Project 2061 Analysis Procedure
- Overview
- Content Analysis
- What the Content Analysis Looked For
- Key Science Ideas Used in Evaluating the Textbooks’ Content Alignment
- Connections Among Ideas Used in Evaluating the Textbooks' Content Coherence
- Instructional Analysis
Key Science Ideas Used in Evaluating the Textbooks' Content Alignment
In evaluating the content of the high school biology textbooks in this study, the review teams examined how completely each textbook's content aligns with specific key ideas in four topics: Cell Structure and Function, Matter and Energy Transformations, Molecular Basis of Heredity, and Natural Selection and Evolution. The ideas were drawn from Science for All Americans (American Association for the Advancement of Science [AAAS], 1989), Benchmarks for Science Literacy (AAAS, 1993), and the National Science Education Standards (National Research Council, 1996).
The key ideas for the Cell Structure and Function and Matter and Energy Transformations topics have been annotated below to provide users with additional guidance about what the reviewers looked for and how they judged the textbooks' content alignment.
- Cell Structure and Function
- Matter and Energy Transformations
- Molecular Basis of Heredity
- Natural Selection and Evolution
Cell
Structure and Function
(See what the reviewers
looked for)
Idea a: Every cell is covered by a membrane that controls what can
enter and leave the cell.
This idea has two components: (1) that every cell is covered by a membrane, which
distinguishes the cell from its surroundings, and (2) that the cell membrane
exercises control over what can enter and exit the cell. A full content match
means that a textbook addresses both components. Details of the cell membrane’s
architecture, such as the lipid bilayer structure of the membrane, structural
features of transport proteins, the fluid mosaic model, and processes of selective
transport across the cell membrane go beyond the expected level of understanding
of this idea.
Idea b: Within the cell are specialized parts for the transportation of
materials, energy capture and release, protein building, waste disposal, passing
information, and even movement.
This idea presents the generalization that the cell has specialized parts
that perform specific functions and gives examples of functions that the parts
carry out. For a complete content match for this key idea, a textbook must
both state the generalization and describe specific functions, such as energy
capture and release. The names of the organelles are not needed and wrongly
focus students and teachers on the names of the parts rather than their functions.
Idea c: The work of the cell is carried out by the many different types of molecules it assembles, mostly proteins. This idea has three components: (1) that cells make molecules, mostly proteins, (2) that proteins do the work of the cell, and (3) examples of cell work that is carried out by proteins. A complete content match for this key idea means that a textbook presents all three components. Specific examples of cell work by proteins, such as catalyzing cellular reactions and helping to move molecules across membranes, may help make this idea less abstract. However, details about protein synthesis go beyond the expected level of understanding for this idea.
Idea d: Most cells function best within a narrow range of temperature
and acidity. At very low temperatures, reaction rates are too slow. High
temperatures and/or extremes of acidity can irreversibly change the structure
of most protein molecules. Even small changes in acidity can alter molecules
and how they interact. Both single cells and multicellular organisms have
molecules that help to keep the cells’ acidity within a narrow range.
This idea has three components: (1) that cells function best within a narrow
range of temperature and acidity, (2) that these conditions are needed for
the proper structure, and hence the function, of a cell’s proteins,
and (3) that cells have molecules that help to maintain these conditions.
For a complete content match, a textbook must present all three of these components
and provide examples (and possibly counter-examples) of cells functioning
in different conditions. Details of how particular amino acids are affected
by changes in pH go beyond the expected level of understanding of this idea.
Idea e: Cell functions are regulated. Complex interactions among
the different kinds of molecules in the cell cause distinct cycles of activities,
such as growth and division. Cell behavior can also be affected by molecules
from other parts of the organism or even other organisms.
This idea focuses on the regulation of cell functions, both internally and
externally. For a complete content match, a textbook needs to both state the
generalization and give examples of regulated activities, such as growth,
division, hormones, and neurotransmitters. However, the details of the phases
of the cell cycle (such as cytokinesis, G1, S, G2, interphase, and the stages
of mitosis) and details about gene regulation (such as operon, lac operon,
operator, repressor, and inducer) are beyond the expected level of understanding
of this idea.
Matter
and Energy Transformations
(See what the reviewers
looked for)
At the high school level, the Matter and Energy Transformations topic is to be treated at the molecular level. Ideas about matter transformation go beyond substances changing into new substances—textbooks must be explicit about atoms combining in new combinations during the transformations. Energy transformations are, as in grades 6–8, still to be viewed in terms of changing energy from one form to another. But now, chemical energy is defined in terms of the configurations of atoms: changing from lower energy configurations to higher energy configurations requires input of energy, whereas energy is released when higher energy configurations are changed into lower energy configurations.
Some materials in this study present considerable detail about metabolism that goes well beyond the level of sophistication of the key ideas. This did not affect judgments about alignment: as long as a key idea is explicitly stated somewhere (even if it is camouflaged in needless detail), a material should receive credit for alignment to a key idea. However, the inclusion of more sophisticated ideas that camouflage the key ideas is noted in the "Beyond Literacy" section of the Matter and Energy Transformations Content Analysis reports.
Another issue is whether the aligned material will be seen by students. For example, will students encounter suggested answers provided in the teacher's guide to questions in the student text? (We gave credit here but noted the basis for the credit in the report.) Will students encounter background information in the teacher's guide that is not accompanied by suggestions to convey the information to students? (We did not give credit here.) Related to this is the question of the author's intent. What happens if alignment occurs only in a stated objective or an assessment task but is not explicitly presented in text or activities? (We gave credit but noted what it was based on in the report.)
Most key ideas state generalizations. While it is certainly important for materials to provide examples to support the generalizations, a material must either point out that these examples are instances of the generalization or state the generalization in order to receive credit for alignment. For example, if a material describes digestion and cellular respiration in humans without making the generalization to other organisms, it was given an incomplete alignment to key Idea c1 or c2. Or if a material presents instances of matter cycles—such as the carbon cycle or the nitrogen cycle—but does not make the point that all elements cycle, it received only incomplete credit for alignment to key Idea d1. These and other issues are described below in the clarifications of the key ideas that were used by the reviewers.
Key ideas about matter transformation.
The essence of all these ideas is transformation (as opposed to just naming the reactants and products). It must be explicit that something is being transformed (or converted, made, changed, etc.) into something else. Furthermore, at the grades 9–12 level transformations of matter are dealt with at the molecular level (as opposed to substances changing into other substances).
Idea a1: Plants make sugar
molecules from carbon dioxide (in the air) and water.
This key idea specifies a molecular treatment of the overall reaction for
photosynthesis, not just starting and final substances. At the molecular level,
the carbon, hydrogen, and oxygen atoms in carbon dioxide and water are rearranged
to form sugars. Presenting the equation with chemical formulas of reactants
and products gets credit, though it would be better if the accompanying text
used such expressions as "atoms of carbon dioxide and water are rearranged
to form sugar molecules" or "the carbon atoms in sugar molecules come from
carbon dioxide and the hydrogen atoms come from water." However, the balanced
equation is not necessary; using molecular models to illustrate how atoms
are recombined to make sugar out of carbon dioxide and water would suffice.
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.
This idea describes the three possible fates of the sugar molecules plants
make: plants can transform some of the sugar molecules back into carbon dioxide
and water molecules, they can assemble them to make body structures, or they
can store them for later use. A material gets credit for an incomplete match
for covering fewer than three of these fates. Look to see there is something
explicit about transforming molecules or about atoms combining or rearranging.
And look to be sure that the material is explicit about what the sugar molecules
will be used for (as opposed to being just used or used up). The material
must also be explicit about plants. Although credit is given for a statement
that "all living things" carry out this process, note in the report if this
is the case.
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.
This idea describes the three possible fates of consumed food in organisms
that don't make their own food: food is broken down (during digestion) into
simpler substances (e.g., sugars) and further transformed into carbon dioxide
and water; the simpler substances can be reassembled into the body structures
of the consumers; some of the reassembled structures (e.g., fat) can serve
as storage forms for later use. As with Idea b1, credit for an incomplete
match is given if all fates are not listed. Also, note if the material truly
deals with "other organisms" or just with humans; though every part doesn't
need to be treated in multiple organisms, at least one should be. The respiration
equation gets credit for the breakdown part.
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 are several parts to this idea: that chemical elements (as
opposed to just examples of elements such as carbon or nitrogen) pass through
food webs, that elements pass repeatedly through food webs (so more
than one round in a cycle needs to be indicated), and that as the elements
pass through food webs they are combined and recombined in different ways.
To receive full credit for a content match, the material must treat all parts.
The material gets incomplete credit for treating only some parts. Furthermore,
full credit is given only if the three parts all deal with matter in terms
of molecules (for an example of a text statement that deals with cycling of
matter repeatedly but not at the molecular level, see page 13s of BSCS Biology:
An Ecological Approach, which is cited in the Content Analysis report
for that textbook). As with other ideas that state generalizations, describing
instances without explicitly stating the generalization receives credit for
an incomplete match. For example, giving examples of elements that recycle
(such as in the carbon cycle or the nitrogen cycle) without making clear that
all the elements that make up the molecules of living things recycle receives
only incomplete credit for this part of the key idea (see, for example, the
Content Analysis report for BSCS Biology: An Ecological Approach).
"Repeatedly" means over and over again, so describing a single cycle of carbon
through a food chain and back to carbon dioxide is insufficient for full credit.
The material should indicate that plants can then reuse the carbon dioxide
(that was released during respiration) to make sugars.
Key ideas about energy transformation.
The common feature of key ideas about energy transformation is that one form of energy is being converted into other forms—for example, light to chemical energy, chemical energy to chemical (or mechanical or electrical) energy and heat.
Idea a2: Plants transfer
the energy from light to make "energy-rich" sugar molecules.
This idea makes explicit the transformation of light energy into chemical
energy (or "energy-rich" sugar molecules). The material must go beyond
stating that energy is used to make sugars or to convert carbon
dioxide and water into sugars (because such statements could give the impression
that energy is used up in the process). While some of the sun's
energy is captured and only some of that is harnessed, some is both captured
and stored in sugar molecules.
Idea b2: Plants get energy
to grow and function by oxidizing the sugar molecules. Some of the energy
is released as heat.
This idea describes the two fates in plants of the energy they stored in sugars:
as plants oxidize (or burn or break down) sugars, plants can harness some
of the energy stored in sugars (e.g., to make other molecules or body structures)
and give some off as heat. Both fates are needed for a full match. The focus
here is on the energy transformations; it does not matter whether matter is
treated in terms of molecules or substances.
In addition, the material must convey the idea that the energy is used for something, such as growing, functioning, making new molecules, producing flowers, etc.
Although the term "oxidizing" appears in the key idea, the term is not required for a complete match. (It's not in Science for All Americans, though it appears in Benchmarks for Science Literacy and Atlas of Science Literacy.) However, some sort of active process must be conveyed—a kind of burning or even "breaking down"—to receive full credit. What isn't sufficient is the less sophisticated idea that organisms get energy from sugars; it must be clear that something is being done to the sugars.
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.
This idea describes the two steps that lead to the release of energy from
sugars (break down or digestion to sugars and then oxidation of sugars), some
of which is used to provide energy for growth and functioning and some of
which is released as heat. As with Idea b2, the material can use "oxidizing,"
"burning," or even "breaking down to release energy" and still receive full
credit. However, as with Idea b2, just indicating that organisms get energy
from food is a less sophisticated idea (e.g., see AAAS,
1993, p. 136, 6C(3–5)/1). The material must also convey the idea
that the energy is used for something, such as growing, functioning, making
new molecules, replacing damaged tissue, etc.
Ideally, the material would make clear that other organisms (not just humans) do all these things; but reviewers should give credit for other organisms if at least one other organism was mentioned for at least one of the fates.
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.
This idea ties together the energy transformations involved in food webs and
between food webs and the environment. Whereas Ideas a2, b2, and c2 deal with
individual organisms, Idea d2 sums across organisms. The first part of the
idea describes the two fates of energy in food webs-storage in the form of
chemical energy (or in the bodies of organisms) and dissipation as heat. (It
does not explicitly state that energy is also used for the growth and functioning
of organisms. That is dealt with in Ideas b2 and c2. However, it's fine if
materials make the connection.) The second part of the idea is the consequence
of the first: since energy is continually dissipated away as heat (hence unable
to be converted to chemical energy for use by organisms), energy must be continually
supplied. For a material to receive full credit, it must state both fates
of energy and indicate that continual input of energy is supplied
by sunlight to keep the process going. The idea that the sun is the ultimate
source of energy is insufficient and earns only incomplete credit.
It is important that materials convey that much of the energy is dissipated as heat—not just that some is. It is also important for the material to make it clear that not all of the energy is dissipated as heat, though the "10% rule" is not necessary. (In fact, biologists on our advisory group mentioned that the "10% rule" wasn't correct for most ecosystems.)
Finally, it is important for materials to make explicit that some of the energy actually goes somewhere else—for example, "used to make the organism's body tissue," "stored in organic material," or "used to make ATP energy." Stating only that energy is stored is insufficient and might convey the notion that "material-free" energy is stored.
Key ideas about matter and energy.
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.
This idea ties together the matter and energy stories at the ecosystem level,
relates transformations within organisms and between organisms and the environment,
and relates living organisms to the principles of transformation and conservation
of matter and energy that apply to all natural systems. There are several
parts to this key idea: (a) living organisms obey the same laws/principles
of conservation and transformation of matter and energy as do physical systems,
(b) matter and energy are transformed among living things and between them
and the physical environment, (c) the total amount of matter and energy remains
constant, and (d) the previous ideas hold even over long time spans. As with
other key ideas, incomplete credit is given if a material treats only some
of the parts.
To receive even incomplete credit, the material must talk about both matter and energy—conservation of matter alone and conservation of energy alone are grades 6–8 prerequisites. However, if the material treats conservation of matter (but not energy) and treats the idea that matter is conserved over long spans of time, it may be given incomplete credit.
Molecular
Basis of Heredity
(See what the reviewers
looked for)
Idea a: The information [for specifying characteristics of an organism] passed from parents to offspring is coded in DNA molecules.
Idea b: DNA molecules are long chains linking just four kinds of smaller molecules, whose precise sequence encodes genetic information.
Idea c: Genes are segments of DNA molecules. Each DNA molecule contains thousands of discrete genes.
Idea d: The genetic information stored in DNA is used to direct the synthesis of the thousands of proteins that each cell requires.
Idea e: A change in even a single atom in the DNA molecule can change the protein that is produced.
Idea f: Insertions, deletions, or substitutions in DNA can alter genes.
Idea g: A mutation of a DNA segment may not make much difference in the operation of the cell, may fatally disrupt it, or may change it in a significant way.
Idea h: An altered gene may be passed on to every cell that develops from it.
Idea i: When mutations occur in sex cells, they can be passed on to all cells in the resulting offspring; if mutations occur in other cells, they can be passed on to descendant cells only.
Idea j: Heritable characteristics ultimately produced in the development of an organism can be observed at molecular and whole-organism levels-in structure, chemistry, or behavior.
Natural
Selection and Evolution
(See what the reviewers
looked for)
Idea a: The basic idea of biological evolution is that the Earth's present-day species developed (over many generations) from earlier, distinctly different species.
Idea b: Modern ideas about evolution (including natural selection and common descent) provide a scientific explanation for the history of life on Earth as depicted in the fossil record and in the similarities evident within the diversity of existing organisms.
Idea c: Natural selection provides the following mechanism for evolution: Some variation in heritable characteristics exists within every species, some of these characteristics give individuals an advantage over others in surviving and reproducing, and the advantaged offspring, in turn, are more likely than others to survive and reproduce. The proportion of individuals that have advantageous characteristics will increase.
Idea d: Heritable characteristics strongly influence what capabilities an organism will have and how it will react, and therefore influence how likely it is to survive and reproduce.
Idea e: New heritable characteristics can result from new combinations of parents' genes or from mutations of genes in reproductive cells.
Idea f: When an environment changes (in this sense, other organisms are also part of the environment), the advantage or disadvantage of characteristics can change.
Idea g: Natural selection leads to organisms that are well suited for survival in particular environments.