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Middle School    |    Daily Do

Why Does Some Food Disappear?

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Why Does Some Food Disappear?

Biology Crosscutting Concepts Disciplinary Core Ideas Is Lesson Plan Life Science NGSS Phenomena Science and Engineering Practices Three-Dimensional Learning Middle School Grades 6-8

Welcome to NSTA's Daily Do

Teachers and families across the country are facing a new reality of providing opportunities for students to do science through distance and home learning. The Daily Do is one of the ways NSTA is supporting teachers and families with this endeavor. Each weekday, NSTA will share a sensemaking task teachers and families can use to engage their students in authentic, relevant science learning. We encourage families to make time for family science learning (science is a social process!) and are dedicated to helping students and their families find balance between learning science and the day-to-day responsibilities they have to stay healthy and safe.

Interested in learning about other ways NSTA is supporting teachers and families? Visit the NSTA homepage.

What Is Sensemaking?

Sensemaking is actively trying to figure out how the world works (science) or how to design solutions to problems (engineering). Students do science and engineering through the science and engineering practices. Engaging in these practices necessitates that students be part of a learning community to be able to share ideas, evaluate competing ideas, give and receive critique, and reach consensus. Whether this community of learners is made up of classmates or family members, students and adults build and refine science and engineering knowledge together.


In today's Daily Do, Why does some food disappear?, students engage in science and engineering practices and use patterns as a thinking tool to make sense of the phenomenon of digesting a graham cracker. Students have an opportunity to apply physical science ideas about chemical reactions and physical changes to develop life science ideas about digestion (the beginning of the science idea "the body is a system of multiple interacting systems"). This task has been modified from its design to be used by students, families, and teachers in distance learning. While students could complete this task independently, we encourage students to work virtually with peers or in the home with family members.


Daily Do Playlist: Digestive System

Why does some food disappear? is a stand-alone task. However, it can be taught as part of an instructional sequence in which students coherently build the science idea "the body is a system of multiple interacting subsystems made up of organs specialized for particular body functions." In this first of three playlist lessons, students raise the question, "Why does some food disappear?", which motivates the need to engage in the next two lessons.

View Playlist


What Phenomenon Am I Exploring Today? (Introduce Phenomenon)

If they are available at home, have students grab a box of graham crackers. Otherwise, share the graham cracker student handout, and ask, "What types of food molecules are in a graham cracker?"

Students may identify what categories are listed in the nutritional label or list ingredients. If students list ingredients, ask, "How could we categorize those?" (Categories include fats, proteins, carbohydrates, etc.)

To motivate students to investigate what happens when they eat graham crackers, say, "I wonder what happens to all these molecules when we eat graham crackers. Does anyone have any ideas?" Accept all student ideas.

Tell students you are going to share food molecule data collected from the graham cracker (out of the box) and three parts of the digestive system—
mouth, beginning of the small intestine, and large intestine (you may choose to point out these digestive system parts on the diagram). 

Share the Follow the Molecules student activity sheet with students. Help students orient themselves to the graph.

  • Ask, "Based on this graph, what food molecules make up an (uneaten) graham cracker?" This is denoted by the blue lines on the graph (water, protein, fats, glucose, other complex carbohydrates, and fiber).
  • Direct students' attention to the x-axis. Ask them to turn and talk with a partner and share ideas about what is meant by "relative amount." You might then ask students to share ideas and give an example from the graph. If students have difficulty understanding what is meant by "relative amount," you might ask, "How much more other complex carbohydrates are in a graham cracker relative to water?" (three times more) and "How much less protein is there relative to water?" (Protein is about half the amount of water.)
  • Support students in interpreting the other bars represented on the graph. Say, "Let's look at water. How does the amount of water molecules in an uneaten graham cracker compare to the amount of graham cracker water molecules in the mouth? (same amount) Beginning of small intestine? (same amount) Large intestine? (about half the number of original water molecules)

Allow students time to independently analyze the data represented in the graph.


Guidance. The student activity sheet directs students to complete an I See—
I Think—I Wonder table for each data set (graham cracker, mouth, small intestine, and large intestine) to support them in analyzing and interpreting the data. You might instead choose to introduce students to the Identify and Interpret (I2) Strategy. Read about students using this strategy in The American Biology Teacher article "Using the I2 Strategy to Help Students Think Like Biologists About Natural Selection."


What Does the Data Tell Us? (Building Consensus)

Place students in small groups. Ask students to share their observations with their group members and answer the following questions:

  • What are similarities and differences in your group's observations?
  • What pattern(s) in the data do you (the group) notice?

Next, ask students, while still in their small groups, to interpret the patterns they identified and move toward reaching a group consensus. Share the following questions with the groups to facilitate their discussion:

  • How do you (the group) interpret these patterns?
  • What science ideas support your interpretation(s) of these patterns?
  • What ideas are you in agreement about?
  • What ideas are you not in agreement about?

Bring the class back together and engage the groups in a class consensus discussion. You might use the following prompts to help the class reach consensus:

  • What pattern(s) in the data did your group identify?
  • How did your group interpret this pattern?
  • Did another group notice the same pattern as _______'s group, but interpret it in a different way?
  • What ideas are we in agreement about?
  • Are there still places where we disagree? Can we clarify these?
  • Where should we go next to help us with areas where we are not sure/not in agreement?

Students will likely identify the following:

  • Amino acids (AA) and fatty acids are not present in the uneaten graham cracker, but are found in the beginning of the small intestine.
  • Proteins, fatty acid, fats, glucose, and other complex carbohydrates are not found in the large intestine. (What happened to them?)
  • Some types of food molecules decrease from the mouth to large intestine, and others increase.
  • The amount of fiber molecules did not change during digestion.
  • The amount of water molecules stayed the same in the mouth and beginning of the small intestine, then decreased in the large intestine.

Students may interpret this as

  • Our body digests (breaks down) proteins, fats, and other complex carbohydrates in the beginning of the small intestine.
  • Our body takes in food molecules (nutrients) in the small intestine, and that's why they aren't found in the large intestine.

Students may ask the following:

  • Why does the amount of complex carbohydrates go down (decrease) in the mouth? Does that "count" as digestion?
  • How does the amount of glucose go up (increase) in the mouth?
  • Why can't our body digest fiber?
  • What is digestion?
  • Are there other kinds of food molecules that make up food?

Make sure students are aware of the phenomenon they have just experienced: Food molecules "disappear" as they move through the digestive system. Ask them, "What are we trying to figure out here?" Listen for student responses to include ideas such as these:

  • Where does the food go? (Where do the food molecules go?)
  • Why don't all the molecules act the same way if they are all food?
  • Why do different carbohydrate food molecules do different things —go up, go down, stay the same—in the digestive system if they are all the same type of molecule?

As you discuss students' ideas, help guide them to ask the driving question, "Why does some food disappear?" (or a similar question). Record the driving question on a shared classroom or virtual space.

Next, you might say, "Many of us have questions about the carbohydrates—
glucose, other complex carbohydrates, and fiber. Does it make sense to investigate these questions first?"

Why Are Some Molecules Disappearing and Others Aren't? (Digging Deeper)

Ask students to turn to a partner and share what they have heard about carbohydrates—specifically glucose, complex carbohydrates (you might offer starch as an example of a complex carbohydrate), and fiber. Students may know that some foods, like bread or potatoes, contain a lot of starch; bread and pasta are high in carbohydrates; and/or fiber helps make you defecate ("poop"). Others may know that glucose is something that diabetics monitor, and eating sugary foods or foods high in carbohydrates makes the amount of glucose in diabetics' blood increase.

Tell students you found molecular models of glucose, starch (a complex carbohydrate), and fiber that might help explain why some of the carbohydrate amounts change (glucose and other complex carbohydrates) and fiber does not. Share the Molecule Structure student activity sheet with students. Give students independent thinking time to observe the molecule structures and record similarities and differences among them. Then assign students to small groups and ask them to share the similarities and differences they identified.

Bring students back together and ask them to share similarities and differences with the class. Students will likely identify the following similarities and differences:

  • All three molecules are made of the same atoms:
    carbon, hydrogen, and oxygen.
  • Glucose is the smallest molecule, and fiber is the biggest molecule.
  • Starch and fiber look like they are made of many glucose molecules connected together.

What Did We Figure Out? (Making Sense)

Lead a building understanding discussion using this prompt: How could the structure of the different carbohydrates explain why some carbohydrates are digested (broken down) and others are not? You might use some of the following prompts to facilitate the discussion:

  • What are some of your claims?
  • What's your evidence? (or Does anyone have any evidence to support Group A's claim?)
  • ___and ___ , you made similar claims. Did you have the same evidence?
  • What can we conclude?
  • What else do we need to find out? What might we do next?

Students may say the large size of a fiber molecule might explain why our body's digestive system can't digest (break down) the fiber. Other students may focus on the smaller-sized glucose and starch molecules and say that because they are smaller, our digestive system has an easier time digesting them (breaking them down).

Say, “Let me restate what I think you are saying. First, we know the graham cracker breaks down into different molecules. We also see that it breaks down into different kinds of carbohydrates (glucose, other complex carbohydrates, and fiber). We think that these three carbohydrates break down differently in the body because of their size. Did I miss anything?” 

Teaching the Daily Do Playlist

Ask students, "What can we now explain about why some foods disappear? What do we still need to figure out?" Have students discuss these questions with a partner or in a small group. Students will likely say they figured out that the size of the molecule affects whether or not a food molecule breaks down (larger molecules don't break down), but not how (mechanism) our body breaks down (digests) food.  

If students use the words digest/digestion, ask them to explain what they mean. This will allow you to see if they understand the concept of digestion. You may need to identify digestion as a word the class will need to more easily communicate with one another about the idea of the body breaking food down into substances that can be used by the body.

Ask students to think about what questions they still have about digestion and share them with a partner or small group before sharing with the class. Listen for students to share questions about the graham cracker, and invite these students to share their questions first when you bring the class back together. Common students' questions will likely include these: 

  • How do you get more glucose than you start with when you put the graham cracker in your mouth?
  • How do you lose "other carbohydrates" as soon as you put the graham cracker in your mouth?
  • Why isn’t stomach on the graph? (Why isn't there any data for the stomach?) Doesn't digestion happen there?
  • Isn’t fiber the stuff that makes you poop?  
  • Does all food break down the same?

If students do not bring up any questions about the graham cracker, say, “We have many questions about digestion in general, but are there any questions we still need to answer about how the body digests the graham cracker?” Lead students to want more information about how the graham cracker is digested before looking at other foods. 

Navigate students to the next lesson by asking, "Many of us noticed changes in the carbohydrate food molecules as soon as the graham cracker was in the mouth. Does it make sense to investigate how this happens first?"

View Playlist

NSTA Collection of Resources for Today's Daily Do

NSTA has created a Why does some food disappear? collection of resources to support teachers and families using this task. If you're an NSTA member, you can add this collection to your library by clicking Add to My Library.  

Check Out Previous Daily Dos From NSTA

The NSTA Daily Do is an open educational resource (OER) and can be used by educators and families providing students distance and home science learning. Access the entire collection of NSTA Daily Dos.


This Daily Do lesson is inspired by and uses materials from the OpenSciEd science unit 7.3 Metabolic Reactions: How do things inside our bodies work together to make us feel the way we do? 

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