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Thursday, September 27, 2012

Microscope Fun!


Last week, I remembered a very important lesson in school teaching..... Sometimes the simple things work the best in the classroom!

What do you do in high school biology on a day that is destroyed by homecoming interruptions?  Pull out the microscopes and let the kids have some fun!  I have a great 2-day lab that I have used in the past on the microscope.  I haven't used it in a few years because I have been favoring labs that are more "technology oriented" that use probes, graphing calculators, and spectrophotometers.  But I was reminded last week that sometimes the kids like the "old stuff" like a good old fashioned microscope.

During two days of homecoming activities at our school, I knew that my students would be bouncing off the walls, and we were running an abbreviated schedule each day.  I pulled out my old tried and true microscope lab and put the students to work.  They looked at all kinds of things and had a blast doing it.  I had forgotten how excited students can get about pond water!

My lab has 5 parts:

  • In the first part, students compare plant cells to animal cells.  I used onion skin as the plant cell and cheek cells as the animal cell.  
  • The second part is called "Cells with Chloroplasts."  Students looked at the leaf from the Elodea plant. 
  • The third part is called "Cells with Chromoplasts."  Students looked at the skin from an apple or a tomato.
  • The fourth part is called "Storage in Cells."  The students placed a bit of potato pulp on a slide, added a drop of iodine, and observed the very large starch grains found inside the cells.
  • The fifth part of the lab is "Fun with Pond Water."  My students had a blast with this.  I gave extra credit to students who brought in pond water samples, and we had many samples to choose from.
It was very gratifying to see the students have so much fun with such a simple activity.

Have fun teaching!!

Saturday, September 22, 2012

Very Simple Diffusion and Osmosis Experiment


The concept of cellular transport (diffusion, osmosis, hypotonic, hypertonic, active transport, passive transport) is fundamental to a biology class.  There are so many great ideas for labs that teach and explore these concepts.  Just this week, our biology students completed an activity that is so very simple, but it really illustrates the concept of semipermeable membranes.


Students are given 2 pieces of dialysis tubing.  One is filled with a starch solution and the other is filled with a glucose solution.  Each is placed into a cup containing tap water.  The cup that contains the starch tube also has iodine added to the water in the cup.

After setting up the experiment, students are asked to wait 20 minutes before recording their results.  The students immediately recognize that the dialysis tube containing starch is beginning to turn purple.  The iodine molecules in the cup of water are diffusing across the dialysis tube membrane and are causing the starch molecules to turn dark blue or black.  In addition to this observation, students are given a glucose test strip and asked to test for the presence of glucose in water of the second cup.

Students allow their experiment to sit overnight.  Observations are made and results are recorded again after 24 hours.  All students quickly determine that:  (1) Starch did not leave the bag.   (2) Iodine moved into the bag.   (3) Glucose moves out of the bag slowly.  (This is evidenced by the fact that the initial test for glucose after 20 minutes is negative, but the test is positive after 24 hours.)  (4) Much water moves into the bag.

From these observations, students are asked to make predictions about the size of the molecules, and must place the molecules in order of their size from smallest to largest.

The lab that I use with my students can be found here:  Diffusion Through a Non-Living Membrane.

FREEBIE:  You might also want to try this lab:  The Effect of Concentration on the Rate of Diffusion. This is a free download....Enjoy!

Sunday, September 16, 2012

New FREEBIE: A Compare and Contrast Graphic Organizer


With the increasing amount of information that our students are expected to learn and master, it is more important than ever to provide them with the tools they need to organize and study difficult concepts.

This free graphic organizer can help your students learn to delve deeper into the content to search for similarities and differences between two topics or concepts.


This can be used in all subject areas and in grades 4 and up.  My students even admit that this technique has improved the way they view the content that we cover each day.  The graphic organizer can be used to compare and contrast any two topics or concepts.  I have used this organizer to have my students compare and contrast:
  • Photosynthesis to cellular respiration
  • Mitosis to meiosis
  • Protostomes to deuterostomes
  • Vascular plants to nonvascular plants
  • Systems of the body
  • DNA to RNA


You can download this free graphic organizer by clicking on any of the above pictures, or on this link:


Enjoy!  ...And have fun teaching!


Friday, September 14, 2012

Math and Biology: Math Every Day!


We must increase the use of biology mathematics in our lessons!

I am WAAAAYYYY up high on my soapbox today.  This is year #29 for me in the biology classroom.  I have been seeing this shameful trend for several years now..... Students cannot do math in the biology classroom!

In the past, biology was a largely descriptive science.  We had our students peer into microscopes day after day.  Lab reports consisted of many drawings, hopefully drawn in pretty colors with the "parts" accurately labeled.  Now don't get me wrong;  I still love a microscope.  I can sit for hours and look at drops of pond water.  It is still, after all these years, absolutely fascinating to me!  Moreover, my students still love these types of labs.  However, several years ago, I began to change the type of lab I use in my biology classroom.  I now favor a lab that is quantitative and requires the use of math in biology.

Math & Science:  The Problems I Face Each Day

This is what I see everyday in my classroom.  I know that science teachers everywhere will shake their heads in agreement with these problems.

  • Students cannot do even the simplest of arithmetic without a calculator!  Why, oh why, did we (educators) ever decide it was okay to let students learn math at the elementary levels by using a calculator?  I would like to be the leader of the "Ban the Calculator" movement.  Yes, I am being overly dramatic.  The calculator is a very useful tool, but many of our students are so "calculator-dependent" that they have lost the meaning of the math.

  • Students do not have any common sense when it comes to math.  In their minds, whatever comes up on the calculator display MUST be the right answer. They do not stop to think if the answer is reasonable.  
  • Students cannot do arithmetic.  I wager to say that if I passed out a test that required the use of long division, many of my students might fail.  Further, many students don't know their times tables.  Over and over, I will see a student reach for calculator to multiply two numbers that they should already know!  Funny (but not funny) is that many of my AP Biology students are excelling in AP Calculus, but can't do arithmetic!
  • In the middle school grades, we need to quite teaching algebra and geometry and teach fractions, decimals, and percents every single year.
The Course That I Now Teach? Mathematical Biology!

I am slowly, but surely, changing the types of materials that I use in my class.  I am making more of my labs, activities, worksheets, and homework assignments quantitative in nature.  I am sometimes restricting the use of a calculator during my class.  Recently I purchased a classroom set of four-function calculators.  They only add, subtract, multiple and divide!  When I do allow students to use a calculator in my class, this is the only calculator they get to use.

If you want to make your science class more math-based, I have several products that you might want to consider.  Let's start with the ones that are FREE!  Click on the links below and you can download these "math in biology" lessons for free.


This school year, I developed three new activities that are math-based.  I have already used these in my classes, and I am very pleased with the results.

Have Fun Teaching!

Monday, September 10, 2012

Great Biology Lab: Testing Foods for Organic Compounds




It's a little messy, but my students love it!

Today, we completed a lab that is always a favorite for my students.   We have been studying the groups of organic compounds:  Proteins, lipids, carbohydrates and nucleic acids.  So today, my students were given the task of determining which of the organic compounds are found in various foods.

We ran 5 different tests.  We tested for glucose using Benedict's solution. We tested for starch using iodine.  We tested for Vitamin C using indophenol.  We tested for protein using Biuret reagent.  And we tested for lipids by using the brown lunch bag test.

Before giving the students any foods to test, it is best to allow them to "practice".  My students were given a starch solution and told to test it for starch.  Amazingly, it contained starch!!  (haha)  The purpose of this is to let the students see what the positive tests look like so that when the foods are tested, they know and can recognize the results they are getting.


I had my students test cereal, egg whites, egg yolks, milk, yogurt, celery, potato,  and pineapple juice.  Solutions can easily be made by placing the food in a blender with a little water.

There is nothing quantitative about this lab, and that is a drawback, but students really love to perform these simple tests.

Biology Lab: Testing foods for Organic Compounds.

Sunday, September 9, 2012

Free Materials for Science Teaching


Always Free!

I currently have 18 free products for teaching biology and chemistry to students in grades 7 - 12.  These freebies are tried and true.  I use them all the time in my classes, so they are guaranteed to be kid tested and user friendly.

These materials are ready to be copied and passed out to your students.  Each product includes worksheets/handouts for the student, and guides for the teacher.  Answer keys are always included.

Click this link to see all of my freebies.

Enjoy!


Sunday, September 2, 2012

How Do Living Cells Deal With Changes in pH? Buffers!



A Biology Lab Favorite for Me....and My Students Love It, Too!!

The chemical reactions that occur within living cells are required for life, but often result in creating a hazardous work place for the cell.  The internal pH of most living cells is close to 7, and even a small change in pH can be harmful.  Many of the reactions of the cell cause changes in pH that can place the life of the cell in jeopardy. Thankfully, cells can produce buffers which help to maintain a stable pH inside of living cells.

The technical definition of a buffer is:  "A substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution."   A great example of buffers in living systems is seen in human blood.  The pH of human blood is close to 7.4.  A person cannot survive for more than a few minutes if the blood pH drops to 7 or rises to 7.8.  It is critical that the pH of 7.4 is maintained.  The presence of buffers in the blood allows for a relatively constant pH despite the addition of acids and bases.  Buffers minimize changes in the concentrations of H+ and OH- ions.  They do so by accepting hydrogen ions when they are in excess and by donating hydrogen ions to the solution when they have been depleted.

This principle can be demonstrated to your students by a very simple, (but pretty amazing!) lab experiment.  I admit that each school year I really look forward to doing this lab.  It is very easy to set up, doesn't require fancy pieces of lab equipment, works every time, and most importantly, my students are usually very impressed by the results.

Here are the key point to the lab:

  • Students begin by placing tap water in a beaker. They add drops of dilute acid one drop at a time and record the pH after each drop.  They repeat a second time, but add a dilute base. Predictably, the pH drops significantly with the addition of the acid and rises significantly with the addition of the base.
  • Now it is time to test living cells.  Students are given a liver solution to which they add drops of acid and base.  There is very, very little change in pH.  Students will often call me over and say that their pH meter is not working because there is so little change in the pH readings.  
  • Students repeat by using a potato solution to show that plant cells produce buffers just as animal cells do.
  • Results are graphed and followed by final analysis questions.
I use the pH meter that you see in the above photo.  These are relatively inexpensive and are pretty durable.  The set that I use has been in use for years, and they are still going strong.  Batteries are easily replaceable, but rarely need to be replaced.  If pH meters are unavailable, this lab can easily be conducted using pH paper.  This lab is suitable for grade 8 and up.  I hope that you will give this lab a try.  You will not be disappointed.

Have fun teaching!