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2.7.3Additional lessons

Measuring Pulse Rate — IB Biology SL Revision Notes & Topical Questions

5 min read 5 parts Lesson 36 of 142

📚 IB Biology SL Hub / Topical Revision
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Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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Section 1 of 5What a Pulse Is

Ventricular contraction
  • Ventricular contraction Each contraction of the left ventricle forces blood into the aorta and sends a pressure wave along the arteries.
Pulse
  • Pulse The pressure wave can be felt where an artery lies near the skin and over a bone, and it matches the heartbeat.
Sites
  • Sites Common sites are the radial artery at the wrist and the carotid artery at the side of the neck.
Resting rate
  • Resting rate A typical resting adult rate lies between about 60 and 100 beats per minute, and fitter people are often lower.
Control
  • Control The sinoatrial node sets the rate and signals from the brain, including adrenaline, can change it.

Section 2 of 5Taking a Measurement

1
Sit the subject down and rest for several minutes so that the starting rate is steady.
2
Press two fingertips lightly on the radial artery, not the thumb, because the thumb has its own pulse.
3
Count the beats for a fixed time such as 15 or 30 seconds, using a stopwatch.
4
Multiply the count to give beats per minute, for example four times a 15 second count.
5
Repeat the reading several times and calculate a mean to reduce random error.

Section 3 of 5Investigating Exercise

Investigating Exercise
Independent variable
  • Independent variable The type or duration of exercise, such as step-ups for a set time, is changed deliberately.
Dependent variable
  • Dependent variable The pulse rate in beats per minute is measured immediately after exercise and again during recovery.
Controlled variables
  • Controlled variables Keep the same person, time of day, step height, rest period and counting method for every trial.
Recovery time
  • Recovery time Record how long the pulse takes to return to the resting rate, since this indicates fitness.
Explanation
  • Explanation Exercise raises demand for oxygen and carbon dioxide removal, so the heart rate increases to deliver more blood.

Section 4 of 5Worked Example

Question

  • A student counts 22 beats in 15 seconds at rest.
  • After exercise the student counts 38 beats in 15 seconds.
  • Calculate both rates and the percentage increase.

  1. Resting rate = 22 × 4 = 88 beats per minute.
  2. Exercise rate = 38 × 4 = 152 beats per minute.
  3. Increase = (152 − 88) ÷ 88 × 100 = 72.7 %.

Answer

  • 88 and 152 beats per minute;
    • an increase of 72.7 %.

Section 5 of 5Exam Checklist & Tips

2.7.3 – Key Points for the Exam

  • Pulse The pressure wave in an artery caused by each heartbeat.
  • Heart rate The number of heartbeats per minute.
  • Resting rate The pulse rate measured when the body has been inactive for a few minutes.
  • Recovery time The time taken for pulse rate to return to its resting value after exercise.

Common Mistakes

  • Counting the pulse with the thumb, which gives an error because it has its own pulse.
  • Pressing too hard on the artery so that the blood flow is blocked.
  • Taking one reading only and treating it as reliable instead of calculating a mean.
  • Not controlling the rest period, so the starting rate differs between trials.

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