Question

during an investigation, a researcher and his team divided an experimental lake with a plastic curtain. the research team added various chemicals to the two sides of the lake. then the research team determined that phosphorus, primarily from detergents and sewage treatment, was responsible for algal blooms.

question 27

in this investigation, the manipulated variable is the

• plastic curtain
• size of the lake
• chemicals added
• presence or absence of algae

Explanation:

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<reasoning>

Identify the experimental setup

Using the Experimental Design knowledge point
The experiment describes a lake divided into two halves by a plastic curtain. One half has no phosphorus added, while the other half has phosphorus added.

Determine the manipulated variable

Using the Manipulated Variable knowledge point
The variable deliberately changed or controlled by the researchers between the two experimental groups is the addition of chemicals (specifically phosphorus).

Evaluate the options

• plastic curtain: This is a controlled element used to divide the lake, not the variable being tested.
• size of the lake: This is a controlled physical characteristic.
• chemicals added: This is the factor changed by the researchers to observe its effect.
• presence or absence of algae: This is the responding variable that changes as a result of the manipulation.

</reasoning>

<answer>
<mcq-option>plastic curtain</mcq-option>
<mcq-option>size of the lake</mcq-option>
<mcq-correct>chemicals added</mcq-correct>
<mcq-option>presence or absence of algae</mcq-option>
</answer>

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Answer:

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<reasoning>

Identify the experimental setup

Using the Experimental Design knowledge point
The experiment describes a lake divided into two halves by a plastic curtain. One half has no phosphorus added, while the other half has phosphorus added.

Determine the manipulated variable

Using the Manipulated Variable knowledge point
The variable deliberately changed or controlled by the researchers between the two experimental groups is the addition of chemicals (specifically phosphorus).

Evaluate the options

• plastic curtain: This is a controlled element used to divide the lake, not the variable being tested.
• size of the lake: This is a controlled physical characteristic.
• chemicals added: This is the factor changed by the researchers to observe its effect.
• presence or absence of algae: This is the responding variable that changes as a result of the manipulation.

</reasoning>

<answer>
<mcq-option>plastic curtain</mcq-option>
<mcq-option>size of the lake</mcq-option>
<mcq-correct>chemicals added</mcq-correct>
<mcq-option>presence or absence of algae</mcq-option>
</answer>

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