Teacher
Instructional for Class Laboratory Activity #1:
Type of Activity:
Inquiry-based, hands on.
The introduction of Biological Oxygen Demand to the
students can be easily achieved by having them perform the laboratory activity
linked to the website. The “from
scratch” component allows them to understand the usage of oxygen for metabolic
processes and supports understanding of any unit you may have on biochemistry.
It is especially important to impart to the students that environmental
scientists and engineers use BOD as a measure of health for water living
organisms in natural waterways.1
Please see references for scientific articles on BOD and Manometers.
Most chemical houses also provide testing kits for BOD, which you may
wish to incorporate in an environmental science unit.
Secondly, the use of heavy metals in industry may have a
deleterious effect on biodegradation. Using
CuSO4 or similar metal compounds demonstrates this effect to the
students.
Recommended Class Set-Up:
It is
advantageous to have the students in groups of three as a cooperative activity.
Some science laboratories will find this difficult; therefore, the
teacher may have to have one classroom set-up giving the student groups a
“part” of the set-up to construct and perform.2
Preliminary Set-Up:
The bacteria for the activity must be grown and harvested
prior to the laboratory activity. An
aerobic soil bacterium is recommended. If
not available any aerobic species may be used.
However, you may have to purchase the species, or grow your own on agar
plates making sure to isolate and harvest only one species.
If you are incorporating this activity with microbiology,
students can grow and harvest the bacterial culture for use in the BOD activity.
A nutrient media may be purchased or made by using broth added to agar
(following manufacturer’s instructions).
Beware, agar goes a long way, and only small amounts are needed to make a
plate. You may streak directly from
the soil sample mixed with water. A
second or even third streaking may be required to isolate a species.
Give each group enough bacterial colonies to fill an
inoculation loop about 20-30 times. The
students will add the total amount to one flask for each lab set-up and then
divide the mixture between the two flasks needed for the 2 manometers.
This procedure guarantees that the two flasks used (the control and the
experimental variable) have exactly the same nutrient and bacterial mixture
before the variable is added.
The Manometer:
The board that is being used has to be wide enough to
accommodate the U of the tubing attached to it. It may be easier to glue graph paper to the board after the
student has plumbed a vertically straight line. You can then tape the ruler next to it aligning the top of
the colored fluid in the tube with 0. Be
aware that the tubing must not be pinched in any way during the activity, since
that would affect results. To
secure the board in place, you may attach to a support in back or directly tape
to the wall.3
It is ideal to have the board and flask on a magnetic
stirrer, but if not available students must make accommodations by manually
stirring at even intervals.
Measurements:
BOD is measured in mg/L or in ppm, which are equivalents.
You may suggest to the students to make a graph with the X-axis as a
function of time and the rise or fall of the color water or indicator on the
Y-axis in millimeters.
There is no difficulty with not taking measurements
overnight since the graph is in points. The
trend will be clearly seen over the week, however, it is important to take the
readings at the same intervals. Assigning
the reading times and giving each group an assigned time can provide group
participation in all aspects of the activity rather than have each cooperative
group repeat the readings. On the
other hand, you may wish to have each group take readings more frequently on a
rotational basis. This allows more
points on the spread for the graph, in other words, one group at one time
another an hour or two later and, therefore, ending up with more overall
readings.
It is recommended that the students present their data and
analysis before the entire class and then present their conclusive remarks.
It is important to delineate between analysis and conclusion; for
example, after the analysis what conclusions can they form about heavy metals in
the environment? The discussion can
be structured to allow students opinion of the research of heavy metals in the
environment.
References: