The Sponge Challenge

Learning Objectives

Students will:

• Brainstorm a way to wet all parts of a dry sponge as quickly as possible.
• Relate the activity to the reason why cells must be small.

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Materials

For each team:

• Thick, light-colored kitchen sponge
  Small pitcher or beaker to hold tinted water (See Preparation section)
• Empty bowl or container
• Scissors
• Tongs
• Paper towels
• (Optional) Latex gloves

For each student:

• Notebook or writing paper
• Pen or pencil

For the leader:

• Stopwatch (may use cell phone app)
• Food coloring

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Preparation

• Read and familiarize yourself with the activity. You may wish to follow step 12 to ensure that the activity works as you expect.
• Obtain bowls, plastic shoeboxes, plastic terrariums, or other containers that are large enough for submerging a sponge. Also gather small pitchers or beakers, which will hold the tinted water for each team.
• Gather all other materials. Make sure the kitchen sponges do not include abrasive surfaces or other attachments. Ideally, all of the sponges should be identical. Reserve at least 2 sponges for use in the demonstration step of the activity.

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Activity Steps

1. Hold up a sponge, and ask students to explain why sponges absorb water. Discuss how the spaces within the sponge as well as the fibrous material of the sponge both act to take up water.
2. Tell students that their challenge is to devise a way to wet all parts of a sponge (inside and outside) within 10 seconds of contact with tinted water. Present possible ideas, such as pouring the water over the sponge, tightly squeezing the sponge underwater, or swirling the sponge underwater water. (Do not invite students to suggest their ideas at this time.)
3. Tell students that you have a limited number of sponges, which means everyone will have only 1 chance to succeed at the challenge. Explain that each group will try to meet the challenge in the same 10-second period, which you will announce.
4. Divide the group into teams, ideally of 2 to 3 students per team. Distribute the materials to the teams, but do not supply the tinted water until later.
5. Invite teams to begin considering ideas for meeting the challenge.
6. Circulate among the group, and respond to student questions and issues. If a team asks if they can tear the sponge into pieces, tell them yes, but do not offer encouragement or suggestions. Try to keep this strategy a secret from the whole group.
7. Announce that the time is arriving to prepare to wet the sponges. Tell students to decide on their plan and to prepare to enact it. At this time, fill the pitchers or beakers with tinted water, or ask students to do so.
8. Explain that when you call “Go”, teams should bring the sponge and tinted water in contact, either by pouring water or by submerging the sponge. When you call “Stop,” teams must separate the sponge from the water, either by lifting the sponge with the tongs onto a dry paper towel, or by pouring out the water into an empty container.
9. When students are ready, set the timer and Call “Go”, and then 10 seconds later, call “Stop.”
10. Ask each team to cut open their wet sponge to determine whether the inside is thoroughly tinted.
11. Reconvene the whole group. Invite students to describe and evaluate their strategies. If any teams succeeded at the challenge, save their report for last.
12. Explain the optimal strategy for completing the challenge, which is to cut or tear the sponge into very tiny pieces. Doing so increases the surface area of the sponge, which is the area that comes in direct contact with the water. You may wish to demonstrate this strategy for the group. Also, if students complain that they did not realize that this strategy was allowed, explain that you deliberately avoided the question to not give away the solution.
13. Discuss the activity with these questions:
    • How does the sponge challenge relate to a real-life problem or observation? Hint: Think about biology and the make-up of living things. (The ratio between surface area and volume helps explain why most cells are extremely small. Water diffuses into cells much like it diffuses into sponges. By being very tiny, cells can take in water and remove wastes at a rapid, useful rate.)
    • To stay alive and functioning, the cells of the human body need water and other materials. Yet the body is covered in waterproof skin. How do human cells get the water and other materials they need? (Blood supplies water, oxygen, and food to cells, and it carries away wastes. Every living cell directly contacts a capillary, which is a thin blood vessel.)

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Variations

1. Present the activity as a whole-group demonstration. Use 3 stations to compare the effects of squeezing a sponge underwater, holding the sponge in water without squeezing, and cutting the sponge into very tiny pieces.

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