FREE Osmosis/Difusion Lab

Cell membranes and the transport of materials across membranes is fundamental to a study of biology.  There are, fortunately, many good lab activities that can be carried out when covering this material.  My students just finished doing this lab today.  It is called "The Effect of Concentration on the Rate of Diffusion", and you can download my version of this lab for free.

The concept is very simple.  First, the students fill dialysis bags with varying concentrations of sugar solutions.  The bags are then massed.

Each dialysis bag is placed in a cup of distilled water. The cups are allowed to sit for some period of time.  I have the students wait for 30 minutes, pull the bags out of the cups, and determine the final mass of the bag.  We get very good results in just thirty minutes.  If necessary, you can leave them overnight and get the final mass the next day.

The results are dramatic.  Students will clearly see the relationship between solute concentration and the rate of diffusion across the membrane.

Results are graphed showing the direct relationship between solute concentration and rate of diffusion.

This is one of my favorite labs and is a free download.  I hope you doing this lab as much as I.

FREE DOWNLOAD

The Effect of Concentration on the Rate of Diffusion

Other products related to this topic include:

Determining the Osmolarity of Cells

Lab: The Effect of Solutions on Cells

Transport Across the Membrane Jeopardy Review Game

The Perfect Hands-On Experiment for Visualizing Osmosis and Diffusion

I love it when I get to this point in my biology curriculum. We have covered the skills of scientific measurement, scientific method, and microscopy. Now the students are prepared to use these skills on more complex topics, and the labs get much more interesting. The concepts of cellular transport, structure of a membrane, movement across the membrane, active and passive transport, cytolysis and plasmolysis are leading us to more complex topics. A solid knowledge of these concepts is needed before diving into cell communication, photosynthesis (thylakoid membrane transport) and cellular respiration (cristae membrane transport).  As students develop their knowledge base, it becomes like a "connect the dot" puzzle. The student has all the dots, and you (as the teacher) are leading them from dot to dot, helping them to make those important connections.

Labs involving cellular transport are often very simple, but they pack an educational punch. The first transport lab I do is a very simple lab called Osmosis and Diffusion: Transport Across a NonLiving Membrane.

Pieces of dialysis tubing are filled with either a glucose or a starch solution which is then placed in a beaker of water. In the beaker containing the starch bag, iodine is added to the water in the beaker. In the beaker containing the glucose bag, students used a glucose test strip to determine if glucose is moving across the membrane. 

Results are recorded after 20 minutes, and again after 24 hours. The results are dramatic and my students immediately grasp the concepts taught by this lab:  

• The smaller the molecule, the faster it can cross the membrane.
• Some substances are too large to cross the membrane.
• Movement of materials occurs in both directions.
• Water is the substance that most dramatically affects the volume of a cell.

This is a very simple way to get the basic concepts of osmosis and diffusion across to our biology students. Hands-on and highly visual is the way to go.

Other resources used in my teaching of cellular transport include the following. Click the links below to view in my TPT store.

• Cell Transport Color By Number
• Cell Chat! A Lab Station Activity
• Cell Transport Worksheets and Study Guide
• Lab: A Qualitative and Quantitative Study of Osmosis and Diffusion
• Lab: Osmosis and Diffusion in Living Cells
• Cell Structure and Function PowerPoint and Notes Set

Have fun teaching cellular transport!

Man -vs- Squirrel (The squirrel wins!)

I love nature and wildlife of all shapes and sizes, but this pesky little squirrel is just about to get on my last nerve!

This has been an ongoing problem.  I really love my bird feeders.  We sit at our kitchen table for every meal and watch the birds out of the large windows that overlook our deck.  The hummingbirds are my favorite.  I have two hummingbird feeders and a nesting pair lives in the tree in the background.

My dear, sweet husband bought this feeder pole system for me to help with the squirrel problem.  It is a single (very skinny) pole that has 4 separate hangers at the top.  It is SUPPOSED to be SQUIRREL-PROOF!  At least, that is what it said on the box!

I do love the squirrels.  They have their own feeding station down by the pond.  I put out corn and sunflower seeds for them.  Why do they have to be so naughty when I provide them with their own separate dining room?

Look at the poor birds on top of the pole.  They are thinking, "Are those squirrels going to leave anything for us?"

Well...... In the battle of man versus squirrel, the squirrel has won.  I am off to Wal-Mart.  I am going to buy a very large can of Crisco Shortening, and I am gonna GREASE that pole.  Let's see if the squirrel can navigate that!  I'll keep you informed!

Science Skills: The Compound Microscope

Is teaching a student how to properly use a microscope considered a "science skill"? I think it is!

The regular followers of my blog know that I consider the teaching of "science skills" to be some of the most important lessons we teach all year long.  Our students probably won't need to be able to label the parts of the crayfish as adults, but they will always need the skills of science in their everyday lives.  I think it is imperative that we teach our students skills that involved problem solving and critical thinking.  Don't get me wrong, the "facts" we teach in science are important, but I have always found that if I do a great job in the "skills" area, the facts always fall nicely into place.

So the question of the day is:  Is having the student peer into a microscope considered a skill that teaches critical thinking and problem solving?  I say "YES",  but it will be up to the teacher to make the activity inquiry-driven and skills-based.  I think microscope work is important for the following reasons:

• Excitement!  Let's face it ... everybody loves the microscope. Kids get excited about science by viewing the microscopic world.
• Students realize there is a "whole new world" out there.  Awareness of Earth's biodiversity will make our students better caretakers of the environment in the future.
• Microscope work reinforces measurement skills.  Students get practice in estimation, comparison, and the use of metric measurements.
• Critical thinking skills are required:  What impact does this microorganism have on other species?  Is the microorganism photosynthetic? If so, how will its disappearance from the aquatic ecosystem affect life on Earth?
• Most of our students have not matured to the "abstract learner" stage.   Microscope work helps a student who is a concrete thinker by allowing them to "see, feel, and touch" things that are not normally visible to them.  You can show them plasmolysis occurring in a plant cell.  You can show them the chromosomes inside a cell.  You can show them sperm cells racing off to fertilize an egg cell.
• You can teach cause and effect.  What happens when a cell is placed in this solution as opposed to that solution?
• If nothing else... it is a great exercise for reinforcing hand-eye coordination!

The bottom line?  The microscope is just plain fun, leading to increased student excitement for your science class.  Plus, it reinforces the skills of science!

Check these out:

Microscope Bundle

Microscope Chat

Quotes from Albert Einstein

Look at this face.....

What's not to love?

I am totally in love with Albert Einstein!  My classroom walls are full of posters with his pictures and quotes.


I find some of his quotes to be simply amazing, and they inspire me everyday as I try to help my students make sense out of the scientific world.   I thought I would share a few of my favorites:

"Two things are infinite: the universe and human stupidity; and I'm not sure about the universe." 
— Albert Einstein

"Insanity is doing the same thing, over and over again, but expecting different results." 
— Albert Einstein

"If you want your children to be intelligent, read them fairy tales. If you want them to be more intelligent, read them more fairy tales." 
— Albert Einstein

"The difference between genius and stupidity is; genius has its limits." 
— Albert Einstein

"When you are courting a nice girl an hour seems like a second. When you sit on a red-hot cinder a second seems like an hour. That's relativity." 
— Albert Einstein

"I speak to everyone in the same way, whether he is the garbage man or the president of the university." 
— Albert Einstein

"Life is like riding a bicycle. To keep your balance, you must keep moving." 
— Albert Einstein

"Once you can accept the universe as matter expanding into nothing that is something, wearing stripes with plaid comes easy." 
— Albert Einstein

"Everybody is a genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is stupid." 
— Albert Einstein

"What is right is not always popular and what is popular is not always right." 
— Albert Einstein

Science Skills: Significant Digits

Every year, the same great debate arises in our science departmental meetings .....  should we or should we not teach the rules of determining significant digits?  The members of the department have their reasons for being "pro" or "con" and it seems to me that the same people have the same reasons year after year.  Are we teaching significant digits because it is an important science skill, or just because it is found in the first chapter of the chemistry text book?

I tend to fall in the "pro" camp.  I think teaching significant digits is an important science skill to teach because:

• It teaches the student the importance of making accurate and precise measurements.
• It teaches the student how to look at the data in a scientific article and determine how accurate others have been in their measurements.
• It teaches students how to learn a set of rules and then apply these rules to many examples.
• It teaches critical thinking and problem solving skills.
• It reinforces basic math skills when completing problems that involve calculations and rounding to a given number of significant digits.
• It allows the opportunity to do a quick review on metric units.  (MANY kids need this!)

The people who think we should leave this out have pretty lame reasons (excuses) for their point of view:

• It's boring.
• Nobody needs to know this stuff any more.
• It's archaic.
• After you teach it in the first chapter, you never use it again.

The bottom line is that this is a tool of science, and for that reason, we need to makes sure our science students have this tool in their arsenal.  All research scientists know that there is "error" in their work.  The use of significant digits allows others a way of recognizing how much error exists in a set of measurements. 

Meanwhile, here are a few of the materials that I have developed and use as I teach significant digits.....I think it is still important!

Significant Figures Bundle

Significant Figures Lab

Significant Figures Jeopardy Review Game

Science Skills: Lab Equipment and Scientific Measurement

At the beginning of each new school year, it is essential that a science teacher instruct his/her students in the basic science skills.  This includes laboratory safety,  instruction in how the lab equipment operates, making proper scientific measurements, how to apply the scientific method, the importance of graphing and data analysis, and a review of basic math skills such as scientific notation.  I have already posted about several of these.  (See the posts below this one.)  Today, I want to emphasize the proper use of lab equipment and how to make scientific measurements.  

During a lab, a variety of tools may be used to allow the student to use an inquiry process to gather information, both qualitatively and quantitatively.  If the student is to reach the desired conclusion, it is imperative that they receive proper instruction on the use of the equipment they will be using. Scientists use a variety of tools to explore the world around them, and these tools are important to the advancement of science.  The tools may be simple or very complex.  One of the first labs I complete with my students is called:  Use of Lab Equipment and Data Analysis.  (You can download this one for free!)  It provides instruction on the basic pieces of lab equipment such as the meter stick, Celsius thermometer, graduated cylinder, and the quadruple-beam balance.  We teachers often assume that all students can use a meter stick, a graduated cylinder, a quad beam balance, and a thermometer, and that they can use all of these accurately.  This is not always true.  It is worth our time to spend one day in lab reviewing the proper use of these basic pieces of lab equipment.  After all, these tools will be used in our classes all year long.

When teaching the proper use of lab equipment, you must also give adequate instruction in how to make precise and accurate scientific measurements. I find that many students will need a short re-fresher on the metric system.  As for accuracy and precision in making measurements, it is the nature of the teenagers I teach to rush, rush, rush to get through with the experiments, giving little thought as to whether or not their data seems reasonable or logical.  If and when time allows, I often require my students to run multiple trials during an experiment to verify their results.  Unfortunately, due to the nature of a school setting, students have learned that science occurs in a 45 minute period of time, and that the first set of data is perfect and acceptable. We, as teachers, do what we can do with the schedule forced upon us by our schools, but you must try to give opportunities that require students to repeat and verify lab data.

Here are some of the materials that I have developed to help with the instruction and reinforcement of these basic science skills:

Free Lab:  Use of Lab Equipment

Lab: Making Metric Measurements (Length, Mass, Volume, and Temperature

Measurement Madness

Significant Figure Lab