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5. The Living Environment

  1. Diversity of Life
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12
  2. Heredity
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12
  3. Cells
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12
  4. Interdependence of Life
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12
  5. Flow of Matter and Energy
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12
  6. Evolution of Life
    1. Kindergarten through Grade 2
    2. Grades 3 through 5
    3. Grades 6 through 8
    4. Grades 9 through 12

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. Thus, all of the physical principles discussed in Chapter 4: 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.

Science for All Americans

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 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 Darwin provided an entirely new framework for explaining evolution and 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. It's a useful model for students to follow in learning about the environment. Chapter 6: The Human Organism augments many of these ideas in the context of human beings.


General similarities and differences among organisms are easily observed. Most children enter kindergarten 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 teacher's 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, ecology, and evolution.


All students, especially those who live in circumstances that limit their interaction with nature, must have the opportunity to observe a variety of plants and animals in the classroom, on the school grounds, in the neighborhood, at home, in parks and streams and gardens, and at the zoo. But observing is not enough. The students should have reasons for their observations—reasons that prompt them to do something with the information they collect. The reason can be to answer the students' own questions about how organisms live or care for their young. Some students may enjoy displaying, with drawings, photographs, or even real specimens, all the living things they can find where they live. The point is to encourage them to ask questions for which they can find answers by looking carefully (using hand lenses when needed) at plants and animals and then checking their observations and answers with one another.

The anthropomorphism embedded in most animal stories causes some worry. One suggestion is to ignore it. Stories sometimes give plants and animals attributes they do not have, but promoting student interest in reading is more important than giving students rigidly correct impressions in their reading. Students can be guided toward making distinctions between stories that portray animals the way they really are and those that do not. Differences among students over the correctness of the portrayal of animals or plants in books should lead the students to reference works, which are another source of information that students must start learning to use.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Some animals and plants are alike in the way they look and in the things they do, and others are very different from one another. 5A/P1
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Some animals and plants are alike in the way they look and in the things they do, and others are very different from one another. 5A/P1
  • Plants and animals have features that help them live in different environments. 5A/P2
    In the current version of Benchmarks Online, this benchmark has been deleted because the ideas in it are addressed in benchmark 5F/P1.
  • Stories sometimes give plants and animals attributes they really do not have. 5A/P3
    In the current version of Benchmarks Online, this benchmark has been deleted.

Students should have the opportunity to learn about an increasing variety of living organisms, both the familiar and the exotic, and should become more precise in identifying similarities and differences among them. Although the emphasis can still be on external features, finer detail than before should be included. Hand lenses, introduced earlier, should now be routinely used by students. Microscopes should come into use, not to study cell structure but to begin exploring the world of organisms that cannot be seen by the unaided eye. Fortunately, a wealth of films exist to supplement direct observation.

As students become more familiar with the characteristics of more and more organisms, they should be asked to invent schemes for classifying them—but without using the Linnean classification system. Hopefully, their classification schemes will vary according to the uses made of them as well as according to gross anatomy, behavior patterns, habitats, and other features. The aim is to move students toward the realization that there are many ways to classify things but how good any classification is depends on its usefulness. A scheme is useful if it contributes either to making decisions on some matter or to a deeper understanding of the relatedness of organisms. Classification schemes will, of course, vary with purpose (pets/nonpets; edible/nonedible).

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • A great variety of kinds of living things can be sorted into groups in many ways using various features to decide which things belong to which group. 5A/E1
  • There are millions of different kinds of individual organisms that inhabit the earth at any one time—some very similar to each other, some very different. 5A/E3** (SFAA)
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • A great variety of kinds of living things can be sorted into groups in many ways using various features to decide which things belong to which group. 5A/E1
  • Features used for grouping depend on the purpose of the grouping. 5A/E2
    In the current version of Benchmarks Online, this benchmark has been deleted.

Science in the middle grades should provide students with opportunities to enrich their growing knowledge of the diversity of life on the planet and to begin to connect that knowledge to what they are learning in geography. That is, whenever students study a particular region in the world, they should learn about the plants and animals found there and how they are like or unlike those found elsewhere. Tracing simple food webs in varied environments can contribute to a better understanding of the dependence of organisms (including humans) on their environment.

Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology. That is not done to teach them the standard system but to show them what features biologists typically use in classifying organisms and why. Classification systems are not part of nature. Rather, they are frameworks created by biologists for describing the vast diversity of organisms, suggesting relationships among living things, and framing research questions. A provocative exercise is to have students try to differentiate between familiar organisms that are alike in many ways—for example, between cats and small dogs.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • One of the most general distinctions among organisms is between plants, which use sunlight to make their own food, and animals, which consume energy-rich foods. Some kinds of organisms, many of them microscopic, cannot be neatly classified as either plants or animals. 5A/M1
  • Animals and plants have a great variety of body plans and internal structures that contribute to their being able to make or find food and reproduce. 5A/M2
  • Similarities among organisms are found in internal anatomical features, which can be used to infer the degree of relatedness among organisms. 5A/M3a
  • In classifying organisms, scientists consider details of both internal and external structures. 5A/M3b*
  • Traditionally, a species has been defined as all organisms that can mate with one another to produce fertile offspring. 5A/M4*
  • The cycles continue indefinitely because organisms are decomposed after death to return food materials to the environment. 5A/M5*
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • One of the most general distinctions among organisms is between plants, which use sunlight to make their own food, and animals, which consume energy-rich foods. Some kinds of organisms, many of them microscopic, cannot be neatly classified as either plants or animals. 5A/M1
  • Animals and plants have a great variety of body plans and internal structures that contribute to their being able to make or find food and reproduce. 5A/M2
  • Similarities among organisms are found in internal anatomical features, which can be used to infer the degree of relatedness among organisms. In classifying organisms, biologists consider details of internal and external structures to be more important than behavior or general appearance. 5A/M3
  • For sexually reproducing organisms, a species comprises all organisms that can mate with one another to produce fertile offspring. 5A/M4
  • All organisms, including the human species, are part of and depend on two main interconnected global food webs. One includes microscopic ocean plants, the animals that feed on them, and finally the animals that feed on those animals. The other web includes land plants, the animals that feed on them, and so forth. The cycles continue indefinitely because organisms decompose after death to return food material to the environment. 5A/M5
    In the current version of Benchmarks Online, the first three sentences of this benchmark have been moved to chapter 5, section D and recoded as 5D/M4**

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.

Current Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5A/H1a
  • 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. 5A/H1b
  • 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. 5A/H2*
  • Similar patterns of development and internal anatomy suggest relatedness among organisms. 5A/H3** (SFAA)
  • 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. 5A/H4** (SFAA)
  • 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. 5A/H5** (SFAA)
1993 Version of the Benchmarks Statements

By the end of the 12th grade, 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, and 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. 5A/H1
  • The degree of kinship between organisms or species can be estimated from the similarity of their DNA sequences, which often closely matches their classification based on anatomical similarities. 5A/H2

Building an observational base for heredity ought to be the first undertaking. Explanations can come later. The organisms children recognize are themselves, their classmates, 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.


Teachers should lead students to make observations about how the offspring of familiar animals compare to one another and to their parents. Children know that animals reproduce their own kind—rabbits have rabbits (but you can usually tell one baby rabbit from another), cats have kittens that have different markings (but cats never have puppies), and so forth. This idea should be strengthened by a large number of examples, both plant and animal, that the children can draw on.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • There is variation among individuals of one kind within a population. 5B/P1
  • Offspring are very much, but not exactly, like their parents and like one another. 5B/P2
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • There is variation among individuals of one kind within a population. 5B/P1
  • Offspring are very much, but not exactly, like their parents and like one another. 5B/P2

Students should move from describing individuals directly (she has blue eyes) to naming traits and classifying individuals with respect to those traits (eye color: blue). Students can be encouraged to keep lists of things that animals and plants get from their parents, things that they don't get, and things that the students are not sure about either way. This is also the time to start building the notion of a population whose members are alike in many ways but show some variation.

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Some likenesses between children and parents are inherited. Other likenesses are learned. 5B/E1*
  • For offspring to resemble their parents, there must be a reliable way to transfer information from one generation to the next. 5B/E2
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Some likenesses between children and parents, such as eye color in human beings, or fruit or flower color in plants, are inherited. Other likenesses, such as people's table manners or carpentry skills, are learned. 5B/E1
  • For offspring to resemble their parents, there must be a reliable way to transfer information from one generation to the next. 5B/E2

Now is the time to begin the study of genetic traits—what offspring get from parents. This topic can be handled as a natural part of the study of human reproduction. Students should examine examples of lineages for which breeding has been used to emphasize or suppress certain features of organisms.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • In some kinds of organisms, all the genes come from a single parent. 5B/M1a
  • In organisms that have two sexes, typically half of the genes come from each parent. 5B/M1b*
  • In sexual reproduction, a single specialized cell from a female merges with a specialized cell from a male. 5B/M2a
  • The fertilized egg cell, carrying genetic information from each parent, multiplies to form the complete organism. 5B/M2b*
  • The same genetic information is copied in each cell of the new organism. 5B/M2c
  • New varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits. 5B/M3
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • In some kinds of organisms, all the genes come from a single parent, whereas in organisms that have sexes, typically half of the genes come from each parent. 5B/M1
  • In sexual reproduction, a single specialized cell from a female merges with a specialized cell from a male. As the fertilized egg, carrying genetic information from each parent, multiplies to form the complete organism with about a trillion cells, the same genetic information is copied in each cell. 5B/M2
  • New varieties of cultivated plants and domestic animals have resulted from selective breeding for particular traits. 5B/M3

DNA provides for both the continuity of traits from one generation to the next and the variation that in time can lead to differences within a species and to entirely new species. Understanding DNA makes possible an explanation of such phenomena as the similarities and differences between parents and offspring, hereditary diseases, and the evolution of new species. This understanding also makes it possible for scientists to manipulate genes and thereby create new combinations of traits and new varieties of organisms.

Current Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5B/H1
  • 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. 5B/H2
  • 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. 5B/H3*
  • 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. 5B/H4*
  • 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. 5B/H5
  • 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. 5B/H6a
  • Different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and past history. 5B/H6b
  • 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. 5B/H7** (SFAA)
1993 Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5B/H1
  • The sorting and recombination of genes in sexual reproduction results in a great variety of possible gene combinations from the offspring of any two parents. 5B/H2
  • The information passed from parents to offspring is coded in DNA molecules. 5B/H3
  • Genes are segments of DNA molecules. Inserting, deleting, or substituting DNA segments 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. 5B/H4
  • Gene mutations can be caused by such things as radiation and chemicals. When they occur in sex cells, the mutations 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. 5B/H5
  • 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 instructions are used in different types of cells, influenced by the cell's environment and past history. 5B/H6

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 young students. Large organisms are composed of about a trillion cells, but this number means little to middle-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.


Emphasis should be placed on examining a variety of familiar animals and plants and considering things and processes they all need to stay alive, such as food and getting rid of wastes. Students should use hand lenses to make things appear 3 to 10 times bigger and more detailed and should be encouraged to wonder what they might see with more powerful lenses.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Magnifiers help people see things they could not see without them. 5C/P1
  • Most living things need water, food, and air. 5C/P2
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Magnifiers help people see things they could not see without them. 5C/P1
  • Most living things need water, food, and air. 5C/P2

Students' experiences should expand to include the observation of microscopic organisms, so the scale of magnification should increase to 30- or 100-power (dissection scope or low power on microscopes). Watching microorganisms is always informative, but some events are so rare that prepared materials are a necessity. Students can observe films of living cells growing and dividing, taking in substances, and changing direction when they run into things. Some students may reason that because these tiny cells are alive, they probably have the same needs as other, larger organisms. That can stimulate discussions about how single-celled organisms satisfy their need for food, water, and air.

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Some living things consist of a single cell. Like familiar organisms, they need food, water, and air; a way to dispose of waste; and an environment they can live in. 5C/E1
  • Microscopes make it possible to see that living things are made mostly of cells. 5C/E2a
  • Some organisms are made of a collection of similar cells that benefit from cooperating. Some organisms' cells vary greatly in appearance and perform very different roles in the organism. 5C/E2bc
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Some living things consist of a single cell. Like familiar organisms, they need food, water, and air; a way to dispose of waste; and an environment they can live in. 5C/E1
  • Microscopes make it possible to see that living things are made mostly of cells. Some organisms are made of a collection of similar cells that benefit from cooperating. Some organisms' cells vary greatly in appearance and perform very different roles in the organism. 5C/E2

Once they have some "magnification sense," students can use photomicrographs to extend their observations of cells, gradually concentrating on cells that make up internal body structures. The main interest of youngsters at this level is the human body, so they can begin with as many different kinds of body cells as possible—nerve, bone, muscle, skin—and then move on to examining cells in other animals and plants. This activity can show students that cells are the fundamental building blocks of their own bodies and of other living things as well. Also, once students see that tissue in other animals looks pretty much the same as tissue in humans, two important claims of science will be reinforced: the ubiquity of cells and the unity of nature.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • All living things are composed of cells, from just one to many millions, whose details usually are visible only through a microscope. 5C/M1a
  • Different body tissues and organs are made up of different kinds of cells. 5C/M1b
  • The cells in similar tissues and organs in other animals are similar to those in human beings but differ somewhat from cells found in plants. 5C/M1c
  • Cells repeatedly divide to make more cells for growth and repair. 5C/M2a
  • Various organs and tissues function to serve the needs of all cells for food, air, and waste removal. 5C/M2b
  • Within cells, many of the basic functions of organisms—such as extracting energy from food and getting rid of waste—are carried out. 5C/M3a
  • The way in which cells function is similar in all living organisms. 5C/M3b
  • About two thirds of the weight of cells is accounted for by water, which gives cells many of their properties. 5C/M4
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • All living things are composed of cells, from just one to many millions, whose details usually are visible only through a microscope. Different body tissues and organs are made up of different kinds of cells. The cells in similar tissues and organs in other animals are similar to those in human beings but differ somewhat from cells found in plants. 5C/M1
  • Cells continually divide to make more cells for growth and repair. Various organs and tissues function to serve the needs of cells for food, air, and waste removal. 5C/M2
  • Within cells, many of the basic functions of organisms—such as extracting energy from food and getting rid of waste—are carried out. The way in which cells function is similar in all living organisms. 5C/M3
  • About two thirds of the weight of cells is accounted for by water, which gives cells many of their properties. 5C/M4

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 science. 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, or which is which.

Current Version of the Benchmarks Statements

By the end of the 12th grade, students should know that

  • Every cell is covered by a membrane that controls what can enter and leave the cell. 5C/H1a
  • In all but quite primitive cells, a complex network of proteins provides organization and shape and, for animal cells, movement. 5C/H1b
  • Within the cells are specialized parts for the transport of materials, energy capture and release, protein building, waste disposal, passing information, and even movement. 5C/H2a
  • In addition to the basic cellular functions common to all cells, most cells in multicellular organisms perform some special functions that others do not. 5C/H2b
  • 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. 5C/H3
  • The genetic information encoded in DNA molecules provides instructions for assembling protein molecules. 5C/H4a
  • The genetic information encoded in DNA molecules is virtually the same for all life forms. 5C/H4b
  • Before a cell divides, the instructions are duplicated so that each of the two new cells gets all the necessary information for carrying on. 5C/H4c
  • 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. 5C/H5
  • 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. 5C/H6
  • 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. 5C/H7
  • 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. 5C/H8
  • Some protein molecules assist in replicating genetic information, repairing cell structures, helping other molecules get in or out of the cell, and generally catalyzing and regulating molecular interactions. 5C/H9** (SFAA)
1993 Version of the Benchmarks Statements

By the end of the 12th grade, students should know that

  • Every cell is covered by a 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. 5C/H1
  • Within every cell are specialized parts for the transport of materials, energy transfer, protein building, waste disposal, information feedback, and even movement. In addition, most cells in multicellular organisms perform some special functions that others do not. 5C/H2
  • 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 the shape the chain takes is a consequence of attractions between the chain's parts. 5C/H3
  • The genetic information in DNA molecules provides instructions for assembling protein molecules. The code used 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. 5C/H4
  • 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. 5C/H5
  • Gene mutation in a cell can result in uncontrolled cell division, called cancer. Exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer. 5C/H6
  • 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. Both single cells and multicellular organisms have molecules that help to keep the cell's acidity within a narrow range. 5C/H7
  • A living cell is composed of a small number of chemical elements mainly carbon, hydrogen, nitrogen, oxygen, phosphorous, and sulfur. Carbon atoms can easily bond to several other carbon atoms in chains and rings to form large and complex molecules. 5C/H8

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.


Students should investigate the habitats of many different kinds of local plants and animals, including weeds, aquatic plants, insects, worms, and amphibians, and some of the ways in which animals depend on plants and on each other.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Animals eat plants or other animals for food and may also use plants (or even other animals) for shelter and nesting. 5D/P1
  • Living things are found almost everywhere in the world. There are somewhat different kinds in different places. 5D/P2
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Animals eat plants or other animals for food and may also use plants (or even other animals) for shelter and nesting. 5D/P1
  • Living things are found almost everywhere in the world. There are somewhat different kinds in different places. 5D/P2

Students should explore how various organisms satisfy their needs in the environments in which they are typically found. They can examine the survival needs of different organisms and consider how the conditions in particular habitats can limit what kinds of living things can survive. Their studies of interactions among organisms within an environment should start with relationships they can directly observe. By viewing nature films, students should see a great diversity of life in different habitats.

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • For any particular environment, some kinds of plants and animals thrive, some do not live as well, and some do not survive at all. 5D/E1*
  • Insects and various other organisms depend on dead plant and animal material for food. 5D/E2
  • Organisms interact with one another in various ways besides providing food. 5D/E3a
  • Many plants depend on animals for carrying their pollen to other plants or for dispersing their seeds. 5D/E3b
  • Changes in an organism's habitat are sometimes beneficial to it and sometimes harmful. 5D/E4
  • Most microorganisms do not cause disease, and many are beneficial. 5D/E5
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • For any particular environment, some kinds of plants and animals survive well, some survive less well, and some cannot survive at all. 5D/E1
  • Insects and various other organisms depend on dead plant and animal material for food. 5D/E2
  • Organisms interact with one another in various ways besides providing food. Many plants depend on animals for carrying their pollen to other plants or for dispersing their seeds. 5D/E3
  • Changes in an organism's habitat are sometimes beneficial to it and sometimes harmful. 5D/E4
  • Most microorganisms do not cause disease, and many are beneficial. 5D/E5

As students build up a collection of cases based on their own studies of organisms, readings, and film presentations, they should be guided from specific examples of the interdependency of organisms to a more systematic view of the kinds of interactions that take place among organisms. But a necessary part of understanding complex relationships is to know what a fair proportion of the possibilities are. The full-blown concept of ecosystem (and that term) can best be left until students have many of the pieces ready to put in place. Prior knowledge of the relationships between organisms and the environment should be integrated with students' growing knowledge of the earth sciences.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • In all environments, organisms with similar needs may compete with one another for limited resources, including food, space, water, air, and shelter. 5D/M1a*
  • The world contains a wide diversity of physical conditions, which creates a wide variety of environments: freshwater, marine, forest, desert, grassland, mountain, and others. In any particular environment, the growth and survival of organisms depend on the physical conditions. 5D/M1b*
  • Interactions between organisms may be for nourishment, reproduction, or protection and may benefit one of the organisms or both of them. Some species have become so dependent on each other that neither could survive without the other. 5D/M2*
  • One organism may scavenge or decompose another. 5D/M2b
  • Given adequate resources and an absence of disease or predators, populations of organisms in ecosystems increase at rapid rates. Finite resources and other factors limit their growth. 5D/M3** (NSES)
  • All organisms, both land-based and aquatic, are interconnected by their need for food. This network of interconnections is referred to as a food web. The entire earth can be considered a single global food web, and food webs can also be described for a particular environment. At the base of any food web are organisms that make their own food, followed by the animals that eat them, then the animals that eat those animals, and so forth. 5D/M4** (BSL)
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • In all environments—freshwater, marine, forest, desert, grassland, mountain, and others—organisms with similar needs may compete with one another for resources, including food, space, water, air, and shelter. In any particular environment, the growth and survival of organisms depend on the physical conditions. 5D/M1
  • Two types of organisms may interact with one another in several ways: They may be in a producer/consumer, predator/prey, or parasite/host relationship. Or one organism may scavenge or decompose another. Relationships may be competitive or mutually beneficial. Some species have become so adapted to each other that neither could survive without the other. 5D/M2

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.

Current Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5D/H1*
  • 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. 5D/H2*
  • Human beings are part of the earth's ecosystems. Human activities can, deliberately or inadvertently, alter the equilibrium in ecosystems. 5D/H3
1993 Version of the Benchmarks Statements

By the end of the 12th grade, students should know that

  • Ecosystems can be reasonably stable over hundreds or thousands of years. As any population of organisms grows, it is held in check by one or more environmental factors: depletion of food or nesting sites, increased loss to increased numbers of predators, or parasites. If a disaster such as flood or fire occurs, the damaged ecosystem is likely to recover in stages that eventually result in a system similar to the original one. 5D/H1
  • Like many complex systems, ecosystems tend to have cyclic fluctuations around a state of rough equilibrium. In the long run, however, ecosystems always change when climate changes or when one or more new species appear as a result of migration or local evolution. 5D/H2
  • Human beings are part of the earth's ecosystems. Human activities can, deliberately or inadvertently, alter the equilibrium in ecosystems. 5D/H3

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.


Children should begin to be aware of the basic parts of the food chain: Plants need sunlight to grow, some animals eat plants, and other animals eat both plants and animals. The key step that plants make their own food is very difficult for elementary students and should be saved for middle school.

An awareness of recycling, both in nature and in human societies, may play a helpful role in the development of children's thinking. Familiarity with the recycling of materials fosters the notion that matter continues to exist even though it changes from one form to another.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Plants and animals both need to take in water, and animals need to take in food. In addition, plants need light. 5E/P1
  • Many materials can be recycled and used again, sometimes in different forms. 5E/P2
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Plants and animals both need to take in water, and animals need to take in food. In addition, plants need light. 5E/P1
  • Many materials can be recycled and used again, sometimes in different forms. 5E/P2

Students should begin to notice that substances may change form and move from place to place, but they never appear out of nowhere and never just disappear. Questions should encourage students to consider where substances come from and where they go and to be puzzled when they cannot account for the origin or the fate of a substance.

It's all right to start students on chains of what eats what in various environments, but labeling the steps in the chain as energy transfer is not necessary. Transfers of energy at this level are better illustrated in physical systems; biological energy transfer is far too complicated.

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Almost all kinds of animals' food can be traced back to plants. 5E/E1
  • Some source of "fuel" is needed for all organisms to stay alive and grow. 5E/E2*
  • Over the whole earth, organisms are growing, dying, decaying, and new organisms are being produced by the old ones. 5E/E3
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Almost all kinds of animals' food can be traced back to plants. 5E/E1
  • Some source of "energy" is needed for all organisms to stay alive and grow. 5E/E2
  • Over the whole earth, organisms are growing, dying, and decaying, and new organisms are being produced by the old ones. 5E/E3

In the middle grades, the emphasis is on following matter through ecosystems. Students should trace food webs both on land and in the sea. The food webs that students investigate should first be local ones they can study directly. The use of films of food webs in other ecosystems can supplement their direct investigations but should not substitute for them. Most students see food webs and cycles as involving the creation and destruction of matter, rather than the breakdown and reassembly of invisible units. They see various organisms and materials as consisting of different types of matter that are not convertible into one another. Before they have an understanding of atoms, the notion of reusable building blocks common to plants and animals is quite mysterious. So following matter through ecosystems needs to be linked to their study of atoms.

Students' attention should be drawn to the transfer of energy that occurs as one organism eats another. It is important that students learn the differences between how plants and animals obtain food and from it the energy they need. The first stumbling block is food, which represents one of those instances in which differences between the common use of a term and the technical one cause persistent confusion. In popular language, food is whatever nutrients plants and animals must take in if they are to grow and survive (solutions of minerals that plants need traces of frequently bear the label "plant food"); in scientific usage, food refers only to those substances, such as carbohydrates, proteins, and fats, from which organisms derive the energy they need to grow and operate and the material of which they are made. It's important to emphasize that the sugars that plants make out of water and carbon dioxide are their only source of food. Water and minerals dissolved in it are not sources of energy for plants or for animals.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • Food provides molecules that serve as fuel and building material for all organisms. 5E/M1a
  • Plants use the energy from light to make sugars from carbon dioxide and water. 5E/M1b
  • Plants can use the food they make immediately or store it for later use. 5E/M1c
  • Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. Then they are consumed by other organisms. 5E/M1de
  • Over a long time, matter is transferred from one organism to another repeatedly and between organisms and their physical environment. As in all material systems, the total amount of matter remains constant, even though its form and location change. 5E/M2
  • Energy can change from one form to another in living things. 5E/M3a
  • Organisms get energy from oxidizing their food, releasing some of its energy as thermal energy. 5E/M3b*
  • Almost all food energy comes originally from sunlight. 5E/M3c
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • Food provides molecules that serve as fuel and building material for all organisms. Plants use the energy in light to make sugars out of carbon dioxide and water. This food can be used immediately for fuel or materials or it may be stored for later use. Organisms that eat plants break down the plant structures to produce the materials and energy they need to survive. Then they are consumed by other organisms. 5E/M1
  • Over a long time, matter is transferred from one organism to another repeatedly and between organisms and their physical environment. As in all material systems, the total amount of matter remains constant, even though its form and location change. 5E/M2
  • Energy can change from one form to another in living things. Animals get energy from oxidizing their food, releasing some of its energy as heat. Almost all food energy comes originally from sunlight. 5E/M3

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 fossil fuels and the recycling of matter and energy are important enough to pay considerable attention to in high school.

Current Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5E/H1*
  • 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. 5E/H3
1993 Version of the Benchmarks Statements

By the end of the 12th grade, students should know that

  • At times, environmental conditions are such that plants and marine organisms grow faster than decomposers can recycle them back to the environment. Layers of energy-rich organic material have been gradually turned into great coal beds and oil pools by the pressure of the overlying earth. By burning these fossil fuels, people are passing most of the stored energy back into the environment as heat and releasing large amounts of carbon dioxide. 5E/H1
    In the current version of Benchmarks Online, the last sentence of this benchmark has been moved to grades 6-8 in chapter 8, section C, and recoded as 8C/M11**.
  • The amount of life any environment can support is limited by the available energy, water, oxygen, and minerals, and by the ability of ecosystems to recycle the residue of dead organic materials. Human activities and technology can change the flow and reduce the fertility of the land. 5E/H2
    In the current version of Benchmarks Online, this benchmark has been deleted because the ideas in it are addressed in benchmark 5D/M3** and 4C/M7.
  • 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 as heat. Continual input of energy from sunlight keeps the process going. 5E/H3

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 that are well substantiated and generally accepted as fact by scientists, and natural selection, the proposed mechanism for these changes. Students should first be familiar with the evidence 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, and of how fossils form and how their ages are determined. Students may very well wonder why the fossil record has so many seeming holes in it. If so, the opportunity should be seized to show the value of mathematics. The probability of specimens of any species of organisms surviving is small—soft body parts are eaten or decomposed, and hard parts are crushed or dissolved. The probability of finding a specimen is small because most are buried or otherwise inexcavable. Mathematics holds that the probability of acquiring a specimen of an extinct species is extremely small—the product of the two probabilities.

Before natural selection is proposed as a mechanism for evolution, students must recognize the diversity and apparent relatedness of species. Students take years to acquire sufficient knowledge of living organisms and the fossil record. Natural selection should be offered as an explanation for familiar phenomena and then revisited as new phenomena are explored. To appreciate how natural selection can account for evolution, students have to understand the important distinction between the selection of an individual with a certain trait and the changing proportions of that trait in populations. Their being able to grasp this distinction requires some understanding of the mathematics of proportions and opportunities for them to reflect on the individual-versus-population distinction in other contexts.

Controversy is an important aspect of the scientific process. Students should realize that although virtually all scientists 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 detailed mechanism for which has not yet emerged.


Students should begin to build a knowledge base about biological diversity. Student curiosity about fossils and dinosaurs can be harnessed to consider life forms that no longer exist. But the distinction between extinct creatures and those that still live elsewhere will not be clear for some time. "Long ago" has very limited meaning at this age level. Even as students make observations of organisms in their own environments, they can extend their experiences with other environments through film.

Current Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Different plants and animals have external features that help them thrive in different kinds of places. 5F/P1
  • Some kinds of organisms that once lived on Earth have completely disappeared, although they were something like others that are alive today. 5F/P2
1993 Version of the Benchmarks Statements

By the end of the 2nd grade, students should know that

  • Different plants and animals have external features that help them thrive in different kinds of places. 5F/P1
  • Some kinds of organisms that once lived on earth have completely disappeared, although they were something like others that are alive today. 5F/P2

Students can begin to look for ways in which organisms in one habitat differ from those in another and consider how some of those differences are helpful to survival. The focus should be on the consequences of different features of organisms for their survival and reproduction. The study of fossils that preserve plant and animal structures is one approach to looking at characteristics of organisms. Evidence for the similarity within diversity of existing organisms can draw upon students' expanding knowledge of anatomical similarities and differences.

Current Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Individuals of the same kind differ in their characteristics, and sometimes the differences give individuals an advantage in surviving and reproducing. 5F/E1
  • Fossils can be compared to one another and to living organisms according to their similarities and differences. Some organisms that lived long ago are similar to existing organisms, but some are quite different. 5F/E2
1993 Version of the Benchmarks Statements

By the end of the 5th grade, students should know that

  • Individuals of the same kind differ in their characteristics, and sometimes the differences give individuals an advantage in surviving and reproducing. 5F/E1
  • Fossils can be compared to one another and to living organisms according to their similarities and differences. Some organisms that lived long ago are similar to existing organisms, but some are quite different. 5F/E2

During middle school, several lines of evidence are further developed. The fossil evidence can be expanded beyond extinctions and survivals to the notion of evolutionary history. Sedimentation of rock can be brought in to show relative age. However, actual age, which requires an understanding of isotopic dating techniques, should wait until high school, when students learn about the structure of atoms. Breeding experiments can illustrate the heritability of traits and the effects of selection. It was familiarity with selective breeding that stimulated Darwin's thinking that differences between successive generations can naturally accumulate.

Current Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • Small differences between parents and offspring can accumulate (through selective breeding) in successive generations so that descendants are very different from their ancestors. 5F/M1
  • Individual organisms with certain traits are more likely than others to survive and have offspring. 5F/M2a
  • Changes in environmental conditions can affect the survival of individual organisms and entire species. 5F/M2b
  • Many thousands of layers of sedimentary rock provide evidence for the long history of the earth and for the long history of changing life forms whose remains are found in the rocks. 5F/M3a
  • More recently deposited rock layers are more likely to contain fossils resembling existing species. 5F/M3b
  • Most species that have lived on the earth are now extinct. Extinction of species occurs when the environment changes and the individual organisms of that species do not have the traits necessary to survive and reproduce in the changed environment. 5F/M4** (NSES)
  • Reproduction is necessary for the survival of any species. 5F/M5*
1993 Version of the Benchmarks Statements

By the end of the 8th grade, students should know that

  • Small differences between parents and offspring can accumulate (through selective breeding) in successive generations so that descendants are very different from their ancestors. 5F/M1
  • Individual organisms with certain traits are more likely than others to survive and have offspring. Changes in environmental conditions can affect the survival of individual organisms and entire species. 5F/M2
  • Many thousands of layers of sedimentary rock provide evidence for the long history of the earth and for the long history of changing life forms whose remains are found in the rocks. More recently deposited rock layers are more likely to contain fossils resembling existing species. 5F/M3

Knowing what evolutionary change is and how it played out over geological time, students can now turn to its mechanism. They need to shift from thinking in terms of selection of individuals with a trait to changing proportions of a trait in populations. Familiarity with artificial selection, coming from studies of pedigrees and their own experiments, can be applied to natural systems, in which selection occurs because of environmental conditions. Students' understanding of radioactivity makes it possible for them to comprehend isotopic dating techniques used to determine the actual age of fossils and hence to appreciate that sufficient time may have elapsed for successive changes to have accumulated. Knowledge of DNA contributes to the evidence for life having evolved from common ancestors and provides a plausible mechanism for the origin of new traits.

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. Schools 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 choose not to believe the scientific story, they should be well informed about what the story is.

Current Version of the Benchmarks Statements

By the end of the 12th grade, 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. 5F/H1*
  • Molecular evidence substantiates the anatomical evidence for evolution and provides additional detail about the sequence in which various lines of descent branched off from one another. 5F/H2
  • 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. 5F/H3*
  • Heritable characteristics can be observed at molecular and whole-organism levels—in structure, chemistry, or behavior. 5F/H4a
  • Heritable characteristics influence how likely an organism is to survive and reproduce. 5F/H4b
  • 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. 5F/H5
  • Natural selection leads to organisms that are well-suited for survival in particular environments. 5F/H6a
  • Chance alone can result in the persistence of some heritable characteristics having no survival or reproductive advantage or disadvantage for the organism. 5F/H6b
  • When an environment, including other organisms that inhabit it changes, the survival value of inherited characteristics may change. 5F/H6c
  • 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. 5F/H7*
  • Life on earth is thought to have begun as simple, one-celled organisms about four billion years ago. Once cells with nuclei developed about a billion years ago, increasingly complex multi-cellular organisms evolved. 5F/H8
  • 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. 5F/H9
  • 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. 5F/H10** (SFAA)
1993 Version of the Benchmarks Statements

By the end of the 12th grade, students should know that

  • The basic idea of biological evolution is that the earth's present-day species developed from earlier, distinctly different species. 5F/H1
  • Molecular evidence substantiates the anatomical evidence for evolution and provides additional detail about the sequence in which various lines of descent branched off from one another. 5F/H2
  • 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. 5F/H3
  • Heritable characteristics can be observed at molecular and whole-organism levels—in structure, chemistry, or behavior. These 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. 5F/H4
  • 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. 5F/H5
  • 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 changes, the survival value of some inherited characteristics may change. 5F/H6
  • The theory of natural selection provides 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. 5F/H7
  • Life on earth is thought to have begun as simple, one-celled organisms about 4 billion years ago. During the first 2 billion years, only single-cell microorganisms existed, but once cells with nuclei developed about a billion years ago, increasingly complex multicellular organisms evolved. 5F/H8
  • 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 changes appear 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. 5F/H9

VERSION EXPLANATION

During the development of Atlas of Science Literacy, Volume 2, Project 2061 revised the wording of some benchmarks in order to update the science, improve the logical progression of ideas, and reflect the current research on student learning. New benchmarks were also created as necessary to accommodate related ideas in other learning goals documents such as Science for All Americans (SFAA), the National Science Education Standards (NSES), and the essays or other elements in Benchmarks for Science Literacy (BSL). We are providing access to both the current and the 1993 versions of the benchmarks as a service to our end-users.

The text of each learning goal is followed by its code, consisting of the chapter, section, grade range, and the number of the goal. Lowercase letters at the end of the code indicate which part of the 1993 version it comes from (e.g., “a” indicates the first sentence in the 1993 version, “b” indicates the second sentence, and so on). A single asterisk at the end of the code means that the learning goal has been edited from the original, whereas two asterisks mean that the idea is a new learning goal.

Copyright © 1993,2009 by American Association for the Advancement of Science