Daphnia magna, A Population Study

Question:   Can a microorganism like Daphnia demonstrate exponential growth?

Materials:      Daphnia culture, clear plastic cups, graph paper, pipettes, de-ionized water, food: blue green algae capsules, dry yeast and Tetra Min, data sheet, petri dish

Procedure:

1.         Prepare food mixture: Take 1/2 capsule of blue-green algae and mix with a small amount of dry yeast about the size of a match head and an equal amount of Tetra Min fish food. Add a couple drops of water and make a paste. Then add additional water (about 1/2 cut) and stir until totally dissolved.

2.         Place several adult Daphnia in 1/2 cup of water. Squirt 5 ml of food mixture into the cup.

3.         Place a grid (graph paper) with a target area 4 cm. square marked off in red. Place the target close to the center of the petri dish. (This will be our apparatus for counting.)

4.         Place cup with Daphnia in a place with indirect lighting.

5.         Each day the student should carefully pour the Daphnia into the petri dish.

6.         At this time they should count the number of Daphnia that appear in the target area, distinguishing between adults and juveniles in the count. This should be recorded on the data sheet. Additional information to be recorded at this time are date, time, and room temperature.

7.         Give an additional 5 ml of the food mixture after each count. Be careful when transferring animals. Don’t shock organisms with rough handling.

8.         Continue this procedure for an extended period of time.

9.         Data will be transferred to a spreadsheet and statistics will be analyzed and graphically shown.

Experiment by Pat Mazzer