This scanning electron micrograph shows individual red and white blood cells flowing through a vein (magnification 3850×).

Procedure

1.   If you are using a heart-rate sensor, see your teacher for instructions.

2. While sitting still, measure your heart rate. To do this, find the pulse in one of your wrists using the first two fingers of your other hand.

3. Count the number of beats you feel in 15 seconds and multiply this number by 4. This will give you the number of beats per minute.

4. What do you think would happen if you stood up? Would your heart rate decrease, increase, or stay the same? Stand up and measure your heart rate to find out.

Think About It

Formulating Hypotheses  Propose an explanation for any difference between your sitting heart rate and your standing heart rate.