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Molecules of different substances are in continuous movement across the semi-permeable cell membranes. Some of the substances that are usually transported across the plasma membrane include water molecules, water products, hormones, nutrients, liquids and compounds. Movement of substances in and out of the plasma membranes can be facilitated either through active transport or passive transport. In passive transport, the substances follow concentration gradient in the sense that they move from an area of higher concentration to the area where their concentration is low. Unlike active transport, movement of substances through passive transport does not need energy (ATP). Osmosis, diffusion and filtration are the common forms of passive transport.

Osmosis is the movement of water molecules (solvent) from the area of high concentration to low concentration across the semi-permeable cell plasma membrane. The rate at which osmosis takes place is influenced by concentration gradient i.e. the difference in concentration of solutes in the cell versus that of the solution in which a cell is placed. The measure of variation in the concentration of two solutions separated by a semi-permeable membrane such as plasma membrane is called tonicity or osmotic pressure gradient. High tonicity envisages increased rates of osmosis through the cell plasma membrane.

Requirements: Two eggs, two experimental jars, a pin, water and vinegar.


  1. A raw egg of known mass and volume was placed in a jar full on vinegar until it was completely submerged in the liquid vinegar. The jar set up was left undisturbed for a period of twenty four hours.
  2. The observation was made after the twenty hours elapsed to establish any visible changes in mass and volume of the egg.
  3. After the twenty four hours the old vinegar was drained into the sink. A strainer was used while draining the old vinegar from the jar to keep the egg from falling down.
  4. The egg was then placed and left undisturbed in a jar of new vinegar for a period of two days (48 hours) after which egg was observed and any noticeable changes recorded for further analysis.
  5. The old vinegar was drained in a jar, the egg removed and carefully rinsed under cold low-running tap water. The observation on the egg shell was made and recorded.


The observations made from the experiment were recorded and summarized in a tabular from as shown in table 1a below


Observable and Measurable Experimental Changes

Egg mass


Egg Shell

There was an erosion exposing the inner membranes

Result Interpretation and Discussion

When the egg is submerged in a the jar full is vinegar (acetic acid) for a period exceeding 24 hours,  the shell is eroded over time due to the reaction of Calcium Carbonate that makes up the shell and the acid (acetic acid in vinegar) thus de-shelling of the egg. The formation of the gas bubbles in the jar containing jar is an indication that the reaction between an acid and calcium carbonate is taking place leading to the evolution of Carbon (IV) Oxide gas.

Once the egg has been de-shelled, the cell plasma membrane is fully exposed to the outside solution of vinegar starting off the process of osmosis in which water molecules (solvent) move from their area of high concentration to area of low concentration through the semi-permeable plasma membrane. In the experimental context, water molecules move from the vinegar (solution of higher water concentration) to the content of the egg where concentration of water is low. The influx of the water molecules through osmosis is what leads to an increase in the mass and volume of the egg.

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