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Pop Science: Inside a Popcorn Kernel

7th grade nonfiction passage about why popcorn pops: 234 words, six questions, an answer key and vocabulary.

7th grade nonfiction why popcorn pops 234 words

Pop Science: Inside a Popcorn Kernel

Most corn does not pop, but one special type does. Popcorn kernels look like tiny stones, yet each one is a sealed package with three main parts. The hard, shiny outer shell is called the hull. Inside is a starchy center, and within that starch is a small amount of water.

When the kernel is heated, the water inside starts to turn into steam. Steam takes up much more room than liquid water, so pressure builds inside the sealed hull. The hull of popcorn is unusually strong and nearly waterproof, so it holds the pressure for a moment longer than the hull of other corn would. Meanwhile the hot starch softens into a gel-like state.

At last the pressure becomes too great. The hull ruptures with a pop, and the soft starch bursts out and expands into a foam. As it cools in the air, the foam hardens into the light, crunchy shape we know. Pieces of the hull often stay attached, and sometimes they get stuck in your teeth.

Some kernels never pop. They may have dried out too much, so there is not enough water to make steam, or they may have a tiny crack in the hull that lets steam leak out. That is why popcorn should be stored in a sealed container instead of an open bag, and why a fresh bag usually pops better than an old one.

Questions

  1. What are the three main parts of a popcorn kernel? in the text

  2. What does the water inside the kernel turn into when it is heated? in the text

  3. Why is the strong hull of popcorn important? in the text

  4. What happens when the pressure becomes too great? in the text

  5. Why might a kernel with a tiny crack in its hull fail to pop? think about it

  6. Why should popcorn be stored in a sealed container? think about it

Words to know

kernel
a single hard seed of corn
hull
the tough outer shell of a seed
starchy
full of a soft food substance found in grains
pressure
a pushing force on the inside of something
ruptures
breaks open suddenly
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One passage, three levels

The same topic and facts written three ways, so a mixed class can read and talk about one text. Each group’s sheet shows only a shape; the key says which is which.

● Easier · 203 words · Flesch-Kincaid grade 2.2

Most corn will not pop, but one special kind will. A popcorn kernel looks like a tiny stone. But it is a sealed package with three parts. The hard, shiny shell is the hull. Inside is a starchy center. In the starch is a small bit of water.

When the kernel gets hot, the water turns to steam. Steam takes up much more room than water. So pressure builds up inside the hull. The hull of popcorn is strong and almost waterproof. It holds the pressure a little longer than other corn would. Meanwhile, the hot starch gets soft like gel.

At last, the pressure is too much. The hull breaks with a pop. The soft starch bursts out and puffs into foam. In the air it cools and turns hard. It becomes the light, crunchy snack we know. Bits of hull often stay stuck on, and they can get stuck in your teeth.

Some kernels never pop. They may be too dry, so there is not enough water to make steam. Or they may have a tiny crack that lets the steam out. So popcorn should be kept in a sealed container. A fresh bag usually pops better than an old one.

▲ This passage · 234 words · Flesch-Kincaid grade 5.7

Most corn does not pop, but one special type does. Popcorn kernels look like tiny stones, yet each one is a sealed package with three main parts. The hard, shiny outer shell is called the hull. Inside is a starchy center, and within that starch is a small amount of water.

When the kernel is heated, the water inside starts to turn into steam. Steam takes up much more room than liquid water, so pressure builds inside the sealed hull. The hull of popcorn is unusually strong and nearly waterproof, so it holds the pressure for a moment longer than the hull of other corn would. Meanwhile the hot starch softens into a gel-like state.

At last the pressure becomes too great. The hull ruptures with a pop, and the soft starch bursts out and expands into a foam. As it cools in the air, the foam hardens into the light, crunchy shape we know. Pieces of the hull often stay attached, and sometimes they get stuck in your teeth.

Some kernels never pop. They may have dried out too much, so there is not enough water to make steam, or they may have a tiny crack in the hull that lets steam leak out. That is why popcorn should be stored in a sealed container instead of an open bag, and why a fresh bag usually pops better than an old one.

■ Harder · 243 words · Flesch-Kincaid grade 8.1

Most varieties of corn never pop, but one special type does so reliably. Popcorn kernels resemble tiny stones, yet each is a sealed package with three principal parts. The hard, glossy outer shell is called the hull; inside it lies a starchy center; and within that starch is a small quantity of water.

As the kernel is heated, the water inside begins to turn into steam. Steam occupies far more space than liquid water, so pressure steadily builds within the sealed hull. The hull of popcorn is unusually strong and nearly waterproof, which allows it to withstand the pressure for a moment longer than the hull of other corn could. In the meantime, the hot starch softens into a gel-like state.

Eventually the pressure becomes too great to contain. The hull ruptures with a pop, and the softened starch bursts outward and expands into a foam. As it cools in the air, the foam hardens into the light, crunchy shape that everyone recognizes. Pieces of the hull often remain attached, and they sometimes become lodged between your teeth.

A few kernels never pop. They may have dried out too much, leaving too little water to produce steam, or they may have a tiny crack in the hull that allows the steam to escape. That is why popcorn ought to be stored in a sealed container rather than an open bag, and why a fresh bag usually pops better than an old one.

Download as one PDF

How to use it

  1. Press Read it big (or B) to put the text on the projector, or Full screen (F) to fill the whole screen.
  2. Ask the questions one at a time and use Show answer when the class has decided. A shows or hides every answer.
  3. Print student copy for the class, or Print with answers for yourself.

Ideas for class

  • Before reading, put kernel, hull, starchy, pressure and ruptures on the board with their meanings from the Words to know section and have students predict what the text will be about.
  • Read it aloud once while students follow along, then have them reread it alone or with a partner. At a calm 100 words a minute it takes about 2 minutes to read aloud.
  • Use the Read it big button (or B) to put the text on the projector, and Show answer on one question at a time so the class commits to an answer first.
  • Question 5 asks the reader to infer. Ask students to point to the words in the passage that led them to their answer.
  • Ask students to write one question the passage did not answer, then look for the answer in a book or on a classroom screen.
  • Print the student copy for independent work and keep the answer-key copy for yourself.

Related

Questions

What reading level is "Pop Science: Inside a Popcorn Kernel"?

It was written for 7th grade. It has 234 words and works out to a Flesch-Kincaid grade level of about 5.7. That is a formula's estimate from sentence length and syllables, and it is not a Lexile or a guided reading level, so check it against your students.

What do the questions ask?

There are six. 4 ask for something the text says directly and 2 ask the reader to work something out from clues. Each has an answer in the key, and the answers are written as a teacher would accept them, not as the only possible wording.

How long does it take to read?

About 2 minutes read aloud at 100 words a minute. For a one-minute fluency check, paste it into the fluency timer and use the word count.

Can I print it?

Yes. Print student copy gives the passage, the questions with lines to write on, and the word meanings. Print with answers gives the same page with the answers filled in. Both are made in your browser.

Is this passage from a published book?

No. It was written for Peabody Teach, so there is no book to buy and no login to read it.

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