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.

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.
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
Select This Item for My Item Bank

BF123003

Molecules from food are absorbed into microscopically small blood vessels (capillaries) located in the walls of the digestive tract and then pass into larger blood vessels that carry the molecules to other parts of the body.

39%

49%

BF012006

Molecules from food get from the digestive tract to the cells of the brain and the cells of the skin by way of the circulatory system.

36%

43%

BF127001

The circulatory system carries products of protein digestion from the digestive tract to cells of both the brain and cells of the skin.

34%

43%

BF039008

After a boy eats a sandwich, there are fewer molecules from food in the blood approaching the digestive tract and more molecules from food in the blood moving away from the digestive tract.

33%

41%

BF129001

The circulatory system carries amino acids from the digestive tract to cells of both the brain and the skin.

35%

37%

BF130001

The circulatory system carries simple sugars from the digestive tract to cells of both the brain and the skin.

33%

38%

BF128001

The circulatory system carries products of carbohydrate digestion from the digestive tract to cells of both the brain and the skin.

34%

37%

BF131001

The circulatory system carries products of digestion from the digestive tract to cells of both the brain and the skin.

32%

40%

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.

32%

33%

BF132001

Molecules from food are absorbed through the walls of microscopically small blood vessels (capillaries). These molecules then move through the circulatory system to all parts of the body.

31%

33%

BF137001

Molecules from food in the digestive tract are absorbed through the walls of capillaries. These molecules then move through the circulatory system to all parts of the body.

29%

24%

BF038004

Amino acids enter the circulatory system from the digestive system by passing through the walls of microscopically small blood vessels (capillaries), but proteins do not.

23%

30%

Frequency of selecting a misconception

Misconception
ID Number

Student Misconception

Grades
6–8

Grades
9–12

BFM040

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

53%

55%

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).

44%

42%

BFM051

Anything can pass through the walls of capillaries (AAAS Project 2061, n.d.).

36%

37%

BFM067

Molecules from food are absorbed through the walls of large blood vessels such as veins and arteries (Minstrell, 2005).

28%

32%

BFM028

The digestive system and the circulatory system are not connected (Buckley, 2000; Carvalho et al., 2004).

24%

22%

BFM080

Molecules from food do not get to the cells of the body by way of the circulatory system.

23%

22%

BFM079

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

15%

12%

BFM043

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

15%

12%

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).

15%

12%

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.