The question
Name: ______________________ Date: ____________ Phosphate and productivity in pond water (10 points)
Model or diagram
Results of a pilot test
(a) A class wants to know how phosphate from lawn fertilizer affects the productivity of algae in a pond. They fill clear bottles with pond water, add different amounts of phosphate, and measure dissolved oxygen at the start and after 24 hours in sunlight. A pilot test gave the results in the graph. Identify the independent variable. [1 point]
(b) Identify the dependent variable. [1 point]
(c) Write a testable hypothesis for this investigation. [1 point]
(d) Identify the control group, and describe its purpose. [2 points]
(e) Identify one variable that should be held constant, and explain why. [2 points]
(f) The class also puts one bottle of each kind in the dark for 24 hours. Explain why the dissolved oxygen in the dark bottles decreases. [1 point]
(g) The pilot graph levels off between 0.10 and 0.20 mg/L of phosphate. Describe what this pattern suggests, and explain one possible reason. [2 points]