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Exercise 23
Thus students should select one of these approaches and should understand that appreciable
time must be allotted for independent study of
these systems. The chemostat requires somewhat
more sophisticated equipment and procedures.
DEVELOPMENT OF AN EXPERIMENTAL DESIGN
Before beginning the experimental study, each student should prepare a research
proposal that describes the objective and plan of the experiment. This proposal should
be evaluated by the instructor and returned to the student. The experimental design
should not be too complex. Manipulate one variable at a time and establish and
evaluate adequate controls. For example, if 1 ml of inorganic phosphorus solution were
added to an experimental ecosystem, then the control would get 1 ml of the same
solution without the inorganic phosphorus. Evaluate all parameters pertinent to the
questions being addressed. Analytical procedures should be rigorous, standardized,
and consistent.
The research proposal should include:
1. A clear statement of the hypothesis.
2. A brief explanation of hypothesis development Uustification of the study).
3. An explicit description of how the hypothesis is to be tested, including manipulation
of parameters, how the manipulation is to be done, to what level, and how often.
4. A description of experimental and control ecosystems, number of each, types of
materials to be used, and so forth.
5. A brief outline of the methods of measurement and evaluation techniques. Indicate a
time schedule for sampling and for the analyses of samples. Identify any plans for
statistical evaluation of the data.
You may want to use flow diagrams or compartmental models to clarify the
experimental design.
A CHEMOSTAT APPROACH
The chemostat is a continuous culture apparatus most commonly used in physiological
studies of algae and bacteria. Basically it consists of a culture vessel into which a fresh
culture medium is fed continuously at a constant, metered rate. The chemostat can
serve as a model of a natural aquatic ecosystem, and its relative simplicity will provide a
starting point for understanding the more complicated interactions which occur
between phytoplankton, bacteria, and their environments. [For more information, see
Herbert et al. (1965), and Barlow et al. (1973).]
The Chemostat
Fresh culture medium is held in a 20-1 Pyrex carboy and forced into the culture
chamber by a metered gas flow (Fig. 23.1). The gas may be generated by electrolytic
decomposition of water from a 250-ml Erlenmeyer flask and connected to the carboy,
which in turn is connected to the culture chamber. Alternatively, a peristaltic pump
could be used to transfer the culture medium to the culture flask. A 12-1 Florence flask is
used for the culture chamber. An overflow tube keeps the volume of the culture
Exercise 23
Thus students should select one of these approaches and should understand that appreciable
time must be allotted for independent study of
these systems. The chemostat requires somewhat
more sophisticated equipment and procedures.
DEVELOPMENT OF AN EXPERIMENTAL DESIGN
Before beginning the experimental study, each student should prepare a research
proposal that describes the objective and plan of the experiment. This proposal should
be evaluated by the instructor and returned to the student. The experimental design
should not be too complex. Manipulate one variable at a time and establish and
evaluate adequate controls. For example, if 1 ml of inorganic phosphorus solution were
added to an experimental ecosystem, then the control would get 1 ml of the same
solution without the inorganic phosphorus. Evaluate all parameters pertinent to the
questions being addressed. Analytical procedures should be rigorous, standardized,
and consistent.
The research proposal should include:
1. A clear statement of the hypothesis.
2. A brief explanation of hypothesis development Uustification of the study).
3. An explicit description of how the hypothesis is to be tested, including manipulation
of parameters, how the manipulation is to be done, to what level, and how often.
4. A description of experimental and control ecosystems, number of each, types of
materials to be used, and so forth.
5. A brief outline of the methods of measurement and evaluation techniques. Indicate a
time schedule for sampling and for the analyses of samples. Identify any plans for
statistical evaluation of the data.
You may want to use flow diagrams or compartmental models to clarify the
experimental design.
A CHEMOSTAT APPROACH
The chemostat is a continuous culture apparatus most commonly used in physiological
studies of algae and bacteria. Basically it consists of a culture vessel into which a fresh
culture medium is fed continuously at a constant, metered rate. The chemostat can
serve as a model of a natural aquatic ecosystem, and its relative simplicity will provide a
starting point for understanding the more complicated interactions which occur
between phytoplankton, bacteria, and their environments. [For more information, see
Herbert et al. (1965), and Barlow et al. (1973).]
The Chemostat
Fresh culture medium is held in a 20-1 Pyrex carboy and forced into the culture
chamber by a metered gas flow (Fig. 23.1). The gas may be generated by electrolytic
decomposition of water from a 250-ml Erlenmeyer flask and connected to the carboy,
which in turn is connected to the culture chamber. Alternatively, a peristaltic pump
could be used to transfer the culture medium to the culture flask. A 12-1 Florence flask is
used for the culture chamber. An overflow tube keeps the volume of the culture