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Why Chopping an Onion Brings Tears

7th grade nonfiction passage about onion chemistry: 238 words, six questions, an answer key and vocabulary.

7th grade nonfiction onion chemistry 238 words

Why Chopping an Onion Brings Tears

Few kitchen jobs bring tears as quickly as chopping an onion. The onion is not sad, and neither is the cook. The tears come from a chemical defense that the plant developed over a very long time, probably to discourage animals from eating it.

Inside an intact onion, two kinds of substances are kept in separate compartments of its cells. One group is made of sulfur compounds. The other is a set of enzymes. While the onion is whole, they never meet. When a knife slices through the cells, the walls break and the contents mix. The enzymes quickly change the sulfur compounds into new ones, and one of them is a gas that drifts upward from the cutting board.

When the gas reaches your eyes, it dissolves in the thin layer of moisture covering them and forms a mild irritant. Nerves on the surface of the eye sense it and warn the brain. The brain answers by telling your tear glands to wash the irritant away. That is why your eyes water and sting.

Cooks have found a few ways to reduce the effect. A very sharp knife crushes fewer cells than a dull one, so less gas escapes. Chilling the onion in the refrigerator first slows the reactions. Cutting near a fan or an open window can blow the gas away from your face. Cooking the onion also ends the problem, because heat damages the enzymes.

Questions

  1. Where are the sulfur compounds and enzymes kept inside a whole onion? in the text

  2. What happens when a knife cuts through the onion cells? in the text

  3. What does the gas do when it reaches your eyes? in the text

  4. Why does a sharp knife cause fewer tears than a dull one? in the text

  5. Why do your tear glands make tears when you chop an onion? think about it

  6. Why does a whole onion not make anyone cry? think about it

Words to know

defense
a way a living thing protects itself
compartments
small separate spaces inside something
enzymes
natural substances that cause chemical changes
irritant
something that makes a body part sting or hurt
sulfur
a yellow element found in many onion chemicals
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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 · 178 words · Flesch-Kincaid grade 2.4

Chopping an onion can make you cry. The onion is not sad. You are not sad. The tears come from a chemical trick the onion uses to protect itself.

Inside a whole onion, two kinds of things are kept apart in the cells. One kind is sulfur compounds. The other kind is enzymes. They never touch while the onion is whole.

When you cut the onion, the cell walls break. The two kinds of things mix. The enzymes change the sulfur compounds. One new thing is a gas. It floats up from the cutting board.

The gas reaches your eyes. It dissolves in the thin wet layer on your eye. This makes a mild irritant. Your eye nerves feel it and tell your brain. Your brain tells your tear glands to wash it away. So your eyes water and sting.

Cooks have some tricks. A sharp knife breaks fewer cells, so less gas escapes. A cold onion makes less gas. A fan can blow the gas away. Cooking the onion stops the problem, because heat harms the enzymes.

▲ This passage · 238 words · Flesch-Kincaid grade 5.9

Few kitchen jobs bring tears as quickly as chopping an onion. The onion is not sad, and neither is the cook. The tears come from a chemical defense that the plant developed over a very long time, probably to discourage animals from eating it.

Inside an intact onion, two kinds of substances are kept in separate compartments of its cells. One group is made of sulfur compounds. The other is a set of enzymes. While the onion is whole, they never meet. When a knife slices through the cells, the walls break and the contents mix. The enzymes quickly change the sulfur compounds into new ones, and one of them is a gas that drifts upward from the cutting board.

When the gas reaches your eyes, it dissolves in the thin layer of moisture covering them and forms a mild irritant. Nerves on the surface of the eye sense it and warn the brain. The brain answers by telling your tear glands to wash the irritant away. That is why your eyes water and sting.

Cooks have found a few ways to reduce the effect. A very sharp knife crushes fewer cells than a dull one, so less gas escapes. Chilling the onion in the refrigerator first slows the reactions. Cutting near a fan or an open window can blow the gas away from your face. Cooking the onion also ends the problem, because heat damages the enzymes.

■ Harder · 245 words · Flesch-Kincaid grade 8.6

Few kitchen tasks bring tears as reliably as chopping an onion. Neither the onion nor the cook is sad; the tears are the result of a chemical defense that the plant developed over an extraordinarily long period, most likely to discourage animals from eating it.

Within an intact onion, two kinds of substances are held in separate compartments of its cells. One group consists of sulfur compounds, and the other is a set of enzymes. As long as the onion stays whole, the two groups never meet. When a knife slices through the cells, however, their walls rupture and the contents mingle. The enzymes rapidly convert the sulfur compounds into new ones, and one of these is a gas that drifts upward from the cutting board.

When that gas reaches your eyes, it dissolves in the thin layer of moisture that covers them and forms a mild irritant. Nerves on the surface of the eye detect it and alert the brain, which responds by instructing the tear glands to flush the irritant away. That is precisely why your eyes water and sting.

Cooks have discovered several ways to lessen the effect. A very sharp knife crushes fewer cells than a dull one, so less gas escapes. Chilling the onion in the refrigerator beforehand slows the chemical reactions. Cutting near a fan or an open window can carry the gas away from your face. Cooking the onion eliminates the problem entirely, since heat damages the enzymes.

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 defense, compartments, enzymes, irritant and sulfur 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 "Why Chopping an Onion Brings Tears"?

It was written for 7th grade. It has 238 words and works out to a Flesch-Kincaid grade level of about 5.9. 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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