What is the major site of digestion? If you answered stomach, you missed it! The correct answer is small intestine.

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1 DIGESTION SIMULATION LAB PAP CLASS SET BACKGROUND INFORMATION What is digestion and where does it begin? Digestion is the breaking down of food into forms that our bodies can use. Your digestive system is responsible for converting the food we eat into energy for our bodies to use. Digestion begins when you put food in your mouth and begin to chew. Your teeth help to break the food apart, saliva helps to soften the food and your tongue helps to push the food into your throat when you re ready to swallow. When we swallow the food goes into a tube called the esophagus. The muscles that surround the esophagus help to squeeze and push the food into the stomach. The stomach is a sack that receives the food from the esophagus. Your stomach is located just below the heart. The stomach makes digestive juices (acids and enzymes) that help to break our food down into a thick liquid or paste. Your stomach is a muscular organ that is able to move in order to mix the food with digestive juices. Food usually remains in the stomach for about two hours. What is the major site of digestion? What is the major site of digestion? If you answered stomach, you missed it! The correct answer is small intestine. Imagine a water hose 1 inch in diameter and 20 feet long. This is the overall size of your small intestine. Most digestion occurs in the first 10 inches, the remaining length is used for absorbing nutrients. Food is squirted into the small intestine through a valve connecting it to the stomach. Small quantities of semi-fluid, approximately 1 teaspoon per minute, are released into the small intestine and combine with fluids from the pancreas and gall bladder. The pancreas secretes fluids to neutralize the stomach acid and carry enzymes for digesting proteins, fats, sugars, and starches. Some proteins and starches are digested earlier in the stomach. Others are digested in the small intestine. The brain tells the body how much enzyme of each type to secrete into the small intestine.

2 The gall bladder secretes bile into the first 10 inches of the small intestine. Bile works like a detergent to break fat globules into smaller droplets for digestion. The enzymes in the pancreatic fluid can now surround these droplets and begin the digestive process. Digested food is absorbed into the walls of the small intestine as it moves through the intestine. The undigested food is not absorbed. It moves through the next part of the digestive system, the large intestine. The large intestine is about five feet long so it is shorter than the small intestine. The large intestine is however thicker or wider than the small intestine and that is why it is called the large intestine. The undigested food enters the large intestine as a liquid paste. In the large intestine water is removed from the liquid paste turning what is left into solid waste. The solid waste then collects in the rectum at the end of the large intestine and will finally leave the body through an opening called the anus. What causes our stomach to growl? Stomach growling occurs when the stomach receives signals from your brain to begin digestion but the stomach is empty. Your brain might sense you're running low on energy (glucose) or even seeing or smelling something you want to eat can get things going. The motion of the stomach muscles begins, but the organ is hollow. The movement of the muscles mixing the acids of the stomach in the hollow space of the stomach produces vibrations we hear as growling, or rumbling, or gurgling. The obvious solution is to eat, but this is not always practical. Because your body responds to things that you do daily, people who eat on very regular schedules may be more susceptible to this problem.

3 INTESTINE DIGESTION LAB Procedure: 1. Add 25 ml of vinegar to a plastic bag. Color the vinegar by adding 3 drops of food coloring. 2. Measure 25 ml of oil. Pour the oil into the bag containing colored vinegar. This mixture represents undigested food leaving the stomach and entering the small intestine. Observe the bag. Write your observations below. 3. After you complete your observation in step #2, add 25 ml of baking soda solution to the vinegar and oil. Seal the bag. The baking soda solution represents fluid from the pancreas that is added to food entering the small intestine. The fluid contains enzymes for digestion which also neutralizes the acid as it leaves the stomach. Record what is happening to the acid. 4. Observe the contents of the bag. Mix the contents, and observe the contents again. What do you see? Did anything change? Explain what you see below. 5. Bile is produced by the liver and stored in the gall bladder. It is secreted into the small intestine to break large droplets of fat molecules into smaller ones. This increases the surface area where fat-digesting enzymes work. Bile works like detergent on food entering the small intestine. What do you think the detergent will do? 6. Measure 10 ml of detergent in a graduated cylinder. Add the detergent to the bag. Seal and mix the contents of the bag. Observe how the detergent (bile) affects the oil. Record what you see happen to the oil.

4 NAME: DATE: PERIOD: PAP Digestion Lab Observation DATA Table 1. Observation Oil and vinegar Write a short description about what is happening. Be sure to give details! What is happening to the acid? Contents of bag Infer: What will detergent do? Bile affect on oil Questions: Use the information in the Background Information passage. 1. What is digestion? 2. What is the body s major site of digestion? 3. Where does most of the digestion occur in the small intestine? 4. What is the remaining length of the small intestine used for? 5. What is the function of the pancreas? 6. Why are enzymes needed for digestion? 7. Which organ secretes bile? 8. What is the function of bile? 9. Where does the undigested food move after it leaves the small intestine? 10. What is the function of the large intestine? 11. What 2 systems are interacting when your stomach growls? &

5 MULTIPLE CHOICE QUESTIONS: 12. The main function of the human digestive system is to A. break down foods for absorption into blood C. release energy from sugars within the cells B. exchange oxygen and carbon dioxide in the lungs D. carry nutrients to all parts of the body 13. Which type of digestion occurs in the mouth when an individual chews a piece of bread? A. mechanical digestion only C. both mechanical and chemical digestion B. chemical digestion only D. neither mechanical nor chemical digestion 14. If too much water is removed from undigested food, the feces hardens and constipation occurs. This malfunction affects which part of the digestive system? A. F B. G C. C D. E 15. In the human digestive system, most nutrients are absorbed into the blood through the lining of the A. esophagus C. large intestine B. stomach D. small intestine 16. Into which parts of the human digestive system are digestive enzymes secreted? A. mouth, esophagus, stomach C. mouth, stomach, small intestine B. stomach, small intestine, large intestine D. esophagus, stomach, large intestine 17. The removal of a human gallbladder interferes most directly with the A. production of gastric juices C. storage of pancreatic juices B. production of saliva D. storage of bile 18. Nutrients from digested food enter the blood stream through the process of A. absorption C. respiration B. elimination D. secretion 19. Fats are important nutrients because they A. provide genetic information B. contain stored energy C. are used in photosynthesis D. maintain bone density 20. In which human organ would the chemical digestion of a piece of meat normally begin? A. oral cavity C. stomach B. small intestine D. liver The diagram below shows several organs in the human digestive system. Explain two ways that food is changed as it passes through the digestive system. (21) (22)