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Cells within cells: An extraordinary claim with extraordinary evidence


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This Science in Action article on endosymbiosis explores the career of microbiologist, Lynn Margulis and how an unlikely idea overcame strong resistance within the scientific community and finally came to be an accepted part of evolutionary theory.



Life Science, Nature and Process of Science

One period

Teaching tips:
Science textbooks are full of content that represents our current understanding of the natural world and how it works. But where did that content come from? This Science in Action story about endosymbiosis provides an excellent opportunity to reinforce the scientific enterprise and how knowledge is built even in the face of strong initial resistance within the scientific community. Use the story to make the following aspects of the nature of science explicit to your students: - Science can test hypotheses about events that happened long ago. - Scientific ideas are tested with multiple lines of evidence. - Scientific ideas evolve with new evidence; however, well supported scientific ideas are not tenuous. - Through a system of checks and balances, the process of science can overcome individual biases. - Evidence is the most important arbiter of which scientific ideas are accepted. Encourage students to use the How Science Works Flowchart to map to follow the efforts of Lynn Margulis as she sought to evaluate the scientific evidence.

Correspondence to the Next Generation Science Standards is indicated in parentheses after each relevant concept. See our conceptual framework for details.

  • What is science?

  • Science is both a body of knowledge and the process for building that knowledge. (NOS5)

  • Science aims to build explanations of the natural world. (P3, P6)

  • Science focuses on natural phenomena and processes.

  • Science works only with testable ideas. (P2, P3, NOS2)

  • Scientists strive to test their ideas with evidence from the natural world; a hallmark of science is exposing ideas to testing. (P3, P4, P6, P7, NOS2)

  • Scientific knowledge is open to question and revision as new ideas surface and new evidence is discovered. (P4, P6, NOS3)

  • Scientific ideas cannot be absolutely proven.

  • Because it has been tested, scientific knowledge is reliable. (NOS3)

  • Science is ongoing; answering one scientific question frequently leads to additional questions to be investigated. (P1)

  • How science works

  • The real process of science is complex, iterative, and can take many different paths.

  • The process of science involves observation, exploration, testing, communication, and application.

  • Scientific observations can be made directly with our own senses or may be made indirectly through the use of tools.

  • Scientists test their ideas (hypotheses and theories) by figuring out what expectations are generated by an idea and making observations to find out whether those expectations are borne out. (P4, P6)

  • Scientists can test ideas about events and processes long past, very distant, and not directly observable.

  • Scientists test their ideas using multiple lines of evidence. (P6, NOS2)

  • Scientists often try to generate multiple explanations for what they observe. (P7)

  • Scientists try to be objective and work to identify and avoid bias.

  • Different scientists may interpret the same data in different ways. (P7)

  • Researchers share their findings with the scientific community through scientific publications. (P8)

  • Hypotheses are proposed explanations for a narrow set of phenomena. (P6)

  • Hypotheses are usually inspired and informed by previous research and/or observations. They are not guesses. (P6)

  • Science depends on communication within the scientific community. (P7, P8)

  • Scientists scrutinize each other's work through peer review and other processes. (P7, NOS5)

  • Through a system of checks and balances (which includes peer review), the scientific community helps ensure science's accuracy and helps detect bias, fraud, and misconduct. (P7, NOS5)

  • Science relies on the accumulated knowledge of the scientific community to move forward. (NOS5)

  • The scientific community is global and diverse. (NOS7)

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