Gas and the Limits of Measurement: teacher key

Burps and Farts, grade 12 edition, written for 12th grade and up. Gas leaves the body in numbers that depend on who counts, and each way of measuring it, from breath tests to muscle pressure tests, leaves part of the picture out. Researchers are developing ingestible capsules that sense gases inside the gut as they travel.

Read the book. Print this page for the key.

Questions and answers

1. What limit does every method for measuring gut gas have?
   • It either measures gases indirectly or is highly invasive (answer)
   • It works only on children
   • It can measure only smell
2. One review reports up to 1 liter of hydrogen made in the gut in 24 hours. Why does that figure sit oddly beside the amount people pass?
   • It is smaller than what the gut holds at one time
   • It is more than the 600 to 700 milliliters of all gas people pass in an average day (answer)
   • It matches the daily belch count
3. What did the 16-person study find about the mix of gases?
   • It was the same every time
   • It was only nitrogen
   • It varied enormously from person to person, so no single recipe describes a typical fart (answer)
4. What does a rise in breath hydrogen after a test sugar show?
   • The person swallowed air
   • Gut bacteria have been fermenting the sugar (answer)
   • Human cells made hydrogen
5. In this passage, what does it mean that a method is invasive?
   • It goes into the body (answer)
   • It is very cheap
   • It measures smell

Words

• sphincters: ring-shaped muscles
• chromatograph: gas-sorting machine
• invasive: entering the body
• sulfate: sulfur compound
• raffinose: bean sugar