Mining for Microbes
Students will quantify the number of culturable bacteria found in a gram of soil using petri dishes and serial dilutions
Objectives
The learner will create a serial dilution to help quantify culturalble soil bacteria.
The learner will use aspetic techniques to plate out serial dilutions onto nutrient agar plates.
The learner will quantify the amount of culturable bacteria in a gram of soil.
Materials
1 gram of soil
100 mL of sterile saline solution
six sterile test tubes
parafilm
scissors
four Petri dishes with nutrient agar
1 permanant marker
1 glass plate spreader
95% ethanol or isopropanol
sterile barrel pipet
Procedure
1.  Follow the diagram and instructions on the Real Student Worksheet for serial dilution preparation.
2.  Take your six test tubes and label them full strength, .1 , .01, .001, .0001, and .000 01.
3.  Add 9 mLs of saline solution to all the test tubes.
4.  Place one gram of soil into the full streanght test tube, seal with parfilm, and shake.
5.  Using a sterile pipet transfer one ml of the solution to the tube labeled .1, and repeat step 2.
6.  Then transfer one ml of the solution in the .1 tube to the .01 tube and repeat step 2.
7.  Continue this for the remaining test tubes.
8.  When you have finished setting up your serial dilution perform a simple self check. Make sure all of your tubes have the same level of sample (9 mL) except for the tube labeled .00001. This tube should have 1 mL more(10 mL).
9.  Once the dilution is set up record your observations of the test tubes and plate out your samples. You should start with the sample labeled .00001 and work your way to sample .01.
10.  To plate out your sample place 2 drops of solution in the middle of a petri dish and use the glass spreader to spread the solution around the petri dish evenly.
References
 
State Standards
1.2.2- The student will pose meaningful, answerable scientific questions.(NTB)
1.2.3- The student will formulate a working hypothesis.
1.2.4- The student will test a working hypothesis.(NTB)
1.2.7- The student will use relationships discovered in the lab to explain phenomena observed outside the laboratory.
1.3.1- The student will develop and demonstrate skills in using lab and field equipment to perform investigative techniques.(NTB)
1.3.2- The student will recognize safe laboratory procedures.
1.3.3- The student will demonstrate safe handling of the chemicals and materials of science.(NTB)
1.3.4- The student will learn the use of new instruments and equipment by following instructions in a manual or from oral direction.(NTB)
1.4.1- The student will organize data appropriately using techniques such as tables, graphs, and webs (for graphs: axes labeled with appropriate quantities, appropriate units on axes, axes labeled with appropriate intervals, independent and dependent variables on correct axes, appropriate title).
1.4.2- The student will analyze data to make predictions, decisions, or draw conclusions.
1.4.4- The student will determine the relationships between quantities and develop the mathematical model that describes these relationships.
1.4.5- The student will check graphs to determine that they do not misrepresent results.
1.4.6- The student will describe trends revealed by data.
1.4.7- The student will determine the sources of error that limit the accuracy or precision of experimental results.
1.5.1- The student will demonstrate the ability to summarize data (measurements/observations).
1.5.2- The student will explain scientific concepts and processes through drawing, writing, and/or oral communication.
1.5.3- The student will use computers and/or graphing calculators to produce the visual materials (tables, graphs, and spreadsheets) that will be used for communicating results.(NTB)
1.5.4- The student will use tables, graphs, and displays to support arguments and claims in both written and oral communication.
1.5.5- The student will create and/or interpret graphics. (scale drawings, photographs, digital images, field of view, etc.)
1.5.9- The student will communicate conclusions derived through a synthesis of ideas.
1.6.3- The student will express and/or compare small and large quantities using scientific notation and relative order of magnitude.
1.6.4- The student will manipulate quantities and/or numerical values in algebraic equations.
1.6.5- The student will judge the reasonableness of an answer.
1.7.1- The student will apply the skills, processes, and concepts of biology, chemistry, physics, and earth science to societal issues.
1.7.2- The student will identify and evaluate the impact of scientific ideas and/or advancements in technology on society.
1.7.4- The student will recognize mathematics as an integral part of the scientific process.(NTB)
Lesson Resources
real student worksheet