Each of the first four volumes provides 25 probes with easy-to-follow steps for uncovering and addressing students’ ideas by promoting learning through conceptual change instruction. Probes cover topics such as physical, life, and Earth and space science; the nature of science; and unifying themes. Each volume on page 23 provides topic-specific probes. These invaluable books include teacher materials that explain content, identify links to standards, and suggest grade-appropriate ways to present materials so students learn the concepts accurately. Teachers, professional development coordinators, and college science and preservice faculty will find these resources essential and exciting.
The purpose of this assessment probe is to elicit students’ ideas about the digestive system. The probe is designed to find out whether students realize a main function of the digestive system is to break food down into molecules that can be used by cells.
Cells, digestive system, food, nutrients
The best answer is Sasha’s: “I think the main function is to break food down into molecules that can be absorbed by cells.” There is no single purpose of the digestive system; rather, it has two major purposes: (1) to break down food and (2) to prepare nutrients for absorption by cells. The digestive system carries out six basic functions: taking food in (ingestion), secretion, movement of food and wastes, breakdown of food, absorption from gastrointestinal tract to cells, and removal of wastes. In regard to Mina’s response, the digestive system does not release energy from food. Instead it breaks food down into molecules that are absorbed by cells and that can then be used to release energy within the cell. Harriet’s response is partially correct. The stomach does break ingested food down into smaller pieces of food. However, there is more to digestion than what happens in the stomach. These small pieces of food are not used directly by the body but are further broken down into small particles (molecules) absorbed by cells as they pass through the intestines. The difference between Sasha’s and Harriet’s responses is that the broken down food must be small enough to be taken in by and used by cells. Even though the mouth and stomach break food down into small pieces of food, it is not until the food is broken down into the molecular units that make up the food that it can be used by the body to carry out the life processes that happen within cells. Todd is partially correct in that the digestive system does move food and nutrients; however, it moves these things through the digestive tract and not through different parts of the body. It is the circulatory system that moves nutrients throughout the body to cells.
In the elementary grades, students learn basic ideas about the human body and body structures that help us take in and digest food, such as the mouth, teeth, and stomach. Young children primarily equate the stomach as the organ responsible for digesting food as they haven’t yet learned how all the parts work together. By third grade, students begin to view the body as a system that works together and they can further explore what happens to food when it is taken into the body. At the upper-elementary level, it is important for students to know that food is broken down to obtain energy and materials for growth and repair, but the molecular aspect can wait until middle school.
Middle School Students
In the middle grades, students develop a more sophisticated understanding of the human body and the organs and systems that work together to enable humans and other organisms to carry out their life processes. This is the time for them to understand that when food is broken down, it must be digested into molecules that can be absorbed and transported to different parts of the body. At this level, they are ready to understand the link between the digestive system and the circulatory system for breaking down food into molecules and transporting nutrients and to understand the role of the digestive and excretory system in eliminating the parts of food that are not used.
High School Students
Students at the high school level expand their understanding to encompass molecular energy release and the biochemical details related to metabolism. Their growing knowledge of cells helps them understand how molecules are taken into cells and used to carry out life processes.
Administering the Probe
If this probe is used with elementary students, consider substituting the word molecules with tiny particles.
K–4 Characteristics of Organisms
5–8 Structure and Function in Living Systems
9–12 The Cell
K–2 Basic Functions
3–5 Basic Functions
6–8 Basic Functions
Crowley, J. 2004. Nutritional chemistry. The Science Teacher (Apr.): 49–51.
Robertson, W. 2006. Science 101: How does the human body turn food into useful energy? Science & Children (Mar.): 60–61.
Schroeder, C. 2007. Inquiring into the digestive system. Science Scope (Nov.): 30–34.
Texley, J. 2001. Anatomy by logic. Science Scope (Sept.): 56–59.
Related Curriculum Topic Study Guides (Keeley 2005) “Human Body Systems” “Food and Nutrition”
American Association for the Advancement of Science (AAAS). 1993. Benchmarks for science literacy. New York: Oxford University Press.
American Association for the Advancement of Science (AAAS). 2008. Benchmarks for science literacy online. www.project2061.org/publications/bsl/online
Driver, R., A. Squires, P. Rushworth, and V. Wood Robinson. 1994. Making sense of secondary science: Research into children’s ideas. London: RoutledgeFalmer.
Keeley, P. 2005. Science curriculum topic study: Bridging the gap between standards and practice. Thousand Oaks, CA: Corwin Press.
Mintzes, J. 1984. Naive theories in biology: Children’s concepts of the human body. School Science and Mathematics 84 (7): 548–555.
National Research Council (NRC). 1996. National science education standards. Washington, DC: National Academy Press.