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AAAS :: Project 2061 :: Textbook Evaluations

Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

Science Insights. Addison-Wesley Publishing Company, 1996 and 1997
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. The idea that food provides fuel and building material is presented in several locations in the student material. It is asserted in introducing the digestive system (Chapter 20: Supply and Transport) and developed further in the context of human nutrition and health (chapter 23: Nutrition, Health, and Wellness). For the most part, the textbook treats the idea at the substance, rather than the molecular, level. Chapter 3: The Chemistry of Living Things introduces briefly atoms, molecules, elements, compounds, and chemical reactions, and equations and asks students several questions about the balanced equation for the chemical breakdown of glucose (p. 69st). However, the text presentation of the molecules of life (chapter 3) and all subsequent references to proteins, carbohydrates, lipids, and the components of food are at the substance, rather than the molecular, level.

The most explicit comments are brief mentions in the text (e.g., “You need food because the cells of your body require a constant supply of energy and materials to build new cells and repair old ones. Food provides the materials and the energy” [p. 415s]). Activities in which students examine food labels (p. 489t) and analyze and evaluate their lunch menus (p. 492t) are not related specifically to the role of food as fuel and building material.

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

There is a content match. The contrast between producers and consumers is treated briefly, in the description of food chains in Chapter 25: Organisms and Their Environment (p. 542s). The text states: “Plants can capture the sun’s energy, which they use to fuel their growth by the process of photosynthesis… Many organisms can’t make their own food. They eat plants, animals, or other organisms” (p. 542s). However, although several animals are given as examples of consumers—the hawk, owl, rabbit, and grasshopper—the generalization that animals do not make their own food is not expressly made. Perhaps it is assumed that students know this already because there is this question, “How are plants different from animals?” that is designed to probe students’ prior knowledge (p. 237t).

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. The concept that plants make sugars from carbon dioxide and water is presented in Chapter 12: A World of Plants, in the section on chemistry in plants. The text states the idea, tells where the carbon dioxide and water come from, where the sugars and oxygen go, gives the symbolic equation for photosynthesis, and then describes its first and second stages (p. 244s). The idea is stated again in the Concept Summary (p. 249s), and, in a single practice task, students are asked what a plant produces as a result of photosynthesis (p. 250st, Check Your Knowledge, item 5).

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 [some of] the sugars they have synthesized into simpler substances—carbon dioxide and water—and assemble [some of the] sugars into the plants' body structures, including some energy stores. In the context of presenting cellular respiration, the text is explicit about the break down of sugars by plants: “The cells of both plants and animals use the chemical energy stored in glucose.... During respiration, glucose breaks down into water and carbon dioxide and releases energy” (p. 99s). The text presents conflicting statements about the assembly of sugars into plant body structures. While the concept that plants store some of the sugars they make is stated explicitly in the student text (“Some glucose made by the plant is stored for later use” [p. 243s]), the same paragraph states, “[T]he glucose is used for energy to help the plant convert soil nutrients to body tissues and grow larger.” This implies that the glucose is used for energy (to do synthetic work) but not as building material. The idea that sugar is incorporated into plant body structures is not spelled out. (While minerals and fixed nitrogen are taken up from the soil, the primary element of plant structures is carbon, which comes from glucose. In fact, polymers of glucose [cellulose] are the main organic component of leaves, stems, bark, etc.)

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 [humans] 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 that food is broken into simpler substances and reassembled into body structures is presented in two different chapters and is treated solely in the context of the human organism. The breakdown part of the story is presented in an introduction to the digestive system (Chapter 20: Supply and Transport) and the reassembly is presented in a discussion of organic nutrients (Chapter 23: Nutrition, Health, and Wellness). The text introduction to the digestive system states:
You need food because the cells of your body require a constant supply of energy and materials to build new cells and repair old ones. Food provides the materials and the energy. But your body can’t use food the way it exists when you eat it. Food must be broken down into simpler parts that your body can use. This process is called digestion. [p. 415s]

The text presentation on digestion concludes with a statement about the fate of the simpler substances:

During this part of the journey, amino acids from proteins, simple sugars from carbohydrates, and broken-down fats are gradually absorbed into the blood. [p. 417s]

Three chapters later the text presents the reassembly of simpler substances:

Your cells need nutrients called proteins for growth and repair. Your body uses the proteins you eat to build its own proteins… Proteins are large, complex molecules made up of smaller units called amino acids. Twenty different amino acids, combined in different ways, make up all the different proteins in your body. Just as the 26 letters of the alphabet form an endless number of words, amino acids join together to create many kinds of proteins. [p. 488s]

The text then distinguishes complete dietary proteins (those containing “all the amino acids your body needs to make its own proteins”) from incomplete proteins (those “missing one or more of the essential amino acids”). On the same page (p. 488s), fat deposits are referred to as a source of stored energy, but the link is not made between consumed food and stored fat.

While an activity involves students in reading food labels and listing common ingredients, no connection is made to the fact that humans transform what they eat into their own body structures (p. 489t).

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

There is a partial content match. The following presentation of Idea c4 shows which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets): Decomposers [break down] transform dead organisms into simpler substances, which other organisms can reuse. The idea that decomposers break down dead organisms is treated in three chapters, in characterizing the role of bacteria (Chapter 10: Viruses and Monerans), the function of fungi (Chapter 11: Protists and Fungi), and the place of decomposers in food chains (Chapter 25: Organisms and Their Environment). Each time it is mentioned, students are asked to consider what would happen if bacteria and fungi (or decomposers) disappeared. However, the answers provided focus on disappearing bodies, rather than on transforming matter into simpler substances that can be reused. For example, students are asked to hypothesize what the Earth would be like if there were no decomposers. The answer states: “Organisms that died would not be broken down. There would be bodies of animals and dead plants littering the earth’s surface” (p. 550t).

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. The idea that plants convert light energy into chemical energy in sugars is presented twice in the student textbook—first, in the context of cell processes, and then in the context of the chemistry of plants. It is listed as an objective (pp. 97s, 243s), stated in the text (pp. 97–98s, 245s), and restated in the chapter summary (p. 249s).

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. The idea that plants release energy stored in glucose is presented in Chapter 5: Cell Processes, in the description of respiration and other cellular processes, and again in Chapter 12: A World of Plants, in the section on the chemistry in plants. It appears entirely as text assertions (e.g., “The cells of both plants and animals use the chemical energy stored in glucose…. During respiration, glucose breaks down into water and carbon dioxide and releases energy” [chapter 5, p. 99s]), with no attempt made to include relevant experiences with phenomena or discussion questions.

The fact that some of the energy is released as heat is not treated. Even while describing energy loss in an energy pyramid, the loss is attributed to the use of energy “by the organisms for life processes” (chapter 25, p. 545s).

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. Several chapters mention the idea that organisms obtain the energy for carrying out life processes by releasing it from sugars. In the discussion of cellular respiration (Chapter 5: Cell Processes), the text states that energy is released from glucose: “The cells of both plants and animals use the chemical energy stored in glucose.… During respiration, glucose breaks down into water and carbon dioxide and releases energy” (p. 99s).

In the description of the human digestive system (Chapter 20: Supply and Transport), the idea that glucose comes from food consumed is mentioned. Chemical digestion is characterized as the process in which “the nutrients in food are broken down into simpler molecules that dissolve in water” (p. 415s), with the process beginning in the mouth (p. 416s). These ideas are summarized in describing the role of carbohydrates in human nutrition (Chapter 23: Nutrition, Health, and Wellness):

Your body gets most of its energy from organic nutrients called carbohydrates.... Starch is a carbohydrate made of large molecules…. When starches are broken down into smaller molecules, they form sugars. Table sugar, or sucrose, is only one of many sugars. During digestion, sucrose splits into two smaller molecules of a simple sugar called glucose. In the cells, glucose combines with oxygen during the process of respiration. During respiration, the stored energy of glucose is released. [p. 487s]

The fact that heat is released during the breakdown of glucose appears later in the same chapter in a discussion of calories stored in food and burned during exercise:

Like wood, food can be “burned.” The heat given off by burning food can change the temperature of water. Scientists define a calorie as the amount of heat needed to raise the temperature of one gram of water 1°C. Of course, food energy in your body is not used to heat water. It is used to keep your body temperature close to 37°C. [p. 495s]

Although some of the activities require students to work with food labels and calorie tables, no experiences with phenomena are provided.

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, in which matter and energy are treated differently. The following presentations of Idea e show which parts of the idea are treated (in bold) and what alternative vocabulary, if any, is used (in brackets):

  • Matter and energy are [is] transferred from one organism to another repeatedly and between organisms and their physical environment.
  • Matter and energy are [is] transferred from one organism to another repeatedly and between organisms and their physical environment.

The transfer of matter among organisms and between them and their physical environment is treated in a section on cycles in an ecosystem (Chapter 25: Organisms and Their Environment). After an introduction that includes the statement, “Many substances, such as water, pass through natural cycles in which they are used and reused. These substances circulate through both living and nonliving things” (p. 548s), there are brief descriptions of the water, nitrogen, and oxygen-carbon dioxide cycles. The account of the water cycle explains how plants and animals fit in. Diagrams of the nitrogen and oxygen–carbon dioxide cycles represent plants and animals, and the questions focus attention on their roles (pp. 550–551st).

The idea that energy flows through ecosystems appears earlier in Chapter 24: Disease and the Immune System in the discussion of food chains, food webs, and energy pyramids. Text and diagrams are used to describe and represent the energy flow through living organisms, but decomposers are not mentioned. Although an energy pyramid is used to represent the decrease in the energy available at each level, the text attributes the decrease to use “by the organisms for life processes” (p. 545s). No mention is made of the flow of energy to the environment.

Building a Case

Science Insights: Exploring Living Things asserts the key ideas but provides no evidence-based arguments to support them. The material does not even provide examples of the phenomena that could be explained by the ideas.


Coherence

The presentation of key ideas on matter and energy transformations in living things moves from molecules to cells to organisms to ecosystems. Chapter 3 presents the molecules of life; chapter 5, cell processes, including photosynthesis and respiration; chapters 10 and 11, bacteria and fungi (in which the idea of decomposers is introduced); chapter 12, the chemistry of plants; chapter 20, the human digestive, circulatory, and respiratory systems; chapter 23, human nutrition and health; and chapter 25, ecosystems. While this sequence has appeal to those familiar with chemistry already, its logic may not be evident to middle grades students (who are not familiar with chemistry or its role in living things). It is not clear why the explication of what food is (chapter 23) comes so much after the presentations of how it is made (chapters 5 and 12) and broken down (chapter 20). No rationale for this sequence is given.

In some cases, parts of ideas are set forth as isolated bits of information, with little attempt to show connections among them. As shown above in describing the alignment of the material to Idea c3, the individual parts of an idea may appear in different chapters, but they are never tied together. Furthermore, little attempt is made to link the key ideas to one another. Almost no attempt is made to relate the presentation of photosynthesis and respiration in cells to the organism or ecosystem. For example, the discussion of the human digestive, circulatory, and respiratory systems is not tied to their role in bringing in raw materials and removing the waste products of cellular respiration. Similarly, photosynthesis and respiration are presented as isolated processes in living things, not as demonstrations of matter and energy transformation more generally. For instance, while the text states that plants convert light energy to chemical energy, it does not include any of the many possible examples of energy transformation in physical systems that may be more comprehensible to students. Furthermore, no attempt is made to link key ideas to their prerequisites, even when the prerequisites are treated. The text includes a chapter on atoms and molecules, but does not make use of them when needed. Specifically, atoms and molecules are not used in the explanations of the flow of matter in photosynthesis, respiration, or ecosystems.

Beyond Literacy

Science Insights: Exploring Living Things can be described best as a “survey course,” containing a little information about a lot of topics. When treating topics like photosynthesis, respiration, and ecosystems, it does not go much beyond the level of sophistication of the key ideas. For example, while two stages in photosynthesis are described, there are no details of light and dark reactions. However, many topics are included that go beyond the scope of the science literacy ideas in Benchmarks for Science Literacy (American Association for the Advancement of Science, 1993) and National Science Education Standards (National Research Council, 1996); for example, eight chapters of Science Insights: Exploring Living Things are devoted to surveying the various phyla of living things.


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 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.


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Copyright 2002 by the American Association for the Advancement of Science. All rights reserved.