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Lab 5: Acid/Base Balance and Fluid Homeostasis
Materials
Activity 1: Fluid Homeostasis o De-shelled raw chicken eggs (4/group) o 250mL beakers (4/group) o Salt solutions of 4% and 20% in water o DI water o Unknown salt solution o Scales o Weigh boats o Graph paper o Gloves Activity 2: Acid/Base Balance of Cardiovascular and Respiratory Systems o Small Test tubes o Test tube racks o Narrow range pH paper o Deionized water and dropper o Animal (sheep) plasma and dropper o 0.01 M HCl dropper bottles o 250 mL beakers o 0.05 M NaOH dropper bottles o Phenol Red o Straws
Activity 1: Fluid Homeostasis
(Adapted from J. Kurushima and Gavilan College General Biology Lab Manuals.) More than half of your body mass is made up of fluids (on average, this is over 90 pounds of water!). For the most part, body fluids are kept in two “compartments”: (1) intracellular fluid (ICF) or cytosol, and (2) extracellular fluid (ECF). In addition, there are many fascial compartments throughout the
body. A fascial compartment is a region of muscle isolated by fascia. If a cell or tissue is to perform its functions, it must maintain a steady state in the midst of an ever-changing environment. In this activity you will observe the osmotic movement of water between the extracellular fluid and the intracellular fluid of a chicken egg (a very large cell). We use the terms hypotonic , hypertonic and isotonic in referring to the relative concentrations of solute particles of different solutions.
1. Define the three tonicity terms (hypotonic, hypertonic and isotonic)
- With your group, use weigh boats to obtain 4 chicken eggs from which the shell has been dissolved away. The remaining membrane (the shell membrane) is differentially permeable and contains the cytosol of the cell. We will assume that each egg contains approximately the same concentration of solutes.
- Weigh each egg separately to the nearest 0.1g and record the weights in Table 1 at time “0”.
- Place eggs 1, 2, and 3 into separate beakers containing solutions of distilled water, 4% salt, and 20% salt. Place egg 4 into a beaker containing the “unknown” solution.
- At 15 minute intervals, that is after 15, 30, 45, 60, and 75 minutes, remove the eggs from the beakers; carefully wipe off all excess water; and again, weigh each egg separately. Record the weight in Table 1.
- Calculate the change in weight of the eggs over time. (This allows us to compensate for the differences in starting weight between eggs.) Record the change in weight over time in Table 2. Table I: Weight of Eggs (g) vs Time (minutes) Time (Min.) 0% salt 4% salt 20% salt Unknown 0 15 30 45 60
Activity 2: Acid/Base Balance of the Cardiovascular and Respiratory Systems
(Adapted from “Role of Respiratory in Acid-Base Balance in Blood”) As cells undergo cellular respiration they produce carbon dioxide (CO 2 ) as a byproduct. This carbon dioxide is released into the blood where is combines with water to create carbonic acid (H 2 CO 3 ) which will lower the pH. Blood pH must be maintained around pH 7.4 for the body cells to function. The carbonic acid-bicarbonate system acts as a buffer in the blood to maintain pH. When the blood becomes too acidic (< pH 7.4) bicarbonate ions will bind to excess H+, if the pH is too alkaline (> pH 7.4) carbonic acid will release H+^ into the blood plasma. Part 1: The role of the Cardiovascular System in Acid/Base Balance Here we will compare the ability of blood plasma to buffer changes in pH to that of distilled water.
- Obtain 2 test tubes.
- Add 2 mL of animal blood plasma into the first test tube. a. Use a pH test strip to measure the pH of the blood plasma. _____ b. Add 2 drops of 0.01 M HCl (hydrochloric acid) into the test tube. Use a fresh pH test strip to measure the pH of the blood plasma + 2 drops HCl. _____
- Add 2 mL of water to the second test tube. a. Use a pH test strip to measure the pH of the water. ______ b. Add 2 drops of 0.01 M HCl (hydrochloric acid) into the test tube. Use a fresh pH test strip to measure the pH of the water + 2 drops HCl. ___________
- Answer the following questions: a. Is the plasma a good buffer? What experimental results above support your answer? b. What component of the blood plasma carbonic acid-bicarbonate buffer system was acting to counteract a change in pH when HCl was added? (you might refer to chemical equation above )
- Pour the plasma and water in the appropriate waste bottles.
Part 2: The role of the Respiratory System in Acid/Base Balance Now we will observe how exhaling CO 2 helps the body to maintain its acid/base balance.
- Fill a beaker with 100 mL of distilled water a. Add 0.5 mL of 0.05 M NaOH and 2 drops of phenol red. Swirl. Phenol red is a pH indicator, it is magenta in alkaline solutions, red in neutral solutions, and yellow in acidic solutions. b. Is the solution currently alkaline, neutral or acidic?
- Use a straw to gently blow bubbles into the solution until it changes color. a. Is the solution now alkaline, neutral or acidic? b. As you exhale into the beaker, what chemical reaction is taking place? (you might refer to the chemical equation on the previous page)
- Discard the straw in the garbage, and pour the phenol red solution in the appropriate waste bottle.
Activity 3: Acid/Base Balance in the Digestive System
(Adapted from “Got Lactase? Blood glucose data analysis” HHMI Biointeractive.org) “Mother’s milk” is packed with the proteins, fats, and carbohydrates that support the growth, development, and survival of baby animals. The sugar lactose is the main carbohydrate in milk. Lactose can be cleaved into two simple sugars, glucose and galactose, by lactase, an enzyme produced in the small intestine. The two smaller sugars are readily absorbed through the intestinal wall into the bloodstream for delivery to the cells of the body, where they are used for energy. After infant mammals are weaned from their mother’s milk, lactase production shuts down, presumably because it is no longer needed. This condition is called lactase nonpersistence—meaning that production of the lactase enzyme does not persist into adulthood. The general condition for
- As we saw during the discussion of Margarete Mylle’s data, quantitative expressions of data are critical in physiology! Replicate the graph below on your own paper and fill in the data for the other individuals in the table above. There will be a place on the exit ticket where you can upload a photo of your graph
- Answer the following questions: a. Why is measuring blood glucose levels an indicator of someone’s lactase activity? b. Based on your graph, which individuals are lactose persistent? c. Which are lactose intolerant? d. Explain your rationale. e. A person taking a blood glucose test is usually told to fast prior to the test. Why do you think that might be necessary? Part 2: Hydrogen Breath Test to Determine Lactose Tolerance Another common test used to determine whether a person is lactose persistent is the hydrogen breath test. This test measure the amount of hydrogen in a person’s breath. As you read above, undigested lactose is fermented by bacteria in the large intestine, producing several gases, including hydrogen. These gases exit the body through the anus; they can also be absorbed into the blood, circulated to the lungs, and eliminated through the breath.
- Review the data in the following table. It shows the hydrogen breath levels of four individuals tested for lactase persistence. Time 0 represents the time before drinking milk and the other times are times after drinking milk. 2. Answer the following questions: a. Which individuals appear to be lactase persistent? Use data to support your answer. b. Which individuals appear to be lactase nonpersistent? Again, use data to support your answer. c. As hydrogen gas from the intestines enters the blood stream, will this affect the blood plasma? (Remember, hydrogen gas is H 2 ). Do you expect this to alter the blood pH? Why or why not? d. Can you think of another test you might do to determine a person’s lactase status?
