“Breathing more rapidly for a period of time prior to running will increase dissolved oxygen in the blood.” In a normal person at rest, blood is normally 96% saturated with oxygen. More rapid breathing’s effect decreases dissolved carbon dioxide much more than increasing dissolved oxygen. Reducing CO2 raises blood pH which affects the breathing center in the brain. As a result there is a delayed sensation for wanting to breathe. If you were in the water, you could stay under water longer than normal before “wanting” to breathe. Perhaps you have heard about this “trick” but it is based on decreasing the breathing stimulus, carbon dioxide, not significantly increasing dissolved blood oxygen.
Demonstrations and Lessons
Exhale into a solution of either limewater of bromothymol blue to show effect of carbon dioxide. Compare with bubbling room air into the same solutions. Elicit from students their knowledge of the % by volume of oxygen and carbon dioxide in room air and in exhaled air. Relate to the results of the demo.
A student lab activity or demonstration to show hydrolysis in solutions and the common ion effect relates to buffered solutions. Use a weak acid (conjugate acid) such as acetic acid along with the salt of acetic acid (conjugate base), sodium acetate. Add one drop of 1.0 M sodium hydroxide and note what if any change in pH occurs. Compare this reaction with using just distilled water (that has been boiled) and the addition of one drop of 1.0 M NaOH. Repeat with a 1.0 M solution of acetic acid instead of 1.0 M NaOH. (There are standard lab procedures that students can follow using a variety of buffered solutions which are a weak acid and the salt of that acid or a conjugate acid with a conjugate base.)
Demo to show degradation of cane sugar by sulfuric acid in which dehydration generates noticeable heat and steam with a black carbon residue remaining. Compare products to that of respiration (carbon dioxide gas and water). Why the difference? (You are comparing two different systems—dehydration or water formation vs. oxidation and the Krebs cycle, a multi-step process that is highly efficient in the “transfer” of bond energies from glucose to ATP (adenosine triphosphate.)
Measure the caloric content of food or calculate the potential energy of the bonds in a glucose molecule and compare with the bond energies of the products, carbon dioxide and water. Is the oxidation of glucose an exothermic or endothermic reaction according to the calculations? Why do we not overheat from the oxidation of glucose in our bodies (in the mitochondria of our cells)? To measure the caloric content of a piece of food, a standard combustion reaction can be done using something like a peanut or walnut to heat a known mass of water in an aluminum soda can (calorimetry). Be aware of student nut allergies before doing this experiment with nuts. Knowing the mass of the fuel converted to energy and products (carbon dioxide and water) by determining the mass before and after combustion, students could calculate a rough value for the heat of combustion of the fuel. This can also be done using a candle (you will have to use a general formula for the candle, such as stearic acid) or vegetable oil with a wick floating in it to provide a flame.
Alcoholic fermentation can be done by students using yeast in a sugar solution. The setup for the system should include a delivery tube from an Erlenmeyer flask, containing the yeast/sugar solution, which goes into a solution of limewater. A second set-up could use water with a universal indicator or Bromothymol Blue indicator (relate to the exhaled air demo, #1 above). This basic experiment can be modified to show the effect of a variety of environmental factors including temperature, amount of yeast which contains the enzyme for fermentation, the pH of the sugar solution, and the effect of having the Erlenmeyer open to the atmosphere for oxygen. Students could distill off the alcohol and test for flammability.
Respiration and effects on rate can be shown using a simple respirometer for measuring the rate of activity of germinating pea seeds. A useful reference for this activity can be found at http://www.phschool.com/science/biology_place/labbench/lab5/intro.html. An advanced lab procedure which is more quantitative and with better background on the chemistry and physics of the setup and procedure can be found at www.jdenuno.com/PDFfiles/Respiration.pdf.
Identifying the major food groups (protein, fats, and carbohydrates) can be done by chemical analysis. One example of this type of lab activity can be found at the Access Excellence site under “Organic Compounds” at http://www.accessexcellence.org/AE/ATG/data/released/0335-HeidiHaugen/index.php.
Related to #7 would be using various digestive enzymes to breakdown the larger polymers of protein, polysaccharides (carbohydrates), and fats (lipids) into smaller molecules for which there are standard tests. In doing these enzymatic activities, various environmental factors can be tested including pH, concentration of the enzyme, concentration of substrate, and temperature. Enzymes, as proteins, are temperature and pH sensitive. Heating the solution beyond body temperature (37 oC) will undo the secondary and tertiary structure of the molecule (breaking a lot of H bonds; “denaturing”) and render the enzyme inoperable.
Additional enzyme activities related to chemical processes in biological systems can be done both qualitatively quantitatively. A qualitative activity using amylase’s action on starch, converting to simple sugars can make use of the amylase contained in a student’s saliva. The saliva can be collected in test tubes by students. Addition of a starch solution to the test tube and subsequent action of the amylase can be analyzed for results by testing samples of the starch-amylase solution for breakdown products including glucose.
Another common enzyme is catalase (found in the liver but also in plant tubers such as potatoes). The action of catalase on hydrogen peroxide, produced in living cells and a potential poison, can be measured quantitatively under a variety of environmental conditions (temperature, pH, concentration of substrate and enzyme). See an example of a lab setup for this activity at http://www.accessexcellence.org/AE/ATG/data/released/0074-GenNelson/index.php.
Some specific background of catalase in biological systems to complement the lab activity can be found at http://www.catalase.com/cataext.htm.
