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Subject Test Biology

Question 21 of 24

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SAT Subject Test

The multiple choice questions have five answer choices — one (and only one) is correct in each case.

Three students added equal volumes of pond water to each of four beakers (I–IV) and placed each in a different constant temperature bath, maintained at 5 degree C, 15 degree C, 25 degree C, and 35 degree C, respectively. The students then added 6 water fleas, Daphnia pulex, to each of the four beakers and recorded the time in each case. After 1 hour, the students removed 3 Daphnia pulex from each beaker and each student immediately observed one Daphnia pulex under low-power magnification of a light microscope. (The transparent body of the Daphnia pulex can be seen easily under a light microscope.)  Heart rates were recorded as beats per minute. The results of the experiment are summarized in the chart below.

Beaker Temperature Time Daphnia Added Time Daphnia Removed Heartbeats Per Minute
(average of 3 Daphnia)
I 5 degree C 2:00 p.m. 3:00 p.m. 41
II 15 degree C 2:10 p.m. 3:10 p.m. 119
III 25 degree C 2:20 p.m. 3:20 p.m. 202
IV 35 degree C 2:30 p.m. 3:30 p.m. 281

The independent variable in this experiment is the

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amount of light

Correct Answer: 

number of water fleas

Correct Answer: 

pH of the water

Correct Answer: 

temperature of the water

Correct Answer: 

average heart rate

Correct Answer: 

An independent variable is one that is being manipulated. In this experiment, the variable being manipulated is the temperature of the water.

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