Permeability Of a Yeast Cell

Permeability of Yeast Cell Membrane

Introduction

The membrane of a living cell plays a vital role in regulating what goes into and out of the cell. Some characteristics of cell membranes were discovered in this experiment.

Background

1. Neutral red is a vital stain. It stains cells without quickly killing them. Many biological stains kill living cells.
2. Neutral red goes through an obvious color change, from red at about pH 6.8 to yellow at pH 8.0.
3. A 1% solution of sodium bicarbonate has a pH of about 8.5.
4. Yeast cells have an internal pH that is slightly acidic (about 5.5 to 6.0).

Preparation

1. Sodium bicarbonate solution: Mix 1 g of sodium bicarbonate in 100 mL of distilled or deionized water.
2. Neutral red solution: Mix 0.2 g of neutral red in 1 L of distilled water.
3. Dilute acid solution: Use 0.01–0.1 M hydrochloric acid.
4. Sodium hydroxide solution: Use 0.01 M sodium hydroxide, 0.40 g/L.
5. Potassium hydroxide solution: Use 0.01 M potassium hydroxide, 0.56 g/L.
6. Ammonium hydroxide solution: Add water to 10 mL of concentrated ammonium hydroxide solution to make 82 mL of a stock solution. Use 10 mL of the stock and dilute to 1 L with distilled water. This gives a 0.01 M solution.
7. Yeast suspension: Add 1 package of dry yeast to 250 mL of 1% sodium bicarbonate solution. Mix thoroughly and swirl when dispensing.
Data

Neutral
Red
Acid
Base
Red
Yellow

Neutral Red
Yeast Suspension
Initial Color
Color after 5 min
Light Red
Darker red

Explain: Neutral red diffuses into yeast cells and turns red since the intracellular fluid is acidic.

Neutral
Red /
Yeast Suspension
1. W/ NaOH
Peach
Red
2. W/ KoH
Peach
Red
3. W/ NH4OH
Yellow peach
Peach Yellow

The neutral red diffuses into the acidic yeast cells and they appear red. Yeast cells are normally off-white.

Neutral Red/
Yeast Suspension