Q: You are asked to prepare 500 $\mu$L of a 2% ethanol solution from a 10% stock. Using the dilution equation $C_1V_1 = C_2V_2$, what volume of 10% stock do you need?

$V_1 = \frac{2\% \times 500\mu L}{10\%} = 100\mu L$

Q: A student wants to achieve a 20% increase in Daphnia heart rate using caffeine. If the baseline heart rate is 120 beats/min, what is the target heart rate?

$120 \times 1.2 = 144$ beats/min

Q: If you need to make 15 mL of a 5% solution from a 30% stock, how much stock solution do you need? Use $C_1V_1 = C_2V_2$.

$V_1 = \frac{5\% \times 15\text{ mL}}{30\%} = 2.5\text{ mL}$

Q: A student prepares a solution by mixing 100 $\mu$L of 10% ethanol stock with 400 $\mu$L of water. What is the final concentration of ethanol in the 500 $\mu$L solution?

$\frac{10\% \times 100\mu L}{500\mu L} = 2\%$

Question 1

Which of the following best describes the role of a hypothesis in the scientific method?

Accepted Answer

A hypothesis is a testable prediction based on background research.

Question 2

When designing an experiment to test the effect of caffeine on Daphnia heart rate, which variable should be considered the independent variable?

Accepted Answer

The concentration of caffeine administered

Question 3

You are asked to prepare 500 $\mu$L of a 2% ethanol solution from a 10% stock. Using the dilution equation $C_1V_1 = C_2V_2$, what volume of 10% stock do you need?

Accepted Answer

$V_1 = \frac{2\% 	imes 500\mu L}{10\%} = 100\mu L$

Question 4

In an experiment, you observe that Daphnia exposed to increasing concentrations of ethanol show a decrease in heart rate. What is the most likely explanation for this observation?

Accepted Answer

Ethanol acts as a depressant, slowing cardiovascular and nervous system activity.

Question 5

Which of the following is NOT a recommended practice for maintaining a proper lab notebook?

Accepted Answer

Writing in pencil to allow for erasing mistakes

Question 6

A student wants to achieve a 20% increase in Daphnia heart rate using caffeine. If the baseline heart rate is 120 beats/min, what is the target heart rate?

Accepted Answer

$120 	imes 1.2 = 144$ beats/min

Question 7

Why is it important to allow the Daphnia to rest for several minutes between experimental treatments?

Accepted Answer

To allow the Daphnia to recover and return to baseline physiological state

Question 8

Which step in the scientific method involves analyzing whether the procedure is working and troubleshooting if necessary?

Accepted Answer

Procedure working?

Question 9

If you need to make 15 mL of a 5% solution from a 30% stock, how much stock solution do you need? Use $C_1V_1 = C_2V_2$.

Accepted Answer

$V_1 = \frac{5\% 	imes 15	ext{ mL}}{30\%} = 2.5	ext{ mL}$

Question 10

Which of the following best describes a dependent variable in the Daphnia heart rate experiment?

Accepted Answer

The heart rate measured after treatment

Question 11

A student prepares a solution by mixing 100 $\mu$L of 10% ethanol stock with 400 $\mu$L of water. What is the final concentration of ethanol in the 500 $\mu$L solution?

Accepted Answer

$\frac{10\% 	imes 100\mu L}{500\mu L} = 2\%$

Question 12

Which of the following is a qualitative observation in the context of the Daphnia experiment?

Accepted Answer

Noting that the Daphnia appears sluggish after ethanol exposure

Question 13

Why is it important to test at least three different concentrations of a chemical when investigating its effect on Daphnia heart rate?

Accepted Answer

To identify the concentration that produces a measurable and reproducible effect

Question 14

Which of the following is the correct sequence of steps in the scientific method as applied to the Daphnia experiment?

Accepted Answer

Observation, Do Background Research, Construct Hypothesis, Test with Experiments, Analyze Data and Draw Conclusions, Communicate Results

Question 15

If a student observes that the Daphnia’s heart rate does not change after adding caffeine, what should be the next step according to the scientific method?

Accepted Answer

Troubleshoot the procedure and check all steps and setup

Question 16

Which of the following is a reason for including both written and graphic/visual data in your lab notebook?

Accepted Answer

To provide comprehensive documentation and facilitate data analysis

Question 17

A student wants to test the effect of a new stimulant on Daphnia heart rate. Which of the following would be the best control for this experiment?

Accepted Answer

Daphnia exposed to water only

Question 18

If the average heart rate of untreated Daphnia is 80 beats per minute, and after exposure to 3% ethanol the heart rate drops to 60 beats per minute, what is the percent change in heart rate?

Accepted Answer

$\frac{60 - 80}{80} 	imes 100 = -25\%$

Question 19

Which of the following is a reason why Daphnia is a useful model organism for studying heart rate?

Accepted Answer

Its heart and body parts can be easily visualized under a light microscope due to its translucent body

Scientific Method and Experimental Design: Effects of Chemicals on Daphnia Heart Rate

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