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String Cells

by Marlys McCurdy

This cell construction is a project that may be incorporated into a unit on the cell. It is a hands-on model construction that is done in a cooperative learning mode that can be used as an authentic assessment following a full unit on the cell. It also reinforces the higher order thinking skill of analogy building.

The target audience would be either a life science, general science or any biology classroom. It would also fit nicely into an integrated science program. I use it as an introduction to my unit on genetics within the general biology curriculum. I use it with both general, advanced and challenged student populations. It is particularly popular with the student population that has diminished reading capacity. Yet my advanced students really enjoy the challenge of analogy formation.

It can be used as a unique assessment tool. I do it as the culminating activity in a cell unit and often videotape the students "teaching" their model to an audience. They know ahead of time the parameters that must be met for grade accomplishment and yet have a great deal of latitude for construction and presentation. Points are given for creativity when this is used for evaluation.


This project involves the construction of a cell model, companion poster and a travel brochure. The cell and companion poster must accurately represent the organelles of the cell for structure and function. The brochure is designed to entice a sub-cellular visitor to visit their "cellular resort".


Students construct the cell membrane using string or crochet yarn coated with 50/50 glue and water applied over an inflated balloon. A 10" balloon works well for size. The nuclear membrane is created the same way using a water balloon. Students are encouraged to watch their level of permeability as they coat the balloon with multiple layers of glue and string. This is the introduction to the concept of analogy building. The string membrane represents the semi-permeable membrane in a very visual format for both structure and function.

Students are then charged to represent organelles using structural and functional analogies. An example of a student-generated analogy is the use of audiotape for DNA. The tape represents the DNA structure as a group of string-like parts. It represents the function of DNA as a linear, sequential code that translates into a different "language". I give the students extra points for achieving analogies that cover both structure and function. Another example is the use of a AA battery for the mitochondria. It has an oblong shape and does energy conversions.

Students also create a companion poster that is a key for their model. The item used for a particular organelle. They must use a short paragraph for each organelle to explain its function in the cell. These posters are not copied from the book. They must explain their own analogies as well as appropriate structure and function.

The final step in the process is the creation of a travel brochure that will define a tour or visiting advantages for a sub-cellular being to visit their cell. Turning their cell construction into a resort or vacation site allows the students to integrate real knowledge-level information about the cell with really creative devices. The mitochondria inevitably becomes the restaurant serving up a fine platter of ATP for your energy needs. The trick to getting the points for this part of the project is to be sure that the information presented is analogically or realistically related to the true function of the organelle.


This construction realistically takes two weeks. Working with small groups it allows the teacher a great deal of one-on-one time to be sure that the learning targeted is accomplished.

Day 1 to 3:

  • Begin formation of the cell model:

    1. Balloons (both 10" and water balloons)-- check with the local balloon store for colors that are not popular and you can usually get a good deal.
    2. 50/50 glue with water solution dishes for each table group
    3. String or yarn (not thick) crochet yarn is perfect and allows for very colorful cells

  • Cover your tables with paper, this is messy!

  • Balloons need to be covered well enough to support the weight of organelles but not solid, one thin coat each day for two days The 3rd day the cells and nuclei will be dry enough to pop the balloon and create the hollow sphere that is now needed for the next step.

Day 3 to 5:

  • Discuss the concept of analogies. You may need to have students do some paper / pencil activities first to get the concept (refer to the cell membrane as your example).

  • Create a "goodie box" of items to share for use as structures Students bring in marshmallow, cereal, balloons, cotton balls, gummi worms, batteries, Christmas lights, matches, etc. I did have to draw the line at condoms! Students can each bring one thing or you may want to give some extra credit. Be sure they each bring enough to share.

  • I usually spend $10 to $15 to get the collection started. I buy things that previous students have used and don't tell the students what the analogy is. Peanuts, rope licorice, string licorice, Honeycomb cereal, jelly beans, orange slices, batteries (old from Physics room), sesame seeds, poppy seeds, various candies, toothpicks, etc. These items are suspended in the now hollow cell using fishline.

  • Have students identify the type of cell they are creating and then challenge them to keep the number and type of organelles consistent with that cell. This may necessitate the creation of a cell wall and some chloroplasts or axons and dendrites!

Day 6 to 8:

  • Students create a companion poster. Have students glue an example organelle on the poster so it is visually accurate with the model.

  • Then the students must create a paragraph of explanation for that organelle including an explanation of the analogy. This is important because sometimes the analogy is a stretch of the imagination and needs clarification.

Day 7 to 9:

  • Students create their travel brochure. Use one 8" x 11" sheet of typing or construction paper for this.

  • Be sure your directions include your parameter for grading because your more capable students will resist the open-creative style of this portion. Students need to know that they must exhibit knowledge about the cell as well as creativity.

Day 9 to 10:

  • Show and Tell-- Have students present their cells and brochures to their peers. Some years we have even shared with the elementary schools.


One nice thing about this project is that the assessment is embedded in the activity itself. As long as the student knows what is expected they accomplish their grading points as they complete the model, poster and brochure. It is difficult for a student to use the book for copying because of the creativity in the brochure and the mandated analogies. I do grade as a group for this activity and allow students to input information to me on their peers performance and contributions.

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