The Effect of Fertilizer on Algae

Determine how excess nutrients affect the growth of algae? Purpose Determine how excess nutrients affect the growth of algae?

Background Information As primary producers, algae form the base of the food web. The term algae is used to describe a range of organisms from the large brown kelp found attached to rocks at the seashore to the tiny green algae found in fish tanks. Like other plants, green algae need nitrogen and phosphorus in order to grow. These nutrients must be available for the algae to grow and reproduce.

Background Information These nutrients must be available for the algae to grow and reproduce. Have you ever seen a pond with a thick, green layer of algae on its surface? This layer is a sign that the pond ecosystem has been disturbed by the presence of too much nitrogen or phosphorus in the water.

Background Information Fertilizers contain these nutrients, which can end up in bodies of water when rainfall flows downhill from farms. In this lab, you will work with a type of algae that is commonly found in ponds and aquariums. You will compare the growth of algae when nutrients are limited and when nutrients are plentiful.

Fertilizer Check the label on the fertilizer and see what it contains. Record the contents.

Build Vocabulary Term Definition Nutrient Controlled experiment Independent Variable Dependent Variable Hypothesis

Materials 3 test tubes tape beaker 2 dropper pipettes algae culture graduated cylinder spring water fertilizer 3 cotton balls grow light

Safety Wear your lab apron. If you have glass test tubes or cylinders, check for cracks or chips. Alert your teacher if you break a glass object. Make sure the test tubes are clean before you use them. Wash your hands thoroughly with soap and warm water before leaving the lab.

Procedure Use tape and a pen to label one test tube Control and the other two Fertilizer A and Fertilizer B. Place the test tubes in a beaker. Use a dropper pipette to add 20 drops of algae culture to each test tube. Add 19 mL of spring water to each test tube. Use a second dropper pipette to add 4 drops of fertilizer solution to the test tube labeled Fertilizer A and 8 drops of fertilizer in Fertilizer B.

Procedure Loosely plug each test tube with a cotton ball to slow the evaporation of the water. Place the test-tubes under a grow light. Turn on the light. Adjust the position of the test tubes so that each test tube will receive an equal amount of light. Observe the test tubes each day for the next week or so and record your observations in the data table.

Pre-Lab Questions Design an Experiment What is the Independent variable in this experiment? What is the dependent variable in this experiment?

Pre-Lab Questions Hypothesize/Predict How will you be able to tell which test tube has more algae? Write a hypothesis that will predict what will happen.

Control Variables Why will you grow algae in spring water instead of pond water? Why do we have one test tube with no fertilizer?

Data Table Day Control Fertilizer A Fertilizer B 1 2 3 4 5 6 7 8 9 10

Analyze and Conclude 1. Compare and Contrast Summarize your observations of the test tubes during this lab. 2. Draw Conclusions How did the addition of fertilizer affect the growth of the algae? 3. Infer Why did you use cotton balls instead of rubber stoppers to plug your test tubes? Hint: Review the diagram of the carbon cycle on page 83 of your textbook. 4. Apply Concepts How could a thick layer of algae on the surface of a pond affect producers that live on or near the bottom of the pond?