Question

1) Yeast are grown in a closed flask in a lighted room. There is an abundance of glucose, oxygen, and carbon dioxide in the flask.

(A) What will happen to the amount of oxygen in the flask during the first several minutes of growth?(circle one)

-O2 Stays the same

-O2 increases

-O2 decreaases

(B) Circle all processes in which O2 is either a reactant or product for the yeast in this flask.

-glycolysis

-Krebs cycle

-regeneration of NAD+(as part of fermentation)

-chemiosmosis

-electron transport in mitochondria

-pyruvate to acetyl-CoA

2) Another flask is set up with the same conditons, except there is no oxygen in the flask. The yeast are still able to grow. If you measured the amount of CO2 over time in the flask, the amount would be: (circle one)

-CO2 staying the same

-CO2 increasing

-CO2 decreasing

(B) Circle all processes in which CO2 is either a reactant or a product for the yeast in this flask

-glycolysis

-krebs cycle

-regerenation of NAD+ (as part of fermentation)

-electron transport in mitochondria

-chemiosmosis

-pyruvate to acetyl-COA

(C) Describe, on a cellular/molecular level, the role of CO2 in the processes you circled.

Answer 1

1.

A] Oxygen decreases, due to respiration in yeast cells.

B] Electron transport chain, here O2 is used to form water and its a part of the process where ATP is generated and O2 acts as the final electron acceptor.

2.

A] CO2 increasing, this is due to anaerobic respiration taking place in yeast cells. CO2 and alcohol are the products formed.

B] Regeneration of NAD+ / Pyruvate to acetyl Co A

C] Yeast can grow in both presence and absence of Oxygen. In presence of limited oxygen, it increases in size and does respiration with usual steps of aerobic respiration. Thus the step where pyruvate is converted into Acetyl Co A, there CO2 is formed as a product.

Again regeneration of NAD + is part where CO2 is formed indirectly. First pyruvate convert into CO2 and acetaldehyde, and then this acetaldehyde and NADH/H+ converts into ethanol and NAD+.