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Exploring Osmosis with Polymers

Grades: Grades 10 - Biology
Author: Danielle Donaldson
Source: Aliginate portion of lab inspired by: http://imaginationstationtoledo.org/content/2011/09/edible-worms/. Osmosis portion of lab adapted from: http://pslc.ws/macrog/kidsmac/activity/bear.htm.


Abstract

In the first part of the lab activity, students will be making their own "gummies" similar to gummy worms and Boba fruit spheres using sodium alginate, a polymer found in green algae. The student will then make a connection to osmosis properties by soaking their polymers in distilled water, tap water and salt water, and collected data on mass change.


Objectives

Students should have an understanding of...

  • Polymer structure and definitions
  • Chemistry processes involved in making alginate “gummy worms” and "Boba"-like spheres
  • Vocabulary associated with passive diffusion and an understanding of how these properties work
  • How varying concentrations can effect osmosis in both the lab demonstrations as well as within the cell
  • How polymers are being used in the field of biochemical engineering for things such as drug delivery and tissue engineering.

Students should be able to...

  • Create alginate “gummy worms” and "Boba" in the lab
  • Demonstrate their knowledge of osmosis by creating Boba of different sizes using differing concentrated solutions
  • Apply a knowledge of both polymers and passive diffusion to present ways in which both can be used in the field of engineering.

Materials

Part 1

  • Distilled water
  • 1 gram of alginic acid sodium salt
  • 2 grams of calcium chloride (CaCl2)
  • Food coloring
  • Pipette or drinking straw
  • Two beakers (larger than 100mL)
  • Tweezers
  • Paper towels
  • Something to use as a sieve such a piece of screen or filter

Part II

  • Three beakers (around 100-250ml)
  • Distilled water
  • Tap water
  • Salt
  • Electronic scale or triple-beam balance
  • Ruler

Procedures

Engagement

This lesson can be used as a reinforcement/inquiry activity during the cell transport unit, as a follow up to information on passive transport (diffusion, osmosis). Students will already have a basic understanding of the cell membrane and passive transport concepts. An opening demonstration can be done for students as an introduction to diffusion where the teacher puts a drop of food coloring in a beaker of water, and asks students to describe what is happening as the food coloring moves from an area of high concentration to an area of low concentration. This can open up discussion about diffusion and passive transport in cells, and why is it important for cells to maintain homeostasis. To get students excited about food chemistry and polymers, bring in various gummy candy such as gummy worms, gummy bears, Boba fruit spheres and other foods in which sodium alginate is used, such as fruit flavored popsicles, yogurt and pie fillings. Ask students to list some of the similarities in these kinds of food (they are gel-like, sticks together, smooth, and thick).

Exploration

For the exploration portion of this activity, students will be combining their knowledge of osmosis properties to explore the polymer created when sodium alginate and calcium chloride are mixed together. The student worksheet first reviews the concept of osmosis and then goes on to introduce students to the definition of a polymer. In the elaboration portion of the activity, polymers and their uses can be discussed in more detail if time permits. Students, working in groups of 2-4 students, will first begin the activity by making their own sodium alginate gummies following the procedure on the student worksheet. Students will then follow the instructions on the worksheet to complete the osmosis portion of the lab activity, soaking the gummies/Boba overnight and collecting data for their results the next day in lab. In the third portion of the lab, students will simulate reverse osmosis according to the directions in the student worksheet and record their results the following day. Each student will complete their own lab worksheet and turn it into the teacher for assessment.

Explanation

After laboratory data has been collected and analyzed, the teacher should further explain the concept of osmosis and how the results of the lab should reflect osmosis occurring.

Elaboration

Students can explore the different uses of sodium alginate in various field such as the food industry, cosmetics, textile printing and pharmaceuticals at the following website: http://www.kimica-alginate.com/alginate/application.html.


Prerequisites

Students must have a basic understanding of cell structure and function, a preliminary knowledge of passive diffusion, laboratory procedure skills and a basic knowledge of the biological polymers


Best Teaching Practices

  • Real-life applications
  • Analogy
  • Hands-on/Minds-on
  • Inquiry Approach

Alignment with Standards

National Standards:

  • LS1.A : Structure and Function
    • Systems of specialized cells within organisms help them perform the essential functions of life. (HS-LS1-1)
    • All cells contain genetic information in the form of DNA molecules. Genes are regions in the DNA that contain the instructions that code for the formation of proteins, which carry out most of the work of cells. (HS-LS1-1) (Note: This Disciplinary C ore Idea is also addressed by HS-LS3-1.)
    • Multicellular organisms have a hierarchical structural organization, in which any one system is made up of numerous parts and is itself a component of the next lev el. (HS-LS1-2)
    • Feedback mechanisms maintain a living system’s internal conditions within certain limits and mediate behaviors, allowing it to remain alive and functional even as external conditions change within some range. Feedback mechanisms can encourage (through positive feedback) or discourage (negative feedback) what is going on inside the living system. (HS-LS1-3)

Ohio Standards:

  • Cells-10th Grade Life Science Grade Level Indicator
    • Compare the structure, function and interrelatedness of cell organelles in eukaryotic cells (e.g., nucleus, chromosome, mitochondria, cell membrane, cell wall, chloroplast, cilia, and flagella) and prokaryotic cells. (ORC Resources)
    • 3. Explain the characteristics of life as indicated by cellular processes including a. homeostasis b. energy transfers and transformation c. transportation of molecules d. disposal of wastes e. synthesis of new molecules

Content Knowledge

  • Biological polymers
  • Cell structure and function
  • Cell transport
  • Laboratory procedures and tool use

Safety

Students should wear gloves during the activity to eliminate the amount of chemicals on their hands, although all materials are safe. Make sure that students understand that unless food grade chemicals and cooking utensils are used, the product IS NOT edible!


Applications

This lesson can be applied to biochemical engineering concepts such as drug delivery and tissue engineering


Assessment

Unit test on membrane transport, lab report


Other Considerations

Grouping Suggestions: Groups student according to supplies available, groups of 2-4 students would work best

Pacing/Suggested Time: If food grade chemicals are used and all measuring materials used are food safe, then "gummies" can be eaten. Add sweetener and flavoring to sodium alginate mixture in order to make them more similar to real gummy worms.


Printable PDF Worksheets

Student Worksheet