Academic achievement standards for biology at taghs
Proposed Academic Achievement Standards for Biology at TAGHS
The purpose of this document is to recommend a conceptual strategy for establishing a new level of academic achievement standards and methods of teaching biology at TAGHS. These standards would be a starting point for a program of continuous improvement in biology literacy. It is largely based on acquiring a specific knowledge base, and achieving certain benchmarks in the classroom that will provide the student with improved skill sets.
The proposed program:
- Is a comprehensive first-year high school biology curriculum that emphasizes cellular and molecular biology as well as genetics, human biology, ecology and evolution.
- Represents an innovative approach to teaching and learning introductory biology. This new approach incorporates the traditional discipline-specific concepts with an emphasis on presenting concepts in depth and in context.
- Not only develops conceptual connections through a storyline that is relevant to students' lives, but also uses inquiry-based activities that focus on process-thinking skills students will use for a lifetime.
- Addresses conceptual knowledge that falls under the category of cognitive processing, understanding, which fosters transfer and meaningful learning rather than rote learning and memorization.
Require students to analyze or evaluate data and/or the results of investigations so that they must use understanding as they demonstrate even more cognitively complex learning.
- Provides levels of understanding and ability that all students are expected to reach on the way to becoming biology literate;
- Concentrates on the common core of learning that contributes to the biology literacy of all students while acknowledging that most students have interests and abilities that go beyond that common core, and some have learning difficulties that must be considered;
- Avoids language used for its own sake, in part to reduce sheer burden, and in part to prevent vocabulary from being mistaken for understanding,
- Is informed by research on how students learn.
- Encourages the teacher to recognize the interconnectedness of knowledge and to build these important connections into the curriculum.
The three major skill specifications that are expected to improve with the proposed strategy are:
1. Knowledge of Fundamental Concepts: remembering specific facts; demonstrating straightforward knowledge of information and familiarity with terminology.
2. Application: understanding concepts and reformulating information into other equivalent forms; applying knowledge to unfamiliar and/or practical situations; solving problems using mathematical relationships.
3. Interpretation: inferring and deducing from qualitative and quantitative data and integrating information to form conclusions; recognizing unstated assumptions
In response to what was widely perceived as inadequate teaching of precollege science in the United States, the National Science Foundation supported the development of the Benchmarks for Science Literacy (AAAS 1993) and the National Science Education Standards (NRC 1996). One of the specific problems addressed by these national standards efforts was that secondary science historically has been taught primarily through lecture with emphasis on long lists of trivial facts and vocabulary words, which often are to be memorized (Bowyer 1990; Brandwein 1981; Champagne & Hornig 1987). This practice has been widely supported by traditional, encyclopedic science textbooks which continually grow in size as more information is added to each new edition.
Both AAAS and the NRC attempted to aid science curriculum developers in content selection by identifying a small subset of the most important science concepts rather than a long set of facts that attempt to cover an entire subject, as is the case for many traditional science curricula. Also, unlike the dominant traditional curricula, AAAS and NRC strongly recommend that science curricula devote significantly more time to developing scientific thinking skills and understanding the nature of science. Both organizations promote student learning through engaged investigation as opposed to passive listening and speak also to the desirable role of the teacher as being distinctly student-centered and inquiry-oriented.
Science curricula recently funded by the National Science Foundation have aligned themselves with the Standards and Benchmarks by reducing numbers of concepts and topics and de-emphasizing less central concepts and topics in favor of additional activities that require student thinking, decision-making, inquiry, collaboration and communication. Observers of students using these new curricula have noted that they are engaged extensively in serious discussion and scientific inquiry.
Since the national standards and corresponding curricula developed to meet the standards are quite recent, there is yet little research literature on the effectiveness of these curricula. ChemCom (Sutman & Bruce 1992, 1993; ACS 1998), a high school chemistry curriculum developed with funding from the National Science Foundation and the American Chemistry Society predated the National Science Education Standards. Developers of ChemCom say that it matches the standards, especially in its 1993 and 1998 editions. One study of ChemCom at the University of Texas (Mason 1998) compared student achievement in college general chemistry by students who had either a traditional high school chemistry curriculum or the 1988 or 1993 editions of ChemCom. After eliminating variables such as having taken AP Chemistry or a second year of advanced chemistry in high school, there were no statistically significant differences in performance between students who had one year of ChemCom versus those who had one year of a traditional chemistry course in high school.
Biology: A Community Context (Leonard & Penick 1998a) is an introductory high school biology curriculum developed in response to the national standards and needs. Funded by a $2.3 million National Science Foundation grant to Clemson University, the project goal was a teacher-developed curriculum that would be standards-based, activity-oriented, inquiry-centered and overtly constructivist. As part of the evaluation component, it was of interested to know if this standards-based curriculum would produce any greater learning of selected science concepts identified in the Standards and Benchmarks and any greater understanding of scientific inquiry skills than did the traditional curricula that dominate schools today. BACC was designed to encourage broad goals (Penick & Bonnstetter 1993) by following a research-based instructional strategy (Leonard & Penick 1998b; Penick 1999).
Much research about teaching and learning was used to support the development of the Standards and Benchmarks. Over the years, a variety of research demonstrates that when students learn actively by being engaged (much the same way as do scientists) they have fuller and more lasting understanding of scientific concepts, science process skills, and the nature of science than they do if instructed primarily by lecture and discussion indicated (Piaget 1964; Mullis & Jenkins 1988; Smilansky & Halberstadt 1986). This active participation is scientific inquiry.
Students benefit from direct experiences with other students as well as the materials, concepts and processes, and best understand them in that manner. With this rationale, considerable laboratory, field and other types of classroom investigation need to precede, rather than follow, discussion, explanation and lecture. Thus, standards-based curricula would be expected to be highly activity-oriented, student-centered, and have the textual narrative that explains scientific concepts placed carefully in the student textbook after the corresponding inquiry activities. In this manner, student investigations are more experimental in that they are seeking answers to questions rather than merely doing laboratory work to confirm answers already given, what Schwab (1963) called a “Rhetoric of Conclusions.” At the same time, by doing the activity first, students develop a need to know and learn more, thus encouraging reading and communication with others.
During the summer of 1997, 16 high school biology teachers representing very diverse educational settings all over the United States, ranging from suburban to urban and rural, as well as small and large, were given an intensive, one-week training on the methodology and contents of Biology: A Community Context by the authors (Leonard & Penick) and Project Manager (Speziale) of the curriculum
Teachers were immersed in all the components of the curriculum (student text, teacher guide, initial inquiry video, and assessment package). Teachers conducted selected and representative activities from the student text and discussed concepts, activities and strategies with the authors, seeking a more thorough understanding of the nature of science and the curriculum. Other discussions emphasized the curriculum's instructional methodology, the nature of scientific inquiry, the constructivist view of learning, active learning and the critical sequencing of the different kinds of classroom instruction.
During the full 1997-98 school year the same 16 high school biology teachers each taught at least one class using the standards-based curriculum, BACC, and at least one other class using their existing traditional curriculum and text. Many of these teachers actually taught multiple classes of both BACC and their traditional curriculum. Since neither students nor classes were randomly assigned at each school, there was some concern about equivalency of student ability in the intact classes using the two different curricula. To accomplish the best possible equivalency given these limitations, each teacher was asked to teach approximately half of their biology classes using each curriculum and to make assignments of classes to each of the two so as to achieve the best possible balance of student ability using each curriculum.
During the first week of school, teachers administered two pretests: “A Test of Understanding Biology Concepts” and “A Test of Science Process Skills.” Both tests were constructed by the authors and BACC staff, reviewed by biology teachers, and revised accordingly. The concept test and the process tests each emphasized higher-order critical thinking skills. The items on the concept test featured biological knowledge and ideas while the process test featured the more traditional processes of science in a biology context. All students in the study repeated the same two tests as posttests during the last week of the school year. Data were analyzed for class differences in mean scores between BACC and the traditional classes.
Teachers used the BACC curriculum and their existing traditional curriculum with the corresponding intact classes during the entire school year. For the BACC class, teachers were asked to use classroom methodologies learned in the summer workshop and consistent with BACC. For the traditional classes, teachers attempted to use methodologies consistent with their past practices in classrooms using a traditional curriculum.
There were both intended and observed differences in the instruction using these different curricula. The primary instructional methodology intended in BACC was investigative inquiry because there were more than a hundred inquiry activities directly in the student text. Individual students spent about 75% of their time in active investigation. The traditional biology curriculum students spent about 90% of their time listening or reading. One of the authors visited and observed all of the sites twice during the school year. In nearly all observations of BACC classes, students were doing activities for the majority of the period. This included what would be recognized as laboratory and field experiments as well as student forums, group presentations, and small and large group discussions. In the classrooms using the traditional biology curricula, lecture or reading were observed most of the time. Those laboratory exercises that were observed in the traditional classrooms were primarily dissections or activities that required students to read and follow directions.
The role of the teacher in the classrooms using the different curricula was also vastly different. In BACC classrooms the teacher staged activities in which the students participated. Although the teacher guided some discussions (especially summary discussions), students spent much more time contributing than did the teacher. The teacher's guiding presence was always noted, however. In the traditional classroom, the teacher was not only the focus of instruction but was also the most active and dominant contributor.
There were also differences in the sequencing of the kinds of actions taken by students. Activities in the BACC classroom appeared to proceed from concrete to more abstract. Students began by manipulating materials in attempts to investigate biological phenomena and questions raised in class. This was followed by guided discussions, short teacher explanations, and reading assignments related to the same concepts. In the traditional classrooms, abstractions of the concepts were first presented by lecture or demonstration, followed by brief opportunities for students to ask questions, laboratory work, then assignments involving vocabulary words or questions in the textbook. Actual investigations occurred only about once a week and were rarely student initiated or planned.
The spirit of the national standards appeared quite prevalent in BACC classrooms. Here there was a greater balance in student time spent on development of biology concepts, science process skills, and understanding the nature of science. Traditional classes focused exclusively on development of biology concepts, as evidenced by clear attempts by the teacher to “cover the material” in all or part of a chapter in the text (teacher's own words). BACC classes spent more time on selected biological concepts and more time relating the concept to the students' lives in familiar settings. There appeared to be little time for students to reflect, evaluate or investigate concepts in the traditional classes, whereas these aspects were observed regularly in BACC classes.
In spite of differences between the BACC and traditional classes, there were also similarities. The teachers appeared well prepared in both kinds of classes. The students acted attentive, interested, and relatively responsive to the teacher's requests for actions or responses. It would appear that these students had been well trained in traditional methodologies and felt comfortable with them. Some students appeared frustrated with the uncertainties presented to them in the BACC curriculum.
Overall, BACC students received lower scores on the pretests of both science concepts and processes than did the students in the more traditional classes. The difference between the two class means was significant at the .005 level on the pretests of science processes. Several teachers mentioned that counselors, on seeing the small size (576 pages) of the BACC student text, sometimes systematically put students of perceived lower ability in these classes and students of perceived higher ability into the traditional classes with the larger textbook (usually over 1000 pages). This practice was consistent with historical observations of counselor practice years earlier with the ChemCom curriculum.
At the end of the school year, students completed the same tests of concepts and processes as posttests. Not only did the BACC classes score significantly higher on the posttests of both science concepts and processes, there was less attrition in the BACC classes than in the more traditional classes. Three hundred seventy-two BACC students completed the “Test of Understanding Biology Concepts” pretest and 365 completed the posttest, a loss of only 2% compared with the more traditional students completing the same test going from 368 to 298, a loss of 19% during the school year. The same pattern was repeated on the “Test of Science Process Skills” with BACC classes losing only 5% and the traditional classes again losing 19%. While some of the losses may be related to student errors in coding their names, there may also be an element of taking the test more seriously in the BACC classes. An anecdote from one of the field test sites may have meaning here.
At a large, urban high school, one class of biology students began the year with BACC.After only a few weeks of class, the local fire marshal closed the school, citing building safety as a factor. All the students were moved to the library of a nearby middle school, and divided up into classes with almost no materials or equipment. The field test teacher persevered, having students do the activities as best they could. Then, after several months in this facility, they were all allowed back into the high school. At that point, the teacher noted that a large number of his students in the more traditional class had dropped out, while all of the BACC students were still attending regularly. When he asked students why they were still there, he heard a lot of statements along the lines of, “This class is fun. It is one of the few reasons we even come to school.”
It was notable that, although the BACC classes scored significantly lower on the science process skills pretest, after a school year of BACC they scored significantly higher on that posttest. Of particular interest were the differences between pretest and posttest gain scores for the two groups. BACC students gained 2.68 more points than the traditional classes on the biology concepts test and 3.83 more points than the traditional classes on the test for science process skills. These differences in gain scores represent approximately one-half standard deviation.
Following up on the anecdote about class attendance, student comments obtained through a structured survey revealed that students in general liked BACC, felt they had done well (and even better than in prior science classes), and enjoyed the activities, finding them useful.
Many have proposed that the traditional science curriculum provides for too much breadth and precious little depth (Sutman & Bruce 1992, 1993). Various anecdotes of teachers teaching fewer concepts but finding that students scored better on exams have been reported (Yager 1990; McComas 1989). Yet, implementation of innovative NSF-funded curriculum is scattered and accounts for only a small fraction of all student materials purchased in the United States. Some of this may be due to a lack of research on the effects of these innovative curricula but equally likely is that few teachers have used such curricula and felt the impact of students feeling. As a related aside, Japanese cars did not come to dominate the U.S. market because drivers read research reports about their quality of construction. Instead, consumers noted the fit and finish, the quality appearance, the fuel economy, the ride and handling, and their reliability. Much of the rush to buy Japanese cars was fueled by word-of-mouth based on experience with the product.
These findings are quite gratifying as progressive educators would have been satisfied to find that BACC students did as well as more traditional students. Having them do better and also report they really liked the curriculum more was surprising. It is also gratifying to find that experienced biology teachers can implement successfully a standards-based high school biology curriculum. And, contrary to some popular mythologies, they also can change their behaviors to match the rationale and methodology of the innovative curriculum. Moreover, these teachers appeared to be persuaded that a standards-based approach is desirable, reasonable and practical to implement.
Based on the limited population used in this study, this standards-based biology curriculum was more productive in teaching an understanding of key biology concepts and science process skills than were more traditional curricula. This study provides some evidence that recently developed; NSF-funded curricula are accomplishing the goals of the National Science Education Standards and the Benchmarks for Science Literacy.
Following is a comparison of the major differences in the implementation of the proposed verses the traditional curricula and in the intended way in which classroom procedures would be carried out at TAGHS. They are modified from Leonard, W. H., Speziale B.J. and J. E. Penick. (2001).
Primary Instruction Methodology
75% investigative inquiry, discussions and forums
75-90% lecture, less then 20% labs, some worksheets
Role of Teacher
Orchestrates activities, guides discussions
Authoritative center of instruction
Sequence of Instructional Activities
Direct experiences first, followed by discussion
Lecture, reading, sometimes followed by lab
Relationship to National Standards
Highly correlated by design, demonstrated in activities and readings.
Correlations claimed but demonstrated only in some readings
Number of Concepts and Topics Covered
Fewer then 180 in great depth
Broad coverage of over 400 topics
Science Process Skills
Highly emphasized on daily basis
Little or moderate emphasis perhaps weekly
Understanding the Nature of Science
Direct experiences and reflections
Little systematic development
Emphasis on Technology
Terms not bolded used only in context
Thousands of terms bolded in text
Applications of Concepts
Related to student's local community
Related to next biological concept(s)
Proposed Academic Standards and knowledge base for TAGHSHigh School Biology
1. The Living Environment
People have long been curious about living things—how many different species there are, what they are like, where they live, how they relate to each other, and how they behave. Scientists seek to answer these questions and many more about the organisms that inhabit the earth. In particular, they try to develop the concepts, principles, and theories that enable people to understand the living environment better.
Living organisms are made of the same components as all other matter, involve the same kinds of transformations of energy, and move using the same basic kinds of forces. The Physical Setting apply to life as well as to stars, raindrops, and television sets. But living organisms also have characteristics that can be understood best through the application of other principles.
What can be anywhere near as awe-inspiring as the vast array of living things that occupy every nook and cranny of the earth's surface, unless it is the array of extinct species that once occupied the planet? Biologists have already identified over a million living species, each with its own way of surviving, sometimes in the least likely places, each readily able to propagate itself in the next generation. Because only organisms with hard shells or skeletons are generally preserved, the fossil record does not preserve a good record of the even greater number of extinct species that have existed over the span of the earth's history.
This sense of wonder at the rich diversity and complexity of life is easily fostered in high school children. They spontaneously respond to nature. However, attempts to give them explanations for that diversity before they are able to handle the abstractions, or before they see the need for explanations, can dampen their natural curiosity.
Nevertheless, the explanations must come, for scientists not only revel in nature but try to understand it. The challenge for educators is to capitalize on the interest that students have in living things while moving them gradually toward ideas that make sense out of nature. Familiarity with the phenomena should precede their explanation, and attention to the concrete object should precede abstract theory.
Perhaps this is another instance in which following the course of history pays off. Long before the microscope led scientists to cells and chemistry led them to protein and DNA, the earth was under close scrutiny.
Botanists, zoologists, geologists, surveyors, explorers, amateur collectors, and even fortune-hunters were busy finding out what was "out there." On every continent, indigenous people had intimate knowledge of the flora and fauna of their regions. Their very survival depended on acquiring this knowledge and passing it on from generation to generation. As information accumulated, interest in classification systems grew, and those systems became more complex, especially after the microscope revealed a whole new world to explore and catalogue. Eventually, scientists produced and tested the theories and models that are used to explain people's observations. They came to understand the living environment first through observations, then classifications, then theories. The Human Organism augments many of these ideas in the context of human beings.
Diversity of Life
General similarities and differences among organisms are easily observed. Most children are interested in living things and already able to distinguish among the common ones. Children know, for example, that fish resemble other fish, frogs resemble other frogs, and that fish and frogs are different. In the beginning, children can focus on any attribute—size, color, limbs, fins, or wings—but then should gradually be guided to realize that for purposes of understanding relatedness among organisms, some characteristics are more significant than others. The task is to move students toward a more sophisticated understanding of the features of organisms that connect or differentiate them: from external features and behavior patterns, to internal structures and processes, to cellular activity, to molecular structure.
Understanding and appreciating the diversity of life does not come from students' knowing bits of information or classification categories about many different species; rather it comes from their ability to see in organisms the patterns of similarity and difference that permeate the living world. Through these patterns, biologists connect the multitude of individual organisms to the theories of genetics and ecology.
Two aims dominate at this level. One is to advance student understanding of why diversity within and among species is important. The other is to take the study of diversity and similarity to the molecular level. Students can learn that it is possible to infer relatedness among organisms from DNA or protein sequences. An investigation of the DNA-fingerprinting controversy may provide an interesting way to approach the question of the nature and validity of molecular evidence.
By the end of the course, students should know that
- The variation of organisms within a species increases the likelihood that at least some members of the species will survive under changed environmental conditions.
- A great diversity of species increases the chance that at least some living things will survive in the face of large changes in the environment.
- The degree of relatedness between organisms or species can be estimated from the similarity of their DNA sequences, which often closely match their classification based on anatomical similarities.
- Similar patterns of development and internal anatomy suggest relatedness among organisms.
- Most complex molecules of living organisms are built up from smaller molecules. The various kinds of small molecules are much the same in all life forms, but the specific sequences of components that make up the very complex molecules are characteristic of a given species.
- A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.
Building an observational base for heredity ought to be the first undertaking. Explanations can come later. The organisms children recognize are themselves, their classmates, their family and their pets. And that is the place to start studying heredity. However, it is important to be cautious about having children compare their own physical appearance to that of their siblings, parents, and grandparents. At the very least, the matter has to be handled with great delicacy so no one is embarrassed. Direct observations of generational similarities and differences of at least some plants and animals are essential.
Learning the genetic explanation for how traits are passed on from one generation to the next can begin in the middle years and carry into high school. The part played by DNA in the story should wait until students understand molecules. The interaction between heredity and environment in determining plant and animal behavior will be of interest to students. Examining specific cases can help them grasp the complex interactions of genetics and environment.
By the end of the course, students should know that
- Some new gene combinations make little difference, some can produce organisms with new and perhaps enhanced capabilities, and some can be deleterious.
- The sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations in the offspring of any two parents.
- The information passed from parents to offspring is coded in DNA molecules, long chains linking just four kinds of smaller molecules, whose precise sequence encodes genetic information.
- Genes are segments of DNA molecules. Inserting, deleting, or substituting segments of DNA molecules can alter genes. An altered gene may be passed on to every cell that develops from it. The resulting features may help, harm, or have little or no effect on the offspring's success in its environment.
- Gene mutations can be caused by such things as radiation and chemicals. When they occur in sex cells, they can be passed on to offspring; if they occur in other cells, they can be passed on to descendant cells only. The experiences an organism has during its lifetime can affect its offspring only if the genes in its own sex cells are changed by the experience.
- The many body cells in an individual can be very different from one another, even though they are all descended from a single cell and thus have essentially identical genetic instructions.
- Different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and past history.
- Heritable characteristics can include details of biochemistry and anatomical features that are ultimately produced in the development of the organism. By biochemical or anatomical means, heritable characteristics may also influence behavior.
Students can get pretty far along in their study of organisms before they need to learn that all activities within those organisms are performed by cells and that organisms are mostly cells. The familiar description and depiction of cells in blood sometimes lead students to the notion that organisms contain cells rather than that organisms are mostly made up of cells. Imagining the large number of cells is also a problem for students. Large organisms are composed of trillions of cells, but this number means little to high-school students. A million millions might have a better chance of making an impression.
Students may have even more difficulty with the idea that cells are the basic units in which life processes occur. Neither familiarity with functions of regular-sized organisms nor observation of single-celled organisms will reveal much about the chemical activity going on inside single cells. For most students, the story should be kept simple. The way to approach the idea of functioning microscopic units is to start with the needs of macroscopic organisms.
Information transfer and energy transformation are functions of nearly all cells. The molecular aspects of these processes should wait until students have observed the transformation of energy in a variety of physical systems and have examined more generally the requirements for the transfer of information. Information transfer may mean communication among cells within an organism or passing genetic codes from a cell to its descendants.
The individual cell can be considered as a system itself and as part of larger systems, sometimes as part of a multicellular organism, always as part of an ecosystem. The cell membrane serves as a boundary between the cell and its environment, containing for its own use the proteins it makes, equipment to make them, and stockpiles of fuel. Students should be asked to consider the variety of functions cells serve in the organism and how needed materials and information get to and from the cells. It may help students to understand the interdependency of cells if they think of an organism as a community of cells, each of which has some common tasks and some special jobs.
The idea that protein molecules assembled by cells conduct the work that goes on inside and outside the cells in an organism can be learned without going into the biochemical details. It is sufficient for students to know that the molecules involved are different configurations of a relatively few kinds of amino acids, and that the different shapes of the molecules influence what they do.
Students should acquire a general picture of the functions of the cell and know that the cell has specialized parts that perform these functions. This can be accomplished without many technical terms. Emphasizing vocabulary can impede understanding and take the fun out of biology. Discussion of what needs to be done in the cell is much more important than identifying or naming the parts that do it. For example, students should know that cells have certain parts that oxidize sugar to release energy and parts to stitch protein chains together according to instructions; but they don't need to remember that one type of part is a mitochondrion and the other a ribosome unless relevant meaning and purpose can be given to these structures,
By the end of the course, students should know that
- Every cell is covered by a highly specialized membrane that controls what can enter and leave the cell.
- In all but quite primitive cells, a complex network of proteins provides organization and shape and, for animal cells, movement.
- Within the cells are specialized parts for the transport of materials, energy capture and release, protein building, waste disposal, passing information, and even movement.
- In addition to the basic cellular functions common to all cells, most cells in multicellular organisms perform some special functions that others do not.
- The work of the cell is carried out by the many different types of molecules it assembles, mostly proteins. Protein molecules are long, usually folded chains made from 20 different kinds of amino acid molecules. The function of each protein molecule depends on its specific sequence of amino acids and its shape. The shape of the chain is a consequence of attractions between its parts.
- The genetic information encoded in DNA molecules provides instructions for assembling protein molecules.
- The genetic information encoded in DNA molecules is virtually the same for all life forms.
- Before a cell divides, the instructions are duplicated so that each of the two new cells gets all the necessary information for carrying on.
- 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.
- Gene mutation in a cell can result in uncontrolled division called cancer. Exposure of cells to certain chemicals and radiation increases mutations and thus the chance of cancer.
- 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 the molecules and how they interact.
- A living cell is composed of a small number of chemical elements mainly carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. Carbon, because of its small size and four available bonding electrons, can join to other carbon atoms in chains and rings to form large and complex molecules.
Interdependence of Life
It is not difficult for students to grasp the general notion that species depend on one another and on the environment for survival. But their awareness must be supported by knowledge of the kinds of relationships that exist among organisms, the kinds of physical conditions that organisms must cope with, the kinds of environments created by the interaction of organisms with one another and their physical surroundings, and the complexity of such systems. Students should become acquainted with many different examples of ecosystems, starting with those near at hand.
The concept of an ecosystem should bring coherence to the complex array of relationships among organisms and environments that students have encountered. Students' growing understanding of systems in general can suggest and reinforce characteristics of ecosystems—interdependence of parts, feedback, oscillation, inputs, and outputs. Stability and change in ecosystems can be considered in terms of variables such as population size, number and kinds of species, and productivity.
By the end of the course, students should know that
- Ecosystems can be reasonably stable over hundreds or thousands of years. As any population grows, its size is limited by one or more environmental factors: availability of food, availability of nesting sites, or number of predators.
- If a disturbance such as flood, fire, or the addition or loss of species occurs, the affected ecosystem may return to a system similar to the original one, or it may take a new direction, leading to a very different type of ecosystem. Changes in climate can produce very large changes in ecosystems.
- Human beings are part of the earth's ecosystems. Human activities can, deliberately or inadvertently, alter the equilibrium in ecosystems.
Flow of Matter and Energy
Organisms are linked to one another and to their physical setting by the transfer and transformation of matter and energy. This fundamental concept brings together insights from the physical and biological sciences. But energy transfer in biological systems is less obvious than in physical systems. Tracing where energy comes from through its various forms is usually directly observable in physical systems. Fire heats water, falling water makes electricity. But energy stored in molecular configurations is difficult to show even with models.
The cycling of matter and flow of energy can be found at many levels of biological organization, from molecules to ecosystems. The study of food webs can start in the elementary grades with the transfer of matter, be added to in the middle grades with the flow of energy through organisms, and then be integrated in high school as students' understanding of energy storage in molecular configurations develops. The whole picture grows slowly over time for students. In their early years, the temptation to simplify matters by saying plants get food from the soil should be resisted.
Now students have a sufficient grasp of atoms and molecules to link the conservation of matter with the flow of energy in living systems. Energy can be accounted for by thinking of it as being stored in molecular configurations constituted during photosynthesis and released during oxidation. Although there is no need to account for all the energy, students should observe heat generated by consumers and decomposers. Discussions of ecosystems can both contribute to and be reinforced by students' understanding of the systems concept in general. The difficulty of predicting the consequences of human tinkering with ecosystems can be illustrated with examples such as the ill-considered fire-prevention efforts in national forests.
This level is also a time to ask what this knowledge of the flow of matter and energy through living systems suggests for human beings. Issues such as the use of organic material inside the Earth and the recycling of matter and energy are important enough to pay considerable attention to in high school.
By the end of the course, students should know that
- At times, environmental conditions are such that land and marine organisms reproduce and grow faster than they die and decompose to simple carbon containing molecules that are returned to the environment. Over time, layers of energy-rich organic material inside the earth have been chemically changed into great coal beds and oil pools.
- The chemical elements that make up the molecules of living things pass through food webs and are combined and recombined in different ways. At each link in a food web, some energy is stored in newly made structures but much is dissipated into the environment. Continual input of energy from sunlight keeps the process going.
Evolution of Life
In the twentieth century, no scientific theory has been more difficult for people to accept than biological evolution by natural selection. It goes against some people's strongly held beliefs about when and how the world and the living things in it were created. It hints that human beings had lesser creatures as ancestors, and it flies in the face of what people can plainly see—namely that generation after generation, life forms don't change; roses stay roses, worms stay worms. New traits arising by chance alone is a strange idea, unsatisfying to many and offensive to some. And its broad applicability is not appreciated by students, most of whom know little of the vast amount of biological knowledge that evolution by natural selection attempts to explain.
It is important to distinguish between evolution, the historical changes in life forms, and natural selection, the proposed mechanism for these changes. Students should first be familiar with the theories of evolution so that they will have an informed basis for judging different explanations. This familiarity depends on knowledge from the life and physical sciences: knowledge of phenomena occurring at several different levels of biological organization and over very long time spans. Students may very well wonder why the fossil record has so many seeming holes in it.
Natural selection should be offered as an explanation for familiar phenomena and then revisited as new phenomena are explored. Students have to understand the changing proportions of a trait in populations.
Controversy is an important aspect of the scientific process. Students should realize that although many scientists may accept the general concept of evolution of species, Scientists do have different opinions on how fast and by what mechanisms evolution proceeds. A separate issue altogether is how life itself began, a scientific detailed mechanism for which has not yet emerged.
History should not be overlooked. Learning about Darwin and what led him to the concept of evolution illustrates the interacting roles of evidence and theory in scientific inquiry. Moreover, the concept of evolution provided a framework for organizing new as well as "old" biological knowledge into a coherent picture of life forms.
Finally there is the matter of public response. Opposition has come and continues to come from people whose interpretation of religious writings conflicts with the story of evolution. The TAGHS Biology course need not avoid the issue altogether. Perhaps science courses can acknowledge the disagreement and concentrate on frankly presenting the scientific view. Even if students eventually do not to believe the scientific story, they should be well informed about what the story is.
By the end of the course, students should know that
- The basic idea of biological evolution is that the earth's present-day species are descended from earlier, distinctly different species.
- Although far from conclusive, molecular evidence substantiates the anatomical theoretical basis for evolution and provides additional detail about the sequence in which various lines of descent branched off from one another.
- 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. As a result, the proportion of individuals that have advantageous characteristics will increase.
- Heritable characteristics can be observed at molecular and whole-organism levels—in structure, chemistry, or behavior.
- Heritable characteristics influence how likely an organism is to survive and reproduce.
- New heritable characteristics can result from new combinations of existing genes or from mutations of genes in reproductive cells. Changes in other cells of an organism cannot be passed on to the next generation.
- Natural selection leads to organisms that are well-suited for survival in particular environments.
- Chance alone can result in the persistence of some heritable characteristics having no survival or reproductive advantage or disadvantage for the organism.
- When an environment, including other organisms that inhabit it changes, the survival value of inherited characteristics may change.
- Modern ideas about evolution and heredity 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.
- Evolution builds on what already exists, so the more variety there is, the more there can be in the future. But evolution does not necessitate long-term progress in some set direction. Evolutionary change appears to be like the growth of a bush: Some branches survive from the beginning with little or no change; many die out altogether; and others branch repeatedly, sometimes giving rise to more complex organisms.
- The continuing operation of natural selection on new characteristics and in diverse and changing environments, over and over again for millions of years, has produced a succession of diverse new species.
2. The Human Organism
As similar as human beings are in many ways to other species, we are unique among the earth's life forms in our ability to use language and thought. Having evolved a large and complex brain, our species has a facility to think, imagine, create, and learn from experience that far exceeds that of any other species. We have used this ability to create technologies and literary and artistic works on a vast scale and to develop a scientific understanding of ourselves and the world.
We are also unique in our profound curiosity about ourselves: How are we put together physically? How were we formed? How do we relate biologically to other life forms? How are we as individuals like or unlike other humans? How can we stay healthy? Much of the scientific endeavor focuses on such questions.
This chapter relates to many ideas in Chapter 1: The Living Environment. Many of the characteristics of the human organism covered in this chapter are common to all mammals, or all animals, or all life forms. They are presented in a human context because that is easiest to learn for most students. Still, some features of life may be less readily recognizable in human beings because they are covered by layers of socialization and language. People sometimes become aware of their own characteristics only when they see them in other animals.
Human fertilization, followed by birth, growth and development, and finally aging and death continue in a cyclic fashion over generations. Birth and death are subjects that have awed and inspired people of all ages. Perhaps no other topic brings individuals closer to a sense of connectedness to people of all cultures and all times. Considerable amounts of society's resources go towards developing technology to control birth and death. The options opened up by technology raise ethical dilemmas for both individuals and society.
Students should know enough about atoms and molecules to make sense of the idea that DNA carries instructions for the assembly of proteins, determining their structure and the rates at which they are made. Students' growing notion of systems can help them understand how turning instructions on and off can sequence developments over a lifetime and that each cell's immediate environment can influence its development, even though nearly all cells carry the same DNA instructions. The use of health technologies raises many social issues—what certainty is necessary before a new drug is marketed, who benefits and who pays, and what constitutes a reasonable quality of life and who should decide. By now, students can take up such controversial issues and consider the trade-offs involved.
By the end of the course, students should know that
- As successive generations of an embryo's cells form by division, small differences in their immediate environments cause them to develop slightly differently, by activating or inactivating different parts of the DNA information.
- The complexity of the human brain allows humans to create technological, literary, and artistic works on a vast scale, and to develop a scientific understanding of the world.
- Both genes and environmental factors influence the rate and extent of development.
- Following fertilization, cell division produces a small cluster of cells that embeds itself in the wall of the uterus. As the embryo develops, it receives nourishment and eliminates wastes by the transfer of substances between its blood and the blood of its mother.
- Patterns of human development are similar to those of other vertebrates.
Like other organisms, human beings are composed of specialized cells grouped in organs that have special functions. However, rather than focusing on distinct anatomical and physiological systems (circulatory, digestive, etc.), instruction should focus on the essential requirements for life—obtaining food and deriving energy from it, protecting against injury, providing internal coordination, and reproducing. These grand body systems and their subsystems illustrate important aspects of systems in general.
Students' understanding of the human organism can expand to encompass molecular energy release, protection by the immune and nervous systems, cognition, and some of the ways in which systems interact to maintain a fairly constant environment for cells. Although some concepts can be learned from print and video, students can have direct experiences examining the effects of exercise on biological rhythms, or of food on body measurements such as temperature, pulse, blood pressure, or oxygen consumption. These types of observations can be linked to mathematical description of changes, to physical and chemical measurements, to statistical summary, and to controlled experiments.
By the end of the course, students should know that
Knowledge of health and knowledge about illness and disease are closely connected. Human beings' knowledge of diseases has helped them understand how the healthy body works, just as knowing about normal body functioning helps to define and detect diseases.
Knowledge of science can inform choices about nutrition and exercise, but that doesn't ensure healthy practices. Some adults have ideas about health that are contrary to scientific facts. Ideas about what constitutes good nutrition change somewhat as new information accumulates, but the basics are quite stable. Students should learn these basics.
Students should learn how to make and graph health-relevant measurements (body temperature, pulse), discuss tradeoffs in using prescription drugs, and so on.