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Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

Science 2000. Decision Development Corporation, 1991 and 1995
Earth Science Life Science Physical Science

1.
About this Evaluation Report
2.
Content Analysis
3.
Instructional Analysis
[Explanation] This section examines whether the curriculum material's content aligns with the specific key ideas that have been selected for use in the analysis.
[Explanation] This section examines whether the curriculum material develops an evidence-based argument for the key ideas, including whether the case presented is valid, comprehensible, and convincing.
[Explanation] This section examines whether the curriculum material makes connections (1) among the key ideas, (2) between the key ideas and their prerequisites, and (3) between the key ideas and other, related ideas.
[Explanation] This section notes whether the curriculum material presents any information that is more advanced than the set of key ideas, looking particularly at whether the “beyond literacy” information interrupts the presentation of the grade-appropriate information.
[Explanation] This section notes whether the curriculum material presents any information that contains errors, misleading statements, or statements that may reinforce commonly held student misconceptions.

Alignment

Idea a: Food (for example, sugars) provides molecules that serve as fuel and building material for all organisms.
There is a content match at the molecular level. However, the teacher’s lesson plan states the idea at the substance level (rather than at the molecular level) as a learning objective (“To understand that our bodies need food for energy, growing, and building new cells”) and again in the background section for teachers (“[F]ood provides energy to fuel metabolism and activity (to do work) and the materials to build new cells” [6.4.25.2, LP2, p. 12]). After students brainstorm why people need to eat, a discussion relates cell replacement to the body’s need for elements and, therefore, for food. A video on the human digestive system describes the breakdown of large food molecules into smaller molecules and indicates that molecules derived from food are used as building blocks for the construction of new molecules needed by the body (6.4.25.2). Pop-apart models are shown in a video to illustrate that food is broken down, transported to cells, and then rebuilt. A demonstration of burning popcorn is used to convey the transformation of energy stored in food into heat. Student learning of this idea is assessed at the end of the cluster by asking students the questions: “What does your body do with food? How does it use food?” (6.4.25.5, SI25–5, p. 29).

Idea b: Plants make their own food, whereas animals obtain food by eating other organisms.

There is a content match. This is an intended learning goal of Science 2000, although there is little specific treatment of it. In grade 5, unit 1, this key idea is listed as a key concept for students to learn (5.1.4.3, LP3, p. 20). But despite considerable study of food chains in grades five and six, the contrast between plants and animals in terms of their source of food or energy is not made unequivocally. In grade 7, unit 2, cluster 11, students observe a video of a swamp ecosystem, which states that plants capture the sun’s energy, and then “provide energy to animals that eat them (see the ‘Food Chain, Swamp’ video clip).” In cluster 12, student groups review the food web concepts and, while learning to distinguish among producers, consumers, and decomposers, are expected to know that plants produce food and animals consume food.

Idea c: Matter is transformed in living systems.

Idea c1: Plants make sugars from carbon dioxide (in the air) and water.

There is a content match. This idea is presented explicitly in grade six, when the material explains photosynthesis (6.4.25), and somewhat peripherally in grade seven, both in the investigation of factors affecting the rate of photosynthesis and in a video on how plants produce food (7.2.12). The sixth-grade unit presents both the word and the symbolic equations for photosynthesis (through text and a teacher-led discussion). The unit also includes a video that describes the raw materials and final products, calling attention to the transformation of matter in this sentence: “The interesting thing is that this newly formed molecule is a kind of sugar, a food, even though it was made out of raw materials that are not food” (6.4.25.4). At the end of the lesson cluster, students are asked to synthesize what they have learned by diagramming matter and energy inputs and outputs in a food chain and responding to several specific questions (6.4.25.5, SI25–5). On their drawing of a green plant, students are asked (a) to identify “what substances the plant must take in to create ‘food’ or carbohydrate molecules” and to indicate the molecules’ entry points with arrows, and (b) to provide the chemical formula of the simple carbohydrate made by plants and to indicate where the carbohydrate molecules leave the plant (6.4.25.5, SI25–5, p. 28) (an error, in that carbohydrates do not “leave the plant”). In grade seven, the text describes photosynthesis in terms of starting materials and final products, and a video develops the notion of raw materials and products through narrative and animation (7.2.12.1).

Idea c2: Plants break down the sugars they have synthesized back into simpler substances—carbon dioxide and water—and assemble sugars into the plants' body structures, including some energy stores.
There is a partial content match. The following presentation of Idea c2 shows which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets): Plants break down the sugars they have synthesized back into simpler substances—carbon dioxide and water—and assemble sugars into the plants' body structures, including some energy stores.

This idea is dealt with minimally in grade six, in the context of cellular respiration, and in grade seven, in the context of respiration in germinating seeds. In grade 6, unit 4, cluster 25, lesson 4, the lesson plan indicates:

As an added note, ask students if they can guess what plants do with the food they produce. What do plants need in order to grow? Like all living things, they need energy as well as new materials to build up new cells and replace the old. So plants undergo cellular respiration too, taking in oxygen and releasing carbon dioxide, water, and energy. However, photosynthesis makes it possible for plants to release more oxygen than they need to take in; thus, plenty of oxygen becomes available for animals as well. [6.4.25.4, LP4, p. 31]

Technically, the idea that plants transform matter—sugars into carbon dioxide and water—is included, but it may become lost in its context of tracing energy in the food chain. In the same cluster, a database describes how fats and proteins are made in plants (Database 25–9: Origins of Nutrients). In a student investigation of nutrient cycles, one of the steps in the nitrogen cycle is given as: “Plants convert the simple nitrogen compounds into amino acids, then proteins” (6.4.25.4, SI25–4, p. 26). Students are asked to put the steps in proper order and then make a drawing of the cycle. However, this is more at the high school level of sophistication. At the end of the lesson cluster, students are asked to demonstrate their new knowledge by diagramming matter and energy inputs and outputs in a food chain and by answering several questions (6.4.25.5, SI25–5). Conspicuously absent is anything related to the idea that plants store the sugars they have made. In grade 7, unit 1, cluster 4–2, students observe carbon dioxide production by germinating seeds, but they are not asked to consider that the carbon dioxide released came from the food stored in the seed.

Idea c3: Other organisms break down the stored sugars or the body structures of the plants they eat (or in the animals they eat) into simpler substances and reassemble them into their own body structures, including some energy stores.

There is a partial content match. The following presentation of Idea c3 shows which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets): Other organisms break down the stored sugars or the body structures of the plants they eat (or in the animals they eat) into simpler substances and reassemble them into their own body structures, including some energy stores.

The concept of breakdown and reassembly is treated explicitly in grade six, while studying why human bodies need food and where the nutrients come from, and is touched on in grade seven, in considering human nutrition and a lake ecosystem. In grade six, the concept is described and illustrated in a video on the human digestive system and then discussed (6.4.25.2, LP2, p. 14). The breakdown and reassembly of nitrogen-containing compounds is dealt with in a student investigation of nutrient cycles. One of the steps in the nitrogen cycle is given as: “Animals eat the plants, digesting plant proteins to get the amino acids their bodies need in order to make animal proteins” (6.4.25.4, SI25–4, pp. 25–26), and students are asked to put the steps in their proper order and then make a drawing of the cycle. Again, at the end of the lesson cluster, students are asked to consolidate their information by diagramming matter and energy inputs and outputs in a food chain and replying to some questions (6.4.25.5, SI25–5). Students are asked to describe what their bodies do with food and how they use it. The desired response from the teacher’s lesson plan explains:

The body’s digestive system breaks down food into smaller compounds. Cells break down carbohydrates—and also fats are rarely proteins—to produce energy for the body. Cells synthesize molecules that the body needs from smaller molecules produced by the breakdown of food…. [6.4.25.5, SI25–5, p. 31, question 7]

The concept is presented in grade seven, but the focus is on energy rather than on matter. In a teacher-led discussion, students are told:

To make the various complicated chemical substances required for replacement in adults, or for growth in young people, cells must build these complicated molecules from simpler ones. Large amounts of energy are needed for this purpose. These are only some of the energy requirements of the living organism. [7.1.5.1, LP1, p. 3]

Later in the same cluster, this key idea is presented in the background section for the teacher, but it is not clear whether it is to be presented to students (7.1.5.5, LP5). In another cluster in the same unit, students use limewater to show that carbon dioxide is a product of respiration, but no connection is made to what is being broken down (7.1.4.4, SI4–4b). In the context of lake ecosystems, a discussion states that “when plants and animals die, decomposers change their remains into carbon dioxide, which is then used by plants to produce more food and the cycle continues” (7.2.12.1, LP1, p. 2). However, none of these instances makes clear that organisms can store consumed food when supply exceeds demand.

Idea c4: Decomposers transform dead organisms into simpler substances, which other organisms can reuse.

There is a content match. This idea is treated in detail in grades five and six, and touched upon in grade seven. In grade five, students are asked these questions before an investigation on composting: “What do crops do with the nutrients in the soil?” “How are nutrients replenished in soils in natural settings?” and “How do farmers replenish nutrients in the soils of their cultivated lands?” (5.1.6.3, LP3, p. 17, procedure 3). The investigation begins by stating the idea: “As a farmer, you need to replace the nutrients in your farm soil. One good way of doing this is by making compost. Compost is created when decomposers break down the bodies of dead organisms to release nutrients that were trapped in those organisms. How can you make compost for your farm?” (5.1.6.3, SI6–3–B, p. 16). The investigation deals with the breakdown, but not with the subsequent reuse, of the nutrients.

The idea is presented in grade six in a discussion about tracing energy in the food chain (6.4.25.4). In an investigation of nutrient cycles, students are asked to unscramble the steps in the nitrogen cycle, one of which states the idea. At the end of the lesson cluster, students are asked to synthesize their information by diagramming matter and energy inputs and outputs in a food chain and answering some questions. Students are asked to “add the necessary elements for the nitrogen cycle” (6.4.25.5, SI25–5, p. 29). In grade seven, in the context of a lake ecosystem, students are asked to review the concept of decomposers (7.2.11).


Idea d: Energy is transformed in living systems.

Idea d1: Plants use the energy from light to make "energy-rich" sugars.

There is a content match. This idea is treated explicitly in grade six in studying photosynthesis and is touched on in grade seven in the contexts of food chains, the mechanism for photosynthesis, and energy pyramids. It is listed as an objective for grade 6, unit 4, cluster 25 and appears in a video and subsequent discussion. While the video emphasizes the role of energy in breaking and making bonds (“Energy from the sun is used to break the molecules apart inside the leaf. Then more energy from the sun is used to put the pieces back together to form a different kind of molecule. It takes a lot of energy to do that” [6.4.25.4, video “Chemistry of Photosynthesis”]), the subsequent discussion expands this more mechanical role of energy to the idea that energy is stored in the sugar. In grade seven, a teacher-led discussion on the role of food treats photosynthesis as an example of energy transformation (7.1.5.1), although, unfortunately, the on-line glossary defines photosynthesis as “A process…involving conversion of energy of sunlight into chemical compounds for nutrition” (6.4.25.4, video “Chemistry of Photosynthesis”), which could lead students to conclude erroneously that energy is converted into matter. Later, in unit 2, cluster 12, as students investigate how various factors affect the rate of photosynthesis, they watch videos that present sophisticated details of the mechanism of photosynthesis—even to the level of “the green membranes in chloroplasts known as thylakoids,” within which “chlorophyll molecules absorb light energy” and “become excited” (6.4.25.4, video “Chemistry of Photosynthesis”). Yet, the investigations themselves emphasize the less sophisticated idea that plants need light.

Idea d2: Plants get energy by breaking down the sugars, releasing some of the energy as heat.

There is a partial content match. The following presentation of Idea d2 shows which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets): Plants get energy by breaking down the sugars, releasing some of the energy as heat.

This idea is mentioned in grade six, in the context of cellular respiration, and again in grade seven, in the context of respiration in germinating seeds. In grade 6, unit 4, cluster 25, lesson 4, the lesson plan states:

As an added note, ask students if they can guess what plants do with the food they produce. What do plants need in order to grow? Like all living things, they need energy as well as new materials to build up new cells and replace the old. So plants undergo cellular respiration too, taking in oxygen and releasing carbon dioxide, water, and energy. However, photosynthesis makes it possible for plants to release more oxygen than they need to take in; thus, plenty of oxygen becomes available for animals as well. [6.4.25.4, LP4, p. 31]

As noted previously, at the end of the lesson cluster, students are asked to synthesize what they have studied by diagramming matter and energy inputs and outputs in a food chain and by responding to several specific questions (6.4.25.5, SI25–5). Conspicuously absent is anything related to the idea that plants break down some of the sugars they make in order to get the energy they need for cell processes. In grade 7, unit 1, cluster 4, lesson 2, students observe carbon dioxide production by germinating seeds and are asked what happens to a seed as it germinates (“Answer: The seed uses the food stored inside it to provide for its increased energy needs as it begins to grow” [7.1.4.2, LP2, p. 6]). However, it is not clear how the connection between the gas exchange and the underlying energy transformations is to be developed.

Idea d3: Other organisms get energy to grow and function by breaking down the consumed body structures to sugars and then breaking down the sugars, releasing some of the energy into the environment as heat.

There is a content match. As with matter transformation, energy transformation by other organisms is dealt with expressly in grade six, in the discussion of why our bodies need food and where the nutrients come from, and is touched on in grade seven, in examining human nutrition. In grade six, it is listed as a key concept (“Our bodies need food for energy and for materials to build new cells”), described and illustrated in a video on cellular respiration, and discussed (6.4.25.2, LP2, p. 14). The video narration states:
When you eat, the molecules of food reach your cells. When you breathe in, oxygen molecules from the air reach your cells. When you need energy, what happened in the leaf is reversed in your cells: the carbon atoms in the food molecules are broken apart, releasing the energy stored between them—and you use it. The complete breakdown of the food molecules in your cells produces just what we started with in the leaf. You use the molecules of water in your body, and you exhale the carbon dioxide molecules back into the air. [6.4.25.2, video “Cellular Respiration”]

The material treats heat loss in a discussion on tracing energy in the food chain. Students are asked:

What is the next link and what happens to the chemical energy? (The next link is a primary consumer; for example, a rabbit eats the plant. It stores some of the energy in fat tissue, releases some as heat, and uses some as mechanical energy in movement.) And the next link? (The next link is perhaps a kind of secondary consumer; for example, a hawk uses energy in the same way as the rabbit.) [6.4.25.4, LP4, p. 31, procedure 5]

In a student investigation of nutrient cycles, one of the steps in the carbon cycle is given as: “Through cellular respiration, plants and animals ‘burn’ carbohydrates with oxygen to produce carbon dioxide, water, and energy” (6.4.25.4, SI25–4, p. 25). Students are asked to put the steps in their proper order and then make a drawing of the cycle. At the end of the lesson cluster, students are asked to coalesce their knowledge by diagramming matter and energy inputs and outputs in a food chain and by responding to several specific questions (6.4.25.5, SI25–5). They are asked to indicate “whether energy is used or released in respiration and what happens to it” (The teacher answer key includes the idea that energy is used for heating the body in the desired response [6.4.25.5, SI25–5, pp. 29, 31, question 8]).

Idea e: Matter and energy are transferred from one organism to another repeatedly and between organisms and their physical environment.

There is a partial content match. The following presentation of Idea e shows which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets): Matter and energy are transferred from one organism to another repeatedly and between organisms and their physical environment.

This idea that matter and energy are transferred is presented explicitly in grade six, and is touched on in grade seven. The transfer of matter is a stated learning objective for grade 6, unit 4, cluster 25 (students will study “how elements in food such as carbon and nitrogen are recombined to form different substances as they move through a food chain and the ecosystem” [6.4.25, LP, p. 1]), and as a key concept in lesson 4 (“Food chains involve the transfer of molecules, and thus chemical energy, from one living thing to the creatures that consume it. The sun is the energy source for all living things” [6.4.25.4, LP4, p. 27]). However, in all instances the focus is on transfer from one organism to another, not between organisms and their physical environment. In lesson 6.4.25.4, the teacher is to demonstrate for students how to trace the matter and energy in their dinner to their origins and then sketch the food chain on the board. Students investigate molecular models of fats, carbohydrates, and proteins to see that they are made of the elements carbon, hydrogen, oxygen, and nitrogen. Next, they practice tracing matter in terms of carbon and nitrogen and then energy through a food chain. Another lesson, 6.4.25.3, has students investigate the role of vitamins and minerals and where they come from (e.g., vitamins are made by plants). In grade seven, the role of decomposers in the transfer of matter and energy is described and a video on a swamp ecosystem illustrates how energy moves from one organism to another. At the beginning of cluster 12, students are asked to review the concept of a food web.

The idea that these transfers of matter and energy occur repeatedly is not explicitly presented. While the lesson plan instructs the teacher to “Let the students come to the realization that the food chain will begin all over again—repeating itself; creating a cycle through which food (energy) is passed from level to level, over and over again,” this statement is confusing. While matter continues to flow through a cycle, the organisms themselves do not. Furthermore, energy flows (rather than cycles) through a food web.

Building a Case

Science 2000 does not attempt to build a case for any of the key life science ideas. A video on how plants produce food briefly notes the experiments of Van Helmont, Priestley, and Ingenhouz (grade 7, unit 2, cluster 12, lesson 1) but does not present their findings or explain how the findings led to conclusions about how plants, in the presence of sunlight, make sugars from carbon dioxide and water. For example, after describing Van Helmont’s experiment, the video notes that “Van Helmont thought it was the water. He wasn’t completely correct.” Furthermore, the lesson plan focuses on how plants make food rather than on how scientists know these ideas or why students should believe them (7.2.12.1, LP1, p. 2, procedure 3).


Coherence

Science 2000 organizes each unit around an interesting problem or question—for example, how to design a snack food for the school cafeteria that meets the school board’s nutrition requirements or how the kuru mystery can be explained—and treats the key life science ideas in several different units. Unfortunately, teachers are not alerted to the individual instances in which the same idea is treated, nor are the individual instances tied together for students. Although the program includes experiences with several of the key ideas in multiple grades, teachers are not alerted to them in either the program introduction (in grades five, six, and eight; see Teacher’s Guide, Chapter 10: Scope and Sequence, p. 10.1) or the cluster story lines (e.g., 6.1.4, 7.2.12). The program introduction identifies only topic headings in the Scope and Sequence Content Data Tables (which are not specific enough usually to give any indication about what ideas are addressed), and the story lines make no mention of treatment of any of the key ideas in earlier grades. While the unit problem does an excellent job of framing the activities in the unit, there does not appear to be a plan for the conceptual development of ideas across units. Quite sophisticated ideas about photosynthesis appear in grade six and are repeated in grade seven. The Atoms, Molecules, and Chemical Notation Database is available in grade six (cluster 25), and similar or simpler questions appear in grade seven.

Furthermore, Science 2000 does not relate adequately the processes of photosynthesis, respiration, digestion, and nitrogen and carbon cycles to the concept of the transformation of matter and energy. For example, at the end of unit 4, grade 6, cluster 25 (in which they are to design a nutritious snack food), students are asked to prepare food chains of the food they eat and then are asked to use colored arrows to represent (a) inputs and outputs of photosynthesis, (b) carbon and nitrogen cycles, (c) energy flow through the food chains, and (d) human respiration and digestion. They are requested to use a different color to represent (a) through (d), but they are never asked to use one color for all of the matter inputs and outputs and a second color for all of the energy inputs and outputs. Consequently, the opportunity is lost to help students see how the various processes and cycles are instances of matter and energy transformation. As the teacher answer key makes no mention of this, the teacher has no guidance in building coherence (6.4.25.5). Only one of the other relevant units attempts to relate individual ideas to one another. Questions at the end of cluster 12 in the seventh-grade lake investigation unit ask students to link the process of photosynthesis to the production of food in the lake under conditions of reduced light and to consider the implications of this (reduced food production) for plants and animals in the lake (7.2.12.5).

Science 2000 develops a few important connections between the key ideas in the life and physical sciences. It relates respiration in living things to the process of combustion (6.4.25.2, LP2, p. 18, procedure 9), links chemical equations for photosynthesis and respiration to the conservation of mass (6.4.25.2, LP2, pp. 17–18, procedure 8), associates food webs with the process of making compost (5.1.6.3), and connects the nitrogen cycle and mineral use in photosynthesis to soil depletion and the need for fertilizers (6.4.25.4).

Beyond Literacy

The lesson plans in the units examined attempt to restrict the topics and ideas taught to those given in Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) and National Science Education Standards (National Research Council, 1996). Key ideas about matter and energy transformations are presented in the context of investigations such as “What is the Earth’s environment?” and “How has it changed over time?” (grade 6, unit 1) or “How can we create a delicious, healthful snack for the school snack bar?” (grade 6, unit 4). Sometimes videos go beyond the level of sophistication appropriate for middle school students. For example, a video on photosynthesis uses terms like palisade layer, thylakoid membrane, and reaction center when describing the process (7.2.12.1, LP1). However, the text does not present light and dark reactions of photosynthesis or details of respiration.


Accuracy

The evaluation teams developed a summary assessment of the most common kinds of errors found in each of the three subject areas—physical science, Earth science, and life science. In this context, “errors” is taken to mean not only outright inaccuracies, but also those instances in which the material is very likely to lead to or support student misconceptions. Overall, inducement to misconstrue is the most serious problem of accuracy in the evaluated materials.

The evaluation teams’ collective findings, presented below, should be taken as having general applicability to all of the evaluated materials, not complete and specific applicability in toto to any one of them.

Identified errors occur most frequently in drawings and other diagrams. They take the form of representations that are likely to either give rise to or reinforce misconceptions commonly held by students. Following are life science examples of the kinds of misleading illustrative materials of most concern to the evaluation teams:

  • Diagrams of energy pyramids that indicate decreases in energy (without indicating that the energy is given off as heat) can reinforce students’ misconception that energy is not conserved.
  • Diagrams and explanations that show the reciprocal nature of respiration and photosynthesis can reinforce the misconception that only animals respire—and that plants do not. Furthermore, emphasizing the notion that these processes are reciprocal or balance one another fails to convey that the rate of photosynthesis is far more than that of respiration. Consequently, plants produce enough food (and oxygen) during photosynthesis both for their own needs and for the needs of other organisms.
  • Diagrams of nutrient cycles in biological systems, such as the carbon-oxygen cycle or the nitrogen cycle, often misrepresent the transformation of matter—showing, for example, atoms of carbon in one form but not in others. By failing to show a particular element throughout the cycle, a text can reinforce the misconception that matter can disappear in one place and reappear in another, as opposed to simply changing forms.

The use of imprecise or inaccurate language is problematic in text and teacher materials, not solely in illustrations. In life science, one significant problem is that imprecise language in explanations of energy transformations can reinforce students’ common misconception that matter and energy can be interconverted in everyday chemical reactions. For example, presenting the overall equation for cellular respiration in which energy appears as a product without indicating where the energy was at the start can lead students to conclude that matter is converted to energy. Similarly, presenting the overall equation for photosynthesis in which energy appears only as a reactant can lead them to conclude that energy has been converted into matter.