High School Biology Textbooks: A Benchmarks-Based Evaluation

Insights in Biology. Kendall/Hunt, 1998

Matter and Energy Transformations: Content Analysis

Map: What the Reviewers Found

This map displays the Content Analysis findings for this textbook in graphical form, showing what the reviewers found in terms of the book’s content alignment and coherence for the set of key ideas on matter and energy transformations. You may find it helpful to print out this map and refer to it as you read the rest of the Content Analysis:

Also helpful for reference are the Matter and Energy Transformations topic maps, which contrast the coherent set of key ideas that the reviewers looked for with a composite of the treatment actually found in all nine evaluated textbooks:

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Alignment

The topic of matter and energy transformations brings together a number of key ideas from both the biological and physical sciences. Insights in Biology treats most of these ideas, either in the module The Matter of Life or the module What on Earth? or in both. The program is unique in its attention to the transformation and conservation of matter and in its use of a Lego analogy to convey a sense of elements combining and recombining but not being lost or gained. The few parts of ideas on the matter side of the story that are not treated are usually implicit in student text or teacher notes and, though not explicit enough to be given credit for a content match, they could easily be made so. Ideas about energy are given far less treatment. While the matter ideas are treated in text, activities, and discussions, the energy ideas are presented mainly as text assertions. 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 text and activities. In the context of describing photosynthesis, the text states the idea in terms of the rearrangement of atoms:

During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch. The sugar molecule contains carbon, oxygen, and hydrogen atoms, all of which were originally found in the carbon dioxide and water.

The Matter of Life, p. 23s

In the activity You Light Up My Life, students compare the amount of starch found in the leaves of plants grown in different conditions—with and without light, and with and without carbon dioxide. Questions help students relate the production of starch to the presence of carbon dioxide (pp. 16–20s).

Later, when introducing an activity on the elements and subunits of various biomolecules, the text reminds students about the role that plants play in recycling the elements carbon, hydrogen, and oxygen:

During photosynthesis, plants take in water and carbon dioxide from their environment. Using solar energy, the elements (hydrogen, oxygen, and carbon) in these molecules are “recycled” and used to make a new, energy-containing molecule: sugar.

The Matter of Life, p. 43s

An accompanying note to the teacher cautions that students may know the equation for photosynthesis but not necessarily relate it to the building blocks that make up plant structures:

Even if students seem to know the equation for photosynthesis and have worked with it before, they still may not make the connection that carbon dioxide, water, and energy from the sun are all converted into a substance (sugar—a simple carbohydrate) that ultimately makes up the components of a plant.

The Matter of Life, p. 31t

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 part of this idea in the module The Matter of Life. The following presentation of Idea b1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Insights in Biology: Plants break down [use] the sugar molecules that they have synthesized into carbon dioxide and water, use them as building materials, or store them for later use.

The idea that plants use the sugars they have made as building materials or store them for later use is treated in text:

Sucrose is synthesized when fructose and glucose are joined together to form a molecule containing two separate sugar molecules (disaccharide). Sucrose is the major sugar that is transported throughout a plant and is the starting material for many other molecules in the plant. Sugar molecules can also join together as links in long chains called polysaccharides. The starch that you tested for in the “You Light Up My Life” investigation is an example of a polysaccharide. Starch consists of many glucose molecules joined together. Starch serves as food storage for the plant: when food is needed the starch is broken down into simple sugars. The sugars can then be transported wherever in the plant they are needed as building blocks and energy sources.

p. 24s

Students are also asked to create a concept map that shows how photosynthesis occurs and how its products enable a plant to survive and maintain the characteristics of life.

The idea that plants break down sugar molecules into carbon dioxide and water is treated only in a question following the text presentation of the metabolism of glucose: “Do you think that photosynthetic organisms carry out this process? Why or why not? Where would the glucose come from?” (p. 67s, question 2). However, the teacher’s guide provides no answer to this question, indicating only that “This reading presents a summary overview of the processes of metabolism and the critical role that oxygen plays” (p. 94t). The reading itself deals with inputs and outputs of glycolysis, the subsequent breakdown of pyruvate, and the transfer of electrons to oxygen in living organisms, but is not explicit about plants (pp. 62–66s). Plants are only mentioned at the beginning of the reading, when mentioning the role plants play in converting sunlight into chemical energy (in sugar) and their use of sugar as building blocks for carbohydrates, proteins, lipids, and nucleic acids (p. 62s).

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 most of this idea, which is extensively treated in four learning experiences in the module The Matter of Life. The following presentation of Idea c1 shows which parts of the idea are treated (in bold) and what alternative vocabulary is used (in brackets) in Insights in Biology: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 [milk, biomolecules], including some energy stores.

The idea that other organisms obtain their building blocks from (but not break down) the plants and animals they eat is treated in Learning Experience 4: Feeding Frenzy. The text states:

The sugars and other carbohydrates that plants synthesize serve as the source of energy and building blocks (that is, food) for the plant. Organisms that do not carry out photosynthesis must obtain all their nutritional needs by eating photosynthesizing organisms (plants) and other organisms in order to obtain the building blocks and energy necessary to maintain the characteristics of life.

p. 27s

Students then analyze various foods to determine what building blocks they contain (pp. 28–32s) and the text reiterates the importance of these building blocks:

If an organism is to sustain life it must be able to obtain building blocks and energy from the biomolecules making up its food. As you have determined, non-photosynthesizing organisms must obtain from their environment three basic types of nutrients: proteins, carbohydrates, and fats.

p. 32s

The same learning experience then treats the idea that organisms can store sources of energy and building material. After presenting a scenario about a young woman with an eating disorder, the text indicates that “[t]he body has no way of storing proteins” but that “[i]n humans, glucose is stored as glycogen in muscle tissue” and that “[f]ats are also a major energy storage form” (p. 33s). However, it is not made clear that fats are rearranged from food.

The idea that organisms break down the food they eat in order to obtain the necessary building blocks is treated in Learning Experience 5: The Lego of Life. The text explains what happens to the hamburger and fries eaten for lunch: “In order to make them accessible to you, these foods must be broken down into forms your body can work with. Food taken into your body gets broken down into smaller and smaller components” (p. 39s).

The text introduces the idea of breakdown and reassembly of building blocks in Learning Experience 6: Turning Corn into Milk: Alchemy or Biochemistry? Students determine the components in corn and milk and compare them (pp. 47–50s). Then they read the text, which contains the following information:

If a cow could break down corn into smaller subunits, it could then rearrange them and build something new....The transformation of corn into milk actually involves many steps in which the starch and other biomolecules are broken down (catabolized) and the components reassembled into the sugars and other biomolecules of milk.

pp. 52–53s

Finally, the teacher’s guide describes three points that should come out in a class discussion. Questions are provided for which these points are the answers:

Although composed of the same organic biomolecules, corn and milk are made up of different arrangements of the elements that make up these biomolecules.

Variation in the way these subunits are put together allows for variation in the kinds of carbohydrate, protein, or lipid that might be made.

The starch (and to some extent the lipids and protein) in corn gets broken down (oxidized) into smaller molecules which are then used in different pathways to generate other biomolecules found in milk such as lactose, protein, and lipids.

pp. 74–75t

However, transforming corn into milk does not convey the idea that other organisms reassemble the subunits into their own body structures.

The idea that glucose is broken down into CO2 is presented in diagrams in Learning Experience 7: A Breath of Fresh Air (pp. 64s, 66s). Analysis questions ask students to describe the fate of the glucose molecule as it is catabolized (p. 67s, question 1).

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 the modules The Matter of Life and What on Earth?

The Matter of Life, which is to be used first in the program, treats the idea that organisms disassemble food into building blocks and then use them to make milk or biomolecules (per Idea c1). In a section entitled “A Mere Six Ingredients,” the text states the idea that there are a few kinds of elements that make up living things:

These nutrients in turn are made up of only six elements which are used to build a tremendous diversity of living things by being arranged in different ways. In living organisms atoms of the six elements (carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen) are joined in different arrangements and in different quantities to form all of the different biomolecules. During photosynthesis, plants take in water and carbon dioxide from their environment. Using solar energy, the elements (hydrogen, oxygen, and carbon) in these molecules are “recycled” and used to make a new, energy-containing molecule: sugar.

p. 43s

The teacher’s guide, in a Science Background section, uses an example of one element (nitrogen) to explain how it is available from different sources (protein in food, or the atmosphere) and therefore passes through plants, other living organisms, and the environment; but it is not clear that this example is to be conveyed to students (p. 92t).

In What on Earth?, the text introduces the idea that elements cycle in ecosystems in the introduction to an activity in Learning Experience 3: Round and Round They Go:

Organic nutrients such as carbohydrates, proteins, and lipids are made up of elements including carbon, oxygen, hydrogen, and nitrogen. However, these elements are also present in the environment in inorganic forms.

The amounts of carbon, oxygen, and nitrogen in the present atmosphere have remained nearly the same since life came into existence about 3.8 billion years ago. That means that the oxygen you breathe could also have been inhaled by your great-grandparents or by George Washington. And the carbon in the food you ate for dinner might once have been part of a dinosaur! How is this possible?

p. 28s

Students work through carbon, nitrogen, and water cycles (see instructions on page 45t) by reading statements in text and drawing a cycle to represent what they have read (pp. 28–31s). One of the Analysis questions asks students to follow what happens to carbon, and another asks them to consider implications of there being a finite amount of each element:

Draw a carbon cycle, using a black marker or crayon. On the same sheet of paper, draw an oxygen cycle, using a blue marker or crayon.

p. 31s, Analysis, question 2

All of the elements in these cycles are finite (of limited amounts). How is this fact important in your thinking about the cycles?

p. 31s, Analysis, question 5

Notes to the teacher emphasize the separateness of the carbon and oxygen cycles, and that cycling is needed for life to continue (pp. 46–47t).

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 module The Matter of Life. In Learning Experience 3: Everything Under the Sun, students observe that starch is present in leaves grown in the light but not in leaves grown in the dark (pp. 16–20s). The text then describes the input form of energy (energy from sunlight) and output form of energy (chemical energy in the bonds between the atoms) in the process of photosynthesis:

The process of photosynthesis can actually be separated into two related biochemical processes: one which is dependent on the presence of light, and one which can occur in the absence of light (see Figure 3.5). During the light-dependent reaction energy in sunlight (solar energy) is absorbed by the green pigment that gives plants their characteristic color, chlorophyll. The chlorophyll, in turn, transfers this solar energy to another molecule, which stores it as chemical energy.

The chemical energy obtained during the light-dependent part of photosynthesis (called the “light reaction”) is then used in the light-independent process (called the “dark reaction”). During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch....The sugar molecule also contains chemical energy in the bonds between the atoms.

p. 23s

However, the above passage does not make clear that light energy is the source of the chemical energy in the bonds of the sugar molecules.

Later in the module, in an introduction to sugar metabolism, the text reminds students of the idea:

As you learned in Learning Experience 3, the origin of energy on Earth [is] the sun. Plants transform solar energy into chemical energy (sugar). Plants then use this sugar to form carbohydrates, proteins, lipids, and nucleic acids through the processes of anabolism and catabolism.

During metabolic processes, the energy from the sun flows, in the form of chemical energy, from molecule to molecule and is used to take molecules apart and build new molecules. During catabolism larger molecules are broken down or oxidized. This reaction requires the input of some energy, but much more energy is released from the chemical energy stored in the chemical bonds in the molecules. During anabolism energy is stored in chemical bonds where it remains until the molecule is catabolized in another reaction.

p. 62s

In What on Earth?, the idea is noted in an introduction to an activity on energy flow through ecosystems (p. 23s).

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, which is treated in fragments in two different modules. The idea that plants get their energy from sugars (but not by oxidizing or breaking down sugars) is presented in The Matter of Life in Learning Experience 3: Everything Under the Sun. After briefly explaining how the sun’s energy is transformed into the chemical energy of sugar, the text notes: “Thus, the sugar molecule becomes the primary source of both energy and building material for the plant” (p. 23s). The idea that the sugar is oxidized is noted later, in Learning Experience 7: A Breath of Fresh Air: “During catabolism larger molecules are broken down or oxidized” (p. 62s).

It is not until the module What on Earth? that the text points out what plants use energy for: “All of life’s processes require energy. After a consumer obtains nutrients from its food source, it processes the nutrients to obtain energy. The energy is then used by the organism for growth, movement, and a variety of other activities” (p. 23s). The module also presents the part of the idea that some of the energy is released as heat. Students calculate the loss of energy at each trophic level of an ecosystem (pp. 23–24s). In introducing the task, the text notes that “The producer is consumed by the primary consumer, but some of the energy is used during metabolic activities of the producer, or lost as heat” (p. 24s).

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 in the module The Matter of Life. The following presentation of Idea c2 shows which parts of the idea are treated (in bold) in Insights in Biology: 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.

The idea that other organisms break down biomolecules (but not consumed body structures) is conveyed in The Matter of Life Learning Experience 6: Turning Corn into Milk: Alchemy or Biochemistry? (pp. 52–53s). The text, which focuses mainly on the matter transformations involved, also notes that usable energy is made available in the process:

The slower oxidation of glucose has several advantages for the organism; it prevents the organism from burning up; it enables the energy in the bonds of the glucose molecule to be transferred to other molecules for use by the organism rather than being released as heat; and it allows the products of the glucose molecule breakdown to be used by the organism to synthesize other biomolecules.

p. 53s

In Learning Experience 7: A Breath of Fresh Air, after briefly describing glycolysis, the subsequent breakdown of pyruvate, and electron transfer, the text notes the idea in introducing the role of oxygen in respiration: “Oxygen is the organism’s key to obtaining, finally, the solar energy that was trapped in glucose” (p. 65s).

The idea that energy is released as heat is not treated. No mention is made of the release of some energy as heat in the discussion of cellular respiration in The Matter of Life. The statement above (from page 53s) is not explicit about heat being released in the process. In fact, it could be interpreted as stating that the slower oxidation of glucose prevents heat from being released.

In What on Earth?, students calculate the loss of energy at each trophic level of an ecosystem, but no mention is made of energy being released as heat (pp. 23–24s, 40–42t). The table of energy loss along a food chain in the student text makes no mention of heat loss, only of energy lost during metabolism or energy lost to waste. The Science Background section in the teacher’s guide notes that the laws of thermodynamics can be applied to ecosystems, that energy is not lost but its capacity to do work is decreased, and that energy is changed into a different form; but teachers are not instructed to discuss these ideas with students. In any event, the idea that heat is the predominant form into which energy is changed is not mentioned.

It should also be noted that the material focuses on a single “other organism”—cows. While the text uses the term “consumers” it does not present another specific organism or generalize from cows to other organisms.

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 not a content match to this idea. Neither the first nor the second sentence is presented completely and the idea that the second sentence is a consequence of the first is not presented at all.

The material treats the idea that energy is lost at each trophic level (part of the first sentence of Idea d2) but not the idea that energy is stored in newly made structures. In What on Earth?, the text introduces an activity on the flow of energy in ecosystems by asking why energy appears to be lost at each level and beginning to relate the process of energy flow in ecosystems to processes occurring in individual organisms:

Think about the number of blades of grass it takes to feed a prairie dog, and the number of prairie dogs to feed a coyote. Why is there such a difference? Why are there fewer consumers in each successive trophic or feeding level?

All of life’s processes require energy. After a consumer obtains nutrients from its food source, it processes the nutrients to obtain energy. The energy is then used by the organism for growth, movement, and a variety of other activities.

Does the amount of energy available in a food source depend on its trophic level? In the process of photosynthesis, producers convert light energy (from the sun) to chemical energy (in the form of sugar) in their chlorophyll-containing structures. Herbivores (plant-eaters) are consumers that use the chemical energy harnessed by producers as their food source; carnivores consume herbivores. In this activity, you will investigate the flow of energy through organisms in successive trophic levels of a food chain.

p. 23s

The Matter of Life (the first module in Insights in Biology) presents part of the second sentence but does not convey the idea that the sun is required to keep the process going. While presenting metabolism, the text notes that the sun is the source of energy and that energy flows from one molecule to the next:

[T]he origin of energy on Earth [is] the sun. Plants transform solar energy into chemical energy (sugar). Plants then use this sugar to form carbohydrates, proteins, lipids, and nucleic acids through the processes of anabolism and catabolism.

During metabolic processes, the energy from the sun flows, in the form of chemical energy, from molecule to molecule and is used to take molecules apart and build new molecules.

p. 62s

But this idea is not repeated in What on Earth? when presenting the idea that there are fewer organisms at each trophic level. Students are asked to calculate the energy loss at each trophic level and graph their results (pp. 24s, 40t). The Analysis questions emphasize the energy loss at each level and the resulting pyramid of numbers. However, no mention is made in the student text that this energy loss is why continual input of energy from the sun is required. The Science Background section in the teacher’s guide makes this link, but it is not clear that the idea will be conveyed to students:

Energy is changed into a different form and is unusable to the organism at the next trophic level. Thus, the flow of energy is unidirectional through the trophic levels. Energy is constantly being replaced in an ecosystem by sunlight and plant photosynthetic activity.

p. 42t

Again, no mention is made that “wasted” energy is released as heat.

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. Some parts of the idea are not treated and other parts are treated only implicitly.

The idea that living systems share the same principles of transformation and conservation that govern the workings of physical systems is not treated.

The idea that energy is transformed in ecosystems is presented in What on Earth? in the introduction to the energy “loss” activity in Learning Experience 3: Round and Round They Go:

In the process of photosynthesis, producers convert light energy (from the sun) to chemical energy (in the form of sugar) in their chlorophyll-containing structures. Herbivores (plant-eaters) are consumers that use the chemical energy harnessed by producers as their food source; carnivores consume herbivores. In this activity, you will investigate the flow of energy through organisms in successive trophic levels of a food chain.

p. 23s

However, the idea that energy is mainly conserved is only implicit in student calculations and in the teacher’s guide, and may not be evident to students. The table on energy loss along a food chain shows only energy loss. Even if students add up the percent of energy lost during metabolism and the percent of energy lost to waste and then subtract the total energy lost from 100 percent to obtain the percent of available energy, they may not appreciate that energy is conserved. Although a marginal note in the teacher’s guide might get at the idea of energy conservation, the question itself, even if asked, is still not explicit about energy conservation: “Do students understand that energy has been used by organisms on each trophic level and is not ‘lost’ but is no longer available to organisms in the next trophic level?” (p. 41t).

And the text states that particular elements have remained constant over long periods of time but does not generalize to all elements that make up the molecules of living things:

The amounts of carbon, oxygen, and nitrogen in the present atmosphere have remained nearly the same since life came into existence about 3.8 billion years ago. That means that the oxygen you breathe could also have been inhaled by your great-grandparents or by George Washington. And the carbon in the food you ate for dinner might once have been part of a dinosaur! How is this possible?

What on Earth?, p. 28s

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Building a Case

Insights in Biology provides some evidence to support some of the key ideas, but typically does not use the evidence to build a case for the key ideas. For example, after reading about the classic van Helmont experiment (Matter of Life, pp. 20–22s), the Analysis questions focus on van Helmont’s experimental design and conclusions rather than on considering how we know that “Plants make sugar molecules from carbon dioxide (in the air) and water” (Idea a1). What on Earth? presents a table showing (for producers, herbivores, and carnivores) the percentage of energy lost during metabolism and the percentage of energy lost to waste (p. 24s). However, the text does not explain how this information was determined or make clear that it constitutes evidence to support 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 and that continual input of energy from sunlight keeps the process going” (Idea d2).

In one instance, students are asked to reflect on how they know one of the key ideas. After students compare the amount of starch they found in leaves of plants grown with and without carbon dioxide (Matter of Life, pp. 16–20s), they are asked to “describe how [they] know starch is a product of photosynthesis” (p. 19s). However, they are not asked to think about other evidence that supports the idea or to imagine familiar phenomena that might be consistent with it.

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Connections

The set of key ideas on matter and energy transformations is highly complex, spanning four levels of biological organization (molecular, cellular, organism, and ecosystem) and depending heavily on knowledge in physical science (e.g., energy forms and transformations among them, and recombination of atoms in chemical reactions).

The Insights in Biology modules are unique in emphasizing the matter side of the story. Most materials emphasize energy, giving matter short shrift. Both matter and energy are treated in The Matter of Life in Learning Experience 3: Everything Under the Sun (where photosynthesis is presented), in Learning Experience 5: The Lego of Life (where atoms and elements are presented), in Learning Experience 6: Turning Corn into Milk: Alchemy or Biochemistry? (where breakdown and reassembly of subunits is dealt with), and in Learning Experience 7: A Breath of Fresh Air (where cellular respiration is described). The ecosystem level is presented in What on Earth?, a module intended to come later in the course. The energy side of the story parallels the matter story but receives far less treatment. Teachers are not alerted to the different places where matter and energy ideas are treated, nor is a rationale for this sequence conveyed. Also, some aspects of the matter sequence do not make sense. For example, the text presents the equation for photosynthesis (with formulas, subscripts, and coefficients) even though atoms have not yet been presented. And the processes of photosynthesis and cellular respiration are introduced before any mention is made of cells.

Matter. Connections among key ideas. The material makes some connections among the key ideas about matter transformation. The Matter of Life relates the idea that plants make sugar molecules (Idea a1) to the idea that the sugar made by the plant is used as building material or stored (Idea b1):

During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch. The sugar molecule contains carbon, oxygen, and hydrogen atoms, all of which were originally found in the carbon dioxide and water....

p. 23s

What happens to these molecules of C6H12O6 sugar in the plant? Some of them remain as simple sugars such as fructose or glucose. Glucose, or grape sugar, gives that fruit its distinctly sugary taste. Another abundant sugar in plants is sucrose, also called table sugar or cane sugar because of its high concentration in the stems (canes) of plants, such as the sugar cane plant. Sucrose is synthesized when fructose and glucose are joined together to form a molecule containing two separate sugar molecules (disaccharide). Sucrose is the major sugar that is transported throughout a plant and is the starting material for many other molecules in the plant.

Sugar molecules can also join together as links in long chains called polysaccharides. The starch that you tested for in the “You Light Up My Life” investigation is an example of a polysaccharide. Starch consists of many glucose molecules joined together. Starch serves as food storage for the plant; when food is needed, the starch is broken down into simple sugars. The sugars can then be transported wherever in the plant they are needed as building blocks and energy sources.

Some sugars form the starting materials for other large molecules in the plant.

p. 24s

The module also makes a connection between the ideas that plants and other organisms use the sugars as building materials (parts of Ideas b1 and c1):

All living organisms must obtain building blocks for making new biomolecules....

How do different organisms obtain these nutrients? For most organisms, there are only two possible ways: by constructing them during photosynthesis, or by feeding on other organisms. During photosynthesis, plants take in water and carbon dioxide from their environment....Since plants do not “eat” and, therefore, do not take in biomolecules such as protein and lipid, plants must use this sugar molecule to construct all the carbohydrates, lipids, and proteins they require to sustain life....

Organisms that do not carry on photosynthesis are required to take in complex biomolecules from their environment by eating plants (with the nutrients the plants have manufactured) or other animals (that have eaten plants or still other plant-eating animals)....

p. 43s

However, other important connections are not made. An activity in What on Earth? stops short of relating the transformation of matter in ecosystems (Idea d1) to photosynthesis in plants (Idea a1) and respiration in both plants and animals (Ideas b1 and c1) (pp. 28–29s, 47t). Students use statements about photosynthesis and respiration and other statements about decomposition and fossil fuels to create a diagram of carbon and oxygen cycling in ecosystems, but none of the statements convey Idea d1.

Connections between key ideas and their prerequisites. The text makes connections between three key ideas and their prerequisites. The Matter of Life relates the idea that sugar is made from carbon dioxide and water (Idea a1) to the prerequisite idea that “Food provides the molecules that serve as fuel and building material for all organisms”:

The chemical energy obtained during the light-dependent part of photosynthesis (called the “light reaction”) is then used in the light-independent process (called the “dark reaction”). During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch. The sugar molecule contains carbon, oxygen, and hydrogen atoms, all of which were originally found in the carbon dioxide and water....The sugar molecule also contains chemical energy in the bonds between the atoms. Thus, the sugar molecule becomes the primary source of both energy and building materials for the plant.

p. 23s

The text restates this connection when introducing an investigation on the basic components of food:

Why do we eat? Why do we eat what we eat? Using only air, sunlight, water, and a dash of minerals and vitamins, plants and other photosynthetic organisms can obtain all of the energy and manufacture all of the materials they need to maintain the characteristics of life. Animals, however, are not so independent. They depend on plants to supply them with many of the resources required to sustain life....

The sugars and other carbohydrates that plants synthesize serve as the source of energy and building blocks (that is, food) for the plant. Organisms that do not carry out photosynthesis must obtain all their nutritional needs by eating photosynthesizing organisms (plants) and other organisms in order to obtain the building blocks and energy necessary to maintain the characteristics of life.

p. 27s

Students then carry out food tests to determine that foods from both plants and animals contain the same basic components (pp. 28–32s). This activity gets at the notion of recombination, though not at the molecular level.

The next activity relates the prerequisite idea that “Food provides the molecules that serve as...building materials for all organisms” to the key idea that “Other organisms break down the stored sugars of the plants they eat....” (Idea c1). The text explains that “In order to make them accessible to you, these foods must be broken down into forms your body can work with” (p. 39s).

The prerequisite idea that “Carbon and hydrogen are common elements of living matter” is presented in The Matter of Life and linked to food making in plants (Idea a1). After its presentation of atoms, elements, and the periodic table, the text states:

All living organisms must obtain building blocks for making new molecules and energy to carry out the essential processes of life. These building blocks and energy are found in the biomolecules that make up food and that also make up all living things: carbohydrates, lipids, nucleic acids, and proteins. These nutrients in turn are made up of only six elements, which are used to build a tremendous diversity of living things by being arranged in different ways. In living organisms atoms of the six elements (carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen) are joined in different arrangements and in different quantities to form all of the different biomolecules.

How do different organisms obtain these nutrients? For most organisms, there are only two possible ways: by constructing them during photosynthesis, or by feeding on other organisms. During photosynthesis, plants take in water and carbon dioxide from their environment. Using solar energy, the elements (hydrogen, oxygen, and carbon) in these molecules are “recycled” and used to make a new, energy-containing molecule: sugar. Since plants do not “eat” and, therefore, do not take in biomolecules such as protein and lipid, plants must use this sugar molecule to construct all the carbohydrates, lipids, and proteins they require to sustain life. The sugar, in conjunction with vitamins and minerals which the plant obtains from the soil, provides all the essential nutrients a plant needs.

Organisms that do not carry on photosynthesis are required to take in complex biomolecules from their environment by eating plants (with the nutrients the plants have manufactured) or other animals (that have eaten plants or still other plant-eating animals). Ultimately, all the nutrients animals take in can be traced back to plants. Thus, the phrase “You are what you eat” is a very literal one. In plants and other photosynthetic organisms, food is manufactured by the process of photosynthesis. In animals, complex biomolecules are taken in as food and the elements which make them up are recycled into biomolecules which make up the animal. Six elements—carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen—joined in different arrangements and in different quantities, are the main ingredients of life.

pp. 43–44s

However, the prerequisite idea from physical science that matter is conserved in all closed systems and that this conservation can be explained by the conservation of atoms is neither treated nor connected to the [re]cycling of elements between ecosystems and the physical environment (Idea e).

Connections between key ideas and related ideas. The material presents the related idea that “The chief elements that make up the molecules of living things are carbon, oxygen, hydrogen, nitrogen, sulfur, [and] phosphorus” and weakly connects it to the cycling of elements in ecosystems (Idea d1). The introduction to the activity A Mere Six Ingredients makes the related idea explicit but does not connect it to the cycling of elements:

All living organisms must obtain building blocks for making new biomolecules....These building blocks and energy are found in the biomolecules that make up food and that also make up all living things....These nutrients in turn are made up of only six elements, which are used to build a tremendous diversity of living things by being arranged in different ways. In living organisms atoms of the six elements (carbon, hydrogen, oxygen, sulfur, phosphorus, and nitrogen) are joined in different arrangements and in different quantities to form all of the different biomolecules.

The Matter of Life, p. 43s

In a later module, a connection is made but the related idea itself is not stated. In introducing an activity in which students create labeled diagrams of the carbon, nitrogen, and water cycles, the text connects the ideas:

Organic nutrients such as carbohydrates, proteins, and lipids are made up of elements including carbon, oxygen, hydrogen, and nitrogen. However, these elements are also present in the environment in inorganic forms.

The amounts of carbon, oxygen, and nitrogen in the present atmosphere have remained nearly the same since life came into existence about 3.8 billion years ago. That means that the oxygen you breathe could also have been inhaled by your great-grandparents or by George Washington. And the carbon in the food you ate for dinner might once have been part of a dinosaur! How is this possible?

What on Earth?, p. 28s

The material does not connect the related idea that “Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules” to ideas about plants making sugars from carbon dioxide and water (Idea a1) or using them as building materials (part of Idea b1), even though The Matter of Life presents the related idea in the teacher’s guide (p. 58t).

Energy. Connections among key ideas. As noted above, energy ideas are treated alongside ideas about matter but receive considerably less extensive treatment. Not surprisingly, the material makes no connections among the key ideas about energy transformation. For example, the idea that usable energy decreases with each trophic level in ecosystems (Idea d2) is not linked to the dissipation of heat in the bodies of organisms (Ideas b2 and c2).

Connections between key ideas and their prerequisites. Only one of the energy prerequisites is treated. The Matter of Life relates the idea that the sun’s energy is stored in “energy-rich” sugar molecules (Idea a2) to the prerequisite idea that “Food provides the molecules that serve as fuel and building material for all organisms”:

The sunlight and air that a plant needs are used in the process of photosynthesis to generate food (substances which provide building blocks and energy for organisms) for a plant....

The chemical energy obtained during the light-dependent part of photosynthesis (called the “light reaction”) is then used in the light-independent process (called the “dark reaction”). During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch....The sugar molecule also contains chemical energy in the bonds between the atoms. Thus, the sugar molecule becomes the primary source of both energy and building materials for the plant.

p. 23s

However, neither The Matter of Life nor What on Earth? treats the ideas that “Arrangements of atoms have chemical energy,” that “Different amounts of energy are associated with different configurations of atoms and molecules,” and that “Most of what goes on in the universe involves some form of energy being transformed into another. Energy in the form of heat is almost always one of the products of energy transformations.” Hence, no foundation is established for the energy transformations in photosynthesis or respiration or the loss of usable energy at each trophic level in ecosystems. Similarly, although the term “oxidized” is used to describe what happens when a molecule loses electrons (The Matter of Life, p. 53s), the prerequisite idea that an especially important reaction involves combination of oxygen with something else—as in burning or rusting—is not treated.

Connections between key ideas and related ideas. The material presents the related idea that “Within cells are specialized parts for the capture and release of energy” (The Matter of Life, p. 95s). However, it does not make a connection between this idea and ideas about energy transformations in organisms (Ideas a2, b2, and c2) and hence loses this opportunity to relate processes in organisms to the cells that compose them.

Matter and Energy. The material makes two connections between key ideas about matter transformation and those about energy transformation. The Matter of Life relates the ideas that plants transform matter (Idea a1) and energy (Idea a2) while briefly describing the light and dark reactions of photosynthesis:

The chemical energy obtained during the light-dependent part of photosynthesis (called the “light reaction”) is then used in the light-independent process (called the “dark reaction”). During this process, the atoms in carbon dioxide and water are rearranged to form new molecules of sugar, the substance that makes up starch. The sugar molecule contains carbon, oxygen, and hydrogen atoms, all of which were originally found in the carbon dioxide and water....The sugar molecule also contains chemical energy in the bonds between the atoms. Thus, the sugar molecule becomes the primary source of both energy and building materials for the plant.

p. 23s

And the material presents a connection between parts of key ideas about matter and energy transformation in other organisms (Ideas c1 and c2). The Matter of Life asks students to consider the chemical reaction for the burning of glucose and to explain how this reaction occurs metabolically, including the source of the raw materials and energy and the fate of the final products (p. 67s, question 1). The teacher’s guide encourages teachers to

Help students to focus on the idea that the metabolic transformation involves a complex series of steps which result in:

  • the generation of products for use in building new molecules;
  • the generation of energy containing molecules that serve as a source of energy for the activities of the organism;
  • the generation of carbon dioxide and water as waste products;
  • the production of carbon dioxide which can be used by plants.

The Matter of Life, p. 95t

However, the material does not make connections between key ideas about matter and energy transformation in plants or ecosystems.

As was previously noted, the culminating idea about transformation and conservation (Idea e) is treated in terms of matter only. There is no corresponding treatment of energy that could be linked to the matter story. While exchange of matter between living things and the environment is presented (What on Earth?, p. 28s), it is not linked to ideas about conservation in closed systems more generally. So there is no potential for students to appreciate 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.

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Beyond Literacy

The program makes a genuine attempt to limit technical terms and details of metabolism, focusing instead on ideas needed for science literacy. For example, The Matter of Life presents only the basic outlines of photosynthesis (p. 23s), glycolysis (p. 63s), the subsequent breakdown of pyruvate (p. 64s), and electron transfer to oxygen (pp. 65–66s). Still, the modules do include terms like “light reaction,” “dark reaction,” “disaccharide,” “polysaccharide,” “anabolism,” “catabolism,” and “pyruvate” that don’t seem necessary.

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