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Digestive System Standards: CA, 5th Grade, Life Science 2. Plants and animals have structures for respiration, digestion, waste disposal, and transport of materials. c. Students know the sequential steps of digestion and the roles of teeth and the mouth, esophagus, stomach, small intestine, large intestine, and colon in the function of the digestive system. Activities: Down the Food Tube, Starch and Saliva Test, Swallowing Up Background All living things need energy to function. Plants produce their own food from non-­‐living components in the environment: sunlight, water, and CO2. Animals have to consume plants or other animals to get their energy. Outside of breathing, the digestive tract is the primary way in which our bodies incorporate the essential chemistry of the outside world. Its amazing machinery safely brings what’s outside in. It is literally the castle gate to the inner kingdom. Like a path winding through a strange land, the digestive tract (alimentary canal) is with filled with twists and turns and exotic places. Let’s take a look at the amazing machinery and the way it works. Parts Function Teeth Rip up food: easier to swallow, more contact with saliva enzymes Saliva Begins chemical digestion of food (breaks starch into sugar) Esophagus Pushes food to the stomach at any angle Stomach Mixes the food with digestive acids Small Intestine Absorbs the nutrients and passes them to the blood Blood Delivers nutrients to all of the body’s cells Large Intestine Absorbs excess water, compacts waste Colon/Rectum Compacts, stores, and ejects indigestible waste Lesson
Engage On the board write: “Question: How does our body get energy to sustain life?” Elicit student responses. Collect student ideas on the white board. Ask students to record their own sentence in their notebook. Come up with an agreed upon sentence. Example: “Hypothesis: Energy is brought into our bodies by eating plants or animals or both.” Explore/Experiment: Activity 1: Down the Food Tube Explain to students that you are about to take them on a trip through the digestive tract. Distribute digestive system part and function cards. Direct students to the prepared tape-­‐lines outside. ©Rock Tree Sky | rocktreesky.org | All rights reserved.
Challenge them to silently (it is possible!) line themselves up in two lines from mouth to rectum in correct order, facing each other. (Assist) Run the prepared “food particle” down the student digestive system, pausing to focus on the learning (part and function) along the way. Reinforce, reinforce, reinforce! At the end, distribute the glucose (craisins) evenly among students. Challenge them to try and feel it go down the esophagus. Action: • Teeth: rip up food; each student tooth rips one, hand sized hole in the plastic bag. • Saliva: begins chemical digestion: the students will spray the bag with their saliva bottle • Esophagus: squeezes the food down to the stomach: passes bag along • Stomach: continues chemical digestion: spray the bag with stomach acid and churn bag • Small intestine: absorbs the nutrients and passes them to the blood; the students will search through the food particle and hand the bags of nutrients to the blood • Blood: distributes nutrients throughout the body; the students will pass out the nutrients to all the students (save this to do after all the digesting is complete) • Large intestine: absorbs excess water; the students will use the sponges to soak up the water off the bag and off the floor • Rectum: removes waste: the students will place the remains of the food particle in the trash can Explain Return to the classroom and check for understanding using the “cold call” technique. Copy the part and function table onto the whiteboard and have students enter it into the notebook as you do. Go over any interesting details from resource pages. Extend Use the 2nd and 3rd activities to extend student’s understanding of how enzymes in saliva decompose starches into sugars and to witness the proof of peristalsis. Activity 2: Starch and Saliva Test Tell students that they can taste the work of the enzyme (amylase) that breaks down starch into sugars. All they need is a soda cracker and few minutes. Have students chew a soda cracker very well and to hold it in their mouth for 3~5 minutes. Elicit reactions to the change in taste. Did it stay the same? Did it get sweeter? Activity 3: Swallowing Up In this activity you can demonstrate the amazing power of esophageal peristalsis by finding a capable volunteer from the class willing to chew a bite of banana, stand on their head supported by a wall (or with help as needed). Swallow! It works! Even against the force of gravity! Evaluate Have students write down three things they learned in science class today. Cold call or turn and tell your neighbor checks for understanding. ©Rock Tree Sky | rocktreesky.org | All rights reserved.
Resources: Making the Food particle: Place pieces of dried fruit (craisins or trail mix work well) in several small wax sandwich bags. The bags of fruit get wadded up in newspaper and then placed in brown paper lunch bags. The paper bags, along with additional wadded up newspaper are placed in a large, thin plastic bag (you want something that rips open easily. Classroom wastebasket bags work great.) Additional supplies: -­‐-­‐Sponges -­‐-­‐Spray bottles filled with water – label two as "Saliva" and two as "Stomach Acid". -­‐-­‐Trash can ©Rock Tree Sky | rocktreesky.org | All rights reserved.
Teeth: tearing and grinding the food into smaller bits which are both easier to swallow and provide more surface needed for better chemical decomposition reactions with saliva and stomach acid. Saliva: moistens food, making it travel more easily down the esophagus; contains an enzyme called amylase, that begin the process of breaking down long chain starches into more readily available sugars for later digestion in the small intestine. (Activity 1) Esophagus: a muscular tube that literally pushes the swallowed food down to our stomachs. The muscles contract and relax rhythmically in a process called peristalsis. (Activity 2) Stomach: A muscular bag about the size of a baseball mitt, whose job it is to churn the food around with a strong acid (Hydrochloric Acid, pH 12) This acid helps to break down complex protein molecules into the amino acids needed by the body to build new cells of all kinds. Blood: delivers the food nutrients (fats, carbohydrates, and sugars) to all the other cells in the body. Small Intestine: a long curly tube (up to 20 ft) with a lining like shag carpet. The walls of the small intestine are lined with tiny, finger-­‐like protrusions called the villi. This is where the nutrients in the food actually pass through the lining of the small intestine and into the bloodstream. At last you can say that the food is digested. Large Intestine: water is absorbed from the non-­‐useful parts of the food (largely indigestible cellulose and strong, connective tissues) as it continues through the digestive tract. The waste gets thicker and thicker as the water is absorbed. Colon/Rectum: compacts, stores, and ejects the indigestible waste. ©Rock Tree Sky | rocktreesky.org | All rights reserved.