occur in lake settings. In this lesson you use microcosms and RUSS data
to investigate changes in oxygen
concentrations that result from photosynthesis and respiration.
Introduction to Cell Respiration and Photosynthesis
before beginning the lesson.
knowledge of photosynthesis
and respiration. Consider how
these processes might affect oxygen
concentrations in lakes.
I - Microcosm Set-up
the following materials for the microcosm set-up.
- 3 - 8 oz or 250 ml jars
- 10 - 8 cm sprigs of Elodea sp.
- 8 - 5 cm fathead minnows
- oxygen, carbon dioxide, and
pH kits (meters may be substituted)
- a sunny window or a grow light
for oxygen, pH, and C02 in each of the three microcosms. You need to
be prepared to explain the rationale for your predictions.
jars A, B, and C. Fill Jar A to overflowing from the supply of aged
water. Add 4 fathead minnows. (Do not worry about spilling water.) Note
the time jar is sealed. Fill Jar B to overflowing with aged water. Add
five 3 inch sprigs of elodea. (Do not worry about spilling water.) Note
the time jar is sealed. Fill Jar C to overflowing with aged water. Add
4 fathead minnows and five 3 inch sprigs of elodea. Note the time jar
is sealed. Place all of your jars on a window sill (the brighter the
better.) They should sit for approximately 30 minutes from the time
they were sealed.
oxygen, pH, and carbon dioxide concentrations in samples of the remaining aged water using the water
chemistry kits or meters. If using Hach or Lamotte kits proceed by testing
the oxygen first in each bottle. Perform the tests rapidly to minimize
the development time between microcosms.
minutes retest the carbon dioxide, oxygen,
and pH in each of the 3 microcosms. Record your results on your Photosynthesis
and Respiration Worksheet.
your worksheet for these lesson components.
II is complete, turn your worksheet in to your teacher.
II - Using WOW Technologies
in the discussion of lab results. How might photosynthesis and aquatic respiration affect water chemistry in a lake environment? Consider how
photosynthesis and respiration might affect oxygen concentrations, temperature,
and pH in a lake.
about oxygen concentrations, temperature, and pH in a lake. What is
the rationale for your predictions? Do you expect a different
lake to study from the WOW web site. Open a data file from midsummer,
WOW data from the web site. If using a spreadsheet select a file in
the Excel format. Otherwise, select the HTML format. You will need to
either download the Excel file or copy and paste the HTML data into
a spreadsheet for analysis.
the oxygen concentration at one meter intervals over a 48 hour period.
Is there a pattern in the data?
the data from top to bottom trends in temperature, dissolved 02 (mg/l),
(% saturation), and pH levels. Are there any patterns
in the data?
graph of temperature, oxygen, and pH profile data.
the questions on the Photosynthesis and Respiration
worksheet and graph in to your teacher.