WATERS Mini Lesson s2

Yakima WATERS Mini Lesson

Bacteria Ecosystem Exploration

Targets and Assessment Lesson Parameters WA Science Standards Addressed: Content Area: Biology, microbiology  4-5 INQA Scientific investigations involve asking and answering questions and comparing the answers with Overview: This is a classroom experiment exploring the evidence form the real world diversity of bacterial life and how to properly conduct an  4-5 INQC An experiment involves a comparison. For experiment. an experiment to be valid and fair, all of the things that can possibly change the outcome of the Grade Level: 5 experiment should be kept the same, if possible.  4- INQE Repeated trials are necessary for reliability Assessments: Suggested Time: 15-30 minutes collecting, few days to weeks for  Proper notes should be kept in the student’s science bacterial growth notebooks with proper definitions of experiment terms. Special Materials:  Petri-dishes with agar, parafilm, sterile cotton swabs

Learning Outcomes: Knowledge: The student will know that an experiment answers a question by exploring the real world. Students will know that as many things as possible must be kept the same for the experiment in order for it to be valid. Students will know that in order for an experiment to be reliable they need to repeat the trials. Skill: Students will know how to experiment using the scientific method.

Science Concept Background: Bacteria are very cells that live everywhere in the environment. Most are harmless to humans eating organic matter they find, reproducing, and dying just like any other living thing. We can only see them when they are masses together in very large numbers. By sampling a very small area we can see what types of bacteria and other microorganisms live there. Wildlife biologists use several methods to determine the species richness in the locations they study. This method can be used on bacteria as well by counting the bacterial masses or colonies. If the bacteria colonies can’t be accurately counted area covered can be determined with a simple grid placed over the bacteria and counting the number of squares they occupy. This is used by other scientist on larger scales.

Materials: Sterile petri-dishes with agar. Sterile cotton swabs, parafilm, wax pencils, and notebooks.

Procedure: 1.) Give each science group two-three sterile petri-dishes with agar gel, two-three strerile cotton swabs, and their notebooks. The petri-dishes must be kept closed to ensure that no bacteria other than where you sampled can get in. Using a wax pencil the students will put their name on the bottom of the petri-dish, this is the part that holds the agar. 2.) After the students have chosen a location to sample and written in down in the science notebook they will be given a sterile cotton swab. These cotton swabs are opened from the end that doesn’t have the cotton. The tip must not touch anything other than the location the students chose to sample or their data will be corrupted. 3.) The petri-dish can now be flipped so the bottom is touching the table and very slightly opened so that the top still covers the bottom. The cotton tip is very carefully put into the dish and very lightly rubbed over the agar while slowly spinning the swab. It is important not to dig the cotton tip into the agar, it will be much harder to determine area cover or to count colonies if this happens. The cotton swabs can be thrown away as nothing that isn’t already found in the classroom is on them. 4.) A thin strip of parafilm is then stretched around the petri-dish where the two halves meet then flipped back over. Have the students chose a location they would like to put their petri-dishes and write that location or trial down in their notebooks. Let the petri-dishes sit in their location for a few days to few weeks depending on the temperature, colder temperatures mean longer growing times. 5.) After the bacteria have grown have the students look at each petri-dish. If there are many circles on them use the Worksheet to construct a “species” chart. If there is a large mass use graph paper to determine the area covered.

Key questions: Why is it important to keep everything sterile? Why do we have more than one petri-dish at each location? Explain the importance of replication and repeated trials. If something is contaminated or one petri-dish breaks we still have another one to use in our experiment. Scientific terms to look for in the students’ notebook: Control, replication, repeated trial.

Extension(s): The students can compare different bacteria from different locations after they have determined what location is the best for growing them.

Teaching Tips: The fifth grade is not expected to know about cells, a short explanation of what cells are and how they relate to the visible world may be needed.

Supplements: http://www.waksmanfoundation.org/labs/washstat/elemexp2000.html

Author: Dale Jansons, Yakima WATERS Project, CWU, Winter 2011 Colony shape Colony color Number of that type of colony

Directions: Find all the different types of colonies on your petri-dishes. In the first column describe the shape on each different type of colony, in the second describe the colony’s color, and in the last column count the number colonies that look like this.