Name ______Period ______Accelerated Biology The Digestive and Excretory Systems Can You Stomach This? Introduction The process of digestion that occurs in humans and other animals from birth to death is an amazing process to many people. The stomach is an expanded portion of the digestive tract. Although there are variations, essentially a stomach is defined as an organ that produces gastric juices, particularly pepsinogen (pepsin in an inactive form) and hydrochloric acid. Since pepsin is a protease, the stomach begins protein digestion. After the partially digested food leaves the stomach, it continues to move through the digestive system by entering the first part of the small intestines called the duodenum.
Purpose The purpose of this experiment is to observe the effects of gastric juices on a variety of food substances that represent proteins and carbohydrates.
Materials (per each group of 6) 200 mL .5% Solution Pepsin 200 mL dilute hydrochloric acid solution 2.5 g Sodium bicarbonate 600 mL beaker 4 1 Qt Ziploc Baggies 2 50 mL graduated cylinders 2 Permanent markers 370 Hot Water Bath 1 of each of he following pieces of food: broccoli, apple, cooked egg white, stew meat
Safety Precautions You are working with glass today so please handle carefully so that it does not break. Also, you will be working with dilute HCl which is an acid. If you get it on your hands, immediately rinse with water and notify the teacher!
Procedure – Day 1 1. Label the 4 Ziploc bags using a permanent marker. Each bag should be labeled with the contents as shown in column 1 of the Data Table 1 below.
Table 1: The Amounts of Pepsin, HCl, and NaHCO3 in the Bags Contents of Bags Pepsin (mL) HCl Acid (mL) NaHCO3 (g) Pepsin 100 0 0 (pH = 4.5) HCl Acid 0 100 0 (pH = 1.0) Artificial stomach 50 50 0 (pH = 1.0) Artificial duodenum 2.5 50 50 (pH = 8.0) (to be added in step 5)
2. Place the 4 labeled Ziploc bags into the 600 mL beaker. 3. Follow the chart in Table 1 to fill the bags with the proper solutions. Use the graduated cylinders to measure the pepsin and HCl solutions into the bags. Do not add the sodium bicarbonate (NaHCO3) to the artificial duodenum yet.
4. Take 1 piece of each food item (broccoli, apple, egg white, and stew meat) and place it into each of the 4 bags so that each bag has all 4 food items. You have just “fed” each of the 4 stomachs.
5. Add the 2.5 g of sodium bicarbonate into the bag labeled “artificial duodenum” and gently mix.
6. Label the beaker with your group member’s names, teacher name, and the period. Bring your beaker to your teacher so that he/she can place them in a 370˚ C environment for 24 hours. Be sure to clean up your station!
7. Construct a Data Table in the space below, so that you can record initial data today and then final data after the “stomachs” sit for 24 hours. You and your team members will need to decide how to best set up this table as well as what kind of data you will collect. Be sure that your table follows all the rules of good data tables.
Create your Data Table below
Procedure – Day 2 1. After the beaker has incubated for 24 hours at 370˚ C, record your final data.
2. Once your final data are collected, you will need to carefully discard all liquids down the sink. The bags with any remaining solids can be thrown into the trash. Be sure to thoroughly rinse out your beaker, remove the label, and return it to its proper place. Also, remember to wash your hands!
Analysis Questions. Answer the following questions in complete sentences! 1. There is no true control for this experiment. What would be a good control (ie. What would you put in another bag and under what conditions)?
2. Why were the “stomachs” incubated at 370˚ C?
3. What do you think would have happened if the “stomachs” were incubated at room temperature, 220˚ C, instead of 370 ˚ C?
4. Which food item(s) were chemically digested in the “bags?” How do you know?
5. Which food item(s) were NOT chemically digested in the “bags?” How do you know?
6. What environmental conditions are required in order for chemical digestions to occur in the human stomach?
7. What enzyme was at work in this experiment?
a) What type of macromolecule did it break down?
b) What monomers was the macromolecule broken into?
c) Which food item(s) were made up of this macromolecule?
8. Why was NaHCO3 added to the bag that simulated the duodenum and NOT the bag that simulated the stomach? 9. Why is it important that NaHCO3 be added to the chyme as it enters the duodenum?
10. If you had shaken the beakers gently every 10 minutes, what physiological activity would you have simulated in a living system?
Conclusion In the space below, summarize what you learned in the lab. Be sure to include your data to support your conclusion(s) and explain why these results were obtained. Use all of the following words and underline them in your conclusion: stomach, duodenum, proteins, lipids, carbohydrates, pepsin, temperature, pH, and chemical digestion.