Lab Assignment 12
April 11, 2015
Introduction: Osmosis is defined as the transport of solvent molecules across a semi-permeable membrane. The movement flows in the direction from a higher water concentration to an area with a lower water concentration. Another way to picture the flow of movement is from a lower solute concentration to a higher solute concentration.
It is important to understand the concept of osmosis when studying cellular membranes. The cell controls the movement of molecules in and out using osmosis and other types of diffusion. The cells use the techniques depending on the environment they are surrounded. These environments can be categorized into isotonic, hypertonic, and hypotonic. Most organisms need an isotonic or slightly hypotonic environment for survival; however there are those that can thrive better in environments with high salt concentration causing the environment to become hypertonic. These salt loving bacteria are known as halophiles.
Isotonic is an environment where both the water and solute concentration are the same inside and outside of the cell. The diffusion of water is dispensed in and out at an equal rate.
Hypertonic refers to a setting where the water concentration is greater inside and the solute concentration is higher outside the cell. Water flows out of the cell. Due to the flow of water out of the cell and into the environment, the cell will shrink and shrivel.
Hypotonic is the opposite of hypertonic. The water concentration is greater outside the cell while the solute concentration is higher inside. Water flows into the cell. A cell in a hypotonic environment will swell and burst.
Another way to view a microorganism’s relationship with water is to measure how available water is to the organism. The water activity (aw) is one such measure. This measure looks at the presence of water in a solution or substance. Water activity can be affected inversely by the amount of solute. It has been concluded that most bacteria cannot grow in environments in which the aw is below 0.91.
Purpose: The purpose of the Osmosis lab is to help students understand the effects of osmosis and gain a basic knowledge of its principles. Through this lab the student twill be able to observe sodium chloride concentrations on both the S. epidermidis and S. cerevisiae cultures. In addition to being able to study sodium chloride concentrations, the student will also be able to gain a better understanding of permeability of membranes upon completion of the lab.
S. epidermidis stock culture
Active dry yeast (S. cerevisiae)
3 regular cup
1 cup provide to you with grooves, 9 oz tall
100% white corn syrup (liquid fructose)
1% NaCl broth in 10 mL glass tube (2)
7% NaCl broth in 10 mL glass tube (2)
15% NaCl broth in 10 mL glass tube (2)
4 long stem pipets
Procedure for Exercise 1:
1) 48 hours prior to the start of the lab place the egg in a pot of vinegar and soak it for the 48 hours. This step is to de-shell the egg. 2) 24 hours place the stock culture of S. epidermidis in the makeshift incubator. 3) At the start of the lab, add ½ teaspoon active dry yeast (S. cerevisiae) to 1/8 cup warm water, using the regular cup. 4) Swirl to mix 5) Let stand for ten minutes. 6) Add the marks to the provided cup, starting with the bottom groove, 50 ml, 60 mL, 70 mL, 80 mL, 90 mL, 100 mL, 110 mL, 122.5 mL, 135 mL, 149.5 mL, 160 mL, and 175 mL. 7) Measure 0.5 cm above the 175 mL mark and label 190 mL 8) Continue to measure in 0.5 cm increments and label each 210 mL, 230 mL, 250 mL 9) Finally label the rim of the cup 270 mL. 10) Gently wash the egg in water in order to remove any soluble calcium salts. 11) Carefully pat the egg dry 12) Measure the volume of the by filling the marked cup with enough water to reach the 150 mL mark and submerging the