Aquatic Solutions and Our Cells (Five-day unit)

Interactive, scaffolded model

Overview and Learning Objectives

The module is focused on the essential ability of water to dissolve and transport some substances and not others, and on the molecular properties underlying these phenomena. Students are asked to reason using the kinetic molecular theory. The power of the kinetic molecular theory in understanding matter in solutions lies in helping students understand that matter does not simply disappear when it is dissolved, but rather remains in the form of hydrated ions and hydrated larger molecules.

Students will be able to understand that:

• water molecules can pull apart ionic compounds into charged atoms, or ions, (dissociation) and form a water shell around the ions (hydration), thereby dissolving them and moving them;
• ions disperse through a solution until they reach equilibrium, and that a semipermeable membrane acts to let through only ions of a certain size;
• after water hydrates ions with watery shells, free water in the region is reduced, thus creating a gradient towards which new water will flow.

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Assessment

1a. Suppose you have three cups of water. In the first cup you add a teaspoon of vegetable oil, in the second cup you add a teaspoon of sugar, and in the third cup you add a teaspoon of very fine sand. You then shake each cup vigorously and let them stand for two hours.

Describe what is happening to the ingredients in each cup immediately after shaking. Then describe what is happening to each ingredient -- including water -- in each cup two hours after shaking the material.

1b. Did the oil, sugar, and/or the sand dissolve? Explain your answer. Be specific as to the forces and interactions that are responsible for dissolving.

2a. Why do vegetables wilt when you put them in salt water?

3a. What happens to salt on an atomic level (include molecules and ions in your description) when it dissolves in water? Describe the way in which the salt and the water interact.

3b. Alcohol is slightly polar. What happens to salt on an atomic level when it is placed in alcohol?

3c. Draw a picture that shows a salt solution in water. Be sure to label your picture or provide a key for any symbol you use.

3d. Draw a picture that shows a salt solution in alcohol. Be sure to label your picture or provide a key for any symbol you use.

4a. Suppose you have a container in which you place 1000 water molecules on the left side of a wall and on the right side 900 water molecules and 100 NaCl molecules (200 ions). Then you remove the wall. How many molecules of water would end up on each side of the container? How many ions would end up on each side of the container?

4b. Now start over again with a water-permeable wall (it lets water flow through it, but not salt) in the container. You place 1000 water molecules on the left side of the wall and on the right side 900 water molecules and 100 NaCl molecules (200 ions). How many molecules of water would end up on each side of the container? How many ions would end up on each side of the container?

4c. If you could take a movie of the molecules and ions in the container with the water-permeable wall, what would you see if you watched the movie? Be specific as to the forces driving any changes that occur.

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Classroom Practice

http://www.concord.org/~barbara/workbench_web/unitIII_mini/index.html

includes extensions, etc.

Other concept maps include:

http://www.concord.org/~barbara/molo/molo_concept_maps/membrane.html

http://www.concord.org/~barbara/molo/molo_concept_maps/intercellular_components.html

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Central Concepts

Key Concept:

There are special forces that contribute to the particular ways materials act in solutions. Molecules in liquids no longer act freely, as they do in a gas, but are constrained by strong and weak forces.

Additional Related Concepts

Concept Map Available

Biology

• Cellular fluid
• Cystic Fibrosis
• Fluids
• Membrane
• Tugor
• Waste Disposal

Molecular Biology

• Cellular solutions
• Osmosis
• Polar molecules
• Polar nature of water

Physics/Chemistry

• Charge
• Dissolving
• Hydrogen bonds
• Ion
• Ionic bonds
• Liquid
• Salt
• Solubility
• Solutions
• Water
• Water shells

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Textbook References

• Biology (Miller and Levine) Prentice Hall 5th Edition - Unit 1: Chapter 4 - The Chemical Basis of Life
• Biology (Miller and Levine) Prentice Hall 5th Edition - Unit 2: Chapter 5 - Cell Structure and Function
• Biology: Concepts and Connections (Pearson) 5th Edition - Chapter 2: The Chemical Basis of Life
• Biology: Concepts and Connections (Pearson) 5th Edition - Chapter 5: The Working Cell
• Biology: Exploring Life - Chapter 4: The Chemical Basis of Life
• BSCS Blue (8th Edition) - Chapter 3: Exchanging Materials with the Environment
• BSCS Human - Chapter 4: The Internal Environment of Organisms
• Cell Biology (Pollard and Earnshaw) Saunders 2002 - Chapter Two: Molecular Structures

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Benchmarks and Standards

AAAS

• THE LIVING ENVIRONMENT: CELLS - Every cell is covered by a membrane that controls what can enter and leave the cell (Full Text of Standard)
  
  
• THE LIVING ENVIRONMENT: CELLS - Most cells function best within a narrow range of temperature and acidity (Full Text of Standard)
  
  

NSES

• Life-Science: Interdependence - 1 The atoms and molecules on the earth cycle among the living and nonliving components of the biosphere (Full Text of Standard)
  
  
• Life-Science: Matter, energy, and organization - 1 All matter tends toward more disorganized states (Full Text of Standard)
  
  
• Physical-Science: Matter Structure/Properties - 5 Solids, liquids, and gases differ in the distances and angles between molecules (Full Text of Standard)
  
  

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Activity Credits

Created by CC Project: Molecular Workbench using Molecular Workbench + Pedagogica

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Requirements

• Java 1.5+ - Java 1.5+ is available for Windows, Linux, and Mac OS X 10.4 and greater. If you are using Mac OS X 10.3, you can download MW Version 1.3 and explore within it instead.
• QuickTime for Java - Important Note: Due to a recent QuickTime update, you may not be able to see some models with embedded Flash components. We are currently trying to develop a workaround.

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