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Osmosis Lab Planning Center

As you and your group prepare for the Osmosis Inquiry Investigation, there are several things you need to consider before you begin. This page has been designed to help you collaborate with your fellow group members to prepare for and document your experiment.

Background Information

Diffusion is the spontaneous tendency of molecules to spread apart and move from areas of high concentration to low concentration. Passive transport occurs when substances diffuse across biological membranes. Biological membranes are selectively permeable, which means that some substances can pass through the membrane and some cannot. Passive transport does not require energy, distinguishing it from active transport, which does require energy.

2625 Aquaporin Water Channel
Aquaporins allow water molecules to cross a phospholipid bilayer
Image from Wikimedia Commons
 

Osmosis is a special type of passive transport involving the diffusion of water molecules down a concentration gradient occurs across a selectively permeable membrane. Osmosis occurs across the plasma membrane that surrounds all living cells. Most of the diffusion of water through the plasma membrane occurs through special proteins called “aquaporins.” Therefore, osmosis through a living membrane is actually an example of facilitated diffusion.

In this investigation, dialysis tubing serves as an excellent representation of the plasma membrane. The enclosed tube may, for the purpose of this experiment, be considered a single living cell in greatly enlarged form. Dialysis tubing membranes are made of purified cellulose containing microscopic pores. The pore size is controlled during manufacturing. The pore size determines the membrane’s permeability to molecules of different sizes. Typically, dialysis tubing will only allow smaller molecules to pass through the membrane, while larger molecules will remain in the dialysis tubing. For example, you learned from the Membrane Function Inquiry Investigation that starch molecules are too large to fit through the pores in the dialysis tubing and therefore will not diffuse through the membrane.

But what about water? Is the dialysis tubing permeable to water? In other words, will osmosis occur through the dialysis tubing?

Planning Your Experiment

Your group will need to develop an experiment or series of experiments that will allow you to answer the following research question:

Does osmosis occur across the dialysis tubing membrane?

Remember that a controlled experiment should test a single independent variable. In order to draw a meaningful conclusion, you need to be able to compare the outcome of your experiment with what would happen if you did not manipulate your the variable you have chosen to test.

With all of this in mind, consider the following questions to help you get started:

  • What variable will you be testing (independent variable)?
  • What variable(s) will you be measuring (dependent variable)?
  • What variables will you hold constant (constant variable)?
  • What evidence would confirm that water has crossed the membrane?
  • How will you be confident in the validity of your results?
  • What will you use as a standard of comparison (control group)?

Navigate to your group’s page below to plan and document your experiment.

Select Your Page Below

Hour 1 Hour 5
Group 1 Group 1
Group 2 Group 2
Group 3 Group 3
Group 4 Group 4
Group 5 Group 5
Group 6 Group 6
Group 7 Group 7
Group 8 Group 8

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Mammal Monday – What DOES the Fox Say?!?!

Find the answer to this most pertinent question here.


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Weedy Wednesday – Horseweed

Did you know?

The Zuni people insert the crushed flowers of the canadensis variety into the nostrils to cause sneezing, relieving rhinitis.


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Membrane Function Lab Planning Center

Semipermeable membrane
Image from Wikimedia Commons

Diffusion is the spontaneous tendency of molecules to spread apart and move from areas of high concentration to low concentration. Passive transport occurs when substances diffuse across biological membranes. Biological membranes are selectively permeable, which means that some substances can pass through the membrane and some cannot. Passive transport does not require energy, distinguishing it from active transport, which does require energy.

Osmosis is a special type of passive transport involving the movement of water molecules. During osmosis, the diffusion of water molecules down a concentration gradient occurs across a selectively permeable membrane. Osmosis occurs across the plasma membrane that surrounds all living cells. In this lab, dialysis tubing membranes will be used to demonstrate the properties of a selectively permeable membrane in relation to osmosis.


Dialysis Tubing is Selectively Permeable

Dialysis tubing membranes are made of purified cellulose containing microscopic pores. The pore size is controlled during manufacturing. The pore size determines the membrane’s permeability to molecules of different sizes. Typically, dialysis tubing will only allow molecules with low molecular weights to pass through the membrane, while larger molecules will remain in the dialysis tubing. In this investigation, dialysis tubing serves as an excellent representation of the plasma membrane. The enclosed tube may, for the purpose of this experiment, be considered a single living cell in greatly enlarged form.

As you and your group prepare for the Membrane Function Inquiry Lab, there are several things you need to consider before you begin. This page has been designed to help you collaborate with your fellow group members in preparation for the the lab.

Your group will need to develop an experiment or series of experiments that will allow you to answer the following research question:

Does starch diffuse across the dialysis tubing membrane?

Remember that a controlled experiment should test a single independent variable. In order to draw a meaningful conclusion, you need to be able to compare the outcome of your experiment with what would happen if you did not manipulate your the variable you have chosen to test.

With all of this in mind, consider the following questions to help you get started:

  • What variable will you be testing (independent variable)?
  • What variable(s) will you be measuring (dependent variable)?
  • What variables will you hold constant (constant variable)?
  • What evidence would confirm that starch has crossed the membrane?
  • How will you be confident in the validity of your results?
  • What will you use as a standard of comparison (control group)?

Navigate to your group’s page below to develop the plan for your experiment.

Select Your Page Below

Hour 1 Hour 5
Group 1 Group 1
Group 2 Group 2
Group 3 Group 3
Group 4 Group 4
Group 5 Group 5
Group 6 Group 6
Group 7 Group 7
Group 8 Group 8

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Mammal Monday – “That’s One Fat Squirrel!”

Beaver lake
American Beaver (Castor canadensis)
Image from Wikimedia Commons

My daughter and I were tagging monarch butterflies last Fall when she spotted what she thought was a squirrel. As we moved in for a closer look, we realized we were actually looking at a very different animal. As I reached for my phone to snap a quick picture, we heard a loud “plop” and realized that a beaver had just slipped back into the creek. Oh well, the picture above is a much better one that I would have been able to obtain with my phone.


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Cell Analogies Project – Due Friday, October 6th

“It takes over then thousand cells to cover the head of a pin, but only one Cell Analogies Project to cover a large part of your Honors Biology grade!”


(Click for larger image)

Instead of an exam for this unit, you will be completing a “Cell Analogies Project.”

Quite a bit of time will be given in class for you to work on this project, so it is important that you come to class fully prepared to work.

This project will count as a 40-point grade in the “Assessments” category, a 15-point grade in the “Science and Engineering Practices” category, and a 20-point grade in the “Class Work” category. It is therefore going to be a major part of your grade for this nine-weeks grading period. As always, you should do your very best work.

The projects will be due on Friday, October 6th. You will be presenting your projects to others in a small group during class that day.

The guidelines and worksheets for the project are available below along with a video that will help you visualize these cell parts:

Guidelines:
Grading Procedures:
Structures and Functions:
Cell Analogies Worksheet:


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