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The Jelly Bean Problem (JBP)

Glenn Westover



Type of Entry:

  • A Class Activity

Type of Activity:

  • Hands-on
  • simulation

Target Audience:

  • Life science
  • Biology
  • Advanced/AP biology

Notes to Teacher:

In preparation for this activity students are asked, "How can large particles get into cells?". If students understand the cell to be a fluid-filled membrane, say like a water balloon, then the problem of maintaining its integrity with a hole in its side presents a problem as a mechanism for taking in food particles. I prepare my students by first letting them play with bubbles to experience fluid-like membranes. Later they feed some Congo Red stained yeast cells to a micro-slide culture of Paramecium and observe that yeast cells are taken in and stay clumped together in one or more separate clusters within the Paramecia cells. Although the students can observe the yeast cell outside and within the Paramecia, they can not observe the details of the actual ingestion process.

Preparation Time: 20 minutes

Class Time: 30-45 minutes


Abstract

In this activity students are challenged to eat some candy as a cell would need to do it. By solving this problem students simulate the cell process called endocytosis.


Background

This activity is intended to simulate endocytosis as observed in some protists and other phagocytic cells. Typically it would be used in a unit dealing with homeostasis or cell function. I use it as the final activity in a unit about how things get into and/or out of cells.


Project

The Jelly Bean Problem

Introduction

The purpose of this activity is to get students to think about some of the problems that arise when a cell ingests food. If possible, allow the students to observe Paramecium feeding on Congo red-stained yeast. Remind them that a cell is a fluid-filled sack, somewhat like a water balloon. Before starting the exploration activity, have the students consider the following (kinds of) questions:

  • How do large particles, those too large to diffuse, get into cells?

  • Do cells have mouths?

  • Does swallowed food mingle or mix with the organelles?

  • Which cell organelle could function as a mouth?

  • Why do swallowed yeast cells stay together in clusters in the Paramecium?

  • How are the yeast clusters distributed within the various Paramecia? e.g., randomly, in a line, identical locations, etc.?

These or other leading questions will set the stage for the simulation. After students have some time to consider the questions, they are given the following materials:

Materials: (per group of two students)

  • 1 plastic shopping bag
  • 1 pair of scissors
  • 15 cm of string
  • 4 pieces of wrapped candy -irrelevant items?

The Problem:

With the materials in hand, the students are challenged to get the candy into their bag according to the following rules:

  • The candy must enter through a solid part of the bag.

  • The inside of the bag may not be directly open to the external environment.

  • The candies entering the bag must remain clustered together.

  • Students may work with their hands in the bag to act as the inside of a cell.

  • The candy may be eaten only if it enters the bag "cell" under the specified conditions.

This is always a fun activity because everyone wants to be first to solve the problem AND eat the candy. The students must show the teacher their solution before they may eat any candy. After a few failed attempts announce that the first group to discover a valid solution will own the rights to it and may "share it with" or "sell it to" their classmates. Eventually a group will arrive at the intended solution. The only workable solution I know for the problem mirrors the process of endocytosis as seen in electron micrographs. If you don't want to fool around with the proprietary issues, usurp the rights of the discoverers and have them demonstrate their solution to the class. All may eat the candy if they follow the correct procedure. The only solution I know is illustrated below.

As with Paramecium, the food particles are held in clusters within the cell; enclosed within a pinched-off portion of the ībag-cell's' membrane. The candies do not penetrate the membrane, but are contained within a portion of it. After the activity I use a transparency of electron micrographs to show how the process actually appears in real cells.


Method of Assessment/Evaluation

Have students do a drawing (like the solution above) to describe the process of endocytosis.


Extension/Reinforcement/Additional Ideas

Other processes, e.g., pinocytosis, phagocytosis, exocytosis, etc. can be described with the same model. An extention of the process might include a discussion of other systems designed to do the same function, e.g., move things from one place to another without allowing the two places to connect (an atrium, a ferry or tram, etc.). It is also possible to bring in and discuss the proprietary issues when one pair of students "owns" the feeding process and gets to control everyones "right to bite."


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