Title: Making and Breaking Carbohydrates: How living things get energy!

Transcription

1 Title: Making and Breaking Carbohydrates: How living things get energy! Author : Meredith Schwendemann Subject Area(s): Science Grade(s): 8 Description of Lesson: Students will learn how the sun provides all living things with energy through the processes of photosynthesis and cellular respiration; through the formation and breakdown of carbohydrates. The lesson includes music and technology with the incorporation of a music video about photosynthesis, note-taking with processing and summarizing, and a hands-on lab demonstration to test for starch and witness the breakdown of starch into simpler sugars. The lesson will conclude with an assessment to measure student learning. Length of Lesson: 3-42 minute sessions Student Objectives: Students will understand that energy for living things comes from the sun through the processes of photosynthesis and cellular respiration. Students will recognize and recall specific vocabulary: carbon, carbohydrate, starch, glucose, organic compound, photosynthesis, cellular respiration. Materials: Teacher computer with internet access and projector Interactive Science Notebooks (students have their own to record their notes and summaries) Copy of readings or textbook with content information (McDougal Littell Science, Cells and Heredity, Chapter 2, pgs 41-42, 47-54) Music Video: "Photosynthesis - They Might Be Giants" found on Youtube Two colors of construction paper with string- 10 pieces of color 1 and 12 pieces of color 2 Starch to Sugar Handout (class set) from Missouri 8th Grade Level Lab Book- B.K. Hixson. Loose in the Lab (an adapted version of this handout is included at the end of the lesson) Materials for lab activity (per lab group): 2-4 saltine crackers, 2 dixie cups, 2 craft sticks, iodine solution, water, 1 pipette Procedure: Day 1: Preview Content and assess prior knowledge: Show the music video, "Photosynthesis- They Might Be Giants", and have students record information they see and hear from the video.

2 Make a list of what students already know about photosynthesis and how living things get energy. Input: Students use Cornell-style notes to add information about the key terms: Carbon, Carbohydrate (starch, glucose, cellulose), Organic Compound, Photosynthesis, Cellular Respiration. Students put the notes in their interactive science notebooks. Carbon: student read the paragraph about carbon found in the readings for this class (project on screen or provide handouts), record information in notes, select students to demonstrate carbon's bonding ability. Have 10 students represent carbon atoms (hang color 1 around each student representing carbon), have 12 students represent hydrogen atoms (hang color 2 around each student representing hydrogen). Have two carbons stand back to back with their arms outstretched at right angles so that there are four hands, one in each direction. These students represent one carbon atom that has the ability to bond four times. Have the other students representing carbon form carbon atoms. Have one student from each carbon pair hold hands with a student from another carbon pair forming a carbon chain. Then have students representing hydrogen only extend one arm, keep the other arm at their sides. Have students representing hydrogen hold hands with the free hands of the carbon atoms. Point out to students that hydrogen can only form 1 bond, but carbon can form 4 allowing it to be the building blocks for important organic compounds for life. (extension: you could add an element, oxygen, by using a 3 rd color. Students would extend both arms, showing that oxygen can form a double bond with carbon, or two bonds between two atoms) Have students draw a picture in their notes to represent carbon and how carbon bonds. Organic Compound: students read the paragraphs about organic compounds in the handout for this class. Record information about organic compounds in their notes. Students may also read other resources about organic compounds to provide additional examples in notes (McDougal Littell Science, Chemical Interactions, Chapter 5) Have students add to their list of examples by thinking of organic compounds in their own lives. Carbohydrate: students read about carbohydrates (pg in handout) or in McDougal Littell Science, Cells and Heredity, pg 42, or in McDougal Littell Science, Chemical Interactions, chapter 5). Have students teach the information they read about to their seat partner for 30 seconds to a minute. Have students record important information about carbohydrates in their notes. Have students draw pictures representing carbohydrates in their notes- pictures may include examples of where carbohydrates are found, or pictures of the molecular structure of carbohydrates. Ask students to identify the last food containing carbohydrates they ate. Photosynthesis: pose the question, how are carbohydrates made? Read information about photosynthesis in the handout (pgs ) or pages in McDougal Littell Science, Cells and Heredity. Have students summarize/teach their seat partner about photosynthesis. Record information in notes. When students record the equation for photosynthesis, highlight the reactants in one color and the products in another. Emphasize that the energy for the reaction comes from the sun, but is not destroyed, it is transformed into chemical energy in the form of glucose (sugar).

3 Cellular Respiration: pose the question, how do living things access the energy stored in sugars? Read information about cellular respiration in the handout (pgs ) or in McDougal Littell Science, Cells and Heredity, pgs Have students teach their seat partner about cellular respiration. Record information in notes. When students record the equation for cellular respiration, highlight the reactants in one color and the products in another. Emphasize that the chemical energy stored in glucose (sugar) has not been destroyed, but converted into another usable form of energy. Ask students if they see anything interesting about the equations for photosynthesis and cellular respiration. Processing activity: have students create a Venn diagram comparing and contrasting photosynthesis and cellular respiration. Summary: students summarize why living things need carbohydrates, how carbohydrates are formed, and how energy is released from carbohydrates. Day 2: Starch to Sugar Lab pgs in Missouri 8th Grade Level Lab Book, B.K. Hixson, Loose in the Lab, Students will learn how to test for starch using iodine and understand how the body begins to break down starch in preparation for cellular respiration. Review lab safety rules. Read lab handout with students. (see attachment at end of lesson) Carryout lab procedures and record observations in data table Answer lab analysis questions Day 3: Review concepts from previous two days. Have students watch the music video "Photosynthesis- They Might Be Giants" again and look for ways to improve the information in the video. Have students do a think-pair-share on what could be added to the video to make it better. Record student ideas on the board. Student ideas may include better images/animation to help explain the content, or additional content that was glazed over in the video. Have students answer the assessment questions to measure how well students learned the concepts. Note: the assessment questions could be used on day 1 as a pre-test in order to measure student gain from the beginning to the end of the lesson. Scientific Explanation: Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen. They are necessary for living things because they provide energy for life. Carbohydrates are made during the process of photosynthesis and the energy stored in carbohydrates is released during the process of cellular respiration. Assessment: 1. Explain why carbon is the major element of life; include the term organic compound in your answer. answer: Carbon has the ability to bond with many different elements in many different

4 ways due to the fact that it has 4 valence electrons. Carbon is the basis of all organic compounds because of it's ability to bond. Carbon can be linked together in long chains to form large molecules necessary for life. 2. What functions do carbohydrates perform for living things? answer: carbohydrates provide living things with energy. 3. List two examples of carbohydrates. answer: Starch, glucose, cellulose. 4. How do plants and animals get energy? answer: plants get energy through the process of photosynthesis. Photosynthesis uses sunlight, CO2, and H2O to make glucose which is used for energy. Animals get energy by eating plants and other animals and breaking down glucose. 5. Why is photosynthesis important to life on earth? answer: it uses energy from the sun to produce energy for most living things on earth. 6. What are the starting materials for photosynthesis? answer: CO2, H2O, sunlight. 7. What are the starting materials for cellular respiration? answer: glucose, O2. 8. How are photosynthesis and cellular respiration similar? How are they different? answer: cellular respiration and photosynthesis both transform energy, but the starting materials and the products are reversed in the two processes. Photosynthesis uses carbon dioxide and water to convert light energy to chemical energy (glucose). Cellular respiration uses glucose and oxygen and produces carbon dioxide and water and transform the chemical energy into another usable form for the body. (questions 2, 7, 8 taken from McDougal Littell Science, Cells and Heredity, Chapter 2) Missouri and Kansas Standards Addressed: Kansas Science Standards: Standard 3, Benchmark 5: The student will understand living systems require a continuous input of energy to maintain their chemical and physical organization. Students understand the sun is the primary source of energy for life through the process of photosynthesis. Students understand food molecules contain biochemical energy, which is then available for cellular respiration. Missouri Science Standards (GLE s): Strand 3.2, Concept B. Photosynthesis and cellular respiration are complementary processes necessary to the survival of most organisms on Earth. Strand 1. 2, Concept A.a. Recognize and describe how chemical energy is stored in chemical compounds (e.g., energy stored in and released from food molecules, batteries, nitrogen explosives, fireworks, organic fuels)

5 Starch to Sugar with your host: Amylase Lab Group Members: The Experiment The digestive process starts in your mouth, when you begin to chew your food- something we are confident your mother has instructed you to do on more than one occasion. Your mouth is full of enzymes. An enzyme is kind of like a chemical key. Enzymes are proteins that unlock long chains of fat, protein, and starch molecules, and releases them as shorter, easier-to-handle molecules, like amino acids and sugars (glucose, fructose, sucrose ). To demonstrate this idea, we are going to ingest a cracker, a food that you will test and determine is made almost exclusively of starch. Rather than swallowing the cracker right away, you are going to keep chewing it to make a cracker mash. As you do, the enzymes in your mouth will continue to break the starch down into sugar. When you perform the test for starch a second time, it will come up negative, because most of the starch has been unlocked and converted into smaller pieces. Background information One enzyme present in your saliva is called amylase. Amylase breaks down starch molecules into smaller sugar molecules. Recall that starch and sugars are examples of carbohydrates; carbohydrates store chemical energy. The enzyme amylase is a protein. Amylase is a protein that speeds up the breakdown of large molecules, a catalyst in chemical reactions. Iodine is a starch indicator. Normally, iodine is a reddish-brown colored liquid. You may have used it to treat minor cuts and scrapes, it leaves a reddish-brown color on your skin. When iodine comes into contact with starch, it reacts to form a deep blue-black color. Scientists use iodine to determine if starch is present. Pre-lab questions 1. Which cells need energy? 2. Which process releases energy from sugar molecules? 3. What are the starting materials for this process (the reactants)? 4. When you ingest food, are the starting materials for this process ready to go? 5. What must your body do to the food in order to prepare it for cellular respiration?

6 Materials: 2-4 saltine crackers 2 dixie cups 2 craft sticks iodine water Student Roles: Timer Chewer Recorder Messenger 1 pipette Procedure 1. Take one saltine cracker and mash it in a Dixie cup using your fingers. Make the pieces as small as you possibly can. Add a pipette full of water to the cracker and mix everything around with the craft stick to make a lovely and appetizing cracker mash. 2. Send one student to the front table with the Dixie cup and cracker mash to receive a pipette full of iodine. Record what happens to the color of the iodine when it hits the mixture. 3. Take the second cracker, pop it into your mouth, and chew it up. Chew for about 2 minutes, the longer you chew the longer the amylase has time to break starch down into simpler sugars. Note any change in flavor as you chew, particularly any sweetness. 4. After two minutes of chewing, spit the cracker mash into the second Dixie cup. 5. Send one student to the front table with the second Dixie cup and chewed cracker mash to receive a couple of drops of iodine. Note the color of the iodine after it is added to the cracker mash. If starch is present, the color will change to a deep black. If there is no starch present, the color will remain reddish-brown. Data and Observations Observation table: Effect of amylase (protein) on starch molecules (carbohydrate) Cracker with water and iodine Cracker with amylase and iodine Additional observations:

7 Concluding Questions 1. Was there starch present in the crackers before the experiment was begun? 2. How do you know? 3. Was there starch present in the cracker mash after it had been chewed for 2 minutes? 4. How do you know? 5. What was the function of the enzyme (protein) in your saliva? 6. Why do we (animals) need enzymes like amylase? 7. Was this an example of mechanical (physical) digestion, or chemical digestion? 8. How do you know? 9. What were the constants in this experiment? 10. What was the independent variable in this experiment? 11. What was the dependent variable in this experiment? How Come, Huh? This lab gives you evidence of what happens in the digestive process. The process starts the minute the grits hit the roof of your mouth. The enzymes in your mouth start to flow when your nose smells food cooking. You ve heard the expression, Mouth-watering good food? Well, that s just your nose telling your brain to inform your mouth that some good eatin is on the way and to fire up those digestive enzymes. That s why your mouth waters when you are hungry-- your body is getting ready to eat! The food hits your mouth and the enzymes go right to work, breaking large, complex protein and carbohydrate molecules into smaller amino acids and sugars. The starch gets chopped up into simple sugars that are needed for your cells to undergo cellular respiration. Your mouth has three sets of glands that secrete saliva into your mouth. They are the parotid gland, located in the back of your throat, the submandibular gland, located in your lower jaw, and the sublingual gland, located under your tongue. Working in concert, these three glands can secrete as much as 2 liters of saliva per day- more if you drive by a hamburger joint venting its grill fumes out into the street! *Adapted from Missouri 8 th Grade Level Lab Book. B.K. Hixson. Loose in the Lab