A Breath of Fresh Air!
Sharon Harris Mother of Mercy High School 3036 Werk Road Cincinnati, OH 45211 (513) 661-2740 email@example.com
Teaching Standard B
Teaching Standard D
Teaching Standard E
TIME FRAME BREAKDOWN
One day for introducing aseptic technique, vocabulary, and the importance of oxygen in bacterial metabolism.
One day for inoculating agar tubes with cultures.
One day for observing results and writing laboratory reports.
Engagement and Exploration (Student Inquiry Activity
Ask the students to define denitrification. (The conversion of nitrate and nitrite to atmospheric nitrogen gas). Most often they will get the idea that it involves the removal of nitrogen from somewhere. Ask students where the nitrogen in our atmosphere originates. How does it get there? (Primarily from microbial activity through the process of denitrification). Does it always comprise approximately 79% of natural air? (Yes, in present day). What would happen if the nitrogen concentration in air decreased? (Accept all reasonable answers). Is the nitrogen cycle related to any other element cyles? (Yes! Some bacteria require anaerobic conditions to 'fix' nitrogen, that is, convert atmospheric nitrogen to ammonia compounds).
Discuss the various bacteria that live under anaerobic conditions. Discuss the processes of nitrogen fixation and denitrification both of which occur under anoxic or suboxic conditions. These processes can give the concept of living without oxygen a defined purpose.
Are all bacteria equally tolerant of oxygen? (No). Can all bacteria fix nitrogen? (No). Do all bacteria parcticipate in the process of denitrification? (No).
Elaboration (Polar Applications)
Describe photosynthetic nitrogen fixation by the purple non-sulfur and the green bacteria. (See "Explanation"). Ask students to read the procedure and write these into their lab notebooks. Writing the procedures will ensure that the students have read the procedures and know what to expect. Explain to them that it is necessary to work quickly once the media has been inoculated with the bacteria. Inoculated cultures (that have been inverted several times for mixing) should be placed in an ice bath immediately for rapid solidification of the agar.
Have students practice the aseptic techniques.
Inoculate and observe cultures that have been incubated under microaerobic conditions to determine the tolerance for oxygen of certain bacteria. Cultures are grown in loosely capped tubes in an agarose medium. The depth at which a culture band is seen can be used as a measure of the oxygen tolerance of the cultures. If the organisms grow on the top of the agar, they are very tolerant of the presence of oxygen. Cultures appearing as bands below the surface of the agar are less tolerant (i.e. the farther below the surface, the less tolerant).
Exchange (Students Draw Conclusions)
1. Which organisms were the most oxygen tolerant? Which were the least oxygen tolerant?
3. Create a scale with which you may rate the oxygen tolerance of the bacteria (eg. on a scale of 1 to 10).
4. Could oxygen possibly be a factor in the process of denitrification in Lake Bonney?
5. What general conclusions can be drawn about the denitrifiers in Lake Bonney and their tolerance for oxygen? Can any conclusions be drawn?
Evaluation (Assessing Student Performance)