National Science Foundation

Education and Outreach

Kartchner Experiments for K-12

Grades K-3:

Growing Crystals.

There is nothing more appealing than candy.  This experiment will allow young scientists to make their own candy in a jar while providing an opportunity to learn about crystal growth.  Many cave formations are actually mineral crystals that form from surrounding mineral-laden water at a site of crystal nucleation and continue to grow for many, many years.  The size of the crystals is determined by 1) the amount of dissolved minerals in the surrounding water, and 2) the amount of time in which the growing crystal is undisturbed.  If disturbed, crystal growth may cease or at least be slowed, which highlights how stable cave environments must be in order for beautiful crystal formations to develop.  Making rock candy can simulate the process of cave crystal formation.  This experiment will give students the opportunity to watch crystal growth over 2-3 weeks and to gain an appreciation for the time necessary for crystals to grow as well as the importance of keeping the environment undisturbed.  And in the end, they can eat their experiment!! 

What you will need:

1) 2 cups of water
2) 4 cups of sugar
3) a small pan
4) a wooden spoon
5) a small, clean glass jar (baby food jar or 1 pint Mason)
6) a cotton string with a small galvanized washer tied to the end
7) a pencil to suspend the string in the jar
8) magnifying glass

 

 

The experiment:
First, heat the water in the saucepan over medium heat until it begins to boil.  Next, add the sugar to the water and stir continuously with the wooden spoon until the sugar completely dissolves and the solution becomes clear.  The water should be held at a slow rolling boil.  Once dissolved, pour the sugar solution carefully into the jar.  Tie the string with the washer to the middle of the pencil (Top Figure) (the tied string should reach about 2/3 to the bottom of the jar). (Bottom Figure)

Dip the string into the sugar solution, remove it, and lay it on a piece of waxed paper in a straight line, and let it dry for a couple of days.  The string will act as the “site of crystal nucleation” for this experiment.  Cover the jar with another small piece of waxed paper.
             
Now comes the fun part.  In a very quiet, still place, out of the way of household traffic, place the jar on a shelf where the water can cool to the point where normally sugar could not be dissolved.  The sugar remains dissolved, however, resulting in an unstable state.  The sugar wants to precipitate out of solution and crystallize, but it can't.  It has no site of crystal nucleation.

Then you add the treated string.  This gives the excess sugar a place it can "grab onto".  Crystals begin to grow as the sugar finds its way onto the "seed crystals" the treated string provides. Over the next weeks, you can watch as the crystals grow larger and larger on the string looking more and more like rock candy .  It’s tempting, but don’t touch the jar until the experiment is finished or else the young crystals may break off and have to start re-growing on the string.  After 2-3 weeks, the crystals will be quite large and strong, and the string can be pulled out and laid again on waxed paper for it to dry.  After the string is dry, look at it using a magnifying glass and observe their very regular crystals that have formed along it full length.  To contrast the formation of large crystals, you can prepare a second jar of dissolved sugar solution, place next to the first jar, and as the crystals are forming you can bump or swirl the solution once a day to disrupt the crystal formation process.  Notice the difference in crystal size and shape between crystals in the undisturbed jar and the jar that has been disturbed periodically.

Once the crystals on the string are dried, you can further enjoy the experiment by sucking on the delicious sugar crystals you have grown!  Remember, don’t eat the string!  You can also add a few drops of food coloring to the sugar solution before cooling to create crystals of different colors, which are even more fun to eat!! 

Grades 4-6:

Growing your own bacteria.

Scientists are becoming increasingly aware that microorganisms can be found in nearly every ecosystem and on nearly every surface imaginable.  This includes rocks, even those found underground in caves and caverns throughout the world.  Although microorganisms living in caves are something most people don’t think about, our work in Kartchner Caverns, Arizona, has revealed complex bacterial and fungal communities on nearly every surface that has been sampled.  It is also known that our bodies have a number of different types of bacteria and fungi naturally present on our skin.  What happens if we touch surfaces that have their own unique microbe community with our fingers, which have their own unique microbe community?  The result is that we often transfer what we have on our skin to the surface that we touch.  This can have interesting, unusual, and often damaging consequences for the surface that was touched!  To demonstrate to students the prevalence of bacteria on their skin, this experiment will allow you to make a microbial growth medium from gelatin that will allow you to grow bacteria from your skin, soil, rocks, grass, or anything else you can think of.

What you will need:


1) Knox gelatin (Roughly 7.0 grams of gelatin (1 pack) per 100 ml of nutrient base or plain water)
2) water
3) nutrient base (fruit juice or sugar water)
4) Petri plates (baby food jars or half-pint jelly jar will also work if sterilized by boiling or pressure cooking).
5 forceps
6) toothpicks and cotton swabs
7) an eyedropper
8 sterile spoons (you can sterilize these by boiling)
9) an assortment of small rocks and pebbles
10) dirty hands
 

The Experiment:
So, first make your microbial growth media by mixing your nutrient substrate or plain water with the gelatin (150 ml of substrate to ~ 7 g of gelatin).  It is important that the medium you are making be sterile so that you can be sure the microbes you are growing are from the soil or other surface under investigation.  You can sterilize your medium by boiling the gelatin and nutrient substrate together for 5 minutes (make sure it is covered).  Let it cool (no peeking under the cover, this will let contaminants in) to about 60°C and then pour the medium into the sterile Petri plates or jars and let it set up.  Do not stir or touch the medium with utensils that are not sterile while pouring.  It is suggested that teachers or parents perform this step as handling boiling gelatin can be dangerous.  After pouring, and when the medium is completely cool and has solidified, inoculate the plates or jars from the following sources:

1. Microbes in the soil: collect 5-10 small pebbles with a sterile spoon and place in a sealable jar.  Add 40 ml of water, and swirl vigorously (but not so vigorously that the jar breaks!!).  Then use an eyedropper to add 3 drops of the dirty water to the surface of the medium and spread it over the surface with a glass plate spreader, back of a sterile spoon, or sterile cotton swab.
   
   
   
   Quickly replace the cover on the plates/jars and let them sit in the dark for up to 2 weeks, checking for growth of bacteria everyday.  It is better if you incubate your plates or jars upside down (then condensation from the lid will not drip onto the gelatin surface).  ***IMPORTANT***  As a control to show that the medium itself doesn’t have any contaminating microbes, set aside one or two plates/jars that have not been inoculated and set them beside the inoculated jars.  There should be no growth on these plates/jars.  If there is, then the medium itself was not sterile to begin with.
2. Microbes from fingers or environmental swabs: follow the instructions as above, except allow the students to use a sterile swab to sample any surface they want (sinks, toilets, etc) and streak on the surface of the media.  Alternatively, they can just get their hands dirty and touch the media on one or two places (this will show them why they need to wash their hands before eating!!).
3. During the course of the experiment, have the student record all the bacteria they see and include the various characteristics of each bacterial colony.  If the students would like to obtain some of their bacteria isolates in pure culture (without any other bacteria present that might obscure or restrict their growth), have them touch the surface of any bacterial colony with a sterile toothpick and then gently rub the toothpick onto the surface of clean media.
   
   
   
   
   Allow to incubate as before and note any differences in growth of the bacteria when there are no other competing bacterial strains around.
   
   

This all relates to the Kartchner caverns project by demonstrating that there are living things everywhere, even in places where you wouldn’t expect it, like rock surfaces.  It also emphasizes why it is so important not to touch the cave formations, because you may introduce foreign bacteria from your hands onto the formation, altering the balance of the native microbial populations, and possibly killing them. 

Grades 7-9:

Growing microbes under different conditions.

For older students, you can use a similar experimental set up as above to look at basic microbial diversity in soils (or other samples substrates).  In these experiments, several types of growth media are made and are incubated in different ways.  Much of the research in Kartchner Caverns incorporates these types of experiments to characterize the microbial diversity from different cave surface and substrates.  Students can also do this with soil, and can keep track of the different kinds of microbes (both bacteria and fungi) based on colony size, color, shape, texture, and other physical properties.  Keeping track of microbial diversity on plates made from different media or that have been incubated differently will allow the students get a basic idea of what kind of microbes live in the soil, what sort of nutrients they need to live, and the different environmental conditions necessary for their optimal growth.

 
What you will need:


1) Knox gelatin
2) water
3) nutritional substrates such as vegetable juice, lemon juice, oatmeal, chicken broth, and/or syrup
4) Petri plates (baby food jars or half-pint jelly jar will also work if sterilized by boiling or pressure cooking).
5) one or two different samples of different soil types
6) sterile spoons or sterile cotton swabs

The Experiment:
So, first make your microbial growth media by mixing your nutritional substrates with the gelatin, and let them set up in the Petri plates overnight.  It is important that the medium you are making be sterile so that you can be sure the microbes you are growing are from the soil sample under investigation.  You can sterilize your medium by boiling the gelatin and nutrient substrate together for 5 minutes (make sure it is covered).  Let it cool (no peeking under the cover, this will let contaminants in) to about 60°C and then pour the medium into the sterile Petri plates or jars and let it set up.  Do not stir or touch the medium with utensils that are not sterile while pouring.  It is suggested that teachers or parents perform this step as handling boiling gelatin can be dangerous.  Make all media to be used in this experiment at one time while you have your sterilizing equipment out.  Designate one medium as the “standard” that you will compare other media to.

After the media is cool, inoculate the media using the following sources.

1. Microorganisms in the soil:  collect 1-2 tablespoons of soil with a sterile spoon and place them in a sealable jar.  Add 100 ml of water, and swirl vigorously (but not so vigorously that the jar breaks!!).  Use an eyedropper to add 3 drops of the dirty water to the surface of the medium and spread it over the surface with the back of a sterile spoon or sterile cotton swab.
   
   
   
   
   Quickly replace the cover on the plates/jars and let them sit in the dark for up to 2 weeks, checking for growth of bacteria every day.  As a control to show that the medium itself doesn’t have any contaminating microorganisms, set aside one or two plates/jars that have not been inoculated and set then beside the inoculated jars.
2. During the course of the experiment, have the student record all the bacteria they see and include the various characteristics if each colony.  If the students would like to obtain some of their bacterial isolates in pure culture (without any other bacteria present that might obscure or restrict their growth), have them touch the surface of any bacterial colony with a tooth pick ad then gently rub the toothpick onto the surface of clean media.  Allow to incubate as before and note any differences in the growth of the bacteria when there are no other competing strains of bacteria around. 
3. Allowing the student to isolate a particular colony will enable them to observer the characteristics of the bacteria by itself growing on several different substrates.  Have the students track the growth and progress f the bacteria at different time points, using colony diameter as one metric for growth.  Also have them observe colony morphology ad look for the production of things like colored exudates.  These data can then be used to plot graphs, make tables, and write a science report.

These experiments provide a wide array of possibilities that will familiarize students with the microorganisms in their world.  As such, experiment with the experiment!!  Change in whatever way imaginable the things you can add to the growth medium that will provide different nutrients for the bacterial or fungi.  Now that students know that microorganisms are there, how do they respond to different acidities or nutrients?  Do some grow better in the dark or in the light?  For more complex experiments, change the nutritional substrates in the media such as using sugar with and with out lemon juice (to acidify the medium), adding chicken broth (for diverse amino acids), or oatmeal (for high carbohydrate content).  Grow the colonies at different environmental conditions such as with light or no light, or at different temperatures like those in Kartchner Caverns.  Depending on the lesson being taught, these experiments can aid in understanding metabolism, ecology, scientific design, or basic laboratory practice.  Have students ask their own questions about microbial communities and come up with a simple experiment to answer that question.

Grades 10-12

Extracting DNA from plants and bacteria.

Scientists today estimate only about 5% of the species of microbes that live on earth can be cultured by standard methods.  The other 95% of all microbes will not grow in the lab because the specific requirement for their normal growth cannot be reproduced.  Some of this is due to a lack of knowledge on what their growth requirements are, and some is due to the technical difficulties in reproducing these requirements in the laboratory.  Because of this, the Kartchner Caverns project relies heavily on non-culturable methods of analysis that require microbial DNA to be extracted directly from samples without the need to culture the organisms.  How do we get DNA?  This experiment will allow students to extract and purify DNA directly from plants and bacteria and see it actually precipitate out in a test tube!  This fascinating technique is the first step used in “molecular” biology and to appreciate its importance is key to understanding the full diversity of microbes that surrounds us everyday.

What you will need:


1) a blender
2) a strainer
3) stiring rods
3) a measuring cup
4) small glass containers
5) rubbing alcohol
6) ½ cup split peas (or 100 ml)
7) 1/8 tsp table salt
8) 1 cup of  water
9) detergent (liquid dishwashing)
10) meat tenderizer (or pineapple juice or contact lens cleaning solution)

 

The Experiment:
DNA is the blueprint of life.  In this experiment, we will extract the DNA from some plant material, like split peas, but you can use just about any plant material to extract DNA from.   In addition, you can extract DNA from a culture of bacteria, such as one you might have isolated from soil in the above experiment, using very similar techniques.

Plant DNA Isolation.

1. Combine peas, salt, and water in the blender and process on high speed for about 15 seconds.  This will break up the peas so that they are more exposed to the action of the detergent in later steps.
   
   
   
   
   
   
2. Next, take theresulting pea soup and put it through a strainer and collect the liquid portion in a separate container.  Then add about 30 ml, or 2 tablespoons, of liquid detergent and mix by swirling. 

   

3. Let the mixture sit at room temperature for 5-10 minutes and then transfer to individual glass test tubes or clear glass containers.  Only fill the containers 1/3 of the way full because you will need room to add more reagents soon.
   
   

4. Next, add a pinch of the meat tenderizer (or above listed alternatives) to each tube so that it can start to break down remaining proteins in the mixture.  Gently stir the solution with a sterile stirrer, but do it gently to avoid breaking up the DNA strands.

5. Now comes the fun part!  Add an equal part volume of rubbing alcohol (70-95% isopropanol) to the tubes. Do this gently so that the alcohol forms a layer on top of the pea mixture.
   
   
   The stringy white stuff you will see forming at the interface of the two liquids is DNA!  You can then gently pulse the wooden end of a cotton swab, or other stirring rod, up and down through the alcohol and pea soup boundary to collect precipitated DNA.  It will collect as long stringy white strands and is pure DNA!
   
   
   
   

Bacterial DNA isolation.

1. Transfer a small amount of a pure bacterial culture using a cotton swab or a toothpick into a test tube containing Tryptic Soy Broth (Difco) or  LB broth (Difco). Use 4 ml of media per tube and exercise STERILE TECHNIQUES when you transfer to prevent other contaminants from being introduced to your growth medium.  Incubate the tubes for 48 hrs at 37C. 
2. Add 3 ml of a 50% dishwashing detergent to the culture and mix well.
3. Incubate the tube in a 70C water bath for 15 minutes.
4. Push a glass rod through the alcohol layer into the bacterial/detergent suspension, then twist and pull the rod up back into the alcohol layer just like you did for the plant DNA isolation.  Repeat until you have a generous supply of "spooled" DNA on the glass rod

Now that you have pure DNA, you can transfer the DNA to a glass slide and stain with 1 drop of Aceto-Orcein to observe the fiber-like nature of the molecule.

Aceto-Orcein:             Orcein                             1 gm
                                   Lactic Acid 85%             28 ml
                                   Glacial Acetic Acid          22 ml

DNA is pretty tough and will remain in the “stringy” state for many days without degrading.  It has to be tough since it contains all the instructions for life in every living cell!  Once purified, molecular biologist use this same type of DNA preparation for many very complex experiments including isolation of specific genes, insertion of new DNA into existing genes, and inserting these modified genes into new organisms.  These basic techniques of molecular biology have revolutionized science over the last 40 years and have led to many of the incredible discoveries we read about daily in areas of agriculture, medicine, and environmental study.  DNA isolation is only the first step into the amazing world of molecular biology!

updated 7/2009