What is the Difference Between Isosmotic and Isotonic Solution

Isosmotic and isotonic solutions are both important concepts in biology, particularly in relation to the movement of water across cell membranes.

What is the difference between isosmotic and isotonic solution? An isosmotic solution refers to two solutions that have the same total solute concentration, whereas an isotonic solution refers specifically to a solution that has the same solute concentration as a particular cell or tissue.

Key Areas Covered

1. What is an Isosmotic Solution 
      – Definition, Features
2. What is an Isotonic Solution 
      – Definition, Features 
3. Relationship Between Isosmotic and Isotonic Solution
      – Outline of Common Features
4. Difference Between Isosmotic and Isotonic Solution
      – Comparison of Key Differences
5. FAQ: Isosmotic and Isotonic Solution
      – Answers to Frequently Asked Questions

Key Terms

Isosmotic Solution, Isotonic Solution

What is an Isosmotic Solution

An isosmotic solution is a solution that has the same total concentration of solutes (dissolved particles) as another solution, resulting in equal osmotic pressure on both sides. This means there’s no net movement of water across a semi-permeable membrane separating the two solutions. An important point to remember is that an isosmotic solution might not always be isotonic to cells.

This can happen if the solution contains solutes that can easily slip through the cell membrane. For instance, imagine a solution with pure alcohol that’s isosmotic to a cell. Since alcohol can readily enter the cell, it becomes hypotonic (less concentrated than the cell’s interior). This can lead to water rushing into the cell and causing it to swell.

There are various applications of isosmotic solutions in the fields of medicine and biology. Intravenous (IV) fluids, for example, are often formulated to be isosmotic with blood plasma. This ensures that they don’t disrupt the delicate water balance within cells when administered.

What is an Isotonic Solution

Isotonic is a term used specifically for solutions that have the same solute concentration (total amount of dissolved particles) as a particular cell or tissue. When a cell is placed in an isotonic solution, there’s no net movement of water into or out of the cell. This is because the concentration of solutes inside the cell is equal to the concentration outside. This results in balanced osmotic pressure on both sides of the cell membrane.

If water moves in or out excessively, the cell can shrink (hypotonic solution) or burst (hypertonic solution). Unlike isosmotic solutions (which focus on any two solutions with equal solute concentration), isotonic solutions are specifically designed to match the concentration within a particular cell.

Common examples of isotonic solutions include normal saline (0.9% sodium chloride solution) used in IV fluids and contact lens solutions formulated to match the tear film’s tonicity.

Relationship Between Isosmotic and Isotonic Solution

1. As a consequence of the equal osmotic pressure, neither isosmotic nor isotonic solutions cause a net flow of water into or out of a cell placed in them.
2. All isotonic solutions are isosmotic, but not all isosmotic solutions are isotonic.

Difference Between Isosmotic and Isotonic Solution

Definition

• An isosmotic solution is a solution that has the same total concentration of solutes (dissolved particles) as another solution, resulting in equal osmotic pressure on both sides. An isotonic solution is a solution that has the same solute concentration (total amount of dissolved particles) as a particular cell or tissue.

Concentration

• Isosmotic compares the total concentration of solutes in two any solutions while isotonic specifically considers the solute concentration in relation to a particular cell or tissue.

Nature

• Isosmotic solutions don’t necessarily guarantee anything about the solution’s effect on cells. An isosmotic solution might be hypotonic or hypertonic to a specific cell depending on the solutes’ ability to permeate the cell membrane. Isotonic solutions are designed to have no net water movement into or out of a specific cell when placed in the solution.

Conclusion

Isosmotic and isotonic solutions are both about solute concentration and water movement across cell membranes. Isosmotic solutions have equal total solute concentration compared to another solution, while isotonic solutions specifically match the concentration of a particular cell.

FAQ: Isosmotic and Isotonic Solution

1. Why is isosmotic not always isotonic?

Isosmotic is not always isotonic because of solute permeability. An isosmotic solution of a non-permeable solute will be isotonic to a cell, but an isosmotic solution of a permeable solute might not be.

2. Is normal saline isotonic or isosmotic?

Normal saline is isotonic. This means that it is designed to have the same concentration of solutes as the cells in the body. Normal saline has an osmolarity close to that of bodily fluids, such as blood plasma, which helps prevent the net movement of water into or out of cells when it is introduced into the body.

3. Which IV fluid is isotonic?

0.9% Normal Saline (NaCl), lactated Ringer’s Solution, and plasmalyte are commonly used isotonic solutions. These solutions have an osmolarity similar to that of bodily fluids and are designed to maintain the balance of fluids and electrolytes within the body’s cells.

4. What is an example of an isosmotic solution?

A solution containing 300 milliosmoles per liter (mOsm/L) NaCl is isosmotic with a solution containing a total of 300 mOsm/L of any other substance or mixture of substances. This is an example of an isosmotic solution.

5. What is an isotonic solution used for?

Isotonic solutions, matching the salt concentration of blood, are used in hospitals to replace fluids lost due to dehydration, bleeding, or other causes. They help restore blood volume and maintain proper cell function.

Reference:

1. “Isotonic Solution.” Science Direct.

Image Courtesy:

1. “Blausen 0685 OsmoticFlow Isotonic” By Blausen.com staff (2014). “Medical Gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. – Own work (CC BY 3.0) via Commons Wikimedia