Life through the lens
Classroom Explorations: Characteristics of Living Things
> Link to Student Pages
Materials & Equipment
Group Size
  • whole class or individuals
Preparation
  • Download the student pages and preview the Web pages by clicking on the links on the data table.
  • If you will be doing the activity with the entire class, print and duplicate the student pages.
Alternative Approaches
  • Do the activity with the whole class by projecting the Web pages and playing the videos.
  • Introduce the activity to the entire class, then have students view the Web pages, play the videos, and complete the student pages independently in a tech center or as homework.
Objective
  • To recognize and describe the characteristics of living organisms.
Getting Started
Review with students these six easily observable characteristics of living things:
  1. movement (which may occur internally, or even at the cellular level)
  2. growth and development
  3. response to stimuli
  4. reproduction
  5. use of energy
  6. cellular structure
Procedure
The student data table includes links to all the information and videos necessary to complete this activity.

Entire class—projecting the videos
  • Click on each link in the "Category" column on the data table. Students can take turns reading the introductions aloud.
  • Show the videos and have the students complete the data table for each organism.

Individual work
Provide students with the URL for the student pages ( www.exploratorium.edu/imaging_station/students/Characteristics_Student.doc ). They can use the links on the data table to access the text and videos, and complete the activity independently.
Going Further
  • Have students conduct Internet research on "characteristics of life." Do all sources agree on the characteristics? Are there characteristics not covered in this activity? Do all scientists agree on a common list of "characteristics of life"?
  • What are the limitations of videos? Discuss which characteristics of life students are unable to identify in the videos. How might they be able to observe these characteristics in select organisms?
  • If all of the characteristics of life are required to classify something as "alive," how can we account for those individuals who are definitely alive, but that do not reproduce (for example, people without children or a sterile mule)?
  • Is a virus alive? Ask students to keep in mind the information from this activity, and to conduct Internet research to discover how scientists answer this question.
What’s Going On?
Defining "life" is a very difficult task, and scientists don’t all agree on a common list of the characteristics of life. Some of the other characteristics that the students may discover in their research, and which are often listed in textbooks, include those listed below. Many of these traits are not limited to living things. For example, fire uses energy, grows, and can reproduce, but it is not considered alive in part because it cannot evolve; its traits are necessary, but not sufficient, for life. NASA scientist Bruce Jakosky, in his book The Search for Life on Other Planets , provides a generally accepted definition of something being “alive” if it 1) utilizes energy from some source to drive chemical reactions, 2) is capable of reproduction, and 3) can undergo evolution.

Characteristics of Living Things
  • All organisms use energy (metabolism).
  • All organisms maintain a stable internal environment (homeostasis).
  • All organisms detect and respond to select external stimuli.
  • All organisms can engage in movement (which may occur internally, or even at the cellular level).
  • All organisms show growth and development; that is, specialization of cells or structures. (Even unicellular organisms show a tiny amount of growth, and single cells repair and use materials from the environment to replace internal structures as needed.)
  • All organisms reproduce. (Even if an individual can’t reproduce, its species can.) In addition, an individual’s cells are constantly reproducing themselves.
  • All organisms have nucleic acid as the hereditary molecule.
  • All organisms show adaptation, which occurs at the individual level and is tightly related to homeostasis.
  • All organisms are made of one or more cells.
  • All organisms exhibit complex organization, grouping molecules together to form cells; at a higher level, cells are organized into tissues, organs, and organ systems.
  • All organisms exhibit evolution over time due to mutation and natural selection (which operates at the species level).
Acknowledgment
Thanks to Bonnie Daley, seventh-grade life sciences teacher in the San Francisco Unified School District, who developed a prototype of this activity.