Activity 4.1: Molecular Models for Potatoes Moving and Functioning: Cellular Respiration (40 min)

Tell students that in today’s activity we will use molecular modeling to begin to answer some of their unanswered questions about what happens when a plant grows.

• Return students’ completed 3.5 Evidence-Based Arguments Tool for Plants and ask them to review their unanswered questions from the last lesson.
• You may have typed and saved students’ unanswered questions on the 3.5 Evidence-Based Arguments Tool for Plants PPT. Or you may have taken a picture of students’ unanswered questions. Display the visual and review what students shared.

Display slide 3 in the PPT.

• Show students the short clip of a plant moving. Follow the link in the PPT, in the materials list, or here (https://www.youtube.com/watch?v=LICDb8nM5rs).
• Help students connect to their unanswered questions about processes at different scales.
• At the macroscopic scale, we wonder, How do potato plants move and function?
• At the microscopic scale, we think about this question in terms of plant cells: How do potato plant cells get energy to help the plant move and function?
• At the atomic-molecular scale, we think about this question in terms of atoms and molecules in chemical changes: What chemical change provides energy to the cells?
• Assure students that we will be able to answer several of their unanswered questions by the end of today’s activity.

Use slide 4 to show students that plants use food in two ways.

• Today we’ll be focusing on energy as one of those uses (cellular respiration).

Show slide 5 of the PPT.

• Use the animation to support students in connecting the atomic-molecular scale to the macroscopic scale.
• Tell students they will be modeling the change that occurs during cellular respiration at the atomic-molecular scale.

Display slide 6 of the PPT. Post a copy of the Three Ways to Represent Glucose 11 x 17 Poster in your classroom and display slide 6 in the PPT. Have students discuss the differences in the three different images we use in the Carbon TIME Units to represent molecules.

• The first form uses letters and numbers. Each letter represents a type of atom and each number indicates how many of that atom are in the molecule.
• The second form uses letters and sticks. Each letter represents an atom, and each stick represents a bond.
• The third form uses balls and sticks. Each ball represents an atom, and each stick represents a bond.

Divide the class into pairs and give each pair a molecular model kit, a set of Forms of Energy Cards, and Molecular Models 11 x 17 Placemat. Pass out one copy of 4.1 Molecular Models for Cellular Respiration Worksheet to each student.

• Tell students that they’ll be using molecular models to model the process of cellular respiration which will help them answer several of their unanswered questions.
• Show students slide 7 to explain the bonding of atoms in molecules. Tell students that the rules on this slide are important because they apply to all molecules that they will make in all Carbon TIME units.

Use slide 8 to show instructions to construct the reactants: glucose and oxygen. Students can also follow instructions in Part B of their worksheet.

Show slide 9 in the PPT.

• Have students compare their own molecules with the picture on the slide.
• Slide 10 shows an important message: after students create their reactant molecules, make sure they put away all unused pieces of their molecule kits. This helps reinforce that the matter and energy in the reactants are conserved through the chemical change, and that only the materials from the reactants are used to build the products.

Show slide 11 of the PPT and have students re-arrange the atoms to make molecules of CO₂ and H₂O. Tell students to follow the instructions in steps 3 and 4 in Part B of the worksheet to construct their products.

• To do this, they will need to move their molecules from the reactants side to the products side of the placemat. Explain to students that atoms last forever, so they should not add or subtract atoms when they change the reactant molecule into product molecules.

Show slide 12 in the PPT.

• Have students compare their own molecule with the picture on the slide.
• Use slide 13 to compare the reactants and products.

Show slides 14-20 in the PPT to help students make connections between what is happening in the animation and the molecular models they made.

• For each slide, focus on different atoms and forms of energy and how they change. The animation draws attention to where they atoms begin and end in the reaction.

Show slide 21 in the PPT.

• Tell students to complete Part C of their worksheet to trace the atoms during the chemical change.

Show slide 22 in the PPT.

• students to complete Part D of their worksheet to trace the energy during the chemical change.

Show slide 23 in the PPT.

• Complete the “check yourself” questions with the class in Part E.

Tell students that now that they have represented a chemical change using molecular models and in animations, they will represent chemical change by writing the chemical equation.

• Show Slide 24 to guide students through the process of writing a balanced chemical equation for cellular respiration. Tell students that these rules apply to all chemical reactions.
• Tell students to write their equations in Part F of their worksheet.
• Have students write their own chemical equations before comparing them with the one on Slide 25.

Show slide 26 of the 4.1 Molecular Models for Potato Cellular Respiration PPT.

• Conclusions: What did you observe during the investigation?
• Predictions: How do you think the plants gained more mass than the paper towel lost?
• 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 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 question can be used as a lead into the next activity.