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Difficulty: EasyIdentifying Independent, Dependent, and Controlled Variables

A marine biology student designs an experiment to measure the rate of oxygen production in *Chlorella* algae. Four identical glass flasks are filled with equal volumes of an algal suspension of the same cell density. Each flask is exposed to a light source of a different wavelength (red, blue, green, and yellow) while keeping the light intensity fixed at 500 lux500\text{ lux} and the temperature constant at 22∘C22^\circ\text{C}. The volume of dissolved oxygen produced by each culture is measured after 3 hours3\text{ hours}.

Match each experimental element from this investigation to its corresponding variable type.

  • Wavelength of the light source (red, blue, green, yellow)Independent Variable
  • Volume of dissolved oxygen produced after 3 hours3\text{ hours}Dependent Variable
  • Temperature of the algal culture (22∘C22^\circ\text{C})Controlled Variable

Answer

Wavelength of light source matches Independent Variable; Volume of dissolved oxygen produced matches Dependent Variable; Temperature of the culture matches Controlled Variable.
In experimental design, the independent variable is the condition purposefully changed by the experimenter (wavelength of light), the dependent variable is the resulting measurement being observed (dissolved oxygen volume), and controlled variables are factors kept uniform to maintain a fair test (culture temperature).

Step-by-Step Solution

1
Identify the factor changed directly by the experimenter.
The researcher intentionally changes the light wavelength (red, blue, green, yellow) for each flask.
The variable directly manipulated by the experimenter to test its effect is the independent variable.
2
Identify the factor measured to observe the response or outcome.
The researcher measures the volume of dissolved oxygen generated after 3 hours3\text{ hours}.
The variable being measured or observed as the output of the experiment is the dependent variable.
3
Identify factors held constant throughout all experimental trials.
The culture temperature is kept unchanged at 22∘C22^\circ\text{C} for all flasks.
Conditions held constant to ensure a fair test are controlled variables.

Key Concept

Experimental Variables (Independent, Dependent, and Controlled)
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Topics

Identifying Independent, Dependent, and Controlled Variables

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