Digestion in a Bag LAB Your digestive system will be represented by a recloseable plastic bag. Your job is to determine which organ the food is in the digestive tract during each step and what is happening in that specific organ. Determine who will be the materials manager for your group. The digestive system has three main functions. 1. It breaks down food into molecules the body can use. 2. The molecules are absorbed into the blood and carried throughout the body. 3.Wastes are eliminated from the body. ·When your body breaks down food into small nutrient molecules, it is called digestion. 1. Open your plastic bag. Send your materials manager to get a piece of food that will be “eaten” by your digestive system. 2. Put the food item into the plastic bag and close it. 3. The food going into the mouth is the first step in digestion. Saliva is important in chemical digestive processes that take place in the mouth. · The process of mechanical digestion begins as you take your first bite of food. ·Your teeth and tongue begin mechanical digestion. 4. Which organ is the food in first and which organ starts the job of breaking down the food? 5. Use your fingers to mechanically break down the food into small pieces. 6. Draw a picture of the chewed food in your digestive system. 7. What parts of your digestive system have the job of mechanically breaking down your food? 8. Why does food need to be chewed and what kind of digestion is this called? 9. What is chemical digestion and what substance does the mouth release that starts this process? 10. The next work of digestion is done by the esophagus. The esophagus is lined with mucus. ·Mucus is a thick, slippery substance produced by the body. Mucus makes food easier to swallow and to be moved along. ·Contractions push the food

toward the stomach. ·Involuntary waves of muscle contraction are called peristalsis ·Peristalsis also occurs in the stomach and throughout the digestive system. ·These muscular waves keep food moving in one direction. 11. What is the job of the esophagus? 12. Normally when you eat, you also drink liquids. These liquids quickly join the chewed food in the stomach. Add about 25 mL of water to your digestive system. 13. Close the digestive system tightly. “Smash” the water and banana until it is essentially all liquid. -

14. Draw a picture of the mushed food in the digestive system. Draw the food in the correct organ. 15. Explain what happens in your stomach to turn chewed solid food into liquid food. 16. What two kinds of chemicals are added to liquid food in the stomach? 17. What do these two chemicals do to the size of food molecules in the stomach?

18. Send your materials manager with your bag to get the “enzyme.” 19. Seal the digestive system tightly. Mix the liquid food and the “enzyme” until it appears to be all one substance. 20. Draw the food now. Draw the food in the correct organ. 21. Food enters the stomach·Food acts as a stimulus. ·Stomach lining releases a fluid called digestive juice. ·Stomach mixes food with the digestive juice. ·Digestive juice contains the enzyme pepsin. ·Pepsin chemically digests the proteins in your food, breaking them down into amino acids. Digestive juice also contains hydrochloric acid. ·Acid required for your stomach to function properly. ·Digestive juice contains mucus which coats and protects the lining of your stomach. ·Cells that line the stomach are quickly replaced when they are damaged or worn out. 22. Where does the digested food go from the stomach? 23. Open the digestive system carefully. Get a piece of paper towel. Stick one edge of the paper in the digested food. Let the towel soak up as much of the digested banana as possible. 24. Place the paper towel on a clean piece of paper towel.

25. ·The small intestine is the part of the digestive system where most of the chemical digestion takes place. ·Almost all chemical digestion and absorption of nutrients takes place in the small intestine. The liquid mixes with enzymes and secretions which are produced in three different organs: the small intestine, the liver and the pancreas. Liver is in the upper portion of the abdomen ·Largest and heaviest organ inside the body. The liver produces bile, a substance that breaks up fat particles into smaller ones (not an enzyme)·Bile flows from the liver into the gallbladder, the organ that stores bile. ·Bile passes from the gallbladder into the small intestine. The pancreas is a triangular organ that lies between the stomach and the first part of the small intestine. The pancreas produces enzymes which help break down starches, proteins, and fats.

The small intestine is well suited for the function of absorption. ·The lining of the small intestine has millions of tiny finger-shaped structures called villi cover the surface. ·Villi absorb nutrient molecules. 26. Explain what happens in the small intestine. 27. Where do the nutrients that have gone through this process go?

The large intestine is the last section of the digestive system. It contains bacteria that feed on the material passing through. Bacteria are helpful in making certain vitamins, including vitamin K. ·Material entering the large intestine contains water and undigested food such as fiber. ·Water is absorbed into the bloodstream from the large intestine. The remaining material is readied for elimination from the body. 28. Take your digestive system to the trash can and dump the leftovers into the trash. In real life this dumping is done privately in a restroom. 29. What happens to the indigestible material? 30. Clean up your lab station.