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Membrane Function Lab Planning Center

Semipermeable membrane
Image from Wikimedia Commons

As you and your group prepare for the Membrane Function 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.

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 movement of water molecules down of concentration gradient 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 channel proteins called “aquaporins.” Therefore, osmosis through a living membrane is actually an example of facilitated diffusion.


Dialysis Tubing is Selectively Permeable

In this investigation, dialysis tubing membranes, living potato cells, living carrot cells, and living Anachris cells will be available to demonstrate the properties of a selectively permeable membrane in relation to osmosis. Dialysis tubing membranes are made of purified cellulose containing microscopic pores. The pore size is controlled during manufacturing and 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. Potato cells, carrot cells, and Anachris cells are surrounded by selectively permeable living membranes composed of phospholipid bilayers with embedded aquaporins allowing diffusion of water through them.

But how do we know that water can cross these membranes? Will osmosis occur through the dialysis tubing? Will osmosis occur through the living membranes of potato cells, carrot cells, or Anachris cells?

Planning Your Experiment

Your group will need to choose one of the provided membrane sources and develop an experiment or series of experiments that will allow you to answer the following research question:

Does osmosis occur across the 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 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 variables)?
  • What evidence would confirm that water has diffused across 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 4Hour 6
Group 1Group 1
Group 2Group 2
Group 3Group 3
Group 4Group 4
Group 5Group 5
Group 6Group 6
Group 7Group 7
Group 8Group 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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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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Election 2019 – “Organelle in Chief”

eukarya_emblem

You and your partner have teamed up to run a campaign for one of the cell organelles in the Domain “Eukarya.” You have been hired for your expertise and knowledge of cells, and their organelles’ structure and function.

Your primary task is to create a campaign that persuades others to vote your organelle as Organelle in Chief of Eukarya. You will have to argue that without your organelle, the cell, the organism, and consequently the world as we know it will collapse. To do this expertly, you must understand the details of the organelle whose campaign you are running. Knowing all about the organelle and its function and why it is the most important one in Domain Eukarya is paramount in winning this election!

Successful campaigns are multifaceted and are composed of many different elements. Your campaign must have the following elements:

Cell Parts: Structure and Function Worksheet

Before you can start your campaign, you must be familiar with all of the organelles that are found in eukaryotic cells. You can think of this assignment as “opposition research.” Most of these organelles will be your potential opponents in the campaign, but your candidate organelle must be able to work alongside each of them for the well-being of the entire cell. You must submit this assignment to Mr. Mohn before you will be allowed to select your organelle. It will be due by the end of the class period on Monday, September 30th.

Campaign poster

Your poster will be uploaded to the course website. It must meet the following requirements:

  • The poster should be very visually striking and in color.
  • Posters should be digitally generated. The program you use to generate your poster is up to you. There are lots of free poster generators available!
  • Your campaign’s poster must champion the greatness and good deeds of your organelle. You may include a description of why voters should choose your organelle above all others in the election.
  • You may include information that can smear another organelle. Of course, it must be school appropriate!
Post your Campaign Poster
Hour 4Hour 6

Campaign Flyer or Newspaper Article

In addition to your poster, you need to create informational campaign flyer or newspaper article that describes how amazing your organelle is.

  • Include a catchy graphic or two as well as details about your organelle’s structure and function.
  • You must relate the structure of the organelle to its function. It is critical for you to make the connection for your voter about why your organelle is the most important. The purpose of the flyer or article is to tell your voter why your organelle is important for the continued survival and growth of the Domain Eukarya. What would happen to an organism/ecosystem if your organelle was NOT the Organelle in Chief?
  • You must have properly cited references for your flyer. Do not use Wikipedia as your only source of information. Be sure you are using other scholarly sources of information, such as university websites, sources from the class website, and your textbook. Make sure you cite your information as well.

Election Day Speech

On election day, you will give your campaign speeches on behalf of your organelle. You and your partner will give the speech to the class and your flyer will be passed out that day as well.

  • In your speech, you need to convince the voters based on structure and function that your organelle is the most important. You should also address how you will work with the other organelles if you win the election.
  • You and your partner will have 3 minutes to give your speech. Your group will need to submit a transcript of the speech on the same day, complete with references. Be creative, be informative, be accurate in the information you present and most importantly, sell your organelle to the voters! You may be as creative as you wish, as long as you are ethical and school appropriate.

Good luck, and may the best organelle win the election!


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