why are yawns contagious? we asked a scientist by teresa carey why do we yawn? there is no scientific consensus on why we yawn. one theory argues that when humans are tired, we stop taking deep breaths, which causes a build - up of carbon dioxide in the body, said douglas parham, a speech scientist at wichita state university. a yawn might be a special kind of respiration, parham said. it builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath. excess carbon dioxide and other chemical changes, such as a drop in oxygen or increase in a compound called adenosine, could also act as yawn gates, said james giordano, a neuroethicist and neuroscientist at georgetown university. these chemicals send out a signal that triggers a yawn. by yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain, giordano said. other proposals state the purpose of yawning is to cool the brain, or to stretch internal organs like tissues and lungs, helping the body to liven up. use the passage from why are yawns contagious? we asked a scientist. to answer the question. effect: we yawn. cause: to quickly expel carbon dioxide cause: to drive oxygen - enriched blood to the brain cause: to stretch internal organs cause: ? cause: ? based on the information in the passage, which cause completes the graphic organizer? select the two correct answers. (1 point) ☐ to increase adenosine levels ☐ to increase the frequency of deep breaths ☐ to cool the brain ☐ to compress facial muscles ☐ to build up oxygen

Question

Accepted Answer

# Brief Explanations:
1. Analyze each option:
   - "to increase adenosine levels": The passage says adenosine increase triggers yawning, not that yawning increases adenosine. Eliminate.
   - "to increase the frequency of deep breaths": The passage says when tired we stop deep breaths, yawning is a special respiration, not about increasing deep breath frequency. Eliminate.
   - "to cool the brain": The passage states "Other proposals state the purpose of yawning is to cool the brain". This is a valid cause.
   - "to compress facial muscles": The passage says "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain". Compressing facial muscles is part of the yawning process that drives blood to the brain, so it's a cause.
   - "to build up oxygen": The passage says "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath". This is a valid cause. Wait, but we need to check the options again. Wait, the options are "to cool the brain", "to compress facial muscles", "to build up oxygen". Wait, let's re - check the passage:
     - "Other proposals state the purpose of yawning is to cool the brain, or to stretch internal organs like tissues and lungs, helping the body to liven up." So "to cool the brain" is a cause.
     - "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain" - so compressing facial muscles is a cause (as it's part of the yawning action that leads to driving blood to the brain).
     - "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath" - so "to build up oxygen" is a cause. But the question says select two correct answers. Wait, maybe I made a mistake. Wait, let's re - examine the options:
       - Option "to cool the brain": Supported by "Other proposals state the purpose of yawning is to cool the brain".
       - Option "to compress facial muscles": Supported by "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain".
       - Option "to build up oxygen": Supported by "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath". But the question is to select two correct answers. Wait, maybe the intended answers are "to cool the brain" and "to compress facial muscles" or "to cool the brain" and "to build up oxygen"? Wait, no, let's check the passage again. The passage says:
         - One theory: expel CO2, build up O2.
         - Giordano: chemical changes (adenosine increase triggers), compressing facial muscles to drive blood to brain.
         - Other proposals: cool brain, stretch internal organs.
         So the causes in the graphic organizer already have "to quickly expel carbon dioxide", "to drive oxygen - enriched blood to the brain", "to stretch internal organs". So the missing causes should be from the other information. So "to cool the brain" (from other proposals) and "to build up oxygen" (from the first theory: "It builds up oxygen quickly") or "to compress facial muscles" (from Giordano's statement). Wait, the options are:
         - to increase adenosine levels: No, adenosine increase triggers yawning, not caused by yawning.
         - to increase the frequency of deep breaths: No, the passage says when tired we stop deep breaths, yawning is a special respiration.
         - to cool the brain: Yes, from "Other proposals state the purpose of yawning is to cool the brain".
         - to compress facial muscles: Yes, from "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain".
         - to build up oxygen: Yes, from "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath". But the question says select two correct answers. Wait, maybe the two correct answers are "to cool the brain" and "to compress facial muscles" or "to cool the brain" and "to build up oxygen"? Wait, no, let's check the original problem again. The graphic organizer has "Effect: We yawn" and causes: "to quickly expel carbon dioxide", "to drive oxygen - enriched blood to the brain", "to stretch internal organs", and two more. The passage says:
           - "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath" - so "to build up oxygen" is a cause.
           - "Other proposals state the purpose of yawning is to cool the brain, or to stretch internal organs like tissues and lungs, helping the body to liven up" - so "to cool the brain" is a cause.
           - "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain" - so "to compress facial muscles" is a cause.
           But the options are five, and we need to select two. Wait, maybe the correct two are "to cool the brain" and "to compress facial muscles" or "to cool the brain" and "to build up oxygen"? Wait, no, let's re - read the passage:
             - The first theory: yawning is a special respiration that builds up oxygen and expels CO2. So "to build up oxygen" is a cause.
             - Giordano: compressing facial muscles to drive blood to brain. So "to compress facial muscles" is a cause.
             - Other proposals: cool brain, stretch internal organs.
             So the causes in the graphic organizer: "to quickly expel carbon dioxide" (from first theory), "to drive oxygen - enriched blood to the brain" (from Giordano's compressing facial muscles leading to this), "to stretch internal organs" (from other proposals). So the remaining causes should be "to cool the brain" (from other proposals) and "to build up oxygen" (from first theory) or "to compress facial muscles" (from Giordano). Wait, the option "to build up oxygen" is there, "to cool the brain" is there, "to compress facial muscles" is there. But the question says two correct answers. Let's check the options again:
               - Option "to cool the brain": Correct (from other proposals).
               - Option "to compress facial muscles": Correct (from Giordano's statement: "By yawning, we compress the muscles of the face...").
               - Option "to build up oxygen": Correct (from "It builds up oxygen quickly...").
               But maybe the intended answers are "to cool the brain" and "to compress facial muscles" or "to cool the brain" and "to build up oxygen". Wait, perhaps the correct two are "to cool the brain" and "to compress facial muscles". Wait, no, let's check the passage again. The sentence "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain" - so compressing facial muscles is a cause (as it's an action of yawning that leads to driving blood to the brain). The sentence "Other proposals state the purpose of yawning is to cool the brain" - so cooling the brain is a cause. The sentence "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath" - so building up oxygen is a cause. But the question is to select two. Maybe the answer is "to cool the brain" and "to compress facial muscles" or "to cool the brain" and "to build up oxygen". Wait, maybe the correct answers are "to cool the brain" and "to compress facial muscles".
# Answer:
C. to cool the brain, D. to compress facial muscles (or C. to cool the brain, E. to build up oxygen - but based on the passage, "to cool the brain" and "to compress facial muscles" are both valid. Wait, let's re - check the options:
- Option C: to cool the brain (correct, from "Other proposals state the purpose of yawning is to cool the brain").
- Option D: to compress facial muscles (correct, from "By yawning, we compress the muscles of the face, driving oxygen - enriched blood to the brain").
- Option E: to build up oxygen (correct, from "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath").

But the question says "select the two correct answers". Maybe the intended answers are C and D or C and E. But based on the passage, "to cool the brain" and "to compress facial muscles" are both causes. So the correct options are C. to cool the brain and D. to compress facial muscles (or C and E). Wait, maybe the answer is C. to cool the brain and E. to build up oxygen. Let's see:

- "to build up oxygen" is from "It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath" - this is a cause.
- "to cool the brain" is from "Other proposals state the purpose of yawning is to cool the brain" - this is a cause.

Yes, these two are also correct. So the correct answers are C. to cool the brain and E. to build up oxygen (or C and D). But let's check the passage again. The first theory: yawning is a special respiration that builds up oxygen and expels CO2. So "to build up oxygen" is a cause. Other proposals: cool brain, stretch internal organs. So the two missing causes should be "to cool the brain" (from other proposals) and "to build up oxygen" (from the first theory). So the correct options are C. to cool the brain and E. to build up oxygen.

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