Bio 11 – Botany – Exercise 14 – Respiration

A. Release of Heat Energy during Respiration

1. Place germinating mung bean seeds previously soaked in distilled water overnight inside a thermos flask or Dewar bulb and suspend a vial containing 20% solution of potassium hydroxide. Stopper the flask with a cork through which a thermometer is inserted. Similarly prepare another flask as control using boiled seeds previously soaked overnight in 5% formalin.

1.2 Why is potassium hydroxide used?

Used to absorb CO2

B. Release of CO2

2. Fill an Erlenmeyer flask with yeast suspension and two other flasks with saturated barium hydroxide solution. One flask with the barium hydroxide solution is tightly sealed with a rubber stopper while the other two are provided with tight fitting rubber stoppers., each with one hole so as to connect the two flasks with a bent glass tubing. The connection is made alright by sealing the holes with melted candles or vaseline. Observe the results after 24 hours.

2.1 From the set-up, what observations indicate that a reaction has occurred?

White precipitate forms in the flask with barium hydorxide solution that is connected to the flask with yeast.

2.2 Explain your results

CO2 + Ba(OH)2 -> BaCO3 + H2O

C. Necessity of oxygen in Aerobic Respiration

3. Place 10-20 bean seeds, previously soaked in water overnight, on two wads of moist cotton. Wrap each wad with gauze. Suspend one in a corked bottle containing a little water, the other in a similar bottle containing alkaline pyrogalllol solution. keep the bottles in a dark warm place for 48 hours.

3.1 Compare the development of the seeds in each of the bottles. Explain your results.

Alkaline pyrogallol absorbs H2O and O2. Seeds did not germinate in the bottle with alkaline pyrogallol.

D. Factors Affecting the Rate of Anaerobic Respiration (Fermentation)

4. Obtain 3 clean fermentation tubes. Fill the first with 10 ml yeast-glucose suspension, the second with yeast suspension and the third with glucose solution.

4.1 Observe the amount of gas produced at half hour intervals during the experiment. Compare the volume of gas displaced in each fermentation tube.

4.2 Account for differences observed

Yeast uses glucose for fermentation therefore the yeast-glucose suspension produces more gas due to fermentation.

5. Fill 3 fermentation tubes with 10 ml of yeast-glucose solution. Place 1 tube in a water bath of 4 degrees Celsius, the second in a  beaker of ice water and the third at room temperature.

5.2 Explain the differences in the amount of gas produced in the tubes.

Temperature is directly proportional to rate of fermentation.

Note:

Some answers differ for each class/group. You need to do the experiment.

For 1.1, 1.3, Table 14.1 and Table 14.2, you need your group’s data.