A student conducted an experiment to investigate the effect of light wavelength on the rat… — ACT

A student conducted an experiment to investigate the effect of light wavelength on the rate of photosynthesis in *Elodea* plants. The student formulated the following hypothesis:

*Hypothesis:* The rate of photosynthesis, as measured by the volume of oxygen ( $O_2$ ) gas produced per hour, increases continuously as the wavelength of light increases from $400\text{ nm}$ to $700\text{ nm}$ .

The student exposed identical *Elodea* plants to different wavelengths of light for 1 hour each, keeping all other environmental variables constant. The results are shown in the table below:

Wavelength	Volume of $O_2$ produced
$400\text{ nm}$	$1.2\text{ mL}$
$450\text{ nm}$	$4.5\text{ mL}$
$550\text{ nm}$	$0.3\text{ mL}$
$650\text{ nm}$	$5.8\text{ mL}$
$700\text{ nm}$	$1.0\text{ mL}$

Based on the results of the experiment, does the data support the student's hypothesis, and how should the hypothesis be modified?

A
Yes; the data show that the overall rate of photosynthesis increases continuously from $400\text{ nm}$ to $700\text{ nm}$ .
No; the rate of photosynthesis does not increase continuously, so the hypothesis should be modified to state that photosynthesis peaks under blue ( $450\text{ nm}$ ) and red ( $650\text{ nm}$ ) light.Answer
C
Yes; the rate of photosynthesis is highest at $650\text{ nm}$ , which is greater than the rate at any lower wavelength tested.
D
No; the rate of photosynthesis decreases continuously, so the hypothesis should be modified to state that the rate is inversely proportional to wavelength.

Answer

No; the rate of photosynthesis does not increase continuously, so the hypothesis should be modified to state that photosynthesis peaks under blue (

450\text{ nm}

) and red (

650\text{ nm}

) light.

The correct answer is correct because the experimental results show that oxygen production does not increase continuously. Instead, it rises and falls, reaching local maxima at

450\text{ nm}

and

650\text{ nm}

, and a minimum at

550\text{ nm}

. Therefore, the hypothesis is unsupported and must be modified to state that photosynthesis is most efficient (peaks) at specific wavelengths corresponding to blue and red light.

Step-by-Step Solution

Analyze the student's hypothesis.

The hypothesis predicts a continuous, monotonic increase in oxygen production as wavelength increases from

400\text{ nm}

700\text{ nm}

Understanding the prediction is necessary to evaluate it against the experimental data.

Examine the trend in the data table.

The volume of oxygen increases from

1.2\text{ mL}

(at

400\text{ nm}

) to

4.5\text{ mL}

(at

450\text{ nm}

), drops to

0.3\text{ mL}

(at

550\text{ nm}

), increases to

5.8\text{ mL}

(at

650\text{ nm}

), and drops again to

1.0\text{ mL}

(at

700\text{ nm}

This determines whether the actual rate of photosynthesis increases continuously.

Compare the data to the hypothesis and determine the appropriate modification.

Because the trend shows peaks at

450\text{ nm}

and

650\text{ nm}

rather than a continuous increase, the hypothesis is not supported and should be modified to describe these dual peaks.

Formulating a modified hypothesis must accurately represent the observed experimental results.

Key Concept

Formulating and Modifying Hypotheses

Estimated Time:1m 30s

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