitrogen and carbon cycles:
Certain bacteria that live on roots of plants such as legumes...change free nitrogen in the atmosphere into nitrogen compounds...that can be used by living things....plants use them to make plant proteins. Animals then eat the plants and use the proteins to make animal proteins. When the plants and animals die, the nitrogen compounds return to the soil.
Eventually, other bacteria in the soil break down these nitrogen compounds....free nitrogen is returned to the atmosphere.
pp. 1024–1025s
The process by which carbon is moved through the environment is called the carbon cycle. During photosynthesis, green plants and algae use carbon dioxide from the atmosphere to form glucose. Consumers and decomposers use glucose in respiration, during which they produce carbon dioxide. Carbon dioxide is then released into the atmosphere, completing the carbon cycle.
p. 1025s
Teacher notes instruct teachers to point out the 20 substances that “must be present in an ecosystem if important life processes are to take place” (p. 1024t) and to indicate that these substances are recycled. However, the idea is presented in terms of recycling of substances rather than in terms of the repeated combination and recombination of atoms and the text is not explicit about these substances making up living things.
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. The idea is first stated in introducing the concept of photosynthesis:
In the process of photosynthesis, plants convert the energy of sunlight into the energy in the chemical bonds of carbohydrates—sugars and starches. Put another way, plants use the energy of sunlight to produce carbohydrates in a process called photosynthesis.
p. 113s
Teachers are encouraged to develop the idea of energy transformation by having students identify what a light bulb, a flashlight battery, and a small green plant have in common. Teachers are to point out that “the plant captures sunlight and changes it into stored chemical energy” (p. 113t). The text takes the idea to the molecular level in introducing glycolysis: “The ability of autotrophs to produce glucose and other food molecules reflects the fact that photosynthesis is able to trap some of the energy of sunlight in chemical bonds” (p. 123s). Finally, the chapter summary restates the idea: “In the process of photosynthesis, green plants capture the energy in sunlight and convert it into chemical energy” (p. 133s).
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 parts of this idea, which is presented in fragments in two widely separated chapters. 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 Biology by Miller and Levine: Plants get energy to grow and function by oxidizing [breaking down] the sugar molecules. Some of the energy is released as heat.
In its introduction to glycolysis and respiration, the text presents the idea that autotrophs get energy by releasing energy stored in glucose:
But organisms—autotrophs and heterotrophs alike—must be capable of making “withdrawals” from that savings account; that is, they must be able to release energy by breaking down food molecules. In this section we will examine two processes used to release energy from glucose.
...If glucose is broken down completely in the presence of oxygen, carbon dioxide and water are produced:
C6H12O6 + 6O2 → 6CO2 + 6H2O glucose + oxygen → carbon dioxide + water This reaction gives off 3811 calories per gram of glucose....
p. 123s
The idea that energy is released as heat is presented in the context of ecological pyramids (though plants are not mentioned explicitly):
Ecologists use ecological pyramids to represent the energy relationships among trophic levels. There are three types of ecological pyramids. A pyramid of energy shows the total amount of incoming energy at each successive level. Notice in Figure 47–15 [sic] that energy (in the form of heat) is lost going from one trophic level to another.
p. 1022s
Figure 47–16 lists the Net Production of Producers as 20,809 and the Net Production of Herbivores as 3368 (p. 1023s).
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 most of this idea. However, the idea is not treated as a whole but rather as individual parts. 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 by Miller and Levine: Other [human] organisms break down the consumed [food] body structures to sugars and get energy to grow and function by oxidizing their food, releasing some of the energy as heat.
The part of the idea that other organisms break down food to sugars is treated only in the context of digestion in humans:
The first task of the digestive system is to break down food into a fine pulp. When food is in the form of a fine pulp, its surface area is increased and more food molecules are exposed to the action of digestive chemicals. The next task of the digestive system is to chemically act on the food, breaking it down into smaller and smaller molecules. For example, starches must be reduced to simple sugars before the cells of the body can oxidize them for energy.
p. 867s
The idea that living things get energy from glucose is described in the context of cell metabolism, but not related to digestion in organisms:
But organisms—autotrophs and heterotrophs alike—must be capable of making “withdrawals” from that savings account; that is, they must be able to release energy by breaking down food molecules. In this section we will examine two processes used to release energy from glucose.
...If glucose is broken down completely in the presence of oxygen, carbon dioxide and water are produced:
C6H12O6 + 6O2 → 6CO2 + 6H2O glucose + oxygen → carbon dioxide + water This reaction gives off 3811 calories per gram of glucose....
p. 123s
The idea that energy is released as heat is presented in the context of ecological pyramids (though other organisms are not mentioned explicitly):
Ecologists use ecological pyramids to represent the energy relationships among trophic levels. There are three types of ecological pyramids. A pyramid of energy shows the total amount of incoming energy at each successive level. Notice in Figure 47–15 [sic] that energy (in the form of heat) is lost going from one trophic level to another.
p. 1022s
Figure 47–16 lists the net production of herbivores as 3368; primary carnivores, as 383; and secondary carnivores, as 21 (p. 1023s).
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. The following presentation of Idea d2 shows which parts of the idea are treated (in bold) in Biology by Miller and Levine: 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 states the first part of the idea in the context of introducing energy flow in ecosystems:
One of the most important factors in any ecosystem is the flow of energy through the ecosystem. Of all the sun’s energy that reaches the Earth’s surface, only a small amount—approximately 0.1 percent on a worldwide basis—is used by living things. Yet this amount, as small as it is, is responsible for the production of several thousand grams of organic matter per square meter of forest per year.
Approximately one half of the energy plants absorb from the sun is used immediately. The rest is stored in plant tissues in the form of energy-containing compounds (carbohydrates). Animals that eat the plants obtain this energy. But because the animals must use much of this energy to carry on their life activities, they store an even smaller amount. Energy cannot be recycled, or used again. Thus energy in an ecosystem is referred to as a flow rather than a cycle.
p. 1021s
The idea is then stated in more sophisticated terms and coupled with the idea that energy is lost as heat:
Each step in this series of organisms eating other organisms is called a trophic, or feeding, level. The term trophic comes from the Greek word trophe which means food. There is no limit to the number of trophic levels in a particular ecosystem. However, at each higher trophic level, less and less of the energy originally captured by the producers is available. This is because the energy obtained from digested food is used to maintain the metabolism of the organism and to power its daily activities. A small amount of the energy taken in by herbivores (primary consumers) is changed into new animal biomass. Biomass is the total mass of all the organisms in a trophic level.
As a rule, approximately 10 percent of the energy at one trophic level can be used by animals at the next trophic level. Thus 10 percent of the energy in plants becomes stored in the tissues of herbivores, and 10 percent of the energy in herbivores becomes stored in the tissues of carnivores. At each successive trophic level, less energy is available to an organism.
Ecologists use ecological pyramids to represent the energy relationships among trophic levels. There are three types of ecological pyramids. A pyramid of energy shows the total amount of incoming energy at each successive level. Notice in Figure 47–15 [sic] that energy (in the form of heat) is lost going from one trophic level to another.
p. 1022s
Concept Mastery questions at the end of the chapter ask students to apply the idea that energy decreases at each trophic level (p. 1031s, questions 2 and 3).
The second part of the idea—that continual input of energy from sunlight keeps the process going—is not explicitly presented.
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.
Building a Case
While most of the key ideas are asserted without evidence, the textbook provides some evidence for the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1). The text description of photosynthesis begins by stating the question: “When a seedling with a mass of only a few grams grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from? From the soil? From the water? From the air?” (p. 113s). The text then describes Van Helmont’s experiment and how it supported his (incorrect) conclusion that the mass of the tree comes largely from the water (p. 114s). The (correct) conclusion—that most of the mass comes from carbon dioxide in the air—is then asserted without evidence.
The text also presents evidence for the idea that plants produce oxygen, through a brief description of Priestley’s experiment (p. 114s), and mentions that Ingenhousz showed that oxygen is only produced in the presence of light (p. 114s).
In the next section, the text links the work of the three scientists to the equation for photosynthesis:
The experiments performed by Van Helmont, Priestley, Ingenhousz, and other scientists reveal that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen. This gives us the basic outline of the process of photosynthesis:
light CO2 + H2O → (CH2O)n + O2 light carbon dioxide + water → carbohydrate + oxygen p. 115s
However, this treatment leaves out much evidence and does not provide a complete argument for either the equation or this key idea.
Connections
The set of key ideas on matter and energy transformations is highly complex, spanning four levels of biological organization (molecular, cellular, organism, 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 by Miller and Levine presents the key ideas or parts of the key ideas as text assertions in different chapters and does not tie these presentations together. For example, the idea that plants store sugars is mentioned several times—first in the context of biochemistry, next in the context of cellular respiration, then in the context of human nutrition and digestion, and finally in the context of ecosystems. However, the same idea is merely restated, not used to relate the various levels of biological organization to one another. For example, no mention is made of the fact that much of the world’s food supply comes from plants’ ability to store glucose for later use. And no mention is made in the text presentation of monocots and dicots, which shows the cotyledons on a newly sprouted bean plant, that the cotyledon stores the food that the parent plant made during photosynthesis (p. 475s). The idea that plants use the sugars they have synthesized to make other molecules or other structures is not mentioned, even though Chapter 22: Plants with Seeds presents information on roots, stems, and leaves (pp. 468–469s), xylem and phloem (p. 469s), and flowers and cones, pollination, and seeds (p. 470s).
Matter. Most of the key ideas about matter transformation are presented in the text, but they are presented as unconnected fragments in different chapters. For example, the text presents the idea that plants break down sugar molecules (p. 123s) but does not indicate that the sugar molecules broken down are those it made in photosynthesis. Similarly, the text indicates that plants convert “excess sugar” to starch (p. 71s) but does not indicate that the excess sugar is what the plant made in photosynthesis. And the text never mentions that glucose molecules are used as building materials for plants. Similarly, the idea that animals break down sugars is presented in the context of cellular respiration (p. 115s), which is widely separated from ideas about human digestion (p. 867s) and energy storage (p. 862s). The text does make a connection between a part of Ideas b1 and c1 by comparing how plants and animals store excess sugar:
POLYSACCHARIDES Very large molecules can be formed by joining together many monosaccharide units. Such compounds are known as polysaccharides. Polysaccharides are the form in which living things store excess sugar. One important polysaccharide is starch. Plants store excess sugar in the form of starch, which is present in potatoes and grains. Starch is a very large molecule formed by joining together hundreds of glucose molecules. Animals store their excess sugar in the form of glycogen in the liver and muscles. Glycogen is an even larger molecule consisting of hundreds or even thousands of glucose molecules. Glycogen is sometimes called animal starch. Do you see why? Because they are polymers of single sugars, both starch and glycogen help store energy in living things.
p. 71s
However, the text does not explain why plants or animals would need to store sugar.
The text presents prerequisite and other ideas related to matter transformations in Chapter 4: The Chemical Basis of Life. In describing chemical compounds in living things, the text presents the idea that “Carbon and hydrogen are common elements of living matter” and most of the idea that “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, calcium, sodium, potassium, and iron”:
Although the Earth’s crust contains 90 naturally occurring chemical elements, only 11 of these elements are common in living organisms. Another 20 are found in trace amounts. Just four elements—carbon, nitrogen, oxygen, and hydrogen—make up 96.3 percent of the total weight of the human body. In varying combinations, the elements carbon, hydrogen, oxygen, and nitrogen make up practically all the chemical compounds in living things.
p. 68s
The text then presents the idea that “Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules,” though it embeds the idea amidst details of bonding and energy levels:
Carbon is a unique element because of its remarkable ability to form covalent bonds that are strong and stable. You will recall that covalent bonds involve the sharing of electrons. Carbon has 6 electrons, 2 in the first energy level and 4 in the second. So only 4 of the 8 positions in its outermost energy level are filled. This means that carbon can form four single covalent bonds. The simplest compound that can be formed from carbon is methane, CH4. Carbon can also form covalent bonds with oxygen, nitrogen, phosphorus, and sulfur atoms. The ability to bond easily and form compounds with these common elements would be enough to make carbon an interesting element. But there’s more!
Carbon can form chains of almost unlimited length by bonding to other carbon atoms. The bonds between carbon atoms in these straight chains can be single, double, or triple covalent bonds—or combinations of these bonds. No other element can equal carbon in this respect. These chains can be closed on themselves to form rings. The ring structures may include single or double bonds, or a mixture of both. This gives even more variety to the kinds of molecules that carbon can form. See Figure 4–9.
pp. 68–69s
However, no link is made between these related ideas or between them and any key ideas. For example, the idea that “Carbon and hydrogen are common elements of living matter” is not related to the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1). The text does not, for instance, indicate that the sugars (and molecules derived from them) contain lots of carbon, which is why carbon is such a common element of living matter. Similarly, when the text describes how plants make sugars from carbon dioxide and water (p. 115s), it does not relate this to the bonding capability of carbon. And when the text mentions how plants and animals store glucose, it does not relate its storage potential to the ability of carbon to form chains and rings:
One important polysaccharide is starch. Plants store excess sugar in the form of starch, which is present in potatoes and grains. Starch is a very large molecule formed by joining together hundreds of glucose molecules.
p. 71s
And even though the book presents information in Chapter 3: Introduction to Chemistry on the structure of atoms and the bonding between them (pp. 47–54s), it does not make use of this information in its later presentation of matter cycling in ecosystems, which presents biogeochemical cycles in terms of substances rather than in terms of the combination and recombination of atoms of these elements (pp. 1023–1025s).
The prerequisite idea that food provides fuel and building materials is presented late in the book in the context of human nutrition and digestion (p. 856s) and teachers are instructed to emphasize the dual role of food:
Emphasize to students that food must serve the body in two ways. First, it must provide energy in the form of calories. Second, it must provide specific substances that are needed for body growth, maintenance, and repair. Point out that if the body needed only calories for energy, it would not really matter if a person ate a chocolate bar or a steak. Yet because the body requires various substances that are found in certain groups of foods, the type of food a person eats is of great importance.
pp. 856–857t
However, food is not treated at the molecular level here and not related to ideas about photosynthesis and respiration, which were presented much earlier (pp. 115s and 123s).
Energy. As with matter, ideas about energy transformation are presented in widely separated chapters and are rarely tied together. Ideas about the transformation of the sun’s energy into chemical energy and the release of that energy by plants and other organisms are presented at the cellular level (p. 123s) but are not related to the cell parts where these processes occur. When the location of energy transformation processes is mentioned, it is related only to the energy needs of living things, not to the transformations that must occur within them:
All living things require a reliable source of energy. On Earth that source is usually the sun or food substances. The mitochondrion...and the chloroplast are key organelles that change energy from one form to another. Mitochondria change the chemical energy stored in food into compounds that are more convenient for the cell to use. Chloroplasts trap the energy of sunlight and convert it into chemical energy.
p. 94s
In its presentation of human digestion, the text briefly relates the breakdown of food to sugars in the human digestive system to its subsequent oxidation to release energy:
The first task of the digestive system is to break down food into a fine pulp. When food is in the form of a fine pulp, its surface area is increased and more food molecules are exposed to the action of digestive chemicals. The next task of the digestive system is to chemically act on the food, breaking it down into smaller and smaller molecules. For example, starches must be reduced to simple sugars before the cells of the body can oxidize them for energy.
p. 867s
However, the text does not relate the processes of photosynthesis and respiration more generally to the functioning of plants or animals. And the release of heat that accompanies these processes is presented only in the context of energy pyramids in ecosystems (pp. 1021–1023s).
Only one prerequisite idea about energy transformation in physical systems is presented and related to key ideas about energy transformation in plants (Idea a2) and organisms that consume them (Idea c2). In presenting information about energy flow in ecosystems, teachers are instructed to remind students about energy conservation:
It is important for students to understand that although energy flows out of an ecosystem, it is not “lost” in the sense that it disappears. Students should be reminded that energy is neither created nor destroyed: it simply changes form. Thus the energy that enters an ecosystem in the form of radiant energy from the sun is converted into potential chemical energy by photosynthesis. The chemical energy stored in food is then converted into mechanical, heat, and other forms of energy by the organisms that eat the food.
pp. 1022–1023t
Other prerequisites are not presented or linked to key ideas.
Matter and Energy. The text does not effectively relate matter and energy. Mostly it presents key ideas in terms of energy transformations, with only an occasional mention of matter. Given that ideas about energy transformation are more abstract than those about matter transformation, students may be quite confused. For example, the following paragraphs are likely to leave students with the impression that matter and energy can be interconverted in living systems:
...at each higher trophic level, less and less of the energy originally captured by the producers is available. This is because the energy obtained from digested food is used to maintain the metabolism of the organism and to power its daily activities. A small amount of the energy taken in by herbivores (primary consumers) is changed into new animal biomass. Biomass is the total mass of all the organisms in a trophic level.
As a rule, approximately 10 percent of the energy at one trophic level can be used by animals at the next trophic level. Thus 10 percent of the energy in plants becomes stored in the tissues of herbivores, and 10 percent of the energy in herbivores becomes stored in the tissues of carnivores. At each successive trophic level, less energy is available to an organism.
p. 1022s
Beyond Literacy
The text goes far beyond the sophistication level of the key ideas, which is considered by both Benchmarks for Science Literacy (AAAS, 1993) and the National Science Education Standards (NRC, 1996) to be the level appropriate for science literacy. For instance, after a basic presentation of the main points of photosynthesis, the text presents many of the intricate details of the light reactions and the Calvin cycle (pp. 118–122s). These advanced ideas and terms also serve to interrupt the flow of key ideas about photosynthesis and make it more difficult to relate them to key ideas about respiration. When the text picks up with respiration, the major concepts of matter and energy transformations have been interrupted by new ideas of electron energy levels and transport chains, and even physics concepts such as light absorption by different types of pigments.
