Viruses are made up of a nucleic acid genome (either RNA or DNA) surrounded by a protein coat. Viruses are not cells; they lack the necessary cellular components to replicate their genomes and make the proteins necessary to produce progeny. Instead, viruses must enter a cell and take over its ‘machinery’ to copy genetic material, synthesize proteins, and assemble the parts to form new viruses.

Without the cellular machinery found in bacterial, plant, or animal cells, a virus cannot reproduce and proliferate. Without this ability, can a virus be considered alive? This question has been debated for decades. In order to answer this question another question must be answered: What does it mean to be “alive” exactly? In the following activity, students will identify the characteristics that define life.

Materials

• Handheld magnifying lens – for each station
• Dissecting needles and tweezers - for each station
• Dissecting microscope – for each station (optional)
• Drawings of several viruses (e.g. Mimivirus, ebolavirus, rhinovirus)
• Samples of some of the following (one of each):
  
  1. resurrection plant
  2. maple seed pod (helicopter pod)
  3. algae
  4. dead tree leaf
  5. living sponge
  6. slime mold
  7. kitchen sponge
  8. puffball mushroom
  9. pink eraser
  10. Gak™ or Silly Putty™
  11. walking stick insect
  12. deceased insect

The Scientific American article Are Viruses Alive? Delves more deeply into this question and provides a rationale for why it may be an important question. You may want to have your students read this at some point during the activity.

Procedure

1. Set up stations around the classroom containing one unknown sample, a handheld magnifying lens, a dissecting needle and dissecting microscope if available.
2. Share the introduction to the activity with students, either by having them read their own copy, projecting a copy, or reading it to them.
3. Working in pairs have students examine the samples at each station. Have them record their observations of each object, noting the object’s number, and decide whether or not each particular sample is “alive.” They should include a short explanation for each decision.
4. For the duration of this activity, have the pictures and labeled diagrams of several viruses either projected onto the board or printed out and placed around the room for comparison.
5. When the students have completed their observations, have them share their decisions and explanations.
6. As students discuss the reasons they consider something is living, encourage them to define specific characteristics. Record on the board or projector characteristics that arise. For example “It is not alive because it does not move”. List motion as a possible characteristic. “It makes a seed”, list ability to reproduce as a possible characteristic. The final list should include the following characteristics:
   
   • able to grow
   • able to reproduce
   • able to extract and use energy and nutrients from the environment
   • able to repair and maintain itself
   • able to respond to environmental stimuli in a controlled manner
   • composed of cells and organic biomolecules
   • maintains a high degree of organization using energy
   • produces waste products (by-products of metabolism)
   • dies
7. After they finish sharing their observations, have students use these characteristics to decide whether viruses are alive or not.

Questions in the Discussion section can be used to open a discussion about what it means to be alive and why it may be important to distinguish live things from nonliving things.