Part B: Heart Rate
Your heart rate can be determined by counting the number of times your heart beats per minute. There are several places you can find your pulse—the rhythmic pressure wave of blood in the arteries. The radial pulse can be found by placing two fingers just below the wrist creases at the base of the thumb. Another common place to feel the pulse is the carotid artery in the neck. Place two fingers, index and middle, between the trachea and large neck muscle. Be sure to sit still without talking, and slowly move the fingers together until you can feel the blood flow.

In this experiment, you’re collecting data to determine how holding your breath affects your heart rate. Write a hypothesis stating whether your heart rate will increase, decrease, or stay the same after holding your breath for 30 seconds. Also, identify the independent and dependent variables.

Hypothesis: _

Independent variable: _
Dependent variable: _
Remember, the hypothesis is a prediction based on observations and past knowledge. For more information on forming hypotheses, refer in your Lab Manual to Appendix A: How to Form a Hypothesis.

Data
Create a chart like the one below. Then, complete the following steps.

Find your pulse. Count the number of times your heart beats in 60 seconds.
Record and repeat two more times. It’s important to have more than one trial in an experiment to reduce errors.
Calculate the average of the three trials, and record the results. The average can be calculated by adding the three trial values together and then dividing by three.
Hold your breath for 30 seconds, and take your pulse immediately afterward.
Record and repeat two more times.
Calculate the average of the three trials and record.

Part A: Identifying Variables

The dependent variable happens as a result of values/changes associated with the independent variable.

Independent variable: number of cigarettes smoked

Dependent variable: risk for lung cancer

Independent variable: number of sharks swimming in a coastal region

Dependent variable: number of shark attacks on humans

Independent variable: amount of milk a person drinks

Dependent variable: the strength of his or her bones

Part B: Heart Rate

Hypothesis: If I hold my breath for 30 seconds, then my heart rate will

(choose 1) increase/decrease.

Independent variable: holding my breath

Dependent variable: heart rate

Part C:

The heart rate decreases because oxygen exchange in the lungs decreases.

This depends on what you chose for heart rate in the hypothesis. If you said the heart rate decreases after holding your breath, and the results showed the heart rate decreased, then the hypothesis is supported. If you said the heart rate decreases after holding your breath, and the results showed the heart rate increased, then you refuted the hypothesis.

Heart rate can change due to an increase or decrease in activity, moving positions such as sitting and standing, and emotions.

Example: Increase in activity—jumping jacks

Hypothesis: If I do five jumping jacks, then my heart rate will increase.

Test hypothesis. You can use the average resting heart rate from the previous experiment. If you do an experiment with an increase in physical activity like jumping jacks, then your data will reflect an increase in heart rate because the body requires more energy, which requires more oxygen, increasing the overall flow of blood in the body.

Support or refute the hypothesis based on the results. The hypothesis is supported if it aligns with the observed results. The hypothesis is refuted if the results don’t match the statement based on the variables.

Testing more than one variable at a time makes it difficult to interpret the results and support or refute the hypothesis. With one variable, the results can be associated with changes to that variable. To get the most reliable data to support or refute a hypothesis, an experiment should be completed several times to see if the results show the same trends. Refer to page 6 in your textbook.

Explanation:

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