UNIT 2 – BIOLOGICAL WORLD The heartbeat and pulse


Doctors listen for a heartbeat using a stethoscope. The lub-dub sound is made when the valves in the heart close after blood passes through. The normal heart rate for an adult at rest is between 60 and 100 beats per minute.


The pulse is a wave of vibration that passes through an artery when blood is forced out of the heart. The pulse can be felt at an artery close to the surface of the skin, such as in the wrist.


The pulse rate and heart rate are the same. The pulse tells us if the heart is beating at a normal rate. A person’s age, sex, physical fitness, diet and stress affect their heart rate. A balanced diet, exercise and rest are very important for a healthy heart.


:Fig. 7.9 A stethoscope being used to listen to a person’s heartbeat


EXPERIMENTAL INVESTIGATION 7.1 How does exercise affect pulse rate?


Equipment Timer


Method


1. Work in pairs. Student A will locate their pulse on their wrist (see Fig. 7.10). Student B will monitor time and record data.


2. Student A remains at rest (stands still) for 2 minutes. Student B will time them.


3. After this, student A will start counting their pulses while student B times them for 30 seconds.


4. Student B will record the number of pulses in a table.


5. Follow steps 1–4 two more times.


6. Calculate student A’s average pulse rate at rest (number of pulses per minute).


7. Follow steps 1–6 after low–moderate exercise (student A walks briskly for 2 minutes) and then after moderate– high exercise (student A jogs or runs at approximately a three-quarter pace for 2 minutes).


SAFETY • Make sure that you are medically fit to do exercise before taking part in this investigation.


Pulse rate monitor (optional)


:Fig. 7.10 How to take the pulse at the wrist


8. Student A and student B swap roles and follow steps 1–7. 9. Plot your data on a suitable chart or graph.


j Go to page 10 of your Experimental Investigations Log to write up this investigation.


62 Elements of Science


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