Diffusion, Membranes, and Cryogenics: Can We Freeze Cells?

Abstract

In this 2-part project on diffusion and cryogenics, I was trying to find out what would pass through membranes. I observed that glucose diffused through a membrane but starch did not. I then used the experience from this investigation to observe what effect salt would have on the preservation of cells. By using salt to allow water to diffuse from a cell, there would be less water in the cell when it expanded upon freezing and thus less damage done to the cell. I thus hypothesized that the greater the salt concentration, the less cell damage done.

I cut a beet into identical weight sections (14 g), and placed then in jars with varying salt concentrations: 0%, 10%, 20%, 30%, 40%, and 50%. I set up 3 sets of these, and placed 1 set in a freezer, 1 set in the refrigerator, and the final set at room temperature. After 24 hours I measured cell damage by measuring the concentration of beet pigment in the water; the rupturing of cells would release the pigment into the water. I used a spectrophotometer to measure the percent transmission of light as a measure of pigment concentration in the water.

There was little cell damage in the refrigerator and none in the room temperature jars, but the freezing caused considerable cell damage. However, when cells were preserved with a salt concentration greater than 20%, there was considerably less damage, and little cell damage at a concentration of 40%.

The significance of these findings is that there is a way to save cells and preserve them. This also indicates that someday, people may be able to freeze animals or humans and bring them back to life.

Problem

What will pass through a cell membrane?

What will pass through a membrane? Starch and sugar are being tested in this experiment to see if they will go through a membrane. The starch molecule is much bigger than the sugar molecule, being that the sugar I used is a simple sugar (glucose). The sugar should be able to go straight through the membrane, however, the starch will be too big to.

I hope to accomplish being able to make a "cell" and really be able to see how a membrane guards the cell. An experiment on cells last year in school prompted my research and sparked my curiosity for chemistry altogether.

Is it possible to preserve cells during freezing?

Being that it is almost impossible to freeze a cell with no protection and still have it live, this project may show a way. Is it possible? It will be (easily) possible to freeze a cell and have it live and function properly.

I hope to accomplish the preservation of cells in freezing conditions. An idea from my science teacher prompted my research. I was very anxious to see how to preserve cells even after freezing them.

Background Information

What Will Pass Through a Membrane?

A membrane is a thin layer of lipids (fats) and proteins around a cell. These decide what can come into or come out of a cell. This movement of going into or out of a cell is called osmosis. Naturally particles go from a place of high concentration to a place of low concentration (diffusion). (The particles might not do this if they are forced to move.)

The two groups within carbohydrates are called starches and sugars. The general formula for carbohydrates is (CH₂O)n. ("n" is the number of carbons in the backbone) One carbohydrate is called a simple sugar or a monosaccaride. Glucose, like galactose and fructose, is an isomer. An isomer is a compound which differs in structure but not in molecular composition. Disaccharides are two monosaccharides combined in a condensed reaction. Polysaccharides are simple sugar building blocks bonded together to form chains.