Download Infer How strong is your heart muscle? Skill Practice LESSON 2: 30 minutes

Name
Date
Skill Practice
Infer
Class
LESSON 2: 30 minutes
How strong is your heart muscle?
Your heart is a muscle that beats about 75 times every minute. With each beat, it pushes
about 60 mL of blood into your arteries. Heart muscle cells differ from skeletal muscle cells.
Heart muscle cells have about 35 percent more mitochondria than skeletal muscle cells do.
More mitochondria means that a heart cell can obtain more energy from the nutrients it
receives. Can you use the skeletal muscles in your hand to pump liquid as fast as your heart
pumps blood—without getting tired?
Learn It
To infer means to reach a conclusion based on facts. Your heart beats continuously to keep
blood flowing through your body. Modeling the function of the heart can help you infer
how hard your heart works.
Try It
1. Read and complete a lab safety form.
2. Fill a plastic basin with enough water to cover your fist.
3. Remove the bulb from a turkey baster. Hold the turkey baster bulb in your fist and
submerge it completely in the water. Move slowly to avoid spilling water.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
4. Aim the opening of the bulb toward the side of the basin. Let the bulb fill with water.
5. Squeeze the bulb repeatedly as quickly as you can to simulate the beating of your heart.
6. Have a partner count the number of times you squeeze the bulb. Have another partner
time the experiment with a stopwatch.
7. Continue the squeezing action for as long as you can, but not more than 3 minutes.
Record the number of squeezes and the time.
8. Repeat steps 3–7 for all the students in your group.
Respiration and Circulation
43
Name
Date
Class
Skill Practice continued
Apply It
9. Describe how your hand felt at the end of the experiment.
10. Compare how tired your hand muscles got with how tired you think your heart
muscle is after the same number of beats.
11. Calculate Suppose a man who lives to the age of 80 has an average heart rate of
75 beats per minute. About how many times would his heart beat in his lifetime?
12.
Key Concept Infer which type of muscle, heart or skeletal, is able to perform
more consistently without tiring.
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
44
Respiration and Circulation