Key Idea: Lungs take in oxygen molecules and eliminate carbon dioxide molecules.

Students are expected to know that:

  1. The air that is taken in through the lungs contains oxygen molecules that react chemically with molecules from food. The carbon dioxide molecules that are produced when molecules from food react with oxygen molecules leave the body through the lungs.
  2. The lungs are connected to the nose and the mouth by means of a tube that carries air. This tube is separate from the tube that carries food to the stomach.
  3. The tube that carries air between the mouth and nose and lungs branches into progressively smaller tubes, and these branching tubes end in many small pouches. These branching tubes and pouches make up the internal structure of the lungs.
  4. The small pouches are in close enough proximity to the capillaries so that oxygen molecules and carbon dioxide molecules can move between the pouches of the lungs and the circulatory system (through the capillary walls).
  5. The large number of small pouches in the lungs creates a large surface area for oxygen molecules and carbon dioxide molecules to move across. When the number of functioning pouches is reduced, the surface area of the lungs and the capacity of the lungs to exchange oxygen molecules and carbon dioxide molecules are also reduced.
  6. Oxygen molecules move from the small pouches of the lungs to the capillaries, and carbon dioxide molecules move from the capillaries to the small pouches of the lungs. As a result, the blood in vessels approaching the lungs has more carbon dioxide and less oxygen than the blood in vessels that has just left the lungs. Note: “move” is being used to represent the net flow of molecules.

Boundaries:

  1. Students are not expected to know the size or capacity of the lungs or the mechanics of how a person breathes.
  2. Students are not expected to know the terms “trachea” or “alveoli.”
  3. Students are not expected to know how oxygen is carried in the blood (i.e., by red blood cells or hemoglobin in the red blood cells).
  4. Students are not expected to know how carbon dioxide is carried in the blood (i.e., that some of the carbon dioxide is carried by hemoglobin, some as dissolved carbonate ions, and some as dissolved carbon dioxide gas).
  5. Students are not expected to know that oxygen molecules and carbon dioxide molecules move in both directions (both from the small pouches of the lungs to the capillaries and vice versa).
Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8
Grades
9–12

BFM079

Molecules from food enter the digestive tract and pass through the body without entering cells of the body.

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BFM078

The lungs do not eliminate carbon dioxide from the body.

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BFM077

The lungs do not take in oxygen for the body to to use.

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BFM069

The respiratory system and the circulatory system are not connected.

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BFM044

The heart is the mixing place for air and blood (Catherall, 1982).

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BFM043

Air is breathed in and out of the body without being absorbed or used in any way (Minstrell, 2005).

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BFM042

Blood gets oxygen from the lungs, but does not transfer carbon dioxide to the lungs (Minstrell, 2005).

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BFM040

Air is distributed through the body in air tubes (Arnaudin & Mintzes, 1985; Catherall, 1982).

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BFM039

After entering the body, air is not distributed throughout the body (Arnaudin & Mintzes, 1985). Air goes to the lungs, or the lungs and the heart, and is then exhaled (Catherall, 1982).

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BFM031

Molecules from food are distributed by way of special tubes, not by way of the circulatory system, to the rest of the body (Catherall, 1982).

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Frequency of selecting a misconception was calculated by dividing the total number of times a misconception was chosen by the number of times it could have been chosen, averaged over the number of students answering the questions within this particular idea.