Activity 5.1 - Tracing the Processes of Cows Growing: Digestion and Biosynthesis (40 min)

Show slide 2 of the 5.1 Tracing the Processes of Cows Growing: Digestion and Biosynthesis PPT.

Display slide 3 in the PPT. Show students the short clip of a cow growing. Follow the link in the PPT, in the materials list, or here (https://www.youtube.com/watch?v=LWJN7li120c). You can opt to only play thirty seconds.

• Introduce students to the macroscopic driving question: How do cows get food to all of their cells?
• Connect this question at the macroscopic scale to an unanswered question at the microscopic scale: How do food molecules get into a cow’s blood?
• Connect this question at the microscopic scale to an unanswered question at the atomic-molecular scale: How are molecules in food changed chemically so that cow cells can use them?
• Assure students that we will be able to answer several of their unanswered questions by the end of today’s activity.

Display Slide 4 to show students that animals use digested food in two ways. Tell students they have learned about one of those uses (cellular respiration). Today they’ll be focusing on what happens to the food cows eat before the food molecules are used for cellular respiration, digestion, and later in the lesson the second way that animals’ use digested food.

• Display Slide 5 to introduce the parts of a cow, focusing on the stomach, intestines, and leg muscle.
• Give each pair of students a Cow 11 x 17 Poster, a copy of 5.1 Tracing the Process for Cow Growing: Digestion and Biosynthesis Directions (you may want to give each student a copy of these directions), 2 nickels, and 5 pennies.
• Explain that they will follow the directions to use their nickels and pennies to trace the path of food in the cow.
• Tell students to pause at the end of the first page.

Display slides 6 and 7 when all pairs have finished the first page of directions.

• Show students the animation of digestion so they can see what happens to carbon atoms and energy during the process.
• When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through digestion.
• Show students the Digestion and Biosynthesis 11 X 17 Posters to help students visualize the process.

Tell students to continue following the directions on 5.1 Tracing the Process for Cow Growing: Digestion and Biosynthesis Directions and pause when they finish step 6.

Use slides 9 and 10 in the PPT to transition to biosynthesis.

• Tell students that cells use digested food for cellular respiration (that they explained in Activity 4.2) and also for growth, which is done through a process called biosynthesis.
• Have students finish the directions on 5.1 Tracing the Process for Cow Growing: Digestion and Biosynthesis Directions to trace biosynthesis.
• Note: biosynthesis occurs in all cells, but here muscle cells are an example.

Display slide 11-12 to show an animation of what happens to the molecules and chemical energy during biosynthesis.

• When watching the slides, ask students what is happening to energy. Listen to see if they notice that chemical potential energy is conserved in the C-C- and C-H bonds through biosynthesis.
• Show students the Digestion and Biosynthesis 11 X 17 Posters to help students visualize the process.

Use slides 13 and 14 to discuss how animal cells use sugar molecules.

• Use slide 13 to point out the problem: Lots of sugar molecules reach animal cells, but they are not made into starch or fiber polymers in animal cells.
• Use slide 14 to explain the two main ways that animals use sugar molecules: (a) they are used to make glycerol and fatty acids and eventually fat (this explains why eating lots of starch and sugar can make someone gain weight), and (b) they are used for cellular respiration, which uses sugar and oxygen to release energy.

Show slide 15 of the PPT. Pass out 5.1 Tracing Atoms and Energy in Animals Worksheet to each student.

• Tell students that now they have considered how molecules move through and are used by a cow, they will now consider the atoms that make up animals.
• 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 slide 16 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 animals all primarily come from food. Water and air are used during cellular respiration.

Show slide 17 of the PPT.

• Have students complete the second chart on 5.1 Tracing Atoms and Energy in Animals Worksheet on energy with a partner.
• Show slide 18. Remind students that chemical energy is in C-C and C-H bonds.
• Discuss students’ answers together. Chemical energy is only found in the food that animals take in. There is no chemical energy in the water or air animals take in.

Use slide 19 and the Metabolic Pathways 11 x 17 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.
• Explain that these processes allow cows who eat mostly carbohydrates in grass to be made up of protein and fat.
• Organisms are complex; this poster also offers students a glimpse of their complexity.