Q: If a Daphnia's heart rate changes from 80 beats per minute to 100 beats per minute after adding caffeine, what is the percent change in heart rate?

$$\frac{100-80}{80} \times 100 = 25\%$$

Question 1

Which of the following best describes the difference between an independent variable and a dependent variable in a scientific experiment?

Accepted Answer

The independent variable is what you change, and the dependent variable is what you measure.

Question 2

Which of the following statements is the best example of a scientific hypothesis?

Accepted Answer

If caffeine is consumed, then the average heart rate of Daphnia will increase.

Question 3

Caffeine and alcohol have different effects on the nervous system. Which of the following best describes their typical effects?

Accepted Answer

Caffeine acts as a stimulant, increasing nervous system activity, while alcohol acts as a depressant, decreasing nervous system activity.

Question 4

You are asked to prepare a 1:10 dilution of a stock solution using the formula $$C_1V_1 = C_2V_2. If $$your stock solution is 2 M and you need 100 mL of a 0.2 M solution, how much stock solution ($$V_1) $$should you use?

Accepted Answer

$$V_1 = 10$$\ 	ext{mL}$$

Question 5

When using a micropipette to measure 100 $$\muL$$, which of the following is the most important step to ensure accuracy?

Accepted Answer

Using the first stop to aspirate and the second stop to dispense.

Question 6

Which of the following is NOT a structure found in Daphnia?

Accepted Answer

Liver

Question 7

In a Daphnia experiment, students add increasing concentrations of caffeine to the water and measure the heart rate of the Daphnia. Which is the independent variable?

Accepted Answer

Concentration of caffeine

Question 8

A student measures the number of heartbeats in 15 seconds and gets 18 beats. What is the average heart rate per minute?

Accepted Answer

72 beats per minute

Question 9

If a Daphnia's heart rate changes from 80 beats per minute to 100 beats per minute after adding caffeine, what is the percent change in heart rate?

Accepted Answer

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

Question 10

You are given a graph showing average heart rate per minute (y-axis) versus solution concentration (x-axis). If the graph shows a positive linear trend, what can you infer?

Accepted Answer

As solution concentration increases, average heart rate increases.

Question 11

Which of the following best describes how to make an XY scatter plot in a spreadsheet program?

Accepted Answer

Plot the independent variable on the x-axis and the dependent variable on the y-axis.

Question 12

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

Accepted Answer

A Daphnia in water with no alcohol added.

Question 13

If a student uses the formula $$C_1V_1 = C_2V_2 to $$prepare 50 mL of a 0.5 M solution from a 2 M stock, what volume of stock solution is needed?

Accepted Answer

$$V_1 = 12.5$$\ 	ext{mL}$$

Question 14

Which of the following is a plausible reason for using Daphnia in experiments on heart rate and drug effects?

Accepted Answer

Daphnia have transparent bodies, making it easy to observe their heart.

Question 15

A student records the following heartbeats in 15 seconds: 20, 22, 18. What is the average heart rate per minute?

Accepted Answer

Average per 15 sec: $$\frac{20+22+18}{3} = 20$$; per minute: $$20 	imes 4 = 80$$ beats per minute.

Question 16

In an experiment, a student observes that after adding a certain solution, the Daphnia's heart rate drops from 120 to 90 beats per minute. What is the percent change?

Accepted Answer

$$\frac{90-120}{120} 	imes 100 = -25\%$$

Question 17

Which of the following is the best example of a dependent variable in a Daphnia experiment testing the effect of a drug?

Accepted Answer

The heart rate of the Daphnia after drug exposure.

Question 18

A student wants to test the effect of different solution concentrations on Daphnia heart rate. Which of the following best describes the experimental design?

Accepted Answer

The student should vary the solution concentration (independent variable) and measure the heart rate (dependent variable).

Question 19

If a student accidentally uses the second stop to aspirate liquid with a micropipette, what is the most likely result?

Accepted Answer

Too little liquid will be aspirated.

Question 20

Which of the following best explains why it is important to use the correct size micropipette for a given volume?

Accepted Answer

Using a micropipette outside its recommended range can lead to inaccurate measurements.

Unit 3 Review: Experimental Design, Data Analysis, and Biological Variables

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