1. Compare tubes 1 and 2. What effect does additional glucose have on the rate of CO2 production in yeast?

Additional glucose will convert sugar molecules into CO2, alcohol and water. The CO2 expands producing gaseous bubbles, which will make the yeast to rise and the same time causing the temperatures to increase. Thus, additional glucose increases the rate of CO2 production.

2. Why do you think additional glucose had this effect?

This is because in the absence of dissolved oxygen, yeast will continue to breathe through searching oxygen from sugar molecules. In the process, it will inhale CO2 but leave the sugar molecules behind in the form of ethyl alcohol (Rongsun and Reid 67).

3. Compare tubes 2 and 3. Did magnesium (a cofactor that activates many enzymes) promote respiration? If not, what are some possible reasons?

Respiration is similar to a chemical process thus in anaerobic bacteria where there is the absence of oxygen, magnesium can promote respiration. This is because many enzymes require presence of magnesium in order for catalytic action to take place. All the enzymes synthesize ATP, which is the main energy source in cells. The balanced magnesium is crucial in respiration process because they interact with substrates thus forming the final products of anaerobic metabolism.

4. Which glyolytic enzymes are activated by magnesium?

Adenosine triphosphate (ATP) and Nicotinamide-adenine dinucleotide (NAD+) are the enzymes activated by magnesium. The glycolysis is the only crucial energy source resulting from carbohydrates, which produces ATP and NAD+ coenzymes. Banaszak (52) points out that ATP and NAD+, which occurs in the cells, are among the glyolytic enzymes activated by magnesium.

5. Compare tubes 2 and 4. What effect did NaF have on the rate of CO2 production?

The effect that NaF had on CO2 production is that in tube 2, the glucose molecule disassembled completely in order to yield CO2 and H2O whereas in tube 4, NaF precipitates Magnesium ions thus inhibiting the pathway for Co2 production. Therefore, NaF increased the rate of CO2 production.

6. What glycolytic enzyme is affected by NaF? How does NaF inhibit the enzyme?

Hexokisane and aldolase are the glycolytic enzymes affected by NaF (Banaszak 56). NaF inhibits the two enzymes through exchanging its new electron with other sodium ions. Furthermore, NaF is not stable in living tissues because it combines with everything it gets on the pathway thus inhibiting an enzyme.

7. Compare tubes 4 and 5. What was the effect of adding pyruvate to the tube that also contained NaF?

Adding pyruvate to tube 4, which contained NaF, caused production of CO2 to decrease whereas adding pyruvate to tube 5, which contains both NaF and pyruvate, stops the production of pyruvate and increases CO2 production at the same time.

8. Why did tube 5 produce CO2 even though an inhibitor of glycolysis was present?

It produced CO2 because of the presence of pyruvic acid, which was produced during aerobic respiration. The covalent bonds of pyruvic acid were broken down by Krebs cycle enzymes yielding CO2 and extra hydrogen combined with electron carriers such as NAD+. The effect was that the CO2 production from yeast increased with increased temperatures.

9. What is the effect of temperature on fermentation by yeast? Compare each tube across all temperatures. Explain why temperature has an effect on respiration in yeast.

Changes in temperatures have profound effect on fermentation. The enzymes catalyzed are sensitive to small changes in temperature. Each enzyme has optimal temperature range at which it performs best. The catalyzation of chemical reactions in the fermentation of yeast in an optimal temperature proceeds more quickly. Thus, bakers using yeast to leaven bread are aware that changes in temperature have an effect on fermentation process thus regulate the temperature. In addition, the temperatures have an effect on respiration in yeast because under anaerobic conditions, CO2 and alcohol are released when yeast burns sugar.

10. Describe the advantage(s) organisms having aerobic metabolism have over those having only anaerobic metabolism.

Organisms having aerobic metabolism use terminal electron acceptor while those having only anaerobic metabolism use other receptors meaning that respiration under anaerobic metabolism is less efficient and leads to a slower growth rate than in aerobic metabolism where there is a higher growth rate. This is because aerobic metabolism utilizes oxygen or can use terminal electron receptors for respiration unlike anaerobic metabolism, which may only try to gain energy from glucose for its survival.


Banaszak, Leonard. Foundations of Structural Biology. San Diego, Calif: Academic, 2000. Internet resource.

Pu, Rongsun, and H B. Reid. Principles of Biology Laboratory Manual. Dubuque, IA: Kendall /

Hunt Publishing Co, 2007. Print.