My Science Box

Physiology is the study of living things – their structure, organization, and biochemistry. This unit gives students an opportunity to discover the fundamental characteristics of living things and explore some basic cell biology. Students begin with several activities culminating in the creation of a list of characteristics that all living things have in common – the characteristics of life list. From here, students learn to test for signs of life by growing microbes on agar plates, conducting biochemical tests, visualizing cells, and experimenting with photosynthesis and respiration. Finally, students learn about the organization plants and animals through dissection and the raising of plants and fish in the classroom. Throughout the unit, students return to the characteristics of life list, refining and revising their list as they learn new concepts. A planning guide for a voyage with the Marine Science Institute is included as a way for students to learn about the many forms of life in the San Francisco Bay.

Summary
What does it mean to be alive? Is a cactus alive? Is a seed alive? Is the air we breathe alive? What are the necessary characteristics? To hook students into the question, they are introduced to “glue monsters” (sometimes known as “scooting glue”) and the class discusses whether the “monsters” are alive or not. Next, students are given cards with the names of various objects and asked to sort them into categories: alive, once was alive, never alive, and not sure. Finally, students create a list defining the characteristics of life – a set of characteristics that all living things share. The list is initially developed in pairs, then in larger groups of 4, and ultimately as a whole class. The final list is turned into a poster that can be referenced and modified throughout the remainder of the unit as students learn more about what it takes to be alive.

Time
10-15 min glue monsters demo
30-40 min alive or not alive card sorting and discussion
30-45 min create characteristics of life lists

Grouping
The card sorting activity and initial creation of a list of the characteristics of life is done in pairs. These pairs will eventually merge in groups of 4 to compare, discuss, and revise their lists. The remainder of the discussion takes place as an entire class.

Teacher Background
Many middle school students believe that the defining characteristic of living things is that they move. When they see the “glue monsters” wiggle in the Petri dish, most will immediately assume they are alive. What is going on? Duco® cement is polymer mixed in a water soluble solvent. When the cement is exposed to air as it drops into the dish, a thin, solid polymer skin quickly forms around the liquid, solvent-polymer mixture. When the bead of cement is immersed in water, the solvent diffuses through the skin, causing the bead to shrink and the skin to rupture on one side of the bead. The solvent squirts out of the hole and the surface tension of the water on that side of the bead suddenly falls. Since the surface tension is now uneven, the bead will move away from the hole, towards the area with greater surface tension. The hole quickly repairs itself but the skin then bursts in another location. Thus, the bead appears to wiggle and twist as the surface tension changes depending on where the skin bursts.

Getting Ready
Glue monsters demo:

1. Place a Petri dish half full of water on the overhead projector.
2. Set aside a small dish of pencil shavings or black pepper.
3. Try the demo yourself first, rehearsing the “release” of the “monsters” into the dish and their “feeding” with pepper or pencil shavings.
4. Optional: wrap the tube of glue in paper or keep it in a brown paper bag so that students cannot tell what the “monsters” really are.

Lesson Plan
Glue monsters demo:

1. Fill a Petri dish half full with water.
2. Place the Petri dish on an overhead projector.
3. Fabricate some story about small, blob-like monsters that live in the local watershed. Add a drop of Duco® glue to the water in the dish.
4. To “feed” the “monster”, sprinkle a small amount of the pencil shavings or pepper near the “monster”. It should move towards the shavings or pepper and “eat” them.
5. Add additional drops of glue and watch “monsters” interacting with one another.
6. When the “monsters” slow down, turn off the projector and ask the students for their observations. What did they see? What happened when “food” was added? How did the monsters interact with each other? Most importantly, were they alive and how could you tell?
7. After students reported their initial observations, do the demonstration again, this time very obviously showing students that it was a trick – the “monsters” were just drops of glue in water and the “food” was pencil shavings. Briefly explain the chemistry behind the demonstration.
8. Discuss what characteristics they used to initially decide that the “monsters” were alive. Students will generally point out how they “moved on their own”. Ask students whether all living things “move on their own” and look for counterexamples like plants.

Assessment
Play the game “5 Alive”. On a piece of paper, the person who is “it” should write the name of any item that they know for sure is alive or not. The rest of the group gets to ask 5 yes or no questions to figure out if the mystery item is alive.

Going Further

1. Many of the other activities in this box extend upon this first lesson.
   • The Life Trap activity demonstrates that living things can be microscopic, grow and reproduce.
   • The Testing for Life activity introduces the idea that all living things are made of the same organic molecules and has students test for proteins, starches and sugars.
   • The Seeing Cells activity introduces students to the idea that all living things are made of cells.
   • The Cell Energy activity brings up the concept of cell metabolism.
   • The Life on Mars project asks students to design 3 experiments to determine whether there is anything living in a sample of “Martian soil”.
2. A great resource for additional lessons on the characteristics of life is the Life in the Universe curriculum, published by the SETI Institute.
3. Another resource is the Searching for Life curriculum from NASA.

Sources
I discovered the “glue monster” or “scooting glue” demo from Flinn Scientific (click on “Glue Monsters” to download the pdf file). Kitchen chemistry also provides a write up for the same activity with a better description of the chemistry behind the demo. For a quicktime movie of a paper boat “fleeing” from a dish soap coated toothpick, see the University of Iowa Physics and Astronomy Lecture Demonstrations.

Summary
Life trapsAs part of recognizing the characteristics of life that all organisms share, students grow microbes on nutrient agar plates. Students swipe surfaces with a sterile Q tip swab and seed plates resulting in a wide range of colorful and prolific bacteria and fungi colonies. Other plates may be simply opened to the air to catch life floating in the air. Through these experiences, students learn that all living things, even those so small and invisible as to be floating in the air, grow and reproduce when provided with the proper nutrients and water. Teachable moments abound since the “dirtiest places”, like the toilet rim, often result in the least bacterial growth while presumably “clean” places, like the surface of your skin, have the most. A fun extension of this activity (see the Going Further section) is to start a sourdough culture from wild yeast in the air and make sourdough bread.

Time
30 min to introduce the activity and seed the plates
5-10 min to make observations every other day over the next 2 weeks

Grouping
Individual or in pairs.

Materials
For approximately 50 plates you need:

• 50 sterile disposable plastic 15 mm x 100 mm Petri dishes (can be purchased from Ward’s Natural Science, item number 18 V 7101, approximately $4 for a package of 20 dishes)
• 15 g agar agar powder (a gelatin substitute made from red seaweed, available at most Asian grocery stores and health food stores, ideally purchase the unsweetened variety but pre-sweetened is OK as long as you ensure that you subtract out the weight of the sugar when measuring out 15 g of agar agar)
• 2 beef bouillon cubes
• 1 liter distilled water
• stove and large pot for preparing nutrient agar and steam sterilizing the Q tips (better yet, if you have a pressure cooker, you will be far more assured of initially sterile conditions in your agar plates)
• 50 Q tips
• paper towels
• permanent markers for labeling plates
• masking tape
• bleach