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THE FOUR CREATURES
by Lenore Kop

Instructional Goal:
This observational activity is used at the beginning of the year to challenge the students to consider these two questions: What is life? What characteristics distinguish living from nonliving things?

Performance objectives:
The students will:

  1. develop/improve observational skills

  2. analyze observations using characteristics of living things generated earlier

  3. hypothesize which of the creatures is really "alive", based on their analysis
Time: 1 hour

Materials: :
General: overhead projector, 20x150 mm petri dish, box or screen to shield preparation from student view
  • Creature 1: "aged" Duco cement, water, talcum powder
  • Creature 2: sea urchin spine or mollusc operculum, vinegar
  • Creature 3: ammonium hydroxide, liquid Ivory soap, water, oleic acid, vegetable oil, food coloring (optional)
  • Creature 4: euglena culture
General Procedures:

  1. Prior class period -- Student groups generate a list of characteristics which they feel distinguishes living from nonliving things. Combine information into a class list; keep this posted.

  2. Out of student view, prepare each of the cultures and display on the overhead. (I place a mat with a 150 mm diameter circle cut out and a three-sided shield onto the overhead surface.)

  3. Students record their observations. As they observe, you can place the petri dish cover on to see if "lack of air" has an effect. You can also stop after this first one to discuss details in observations, and distinctions between observations and interpretations.

  4. Creatures can be all viewed on the same day, or they can be spaced out over several days. After viewing a creature, ask students to identify which of the "living characteristics" they felt they observed in this creature.

  5. After viewing all creatures, students identify each one in writing as being living or nonliving, and explain their reasoning. (I look at the reasoning, not whether they are correct about it being alive.) This can be done in class, or for homework.

  6. After writing/next class period, discuss student reasoning. Reveal that only one creature was truly alive, and will be met again sometime during the year. (This may leave some students frustrated, but I've chosen never to reveal what the other creatures are because I don't want future classes to already know the "answer". )
Specific Creature Procedures:

Creature 1:

  1. Fill 1/3 of petri dish with water. Add a drop of Duco cement; it should form a teardrop/tadpole shape which spins and moves around the surface. (Fresh Duco will spread out and form a thin film on the water.)
  2. Talcum powder "food" can be sprinkled on.
  3. Covering the dish doesn't seem to have an effect.
  4. Over time, the creature will "darken" and slow down.
  5. Smaller petri dishes don't seem to work as well; maybe too much surface tension.
Creature 2:
    Fill 1/3 of petri dish with vinegar. Add sea urchin spines (or any calcium carbonate material). Bubbles will form.
Creature 3:
  1. Prepare the following solutions in advance:
    solution A: 7% ammonium hydroxide solution
    solution B: 5% ivory soap solution; red food coloring optional
    solution C: 2 drops oleic acid + 10 ml vegetable oil

  2. During presentation, mix 50 ml solution A with 10 ml solution B.

  3. Add a few drops of solution C. Creature should pulsate.

  4. Covering the dish causes creature to spread out and stop pulsating. Pulsating resumes when cover is removed.

  5. Over time, creature may fragment into smaller pieces; pulsation slows/stops.
Creature 4:
  1. Fill 1/3 of petri dish with euglena culture.

  2. Wait...it takes a while, but the euglena congregate to form an intestine-like pattern.

  3. This reaction seems to be temperature dependent, and should be done when the overhead surface is warm/hot.

  4. I also show them the culture in a beaker, so that they can record color.
References:
  • Creature 1: Alan J. McCormack (NABT 1989 National Convention presentation, San Diego, CA)

  • Creature 2: Curriculum Research & Development Group, FAST 3: Change Over Time , Honolulu, Hawaii: University of Hawaii, 1987

  • Creature 3: Alan Chan (NSTA 1992 National Convention presentation, Boston, MA)


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