Activity 5.1: Tracing the Process of Potatoes Growing: Biosynthesis (40 min)

Show slide 2 of the 5.1 Tracing the Process of Plants Growing: Biosynthesis PPT.

Display slide 3 in the PPT.

• Show students the short clip of a potato plant growing. Follow the link in the PPT, in the materials list, or here (https://www.youtube.com/watch?v=YbTFCh_XdYI).
• Introduce students to the new driving question: How do potatoes grow?
• Connect this question at the macroscopic scale to an unanswered question at the microscopic scale: How do potatoes’ cells use food to grow?
• Connect this question at the microscopic scale to an unanswered question at the atomic-molecular scale: How are molecules from food used for growth? Where do the glucose molecules used in cellular respiration come from?
• Assure students that we will be able to answer several of their unanswered questions by the end of today’s activity.

Use slides 4-6 to lead a discussion about how atoms enter the plant and get to plant cells.

• Use slides 4-5 to ask students where glucose made from carbon dioxide and water in photosynthesis goes.
• Use slide 6 to remind students that glucose moves from the leaves to all the cells of the plant to be used for growth or energy. They have already learned how plants use glucose for energy. In this activity they will trace the chemical processes involved in growth.

Display slide 7. Give each pair of students a Potato 11 x 17 Poster, a copy of the Tracing the Process of Potatoes Growing: Biosynthesis Directions, 5 pennies, a nickel and several soil minerals (cut out from 5.1 Soil Minerals for Tracing the Process of Potatoes Growing). Explain that they will follow the directions to use their nickels and pennies to trace the path of how matter moves and changes in plants for growth.

Use slide 8-9 to show students what happens to carbon atoms and chemical energy when plants make large organic molecules.

• Ask students what is happening to energy during biosynthesis. Listen to see if they notice that chemical potential energy is conserved in the C-C and C-H bonds through the chemical change.
• Refer to the Digestion and Biosynthesis 11 x 17 Posters in your classroom to help students visualize the biosynthesis of small organic molecules to large organic molecules. You do not need to focus on what small organic molecules are combined to produce the large organic molecules (carbohydrates, fat, and proteins).
• Make sure students understand that cells increase in size as they perform biosynthesis, because atoms enter the cells and do not leave. Eventually, the cells grow large enough to divide. The growth and division of cells results in plant growth.

Use slides 10 to discuss the other ways plant cells use glucose molecules, which include cellular respiration and making cellulose and starch.

Show slide 11 of the PPT. Pass out 5.1 Tracing Atoms and Energy in Plants Worksheet to each student.

• Tell students that now they have considered how molecules move through and are used by a plant they will now consider the atoms that make up plants.
• Read the top portions of the worksheet with students.
• Have students work with a partner to complete the first chart on the worksheet about atoms.

Show slides 12-13 of the PPT.

• Remind students that in Lesson 2 they learned about the molecules that make up cells and the atoms that make up the molecules.
• Discuss the answers to the first chart on the worksheet. The atoms in the large organic molecules of plants all primarily come from the air. Some of the oxygen atoms do come from the soil and water, as well as air. The hydrogen atoms do come from soil and water. The other elements come from minerals in the soil.
• Although some atoms come from soil, students should recognize at this point in the unit that the majority of the atoms in plants come from the air. You can remind students of the results of the plant investigation as further evidence.

Show slide 14 of the PPT.

• Have students complete the second chart on 5.1 Tracing Atoms and Energy in Plants Worksheet on energy with a partner.
• Show slide 15. Discuss students’ answers together. Energy, in the form of light, is only found in the sunlight that plants take in. There is no energy in the water, air, or soil plants take in.

Use slide 16and the Metabolic Pathways Poster to show students that there are many more metabolic pathways besides what they learned about in this lesson.

• This poster only shows pathways in which small organic molecules are changed into other small organic molecules. There are other pathways that change small organic molecules into large organic molecules.
• Organisms are complex; this poster also offers students a glimpse of their complexity.