The Beat in the Dish
Leo counts his pulse: 72 beats a minute. In a lab video, a single heart muscle cell in a dish twitches on its own.
If one heart cell only twitches, where does the pumping of a heart come from?
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Science · Grade 7 Science
Chapter 1: Cells: The Unit of Life
New properties appear as you go up.
Leo counts his pulse: 72 beats a minute. In a lab video, a single heart muscle cell in a dish twitches on its own.
If one heart cell only twitches, where does the pumping of a heart come from?
Make your guess to turn the page.
Still to come: 10 pages · Words to Know · What We Learned · 4 questions · Explain It in Writing · Ask and Wonder
The idea this lesson is working on — Children imagine an organ as a large lump of one kind of cell, so a heart is "lots of heart cells". The dish separates the levels: single cells twitch, a sheet beats together and pumps nothing, and only a heart with chambers, valves and several tissues pumps. Ask: the sheet beats, so why does it not pump? The idea to reach is that the arrangement of several tissues is what produces the job.
New properties appear as you go up — No single heart cell pumps blood, and no single neuron thinks. A property that belongs to an arrangement rather than to its parts is called emergent, which is why studying the parts alone is never enough. Heart muscle cells in culture really do beat spontaneously and synchronise once they connect through gap junctions.
About the numbers — A resting stroke volume of about 60 mL and a pulse of 72 are realistic for a 12-year-old; adults at rest pump about 5 L a minute. The rates for single cells in the dish are an illustration of the range such cells show, not a published measurement.