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NOVA scienceNOW: Artificial Life

Viewing Ideas

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Before Watching

1. On the board, write the following question: "What is the difference between nonliving and living things?" Have student pairs generate a list of characteristics necessary for life. On the board, draw two columns labeled living and nonliving. Ask each pair to share its list of characteristics and come up with a class definition. Ask if a leaf would be considered alive using this definition. (i.e., It is part of a living organism but is not itself alive.) Other thought-provoking examples include fire, a mule, an icicle, clouds, lights, crystals, televisions, cars, and rusting metal. Review with students that each living thing has the following qualities or characteristics:

   • has a structure enclosing a space, such as a cell membrane or cell wall
   • will grow or change by using energy and giving off waste products
   • is able to reproduce and pass traits to offspring
   • belongs to a population that responds over generations to changing environmental conditions

2. The program considers what Earth may have been like when life emerged. Have student teams make a time line of Precambrian time. Using a scale in which one millimeter equals a million years, the time line would be 4.5 meters long. Stretch the string across the classroom and mark each meter. Have teams research one or two events relating to Earth's geology and to life on Earth during the Azoic, Archaean, and Proterozoic Eons. Write these events on index cards and paperclip them to the correct position on the timeline. Students will likely be surprised by how long single-celled life was the only life-form on Earth.

   Time Period	Geologic Changes	Life-forms and their Changes
   Azoic Eon 4.5-3.9 billion years ago	Earth becomes a solid planet	No living organisms
   Archaean Eon 3.9-2.5 billion years ago	Earth's crust forms. Volcanic eruptions vent gases, resulting in the oceans and the atmosphere. Vast quantities of minerals deposited.	Life emerges in the sea. Single-celled organisms without a nucleus emerge (prokaryotes). Early forms include bacteria that get their energy from molecules, such as methane.
   Proterozoic Eon 2.5 billion-540 million years ago	Earth's plates move but more slowly than in the Archaean eon. Plates collide and form large mountain chains. Oxygen levels increase.	Single-celled organisms with a nucleus evolve (eukaryotes). They can reproduce sexually and adapt to changes in the environment. Some types of soft-bodied marine life evolve (metazoans). Some life-forms develop the ability to photosynthesize.

   
   

3. The program discusses the property of self-assembly in relation to DNA and its chemical subunits—thymine, adenine, guanine, and cytosine. Students can observe the self-assembly of chemical units by growing crystals. The crystal grows—or self-assembles—because of the chemical properties of its subunits. They grow when the constituent particles come out of solution and bond to form a regular lattice to which particles can continue to connect. Salt crystals are some of the easiest to grow.

Procedure

1. Make a saturated solution of salt water.

2. Place a sponge in a plastic container (crystals form best on a rough surface).

3. Saturate the sponge with the salt solution.

4. Allow the water to slowly evaporate, enabling the dissolved salt ions to come in contact and connect with each other to form crystals.

5. Allow the water on the sponge to evaporate.

6. Observe each day, and keep a log of your observations.

Have students share their observations. Ask students to brainstorm aspects of living systems where self-assembly is an important mechanism, such as DNA synthesis, protein synthesis, and cell membrane formation.

After Watching

1. Conduct a class discussion about some possible uses for the bioengineered, laboratory-made organisms of the future. (Organisms may be designed to "eat" oil spills, kill tumors, or rid the atmosphere of excess carbon dioxide to slow down global warming.) Ask pairs of students to brainstorm a health or environmental issue that may be helped by a specially designed organism. Have them imagine and draw their organism; point out the organism's special, bioengineered features that allow it to do its job, and describe how it can help the world.

   Try NOVA scienceNOW's "Let's Make a Microbe!" interactive to further explore engineering new forms of life

2. Discuss the notion that generating life in the laboratory may have both positive and negative consequences. Divide students into teams. Ask half of them to brainstorm three or four potential positive consequences and the other half to generate three or four potential negative consequences. Have teams share their ideas. As a class, develop a list of precautionary measures that might help prevent problems associated with each of the students' suggestions.

3. Researchers talk about making artificial life in two ways—top-down and bottom-up. The bottom-up approach builds cells from nonliving components. The top-down method involves modifying cellular structures (often by simplifying the genetic material) to make the cell less complex and to identify its essence by stripping away unnecessary elements. Students can use poetry as an analogy to contrast these two methods. In this activity, life is represented by meaning—when there is meaning, there is life. To model the top-down approach (i.e., deconstructing a complex life-form into something simpler), give half the class copies of a short poem, such as Robert Frost's "The Road Not Taken." Have students work individually or in pairs to eliminate words or lines from the poem, paring it down and making it simpler but not losing its meaning. To model the bottom-up approach (i.e., constructing a simple life-form from nonliving components), give the remaining students the same poem. Have them cut the words apart and use them to create a new poem with a new meaning. Have student volunteers share their poems and tell about the poems' meaning. Judge how the meanings of the original and new poems compare. Ask for opinions about which method, top-down or bottom-up, was more difficult to complete. Have students predict which method will succeed first in creating artificial life. They should be able to give reasons for their prediction. Have students brainstorm some of the difficulties inherent in creating a life-form from nonliving components.

4. Conduct an activity in which students extract DNA (and also some RNA) from bananas. They see first-hand that DNA is a component of living and once-living things and that DNA can be extracted and observed. The activity uses household materials and can be done in one class period. It is suitable for middle and high school students. The classroom activity titled "Extracting DNA from Bananas", contains teacher notes, a student sheet with a step-by-step procedure, answers to the student sheet questions, a glossary of key terms, and a standards correlation.

Web Sites

Geologic Time Line
www.sdnhm.org/fieldguide/fossils/timeline.html
Presents a time line of Earth, highlighting geologic events and noting when different life-forms arose.

Origin of Life: In Search of the Simplest Cell
scienceweek.com/2005/sw050325-1.htm
Summarizes articles related to simple life-forms and their origins.

Origin of Life: On Replication in the RNA World
scienceweek.com/2005/sw050429-1.htm
Considers RNA as the first reproducing macromolecule.

Transitions from Nonliving to Living Matter
www.sciencemag.org
Discusses the definition of living versus nonliving and describes the top-down and bottom-up approach to producing artificial cells.

Books

Essential Cell Biology by Bruce Alberts, Dennis Bray, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, and Peter Walter. Garland Publishing, Inc., 1998.
Covers cell biology topics, such as proteins, DNA, protein synthesis, genetics, and many more. High school and college textbook.

Evolution: A Beginner's Guide to How Things Adapt and Survive by David Burnie. Dorling Kindersley, 2002.
Examines the origin of life on Earth and how natural selection works.

The Human Genome by Jeremy Cherfas. Dorling Kindersley, 2002.
Explains DNA, inheritance, and genetics.