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Cells and Systems 6-8 / Week 05 / Wednesday
3/6
Week 05 · Cells to Tissues to Organs

Wednesday

Windowsill Lab: Counting a pulse
// Levels of organization in a living body
⏱ about 20 min

Wednesday: Windowsill Lab: Counting a Pulse

Rocket is already bouncing on his toes beside the Windowsill. "Twenty jumps, then count. Let me go first!"

"Rest first," Raven says, pointing at a chair. "A resting pulse means you have been sitting still for ten minutes."

Rocket sits. He fidgets. He sits some more. Nova counts the minutes with a slow blink of her light.

"Now find it," Raven says. Rocket presses two fingers below his thumb and goes quiet. "Got it."

"Count for thirty seconds," Nova says, "then double it. What do you predict happens after the jumps?"

"It goes up," Rocket says. "Way up." Raven writes the prediction in the Log before anyone jumps.

Your mission

Today you take two science readings of your own heart: a resting pulse and a pulse right after twenty gentle jumps.

The pulse is the number of heartbeats per minute. You will count beats at your wrist and turn the count into beats per minute.

These numbers are science readings, like the height of a seedling. They are not a health check, and you do not compare them to anyone else.

  • A kitchen timer or a phone timer that shows seconds
  • A chair, and a flat clear space on the floor for jumping
  • Shoes on, water nearby
  • Your Windowsill Log and a pencil
Safety first
Jump on flat ground with shoes on, only as hard as you are used to. Twenty small jumps is plenty.
Anyone who feels dizzy sits down right away and drinks some water.
Count your pulse with two fingers on your wrist. Never press a thumb or fingers on your neck.
This is a science reading, not a health check. Your numbers go in your own Log and nowhere else.
  1. Sit still in the chair for ten full minutes. Read or draw, but do not get up.
  2. Place your index and middle finger on the underside of your opposite wrist, below the base of the thumb.
  3. Press with flat fingers until you feel the beat. Start the timer.
  4. Count the beats for 30 seconds. Multiply by 2. Write the number in the table as beats per minute at rest.
  5. Stand up and do twenty gentle jumps in place, one per second.
  6. Sit down at once, find the pulse again, and count for 30 seconds. Multiply by 2 and record it.
  7. Rest for five minutes, then count once more. Record this as your pulse after resting again.
ReadingBeats in 30 secondsBeats per minute (times 2)
At rest, after 10 minutes sitting
Right after 20 jumps
After 5 more minutes of rest
PREDICT BEFORE YOU JUMP
  • Read the question.
  • Tap your answer.
Compared with your resting pulse, your pulse right after twenty jumps will probably be:
You count 36 beats in 30 seconds. How many beats per minute is that?
Which fingers do you use to find the pulse at the wrist?

Reading your result

To count a resting pulse, you must have been resting for at least ten minutes. That is why step one felt so long.

An exercise pulse is counted while you exercise or right after. Waiting even a minute changes the number.

Counting for 30 seconds and doubling is accurate. Counting for 10 or 15 seconds and multiplying by 6 or 4 usually works too.

Your heart is cardiac muscle doing more work after the jumps. Next week you will find out what the extra beats carry.

Your third reading shows the heart settling again. The muscle slows down on its own, with no instruction from you.

What the lab showsTrue or false?
A resting pulse is counted after at least ten minutes of rest.?
The pulse is counted with the thumb pressed on the neck.?
Counting beats for 30 seconds and doubling gives beats per minute.?
You can make your heart slow down by deciding to.?
WHY THIS EXERCISEA careful method is what makes a pulse count a real science reading.
You count beats for 15 seconds. What number do you multiply by to get beats per minute? Type a number.
WHY THIS EXERCISEScientists shorten a count when they must, but they always scale it back to one minute.
Draw your three readings as three bars on a simple bar graph. Label them rest, after jumps and rest again.

Careful counting. Tomorrow you will read a real table of resting pulse ranges and see where they come from.

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