Biology: Visualizing Life. 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: Visualizing Life treats most of these ideas and distributes them over several chapters: Chapter 2: Discovering Life, Chapter 5: Energy and Life, Chapter 14: Ecosystems, and Chapter 22: Plants in Our Lives. The ideas appear mostly as assertions in text, although occasionally illustrations and chapter review questions deal with the ideas. Matter and energy are usually discussed together. Little attention is given to the cycling of matter. The material does not address the important idea of the conservation of matter and energy: “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....” (Idea e). 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 material states this idea in several places. The idea is introduced in the context of describing cellular organelles:
Plant cells contain chloroplasts, organelles that have the amazing ability to make chemical energy in the form of sugars, using air, water, and the energy from sunlight. This process is called photosynthesis.
p. 52s
Near the beginning of Chapter 5: Energy and Life, the text addresses the first part of this idea by stating, “In plant cells, chemical reactions that absorb energy make glucose and other organic molecules that plants use for energy and growth” (p. 77s). A few pages later, in the discussion of photosynthesis, the text states, “During the third stage, the ATP and NADPH are used to power the manufacture of energy-rich carbohydrates using CO2 from the air” (p. 85s). In the same section, the text goes on to say, “In the final stage of photosynthesis, carbon atoms are captured from carbon dioxide in the air and used to make organic molecules, which store energy” (p. 89s). On the same page, the overall reaction for photosynthesis is given in the form of symbols and words, showing that both carbon dioxide and water are needed for this process. The presentations of Idea a1 in Chapter 5 are set among biochemical details that go well beyond the key idea. The relevant chapter review questions (p. 96st, questions 12, 13, and 14) also focus on biochemical details rather than on Idea a1.
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 parts of this idea, but the complete idea is never presented. The following representation of Idea b1 shows which parts of the idea are treated (in bold) in Biology: Visualizing Life: Plants break down the sugar molecules that they have synthesized into carbon dioxide and water, use them as building materials, or store them for later use.
In the context of describing organic molecules, plants’ synthesis and use of cellulose molecules for structural and storage purposes is noted, but the text is not explicit about plants making cellulose from sugar molecules they have synthesized:
Many organisms use polysaccharides as structural molecules as well as for energy storage. Plants manufacture a polysaccharide called cellulose....Cellulose forms the major part of the cell walls of plants.
p. 30s
After describing the cycling of carbon atoms in the Calvin cycle (p. 89s), the text gives a nice example to illustrate the fate of the glucose made in photosynthesis:
Plants use the organic molecules they produce during photosynthesis for their life processes. For example, sugar made in the leaves of a potato plant can be used to make cellulose for building new cell walls. Some of the sugar is stored as starch in the potato tuber. The plant may later break down the starch to make the ATP needed for energy, as you will see in Section 5-4.
p. 89s
However, there is no mention that plants’ carbohydrates are broken down into carbon dioxide and water. While the text mentions that “All living things use a process called cellular respiration” (p. 84s), gives the equation for glucose breakdown to carbon dioxide and water (p. 92s), and asks teachers to “Remind students that mitochondria are the organelles in eukaryotic cells with the special function of releasing energy stored in food” (p. 92t), the material does not mention that plants break down sugar molecules into carbon dioxide and water.
The idea that plants store sugars is presented again, much later, in the context of describing specialized functions of roots: “Roots often store nutrients. For example, carrots and sweet potatoes have roots that store large amounts of carbohydrates” (p. 391s). However, no mention is made of the fact that the carbohydrates stored are those originally made during photosynthesis.
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. Parts of the idea are mentioned on widely separated pages, but the complete idea is never stated. The following representation of Idea c1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Biology: Visualizing Life: Other organisms break down the stored sugars or the body structures of the plants [food] they eat (or animals they eat) into simpler substances, reassemble them into their own body structures, including some energy stores [as glycogen].
In the introduction to the human digestive system, the text notes that “Whatever we eat must be processed into smaller pieces before it can be used by the body. Food undergoes this transformation in the digestive system....” (p. 706s). In describing the role of the liver, the text notes its role in storing excess glucose: “...when you eat a meal, the liver removes excess glucose from the blood and stores it as glycogen. When the level of glucose in the blood falls, glucagon causes the liver to release some of this glucose back into the blood” (p. 709s).
Much earlier in the text, in the context of describing chemical reactions in living things, the text mentions that atoms are rearranged: “In your cells, chemical reactions rearrange the atoms in glucose molecules, making new products and releasing energy” (p. 77s). The text does not mention body structures of plants. A figure caption indicates that “When you eat a potato, chemical reactions in your mouth convert starch into glucose” and the accompanying text states that a potato “is an excellent food because it is crammed with starch (long chains of glucose molecules)” (p. 77s).
In the context of describing the carbon cycle in ecosystems, the text mentions that other organisms break down carbon-containing molecules to carbon dioxide, but the focus is on the cycling of carbon rather than on the consumers’ use of the plant molecules:
Consumers obtain energy-rich molecules that contain carbon by eating plants or other animals. As these molecules are broken down, carbon dioxide is produced and released into the Earth’s atmosphere.
p. 262s
The idea that sugars are reassembled into body structures is not presented.
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 representation of Idea d1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Biology: Visualizing Life: The chemical elements [Nitrogen and carbon] 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 describes the nitrogen cycle (p. 260s) and the carbon cycle (p. 262s) but does not state the generalization about the repeated passage through food webs of all elements that make up the molecules of living things or that in this cycling these elements are combined and recombined in different ways. Of the chapter review questions, only one relates at all to this key idea, but it, too, focuses on an example rather than the generalization and does not get at the idea of repeated passage:
Question: Imagine an atom of nitrogen that is in a protein in the leaf of a plant. Trace the steps of the nitrogen cycle this atom must pass through in order to reach the atmosphere.
Suggested Response: The leaf falls and decays by bacterial action, and the nitrogen in the leaf becomes ammonia. The ammonia is then further broken down by other bacteria to produce nitrogen.
p. 270st, question 10
The diagram of the nitrogen cycle (p. 260s) shows nitrogen in two different combinations, whereas the diagram of the carbon cycle (p. 262s) only shows carbon in one combination. The text assumes that students will recall the meaning of the phrase “organic molecules,” which was defined much earlier: “Molecules with carbon-carbon bonds are called organic molecules” (p. 29s).
Energy is transformed in living systems.
Idea a2: Plants transfer the energy from light into “energy-rich” sugar molecules.
There is a content match to this idea, which is treated in text only. In the context of describing cell parts and functions, the text states the idea:
Plant cells contain chloroplasts, organelles that have the amazing ability to make chemical energy in the form of sugars, using air, water, and the energy from sunlight. This process is called photosynthesis.
p. 52s
The idea is presented again in the context of describing energy flow in food chains:
Plants, algae, and some bacteria capture energy directly from sunlight and use that energy to produce ATP, energy-storing carbohydrates, and other types of organic molecules.
p. 84s
In introducing details of light and dark reactions, the text again states the idea, this time noting some chemical intermediates:
In the first stage of photosynthesis, energy is captured from light. During the second stage, the energy is used to make ATP and an energy-carrying compound called NADPH. During the third stage, the ATP and NADPH are used to power the manufacture of energy-rich carbohydrates using CO2 from the air.
p. 85s
One of the chapter review questions relates to the key idea:
Question: Describe the role of chlorophyll in photosynthesis.
Suggested Response: Chlorophyll absorbs light energy that will be converted to chemical energy.
p. 96st, question 11
The idea is presented once again in the context of describing energy flow in ecosystems: “Nearly all producers are photosynthetic; they capture the sun’s energy to synthesize carbohydrates. Plants, some bacteria, and algae are producers” (p. 256s).
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 two parts of the idea are treated separately. In the context of describing how energy is involved in chemical reactions, the text notes that plants use the glucose they have made for energy and growth: “In plant cells, chemical reactions that absorb energy make glucose and other organic molecules that plants use for energy and growth” (p. 77s). Later in the same chapter, the text explicitly states that “Both plants and animals use the process of cellular respiration to release energy stored in organic molecules” (p. 90s) and then notes that “Glycolysis breaks down glucose into smaller molecules” (p. 91s), thus explicitly mentioning the breaking down (though not the oxidizing) of sugar molecules. Review questions are provided to check student knowledge of this idea (pp. 96s and 95–96t, questions 3, 4, and 15).
The second part of this idea, that some of the energy is released as heat, is presented nine chapters later, when energy flow in ecosystems is described:
A plant absorbs energy from the sun and uses it to make carbohydrates....Only about one-half of the energy captured by a plant becomes part of the plant body, however. Part of the remaining energy is stored in ATP made during cellular respiration. Most of the remaining energy escapes as heat.
p. 258s
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. In the context of describing the role of energy in living things, the text notes that humans break down (rather than oxidize) glucose and release energy from it: “In your cells, chemical reactions rearrange the atoms in glucose molecules, making new products and releasing energy” (p. 77s). The text then points out that some of the energy is used to do work (“Other reactions break down glucose and release energy that your body uses to do work” [p. 77s]) but that some is released as heat (“When living cells break down molecules, some of the energy released from the molecules is in the form of heat” [p. 83s]).
Two figures and accompanying captions extend the idea to organisms other than humans:
- Figure 5-10 shows a series of organisms in a food chain. In one picture, a deer is eating plants. The figure caption states, “Light energy...is converted into carbohydrates by plants. When an animal eats plants, it gets energy from the carbohydrates in the plants....” (p. 84s).
- Figure 5-16 shows a cow eating grass. The caption states, “...Both plants and animals use the process of cellular respiration to release energy stored in organic molecules” (p. 90s).
The reaction by which energy is released from starch is contrasted with burning but is not characterized as being an oxidation:
When logs burn, the energy stored in wood is released in a single reaction as heat and light. But this is not what happens in cells. Instead, energy stored in food molecules is released at each step in a series of enzyme-catalyzed chemical reactions, as shown in Figure 5-8.
p. 82s
The text subsequently refers to the process as “oxidative respiration” but does not indicate that sugars are oxidized in the process:
In most living things, a second stage of cellular respiration, called oxidative respiration, follows glycolysis. Oxidative respiration, which requires oxygen, happens within the mitochondria. It is far more effective than glycolysis at recovering energy from organic molecules. Oxidative respiration is the method by which most living cells get the majority of their energy.
p. 90s
Chapter review questions 1c, 3, and 4 relate to the idea (p. 96st).
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 part of the idea is treated (in bold) in Biology: Visualizing Life: 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.
In the section on energy flow in ecosystems, the text states the first part of the idea—that energy is lost at each link in a food web—and describes ecologist Howard Odum’s findings that the loss amounts to about 90%:
A plant absorbs energy from the sun and uses it to make carbohydrates....Only about one-half of the energy captured by a plant becomes part of the plant body, however. Part of the remaining energy is stored in ATP made during cellular respiration. Most of the remaining energy escapes as heat. Similar losses of energy occur at each trophic level of an ecosystem.
....Odum found that when a herbivore eats a plant, only about 10 percent of the energy present in the plant’s molecules ends up in the herbivore’s molecules. The other 90 percent of the energy is “lost,” some as the cost of doing work (breathing, moving, chewing) and much more as heat. Likewise, when a carnivore eats the herbivore, only 10 percent of the energy in the herbivore goes toward making carnivore molecules. At each trophic level, the energy stored in the organisms is about one-tenth that of the level below it.
p. 258s
However, the text does not present the second part of the idea that continual input of energy from sunlight keeps the process going. The idea that living organisms require a constant input of energy is presented early in the text, in the context of describing the six themes that unify biology:
Organisms use energy to grow and to carry out their activities. Without it, life soon stops. Almost all the energy that drives life on Earth is obtained from the sun. Plants capture the energy of sunlight and use it to make complex molecules in a process called photosynthesis. These molecules then serve as the source of fuel for animals that eat them. Maintaining the complexity of living organisms requires a constant input of energy....The availability of energy is a major factor in limiting the size and complexity of biological communities.
p. 18s
And in the context of describing energy flow in living food chains, the text notes that the sun is the ultimate source of most energy and that it shines continuously: “Almost all of the energy needed for life comes ultimately from the sun, which shines continuously on Earth” (p. 84s). However, neither of these two examples relate the second part of the key idea to the first part.
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
The material asserts the key ideas; it does not develop an evidence-based argument to support them. The one phenomenon that could support a key idea (the demonstration that saliva transforms starch in a cracker into sugar [p. 77t]) is not used to do so. And 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: Visualizing Life treats most of the key ideas and presents most of them in their entirety. However, in some instances key ideas are presented in pieces and the pieces are not tied together. For example, the two parts of Idea d2—that energy is lost as heat at each trophic level and that continual input of energy keeps the process going—are treated more than 150 pages apart and are not tied together. Similarly, the key idea that “Plants break down the sugar molecules that they have synthesized into carbon dioxide and water, use them as building materials, or store them for later use” (Idea b1) is presented in separate parts that are not tied together: plants’ use of synthesized sugars as building material or storage of such sugars is presented in the context of describing the Calvin cycle (p. 89s) and the breakdown of sugar to carbon dioxide and water is presented in the context of describing oxidative respiration but is not linked to plants (p. 92s). Nor are the ideas put together in Chapter 21: Plant Form and Function, which mentions carbohydrate storage in roots (p. 391s) but does not relate it to photosynthesis in leaves (p. 393s). And while the same chapter describes the distinction between monocots and dicots (p. 395s), it does not point out that cotyledons store food made during photosynthesis in the parent plant for its offspring.
Biology: Visualizing Life focuses mainly on the energy side of the story, which is more abstract than the matter side. The energy ideas are introduced at the cell level (p. 52s), then presented in the context of the chemistry of photosynthesis (pp. 85–89s) and respiration (pp. 90–94s), then in terms of energy flow and nutrient cycles in ecosystems (pp. 256–262s), and finally in terms of human nutrition and digestion (pp. 700–709s). Teachers are not alerted to these different places where ideas about energy transformations 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 several connections among key ideas about energy transformations. For example, the text relates the idea that “[Humans] break down...sugars [to] get energy to grow and function” (part of Idea c2) to the idea that “Plants get energy to grow and function by [breaking down] the sugar molecules” (part of Idea b2) and relates both to the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2) in the context of describing the role of cell organelles:
The energy that drives a cell’s activities is converted within organelles called mitochondria (myt uh KAHN dree uh). These organelles are specialized to convert energy stored in food. The number of mitochondria in most cells varies. A muscle cell in your heart, which may pump more than 70 times per minute, can contain thousands of mitochondria. A mature red blood cell has none.
The significant differences between you and plants is the source of the food processed by mitochondria for your energy. How do plants provide their mitochondria with food molecules? Plant cells contain chloroplasts, organelles that have the amazing ability to make chemical energy in the form of sugars, using air, water, and the energy from sunlight.
p. 52s
In addition, the text again relates the idea that “[Humans] break down...sugars [to] get energy to grow and function” (part of Idea c2) to the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2) in the context of introducing the energy transformations in photosynthesis and respiration:
Have you ever eaten beef enchiladas? The beef came from a cow that ate grass. Other parts of the enchiladas came directly from plants. With few exceptions, you end up with plants (or some other photosynthetic organism) if you trace your food back to its origin. Clearly, you depend on plants for food, as do all plant eaters and organisms that eat plant eaters. The energy in that food came from sunlight.
p. 85s
The text also relates the energy transformations (including heat “loss”) in individual organisms (Ideas a2, b2, and c2) to the loss of energy at each trophic level in an ecosystem (Idea d2):
A plant absorbs energy from the sun and uses it to make carbohydrates....Only about one-half of the energy captured by a plant becomes part of the plant body, however. Part of the remaining energy is stored in ATP made during cellular respiration. Most of the remaining energy escapes as heat. Similar losses of energy occur at each trophic level of an ecosystem.
....Odum found that when a herbivore eats a plant, only about 10 percent of the energy present in the plant’s molecules ends up in the herbivore’s molecules. The other 90 percent of the energy is “lost,” some as the cost of doing work (breathing, moving, chewing) and much more as heat. Likewise, when a carnivore eats the herbivore, only 10 percent of the energy in the herbivore goes toward making carnivore molecules. At each trophic level, the energy stored in the organisms is about one-tenth that of the level below it.
p. 258s
Connections between key ideas and their prerequisites. Biology: Visualizing Life makes only one connection between a key idea and its prerequisite and this connection is weak. In the context of describing human digestion, the text somewhat connects the idea that humans break down the food they eat into simpler substances (part of Idea c1) to the prerequisite that food provides the molecules that serve as building materials for all organisms: “Supplies of energy and building materials for the body exist only in potential forms in food. Whatever we eat must be processed into smaller pieces before it can be used by the body” (p. 706s). However, the term “smaller pieces” does not adequately convey that food provides molecular building blocks, which is needed for students to appreciate that these molecules can be assembled, restructured, or broken down during respiration.
The material makes no other connections between key ideas and prerequisites. For example, the text does not present the prerequisite idea that “...Some [reactions] require an input of energy whereas others release energy” or the prerequisite about energy conservation. And it does not use them to explain that since energy is lost as heat at each trophic level (first part of Idea d2), energy must be supplied from somewhere else. Thus it misses the opportunity to relate the first part of Idea d2 to the second part—that “Continual input of energy from sunlight keeps the process going.” The text does not treat the prerequisite idea that “An especially important kind of reaction between substances involves combination of oxygen with something else—as in burning or rusting” or relate it to the oxidation of glucose, even though it refers to the process as “oxidative respiration” (p. 92s). Furthermore, even though the text goes into detail about light “excit[ing] an electron” in chlorophyll (pp. 87–88s) and shows energy diagrams of exothermic and endothermic reactions (pp. 77–78s) and of the role of enzymes in lowering activation energy (p. 79s), it fails to point out or make use of the prerequisite idea that “Arrangements of atoms have chemical energy” or that “Different amounts of energy are associated with different configurations of atoms” to make sense of energy transformations in photosynthesis and respiration.
Connections between key ideas and related ideas. The text presents the related idea that “Within cells are specialized parts for the capture and release of energy” and makes a connection to energy release in other organisms (Idea c2) and the idea that plants transfer the energy from light into “energy-rich” sugar molecules” (Idea a2). First, the section title “Organelles: A Cell’s Laborers” captures the idea that cells have specialized parts that do the work of the cell and the introductory paragraph states that “cells perform basic functions of life....” (p. 52s). Next, a paragraph heading calls attention to the work of capturing and releasing energy: “Cells manufacture and release energy” (p. 52s). Finally, the text presents parts of both key ideas and connects them to the related idea:
Cells manufacture and release energy
By now you are aware that the life of a cell is not a restful one. Your cells are always at work. Where do they get the energy to perform all of life’s tasks? The energy that drives a cell’s activities is converted within organelles called mitochondria (myt uh KAHN dree uh). These organelles are specialized to convert energy stored in food. The number of mitochondria in most cells varies. A muscle cell in your heart, which may pump more than 70 times per minute, can contain thousands of mitochondria. A mature red blood cell has none.The significant differences [sic] between you and plants is the source of the food processed by mitochondria for your energy. How do plants provide their mitochondria with food molecules? Plant cells contain chloroplasts, organelles that have the amazing ability to make chemical energy in the form of sugars, using air, water, and the energy from sunlight.
p. 52s
Matter. Biology: Visualizing Life does a much less complete job of presenting the matter side of the story. As noted in the discussion of alignment, key Ideas b1 and c1 are each presented as separate parts that are not tied together and key Idea d1 is presented only through examples that are not tied to the general idea about the repeated cycling of elements through their combination and recombination into different molecules and organisms. The idea that atoms that make up molecules combine and recombine is explicit for nitrogen but not for carbon.
Connections among key ideas. The text makes only one connection among key ideas about matter transformation. The text relates the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1) to the idea that “Plants...use [sugars] as building materials, or store them....” (part of Idea b1) and to the idea that “Plants get energy to grow and function by [breaking down] the sugar molecules” (part of Idea b2) through an example of a potato plant. After describing how plants make organic molecules from carbon dioxide and water, the text describes the fate of these molecules:
Plants use the organic molecules they produce during photosynthesis for their life processes. For example, sugar made in the leaves of a potato plant can be used to make cellulose for building new cell walls. Some of the sugar is stored as starch in the potato tuber. The plant may later break down the starch to make the ATP needed for energy, as you will see in Section 5-4.
p. 89s
The text makes only weak connections between the combination and recombination of atoms in photosynthesis (Idea a1) and respiration (Ideas b1 and c1) and the repeated combination and recombination of atoms in ecosystems (Idea d1). For example, the text description of the carbon cycle does not convey the idea that carbon atoms combine and recombine as they move through the organisms in ecosystems and are released into the environment. Nor does it indicate that the repeated combination and recombination results from the repeated occurrence of either photosynthesis and respiration or photosynthesis and the use of the sugar products to build other molecules:
Like water, carbon also cycles between the nonliving environment and organisms. The Earth’s atmosphere contains carbon in the form of carbon dioxide. Plants use carbon dioxide to build organic molecules during photosynthesis. Consumers obtain energy-rich molecules that contain carbon by eating plants or other animals. As these molecules are broken down, carbon dioxide is produced and released into the Earth’s atmosphere. Cellular respiration by decomposers and photosynthetic organisms also returns carbon dioxide to the atmosphere. Figure 14-11 shows how carbon cycles within an ecosystem.
p. 262s
Connections between key ideas and their prerequisites. Even though the text presents two prerequisite ideas, it makes only one weak connection between them and key ideas. The text attempts to connect the prerequisite idea that “Food provides the molecules that serve as fuel and building materials for [humans]” (but not for “all organisms”) and the idea that humans break down food into simpler substances (part of Idea c1) in the introduction to the human digestive system:
Supplies of energy and building materials for the body exist only in potential forms in food. Whatever we eat must be processed into smaller pieces before it can be used by the body. Food undergoes this transformation in the digestive system....
p. 706s
However, the connection is not made at the molecular level.
And while the text presents the prerequisite idea that “Carbon and hydrogen are common elements of living matter” (pp. 26s and 29–30s) and shows examples of the related idea that “Carbon atoms...bond to several other carbon atoms in chains and rings to form large and complex molecules” (pp. 29–31s), connections are not made between these ideas and the key idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1).
Furthermore, the idea that matter is conserved is neither presented nor related to matter cycles between ecosystems and the physical environment.
Connections between key ideas and related ideas. While the text presents two ideas that are relevant to key ideas about matter transformation, it does not make the connections between them explicit. For example, the text presents the related idea that “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen, nitrogen....” (p. 26s) but does not relate it to the combination and recombination of these elements in ecosystems. When the nitrogen cycle is presented, the text only notes that “Organisms must have nitrogen to produce proteins and nucleic acids” (p. 260s). It does not restate the idea that nitrogen is one of the elements that make up the molecules of living things or make explicit that nitrogen is incorporated into the molecules of living things.
Matter and Energy. The material makes a brief connection between two key ideas about matter and energy transformation. In describing the chemistry of living things, the text makes the connection between matter and energy transformation in humans (part of Ideas c1 and c2) by noting that “In your cells, chemical reactions rearrange the atoms in glucose molecules, making new products and releasing energy” (p. 77s). The text attempts to connect key ideas about matter and energy transformation in ecosystems, but the connection does not relate the combination and recombination of atoms to the energy “loss” at each trophic level (and, hence, relates less sophisticated ideas about matter and energy in ecosystems). After describing how energy is lost (as heat) at each trophic level, the text introduces the topic of nutrient cycling by noting, “Unlike energy, which flows through an ecosystem, nutrients such as calcium and nitrogen circulate within an ecosystem” (p. 259s).
The material does not present the key idea that “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....” (part of Idea e). No connections are made between ideas about matter transformations and those about energy transformations in individual organisms.
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 cells break down sugars into carbon dioxide and water, releasing energy in the process, the text includes details of enzymes, activation energy, and active sites (pp. 78–80s), the structure, synthesis, and decomposition of ATP (p. 83s), details of chloroplast structure and steps in capturing light and pumping protons across the thylakoid membrane (pp. 87–88s), and details of cellular respiration (pp. 90–93s) that contribute little to developing the key idea. This excessive detail is illustrated in the following text, which describes the role of water molecules in photosynthesis:
Before excited electrons can leave their chlorophyll molecules, the electrons must be replaced by other electrons. Water supplies these electrons. Plants obtain electrons from water by splitting water molecules, H2O. As water molecules split, chlorophyll takes the electrons from the hydrogen atoms, leaving protons. The remaining oxygen atoms combine to form oxygen gas.
p. 87s
The sophistication of these ideas is well beyond benchmarks and interrupts the central story being told.
