Page 29 - SpringBoard_Writing_Workshop_Grade7_Flipbook

Writing Workshop 3 (continued)
My Notes
During Reading
4. Read the following essay, and determine the purpose or controlling
idea. As you read, mark the thesis (the point the writer is making) and supporting information, along with the topic sentences in each paragraph.
What’s in Your Toothpaste?
Excerpted from The Secret House: Twenty-Four Hours in the Strange and Unexpected World in Which We Spend Our Days and Nights
by David Bodanis
Into the bathroom goes our male resident, and after the most pressing need is satisfied it’s time to brush the teeth. The tube of toothpaste is squeezed, its pinched metal seams are splayed, pressure waves are generated inside, and the paste begins to flow. But what’s in this toothpaste, so carefully being extruded out?
Water mostly, 30 to 45 percent in most brands: ordinary, everyday simple tap water. It’s there because people like to have a big gob of toothpaste to spread on the brush, and water is the cheapest stuff there is when it comes to making big gobs. Dripping a bit from the tap onto your brush would cost virtually nothing; whipped in with the rest
of the toothpaste the manufacturers can sell it at a neat and accountant-pleasing
$2 per pound equivalent. Toothpaste manufacture is a very lucrative occupation.
Second to water in quantity is chalk: exactly the same material that school teachers use to write on blackboards. It is collected from the crushed remains of long-dead ocean creatures. In the Cretaceous seas chalk particles served as part of the wickedly sharp outer skeleton that these creatures had to wrap around themselves to keep from getting chomped by all the slightly larger other ocean creatures they met. Their massed graves are our present chalk deposits.
The individual chalk particles—the size of the smallest mud particles in your garden—have kept their toughness over the aeons, and now on the toothbrush they’ll need it. The enamel outer coating of the tooth they’ll have to face is the hardest substance in the body—tougher than the skull, bone, or nail. Only the chalk particles in the toothpaste can successfully grind into the teeth during brushing, ripping off the surface layers like an abrading wheel grinding down a boulder in a quarry.
The craters, slashes, and channels that the chalk tears into the teeth will also remove a certain amount of build-up yellow in the carnage, and it is for that polishing function that it’s there. A certain amount of unduly enlarged extra-abrasive chalk fragments tear such cavernous pits into the teeth that future decay bacteria will be able to bunker down there and thrive; the quality control people find it almost impossible to screen out these errant super-chalk pieces, and government regulations allow them to stay in.
In case even gouging doesn’t get all the yellow off, another substance is worked into the toothpaste cream. This is titanium dioxide. It comes in tiny spheres, and it’s the stuff bobbing around in white wall paint to make it come out white. Splashed around your teeth during the brushing it coats much of the yellow that remains. Being water soluble it leaks off in the next few hours and is swallowed, but at least for the quick
2 SpringBoard® Writing Workshop with Grammar Activities Grade 7
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