Hypotonic Solution - Definition and Examples

Introduction

Tonicity is gauging the effective osmotic pressure gradient. Here, the water potential of both solutions is segregated by a partially permeable cell membrane. Tonicity is based on the relative concentration of selective membrane permeable to the solutes across a cell membrane, determining the extent and direction of osmotic flux.

A solution can have one of the three classifications of tonicity comparative to another – hypotonic, hypertonic and isotonic.

In this article, we shall learn about the Hypotonic solutions.

Hypotonic Solution Definition

Hypotonic solution refers to a solution containing a lower amount of solute in comparison to the solute concentration in other solutions, across a semipermeable membrane. Such a solution has a decreased solute concentration and a total movement of water in the cell. This causes breakage of swelling. Consequently, the osmotic pressure in a hypotonic solution is low in comparison to other solutions.

What happens to a cell in a hypotonic solution? – Cells in a hypotonic solution

When a cell is immersed in a hypotonic solution, the water molecules pass into the cell from the solution as a result of the osmotic potential. The continuous diffusion of the molecules of water into the cell can lead to cell swelling. Also, it can lead to cytosis of the cell or rupturing. But, plant cells do not tend to burst as they possess a rigid cell wall, unlike animal cells.

Hypotonic Solution Example

As we have learnt, there are three classifications of tonicity – hypertonic solution, isotonic solution and hypotonic solution. In a hypertonic solution, there is a higher concentration of solutes compared to that of the inside of the cell. On the contrary, in an isotonic solution, there is no net flow of water in or out of the cell, and the concentration of the solute is the same, both inside and outside the cell.

The first solution in the figure is a hypotonic solution. Here, the size of the cell increases and the cell swells as there is a net flow of water in the cell. If the concentration of solute outside the cell is lower compared to that of the inside, solutes cannot move across the membrane.

The second solution in the figure is a hypertonic solution. Here, the size of the cell decreases, it shrinks. The water molecules move out of the cell into the solution. As a result of the movement of water from the cell to the outside, cells get distorted and wrinkled. The effect is referred to as the crenation of the cell.

The last solution seen in the figure is an isotonic solution. Here, the size of the cell remains intact, it does not change. There is no net flow of water either way, into the cell or out of the cell. The volume of the cell remains stable. If the concentration of solutes outside the cells is the same as that of the inside, the solutes are unable to cross the membrane.

Hypertonic vs. Hypotonic Solution – Important Differences

The following table depicts important differences between hypertonic and hypotonic solutions.

This was a brief on Hypotonic solutions, an example of hypotonic solution and the important differences between hypertonic and hypotonic solutions.

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Also see:

• What Happens To A Cell If It Is Placed In A Hypotonic Solution?
• Plasma membrane structure