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Middle Grades Science Textbooks: A Benchmarks-Based Evaluation

Glencoe Earth Science, Life Science, and Physical Science. Glencoe/McGraw-Hill, 1997
Earth Science Life Science Physical Science

About this Evaluation Report
Content Analysis
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.


Idea a: Food (for example, sugars) provides molecules that serve as fuel and building material for all organisms.
There is a content match, mainly at the substance level rather than at the molecular level. The idea that food provides energy and building materials for all organisms is fundamental for student understanding of the other key life science ideas, and it is especially important because the everyday meaning of the term "food" is inconsistent with its biologic meaning. The key idea is addressed exclusively in the text and only in fragments. In Unit 1: Life, describing the characteristics of living things, the material states that "All living things need food to produce the energy needed to live" (p. 3s) but does not make clear that the energy comes from the food.

The text also contains a simpler form of the idea-"All organisms need energy and raw materials" (p. 8s)-but does not indicate that food is the source of energy and materials. In Chapter 2: The Structure of Viruses and Cells, while describing cell organelles, the text states that in mitochondria, "[F]ood molecules are broken down, and energy is released" (p. 49s). In Chapter 3: Cell Processes, while describing organic compounds, the text discusses the roles of carbohydrates, lipids, and proteins but does not make it clear that they are the components of food:

Carbohydrates supply energy to power cell processes. But lipids, commonly called fats and oils, are organic compounds that store and release even larger amounts of energy than carbohydrates. [p. 68s]

Proteins are the building blocks of many structural components of organisms. [p. 69s]

In the same chapter, the text points out that basketball players get the energy they use in a game "from the food they eat" (p. 78s) but does not generalize the idea to other consumers. However, in Chapter 12: Plant Processes, describing photosynthesis, the text generalizes to plants: "The sugar formed is glucose, the food a plant uses for maintenance and growth" (p. 318s). In Chapter 22: Nutrients and Digestion, the text states that, "Nutrients, as shown in Figure 22-1, are substances in foods that provide energy and materials for cell development, growth, and repair," and then goes on to list the six kinds of nutrients available in food: carbohydrates, proteins, fats, vitamins, minerals, and water (p. 600s). Figure 22-2 uses structural formulas to represent glucose and the complex carbohydrates starch and cellulose (p. 601s), but the emphasis is on food as a substance rather than as a source of molecules.

No activities or student practice questions focus on this key idea.

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

There is a content match. The idea is presented in chapter 1, under the heading Basic Needs of Living Things (pp. 8-9s); in chapter 3 in Section 3.3: Energy in Cells (pp. 78-81s); and in chapter 12 as one statement in a brief presentation of photosynthesis ("Photosynthetic organisms.provide food for nearly all the consumers on Earth" [p. 320s]).

Three student practice questions also address the key idea: students are asked to "[e]xplain the difference between producers and consumers" (p. 81s, Section Wrap-up, item 1), explain what would happen to the animals in an ecosystem if all the plants died and vice versa (p. 78t, Bellringer activity; p. 62Ct, Section Focus transparency 11, L3), and identify producers and consumers in four different communities (p. 482t, Program Resources; Lab 42, p. 119).

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 text presents both word and symbolic equations in the context of describing cell processes (pp. 78-80s); mentions that cyanobacteria make their food from carbon dioxide, water, and the energy from sunlight (p. 212s); and states that green algae undergo photosynthesis (p. 232s). Students are to design an experiment to show that plants carry out both photosynthesis and respiration (pp. 82-83s); and, if the supplementary laboratory activity is done, that extra carbon dioxide increases the amount of starch produced by plants (p. 314t; Lab 30, pp. 79-82).

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 content match. Chapter 3: Cell Processes states that both producers and consumers must "have some way to release energy from food" and that both "break down food in their cells in a process called cellular respiration" (p. 79s). The text then says that carbon dioxide and water are given off as waste products, and it presents both the word and symbolic equations for photosynthesis and respiration (pp. 79s, 80s). In Chapter 11: The Seed Plants, in the context of describing the parts of plants, the text notes that seeds (p. 286s), roots (p. 293s), and stems (p. 293s) contain stored food, but it does not indicate where this food comes from. In Chapter 12: Plant Processes, the text explains photosynthesis in terms of the key idea (pp. 318-319s). The text also notes that "sugar produced during used to make cellulose to build cell walls" (p. 323s).

In an activity focused on the key idea, students are asked to design and perform experiments to learn whether plants carry out both photosynthesis and respiration (pp. 82-83s). However, the emphasis is on gas exchange and energy release and not on what happens to the sugar.

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 content match. In the section on energy in cells, the text uses word and symbolic equations in explaining that during cellular respiration, the sugar is broken down and carbon dioxide and water are given off as waste products (pp. 79-80s). However, the focus is on the release of energy, rather than on the transformation of matter.

Although Chapter 22: Nutrients and Digestion says that carbohydrates, fats, and proteins "need to be broken down into simpler molecules before the body can make use of them" (p. 600s) and "Your body uses proteins for growth" (p. 602s), it does not illustrate or simply explain the breakdown and reassembly of molecular building blocks.

Similarly, an activity in which students are to compare what happens when live (as opposed to heat-killed) yeast is incubated in a sugar solution focuses them on the carbon dioxide given off, rather than on the matter transformed (the breakdown of the sugar or an increase in the mass of the yeast) (p. 78t; Lab 7, pp. 21-22).

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

There is a content match. Chapter 8: Monerans explains that most monerans do not make their own food and have to break down other living things to obtain energy. An illustration shows decomposing pears, and the text notes that monerans keep the world free of wastes by breaking them down and releasing nutrients into the soil for use again (p. 210s). Students are told that without monerans, there would be deep layers of dead materials all over the Earth (p. 216s).

Student activities related to the key idea include researching the components of a successful compost heap and setting up a model composting project (p. 227s). Unfortunately, these activities emphasize preventing the accumulation of waste as opposed to the key idea. In a unit 3 project, students are asked to design experiments to compare composting recipes and techniques (pp. 254-255s). Again, their attention is not focused on the reuse of simpler substances formed through decomposition.

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 text presents the word equation for photosynthesis and states that the sun's energy splits water into hydrogen and oxygen and that light energy is used to combine these hydrogen atoms and carbon dioxide to form sugar (p. 79s); the equation and statement are repeated in describing the food-making process in plants (p. 318s).

In a related activity, students are to design an experiment to show that plants carry out photosynthesis in the light (pp. 82-83s) and observe (if the supplementary laboratory activity is done) that plants produce starch only if they are grown in the light (p. 314t; Lab 30, pp. 79-82).

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

There is a content match. However, the material treats two parts of this key idea in three widely separated chapters.

In Chapter 3: Cell Processes, the text states that plants get energy by breaking down sugars, and that both producers and consumers must "have some way to release energy from food" and that both "break down food in their cells in a process called cellular respiration" (p. 79s). Unfortunately, the text then shifts from discussing all organisms to discussing animal cells only. A subsequent statement, "The breakdown process takes place within mitochondria and uses the oxygen that you take in as you breathe" (p. 80s), directs students to think about themselves, thus narrowing the focus on respiration even more-from animals to humans. Later, the text asserts that, "Some of the energy released in respiration is used to produce high-energy molecules, and some of the energy is lost as heat" (p. 80s).

In Chapter 12: Plant Processes, the text states that plants respire to release energy from food. Pictures of a cheetah and a tree make the point that all organisms respire, but heat loss is not mentioned (pp. 320-322s).

In Chapter 18: Life and the Environment, the text indicates that most of the energy flowing through ecosystems is given off as heat, but it does not relate the heat loss to cellular respiration or point out that plants give off heat (p. 498s).

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. The relevant material consists mainly of text assertions. Chapter 3: Cell Processes states that organisms get their energy by breaking down their food; word and symbolic equations are presented (pp. 79-81s). Chapter 12: Plant Processes states that all organisms break down food to release energy, and repeats the equations (pp. 320-321s). The text goes on to say that respiration takes place in the mitochondria of all eukaryotic cells (p. 321s) and compares the process to photosynthesis (p. 322s). The idea that some of the energy is lost as heat is presented in the context of food chains and food webs (pp. 497-498s). Notes in the Teacher Wraparound Edition remind teachers to convey this idea to students (p. 496t).

Finally, in Chapter 21: The Human Body, the text states that, "Muscles use chemical energy in the form of glucose. As the bonds in glucose break, chemical energy changes to mechanical energy and the muscle contracts.. Muscles also produce thermal energy.. The heat produced...helps to keep your body temperature constant" (p. 587s).

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

There is a content match. This key idea appears mainly in Unit 6: Ecology. At the beginning of the chapter, students are asked to describe and give examples of how energy flows through an ecosystem (p. 479t). The idea that matter and energy flow through ecosystems is explained in the text (pp. 496st) and illustrated with a drawing of a pond's  ecosystem (pp. 496-497s). The text explains that at each link of the food web, energy is lost in the form of heat and renewed constantly by sunlight; asserts that matter is never lost or gained but used over and over again; and describes the water cycle and the nitrogen cycle (pp. 497-501s). The section review asks students to compare the flow of energy through an ecosystem with the cycling of matter (p. 501s).

Building a Case

Typically, the text asserts the key ideas without developing an evidence-based argument to support them. For example, the idea that food provides fuel and building material is stated in the text, but there are no supporting illustrations. Phenomena are included that illustrate the idea that plants use carbon dioxide to produce starch and that light is needed for them to do so (p. 317t; Lab 30, pp. 79-82). However, these observations are not used to establish the fruitfulness of the idea in explaining a variety of observations.


Although all of the key life science ideas are introduced, they are distributed over a wide expanse of chapters and are not tied together. The ideas are presented as isolated processes of cells, organs, ecosystems, or human organisms, rather than as instances of general principles of matter and energy transformation.

Energy transformation appears in the context of cells, plants, ecosystems (as energy flow but not as successive energy transformations), and the human organism. However, the material rarely connects processes that are going on at different levels of biologic organization.

Matter transformation, which might be explained more easily than energy transformation or flow, receives little attention and is mentioned last. It is not until the ecology unit (unit 6) that matter is a focus, and not until the nutrition chapter (chapter 22) that attention is paid to the meaning of "food."

Connections that might facilitate understanding of the key ideas-such as the conservation of matter or the transfer of energy in physical systems, which are observable more directly than in living systems-are not mentioned. Also ignored are ideas about the usefulness in  systems thinking of keeping track of inputs and outputs.

Beyond Literacy

When presenting the key ideas on matter and energy transformation, the text usually refrains from presenting more sophisticated ideas. For example, the text does not present light and dark reactions of photosynthesis or details of respiration. However, sometimes key ideas about matter and energy transformation are only a small part of chapters containing a lot of additional information that is outside the scope of science literacy as defined in Benchmarks for Science Literacy (AAAS, 1993) and National Science Education Standards (NRC, 1996 ). For example, the idea that "[c]yanobacteria.make their own food using carbon dioxide, water, and energy from sunlight" (p. 212s) is tucked into a much longer chapter on bacteria (pp. 208-227s), and the idea that plants store food (p. 293s) is tucked into a much larger chapter on the seed plants (pp. 284-311s).


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.