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Animals | Activity 5.2

Activity 5.2: Molecular Models for Cows Growing: Digestion and Biosynthesis (40 min)

Students construct a model of the break down and rebuilding of molecules through digestion and biosynthesis.

Note: This is a 2-turtle lesson, which is appropriate for advanced middle school or high school students and classes. If you decide not to teach this lesson, you can move directly from 5.1 to 5.3.

Materials You Provide

  • scissors (1 per pair of students)
  • removable or restick tape (1 dispenser per pair of students)
  • marker such as a penny (1 per pair of students)

Resources Provided


Prepare one Molecular Models 11 x 17 Placemat, one pair of scissors, one set of Forms of Energy Cards, and one removable tape dispenser for each pair of students. Print one copy of 5.1 Polymers for Cutting Handout for every four students. Cut each handout in half so you can give each pair one of each polymer (protein, carbohydrate, and fat) and the attached water molecules. Prepare a computer and a projector to display the PPT. Print and hang the Digestion and Biosynthesis 11 X 17 Posters, the Cow 11 x 17 Poster, and the Metabolic Pathways 11 x 17 Poster.


1. Have students start to think about how cows grow.

Tell students that in today’s activity we will use molecular modeling to think more about how cows grow through digestion and biosynthesis.


  • Matter tracing: note if students are able to recognize that the same atoms that were in the reactants are also in the products.
  • Energy tracing: note the ways that students explain how chemical energy is conserved through both digestion and biosynthesis.


  • This activity may not be appropriate for middle school students due to its emphasis on molecular details of digestion and biosynthesis.
  • Laminate the Molecular Models 11 x 17 Placemat. These will be used multiple times in each unit.
  • During the molecular modeling activity and animation, focus on how matter and energy are conserved through the chemical change. This is the main goal of the activity!


  • At the end of the Activity, have students explain the difference between biosynthesis and digestion to a partner.
  • Have the students “act out” digestion and biosynthesis by assigning them molecules using signs. Have them move around the room to represent the two processes by linking and unlinking hands.

Extending the Learning