Lab Report 9 Microbiology Osmosis

Introduction

To sustain life cells must take in nutrients and excrete wastes via their membranes. Transportation into the cell can be done passively or actively. Active transport requires the cell to use energy, so the easier passive transport is utilized most often. One example of passive transport is diffusion. During diffusion "molecules spread from areas of high concentration to areas of low concentration" through the membrane (Lab Manual, pg 172). Osmosis, a type of diffusion, involves the transport of water molecules from an area of higher concentration to a lower concentration. A solution a cell resides in can be isotonic, hypertonic, or hypotonic. An isotonic environment is preferred because the concentrations of solutes are equal inside and outside of the cell so water will move at an equal rate in and out. A hypertonic solution consists of more solutes outside of the cell and more water inside of the cell, therefore water will leave the cell. In a hypotonic solution there is more water outside of the cell, more solutes inside of the cell which causes water to enter the cell.

During this experiment osmosis is being observed by placing a shell-less egg in water as well as liquid fructose. The membrane that surrounds the egg is semi-permeable which allows water to diffuse easily. This experiment will show us the differences in osmotic pressure when the egg is placed in both substances. My hypothesis is if the egg is placed in the liquid fructose then it will lose water, however if the egg is placed in water then it will absorb the water.

When exposing S. Epidermidis and S. Cerevisiae to environments with different salt concentrations we will be able to observe the affects of osmotic pressure on microbial growth. "Microorganisms are very sensitive to changes in water activity" (Lab Manual, pg 176). The knowledge of how osmotic pressure affects the growth of bacteria has been utilized by the food industry to preserve foods. Salt and sugar can be added to foods to create a hypertonic environment that bacteria cannot survive in. Without this valuable knowledge our food would not be as safe to eat and would perish quickly. Considering my prior knowledge of how osmosis works it is my prediction that if S. Epidermidis and S. Cerevisiae are subjected to higher concentrations of NaCl then they will show less growth.

Methods

Experiment 1:

24-48 hours prior to the experiment soak 2 raw chicken eggs in vinegar to remove the shells. Rinse the egg off carefully and lightly dry with a paper towel. (The second egg is just in case the first one breaks)

Label 9 oz. sample cup to determine volume of the egg. (Bottom line is 50 mL, each line after that increases by 10 mL, the top line is 175 mL, .5 cm above top line is 190mL, ever .5 cm after that increases by 20 mL, The rim of the