Hands-on science (no lab required).

After reading "It's Not Easy Being Green" (p. 8), complete this activity to learn more about how desert amphibians conserve water.

PREDICT

Which material do you predict will absorb, or soak up, the most water: sponge, Styrofoam, or wax paper? Which will retain the most water over time: a sponge covered with plastic wrap, or an uncovered sponge?

YOU NEED

5 small plastic bowls * marker * 2 sponges, 1 piece of Styrofoam cup material, and wax paper (each about 5.8 cm by 3.8 cm, or 2.3 in. by 1.5 in.) * pan balance * paper and pencil * 2-liter soda bottle with the top quarter cut off * tap water (1.5 liters, or 6 cups) * watch with second hand * plastic wrap (25 cm by 15 cm, or 10 in. by 6 in.) * sunny window

TO DO

STEP 1: Test how well different materials absorb water.

1. Place four plastic bowls on a clean surface. Label the rim of each bowl with one of the following: sponge (covered), sponge (uncovered), Styrofoam, and wax paper.

2. Place the remaining bowl on a pan balance and record its weight.

3. Place a sponge into the weighing bowl on the pan balance. Record the combined weight of the bowl and the sponge. Then, place the sponge into the "sponge (covered)" bowl. NOTE: You will cover this sponge in a later step.

4. Repeat for the other sponge, the Styrofoam, and the wax paper, weighing and then placing each item into its corresponding bowl.

5. Fill the soda bottle with 1.5 liters (6 cups) of water.

6. Place one sponge into the water. Allow it to soak for one minute. Then, remove the sponge and let any excess water drip back into the soda bottle for about 30 seconds.

7. Place the wet sponge into the weighing bowl on the pan balance. Record its weight.

8. Repeat Steps 6 and 7 for the other three materials.

STEP 2: Test out ways a sponge can retain the most water.

1. To make the "sponge (covered)," wrap the appropriate sponge with plastic wrap so that the entire sponge is covered. Place the sponge back into its bowl.

2. Place the two bowls each containing a sponge near a sunny window and leave the bowls there overnight.

3. The next day, weigh each sponge in the weighing bowl on the pan balance, and record. NOTE: For the covered sponge, remove the plastic wrap before weighing.

CONCLUSIONS

1. Which material soaked up the most water? Why? HINT: Water absorbed = (weight of wet material) - (weight of dry material). Make sure to subtract the weight of the empty bowl from each recorded weight.

2. Which sponge--covered or uncovered--retained the most water? Explain. HINT: Water retained = (weight of wet sponge) - (weight of sponge after sun exposure).

3. Would a desert amphibian retain its moisture best by wiping a plastic-like coating all over its skin, or not? Explain.

1. The sponge should have soaked up the most water. That's because a sponge contains lots of tiny pores that act like thin tubes. When dipped into water, capillary action (process by which water molecules are attracted to the tube's molecules) pulls water into the pores. The Styrofoam--a type of plastic--and wax paper repel water,

2. The covered sponge retained much more water than the uncovered sponge. That's because the uncovered sponge allowed the water to evaporate into the air. The water-resistant plastic wrap, however, prevented evaporation of water from the covered sponge.

3. Yes, a plasticlike coating would help a desert frog retain water the most. The waterproof plastic would create a barrier, keeping the collected water in the frog's skin from evaporating under the scorching sun.