Origin of Life Module
Current evidence from the rock and fossil record indicates that life on Earth began about 3.8 billion years ago. Yet how life first formed, or even how the biochemical precursors of life developed, and under what conditions these events happened, are not yet understood. The origin of life is an area of active research, with considerable debate among scientists from various disciplines. Better understood are the fundamental characteristics of life, including basic structures and functions; the approximate timing of key events, such as the buildup of oxygen in the atmosphere and the appearance of eukaryotic cells; and something of the history of the relationships among the three major groups of extant organisms: archaea, bacteria, and eukaryotes. The Origin of Life module combines what is known about life with the research and debate about life's beginnings and early history.
The first lesson, Introduction, assesses students' understanding of life, its processes, and the interrelatedness of life via a concept map.
In the second lesson, What is Life?, students begin by considering the characteristics of all life, and then examine its basic chemistry, functions, and structure. These explorations lead into a series of activities that focus on the fundamental life processes of information storage and its translation. Students examine the building blocks of proteins, carbohydrates, fat, and DNA, and simulate the translation of DNA into a protein.
The evidence for the early evolution of life is the focus of the third lesson, History of Life on Earth. In addition to examining the fossil and rock records, students also explore the molecular evidence that can be found in modern day organisms. By comparing DNA and RNA, scientists have inferred relationships between current organisms and postulated a common, prokaryotic-like ancestor. Students examine the aspects of the physical environment under which life began. This lesson focuses on conveying not only what scientists know, but also how they know what they know. In the concluding activity students construct a timeline that highlights the fact that most of life's history on Earth has been in the form of single-celled organisms.
The fourth lesson, Life Gets Started, poses the fundamental question: How did life begin? Students explore some of the prevailing scientific ideas and the supporting evidence for them through readings and videotaped interviews of scientific experts. A computer database activity helps students research the question: Could Earth-like life be sustained on other solar system bodies and if so, what would that life form require? Students then gain experience with the diversity of single-celled organisms through Winogradsky columns and microscope images.
In Life Keeps Evolving, the fifth lesson, students explore the evolution and diversification of eukaryotic cells. Students study the Theory of Endosymbiosis as a possible explanation for the evolution of cells with nuclei and other organelles. Then students explore the inner workings of the cell, its structures and functions. Students further compare single-celled, colonial, and multicelled organisms, and consider the adaptive advantages and disadvantages of multicellularity. The lesson ends with an introduction to a cell's life cycle (mitosis) and sexual reproduction (meiosis).
The final Closing lesson provides two assessments of students' achievement of the learning objectives for the module: a pencil and paper test and another concept map.
This educational program is exceptional. The introduction of the first module, The Origin of Life set a pace of instruction that no biology textbook to date has done. The use of animation and short videos to present the instructional material captured the attention of the students. In todays age, they are fascinated by computer technology. The sheer fact that science can utilize this mode for a smooth course of learning and, hopefully, wetting the appetite for a future career in the sciences is phenomenal.
- Marie Flynn, Martin Luther King HS, Philadelphia, PA
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