Digestive System: Where does food go?, Study notes of Cell Biology

Download Digestive System: Where does food go? and more Study notes Cell Biology in PDF only on Docsity! Created by LABScI at Stanford 1 Digestive System: Where does food go? Teacher Version In this lab you will learn about your digestive system. We will use everyday objects like yarn and a ziplock bag to understand how long our digestive system is and how it breaks down all of the tasty food you eat. California Science Content Standards: • 1. Cell Biology: The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism’s cells. • 1b. Students know enzymes are proteins that catalyze biochemical reactions with altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings. • 9. Physiology: As a result of the coordinated structures and functions of organ systems, the internal environment of the human body remains relatively stable (homeostatic) despite changes in the outside environment. • 9a. Students know how the complementary activity of major body systems provides cells with oxygen and nutrients and removes toxic waste products such as carbon dioxide. • **9f. Students know the individual functions and sites of secretion of digestive enzymes (amylases, proteases, nucleases, lipases), stomach acid, and bile salts. • How each section of the digestive tract contributes to the processing of the food you eat Prerequisites: • Good for most students • Some basic multiplication required • Concept questions require critical thinking about the functions of the digestive system. More challenging questions can be skipped with younger students. Complete list of Materials: • 5 different colors of yarn (white, yellow, pink, red, purple) • Scissors • Ruler • Calculator • 1 cup corn flakes (cereal) • 1 tsp lemon juice • Food coloring • 1 quart ziplock bag • Water • Measuring spoons (1 tablespoon, 1 cup) • 1 large width straw • 1 gallon ziplock bag • 1 empty paper towel roll • 1 plastic cup • Gloves • 1 leg of pantyhose • Small tub (or towel to put over table) Created by LABScI at Stanford 2 Key Concepts: • The digestive system is very long and contains multiple organs to help break down food and adsorb nutrients from the food we eat. This requires both chemical digestion, when chemicals and enzymes break the food down into its nutrient components, and mechanical digestion, when food is physically broken into smaller pieces. • The mouth is the first organ in the digestive system. Both chemical digestion and physical digestion occur in the mouth. • The esophagus connects the mouth to the next organ in the digestive system, the stomach. • The stomach contains hydrochloric acid which helps to chemically digest proteins. Mechanical digestion also occurs in the stomach due to the churning motion. • The small intestine is the longest part of the digestive system, and most of the nutrients are absorbed here. • In the small intestine, other digestive juices from the pancreas and the liver are added. These digestive juices help to continue the chemical digestion of food. • In the large intestine, water is removed from the food, and the final nutrient absorption occurs. Introductory Mini-Lecture: Why do we eat food? Because it gives us the energy we need to do everything including growing and repairing our cells. How do we get this energy from our food? We need to break it down. This doesn’t just mean breaking it down into smaller chunks of food, this means breaking it down into its building blocks – proteins into amino acids, complex carbohydrates into sugars, and fats into fatty acids and glycerol. In order to break down our food into these basic units, our digestive systems use two broad categories of digestion: mechanical digestion and chemical digestion. Mechanical digestion involves physically breaking the food down into smaller pieces without any chemical changes to the food. Chemical digestion involves breaking chemical bonds to split the food into simpler nutrients. As you work through this lab you will see both mechanical and chemical digestion at work. Created by LABScI at Stanford 5 DIGESTIVE ORGAN LENGTH (CM) Mouth ≈ 10 cm Esophagus ≈ 38 cm Stomach ≈ 18 cm Small Intestine ≈ 650 cm Large Intestine ≈ 163 cm TOTAL ≈ 879 cm Convert this to meters using the formula: (total # of centimeters) multiplied by (0.01 meters/centimeter) Length of your digestive tract in meters: ≈ 8.8 m Questions: Q1. How does the length of your digestive system compare to your height (if you know your height in feet and inches, convert your height to inches knowing that there are 12 inches in a foot, then multiply it by 0.0254 meters/inch to get your height in meters)? How do you think your digestive system is able to fit inside your abdomen? The length of the digestive system is approximately 5 times greater than one’s height. The digestive system is able to fit inside the abdomen by being coiled up. Q2. Why do you think your digestive system is so long? How do you think this helps digestion? What is the longest section of your digestive system? What important processes do you think happen to the food in this section? The digestive system is so long to be able to digest food. This helps digestion by allowing time and space to break down food, absorb nutrients, and absorb water. The longest section of the digestive system is the small intestine. In the small intestine, the nutrients from the food are absorbed. Q3. How long do you think it takes (on average) to digest food? The time it takes to digest food from the time you eat it to the time you excrete it is about one to three days. Created by LABScI at Stanford 6 Q4. What percent of your entire digestive system is the small intestine? length of small intestine / length of entire digestive tract = (650 cm/879 cm) x 100% ≅ 74% The small intestine makes up about 74% of your entire digestive system. Part 2: What happens to the food you eat? Introduction: In this part of the lab, you will work in groups and use real food to simulate what happens to the food you eat as it travels along your digestive system. We will pause at each section of the digestive system to identify any unique features and to try to better understand how these features contribute to the digestive process. Procedure: 1) The quart ziplock bag represents your mouth. Put 1 cup of corn flakes into the quart ziplock bag. Add 2 tablespoons of water, representing your saliva. Close the bag tightly. Let each person in your group crush the corn flakes in the bag for 5 seconds. Remind students about the mechanical and chemical digestion taking place in the mouth. 2) The straw represents your esophagus. Try to “swallow”, or pass the corn flake mixture through the straw esophagus by cutting a small hole in one corner of the bag and squeezing the mixture into the straw. Hold the gallon ziplock bag under the straw to catch anything that comes through the straw. This is really hard to do, so just do a little to demonstrate peristalsis (muscles squeezing the food down into the stomach). Q5. What do you have to do to get the mixture through the straw? You have to squeeze the mixture to get it through the straw. Q6. Do you think gravity is necessary for food to pass through the esophagus? (optional) Have one person in your group try to chew and swallow a cracker laying down flat on the ground. Were they able to do it? No, gravity is not necessary for food to pass through the esophagus. Yes, if someone tries to swallow a cracker lying down they should be able to do it. Q7. What is this movement of your real esophagus called? This movement of your real esophagus is called peristalsis. 3) The gallon ziplock bag represents your stomach. Move all of the corn flake mixture into the gallon ziplock bag. Add 1 cup of water and 1 teaspoon lemon juice to your bag. This Created by LABScI at Stanford 7 represents the gastric juices in your stomach. Close the bag tightly. Let each person in your group squish around the mixture for 30 seconds. Remind students about the mechanical and chemical digestion occurring in the stomach. Why doesn’t the acid in our stomachs burn through our stomachs? There is a mucous membrane (very similar to mucous, or snot, in your nose) which protects our stomach from the acid. Q8. What kind of digestion occurs in your stomach? In the stomach, food is broken down by acid and mashed up by the churning. Q9. Your real stomach secretes hydrochloric acid (not lemon juice), which has a very low pH. What is the purpose of this acid? What other key ingredient in digestion is our simulated system missing? The purpose of this acid is to make enzymes work (the missing key ingredient). 4) The paper towel roll represents your small intestine. Have someone in your group hold the roll at a 45 degree angle over the plastic cup. Before pouring the mixture through the tube, add some food coloring to your gallon ziplock bag. This food coloring represents other digestive juices from the liver, gallbladder, and pancreas that are required to complete chemical digestion of food. Once you’ve added food coloring, pour your corn flakes mixture from the 1 gallon ziplock bag into the top end of the roll. The other digestive juices are bile (produced in the liver and stored in the gallbladder) and enzymes produced in the pancreas. Remind students about the important nutrient adsorption occurring in the small intestine. If we couldn’t absorb the nutrients from our food, digestion would be a futile endeavor. Q10. What do you notice about the food that emerges from the other end of the paper towel roll? It is not quite as watery. The small intestine has some interesting features which make it highly specialized for maximizing nutrient absorption. Although our paper towel roll intestine has smooth walls, your real small intestine has many folds, big folds you can see, and tiny folds that are only visible under the microscope. Let’s calculate the surface area of your small intestine! The formula we will use is for calculating the surface area of a tube is: 2 x  x radius x length. Let’s simplify by approximating  with 3, and the radius as 2 cm, which makes the formula: 2 x 3 x 2 cm x length. Q11. Using the length of your small intestine you just calculated, what is the surface area of your small intestine? ≈ 7,800 cm2