Science and Technology/Engineering
Strand 2 : Life Science (Biology)
The life sciences investigate the diversity, complexity, and interconnectedness of life on earth. Students are naturally drawn to examine living things, and as they progress through the grade levels, they become capable of understanding the theories and models that scientists use to explain observations of nature. In this respect, a PreK-12 life science curriculum mirrors the way in which the science of biology has evolved from observation to classification to theory. By high school, students learn the importance of Darwin's theory of evolution as a framework for explaining continuity, diversity, and change over time. Students emerge from an education in the life sciences recognizing that order in natural systems arises in accord with rules that seem to govern the physical world, and can be modeled and predicted through the use of mathematics.
As Piaget noted, young children tend to describe anything that moves as alive. For purposes of working with young children, who do not yet understand the continuity of life (e.g., from seed to seedling to tree to log), living can be defined as anything that is alive or has ever been alive (e.g., muskrat, flower, roadkill, log) and nonliving can be defined as anything that is not now and has never been alive (e.g., rock, mountain, glass, wristwatch). Over time, students refine their intuitive understanding. They begin to include in their definition of living such behaviors as eating, growing, and reproducing. Young children learn to use their senses to observe and then describe the natural world. Noticing differences and similarities and grouping organisms based on some common features is fundamental to the life science curriculum at this grade span. For a more in-depth discussion of this issue, please refer to the National Science Education Standards under Content Standard C: Developing Student Understanding.
As children move through the elementary grades, they expand the range of observations they make of the living world. In particular, children record details of the life cycles of plants and animals, and explore how organisms are adapted to their habitat. In these grades, children move beyond using their senses to gather information. They begin to use measuring devices to gather quantitative data that they record, examine, interpret, and communicate. Children are introduced to the power of empirical evidence as they design ways of exploring questions that arise from their observations. Learning standards in PrePreK-2 fall under the topics of Characteristics of Living Things, Life Cycles, Evolution and Biodiversity, Heredity, and Living Things and Their Environment. The standards for grades 3-5 fall under the topics of Characteristics of Plants and Animals, Plant Structures and Functions, Life Cycles, Heredity, Adaptations of Living Things, and Energy and Living Things.
As students enter the middle school grades, the emphasis changes from observation and description of individual organisms to the development of a more connected view of biological systems. Middle school students begin to study biology at the microscopic level without delving into the biochemistry of cells. They learn that organisms are composed of cells and that some organisms are unicellular and must therefore carry out all of the necessary processes for life within that single cell. Other organisms, including human beings, are multicellular, with cells working together. Students should observe that cells of multicellular organisms can be physically very different from each other and relate that fact to the specific role that each cell has in the organisms (specialization). For example, cells of the eye or the skin or the tongue look different and do different things. Middle school students develop the understanding that the human body has organs, each of which has a specific function of its own, and that these organs together create systems that interact with each other to maintain life. As is outlined in the National Science Education Standards, students should be exposed in a general way to the systems of the human body, but are not expected to develop a detailed understanding at this grade level. Middle school students also examine the hierarchical organization of multicellular organisms and the roles and relationships that organisms occupy in an ecosystem.
At the macroscopic level, students focus on the interactions that occur within ecosystems. They explore the interdependence of living things, specifically the dependence of life on photosynthetic organisms such as plants, which in turn depend upon the sun as their source of energy. Students use mathematics to calculate rates of growth, derive averages and ranges, and represent data graphically to describe and interpret ecological concepts. The standards for grades 6-8 fall under the topics of Classification of Organisms, Structure and Function of Cells, Systems in Living Things, Reproduction and Heredity, Evolution and Biodiversity, Living Things and Their Environment, Energy and Living Things, and Changes in Ecosystems Over Time.
At the high school level, students study the molecular basis of life by looking at the processes occurring in cells. In particular, these students learn that the DNA molecule dictates all of our physical traits and that we inherit our parents' DNA and therefore their physical traits. They learn that genetic variation is inherited and that the unit of inheritance is the gene. It is the inherited traits that provide the variation on which natural and manipulated selection act. It is changes in the DNA over time (mutations) that lead to diversity and the appearance of new traits that can give an organism a selective advantage, allowing it to become more competitive in a given environment, survive better, or adapt to changes in the environment (basis of natural selection).
The theory of organic evolution is fundamental to understanding modern biology. It provides a framework for explaining why there are so many different kinds of organisms on earth; why organisms of distantly related species share biochemical, anatomical, and functional characteristics; why species become extinct; and how different kinds of organisms are related to one another.