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Monday, February 25, 2013

Leaf Pigment Chromatography

Our Biology I students just finished up a lab in which the leaf pigments are separated by paper chromatography.  It might seem like an odd time of year to be studying leaf pigments and photosynthesis, but our school runs a trimester system, and a student might be in any given semester of a class at an odd time of the year....... A discussion topic for another day!

As I am writing this, it has occurred to me that I have written on this topic before.  I just took a look back through all of my old blog posts, and I have indeed discussed this topic previously!  Now that I have re-read that old post, I am pretty pleased with how it turned out.  Check out this link to the previous post, and I will not cover the same content again:


Here are some new pictures that I took as my students were working on their lab.


Spinach leaves are placed in a mortar and pestle along with a little acetone.  Students grind the leaves until the acetone turns a dark green.  A small piece of capillary tubing is used to transfer drops of the pigment extract to a piece of chromatography paper.


When enough drops have been placed on the chromatography paper to make a dark green circle on the paper, it is ready to be placed into a large 25x200 test tube.


The large test tube has about 1/2 inch of petroleum ether in the bottom of the tube.  The pigments will immediately begin to separate.

Here is the finished chromatogram:

Here is the lab that I use with my students:

Click picture to see product.



Sunday, February 17, 2013

AP Biology Exam: Teacher In Panic, Students Oblivious



<-------- The teacher feels 
      like this.....

.....and the students feel 
like this!  ----->




Sound familiar?

It is the time of the year when the AP Biology teacher (me) begins to panic.  There are only "x" number of teaching days left, and there is still "y" amount of material that must be covered!  PANIC!

Actually, my students are great.  But it is getting on toward spring time in my part of the country.  The students are tired....very tired!  They have worked hard all year, participated in a ton of extracurricular activities, and they are just worn out!!

It is a difficult time of the year to be sure.  I must continue to teach hard everyday to get all of the material covered.  At the same time, I need to get my students motivated for reviewing for the exam.  It is a fine line to balance.  Push them hard, but don't overload them.

I am fortunate to have a 70 minute class period. (Don't kill me....I realize how lucky I am!!)  Starting this week, we are going to spend the first 15 to 20 minutes of each class period reviewing.  I have written a set of review PowerPoints to use just for this purpose.  These are not teaching PowerPoints.  They are simply slide after slide of questions and answers.  I generally let the students get into groups and make a game out of it.  The group getting the most questions correct wins a prize.  Little Debbie Snake Cakes are a particular favorite award for my students.

Freebie:  Here is the link to one of my review PowerPoints that I have in my TpT store.  It is on organic compounds.  You can easily delete some of my slides and add more slides of your own.

Click picture to download.

If you like the free PowerPoint, you might be interested in my entire set of 25 different review PowerPoints.


How many days are left before Monday, May 13???   :)

Monday, February 11, 2013

Daphnia, Daphnia, How do I Love Thee?



Let Me Count The Ways (of Measuring Your Heart Rate!)

Valentine's Day does not have to go unnoticed in our high school biology classes!  We might not discuss the emotional affairs of the heart, but we can definitely discuss the physiology of the heart!

Each year, during the week of Valentine's Day, I take my biology students to the lab to measure the heart rate in the crustacean, Daphnia.  Since Daphnia is an ectotherm, its heart rate will vary with changes in its body temperature.  (I also pass out a few Dove chocolate hearts along with the lab supplies!)

First we place the Daphnia into a small, water-filled chamber like the one seen in this photo.  A few strands of cotton fibers placed in the chamber helps to restrain the Daphnia while viewing!

A Petri dish is filled with ice water, and the Daphnia viewing chamber is placed on top of this ice water to cool the internal body temperature of the Daphnia.  After a minute or two, the Daphnia is placed under a dissecting microscope, and the fun begins!

Some students have difficulty at first, finding the heart.  Since the exoskeleton of Daphnia is clear, the heart is easily seen.  Once the students find the heart, they are ready to start counting the number of heart beats per minute.


After repeating three trials at the ice water temperature, students fill the Petri dish with water that is at room temperature and repeat.  Finally the students fill the Petri dish with warm water to finish the experiment.  The data from the experiment is fairly consistent from year to year, and students can quickly conclude that the heart rate of Daphnia speeds up as the temperature increases.


My favorite part of the experiment comes on the next day!  On day 2 of this lab, I have my students design their own experiment.   They are asked to design an experiment to test the effect of caffeine and alcohol on the heart rate of Daphnia.  The students must state a hypothesis, describe their experimental and control groups, carry out the experiment, collect their data, graph their data, and come to a conclusion based on their data.


For my honors level and AP Biology students, I have them complete this worksheet to determine the Q10 Temperature Coefficient.


This lab, along with all of the worksheets and a teacher guide, has recently been added to my TpT store.  You can view it here:

Measuring the Heart Rate in Daphnia


Tuesday, February 5, 2013

Biology Careers Mini Posters - A Freebie!



What can you do as a career if you love Biology?

The answer is "Lots and lots of things!!"  Career week is a really big event at my high school.  I was asked to put together a display illustrating some of the many careers that are possible in the field of biology, so I  made a set of 26 mini-posters.  Each poster highlights one career.  There is a picture of a person "doing the career" as well as a very brief description of the career.

I am sharing these as a free download in my TpT store.  

Click on this link ---> Biology Career Posters <--- to download these for free.

These will make a great display in your classroom!







Friday, February 1, 2013

Give the Kids a Brain-Break!



<-----  What I DON"T want to see in my class!

Over the years of teaching I have come to realize that some topics are very difficult for my students.  I find that the students learn and perform much better if I teach in spurts.  I teach a new concept for 15-20 minutes, and then I give my students a "brain-break".  What is a "brain- break"?  I am glad you asked!!

A "brain-break" is a 2 or 3 minute break away from the topic currently being taught.  It is a couple of minutes where the student can relax, and it relieves the tension of a very complex lesson.  I am still a teacher who wants every minute to count.  So during a "brain-break" I usually throw out a bit of science trivia.  These are just fun and interesting facts that teach the student about the amazing natural world we live in.  Over the last few months my "brain-breaks" have consisted of the Mother Nature Awards for Planet Earth.

Here is an example:

These are PowerPoint slides.  I insert one of these slides into a PowerPoint on cellular respiration or photosynthesis or enzyme-catalyzed reactions.  My students have come to expect these little surprises and they get so excited when one of these pops up into my otherwise overly technical lecture.  This is fun, it teaches a bit about the wonders of nature, and best of all, it gives the student just a minute to relax and get focused again before I launch back into the real topic of the day.

After a slide has been viewed, I print it, laminate it, and place it on the wall in my classroom.  I have been very pleasantly surprised at how often students stop by the wall to look at the Mother Nature Awards.

I have put together a group of 20 of these awards and placed them in my store on TeachersPayTeachers.com.  There are two product listings, one for Grades 2-5 and a separate listing for grades 6-12.

The listing for grades 2-5 comes with a set of activity worksheets (42 pages) for the students to complete as the PowerPoint slide is being viewed.  The finished worksheets can be put together to make a great Mother Nature Award book.






The listing for grades 6-12 comes with a worksheet for students to conduct their own research to develop a PowerPoint slide for a Mother Nature Award of their own choosing.  This makes a nice homework assignment for a grade, or for a great extra credit opportunity.



Don't forget that Earth Day is coming up soon.  The Mother Nature Awards are a perfect Earth Day activity.

Have fun teaching!