Biology: Principles & Explorations. Holt, Rinehart and Winston, 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: Principles & Explorations treats most of these ideas and distributes them over several chapters: Chapter 2: Nature of Cells, Chapter 5: Photosynthesis and Cellular Respiration, Chapter 16: Ecosystems, and Chapter 38: Digestive and Excretory Systems [in humans]. 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 conservation and 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, which is treated in the text only. No discussions or investigations focus on this idea. The idea is introduced in the context of describing cellular organelles:
Chloroplasts are organelles that make food in the form of sugars, using water, carbon dioxide in the air, and energy from sunlight. This process is called photosynthesis. Chloroplasts are found only in algae...and plants....
p. 45s
Later, in the context of describing photosynthesis and cellular respiration in chapter 5, the text develops the idea at the molecular level:
The carbon atoms needed to make all the organic molecules of living things ultimately come from a nonliving part of the environment. During photosynthesis, carbon atoms are pulled from the carbon dioxide gas, CO2, in air and used to form carbohydrates and other organic compounds. These materials are made, step by step, in biochemical pathways that are powered by transferring hydrogen atoms from one reaction to the next. The hydrogen atoms needed for these pathways are extracted from water molecules, H2O. Leftover oxygen atoms combine to form oxygen gas, O2, as a byproduct.
p. 95s
After describing how energy is stored in carbon compounds, the text then devotes nine pages to biochemical details that go well beyond the key idea (pp. 98–106s). In addition, all of the chapter review questions focus on the biochemical details rather than on the application of the key idea (pp. 113–115s).
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 in the text, but no discussions or investigations focus on it. The text introduces the idea in the context of cellular respiration:
During cellular respiration, hydrogen atoms are pulled from carbohydrates and joined with oxygen atoms from oxygen gas, forming water. In biochemical pathways, the carbon chains of carbohydrates and other organic molecules are systematically dismantled....Carbon atoms that are split from carbohydrates are linked to oxygen gas, forming carbon dioxide gas as a byproduct.
p. 96s
The text then connects what is happening to the molecules to the lives of plants:
Sugars can be transported from leaves to other parts of a plant. In that way, parts of a plant that are not exposed to light, such as roots, are supplied with carbohydrates....
Plants also use sugar molecules made during photosynthesis for making other organic molecules, such as proteins, lipids, nucleic acids, and other carbohydrates....
Plants usually produce more sugars by photosynthesis than they can immediately use. Excess sugar is stored for future uses such as providing energy for the next day’s activities or for rapid growth in the spring.
Plants mainly convert excess sugar to starch for both short-term and long-term storage.
p. 96s
After giving biochemical details of photosynthesis, the text describes and represents the biochemical reactions of glycolysis, the Krebs cycle, and the electron transport chain, which go well beyond the key idea (pp. 107–110s). The only relevant chapter review questions focus on terms or biochemical details (pp. 113–115s, questions 6, 7, 8, 9, 11, and 12) rather than applying the key idea.
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. Fragments are presented in different parts of the textbook but the complete idea is not presented in a single place.
In the context of discussing the flow of energy through ecosystems, the text states the first part of the idea and gives examples:
At the second trophic level are herbivores, animals that eat plants. They are the primary consumers in ecosystems. Cows and horses are herbivores, as are caterpillars and ducks. A herbivore must be able to break down the plant’s molecules. Simple sugars and starches present no problem, but the digestion of cellulose, a molecule made of sugar units linked together, is a chemical feat that only a few organisms have evolved the ability to perform.
pp. 343–344s
However, the focus is on breaking down molecules to release energy stored in them rather than obtaining necessary building materials. There is no specific mention of the breakdown to simpler structures or the production of energy stores.
Even in the context of presenting the human digestive and excretory systems, the focus is on breaking down food into simpler substances so that cells can extract energy (but not building materials) from them:
Your cells obtain the energy they need by extracting it from sugars, fatty acids, and amino acids during cellular respiration. Eating a plant or an animal provides you with a rich source of complex starches, fats, and proteins. These molecules occur as long chains composed of individual sugars, fatty acids, or amino acids, like strings of beads. Your cells cannot extract energy from these large chains. First, these large molecules must be broken down into their individual components during a process called digestion.
p. 904s
The idea that digestion products are used for building materials is mentioned in the chapter introduction: “In addition to providing energy, the food you eat provides raw materials that your body uses to manufacture molecules for its own use” (p. 899s). The introduction goes on to note briefly that proteins are used “mainly as building materials for cell structures, enzymes, hormones, muscles, and bones” and that fats are used “to construct cell membranes and other cell structures....” (p. 900s).
The idea that other organisms use (though not reassemble) carbohydrates appears in teacher notes in a suggested response to a chapter review question:
Question: Energy flow in an ecosystem is described in terms of the activities of producers, consumers, and decomposers. What is the role of each of these in the carbon cycle?
Suggested Response: Producers, such as plants, use carbon dioxide to build carbohydrates. They also release carbon dioxide when carbohydrates are broken apart during respiration. Consumers take in carbon as carbohydrates when they eat foods and use the carbohydrates to build their own bodies....
pp. 357s and 356–357t, question 28
The idea that humans store energy as fat is presented in the context of describing how the body uses carbohydrates, fats, and proteins: “Although fats may be used as an energy source by cells, fats are also a very efficient way to store energy in the body. Calories that are not used by your body are converted into fat tissue” (pp. 900–901s).
The text discussion of the carbon cycle deals only with the exchange of carbon between carbon dioxide in the nonliving environment and the organic molecules that are made by photosynthesizing organisms (p. 351s).
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 text presents the carbon and nitrogen cycles but does not generalize to all elements that make up the bodies of living things. The following representation of Idea d1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Biology: Principles and Explorations: 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.
In the context of describing how photosynthesis and cellular respiration form a cycle, a sidebar instructs teachers to
Remind students that the materials needed to sustain life ultimately come from the environment. Living systems are efficient recycling factories. The materials (elements and compounds) needed to sustain life cycle through the biosphere in the processes of photosynthesis and cellular respiration.
p. 96t
Later, in the context of presenting materials cycling in ecosystems, the text states, “Unlike energy, which flows through the Earth’s ecosystems in one direction (from sun to producers to consumers), the physical components of ecosystems often cycle constantly” (p. 349s). The text then describes how water, carbon, nitrogen, and phosphorus cycle (pp. 349–352s) and does so in terms of the combination and recombination of atoms. For example, in the context of presenting the carbon cycle the text states:
Carbon dioxide in the air or dissolved in water is used by photosynthesizing plants, algae, and bacteria as a raw material to build organic molecules. In effect, they trap the carbon atoms of carbon dioxide within the living world. Carbon atoms return to the pool of carbon dioxide in the air and water in three ways....
p. 351s
Energy is transformed in living systems.
Idea a2: Plants transfer the energy from light into “energy-rich” sugar molecules.
There is a content match to this idea, which is treated mainly in the text. In the context of describing cell parts and functions, a figure legend introduces the idea that “Chloroplasts in green plants capture sunlight, which enables them to make sugars. These sugars are the ultimate source of energy for all living things” (p. 45s).
An accompanying teacher note instructs teachers to “Use this figure to emphasize that the sun is the source of energy of most of life on Earth. The energy-requiring reactions of photosynthesis transform sunlight energy into chemical energy” (p. 45t).
The idea that plants transform the sun’s energy into chemical energy is presented again, though this time in the context of details about energy states of electrons:
[A]lmost all of the energy for living systems comes from the sun. Energy from the sun enters living systems when sunlight is absorbed by molecules found in plants, algae, and certain bacteria. In the process, electrons in these molecules are boosted to higher energy states. Like a boulder on top of a hill, an electron that has been boosted to a higher energy state has additional energy because it is farther away from the nucleus of an atom....
Organisms that harvest energy by boosting electrons use it to produce energy-storing macromolecules. Most of these organisms boost electrons with energy from sunlight and convert light energy into chemical energy. The process that converts light energy to chemical energy is called photosynthesis.
p. 77s
Students are expected to appreciate that some of the sun’s energy is stored in the newly synthesized sugars, as indicated by the suggested response to a chapter review question:
Question: What roles do photosynthesis and cellular respiration play in the flow of energy through living systems?
Suggested Response: Photosynthesis traps the energy of sunlight, storing it in sugars....
p. 79st, question 3
In the next chapter, the text explains that “energy is stored in carbon compounds” in the context of describing how energy cycles in photosynthesis and cellular respiration:
Some of the energy that is required to link carbon atoms together is stored within the resulting molecules. In plants carrying out photosynthesis, energy from sunlight is stored within newly made carbohydrate molecules such as sugars.
p. 96s
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 describing how energy is stored in carbon compounds, the text indicates that plants get energy for activity and growth from cellular respiration:
Some of the energy that is required to link carbon atoms together is stored within the resulting molecules. In plants carrying out photosynthesis, energy from sunlight is stored within newly made carbohydrate molecules such as sugars. Sugars can be transported from leaves to other parts of a plant. In that way, parts of a plant that are not exposed to light, such as roots, are supplied with carbohydrates. Later, the energy in sugars can be converted to ATP by cellular respiration, making energy for metabolic activities available to root cells....
Plants usually produce more sugars by photosynthesis than they can immediately use. Excess sugar is stored for future uses such as providing energy for the next day’s activities or for rapid growth in the spring.
p. 96s
The last part of the idea—that some of the energy is released as heat—is presented as a generalization (though it is never explicitly related to plants). For example, in the context of a brief explanation of the second law of thermodynamics, the text states that “Not all of the potential energy in food is recovered when it is transformed into kinetic energy. Almost half escapes into the environment as heat (thermal energy transferred by moving particles)” (p. 77s).
In another context, the text notes that “Every transfer of energy within an ecosystem dissipates energy as heat” (p. 345s) and gives as examples of heat loss the harvesting of the sun’s energy and the conversion by herbivores of energy stored in plants (p. 345s). The text neither connects the generalization to the oxidation of the sugar by plants, nor does it explicitly state that in converting the sugars they have made, plants also lose much of the energy as heat.
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. However, the idea is not treated as a whole but rather as individual parts.
The part of the idea that other organisms break down food to sugars is treated only in the context of digestion in humans:
Your cells obtain the energy they need by extracting it from sugars, fatty acids, and amino acids during cellular respiration. Eating a plant or an animal provides you with a rich source of complex starches, fats, and proteins. The molecules occur as long chains composed of individual sugars, fatty acids, or amino acids, like strings of beads. Your cells cannot extract energy from these large chains. First, these large molecules must be broken down into their individual components during a process called digestion.
p. 904s
A figure illustrates the idea that more complex molecules are broken down into simpler molecules, but the legend and accompanying text focus on the details rather than the key idea. Similarly, the rest of the section on digestion emphasizes details and terms.
The idea that living things get energy to grow and function by burning (but not oxidizing) fuel is described in the context of cell metabolism, but not related to digestion in organisms:
Each of the significant properties we use to define life—growth, movement, reproduction, heredity—uses energy. To sustain life, energy must be continually supplied (like putting more logs on a fire) and converted into useful forms (like boiling water for cooking). But unlike burning wood in a fire, energy must be released slowly to prevent living cells from burning up. The energy must also be released in such a way that it can be put to use doing the work of cells....
p. 85s
However, in the context of describing the carbon cycle the text presents the idea that organic molecules are oxidized during cellular respiration: “Nearly all living organisms, including plants, perform cellular respiration. They use oxygen to oxidize organic molecules during cellular respiration, and carbon dioxide is a byproduct of this reaction” (p. 351s).
The previous quote also makes clear that other organisms (not just humans) carry out cellular respiration (p. 351s). That other organisms also give off energy as heat is presented in the context of describing energy flow in ecosystems:
The deer that you see browsing on leaves in Figure 16-10 is busy acquiring energy. There is potential energy in the leaves, stored in the chemical bonds within their molecules. What happens to a leaf’s energy after the deer consumes it? You can see what happens to the energy in Figure 16-10. Some of the energy is transformed to other forms of potential energy, such as fat. Another portion accomplishes mechanical work such as running, breathing, and eating more leaves. However, almost half is dissipated to the environment as heat.
p. 345s
Also, a diagram that appears earlier in the text indicates that rabbits carry out cellular respiration and give off heat (p. 78s, Figure 4-4).
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 representation of Idea d2 shows which parts of the idea are treated (in bold) in Biology: Principles and Explorations: 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 mentions the concept of heat loss in a figure legend in the context of introducing energy flow in ecosystems:
Energy flows through an ecosystem from sunlight or inorganic chemicals to autotrophs and then to heterotrophs. Because some heat escapes with every energy conversion, much of the energy captured by autotrophs eventually flows out of living systems.
p. 78s
The instructor is then advised to “Trace the flow of energy through the ecosystem shown in the figure. Emphasize the dissipation of heat at each level” (p. 78t). However, no mention is made that at each step some energy is stored in newly made structures.
The second part of the idea—that continual input of energy from sunlight keeps the process going—is not presented here. Instead, the text presents the less sophisticated idea that the sun is the ultimate source of energy: “All organisms need a constant supply of energy to fuel the activities of life. Directly or indirectly, almost all of the energy for living systems comes from the sun” (p. 77s).
In the context of describing ecosystems, a figure legend again indicates that the sun is the ultimate source of energy but not that continual input of energy is needed to keep the process going (p. 343s). (While a teacher note is explicit about the idea of continual input—“An ecosystem is self-sustaining only if there is a continuous flow of energy into it. The energy flow is always one-way, originating as radiant energy emitted by the sun....” [p. 336t]—there is no indication that this information is to be conveyed to students.)
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.
The idea that living things share physical principles with nonliving systems is implied in examples given in the text, but is not explicitly stated. The chapter on energy and metabolism (chapter 4) begins with a reference to physics: “Energy may sound like a topic that belongs in a physics course, but it is vital to living things” (p. 75s). It then presents the idea that energy can be transformed, giving examples of energy transformations in the physical setting (e.g., potential to kinetic energy as a boulder rolls downhill, electric to mechanical energy in an electric fan, chemical to mechanical energy and heat as gasoline burns in a car’s engine) before moving to energy transformations in living things:
Much of the work done by living things involves energy transformation. When you use food as a source of energy for movement, you are converting chemical energy into mechanical energy. When you use food to help maintain your body temperature, you are converting chemical energy into thermal energy (the random movement of all particles of matter).
p. 76s
The conservation of energy principle is presented in the section on energy transformation but only implies that conservation principles apply to living organisms (an inference from the statement that says an organism is a system) and does not include matter:
All energy conversions are governed by the laws of thermodynamics, the study of energy transformations. One of these laws describes the observation that the total amount of energy in a closed system never changes. In science, a system is a collection of related objects (matter) that can be studied. For example, an organism is a system, as is the universe and Earth. No energy or matter can enter a closed system from the outside. The universe can be thought of as a closed system. A system that exchanges matter and energy with its surroundings (like Earth) is called an open system. The fact that the total amount of energy in a closed system remains constant is stated as the first law of thermodynamics: Energy cannot be created or destroyed; it can only be converted from one form to another.
p. 76s
The same is true for the Capsule Summary: “Energy can be changed from one of its forms to another. Energy cannot be created or destroyed” (p. 76s).
Much later in chapter 16 the text presents the cycling of matter idea: “Unlike energy, which flows through the Earth’s ecosystems in one direction (from sun to producers to consumers), the physical components of ecosystems often cycle constantly” (p. 349s). However, the text does not indicate that this is an instance that applies the principle of matter conservation (observed in physical systems) to living systems.
The idea that matter changes location repeatedly is explicit in the text presentation of materials cycling within ecosystems, but it is not explicitly linked to conservation:
The paths of water, carbon, nitrogen, and phosphorus, as they pass from the nonliving environment to living organisms and then back to the environment, form closed circles, or cycles, called biogeochemical cycles. In each biogeochemical cycle, a substance enters living organisms from the atmosphere, water, or soil, resides for a time in the organisms, then returns to the nonliving environment. Ecologists often speak of such substances as cycling within an ecosystem between a living reservoir (organisms that live in the ecosystem) and a nonliving reservoir. In almost all cases, there is much less of the substance in the living reservoir than in the nonliving reservoir.
p. 349s
Other parts of the idea are not treated.
Building a Case
Biology: Principles and Explorations asserts the key ideas, but it does not develop an evidence-based argument to support them. Only one phenomenon is used to illustrate a key idea (The phenomenon that “[A] large human population could not survive by eating lions captured on the Serengeti Plain of Africa” [p. 347s] is explained by the idea that “At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat....” [Idea d2]). After presenting and explaining this phenomenon, the text does not go on to make the case that the ability of Idea d2 to explain many such phenomena gives scientists confidence in the idea. And the text does not present data to demonstrate the loss that occurs at each level. No other phenomena are provided or explained by the key ideas to lend support for them.
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: Principles and Explorations mainly focuses on telling the energy side of the story, which is more abstract than the matter side. The energy ideas are introduced at the cell level (p. 45s), then presented in the context of thermodynamics (p. 77s), then in terms of the chemistry of photosynthesis (p. 96s), then at the ecosystem level (p. 343s), and finally in terms of human nutrition and digestion (p. 904s). Teachers are not alerted to these different places where energy ideas are treated nor is a rationale for this sequence conveyed. Given that students are more likely to be familiar with energy phenomena at the level of the human organism, the sequence followed in the text makes little sense. If the implied sequence is followed, a course might end without ever treating energy ideas in human organisms, relating human energy needs to processes occurring at molecular and cellular levels, or using processes of energy transformation in an individual organism to shed light on the sequence of such transformations in ecosystems.
Energy. Connections among key ideas. The text makes connections among many of the key ideas about energy transformation. For example, the text relates the idea that plants transfer the sun’s energy to energy-rich sugar molecules (Idea a2) (pp. 77s and 96s) to the idea that other organisms get energy to grow and function by “burning” their food, releasing some of the energy as heat (Idea c2) (p. 85s) in several ways. In its presentation of photosynthesis and cellular respiration, the text notes that “because they are rich in organic molecules that store energy, plants often serve as food for animals” and then discusses plant species cultivated for food (p. 96s). This connection is reinforced in the Capsule Summary and in the Connections notes to teachers:
Remind students that carbon compounds, which store the energy from boosted electrons in their bonds, are a transportable form of energy and that carbon compounds act as an energy supply conduit for the biosphere.
p. 96t
In introducing Chapter 26: Plants in Our Lives, the text notes that
Humans and other animals depend on the sugar that plants produce during photosynthesis. Certain plants produce far more sugar during photosynthesis than they can immediately use. Such plants store this extra sugar and use it later for activities such as spring growth. Plants with large energy stores are attractive to humans and other animals as food.
p. 591s
The text then illustrates various foods and the parts of the plant that they come from.
The text also relates the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2) to the idea that “Plants get energy to grow and function [from] sugar molecules” (part of Idea b2):
Some of the energy that is required to link carbon atoms together is stored within the resulting molecules. In plants carrying out photosynthesis, energy from sunlight is stored within newly made carbohydrate molecules such as sugars. Sugars can be transported from leaves to other parts of a plant. In that way, parts of a plant that are not exposed to light, such as roots, are supplied with carbohydrates. Later, the energy in sugars can be converted to ATP by cellular respiration, making energy for metabolic activities available to root cells....
Plants usually produce more sugars by photosynthesis than they can immediately use. Excess sugar is stored for future uses such as providing energy for the next day’s activities or for rapid growth in the spring.
p. 96s
And the text makes explicit that plants and other organisms share the main process of energy release. In the context of its presentation of the carbon cycle in ecosystems, the text states that “Nearly all living organisms...perform cellular respiration” and an accompanying diagram shows that both plants and a deer carry out respiration (p. 351s, Figure 16-16), thus relating Ideas b2 and c2.
The chapter on ecosystems also makes several connections between key ideas about energy transformation in organisms and energy transformation in ecosystems. For example, the chapter relates the failure of plants to harness all of the sun’s energy during photosynthesis (Idea a2) and the loss of heat by other organisms (part of Idea c2) to the dissipation of heat in ecosystems (Idea d2) (pp. 345–346s). However, the text makes only weak connections between the heat lost in plants (part of Idea b2) and other organisms (part of Idea c2) and the loss of energy in ecosystems (part of Idea d2): “Because some heat escapes with every energy conversion, much of the energy captured by autotrophs eventually flows out of living systems” (p. 78s).
Connections between key ideas and their prerequisites. The text makes few helpful connections between key ideas about energy transformation and their prerequisites. For example, in Chapter 4: Energy and Metabolism, the teacher’s guide characterizes chemical energy as “a form of potential energy due to the attraction between the nucleus and electrons....” (p. 78t) (rather than in terms of the arrangements of atoms) and the student text attempts to relate the idea to energy transformation in living things through a brief presentation of how energy is carried by electrons, including oxidation-reduction reactions (pp. 78–79s). Similarly, in its presentation of energy in chemical reactions, it uses a free-energy diagram to show that reactants and products (but not configurations of atoms and molecules) can have different amounts of energy (p. 81s). The text does state the prerequisite that “heat is almost always one of the products of an energy transformation,” but the presentation is too abstract to be helpful:
Not all of the potential energy in food is recovered when it is transformed into kinetic energy. Almost half escapes into the environment as heat (thermal energy transferred by moving particles). Thermal energy is generally not a useful form of energy. It can do work only when it is concentrated and can flow from one object to another. Many systems, including living systems, cannot concentrate thermal energy enough to make it do work. A burning match can ignite wood, for example, but the thermal energy of air molecules cannot.
The reason some thermal energy is lost as heat when energy is transformed is stated in another law that also governs energy conversions. The basis of this law is that all systems tend to change in ways that make them more stable....
p. 77s
This does not provide an adequate basis for the material’s later attempt to make a connection to heat loss in ecosystems (p. 345s).
The text also misses an opportunity to connect the oxidation of sugars by plants (Idea b2) and other organisms (Idea c2) to the prerequisite that “An especially important kind of reaction between substances involves combination of oxygen with something else—as in burning or rusting.” Although teachers are to demonstrate the burning of alcohol and then relate burning to cellular respiration, the material stops short of stating the prerequisite idea.
The text does make a connection between the prerequisite that “Energy can only change from one form into another” and the idea that “Other organisms...get energy to grow and function [from] food” (part of Idea c2):
Much of the work done by living things involves energy transformation. When you use food as a source of energy for movement, you are converting chemical energy into mechanical energy. When you use food to help maintain your body temperature, you are converting chemical energy into thermal energy (the random movement of all particles of matter).
p. 76s
The text also relates part of the prerequisite idea that “Food provides the molecules that serve as fuel...” to ideas about energy transformation in plants (Ideas a2 and b2) in Chapter 5: Photosynthesis and Cellular Respiration. In describing how energy cycles in these two processes, the text states:
Some of the energy that is required to link carbon atoms together is stored within the resulting molecules. In plants carrying out photosynthesis, energy from sunlight is stored within newly made carbohydrate molecules such as sugars. Sugars can be transported from leaves to other parts of a plant. In that way, parts of a plant that are not exposed to light, such as roots, are supplied with carbohydrates. Later, the energy in sugars can be converted to ATP by cellular respiration, making energy for metabolic activities available to root cells....
Plants usually produce more sugars by photosynthesis than they can immediately use. Excess sugar is stored for future uses such as providing energy for the next day’s activities or for rapid growth in the spring.
p. 96s
Much later, in the beginning of Chapter 38: Digestive and Excretory Systems, the text again states the prerequisite, “You obtain energy from the foods you eat to fuel your every activity” (p. 899s), and then connects it to the processes of digestion and cellular respiration (Idea c2):
Your cells obtain the energy they need by extracting it from sugars, fatty acids, and amino acids during cellular respiration. Eating a plant or an animal provides you with a rich source of complex starches, fats, and proteins. These molecules occur as long chains composed of individual sugars, fatty acids, or amino acids, like strings of beads. Your cells cannot extract energy from these large chains. First, these large molecules must be broken down into their individual components during a process called digestion.
p. 904s
Connections between key ideas and related ideas. While the text treats the related idea that “Within cells are specialized parts for the capture and release of energy” (pp. 44–45s), it does not relate this information to the processes in organisms (for example, it does not point out that cells with high-energy needs have lots of the parts for releasing energy from sugar molecules).
Matter. Connections among key ideas. Ideas about matter are introduced at the cell level (p. 45s), presented next in terms of the chemistry of photosynthesis and respiration (p. 96s), then in terms of matter cycles in ecosystems (pp. 349–352s), and finally in terms of the building materials food provides for human organisms (pp. 900s, 904s). While the text mentions some of the matter ideas, they are not well developed. Furthermore, matter is treated only at the substance level, even though atoms, molecules, and chemical bonds are introduced early on (pp. 29–31s). As noted above, the discussion of carbon, water, and nitrogen cycles does not convey that the Earth contains an essentially constant number of a few kinds of atoms that, like a kit of Legos or Tinkertoys, can combine and recombine (pp. 349–351s).
The text makes a brief connection between the key ideas about matter transformation in organisms (Ideas a1, b1, and c1) and ecosystems (Idea d1) in its presentation of the carbon cycle in ecosystems:
[Photosynthesizing plants, algae, and bacteria] trap the carbon atoms of carbon dioxide within the living world. Carbon atoms return to the pool of carbon dioxide in the air and water in three ways.
One way is through cellular respiration. Nearly all living organisms, including plants, perform cellular respiration. They use oxygen to oxidize organic molecules during cellular respiration, and carbon dioxide is a byproduct of this reaction....
p. 351s
An accompanying diagram indicates that plants and a deer carry out respiration, returning carbon dioxide to the atmosphere.
The text makes another connection between photosynthesis and respiration in plants (Ideas a1 and b1) in Chapter 5: Photosynthesis and Cellular Respiration (p. 96s).
Students are expected to make a connection between cellular respiration in plants (Idea b1) and other organisms in a Critical Thinking question at the end of Chapter 16: Ecosystems, as shown below in the phrase “[l]ike producers” in the answer in the teacher’s guide:
Question: Making Inferences Energy flow in an ecosystem is described in terms of the activities of producers, consumers, and decomposers. What is the role of each of these in the carbon cycle?
Suggested Response: Producers, such as plants, use carbon dioxide to build carbohydrates. They also release carbon dioxide when carbohydrates are broken apart during respiration. Consumers take in carbon as carbohydrates when they eat foods and use the carbohydrates to build their own bodies. Like producers, consumers release carbon to the air as carbon dioxide during respiration....
pp. 357s and 356–357t, question 28
Connections between key ideas and their prerequisites. The text makes one connection between a key idea and its prerequisite, but it is made quite late in the book. In the introduction to Chapter 38: Digestive and Excretory Systems, the text states the prerequisite that “Food provides molecules that serve as fuel and building materials...” (though it does not mention “for all organisms”):
In addition to providing energy, the food you eat provides raw materials that your body uses to manufacture molecules for its own use. For example, calcium is used to make bone, and amino acids are used to make proteins. Every molecule in your body, every hair and bone and cell, is built from raw materials that came from food you ate.
p. 899s
The same chapter connects the prerequisite to the idea that humans break down the food they eat into simpler substances (part of Idea c1) (pp. 904–909s).
No other explicit connections are made between the key ideas and their prerequisites. Although the text treats the prerequisite idea that “Carbon and hydrogen are common elements of living matter” (p. 29t), it does not relate it to the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1). For example, the text does not 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. The prerequisite idea about matter conservation is neither presented nor connected to matter cycling in ecosystems.
Connections between key ideas and related ideas. The text presents related ideas about matter transformation but does not use them to strengthen the key ideas. For example, after introducing the periodic table, teachers are to inform students that “The five most important elements to living things are C, H, O, N, and S” and to “Have students locate these on the table and note the names of these elements” (p. 29t), but this idea is not connected to the cycling of these elements between food webs and the physical environment (Idea d1). And though the text shows diagrams of rings and chains involving carbon atoms (pp. 34–35s), this idea is not connected to the related idea about the bonding capacity of carbon atoms or to the idea that plants assemble sugar molecules from carbon dioxide and water (Idea a1).
Matter and Energy. The text relates ideas about matter transformations to ideas about energy transformations at the level of organisms but not of ecosystems. In Chapter 5: Photosynthesis and Cellular Respiration, the text relates the matter and energy transformations involved in both respiration and photosynthesis:
The carbon atoms needed to make all the organic molecules of living things ultimately come from a nonliving part of the environment. During photosynthesis, carbon atoms are pulled from the carbon dioxide gas, CO2, in air and used to form carbohydrates and other organic compounds....
During cellular respiration, hydrogen atoms are pulled from carbohydrates and joined with oxygen atoms from oxygen gas, forming water. In biochemical pathways, the carbon chains of carbohydrates and other organic molecules are systematically dismantled. Energy stored in the molecules is then made available for the activities of cells. Carbon atoms that are split from carbohydrates are linked to oxygen gas, forming carbon dioxide gas as a byproduct.
Some of the energy that is required to link carbon atoms together is stored within the resulting molecules. In plants carrying out photosynthesis, energy from sunlight is stored within newly made carbohydrate molecules such as sugars.
pp. 95–96s
However, the text does not effectively relate matter and energy transformations in ecosystems (Ideas d1 and d2). And, as noted above, the idea that living organisms “share with all other natural systems the same physical principles of the conservation and transformation of matter and energy....” (Idea e) is not treated.
Beyond Literacy
In presenting key ideas about matter and energy transformation, the text often includes more sophisticated material that interrupts the central story. For example, in presenting the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2), the text includes details of metabolism such as reactions of photosystems I and II and the Calvin cycle and terms like “thylakoid space,” “electron transport chain,” “NADP+,” and “NADPH” (pp. 101–105s). When presenting the idea that “[cells] get energy by [breaking down] sugar molecules” (part of Ideas b2 and c2), the text presents reactions of glycolysis, the Krebs cycle, the electron transport chain, and fermentation and uses terms such as “pyruvate,” “acetyl-CoA,” “oxidative respiration,” “FADH2,” and “NAD+” (pp. 107–111s). These details go beyond what is needed for science literacy (see AAAS, 1993 and NRC, 1996) and interfere with the central story being portrayed.
