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Sunday, January 6, 2013

Lab: Making Coacervates



Two activities in one:  
A guided lab activity plus a student designed lab activity!

I just tried this lab for the first time this year.  And I liked it so much that I will definitely use it again next year!

Each school year I make myself try new and different activities.  The idea of this lab has been around for a long time, and when I  finished teaching my unit on "The Origin of Life on Earth" I though I would give this lab a try. The lab is called "Making Coacervates."

What are coacervates? Coacervates are simply droplets that are composed of molecules of different types.  Coacervates are not alive, but they do share some of the same characteristics as those found in living cells.  Because of this, many scientists have hypothesized that structures similar to coacervates may have been the precursors to the first living cells.  Although the origin of life has not been duplicated in the laboratory, it is very simple to observe the formation of coacervates.  This activity was a thought-provoking one for my students.  They clearly were able to see, using a microscope, how it is possible for molecules to come together to form cell-like structures.

This lab kills two birds with one stone!  The first part of my lab was a guided lab activity.  The students followed a lab procedure that I gave them to test the effect of different pH levels on the formation of coacervates.  But the second day of the lab packed a much bigger punch!!  I assigned each lab group a different variable to test.  The group had to form a hypothesis and then design a lab to test their hypothesis.  For example, some groups had to test the effect of temperature on coacervate formation, while other groups tested the effect of changing solution concentrations on the formation of coacervates.  

Six different variables were tested by the students.  At the conclusion of their experiment, each student group had to make a very short report to the class discussing the results they obtained.  This is a time consuming activity, but it is time well spent!  Common Core standards are demanding that science students spend more time in analysis, problem solving activities.  

I am particularly proud of my 5-page handout that I designed for my students to use as they designed their experiment.  I required them to form a hypothesis, write a procedure that would gather quantitative data, design a control for the experiment, describe their experimental and control groups, graph their data, form a conclusion, and much more.

Materials needed:     Glass test tube with cap, Graduated cylinders, Gelatin solution (protein), Gum Arabic (carbohydrate),  Glass stirring rod, pH paper,  .1M HCl solution, Dropping pipets, Microscope, Test tube rack,  and Microscope slides. Additional materials are needed for the student designed experiments.


What are the pros and cons of this lab?

Pros include:

  • Students gained a better understanding of coacervates and how they might have formed in the seas on early Earth.
  • Materials list is simple and inexpensive.
  • Teaching students how to design and carry out a controlled experiment is a MUST in the science classrooms of today.
Cons include:
  • This lab takes a bit of time.  Students completed the guided activity in one class period, they wrote and designed their experiment in a second class period, and they carried out their experiment in a third lab period.  Some parts of the lab report had to be completed as a homework assignment.
  • The coacervates are very easy to find under the microscope, but they are difficult to count.  The student has to scan the entire slide and count the number of coacervates that were formed.  This is a source of error.
This lab was used as a conclusion to my unit on "The Origin of Life." Some of the materials I used to teach this unit can be found here:


 





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