[POST LAB] EXPT 6: Yeast Formation

Pyruvate

• the product of glycolysis

• in anaerobic conditions, it can undergo:

  • homolactic fermentation

  • alcoholic fermentation

Lactate

• pyruvate undergoes homolactic fermentation to produce it

• catalyzed by lactate dehydrogenase

Ethanol

• pyruvate undergoes alcoholic fermentation to produce it

• pyruvate is first turned into acetyldehyde by pyruvate decarboxylase then finally turned into ethanol by alcohol dehydrogenase

Saccharomyces cerevisiae

• baker's yeast or brewer's yeast

• practical and commerical applications:

  • winemaking

  • brewing

  • baking

Facultative aerobes

• organisms that can undergo aerobic or anaerobic ATP production

• in anaerobic conditions, fewer generations will grow

Objectives

• demonstarte fermentation of glucose into yest cells

• determine the products of yeast fermentation

• compare the effects of varying yeast concentration on fermentation

Methodology

• prepare yeast stock solution

• add 50mL glucose solution + yeast in suction flask

• submerge tube in Ca(OH)2 solution

• count bubbles in test tube

• add HCI to Ca(OH)2 after fermentation

Yeast

• consumes sugar and breaks it down

• produces carbon dioxide gas and ethanol as waste products

Glucose

In the experiment, it was used with constant concentration among all set ups

Gas bubbles in the form of CO2

Observed in the test tube with Ca(OH)2 solution

Ethanol/alcohol

a physical characteristic of the reaction mixture is expected to smell like…

Boiled and cooled distilled water

to reduce or remove any dissolved CO2 that may interfere with the experiment

Covering suction flask

to induce anaerobic conditions

Elevated suction flask

to ensure that the gas bubbles flow more easily from the suction flask to the test tube

Rubber tube submerged in Ca(OH)2

to confirm the identity of the gas bubbles formed

Addition of HCI

• to confirm the identity of the precipitate formed

• observed as clear solution due to dissolution of the white precipitate formed in the tube

CaCO3

observed as turbidity in solution due to white precipitate formed in the tube

CaCO3 + H2O

product of Ca(OH)2 + CO2

CaCI2 + H2O + CO2

product of CaCO3 + 2HCI

Setup 1

• vol of glucose: 50

• Vol of yeast mixture (mL): 25

Setup 2

• vol of glucose: 50

• Vol of yeast mixture (mL): 50

Setup 3

• vol of glucose: 50

• Vol of yeast mixture (mL): 75

Setup 4

• vol of glucose: 50

• Vol of yeast mixture (mL): 100

At constant glucose concentration and increasing volume of yeast

increase in yeast concentration, fermentation rate, and bubbles per minute