Modern Biology. Holt, Rinehart and Winston, 1999
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. Modern Biology treats most of these ideas and distributes them over several chapters: Chapter 6: Photosynthesis, Chapter 7: Cellular Respiration, and Chapter 22: Ecosystems and the Biosphere. Isolated sightings can be found in chapters 1 (overview), 3 (biochemistry), and 24–45 (the biodiversity chapters). The key ideas appear mostly in text, but also in photographs, diagrams, and student activities. Energy transformation is treated more extensively than matter transformation. The material treats fully the idea that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1), the ideas describing the fates of sugar molecules in plants (Idea b1) and other organisms (Idea c1), and the idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2). Other key ideas related to the transformation of matter and energy are treated incompletely or minimally. The following analysis provides details on how the textbook treats each of the specific key ideas.
The teacher’s guide for units 2 (p. 67A) and 5 (p. 357A) claims a correlation between unit goals and descriptions of the relevant Life Science Standards from the National Science Education Standards:
- The atoms and molecules on the Earth cycle among the living and nonliving components of the biosphere. (pp. 67A and 357A)
- The energy for life primarily derives from the sun. (pp. 67A and 357A)
- The chemical bonds of food molecules contain energy. (pp. 67A and 357A)
- Energy flows through ecosystems in one direction, from photosynthetic organisms to herbivores to carnivores and decomposers. (p. 357A)
- Matter and energy flow through different levels of organization of living systems and between living systems. (p. 357A)
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 several contexts, mostly in text, but also in a figure and in a student activity. In the context of presenting a unifying theme of biology, the text presents Idea a1 explicitly:
Organisms that obtain their energy by making their own food, like plants, are called autotrophs (AWT-oh-trohfs). Using the energy they trap from the sun, some kinds of autotrophs convert water and carbon dioxide from the environment into energy-rich substances such as sugars and starches.
p. 10s
In the opening text for Chapter 6: Photosynthesis, students read, “As you can see in Figure 6-1, autotrophs use the biochemical pathways of photosynthesis to manufacture organic compounds from carbon dioxide, CO2, and water” (p. 111s). These “organic compounds” have been identified as “primarily carbohydrates” in the first paragraph of the section (p. 111s). The text then devotes seven pages to biochemical details that go well beyond the key idea. However, the text later presents the idea explicitly by giving a simple equation for photosynthesis (showing the general formula for a carbohydrate) as well as the equation for the formation of glucose (p. 118s). A Teaching Strategy activity called Photosynthetic Products directs the teacher to have students use a microscope to examine starch granules in thin sections of a potato and to explain that “the organic compounds plants make through photosynthesis are stored mainly as starch” (p. 119t). Two summary statements in the chapter 6 Review restate the idea:
Photosynthesis converts light energy into chemical energy through complex series of reactions known as biochemical pathways. Autotrophs use photosynthesis to make organic compounds from carbon dioxide and water.
p. 121s, 6-1
In the overall equation for photosynthesis, CO2 and water are the reactants, and carbohydrate and O2 are the products.
p. 121s, 6-2
Number 6 in the chapter review questions pertains to the idea: “A product in the overall equation for photosynthesis is (a) O2 (b) CO2 (c) H2O (d) RuBP” (Answer: a) (p. 122s). All the other questions require knowledge considerably beyond the level of the key idea (pp. 122–123s). In the context of presenting the carbon cycle, Idea a1 is presented again: “During photosynthesis, plants and other autotrophs use carbon dioxide (CO2), along with water and solar energy, to make carbohydrates” (p. 421s). The idea is also presented in Chapter 29: Plants and the Environment: “In photosynthesis, plants absorb carbon dioxide from the air, produce sugar and starch, and break apart water, releasing oxygen into the air” (p. 570s).
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, though the parts on breakdown, use as building material, and storage are presented in widely separated chapters. In the context of presenting a unifying theme of biology, the text presents the idea of breakdown and reassembly: “In living things, complex chemicals are broken down. Their parts are then reassembled into chemicals and structures needed by the organism” (p. 10s). In presenting photosynthesis, both text and an accompanying figure indicate that autotrophs carry out cell respiration, giving off carbon dioxide and water:
As Figure 6-1 indicates, both autotrophs and heterotrophs perform cellular respiration. During cellular respiration in most organisms, organic compounds are combined with O2 to produce ATP, yielding CO2 and water as waste products.
p. 112s
The previous page made the link between autotrophs and plants:
Organisms that manufacture their own food from inorganic substances and energy are autotrophs. Most autotrophs use photosynthesis to convert light energy from the sun into chemical energy....Plants are the most common example of photosynthetic organisms....
p. 111s
In the context of describing producers in ecosystems, the text summarizes the fates of sugar molecules in plants:
Photosynthetic producers use the energy they capture to make sugar. Some of the sugar is used for cellular respiration, some for maintenance and repair, and some to make new organic material through either growth or reproduction.
p. 415s
Previously, in the context of presenting cellular respiration, the text had characterized the use of sugar molecules as building materials in molecular terms:
[T]he molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make the compounds that are missing in food. Thus, another important function of cellular respiration is to provide carbon skeletons that can be built up into larger molecules needed by cells.
p. 138s
In presenting the carbon cycle, the text notes that plants “use oxygen to break down carbohydrates” (p. 421s).
Elsewhere, in describing the functions of roots, the text notes their role in food storage:
Roots are often adapted to store carbohydrates or water. Phloem tissue carries carbohydrates made in leaves to roots. Carbohydrates that roots do not immediately use for energy or building blocks are stored. In roots, these excess carbohydrates are usually converted to starch and stored in parenchyma cells. You are probably familiar with the storage roots of carrots, turnips, and sweet potatoes.
p. 607s
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, which is treated in text, a demonstration, and a student activity. In the context of presenting a unifying theme of biology, the text introduces the idea of breakdown and reassembly: “In living things complex chemicals are broken down. Their parts are then reassembled into chemicals and structures needed by the organism” (p. 10s). In this same opening chapter, students observe a demonstration of how yeast cells metabolize sugar and produce carbon dioxide in cellular respiration (p. 12t).
In the context of summarizing cellular respiration, the text makes the point that providing energy is not the only function of cellular respiration:
Cellular respiration provides the ATP that all cells need to support the activities of life. But providing cells with ATP is not the only important function of cellular respiration. Cells also need specific organic compounds from which to build the macromolecules that compose their own structure. Some of these specific compounds may not be contained in the food a heterotroph consumes. However, the molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make the compounds that are missing in food. Thus, another important function of cellular respiration is to provide carbon skeletons that can be built up into larger molecules needed by cells.
p. 138s
In the context of discussing the flow of matter in ecosystems, the text presents an example of an organism breaking down stored body structures into simpler substances:
Detritivores (dee-TRIE-ti-vorz) are consumers that feed on the “garbage” of an ecosystem, such as organisms that have recently died, fallen leaves and branches, and animal wastes....Bacteria and fungi belong to a class of detritivores called decomposers. Decomposers cause decay by breaking down the complex molecules in dead tissues and wastes into simpler molecules. Some of the molecules released during decay are absorbed by the decomposers, and some of them are returned to the soil or water.
pp. 416–417s
And in the context of describing the six basic ingredients in foods, the text notes that the body stores excess food as fat: “The body stores excess fat from the diet in special tissues under the skin and around the kidneys and liver. Excess carbohydrates may be converted to fat for storage” (p. 979s).
In an activity suggested in the teacher’s guide, students observe mold growing on leaf litter and are asked what role a mold plays in a forest ecosystem (p. 417t). The suggested response specifies that matter is transformed: “Mold is a detritivore in a forest ecosystem, breaking down leaves and other plant debris to organic molecules” (p. 417t).
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 a content match to this idea, which is treated in text, diagrams, a student activity, and several review questions. In Chapter 1: The Science of Life, the concept of combining and recombining is introduced for the teacher in Focus Concept: “In living things, matter is constantly being rearranged through changes called chemical reactions, which involve energy” (p. 30t). An example of recycling of elements is given as the role of decomposers is discussed in Chapter 22: Ecosystems and the Biosphere:
Decomposers cause decay by breaking down the complex molecules in dead tissues and wastes into simpler molecules. Some of the molecules released during decay are absorbed by the decomposers, and some of them are returned to the soil or water. The action of the decomposers makes the nutrients contained in the dead bodies and wastes of organisms available to autotrophs. Thus, the process of decomposition recycles chemical nutrients.
pp. 416–417s
The decomposition phase of the cycling of matter is also the topic of a review question at the end of this section: “What role do decomposers play in an ecosystem? Why is this role important?” (p. 419s). The suggested answer is, “Decomposers cause decay, which releases the nutrients contained in the organism. They return these nutrients to the ecosystem” (p. 419t). Later in the same chapter, in the context of discussing recycling in ecosystems, the text notes that minerals are recycled:
While energy flows through an ecosystem, water and minerals, such as carbon, nitrogen, calcium, and phosphorus, are recycled and reused. Each substance travels through a biogeochemical (BIE-oh-GEE-oh-KEM-i-kuhl) cycle, moving from the abiotic portion of the environment, such as the atmosphere, into living things, and back again.
p. 420s
The carbon cycle is presented in Figure 22-6 (p. 421s), which shows how carbon is cycled through an ecosystem but does not illustrate the rearrangement of atoms as they pass from one part of the cycle to the next. Nor does it show that this cycle occurs repeatedly. The combination and recombination of atoms is given more attention in the material’s presentation of the nitrogen cycle (Figure 22-7, p. 422s). Although the role of nitrogen in molecules in living things is not shown in the diagram, the text makes this role clear at several points in the discussion:
All organisms need nitrogen to make proteins and nucleic acids....Nitrogen gas, N2, makes up about 78 percent of the atmosphere....Nitrogen-fixing bacteria convert nitrogen gas into ammonia, NH3, which plants can absorb and use to make proteins. Nitrogen-fixing bacteria produce ammonia for their own use and release the excess, which can be taken up by other organisms....The bodies of dead organisms contain nitrogen, mainly in proteins and nucleic acids. Urine and dung also contain nitrogen. Decomposers break down the corpses and wastes of organisms and release the nitrogen they contain as ammonia. This process is known as ammonification (ah-MAHN-i-fi-KAY-shuhn). Through ammonification, nitrogen that would otherwise be lost is reintroduced into the ecosystem. Bacteria in the soil take up ammonia and oxidize it into nitrites, NO2–, and nitrates, NO3–....The erosion of nitrate-rich rocks also releases nitrates into an ecosystem. Plants use nitrates to form amino acids....anaerobic bacteria break down nitrates and release nitrogen gas back into the atmosphere.
p. 423s
By presenting the formulas of nitrogen gas and various nitrogen compounds, the text also supports the idea that nitrogen is combined and recombined in various ways as it passes through the cycle. However, as in the carbon cycle diagram, only one animal, a rabbit, is shown in the nitrogen cycle diagram. Thus, the idea that carbon and nitrogen move through food webs is not presented.
Two section review questions relate to the key idea:
Question: Describe the biogeochemical cycle.
Suggested Response: A biogeochemical cycle is the movement of water, carbon, nitrogen, or other mineral from the abiotic portion of the environment into living things and back again.
p. 423st, question 1
Question: Describe the role of decomposers in the nitrogen cycle.
Suggested Response: Decomposers break down the nitrogen-containing molecules in dead organisms and wastes and release nitrogen, making it available to other organisms.
p. 423st, question 3
The recycling of other materials is treated in Section 29-2: Plants and the Environment in a discussion of Plant Ecology, which also makes explicit the idea of repeated cycling:
Plants also provide organisms with inorganic nutrients. Plant roots are very efficient at mining the soil for inorganic nutrients, such as nitrogen, phosphorus, potassium, iron, and magnesium. Plants use these inorganic nutrients in the organic compounds they make. Consumers ingest these organic compounds and incorporate the inorganic nutrients into their own bodies. Eventually these same inorganic nutrients are returned to the soil when the consumer’s waste material or dead body is decomposed by bacteria and fungi. Plants thus play a major role in the continuous cycling of the Earth’s water, oxygen, carbon dioxide, and inorganic nutrients.
pp. 570–571s
A section review question focuses on the content of this passage, but the suggested response does not make explicit the idea of repeated cycling:
Question: How do plants continuously recycle the Earth’s inorganic nutrients? (p. 572s, question 2)
Suggested Response: Plants absorb carbon dioxide from the air and water and inorganic nutrients from the soil. In photosynthesis, the water is split, producing oxygen gas, which is released to the air. Then carbon dioxide and hydrogen from water are combined to form organic compounds. Animals breathe in the oxygen produced by plants and eat the plants as food. In cellular respiration, animals use the oxygen and most of the organic compounds provided by plants to produce energy, carbon dioxide, and water. When the animal’s waste material or its dead body is decayed by bacteria and fungi, the inorganic nutrients are returned to the soil.
p. 572st, question 2
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 mostly in text but also in the study of two photographs. In the context of presenting a unifying theme of biology, the text introduces the idea that energy is transformed:
Through the process of photosynthesis (FOH-toh-SIN-thuh-sis), plants...capture the energy from the sun and change it into a form of energy that can be used by living things....Using the energy they trap from the sun,...[plants] convert water and carbon dioxide from the environment into energy-rich substances such as sugars and starches.
p. 10s
In the introduction to Chapter 6: Photosynthesis, the text shows a photograph of a field of corn and notes that corn transforms the sun’s energy: “Through photosynthesis, these corn plants obtain energy from the sun and store it in organic compounds” (p. 110s). The text then makes the transformation more explicit:
Most autotrophs use photosynthesis to convert light energy from the sun into chemical energy, which they then store in various organic compounds, primarily carbohydrates. Plants are the most common example of photosynthetic organisms....
p. 111s
Later, the text presents the overall equation for photosynthesis (showing the general formula for a carbohydrate) as well as the equation for the formation of glucose (p. 118s). The equations include the role of light energy as well as the chemical reactants and products. A summary statement in the chapter 6 Review includes the idea:
Photosynthesis converts light energy into chemical energy through complex series of reactions known as biochemical pathways. Autotrophs use photosynthesis to make organic compounds from carbon dioxide and water.
p. 121s
The introductory photograph for Chapter 7: Cellular Respiration shows a panda eating leaves (p. 126s). In the feature Understanding the Visual, the teacher is told to ask students how animals like the panda are either directly or indirectly dependent on plants for energy. The suggested answer includes a statement of the idea: “Plants capture energy from the sun and store it in carbohydrates” (p. 126t). The idea is reiterated in the opening paragraph of the chapter: “[A]utotrophs, such as plants, use photosynthesis to convert light energy from the sun into chemical energy, which is stored in carbohydrates and other organic compounds” (p. 127s). The idea is presented again in the context of discussing energy transfer in ecosystems (p. 415s).
Idea b2: Plants get energy to grow and function by oxidizing the sugar molecules. Some of the energy is released as heat.
There is an incomplete content match to this idea, which is presented entirely in text. 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 Modern Biology: Plants get energy to grow and function by oxidizing [breaking down] the sugar molecules. Some of the energy is released as heat.
In the context of presenting a unifying theme of biology, the text presents a less sophisticated version of the idea that does not mention what plants need energy for or the fact that some of the energy is released as heat: “These substances [sugars and starches] are then used by the organisms [plants] for their own energy needs” (p. 10s).
Later, in the context of describing photosynthesis and respiration, the text notes that energy is released in cell respiration but does not equate the organic compounds with sugars or mention the release of energy as heat:
Some of the energy stored in organic compounds is released by cells in another set of biochemical pathways, known as cellular respiration....both autotrophs and heterotrophs perform cellular respiration.
pp. 111s–112s
Both autotrophs and heterotrophs depend on these organic compounds for the energy to power cellular activities. By breaking down these compounds into simpler molecules, cells release energy.
p. 127s
Subsequent details focus on ATP production but not on heat loss (pp. 134–137s).
The idea of heat loss is presented much later, in the context of energy transfers in ecosystems:
[C]onsider what happens when a deer eats 1,000 kcal of leaves. About 350 kcal are eliminated as urine, dung, and other wastes. Another 480 kcal are lost as heat. Only about 170 kcal are actually stored as organic matter, mostly as fat. Producers use and transfer energy in a similar way. A plant stores only about 1–5 percent of the solar energy that it converts to sugar as organic material. The rest is reflected off the plant, used in its life processes, or lost in the form of heat.
p. 419s
Idea c2: Other organisms break down the consumed body structures to sugars and get energy to grow and function by oxidizing their food, releasing some of the energy as heat.
There is an incomplete content match to this idea and the parts of the idea that are treated are presented in widely separated chapters. 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 Modern Biology: Other organisms [Humans] break down the consumed body structures [food] to sugars and [living things] get energy to grow and function by oxidizing their food, releasing some of the energy as heat.
The idea that humans break down consumed food is presented in the introduction to human digestion, but the end products of digestion are not mentioned until the end of the section:
Before your body can use the nutrients in the food you consume, the nutrients must be broken down physically and chemically. This process of breaking down food into molecules the body can use is called digestion.
p. 983s
The end products of digestion—amino acids, monosaccharides, glycerol, and fatty acids—are absorbed into the circulatory system through blood and lymph vessels in the lining of the small intestine.
p. 988s
In the context of introducing energy transfer in chemical reactions, the text points out that humans need energy and obtain it through the breakdown of sugars; but it does not explain why energy is needed or that some of the energy is released as heat:
Much of the energy your body needs is provided by sugars from foods. Your body continuously undergoes a series of chemical reactions in which sugar and other substances are broken down to carbon dioxide and water. In this process, energy is released for use by your body.
p. 36s
In the context of describing cellular respiration, the text and teacher’s guide make clear that other organisms need energy and obtain it from the breakdown of macromolecules:
Like other heterotrophs, the giant panda...obtains organic compounds by consuming other organisms. Biochemical pathways within the panda’s cells transfer energy from those compounds to ATP.
p. 126s
Living things are highly organized and require an input of energy to maintain their organization. They obtain the needed energy by breaking down carbohydrates and other macromolecules in chemical pathways that are highly efficient.
p. 126t
Teachers are instructed to demonstrate the burning of sugar in a crucible and to ask students how what they have observed differs from what happens in cells:
Explain that as the sugar burns, it is oxidized and releases energy, much of it in the form of heat. Remind students that when they eat sugar, it is oxidized within their cells through the chemical reactions that make up intermediary metabolism.
p. 127t
However, the teacher notes do not make clear that heat is also released when living things oxidize sugar. Students might conclude that heat is released only when sugar burns outside the body.
The idea of heat loss in living organisms is explicitly presented later, in the context of energy transfers in ecosystems:
[C]onsider what happens when a deer eats 1,000 kcal of leaves. About 350 kcal are eliminated as urine, dung, and other wastes. Another 480 kcal are lost as heat. Only about 170 kcal are actually stored as organic matter, mostly as fat. Producers use and transfer energy in a similar way. A plant stores only about 1–5 percent of the solar energy that it converts to sugar as organic material. The rest is reflected off the plant, used in its life processes, or lost in the form of heat.
p. 419s
Idea d2: At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment as heat. Continual input of energy from sunlight keeps the process going.
There is an incomplete content match to this idea, which is treated in text and a diagram as well as in some review questions. The following presentation of Idea d2 shows which parts of the idea are treated (in bold) in Modern Biology: 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 sun is described only as the source of energy for life on earth; there is no mention of the need for continual input of energy from the sun or that this continual input is needed to “keep the process going.”
In the context of describing energy transfers in ecosystems, the text presents the idea that available energy decreases with each trophic level, explains that some is lost as heat, and gives a specific example:
Roughly 10 percent of the total energy consumed in one trophic level is incorporated into the organisms in the next level....
Why is the percentage of energy transfer so low?...Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellular respiration cannot be used by predators to synthesize new biomass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat.
To understand this idea better, consider what happens when a deer eats 1,000 kcal of leaves. About 350 kcal are eliminated as urine, dung, and other wastes. Another 480 kcal are lost as heat. Only about 170 kcal are actually stored as organic matter, mostly as fat. Producers use and transfer energy in a similar way. A plant stores only about 1–5 percent of the solar energy that it converts to sugar as organic material. The rest is reflected off the plant, used in its life processes, or lost in the form of heat.
pp. 418–419s
Section and chapter review questions focus on the idea of energy loss at each trophic level:
Question: Explain why the same area of land can support more herbivores than carnivores.
Suggested Response: Because the transfer of energy from one trophic level to the next is small, more herbivores than carnivores are required in an area to support the energy requirements of the carnivores.
p. 419st, question 5
Question: How does the transfer of energy in an ecosystem differ from the transfer of nutrients?
Suggested Response: Energy flows through an ecosystem, from producers to consumers, and some energy is continually being lost from the ecosystem. Nutrients cycle within an ecosystem and can be used again.
pp. 437s and 436t, question 20
Question: Nitrogen, water, and carbon are recycled and reused within an ecosystem, but energy is not. Explain why energy cannot be recycled.
Suggested Response: At each trophic level, energy is dissipated as heat, a form of energy organisms cannot use. Thus, energy is continually lost to the ecosystem.
pp. 437s and 436t, Critical Thinking, question 2
The text does not present the second part of the idea, that “continual input of energy from sunlight keeps the process going.” Although early on the text presents the idea that “Almost all the energy for life on Earth comes from the sun” (p. 10s) and later notes that energy transfer in ecosystems starts with the sun (“In an ecosystem, energy flows from the sun to autotrophs, then to organisms that eat the autotrophs, then to organisms that feed on other organisms” [p. 415s]), these statements do not make explicit the need for the sun’s energy to sustain ecosystems.
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 text does present the prerequisite idea that “Energy can only change from one form into another”: “One important characteristic of all living things is that they use energy. The amount of energy in the universe remains the same over time, but energy can change form constantly” (p. 35s).
In the context of explaining that living things undergo many complex chemical reactions, the text presents an example of a chemical reaction and then says, “Notice that the number of each kind of atom must be the same on either side of the arrow” (p. 36s). However, this single example is never related to the conservation of matter more generally.
Building a Case
For the most part, Modern Biology asserts the key ideas rather than developing an evidence-based argument to support them. The text does present several observations to support the key 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” (part of Idea d2):
In a recent study of wolves and moose on Isle Royale, Michigan, ecologists found that only 1.3 percent of the total energy consumed by the moose on the island was transferred to the wolves through the wolves' predation on the moose.
p. 418s
[C]onsider what happens when a deer eats l,000 kcal of leaves. About 350 kcal are eliminated as urine, dung, and other wastes. Another 480 kcal are lost as heat. Only about 170 kcal are actually stored as organic matter, mostly as fat.
p. 419s
If you go on a safari in Kenya or Tanzania, for example, you will see about 1,000 zebras, gazelles, wildebeest, and other herbivores for every lion or leopard you see, and there are far more grasses, trees, and shrubs than there are herbivores.
p. 419s
These phenomena are effectively linked with the key idea in the text that introduces the section where these phenomena are presented, Quantity of Energy Transfers:
Roughly 10 percent of the total energy consumed in one trophic level is incorporated into the organisms in the next level. The ability to maintain a constant body temperature, the ability to move, and a high reproductive rate are functions that require a lot of energy. The kinds of organisms that have those characteristics will transfer less energy to the next trophic level than organisms that do not....Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat.
pp. 418–419s
However, the text does not provide evidence for other key ideas and develop an evidence-based argument for them.
Connections
The set of key ideas on matter and energy transformation 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).
Modern Biology presents these ideas in this same order: the molecular level (chapters 2 and 3), the cellular level (chapter 4), the organism level (chapters 6 and 7), and the ecosystem level (chapter 22). The material focuses mostly on telling the energy side of the story.
Energy. Connections among key ideas. Connections are made among the key ideas about the transformation of energy in organisms and between them and ideas about energy transformation in ecosystems. In the introduction to cellular respiration, the text reminds students about the relationships between energy transformation in producers and consumers:
You learned in Chapter 6 that autotrophs, such as plants, use photosynthesis to convert light energy from the sun into chemical energy, which is stored in carbohydrates and other organic compounds. Both autotrophs and heterotrophs depend on these organic compounds for the energy to power cellular activities. By breaking down these compounds into simpler molecules, cells release energy. Some of the energy is used to make ATP from ADP and phosphate. Remember from Chapter 3 that ATP is the main energy currency of cells. The complex process in which cells make ATP by breaking down organic compounds is known as cellular respiration.
p. 127s
Teacher notes point out the Focus Concept and suggest an activity to introduce it:
FOCUS CONCEPT
Matter, Energy, and Organization
Living things are highly organized and require an input of energy to maintain their organization. They obtain the needed energy by breaking down carbohydrates and other macromolecules in chemical pathways that are highly efficient.UNDERSTANDING THE VISUAL
Have students examine the photograph [of a giant panda eating bamboo]. Ask them how animals, such as the one shown here, are either directly or indirectly dependent on plants for energy. (Plants capture energy from the sun and store it in carbohydrates. Animals acquire a portion of this energy by eating either the plants themselves or other animals that have eaten the plants.) Tell students that the focus of this chapter is the process by which organisms convert some of the energy in carbohydrates into a form they can use to drive cellular activities.p. 126t
The text connects ideas about energy transformation in organisms to ecosystems by explaining the energy loss at each trophic level in ecosystems in terms of the amount of energy transfer from one type of organism to another:
Quantity of Energy Transfers
Roughly 10 percent of the total energy consumed in one trophic level is incorporated into the organisms in the next level. The ability to maintain a constant body temperature, the ability to move, and a high reproductive rate are functions that require a lot of energy. The kinds of organisms that have those characteristics will transfer less energy to the next trophic level than organisms that do not. For example, grass transfers more energy to a moose than the moose transfers to a wolf. The measured values for energy transfer from one trophic level to the next can range from 20 percent to less than 1 percent. In a recent study of wolves and moose on Isle Royale, Michigan, ecologists found that only 1.3 percent of the total energy consumed by the moose on the island was transferred to the wolves through the wolves’ predation on the moose. Figure 22-4 represents the rate at which each trophic level in an ecosystem stores energy as organic material. The pyramid shape of the diagram represents the low percentage of energy transfer from one trophic level to another.Why is the percentage of energy transfer so low? One reason is that some of the organisms in a trophic level escape being eaten. They eventually die and become food for decomposers, but the energy contained in their bodies does not pass to a higher trophic level. Even when an organism is eaten, some of the molecules in its body will be in a form that the consumer cannot break down and use. For example, a cougar cannot extract energy from the antlers, hooves, and hair of a deer. Also, the energy used by prey for cellular respiration cannot be used by predators to synthesize new biomass. Finally, no transformation or transfer of energy is 100 percent efficient. Every time energy is transformed, such as during the reactions of metabolism, some energy is lost as heat.
To understand this idea better, consider what happens when a deer eats 1,000 kcal of leaves. About 350 kcal are eliminated as urine, dung, and other wastes. Another 480 kcal are lost as heat. Only about 170 kcal are actually stored as organic matter, mostly as fat. Producers use and transfer energy in a similar way. A plant stores only about 1–5 percent of the solar energy that it converts to sugar as organic material. The rest is reflected off the plant, used in its life processes, or lost in the form of heat.
pp. 418–419s
Connections between key ideas and prerequisites. The material presents only one prerequisite on energy transformation and relates it to part of a key idea. The text states the prerequisite that “[As in physical systems] Energy can only change from one form into another” and relates it to the idea that “[Humans] get energy [from] their food, releasing some of the energy as heat” (part of Idea c2). In its introduction to energy, the text states the prerequisite: “The amount of energy in the universe remains the same over time, but energy can change in form constantly” (p. 35s). The text states the prerequisite again and gives an example in physical systems:
Energy can occur in various forms, and one form of energy can be converted to another form. In a light bulb’s filament, electrical energy is converted to radiant energy (light) and thermal energy (heat).
p. 35s
Then the text notes the forms of energy involved in biological systems, including free energy, and gives an example of an energy transformation in a living system:
As energy flows through a single organism, it may be converted from one form to another. For example, if you ate breakfast this morning, your body is at work now changing the chemical energy found in food into thermal and mechanical energy, among other things.
p. 35s
However, other prerequisites are not presented and connected to key ideas. For example, the text defines exergonic reactions as “[c]hemical reactions that involve a net release of free energy” (p. 36s) and endergonic reactions as “[r]eactions that involve a net absorption of free energy” (p. 36s) but does not present the prerequisite idea that “Different amounts of energy are associated with different configurations of atoms and molecules. Some changes of configuration require an input of energy whereas others release energy.” And the idea that “arrangements of atoms have chemical energy” is not treated in the section on Energy Currency, despite the fact that the text shows the structure of ATP and ADP (p. 54s). Similarly, the text does not treat the prerequisite idea that “Energy in the form of heat is almost always one of the products of an energy transformation,” thereby missing the opportunity to relate physical systems to living systems in its discussion of heat loss in ecosystems (pp. 418–419s).
The text makes several statements that, taken together, state the prerequisite idea that “Food provides the molecules that serve as fuel...for all organisms”:
All of the different foods in the world contain at least one of six basic ingredients: carbohydrates, proteins, lipids, vitamins, minerals, and water....Four of these nutrients—carbohydrates, proteins, fats, and vitamins—are organic compounds because they contain the elements carbon, hydrogen, and oxygen....Carbohydrates are broken down in aerobic respiration to provide most of the body’s energy. Although proteins and fats also supply energy, the body most easily uses the energy provided by carbohydrates. Carbohydrates contain sugars that are quickly converted into the usable energy ATP, while proteins and fats must go through many chemical processes before the body can obtain energy from them.
p. 977s
However, these statements are not explicitly connected to key ideas about energy transformation in organisms (Ideas a2, b2, and c2) or in ecosystems (Idea d2). The phrase “aerobic respiration” used in the text on page 977s is at best a weak connection to the idea that “other organisms get energy...by oxidizing the sugar molecules” (part of Idea c2), given that the key idea is presented 839 pages earlier in the text (p. 138s).
Connections between key ideas and related ideas. The text makes some attempt to connect related ideas to the topic of matter and energy transformations, but it does so in ways that go well beyond the key ideas. For example, the text relates the electron transport in the light reactions of photosynthesis to the structure of the chloroplast membrane (p. 114t). Similarly, a connection is made between mitochondria and energy transformation in the context of presenting the Krebs cycle and the electron transport chain (pp. 134–136s), but appreciating the connection requires an understanding of matter and energy transformations that goes considerably beyond the key ideas:
Scientists report large increases in the life span of a variety of animals that have been fed a low-calorie diet. The increases appear to be due to a reduction in the amount of free oxygen that is present inside mitochondria. Free oxygen can pick up electrons from the electron transport chain and form free radicals, highly reactive substances that injure mitochondria, reducing their ability to produce ATP.
p. 134t
A simpler connection is made between the existence of specialized cell parts for energy transformation and the idea that organisms get energy from oxidizing sugars (part of Idea c2) in the text passage and chapter review question shown below:
Scattered throughout the cytosol are relatively large organelles called mitochondria....Mitochondria are the sites of chemical reactions that transfer energy....mitochondria are usually more numerous in cells that have a high energy requirement. Liver cells, for instance, carry out a host of biochemical activities, and each cell may contain as many as 2,500 mitochondria. Muscle cells also contain many mitochondria.
p. 76s
Question: If a cell has a high energy requirement, would you expect it to have many or few mitochondria? Explain your answer.
Suggested Response: Cells with a high energy requirement should have many mitochondria, since mitochondria are the organelles in which energy in organic compounds is transferred to ATP.
pp. 91s and 90t, question 21
Matter. Connections among key ideas. No connections were noted among key ideas about the transformation of matter. Chapters 6, 7, and 8, which focus on photosynthesis, glycolysis, and respiration respectively, emphasize the energy transformations and energy yield rather than the matter transformations involved in these processes. In the context of nutrient cycles in ecosystems, the text presents the carbon cycle briefly and in the abstract, providing no concrete examples to illustrate the sequences of matter transformations:
During photosynthesis, plants and other autotrophs use carbon dioxide (CO2), along with water and solar energy, to make carbohydrates. Both autotrophs and heterotrophs use oxygen to break down carbohydrates during cellular respiration. The byproducts of cellular respiration are carbon dioxide and water. Decomposers release carbon dioxide into the atmosphere when they break down organic compounds.
pp. 421–422s
The diagram of the carbon cycle represents carbon dioxide with molecular models (p. 421s, Figure 22-6) but does not use models to represent where the molecules came from or what they might become.
Connections between key ideas and their prerequisites. The material makes no connections between key ideas about matter transformation and their prerequisites. The text presents the prerequisite idea that “Carbon and hydrogen are common elements of living matter” in the context of discussing the composition of matter: “In fact, more than 90 percent of the mass of all kinds of living things is composed of combinations of just four elements: oxygen, O, carbon, C, hydrogen, H, and nitrogen, N” (p. 31s). However, this is not linked to key ideas about matter transformation.
Similarly, the text presents the prerequisite idea that “Food provides the molecules that serve as...building materials for [humans]” (though not for “all organisms”) but does not relate it to the synthesis of food molecules by plants or the breakdown and reassembly of those molecules by other organisms:
All of the different foods in the world contain at least one of six basic ingredients: carbohydrates, proteins, lipids, vitamins, minerals, and water....Four of these nutrients—carbohydrates, proteins, fats, and vitamins—are organic compounds because they contain the elements carbon, hydrogen, and oxygen.
p. 977s
Proteins are the major structural and functional material of body cells. Proteins from food help the body to grow and to repair tissues. Proteins consist of long chains of amino acids. The human body uses about 20 kinds of amino acids to construct the proteins it needs.
p. 978s
And the material does not treat at all the prerequisite idea that “No matter how substances within a closed system interact with one another, or how they combine or break apart, the total mass of the system remains the same. The idea of atoms explains the conservation of matter: If the number of atoms stays the same no matter how they are rearranged, then their total mass stays the same.”
Connections between key ideas and related ideas. The material presents one related idea and connects it to a key idea about matter transformation. The text presents the related 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” (at least for some of the elements mentioned): “[m]ore than 90 percent of the mass of all kinds of living things is composed of combinations of just four elements: oxygen, O, carbon, C, hydrogen, H, and nitrogen, N” (p. 31s). Much later, in the context of describing how plants provide other organisms with inorganic nutrients, the text provides a longer list of elements and relates it to the cycling of nutrients in food webs (part of Idea d1):
Plant roots are very efficient at mining the soil for inorganic nutrients, such as nitrogen, phosphorus, potassium, iron, and magnesium. Plants use these inorganic nutrients in the organic compounds they make. Consumers ingest these organic compounds and incorporate the inorganic nutrients into their own bodies. Eventually, these same inorganic nutrients are returned to the soil when the consumer’s waste material or dead body is decomposed by bacteria and fungi.
pp. 570–571s
However, while the text also presents the related idea that “Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules” (see text and Figure 3-5 on page 52s), it does not connect this idea to key ideas about matter transformation in organisms (Ideas a1, b1, or c1) or ecosystems (Idea d1).
Matter and Energy. Connections among key ideas. The material makes one connection between ideas about matter and energy transformations and asks students to make another. In describing the dual role of cellular respiration in providing both energy and matter, the text connects key Ideas c1 and c2:
Cellular respiration provides the ATP that all cells need to support the activities of life. But providing cells with ATP is not the only important function of cellular respiration. Cells also need specific organic compounds from which to build the macromolecules that compose their own structure.
p. 138s
Later, the text connects these two ideas again by attempting to relate energy lost as heat to the inability of organisms to use those molecules of glucose that are oxidized to release energy: “Also, the energy used by prey for cellular respiration cannot be used by predators to synthesize new biomass” (p. 419s).
Lastly, two chapter review questions ask students to compare the transfer of energy with the transfer of nutrients in ecosystems, though the suggested answers require only that students know that energy is lost as heat at each trophic level:
Question: How does the transfer of energy in an ecosystem differ from the transfer of nutrients?
Suggested Response: Energy flows through an ecosystem, from producers to consumers, and some energy is continually being lost from the ecosystem. Nutrients cycle within an ecosystem and can be used again.
pp. 437s and 436t, question 20
Question: Nitrogen, water, and carbon are recycled and reused within an ecosystem, but energy is not. Explain why energy cannot be recycled.
Suggested Response: At each trophic level, energy is dissipated as heat, a form of energy organisms cannot use. Thus, energy is continually lost to the ecosystem.
pp. 437s and 436t, Critical Thinking, question 2
Beyond Literacy
Much of the material on the topic matter and energy transformations is presented at a level considerably beyond that required for understanding the key ideas. For example, in presenting the topic of photosynthesis, the text devotes nine pages to such topics as Light Absorption in Chloroplasts (pp. 112–113s), Electron Transport (pp. 114–115s), Chemiosmosis (p. 116s), Carbon Fixation by the Calvin Cycle (pp. 117–118s), Alternative Pathways (p. 119s), and Rate of Photosynthesis (p. 120). All of the chapter review Critical Thinking questions (p. 123s) require a great deal more than understanding the key ideas. And the investigation provided for the chapter goes well beyond ideas required for science literacy. A computer-based investigation engages students in Examining the Rate of Photosynthesis (pp. 124–125s). This investigation establishes that plants use light in making sugars but details of both the experimental design and the conclusions go well beyond the key idea that “Plants transfer the energy from light into ‘energy-rich’ sugar molecules” (Idea a2).
In Chapter 7: Cellular Respiration, the text devotes about nine pages to presenting biochemical details of the process (including such topics as glycolysis, fermentation, aerobic respiration, the Krebs cycle, and electron transport chain) rather than focusing on the application of key ideas. It is unclear how helpful this is to the student. Consider, for example, the following passage:
However, the molecules formed at different steps in glycolysis and the Krebs cycle are often used by cells to make the compounds that are missing in food. Thus, another important function of cellular respiration is to provide carbon skeletons that can be built up into larger molecules needed by cells.
p. 138s
This passage presents part of Idea c1: “Other organisms...reassemble [structures of plants or animals they have eaten] into their own body structures....” Students can understand this part of Idea c1 if they know that the breakdown of the stored sugars or the body structures of the plants or animals that have been eaten happens in steps and that different molecules are produced at different points in the process; students do not need to know the details of glycolysis and the Krebs cycle (or even the term “cellular respiration”) to comprehend this part of Idea c1.
