Lab 12: Metabolism Dr. Kim Wilson

PART 1: RESPIRATION AS AN INDIRECT MEASURE OF CATABOLISM Metabolism (food usage) is the end result after digestion and absorption of food molecules. Occurs within cells and consists of a series of enzyme catalyzed chemical reactions Two major processes: catabolism (breakdown) and anabolism (building). Catabolism can be summarized as follows: Nutrient Building Blocks + O2 > CO2 + H2O + Energy* * 2 kinds of energy: 1) Heat: released from the cell 2) Chemical: stored in ATP The CO2 gas produced by catabolism is a waste product and is exhaled by humans in normal expiration. The rate at which CO2 is produced is directly proportional to the rate of catabolism.

PART 1: RESPIRATION AS AN INDIRECT MEASURE OF CATABOLISM In this lab, we will use yeast cells to produce data concerning the catabolism of various foods. (Metabolism occurs in cells and yeast cells are similar to human cells.) CO2 will be produced by yeast cells in direct proportion to the ease at which food is catabolized. In this experiment, the CO2 gas will be released into the water of the gas collection test tubes; by counting the bubbles of CO2 released over a period of time, a fairly accurate rate of catabolism for that food can be obtained.

INSTRUCTIONS: (for a group of 3 students) 1. Suspend yeast (3/4 tsp.) in 45 ml. very warm water (45‑50 C). Stir until dissolved. 2. Obtain 3 large test tubes and a large beaker. Label the test tubes as A, B, and C. 3. Add 15ml of each of the 3 food samples to each of the 3 test tubes (Place food sample A in test tube A, food sample B in test tube B, etc.) 4. Obtain 3 more large test tubes (label as A,B,and C) and a test tube rack. Fill these test tubes with warm water. (These will serve as the gas collection test tubes.) 5. Obtain and place 3 stoppers into the 3 test tubes containing the food samples, making certain that the stoppers fit securely. Be certain that the rubber tubing will reach into the water in the gas collection test tubes (i.e., food sample A test tube will be connected to gas collection A test tube, food sample B test tube will be connected to gas collection B test tube, etc.). Remove the stoppers.

Instructions cont. 6. Fill the large beaker with warm water (40 ‑ 45 C). This is the water bath and will need to be maintained at this temperature throughout the experiment. 7. Divide the yeast suspension into 3 equal portions (15ml each), and add one portion to each of the test tubes with the food sample. Gently shake the tubes to disperse the yeast. 8. Quickly, tightly place the stoppers into these test tubes (the ones containing yeast and food), place the test tubes in the water bath, place the rubber tubes into the gas collection test tubes (i.e., A to A, B to B, etc.) and begin timing and counting bubbles. Record the number of bubbles counted at the specified time intervals in the chart on the Results Sheet. 9. Answer related questions on the Questions Sheet.

PART 2: BASAL METABOLIC RATE INSTRUCTIONS: 1. Complete Part 2: Basal Metabolic Rate from the Results Sheet, recording all the data on the Results Sheet. 2. Answer related questions on the Questions Sheet.