• [What is science?: Grades 9-12] Science is both a body of knowledge and the process for building that knowledge. (NOS5)
• [What is science?: Grades 9-12] Science aims to build explanations of the natural world. (P3, P6)
• [What is science?: Grades 9-12] Science focuses on natural phenomena and processes.
• [What is science?: Grades 9-12] Science works only with testable ideas. (P2, P3, NOS2)
• [What is science?: Grades 9-12] 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)
• [What is science?: Grades 9-12] Scientific knowledge is open to question and revision as new ideas surface and new evidence is discovered. (P4, P6, NOS3)
• [What is science?: Grades 9-12] Scientific ideas cannot be absolutely proven.
• [What is science?: Grades 9-12] Because it has been tested, scientific knowledge is reliable. (NOS3)
• [What is science?: Grades 9-12] Science is ongoing; answering one scientific question frequently leads to additional questions to be investigated. (P1)
• [What is science?: Grades 13-16] Science is both a body of knowledge and the process for building that knowledge.
• [What is science?: Grades 13-16] Science aims to build increasingly broad and coherent explanations of the natural world.
• [What is science?: Grades 13-16] Science focuses on natural phenomena and processes.
• [What is science?: Grades 13-16] Science works only with testable ideas.
• [What is science?: Grades 13-16] Scientists strive to test their ideas with evidence from the natural world; a hallmark of science is exposing ideas to testing.
• [What is science?: Grades 13-16] Scientific knowledge is open to question and revision as new ideas surface and new evidence is discovered.
• [What is science?: Grades 13-16] Scientific ideas cannot be absolutely proven.
• [What is science?: Grades 13-16] Because it has been tested, scientific knowledge is reliable.
• [What is science?: Grades 13-16] Science is ongoing; answering one scientific question frequently leads to additional questions to be investigated.
• [How science works: Grades 13-16] The real process of science is complex, iterative, and can take many different paths.
• [How science works: Grades 9-12] The real process of science is complex, iterative, and can take many different paths.
• [How science works: Grades 9-12] The process of science involves observation, exploration, testing, communication, and application.
• [How science works: Grades 9-12] Scientific observations can be made directly with our own senses or may be made indirectly through the use of tools.
• [How science works: Grades 9-12] 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)
• [How science works: Grades 9-12] Scientists can test ideas about events and processes long past, very distant, and not directly observable.
• [How science works: Grades 9-12] Scientists test their ideas using multiple lines of evidence. (P6, NOS2)
• [How science works: Grades 9-12] Scientists try to be objective and work to identify and avoid bias.
• [How science works: Grades 9-12] Different scientists may interpret the same data in different ways. (P7)
• [How science works: Grades 9-12] Researchers share their findings with the scientific community through scientific publications. (P8)
• [How science works: Grades 13-16] The process of science involves observation, exploration, testing, communication, and application.
• [How science works: Grades 13-16] Scientific observations can be made directly with our own senses or may be made indirectly through the use of tools.
• [How science works: Grades 13-16] 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.
• [How science works: Grades 13-16] Scientists can test ideas about events and processes long past, very distant, and not directly observable.
• [How science works: Grades 13-16] Scientists test their ideas using multiple lines of evidence.
• [How science works: Grades 13-16] Scientists often try to generate multiple explanations for what they observe.
• [How science works: Grades 13-16] Scientists try to be objective and work to identify and avoid bias.
• [How science works: Grades 13-16] Different scientists may interpret the same data in different ways; data interpretation can be influenced by a scientist's assumptions, biases, and background.
• [How science works: Grades 13-16] Researchers share their findings with the scientific community through scientific publications.
• [Hypotheses and theories: Grades 9-12] Hypotheses are proposed explanations for a narrow set of phenomena. (P6)
• [Hypotheses and theories: Grades 9-12] Hypotheses are usually inspired and informed by previous research and/or observations. They are not guesses. (P6)
• [Hypotheses and theories: Grades 13-16] Hypotheses are proposed explanations for a narrow set of phenomena.
• [Hypotheses and theories: Grades 13-16] Hypotheses are usually inspired and informed by previous research and/or observations. They are not guesses.
• [The social side of science: Grades 9-12] Science depends on communication within the scientific community. (P7, P8)
• [The social side of science: Grades 9-12] Scientists scrutinize each other's work through peer review and other processes. (P7, NOS5)
• [The social side of science: Grades 9-12] 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)
• [The social side of science: Grades 9-12] Science relies on the accumulated knowledge of the scientific community to move forward. (NOS5)
• [The social side of science: Grades 9-12] The scientific community is global and diverse. (NOS7)
• [The social side of science: Grades 13-16] Science depends on communication within the scientific community.
• [The social side of science: Grades 13-16] Scientists scrutinize each other's work through peer review and other processes.
• [The social side of science: Grades 13-16] 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.
• [The social side of science: Grades 13-16] The scientific community motivates researchers in their investigations by providing recognition and, sometimes, a sense of competition.
• [The social side of science: Grades 13-16] Science relies on the accumulated knowledge of the scientific community to move forward.
• [The social side of science: Grades 13-16] The scientific community is global and diverse.

• NOS Matrix understanding category 2. Scientific knowledge is based on empirical evidence.
• NOS Matrix understanding category 3. Scientific knowledge is open to revision in light of new evidence.
• NOS Matrix understanding category 5. Science is a way of knowing.
• NOS Matrix understanding category 7. Science is a human endeavor.
• Science and Engineering Practice 1. Asking questions and defining problems
• Science and Engineering Practice 2. Developing and using models
• Science and Engineering Practice 3. Planning and carrying out investigations
• Science and Engineering Practice 4. Analyzing and interpreting data
• Science and Engineering Practice 6. Constructing explanations and designing solutions
• Science and Engineering Practice 7. Engaging in argument from evidence
• Science and Engineering Practice 8. Obtaining, evaluating, and communicating information

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.

• Hypotheses/theories
• Process of science
• Scientific arguments/evidence/testing ideas
• Scientific community
• What is science/nature of science