Science Grade 8

Activity 3How does pH affect enzyme activity?Objectives:After performing this activity, you should be able to:1. describe the process of chemical digestion; and2. explain how enzymes act as catalyst during digestion.Materials Needed:1 tablespoonful of granulated gelatin10 mL fresh pineapple juicewatermeasuring cupspoon100 mL graduated cylinder10 mL graduated cylinder3 droppers3 test tubestest tube rackmarkershot plate TAKE Do not get1 M HCl CARE! any acid or1 M NaOH base on your skin.Procedure:1. Label the test tubes (A – acid, B – base, C – control <water>)2. Prepare one tablespoonful of granulated gelatin in the measuring cup using 100 mL of boiling water.3. Stir well with a spoon until the gelatin is dissolved.4. Place 3 mL of pineapple juice into each of the labeled test tubes. Transfer 1 mL each of HCl, NaOH, and water into the corresponding test tubes of pineapple juice. 301

5. Transfer 10 mL of gelatin mixture to each test tube.6. Using a spoon, stir the gelatin well until it dissolves completely.7. Refrigerate the test tubes overnight.8. On day 2, observe the contents of each test tube. Record your observations.Table 2. Effect of pH on enzyme activityTest Tube Contents How do the contents of the test tube A look like on Day 2? Acid added on gelatin with pineapple juiceB Base added on gelatin with pineapple juiceC Water added on gelatin with pineapple juice (Control) What is chemical digestion? Where does chemical digestion take place in thehuman digestive tract?Q10. What role do the digestive enzymes have in digestion?Q11. In which test tube did you observe the greatest amount of protein digestion?Q12. In which test tube did you observe the least amount of protein digestion?Q13. How do you explain your results?Q14. Did your results support your hypothesis? Explain your answer.Q15. In the human digestive tract, where is protein digested chemically? 302

Carbohydrates are broken down to simple sugars that are absorbed in thesmall intestines; they are circulated to the different parts of the body as they join thebloodstream. They are used up as sources of energy once they are assimilated bythe cells; those that are circulated into the liver are stored. Proteins are broken down to their component parts -- also called amino acids-- in the stomach. This process is aided by acids secreted by the cells that make upthe walls of the stomach and enzymes that are present in the gastric juice. Like thesimple sugars, amino acids are absorbed in the small intestine through the villi -- thefingerlike structures that line the walls of the small intestines -- and circulated to thedifferent parts of the body. Those that are circulated into the liver are stored asglycogen. In the case of fats and lipids, their digestion is completed in the smallintestine where bile secreted from the liver disintegrates them into fatty acids andglycerol – particles that are circulated to the rest of the body and stored in fattytissues.Activity 4A journey into the digestive systemObjectives: After performing this activity, you should be able to: 1. Infer how the organs of the digestive system work together to carry out digestion of food and assimilation of nutrients; and 2. explain what happens to food as it gets digested.Materials Needed: Video clip: Journey of the digestive system Link: http://www.youtube.com/watch?v=e3O1AdlC8bI Writing materials 303

Procedure:1. Your teacher will show a movie clip titled, Journey of the Digestive System.2. Take down notes as you watch the movie clip.3. On a separate sheet of paper, answer the following questions.Q16. What does the movie clip say about the digestion of food?Q17. What changes happened to the food as it was moved through the digestive tract?Summary Figure 4. Peristalsis in the esophagus. Digestion starts whenfood is taken into the mouth.This is called ingestion. As youchew, you are breaking the foodinto small pieces as a means ofmechanical breakdown. Thepieces mix with saliva before youswallow. Saliva is a watery liquidmade by the salivary glands. Itsoftens and wets the food in themouth and also initially startschemical digestion through theenzymes present in it. Then thefood passes through theesophagus. Muscle contractionsin the esophagus help move thefood down to the stomach. Thisprocess is called peristalsis(see Figure 4). 304

Stomach juices are chemicals made by the body that help digest food. Thestomach is made up of muscles that churn and help mix the food and break it intoeven smaller pieces. The digestive glands in the stomach lining produce acids and enzymes thatdigest proteins. These digestive juices could, in fact, harm the stomach. However, athick mucus layer helps keep this acidic chemical environment from destroying thetissues of the stomach. Digested molecules of food are absorbed through the small intestine. Thewalls of the small intestine contain many folds that are lined up with tiny fingerlikeprotrusions called villi. These villi are in turn covered with even smaller protrusionscalled microvilli. These structures increase the surface area through which nutrientsare absorbed. During absorption, these nutrients pass through the walls of theintestine and into the bloodstream where they get transported to the different parts ofthe body. The undigested parts of food or those that were not absorbed by the body areeliminated as feces. This process is called elimination or defecation. Figure 5 showshow food is changed to soluble forms as it is moved from one part of the digestivesystem to another. Figure 5. The process of digestion. 305

ReferencesBeckett, B. & Gallagher, R. (2001). Modular science: Biology. Oxford: Oxford University Press.Goldsmith, I. (1969). Human anatomy for children. New York: Dover Publications.Guyton, A. (1964). Function of the human body. Philadelphia: W. B. Saunders.Ravielli, A. (1963). Wonders of the human body. New York: The Viking Press.VanCleave, J. (1995). Jan VanCleave’s the human body for every kid: Easy activities that make learning science fun. New York: John Wiley.LinksBeacon Lesson Plan Library. (n.d.). You are what you eat. Retrieved from http://www.beaconlearningcenter.com/Lessons/2719.htmDigestive disorders. (2013). Retrieved from http://www.nutrition.gov/nutrition-and- health-issues/digestive-disordersEat right. (1997). Retrieved from http://www.eduplace.com/rdg/gen_act/cooking/eatrigh.htmlHealthy or not healthy? (1999-2010). Retrieved from http://www.teachnology.com/ teachers/lesson_plans/health/healthyornot35.htmlNational Geographic. (1996-2013). Your body’s fuel factory. Retrieved from http://science.nationalgeographic.com/science/health-and-human- body/human-body/digestive-system-article.htmlNational Geographic Channel. (2010). Journey of the digestive system. Retrieved from http://www.youtube.com/watch?v=e3O1AdlC8bINutrition games and activities. (n.d.). Retrieved from http://www.wartgames.com/themes/nutrition.htmlWard, V.L. (n.d.). A walk through the gut. Retrieved from http://www.accessexcellence.org/AE/AEC/AEF/walk.php 306

Suggested time allotment: 2 to 3 hours Unit 4 NUTRITION ANDMODULE WELLNESS4Overview In the previous module, you have explored how the body obtains the nutrientsit needs to fuel its activities. In addition to providing energy, our diet must alsosupply the raw materials needed for building complex molecules the body needs togrow, maintain itself, and reproduce. In this module, you will survey the nutritional requirements of our body. Thismodule will discuss nutrition and consider the choices we make that affect the properfunctioning of the digestive system. This module will also consider how our diet andlifestyle contribute to the functioning of the human body as a whole. What are the nutritional needs of our body? What happens when the body’s nutritional needs are not adequately met? Your body needs food for energy, growth and repair, and as a source ofsubstances for body processes. Different types of food provide different nutrients.How do you know if you are getting the right kind and amount of nutrients from thefood that you eat? 307

Activity 1Am I eating right?Objectives: After performing this activity, you should be able to: 1. make a record of your daily meals, and 2. determine if your food intake adequately meets nutritional requirements.Procedure:A.1. Record in a Daily Meal Journal what you eat for three days. Table 1 shows a sample meal record for one day. Table 1. Sample daily meal journal Date Meal Food and Beverage Amount June 15 Breakfast Rice 1 cup 1 pc Snack Tinapa 1 pc Lunch Fried egg 1 glass 2 pcs Snack Water 1 glass Dinner Pandesal 1 cup ½ cup Water 1 glass Rice 1 pc Ginisang munggo 1 glass Water 1 cup Boiled banana 1 pc Water ½ cup Rice 1 glass Fried galunggong Kamote tops Water 308

2. Interview your school nutritionist, school nurse, or barangay health worker on the kind and amount of food that you should eat to meet your nutritional requirements. You should have gathered from your interview that you need to eat a varietyof foods since no naturally occurring food has every nutrient. The Food and NutritionResearch Institute (FNRI) has developed a food pyramid for Filipinos, a simple andeasy to follow daily eating guide. This guide is useful in helping people select foodthat supply all the nutrients for energy and growth. Figure 1 shows a food pyramid which illustrates the recommended dietaryallowance for teenagers. Figure 1. The Food Pyramid for teenagers recommends eating a variety of foods to ensure that all nutrients are provided in proper amount and balance. Source: Food and Nutrition Research Institute, Department of Science and Technology 309