Explain the purpose of each step in the yeast fermentation experiment, and what would happen if...

Boiling removes dissolved oxygen from the glucose solution. This creates anaerobic conditions necessary for fermentation by yeast.

• To remove dissolved oxygen.

1. b)

Yeast are living organisms. High temperatures would denature their enzymes and kill them, preventing fermentation. Cooling allows the yeast to remain active.

• To prevent the denaturation of yeast enzymes and killing of yeast cells.

1. c)

The oil layer prevents atmospheric oxygen from dissolving back into the glucose solution, maintaining the anaerobic environment.

• To prevent atmospheric oxygen from dissolving into the glucose solution.

1. d)

Fermentation produces carbon dioxide. Carbon dioxide reacts with lime water (calcium hydroxide) to form calcium carbonate, which is a white precipitate.

• The lime water would turn cloudy/milky.

1. e)

A control experiment should be identical to the main experiment but without the variable being tested (in this case, the yeast).

• Set up an identical experiment without adding yeast suspension.

2.

Accumulation of lactic acid during vigorous exercise leads to an oxygen debt and a decrease in blood pH.

• Lactic acid causes an oxygen debt in muscles, which the body tries to repay by increasing oxygen supply, thus increasing heart rate to pump more oxygenated blood.
• Lactic acid lowers the blood pH, stimulating chemoreceptors that signal the brain to increase heart rate and breathing rate to remove acidic byproducts and bring in more oxygen.

• 1. Lactic acid causes an oxygen debt, requiring increased oxygen supply to muscles. 2. Lactic acid lowers blood pH, stimulating chemoreceptors to increase heart rate and breathing.

3.

The equation shows glucose being broken down into ethanol, carbon dioxide, and energy in the absence of oxygen. This is characteristic of anaerobic respiration in plants and yeast.

$$\text{C}_{6}\text{H}_{12}\text{O}_{6} \rightarrow 2\text{C}_{2}\text{H}_{5}\text{OH} + 2\text{CO}_{2} + \text{Energy}$$

• Alcoholic fermentation / Anaerobic respiration.