Sam wished to investigate how fertilizer run-off affects the growth of algae in freshwater lakes and streams. He set his experiment up in this way. Me placed 900 mL of water into each of five 1000 mL. glass beakers. To each beaker he added 5 mL of water from an aquarium that contained a large concentration of algae. The beakers were placed under a grow light that was timed to provide 12 hours of light each day. Liquid fertilizer was added to the beakers in the following amounts: Beaker A - 8 mL fertilizer, Beaker
B - 6 ml. fertilizer, Beaker
C - 4 mL fertilizer, Beaker
D - 2 mL fertilizer, and Beaker
E - no fertilizer.
Each week a random sample from each of the beakers was examined under a microscope to get a count of the number of algae cells present.
i) What is the dependent variable in this experiment?
a. Amount of fertilizer
b. Amount of water
c. Number of algae cells
d. Hours of daylight
ii) What is the independent variable in this experiment?
a. Hours of daylight
b. Number of algae cells
c. Size of the beakers
d. Amount of fertilizer
iii) Which of the following is NOT a controlled variable in this experiment?
a. Amount of light
b. Amount of aquarium water
c. Amount of fertilizer
d. Size of the beakers

I) option A - Amount of fertilizer

II) Option B - Number of Algae cells

II) Option C - Amount of fertilizer

Explanation:

I) A dependent variable in an experiment is basically the output/byproduct of other elements and they are therefore dependent on the the independent variables.

In this experiment, the growth in amount of algae depends on the amount of fertilizer added to the beakers.

Thus, the dependent variable in the experiment is the number growth of algae cells.

So option B is correct.

II) In the experiment, an independent variable could be defined as the inputted substance or quantity that can be changed.

For example, the amount of fertilizer can be changed independently because it does not depend on anything whereas other results depends on it.

Thus, the independent variable in this experiment is the amount of fertilizer added to the beakers.

Option d is correct

III) A controlled variable is defined as one which is kept constant throughout an experiment/study.

A controlled variable doesn't alter with the result of an experiment/study. However, if it is altered, it can affect the relationship/correlation between the Independent and Dependent Variable.

Thus, the amount of fertilizer is not the controlled variable in this experiment.

Option C is correct.

h let me think