Science, Engineering and Info Technology Career Day

Date: Saturday, April 14, 2007
Time: 10:00 a.m.
Sponsor: Science Pioneers
Location: Union Station
Description: An new opportunity presented by Science Pioneers in Career Day from 10:00 a.m. to 1:00 p.m. on Saturday, April 14, 2007 at Union Station. Students in grades 8-12 can visit one-on-one with over 30 professionals in a variety of careers. Students will benefit from the expertise of these professionals- coursework, schools and colleges, and related job experience. To ensure adequate materials, pre-registration is required at There is no fee. Please call 816.460.2261 for further questions. Careers represented are aviation, biology, chemistry, clinical hematology, clinical laboratory, dietary, engineering, environmental, fitness, human resources, immunology, informational technology, laboratory management, meteorology, microscope design, nursing, paleontology, pathology, pharmacy, reference librarian, veterinarian and many more.

KC Science, INC–Inspiring Natural Curiosity

KC Science, INC

We have talked a good deal about science communication. I would like to let the list know about a new collaboraton in our region – KC Science, INC, is a partnership of KCPT Public Television, Johnson County Library, Linda Hall Library, Science City at Union Station, Pathfinder Science, Science Pioneers and the Center for Science Education at the University of Kansas, focused on promoting science-related events, encouraging interest in science, advocating for science-based careers and inspiring natural curiosity throughout the community. There is a longer description of our activities below however, I want to let you know about an upcoming events;

Thursday, April 5 @ 8 pm


On Thursday, April 5 @ 8 pm KCPT presents YOUNG SCIENTISTS with John Merrow an inspiring documentary that follows the fortunes of twenty dedicated high school students who, as part of their high school science program, are competing in
the “Super Bowl” of science fairs, the Intel International Science and Engineering Fair. This one-hour PBS documentary tackles the problem of scientific “illiteracy” by showing a powerful way of engaging students in real science.

KCPT will continue the conversation by examining the concerns over “Scientific Illiteracy” in this community and to get the citizens in the region thinking more about the role of “science” in this community. The town hall conversation” featuring people from the world of science, business, education, a couple of young people and a couple of connect-the-dots type trend thinkers: DR. STEVEN CASE is Assistant Director of the Center for Science Education at the University of Kansas, BETTY PAULSELL is program director of SCIENCE PIONEERS, JULIE EDGE is President and Founder of Inside Edge Solutions LLC, JACK CASHILL is Executive Editor of INGRAMS MAGAZINE, DAVID KETCHUM is Science Coordinator for the Kansas City, MO School District, CHRIS KUEHL, founder and Managing Director of Armada Corporate Intelligence, DAVID JEWELL is president of Jewell Baker Zander Inc., ELENA OVAITT is a senior at West Platte High School, DAVID BEIER is a science teacher at Barstow School abd ERIK BERGRUD, Director of Park University’s International Center for Civic Engagement

More on Darwin and his times

John Wilkins at Evolving Thoughts is on a roll. Today he adds more fodder to think about the historical and scientific context in which Darwin worked. Biology teachers preparing to introduce the historical background for the development of Darwin’s Theory of Natural Selection would do well to explore this essay. It’s deeper than you’ll want to present in class or expect students to learn but it may help you to present the process of science in a realistic manner…..

Mammalian Adaptive Radiation at the KT boundary???

This week a paper was published in Nature that calls into question the idea that mammals took off and diversified filling niches vacated by the extinction of the dinosaur megafauna at the end of the Cretaceous. The data is molecular and the paper is at least somewhat controversial. You can find a nice write up about it at PZ Meyer’s Pharyngula Blog with graphs, trees and links. Another good coverage of this article is at: Mike Dunford’s Blog, The Questionable Authority


Darwin’s Delay

One of the most discussed events in the history of biology is the delay between Darwin’s original conception of the theory of natural selection and the publishing of “Origin”. We all know the story. For more than 20 years Darwin kept his ideas mostly to himself and a close circle of colleagues who kept encouraging him to publish. Darwin’s delay has been attributed to his reticence to confront the religious and scientific establishment. Darwin keeps working but eventually he receives a letter from Wallace with essentially the same concepts outlined. Darwin’s colleagues arrange for a mutual presentation and the rest is history. Or is it? Here is a blog entry from John Wilken’s Evolving Thoughts that discusses this situation and a reference to a paper [pdf] presented recently by Darwin scholar, John van Wyhe that suggests that Darwin’s delay was only the result of underestimating the time it would take to complete a scheduled and well thought out research plan. Check it out. It will give you something to think about next time you discuss the history of evolutionary thought in your class.


Authentic Science Activity

Click here to download a pdf of the Worm Lab Directions

Dorsal Blood Vessel

Key terms: toxicity, pulse rate, blood circulation, Phylum Annelida, Class Oligochaeta, freshwater invertebrate

a model for students to conduct real experiments that they design based on a simple “model organism”known as black worms. With very little effort it is possible to provide students

The student will be able to observe and record the pulse rate of Lumbriculus variegatus ( an aquatic segmented worm).

The student will design and carry out an experiment showing the effect of various substances on the pulse rate of Lumbriculus variegatus.

Follow the link to an Adobe PDF copy of this lab developed by Randy Dix and the American Physiology Society. Additional teaching resources at my site.

These worms were made famous by the late Charlie Drewes and many of the techniques are of his design. His website is an invaluable resource and many thanks go to those that maintain and support his teachings. Continue reading

Bloggers Bioblitz

Last spring the KABT field trip attempted to take part in a Bioblitz. KABT was originally going to do their own a Kanopolis with cooperation of Kansas Wildlife and Parks. However, we weren’t sure that our inexperience would get in the way so at the last minute we decided to take part in a KC metro bioblitz. Unfortunately, only KABT president Randy Dix was able to participate. Here’s a link to a group of bloggers that are putting on a blogger’s bioblitz. This is definitely something an individual biology class could do and report on…..

Studying Photosynthesis with the Floating Leaf Disk Assay

Post edited and modified Aug. 23, 2014

For years, I have promoted the floating leaf disk assay as one of the best ways for students to explore factors that affect photosynthesis. It’s replicable, it’s cheap, it’s accessible, and most of all it’s fun.

In my classes we introduce the technique with a structured lab investigation where the students acquire the skills needed so that they can explore their own questions later. To introduce the technique we compare photosynthesis with carbon dioxide and without. Each student is required to successfully navigate through the procedure and as they do, together as a class, we generate questions that will guide the students later on their own independent investigations.


Here is the original web page that I published several years ago that biology teachers and students found helpful:




The Floating Leaf Disk Assay for Investigating
(A resource page)
Brad Williamson


Trying to find a good, quantitative procedure that students can use for exploring photosynthesis is a challenge. The standard procedures such as counting oxygen bubbles generated by an elodea stem tend to not be “student” proof or reliable. This is a particular problem if your laboratory instruction emphasizes student-generated questions. Over the years, I have found the floating leaf disk assay technique to be reliable and understandable to students. Once the students are familiar with the technique they can readily design experiments to answer their own questions about photosynthesis.


The biology behind the procedure:

Leaf disks float, normally.  When the air spaces are infiltrated with solution the overall density of the leaf disk increases and the disk sinks. The infiltration solution includes a small amount of Sodium bicarbonate. Bicarbonate ion serves as the carbon source for photosynthesis.  As photosynthesis proceeds oxygen is released into the interior of the leaf which changes the buoyancy–causing the disks to rise.  Since cellular respiration is taking place at the same time, consuming oxygen, the rate that the disks rise is an indirect measurement of the net rate of photosynthesis.

Basis for leaf disk

  • Sodium bicarbonate (Baking soda)
  • Liquid Soap
  • Plastic syringe (10 cc or larger)—remove any needle!
  • Leaf material
  • Hole punch
  • Plastic cups
  • Timer
  • Light source

    Materials image

  • Buffer Solutions
  • Colored Cellophane or filters
  • Leaf material of different ages
  • Variegated leaf material
  • Clear Nail polish
  • Prepare 300 ml of bicarbonate solution for each trial.
Bicarb photo




  • The bicarbonate serves as an alternate dissolved source of carbon dioxide for photosynthesis. Prepare a 0.2% solution. (This is not very much it is only about 1/8 of a teaspoon of baking soda in 300 ml of water.)
  • Add 1 drop of dilute liquid soap to this solution. The soap wets the hydrophobic surface of the leaf allowing the solution to be drawn into the leaf.  It’s difficult to quantify this since liquid soaps vary in concentration. Avoid suds. If your solution generates suds then dilute it with more bicarbonate solution.





  • Cut 10 or more uniform leaf disks for each trial.


Leaf Disks



  • Single hole punches work well for this but stout plastic straws will work as well.
  • Choice of the leaf material is perhaps the most critical aspect of this procedure.The leaf surface should be smooth and not too thick. Avoid plants with hairy leaves. Ivy, fresh spinach, Wisconsin Fast Plant cotyledons–all work well. Ivy seems to provide very consistent results.Many different plant leaves work for this lab.  My classes have found that in the spring, Pokeweed may be the best choice.
  • Avoid major veins.
  • Infiltrate the leaf disks with sodium bicarbonate solution.
  • Remove the piston or plunger and place the leaf disks into the syringe barrel. Replace the plunger being careful not to crush the leaf disks. Push on the plunger until only a small volume of air and leaf disk remain in the barrel (< 10%).

Disks in syringe

  • Pull a small volume of Sodium bicarbonate solution into the syringe.  Tap the syringe to suspend the leaf disks in the solution.
  • Holding a finger over the syringe-opening, draw back on the plunger to create a vacuum.  Hold this vacuum for about 10 seconds.  While holding the vacuum, swirl the leaf disks to suspend them in the solution.  Let off the vacuum.  The bicarbonate solution will infiltrate the air spaces in the leaf causing the disks to sink. You will probably have to repeat this
    procedure 2-3 times in order to get the disks to sink. If you have difficulty getting your disks to sink after about 3 evacuations, it is usually because there is not enough soap in the solution.  Add a few more drops of soap.


Evacuating leaf disks






  • Pour the disks and solution into a clear plastic cup.  Add bicarbonate solution to a depth of about 3 centimeters.  Use the same depth for each trial.  Shallower depths work just as well.




  • For a control infiltrate leaf disks with a solution of only water with a drop of soap–no bicarbonate.
  • Place under the light source and start the timer.  At the end of each minute, record the number of floating disks. Then swirl the disks to dislodge any that are stuck against the sides of the cups. Continue until all of the disks are floating.



Data Collection and Analysis

These data are from a investigation using grape ivy leaf disks.

Minutes Disks
1 0
2 0
3 0
4 0
5 0
6 0
7 1
8 1
9 1
10 1
11 4
12 7
13 8
14 10





The point at which 50% of the leaf disks are floating (the median) is the point of reference for this procedure. By extrapolating from the graph, the 50% floating point is about 11.5
minutes.  Using the 50% point provides a greater degree of reliability and repeatability for this procedure.  Steucek, et. al. (1985) described this term is referred to as
the ET50.


The problem with ET50 is that it goes down as the rate of photosynthesis goes up–it is an inverse relationship and creates the following type of graph (data from Steucek, et. al. 1985):  




To correct for this representation of the data and present a graph that shows increasing rates of photosynthesis with a positive slope the ET50 term can be modified by taking the inverse or 1/ET50.  This creates a graph like this (data from Steucek, et al. 1985.):  




In this graph, the light was turned off at 14 minutes and the cups with their floating disks (grape ivy) were placed in the dark.


Photosynthesis and Respiration



Every minute, I removed the dark cover and counted how many were still floating.  Then I stirred the disks.  Note that after a while the disks begin to sink.  Why?  Cellular respiration
removes the oxygen from the cell spaces.  The rate that the disks sink is an indirect measure of the rate of cellular respiration.   Can you think of a way to how you might measure the gross rate of photosynthesis with this technique?

Print and Web Resources:

Wickliff, J.L. and Chasson, R.M. 1964. Measurement of photosynthesis in plant tissues using bicarbonate solutions.  Bioscience, 14: 32-33.

Steucek, Guy L. Robert J. Hill and Class/Summer 1982. 1985. Photosynthesis I: An Assay Utilizing Leaf Disks. The American Biology Teacher, 47(2):96-99.

Tatina, Robert E. 1986.  Improvements to the Steucek and Hill Assay of Photosynthesis. The American Biology Teacher, 48(6): 364-366.

Juliao, Fernando and Henry C. Butcher IV. 1989. Further Improvements to the Steucek and Hill Assay of Photosynthesis. The American Biology Teacher, 51(3): 174-176.

Armstrong, Joeseph E. 1995. Investigation of Photosynthesis using the Floating Leaf Disk Assay.

Rukes, Kari L. and Timothy J.Mulkey. 1994. Measurement on the Effects of Light Quality and Other Factors on the Rate of Photosynthesis. Bioscene, 20(3): 7-11.

Greenler, John. 1990. Exploring Photosynthesis with Fast Plants. WisconsinFast Plant Notes, 4(1): 4-5.

Richard, David S. Measure of Photosynthetic Rate In Spinach Leaf Disks



New Feature to the KABT site.


I’ve added a new feature in the right hand panel of the KABT News site. This is a feed from AAAS’s Eurekalert’s Biology news updates. You’ll find the headlines of the 6 most recent news items related to biology listed here and the link: Eurekalert Biology will take you to the AAAS with more detailed postings.

Notice also that Todd has commented about citizen science participation and I have added a link to web sites about citizen science.