Key Idea: 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).
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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BF051004

Blood carries oxygen to cells and carries carbon dioxide away from cells.

56%

64%

BF135001

Blood stays within blood vessels and moves to all parts of the body.

51%

58%

BF122003

Blood stays within blood vessels and moves to all parts of the body.

49%

56%

BF075004

Blood carries both oxygen molecules and simple sugar molecules to cells of your leg muscles.

46%

58%

BF134001

Molecules from food and molecules of oxygen are carried by a network of arteries, veins, and microscopically small blood vessels (capillaries) to the rest of the body.

46%

56%

BF018005

Small molecules like amino acids can pass through capillary walls but large molecules like proteins cannot.

42%

55%

BF136001

Small molecules like amino acids can pass through capillary walls, but large molecules like proteins cannot.

43%

47%

BF016005

Oxygen is carried by blood to cells of the body, but carbon dioxide is not carried by the blood to cells of the body.

41%

48%

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%

BF095004

Capillaries are found in body organs such as the brain, lungs, and intestines, and capillaries are also found inside external parts of the body such as arms, legs, hands, and feet.

35%

40%

BF056006

Capillaries allow small molecules like amino acids to pass through their walls but not large molecules like proteins. Molecules do not pass through the walls of large blood vessels.

35%

38%

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%

BF144002

Molecules from food travel from the mouth to the digestive tract and then travel through a series of blood vessels to the cells in the rest of the body.

31%

39%

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%

BF057007

Molecules pass through the walls of microscopically small blood vessels but not through the walls of large blood vessels.

28%

30%

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%

BF126001

Neither large molecules like proteins nor small molecules like amino acids can pass through the walls of arteries and veins.

14%

14%

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).

49%

46%

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%

40%

BFM070

Blood does not carry simple sugar molecules to the cells of the body.

38%

31%

BFM065

Blood flows freely through the walls of blood vessels.

35%

33%

BFM010

Carbon dioxide, oxygen, water, and molecules from food pass directly through the walls of arteries and veins to and from other parts of the body rather than through the walls of the capillaries (Minstrell, 2005).

32%

33%

BFM051

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

31%

29%

BFM067

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

28%

32%

BFM057

Capillaries are found only in internal organs, such as the lungs and the intestines (AAAS Project 2061, n.d.).

30%

28%

BFM028

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

24%

22%

BFM056

Capillaries are found only in the extremities, such as the hands and feet (AAAS Project 2061, n.d.).

23%

23%

BFM080

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

23%

22%

BFM053

Blood does not carry oxygen to the cells of the body (AAAS Project 2061, n.d.).

25%

17%

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%

BFM050

Nothing can pass through the walls of capillaries (AAAS Project 2061, n.d.).

12%

13%

BFM064

Molecules from food move directly from the mouth to the rest of the body without going through any kind of tubes.

8%

5%

BFM063

Molecules of oxygen move directly from the mouth and nose to the rest of the body without going through any kind of tubes.

8%

5%

BFM027

Food is free in the body (no links to digestive structures) (Carvalho et al., 2004).

8%

5%

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.