Semi- Permeable Membranes (Russell)
Principles investigated: Selective permeability of a membrane as a function of molecule size in general, diffusion, concentration gradients, states of equilibrium, volatility
Standard: 7th-10th grade, Biology/Life science, 1A
Materials: (modified from Janice Vancleave “Spicey Escape”)
§ A large gallon sized ziplock bag or some other large container that can be sealed (almost any grocery store)
§ A balloon (Craft or party store, many convenience stores, some drug stores)
§ Small funnel (craft or grocery store)
§ Vanilla extract (grocery store)
§ A small glass baby food bottle that has been cleaned (craft stores, Target, Kmart etc, some grocery stores)
§ Molasses (grocery store)
§ Tape or some other means to seal glass jars
§ String or some other means to seal the balloon
§ 1 tbsp of vanilla extract
§ 1 tbsp of molasses
Procedure: Can be done in groups of two or four ideally
Step 1
Assign the following jobs:
The principle smeller
The principle recorder
Who is going to set up the jars?
Who is going to set up the balloons? (The person or person s that can actually blow up balloons is ideal)
Step 2
Prepare your jars including labels (One jar is molasses and one jar is vanilla)
Prepare your bags including labels (One bag is molasses and one bag is vanilla)
Step 3
Safety note: Use your hands to wave the odor towards you if needed
Smell
Record
Consider
Preparing balloons
Place 1 tbsp of vanilla extract in a balloon (be careful not to get any on the outside of the balloon)
Blow the balloon up just enough so that it will fit in your ziplock bag
Place in ziplock bag and seal and leave in for one hour
Preparing jars
Pour 1 tbsp of molasses in a jar; seal, and label
Pour 1 tbsp of vanilla extract in a jar; seal, and label
Student prior knowledge:
Should be aware of the fundamental difference between
Prokaryotes: Prokaryotes are cells in which the genetic material is not enclosed by a central nucleus
which is not surrounded by a membrane, has no organelles enclosed by a membrane,
and tends to be smaller than eukaryotes
Eukaryotes: Eukaryotes are cells with a central nucleus surrounded by a nuclear membrane
and membrane bound organelles
All things once living or living is made up of cells containing at least one membrane. In the case of prokaryotes the only membrane is the one that separates the organism from its environment
Everything in a cell has a role or function that is dependent at least in part on its construction and composition.
Every living or once leaving organism is made of cells of some sort although the parts can very greatly
Questions & Answers:
At the beginning (In groups or individually by white boards)
1. Is all living or once living organism made up of cells in some form? Yes No
2. Prokaryotes are cells in which the genetic material is not enclosed by a central nucleus Yes No
which is not surrounded by a membrane, has no organelles enclosed by a membrane,
and tends to be smaller than eukaryotes
3. Eukaryotes are cells with a central nucleus surrounded by a nuclear membrane Yes No
and membrane bound organelles
After data collection:
What possible reason is there that can account for the fact that you could smell both the vanilla and the molasses when you opened the bag but could not smell either outside of the bottle?
1st part of the answer: Relative volatility
The vanilla extract has substances in it that are highly volatile. In the case of Vanilla extract the oils are suspended in a form of alcohol which was used in a distillation process. The type of alcohol commonly used is highly volatile and easily vaporizes at relatively low temperature which is in this case room temperature. In the process of making molasses a wide range of volatile substances become present from the breakdown of sugars. In one particular study hydroxymethylfurfural, acetoin, levulinic, and formei acids were found that are organic and highly volatile.
2nd part of the answer: Composition
The balloon has microscopic holes in it assuming the balloon has not been damaged. The glass in the bottles is nonporous so once the top is sealed its volatile components are trapped inside
What are some places that you might find semipermeable membranes? (After ideas are given if none of yours are mentioned add those that have not been)
Follow up activities and subjects
There are some labs that directly model a cellular membrane
Next you could do labs that use illustrate both semipermeable membranes and concentration gradients
Discuss cellular transport
Compare and contrast how stomata in leaf structure and proteins embedded in cellular membranes act as physical gateways
Applications to everyday life:
SPMDs that use a very specific kind of semipermeable membrane can be used to monitor potruelom spills: The preferred characteristics of chemicals samples by this device is a log octanol – water partition coefficient greater than 3 and a cross sectional diameter less than 1 nanometer that is suspended in the water column. The chemicals in a broad sense that fit the criteria are a range of petroleum constituents and other non-ionic hydrophobic chemicals.
Used to purify water by the use of a semipermeable membrane: Water is forces through a semipermeable membrane that is designed to stop particles of a certain size the primary one being salt but other containmenants can be strained as well. This works against the tendency of water to move from a less salty to a saltier concentration in an attempt to dilute the much saltier concentration therefore bring about a state of equilibrium.
Semipermeable membranes and power generation: Work is underway to create a power plant that uses semipermeable membranes as part of a power generating process. This process begins usually with fresh water that has a very low salt concentration and another solution with a very high salt content under high hydralic pressure. The high hydraulic pressure makes it very sensitive to any increase in pressure assuming its container volume stays constant. When the fresh water begins moving into the saltier concentration in an attempt to reach equilibrium across the membrane the volume of the saltier solution increases. The increase of pressure is then released through a turbine. The applied hydrolic pressure is recovered through the use of a pressure exchanger system.
References:
Snedden, Robert. The World of The Cell; Life On A Small Scale. Heinemann Library; Chicago, Illinois 2003 Reed Educational & Professional Publishing
VanCleave, Janice. Biology, For Every Kid; 101 Easy Experiments That Really Work. Spicey Escape P.1 San Francisco, Ca. 1990 Jossey-Bass A Wiley Imprint
Biology by McDougal Littell. 2008 McDougal Little
Alvarez, David, 2010, Use of semipermeable membrane devices (SPMDs) in petroleum polluted waters: U.S. Geological Survey Fact Sheet 2010–3051, 2 p. Retrieved on December 3, 2011. From http://pubs.usgs.govv/Fs/2010/3051
Olbrich, Hubert. Fermentation Technologist, Institut Fur Zuckerindustrie. Molasses. Retrieved on December 3, 2011 from www.btkempe.de-Molasses
Fresh Water and Electricity Through Osmosis] The Green Optimistic. Posted by Christi on January 15, 2009 and retrieved on December 3, 2011 from http://www.greenoptimistict.com/2009/01/15/freshwater-and-electricity-through-osmosis
Water Treatment Alternatives-Reverse Osmosis. Retrieved on December 3, 2011 from http://www.allaboutwater.org/reverse-omosis.html
Volatility-Volatility, Animal, Liquid, and Animals-Jrank Articles. Retrieved on December 3, 2011 from http://www.science.jrank.org/pages/7250/Volatility.org
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