What is the difference between isotonic hypotonic and hypertonic solutions?

The difference between isotonic, hypotonic, and hypertonic solutions is determined by the concentration of solutes dissolved in them compared to the concentration inside a cell, which dictates the direction of water movement via osmosis.

To understand the difference between these three types of solutions, you first need to understand the concept of osmosis. Osmosis is the passive movement of water molecules across a semi-permeable membrane from an area of higher water concentration to an area of lower water concentration.

This movement continues until the concentration of water is balanced on both sides. The terms isotonic, hypotonic, and hypertonic describe the tonicity of a solution, which is its ability to cause water to move in or out of a cell. This is particularly important in biology, as it affects the shape and function of cells, especially red blood cells in the human body.

An isotonic solution is one where the concentration of solutes outside the cell is the same as the concentration of solutes inside the cell. In this state, there is no net movement of water. Water molecules move in and out of the cell at an equal rate, and the cell maintains its normal shape and size. For example, a 0.9% saline solution is isotonic to human red blood cells, which is why it's often used in intravenous drips. 

The environment is perfectly balanced, and the cells are happy. Hypotonic solution is a solution that has a lower concentration of solutes and, therefore, a higher concentration of water compared to the inside of a cell. When a cell is placed in a hypotonic solution, water rushes into the cell through osmosis. 

This influx of water causes the cell to swell. In animal cells, which lack a rigid cell wall, this can lead to lysis, or bursting, because the cell membrane can't withstand the pressure. This is what happens if you put a red blood cell in pure distilled water. Plant cells, however, have a strong cell wall that prevents them from bursting; instead, they become turgid, which is the firm and rigid state essential for a plant's structure. 

Finally, a hypertonic solution is a solution with a higher concentration of solutes and a lower concentration of water compared to the inside of a cell. When a cell is placed in a hypertonic solution, water moves out of the cell and into the surrounding solution. This outward flow of water causes the cell to shrink or shrivel, a process called crenation in animal cells. In plant cells, the cell membrane pulls away from the cell wall, a process known as plasmolysis. 

This is why putting too much salt on a garden plant can cause it to wilt; the soil becomes hypertonic, and the plant's cells lose water. Understanding these concepts is vital in fields like medicine, where saline solutions must be carefully chosen, and in food preservation, where salting or sugaring foods uses a hypertonic environment to draw water out of microorganisms, preventing spoilage.