Lesson
2
Materials:
3 test tubes with screw caps
distilled water
graduated cylinder
10% nitrate/phosphate solution
20% nitrate/phosphate solution
Chlorella culture
light source
After reading through the activity, develop a hypothesis which states which of the solutions, distilled water, 10% nitrate/phosphate solution or 20% nitrate/phosphate solution, will contain the largest amount of Chlorella after a five day period.
Hypothesis:
Procedure:
Working with a partner:
1. Write your name and your lab partner's name on each test tube.
2. Label the first test tube distilled water and fill in three quarters
full with distilled water. This is the control.
3. Label the second test tube 10% nitrate/phosphate solution and the
third test tube 20% nitrate/phosphate solution. Fill both test tubes three
quarters full with the appropriate solution.
4. Gently mix the Chlorella culture. Using the dropper, place 10 drops
of the Chlorella culture into each tube. Shake each tube gently to mix
the contents.
5. Place the caps on the test tubes tightly and lay them on their sides
in a well lit area where they will be undisturbed for the five day period.
Note: A light source may be used to provide a well lit area.
6. Check the test tubes every day for the next five days. Record the observations on the data table. Growth of Chlorella can be determined by an increase in the density of the algae as well as an increase in the darkness of the green color in the tubes. Record your results on the data table each day.
Data Table:
2. Were there any changes in the distilled water tube? Explain.
3. At what level of nitrate, 10% or 20%, did the most growth occur?
Why?
4. Based on your observations, what would you conclude about the effects
of excessive
nitrates and phosphates on the growth of algae?
5. How could the increased use of nitrates and phosphates (fertilizers),
adversely effect an
aquatic ecosystem?