Activity 5.3 - Explaining How Cows Grow: Digestion (40 min)

Using slide 3 of the PPT have students revisit their arguments and unanswered questions from the Mealworm Investigation by looking at 3.3 Evidence-Based Arguments for Mealworms Eating.

• Remind students that after explaining cellular respiration in Lesson 4.2 there were still unanswered questions about how animals grow and where the glucose needed for cellular respiration comes from.
• In today’s lesson, students will use what they learned in Lesson 5.1 (and 5.2) to explain how cows get food to their bodies’ cells.

Use slides 4-5 of the 5.3 Explaining How Cows Grow: Digestion PPT to guide students through a review of digestion.

• Use Slide 4 to review how animals use food to grow. Ask students for their ideas about what they remember from the previous activity.
• Use slides 5 to remind students what happens to the food that IS digested: Large organic molecules (polymers) are divided into small organic molecules (monomers) that go into the blood.
• Display the following posters in your classroom to help students visualize the digestion of polymers to monomers.
• Carbohydrates: Use the Digestion and Biosynthesis of Carbohydrates to offer students a visualization of how polymers like starch (which is a type of carbohydrate) are broken apart into monomers like glucose.
• Fat: Use the Digestion and Biosynthesis of Fat to offer students a visualization of how polymers like fat are broken apart into monomers like fatty acids and glycerol.
• Proteins: Use the Digestion and Biosynthesis of Protein to offer students a visualization of how polymers like proteins are broken down into amino acids.
• Note: If you only taught 5.1, you can use the posters to help students visualize the process, but do not need to focus on the names of the small organic molecules.

Show slide 6 of the 5.3 Explaining How Cows Grow: Digestion PPT. Give each student one copy of 5.3 Explanations Tool for Cow Digestion.

• Tell students that in this part of the investigation, they will combine everything they learned about how cows get food to their body’s cells into an explanation.
• Remind them to consider both their evidence from the investigation as well as what they learned in the molecular modeling (or tracing) activity to construct their explanations.
• Give students about 10 minutes to complete the Explanations process tool.

Show slide 7 of the 5.3 Explaining How Cows Grow: Digestion PPT. Divide students into pairs and have them compare explanations for the Three Questions and the final explanation on the process tool.

• Have students use the Three Questions 11x17 Poster (or Handout) as a reference. Have students check their explanations with the middle and right-hand columns of the poster or handout to make sure they are following the “rules.”

Use slides 8-13 in the PPT to have the students discuss what is happening to matter during digestion and to have them check their answers to the Matter Movement Question on their 5.3 Explanations Tool for Cow Digestion.

• Show students slides 8-10 to have them think about where atoms are moving from and moving to during digestion.
• Display slides 11-13 to have students compare their answers to the Matter Movement Question with the answers on the slides. Have students use a different colored writing utensil to make any needed changes to their answers. Allow students to ask questions if they do not understand why their ideas are incorrect.
• If students have model explanations to share, display student work and discuss. If students have common areas of weakness in their explanations, ask for a volunteer to share, display student work, and discuss ways of strengthening the response.

Show slide 14 to begin discussion the Matter Change Question.

• Display slides 15-16 to have students compare their answers to the Matter Change Question on the 5.3 Explanations Tool for Cow Digestion with the answers on the slide. Have students use a different colored writing utensil to make any needed changes to their answers. Allow students to ask questions if they do not understand why their ideas are incorrect.
• If students have model explanations to share, display student work and discuss. If students have common areas of weakness in their explanations, ask for a volunteer to share, display student work, and discuss ways of strengthening the response.

Display slide 17 to begin discussion the Energy Change Question.

• Display slide 18 to have students compares their answers to the Energy Change Question on the 5.3 Explanations Tool for Cow Digestion with the answers on the slide. Have students use a different colored writing utensil to make any needed changes to their answers. Allow students to ask questions if they do not understand why their ideas are incorrect.
• If students have model explanations to share, display student work and discuss. If students have common areas of weakness in their explanations, ask for a volunteer to share, display student work, and discuss ways of strengthening the response.

Display slide 19 of the PPT for the full story of digestion. Have students look at two handouts: (a) The Three Questions Handout, and (b) the Example Animal Explanations Handout.

• Ask students to evaluate the two example explanations of cow digestion on the Example Animal Explanations Handout: Which explanation is better? Why?
• Have students use the Three Questions Explanation Checklist on the back of the Three Questions Handout to justify their critiques of the explanations.

Display slide 19 of the PPT for the full explanation. Have students use the Three Questions Explanation Checklist on the back of the Three Questions Handout to check that their story includes each of the parts (matter movement, matter change, energy change, and matter movement).

• If students don’t have all four parts in their explanation, instruct them to add to their explanation using a different colored writing utensil.
• If students have model explanations to share, display student work and discuss. If students have common areas of weakness in their explanations, ask for a volunteer to share, display student work, and discuss ways of strengthening the response.

Pass out 5.3 How do Digest Food? Reading. The reading provides a summary explanation of digestion and additional information about the digestion of fiber. Higher level students may not need the review of content provided in this reading, but you may want them to add to the matter tracing tool started in Activity 4.2.

• Students can complete the reading individually or in pairs.
• After reading, students can complete the digestion section of the Assessing the Animals Matter Tracing Tool that they started completing in Activity 4.2.

Show slide 20. Have students get out their Animals Matter Tracing Tool. Have students individually:

• Draw arrows showing matter movement for digestion.
• Use the steps in the Three Questions to explain how matter moves and change during digestion.

Show slides 21 and 22. Have students compare their answers to the answers on the slides, discuss, and revise their answers if necessary.

Show slide 24 of the 5.3 Explaining How Cows Grow: Digestion PPT.

• Conclusions: What happens to the food that a cow eats in the digestive system?
• Predictions and planning: How do you think a cow uses digested food to grow?
• On a sheet of paper or a sticky note, have students individually answer the exit ticket questions. Depending on time, you may have students answer both questions, assign students to answer a particular question, or let students choose one question to answer. Collect and review the answers.
• The conclusions question will provide you with information about what your students are taking away from the activity. Student answers to the conclusions question can be used on the Driving Questions Board (if you are using one). The predictions and planning question allows students to begin thinking about the next activity and allows you to assess their current ideas as you prepare for the next activity. Student answers to the predictions and planning question can be used as a lead in to the next activity.