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

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Author: Stephanie, Grade 8

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.


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.

Glycogen, or animal starch, is a place to store energy in animals. Glycogen is made up of glucose molecules strung together in a highly branched chain for animals. In plants, however, glucose in the form of a polysaccharide and a monosaccharide is also called a starch. Starches are metabolic reserves which are manufactured by green plants through photosynthesis. (Starches occur in the form of grains.) There are two basic forms of starches, unbranched chains that coil, and branched chains which are similar to glycogen.

Feezing Cells

If the liquid in a cell is not reduced when the cell freezes, then when the water in the cell freezes and expands, the membrane of the cell will break. (A cell membrane is the outermost part of the cell which lets the objects come into or go out of the cell through diffusion.) The inside of the cell will then leak out and the cell dies. (There are some cells in certain animals such as the wood frog which are protected from freezing due to inner body liquids.)

Some water may be taken out of cells that are not protected, through, by using a hypertonic solution. ( Through there are many types of hypertonic solutions; this one would probably contain either sugar or salt in it.) This hypertonic solution would also probably also have to totally surround the cell so that there will be diffusion taking place going out of the cell. Diffusion is the movement going into or out of a cell from a place of high concentration to a place of lower concentration. Not all things, however can diffuse into a cell. The object must be small enough to pass through the cell membrane. (The cell membrane is made of mostly lipids which have very tiny holes in them.)

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