Key Idea: Oxygen, carbon dioxide, and molecules from food are carried to or from cells of the body by means of the circulatory system.
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Molecules from food are broken down into smaller molecules in the digestive tract and then enter the circulatory system by way of capillaries located in the lining of the digestive tract.
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Lungs take in oxygen molecules and eliminate carbon dioxide molecules.

These items have been aligned to more than one key idea. To view the sub-ideas click on a key idea below.

  • Oxygen, carbon dioxide, and molecules from food are carried to or from cells of the body by means of the circulatory system.

    Students are expected to know that:

    1. The circulatory system is made up of a variety of blood vessels, which carry blood throughout the body.
    2. Blood stays within a system of blood vessels: arteries, veins, and microscopically small blood vessels called capillaries.
    3. Larger diameter blood vessels branch into progressively smaller blood vessels and eventually into microscopically small blood vessels known as capillaries.
    4. Blood carries needed molecules (e.g., simple sugars, amino acids, fatty acids, and oxygen) to cells of the body and carries carbon dioxide and other waste molecules away from cells of the body.
    5. Small molecules such as amino acids, simple sugars, fatty acids, oxygen, and carbon dioxide (but not large molecules like proteins, complex carbohydrates, and fat molecules) can cross the capillary walls.
    6. Small molecules can pass through capillary walls but not through the walls of other blood vessels.
    7. Capillaries are spread out throughout the entire body (and are in very close proximity to each of the cells of the body) so that needed molecules can get to the cells and waste materials can be removed from the cells.
    8. All cells receive molecules from food by way of the circulatory system.

    Boundaries:

    1. The terms capillaries, veins, and arteries will be defined for students when they are used in the items.
    2. Students are not expected to know the names of waste molecules other than carbon dioxide.
    3. Students are not expected to know that white blood cells can pass (by squeezing) through capillary walls.
    4. Students are not expected to know the names or functions of the components of blood (e.g., red blood cells, white blood cells, plasma).
  • Molecules from food are broken down into smaller molecules in the digestive tract and then enter the circulatory system by way of capillaries located in the lining of the digestive tract.

    Students are expected to know that:

    1. Digestion takes place in body organs (e.g., mouth, stomach, intestines) that collectively are known as the digestive tract.
    2. The food humans eat moves from the mouth to the stomach by way of a tube that is separate from the tube that carries air to and from the lungs.
    3. The breakdown of food into smaller molecules usually involves a combination of mechanical processes (mechanical digestion) and chemical reactions (chemical digestion).
    4. During mechanical digestion, more of the carbohydrate, fat, and protein molecules from food come in contact with digestive enzymes, which increases the number of carbohydrate, fat, and protein molecules that are chemically broken down.
    5. Examples of mechanical digestion include chewing food in the mouth and mixing food in the stomach.
    6. Molecules that result from the digestion of carbohydrate and protein molecules leave the digestive tract and enter the circulatory system by way of the capillaries located in the lining of the digestive tract.
    7. Not everything that we eat is digested: In some cases mechanical digestion is incomplete (e.g., inadequate chewing of food) so that digestive enzymes cannot come in contact with the molecules from food. In other cases, the body does not have the digestive enzymes needed to break down the molecules that we eat (e.g., cellulose). In still other cases, some of the molecules from food do not have to be digested because they are already small enough to enter the circulatory system and cells of the body.
    8. Undigested fats, proteins, complex carbohydrates or other undigested material that is too large to be used by the cells of the body leave the body at the end of the digestive tract.

    Boundaries:

    1. Students are not expected to know he terms “alimentary canal,” “esophagus,” “small intestine,” or“large intestine.”
    2. Students are not expected to know that most chemical digestion and absorption occurs in the small intestine.
    3. Students are not expected to know the different types of digestive enzymes or the specific role they play in chemical digestion.
    4. Students are not expected to know when digestion involves primarily chemical reactions or primarily mechanical processes.
    5. Students are not expected to know that stomach acid and bile are also molecules involved in chemical digestion.
    6. Students are not expected to know the role of microorganisms in digestion.
    7. Students are not expected to know that fatty acids enter the blood stream through the lymphatic system.
    8. Students are not expected to know that dipeptides are molecules that are small enough to enter capillaries.
  • 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).
Percent of students answering correctly (click on the item ID number to view the item and additional data)
Item ID
Number
Knowledge Being Assessed Grades
6–8
Grades
9–12
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BF133001

Molecules from food and molecules of oxygen move from the mouth and the nose to cells of the body through a series of blood vessels, including veins, arteries, and microscopically small blood vessels (capillaries), that extend throughout the body.

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