Students discover how plants use energy from the sun to change air and water into matter needed for growth. Using dairy cows as an example, students investigate how animals obtain energy from the plants they eat to produce milk for human consumption. Further exploration is facilitated by a live virtual visit to a dairy farm or the option of viewing a pre-recorded virtual dairy farm tour. Grades 3-5

by-product: an incidental or secondary product made in the manufacture or synthesis of something else

digestion: the process of breaking down food by mechanical and enzymatic action into substances that can be used by the body

energy: power derived from the utilization of physical or chemical resources

nutrient: a substance that provides nourishment essential for growth and the maintenance of life

photosynthesis: the process by which plants convert carbon dioxide, water, and light energy into sugars and oxygen in order to store energy; the opposite of cell respiration

respiration: the process through which a plant exchanges oxygen and carbon dioxide with its environment

There is a constant flow of energy in our world. This results in an energy supply chain which begins with the sun. Energy is transferred along this chain in different forms, which is important because all the living things require energy in specific forms. Energy helps organisms live and grow. 

Plants use photosynthesis to capture light energy from the sun and convert it into food energy plants need to grow. This process requires sunlight, carbon dioxide, and water, which combine and convert to glucose and oxygen.³ Humans and animals use respiration to obtain energy by combining oxygen and glucose, which results in the release of carbon dioxide, water, and ATP (cellular energy).

Cattle assist in the energy supply chain by converting energy that humans cannot use into energy that humans can use. Cattle have a four-compartment stomach which allow them to eat, digest, and use the energy from some parts of plants that humans cannot.⁵ This is the case with 75–80% of the feed dairy cows will eat.⁶ They eat byproducts like cotton seeds, almond hulls, distillers grain (leftover from processing cereal grains or beer), and sugar beet pulp.⁷ An animal nutritionist will help farmers decide exactly what goes into the feed to provide all the nutrients dairy cows need to grow and produce milk. Humans can then drink the milk the cows produce (or a variety of other dairy products) to get their own nutrition and energy. Dairy products provide a variety of nine essential nutrients, including all of the macronutrients (carbohydrates, fat, protein, and water). This makes dairy products an important part of a healthy diet for all age groups, and especially kids who are still growing.⁸ 

The movement of energy through the world is very important to keeping living things alive. It starts with the sun and plants through photosynthesis. Cows are then able to eat these plants (several that humans can't digest), use the energy to produce milk that humans can digest, and use the energy and nutrients to live and grow. 

1. Explain to students that they are going to look at three different meals that contain energy.
2. Project slide 2 from the Energy's Journey from Farm to You PowerPoint Slides. Ask students what products they recognize. Point to each picture and have students name the food items. They will likely recognize the foods on the left, but you may need to tell them that the food on the right is called silage. Silage is a grass or other green plant that was chopped up and stored in airtight conditions to be fed to animals. Ask the following questions to lead a class discussion:
   • Ask students to raise their hand if they would like to eat each item for their next meal. (Point to each picture individually.)  
   • Discuss with the students why they did not choose silage (ex. it doesn’t look appetizing, never seen it before, humans can’t digest it).  
   • Ask why students like to eat food (tastes good, they are hungry, like to eat etc.). Try to pull out answers that refer to needing food so they aren’t tired and it gives them energy. 
   • Why do you need energy? Have you heard of it?  
   • What is energy?  
   • Which food item do you get energy from? 
   • Can you (a human) get energy from silage? Why?  
   • Can you think of an animal that might get energy from silage?
3. As you go through the discussion questions, point out that the food in the first two pictures gives us (humans) energy to run, play, go to school, and helps our bodies grow healthy and strong. There is some food that grows (like in the last picture) that we can’t use for energy because our body can’t digest it.  
4. Ask students, “If we can’t eat silage, is there a way we can still receive energy and nourishment from it? Why or why not?” Allow students to brainstorm thoughts and ideas.  

Activity 1: Virtual Dairy Farm Tour

1. Show slide 3 of the Energy's Journey from Farm to You PowerPoint Slides. Explain to the students that they are going to discover the energy chain from farms to them. Through this lesson, they are going to investigate and uncover clues to find out what each one of these question marks (slide 3) represents. Each question mark is a step in this energy chain. They will work as a class to come up with each of the five steps of this energy chain by exploring clues and asking questions.  
2. Ask students to think of all of the foods that are in the dairy food group (milk, yogurt, ice cream, butter, etc.) Ask, "How does energy get to our bodies when we consume dairy products?" Allow students to offer answers using their prior knowledge. Explain that they are going to look at the energy supply chain of dairy products to their plate. 
3. Give each student one copy of the Energy’s Journey from Farm to You activity sheet (page 1) and pictures (page 2). Instruct students to cut the pictures out and place them in the order they think the energy flows.
   • Note: Students should not glue or tape the pictures yet. If using an interactive notebook, they can place the pieces there as well. 
4. Once students have placed the pictures in their initial order, explain that they will learn more about this process and see how close they are to the right answer.
5. Explain that the first step of investigation is to join a virtual farm field trip. As students watch the virtual tour, instruct them to look for clues to figure out what the question marks stand for and the correct order of this energy chain. 
6. Show a virtual tour of a dairy farm using one of the following options:
   • Visit the website for your regional dairy council to access local resources and potential tours.
   • If a live virtual tour is not possible, use a pre-recorded Virtual Field Trip.
7. After the tour, ask students to share if/how they changed their energy flow diagram based on what they learned from the tour. Allow students time to share. 

Activity 2: Energy from Sun to Plants

1. Ask students, “What is the ultimate source of energy?” (The sun.) Confirm that the first step in the energy chain is the sun (slide 5).
2. Moving to the next step in the energy chain and ask, “What does the sun's light give energy to?” (plants) (slide 6). Clarify that water and carbon dioxide provide nutrients for a plant to grow, but the sun is the energy source.
3. Have students secure the picture of the corn in step 2 of the energy flow diagram. As they are working, clarify that this picture could be any plant. All plants convert the light of the sun to energy (slide 7).
4. Ask students, “What is the process called when plants use sunlight and water to grow?” Explain to students that water and light energy from the sun are part of a process called photosynthesis.
5. Lead students through the following activity to help them understand photosynthesis. Instruct the students to turn their Energy’s Journey from Farm to You activity sheet to the back side where they are going to draw out the process of photosynthesis. (Slide 8 walks through all of the steps.)
   1. Draw a plant with the sun above it and a water source (rain, groundwater, a stream). Write the words “Light Energy” next to the sun with arrows going toward the plant.  
   2. On the left side of the picture, write the words “Carbon Dioxide,” and draw an arrow from this word to the plant, indicating that the plant takes in carbon dioxide from the air.  
   3. On the right side of the paper, write the word “Oxygen,” and draw an arrow pointing away from the plant to this word to show that plants release oxygen into the air.  
   4. Draw a sugar cube next to the plant and an arrow going from the plant to the sugar cube. This shows that photosynthesis is how plants can transfer the energy from the sun to help them grow. This process converts the energy to a food (glucose or sugar) the plant needs to grow.  

Activity 3: Energy from Plant to Cow  

1. Summarize that so far we have learned that the ultimate source of energy is the sun and that the sun gives plants energy through the process of photosynthesis. Photosynthesis converts the sun’s energy into glucose, or sugar.
2. Ask the students, “Who (or what) do you think can use this glucose, or sugar for energy?” Students may answer with humans or animals, and these are both correct. Point out that cows are the center of our energy chain today (slide 9). Have students place the picture of the cow in the third box along the energy chain. 
3. To better illustrate this step in the energy transfer, students need to learn a little more about what cattle eat. 
4. Referring back to the virtual dairy farm tour (Activity 1) ask students, “What were some of the plants or food items the farmer showed us that cows eat?” Prompt them as necessary or show the pictures on slide 10.
5. Point out that cattle can obtain nutrients from plants that humans cannot digest. Cattle have this ability because they have a stomach that has four chambers rather than just one. This allows them to digest and gain nutrients from food that humans cannot. Show the next slide and read through the material (slide 11).
6. Show the pictures of some of the different plants cows eat (slide 12). Have the students guess the plant based on the picture.  
   • Show optional video Cow Diet. 
7. Explain that many of the foods that cattle eat are actually byproducts. To explain what a byproduct is, project slide 12 on the board. Using whiteboard markers, allow students to come up in small groups and create lists of products made from cotton, wheat, alfalfa, and corn. For example, they could list clothing, cotton balls, and denim to the side of the cotton photo. Cereals, breads, pastas, pastries, etc. can be listed to the side of the wheat photo. 
8. Explain that part of a cotton plant is used to make clothes. That is the primary purpose of growing cotton. Wheat is primarily grown to be processed into flour to make products like pasta, breads, and cereals. You may have also eaten corn on the cob, corn tortillas, or corn flour in cereal. Fresh alfalfa sprouts are commonly eaten on sandwiches (slide 13).  
9. Discuss the importance of not being wasteful and just throwing things in the garbage. We have found a really cool way to use some of our “leftovers” or byproducts.
10. Referring back to what students learned in step 5 ask, “Who do you think can digest these byproducts?” (cows!) 
11. Ask students, “Why are cows able to digest byproducts that humans can’t digest?” Students might answer that cows have four stomachs. Explain to students that cows don’t have four stomachs, but have four stomach compartments. Humans have one simple stomach (slide 14). If students don’t know the answer, show them slide 14 and ask, “What are some of the differences between these two stomachs? Which is a human stomach and which is a cow stomach?” Since cows have a different digestive system than us, they are able to eat and digest some parts of these plants that we can’t digest.  
12. Show students the same plant photos with the photos of what cows eat (slide 14). Ask students to compare the products we eat to the products in a cow’s diet. Show the picture of how the plant looks when the cow eats it (slide 15). Explain the following concepts.  
    • Cotton: After cotton is used for clothing, there is a seed byproduct that cows can eat. When it is fed to cows, it is known as cottonseed meal. 
    • Wheat: When wheat is processed, the byproduct of the grain not used in flour is called distillers grain.  
    • Alfalfa: This crop is grown, cut, and dried out to make hay. 
    • Corn: Explain to students that unlike humans, who only eat the kernels on the cob, cows can eat the entire corn stalk. The corn stalks are chopped into small pieces and kept very moist. This is called silage (seen on slide 2). Corn used for cow feed and silage is not the same variety of corn as sweet corn grown in gardens.  
13. Explain to the students that a cow’s diet is 75–80% food that human’s can’t digest, or is part of the plant that we don’t use.⁶ This is another great thing about cows—they help us use all the energy produced by plants so none of it goes to waste.  
14. Review the energy chain so far. Walk students through each step, and have them repeat what they have learned (slide 16). They should be able to explain how cows receive energy from the ultimate source (sun).

Activity 4: Energy from Cow to You

1. Remind students that we just learned all about cows and the different types of food they eat. Remember that cows can digest these foods because of their 4-compartment stomach. This stomach allows their body to better break down the nutrition and energy in the foods they eat. Once they breakdown these foods through digestion, their body then uses the nutrition and energy from the plants to grow, move, and stay healthy. In a dairy cow’s case, their body also uses the energy to produce a product that we can use, and it happens to be the next step in our energy chain (slide 16).
2. Tell the students, "I am going to ask you a question and on the count of three I want everyone to tell me the answer at the same time." Ask, "What food product do dairy cows produce?" (milk!) (slide 17) In order for cows to produce milk, a farmer has to take care of the cow by providing a safe place for it to live, regular veterinarian check-ups (just like you go to the doctor), and a nutritious diet.  
3. Tell the students that the next slide (slide 18) is going to show some different foods. If it is a dairy food, the students should stand up. The slide will go through five different foods and have an ‘x’ come up if it is not a dairy food.
4. Review the energy map they have learned so far (slide 19).  
5. Ask the students, "Who eat/drinks the dairy products for energy?" That’s right, YOU are the final question mark in our energy map (slide 20). Tell the students that they have made it all the way through the energy map.  
6. Take a couple of minutes to let the students either glue or tape their pictures down on their activity sheet in the correct order. You may review the steps with them as they are taping or gluing.  
7. Explain to the students that cows eat and digest all the different plants we talked about to get the energy and nutrients their body needs to grow and stay healthy. Dairy foods are just one of the food groups they can eat to get energy and nutrients their body needs to stay healthy and grow strong.  

1. Ask students to walk through each step of the energy chain now that they have learned all the steps (slide 20). They should be able to explain how we receive energy from the ultimate source (sun). Sunlight is used by plants during photosynthesis, a cow eats that plant or part of the plant, the cow then produces milk that humans can consume. 
2. Show slide 21. This is the same slide as the very beginning of the lesson. Ask the students to raise their hands if they get energy from the pictures on the left (everyone should raise their hand). Then ask the students to stand up if they can get energy from the first two pictures (everyone should stand up). Call on one student to answer how they can get energy from the picture on the right. If needed, help guide their answer to say they can get energy from the silage because cows are able to digest it and use the energy to make milk, and our bodies can digest the milk which gives us energy.  
3. Emphasize that we help to take care of plants and animals so that we can use the energy to live, work, and play. Isn’t that cool that we can all work together to use the energy in the world?   
   • Optional: Tell the students there are lots of people that help to make sure they have food at school or food to buy at the store. They were able to meet one farmer that helps to make sure they have dairy products. Encourage the students to write the farmer a thank you note.  

1. https://outagamie.extension.wisc.edu/files/2012/10/Using-Food-Waste-as-Livestock-Feed.pdf 
2. https://www.sciencedirect.com/science/article/pii/S0022030217309037#bib125 
3. https://ssec.si.edu/stemvisions-blog/what-photosynthesis 
4. https://wa.kaiserpermanente.org/healthAndWellness?item=%2Fcommon%2FhealthAndWellness%2Fconditions%2Fdiabetes%2FfoodProcess.html
5. https://www.fda.gov/animal-veterinary/animal-health-literacy/how-cows-eat-grass 
6. Estimation of human-edible and inedible materials computed from the average Midwestern lactating cow ration. Thoma et al 
7. https://library.ndsu.edu/ir/handle/10365/9250 
8. https://health.gov/dietaryguidelines/2015/resources/2015-2020_Dietary_Guidelines.pdf 

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