Answer:
I) option A - Amount of fertilizer
II) Option B - Number of Algae cells
II) Option C - Amount of fertilizer
Step-by-step 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.