What is hypotonic solution? examples and types

A hypotonic solution is one of the types of solution in relation to tonicity. Hypotonic solution examples include anything that has less solute and more water compared to the cells. This means a hypotonic solution has a lower solute concentration compared to another solution.

In science, a solution is referred to as a homogenous system that consists of two or more constituents. The ‘solutes’ are the constituents that are dissolved and the ‘solvent’ is the other constituent that dissolves the solute. In relation to tonicity, there are three types of solutions which include the isotonic, hypotonic, and hypertonic solutions. Tonicity is literally how an extracellular solution can change a cell’s volume by affecting osmosis. Hence, a solution cannot be described as hypotonic, isotonic, or hypertonic without a solution for comparison.

In this article, we will be discussing the hypotonic solution, its examples, types, and uses.

Contents

What is a hypotonic solution?

A hypotonic solution is a solution that contains a lower amount of solute as compared with the solute concentration in the other solution across a semipermeable membrane. This means a hypotonic solution contains fewer dissolved particles e.g salt and other electrolytes than is found in cells. This is why hypotonic solutions are usually used to give fluids intravenously to patients in hospitals in order to avoid or treat dehydration. Usually, the relative concentration of water in a hypotonic solution is high, and drinking the hypotonic solution would cause urine specific gravity to decrease.

Hypotonic solution definition in biology

In biology, one can define a hypotonic solution as a solution that has lower osmotic pressure than the other solution it is compared with. In other words, it is a solution that has a lower amount of solute as compared to the solute concentration in the other solution across a semipermeable membrane. A cell exposed to a hypotonic solution will eventually swell as the water molecules enter the cell via passive transport.

Hypotonicity is therefore a relative term whereby the property of the solution is defined relative to the other solution. Most times, in biology the solution of comparison is the cytosolic fluid or the fluid present inside a cell. This means a solution would be described as hypotonic when it has a lower amount of solutes than the cytosol of a cell and the semipermeable membrane is usually the cell membrane.

Hypotonic solution definition
An explanatory hypotonic solution picture

In biology, scientists use hypotonicity to enable them to describe cells. A scientist knowing the osmolarity of different solutions can enable the scientist to know which way the solute gradients and water gradients will form. Osmolarity is defined as the concentration of a solution in number of solutes per liter. Furthermore, hypotonic solutions are classified in biology, with reference to blood serum. Therefore, with respect to blood serum, the solutions that have osmolarity that is less than 280mOsm/liter are referred to as hypotonic solutions.

What happens to a cell in a hypotonic solution?

A cell in hypotonic solution will have an influx of water and due to this, the cell swells and bloats. This occurs because hypotonic solutions have a lower solute concentration (such as salt and electrolytes) than the cells inside of them. Due to this, the water from the solution will cross the cell membrane and enter the cell.

However, from the explanation given, it can be seen that the conception that cells placed in a hypotonic solution tend to lose water due to osmotic pressure is false and incorrect. The plasma membrane that surrounds cells keeps solutes from diffusing across the cell membrane. As the membrane does that, it allows water to diffuse across the membrane via osmosis into the cytoplasm. The special proteins that are embedded in the membrane known as membrane transport proteins help to transport specific solutes across the membrane. Whereas, other proteins known as aquaporins keep channels open such that only water can pass through.

It is important for all cells to regulate their solute content in order to avoid drying up or becoming too full of water. Cells with cytosol that are hypotonic solutions to the environment will definitely lose water to the more hypertonic environment that has more solutes. The water that is driven to equalize the two solutions is actually drawn from the cell. Therefore, a cell with a cytosol that is an extremely hypotonic solution compared to its environment will shrink and is said to be plasmolyzed. This is a bad state for cells that require water for several chemical reactions.

On the other hand, an environment can be a hypotonic solution compared to a cell. In such cases, water from the environment tends to diffuse into the cell. However, the cell may lyse if the hypotonic solution of the environment is too strong. Nevertheless, there are many mechanisms that cells use to control this flow of water. For instance, the cells of plants, fungi, and bacteria have a cell wall around the cell that prevents the cell from bursting. This cell wall is made up of various proteins, polysaccharides, and other molecules; and turgor pressure is created as water fills the cell and goes against this cell wall. The turgor pressure created, thus helps to force water back out of the cell, countering the inward flow of water.

Types of hypotonic solution effect on cells

Usually, in a hypotonic solution, there is a net movement of water from the solution into the body. A cell placed in a hypotonic solution will swell and expand and may burst. The process of the cell bursting is known as cytolysis. The various types of hypotonic solution effects on different cells are discussed below.

Protist in hypotonic environment

Even though protists, such as paramecia and amoebae do not have a cytoskeleton or cell wall, they can retain a rigid structure due to tonicity regulation. These protists usually live in the hypotonic environment, and hence continuous water influx occurs. In order for these protists to maintain the cell structure and prevent cell lysis, they have a specialized organ known as contractile vacuoles. The contractile vacuoles function to accumulate excess water from the cell and eventually discard this excess water.

Plant cell in hypotonic solution

The way plants are built, they can maintain a hypotonic solution in the soil and environment around them. Plants normally regulate their surroundings in order to maintain hypotonic conditions in their cells. The continuous influx of water in a hypotonic environment then causes a turgor pressure in plant cells which they utilize for rigidity and structure. Hence, plant cells remain in erect condition maintaining the rigidity of their structure. Apart from rigidity and structure, plants utilize the turgor pressure generated for the transportation of water throughout their body. Due to this turgor pressure generated, water is transported from the roots to the top stem of the plants.

What prevents a plant cell from bursting in a hypotonic solution?

As earlier said, in a hypotonic solution, a plant cell will become turgid (swell up) but not burst. This is because when a plant cell is placed in a hypotonic solution, the cell wall prevents the cell from bursting by maintaining the integrity of the plant cell. This enables plants to withstand periods without water and still sustain an ideal structure for photosynthesis. Therefore, a plant cell in a hypotonic solution would swell but not burst.

When plants are watered, the water flows from the wet soil into the plant cells through the roots. The plant cells in hypotonic solution take up water and maintain their turgor pressure (internal pressure) in the vacuole. This means plant cells require hypotonic solutions. When they are placed in hypotonic solutions e.g distilled water, water rushes into the cell and fills the central vacuole. The cell then expands but doesn’t burst because of the cell wall that maintains the integrity of the cell. This categorically explains why grocers spray their veggies with distilled water. What happens when they do this, is that the water flows into the plant cells and makes the vegetable look crisp and fresh.

It is important to know that a hypertonic environment is created around plants when they are not watered for a long time. Due to this, they lose the turgor pressure and appear wilted. However, on re-watering such plants, the turgor pressure regenerates and the plants regain their shape and structure. This is why a normal plant would wilt away in extreme hypertonic environments such as marshy areas and mangroves. These areas have a highly hypertonic environment due to high salt content. Nevertheless, plants that exist in such marshy areas and mangroves have adapted themselves to create a hypertonic cytosolic condition in their root cells. This results in a hypotonic external environment around roots that helps these plants absorb water from the surroundings.

Animal cell in hypotonic solution

When humans and animals take a big drink of water, the water goes into the cells. Humans, as well as animals, become dehydrated if the fluid outside the cell has more solutes than the cells do. The cells take in the water from the extracellular fluid and become saturated. Since animal cells don’t have structured cell walls like plants, too much water can cause the cells to burst. This is why a well-hydrated body has slightly more water in the extracellular fluid than in the cells themselves. Therefore, when an animal cell is placed in a hypotonic solution, it will swell and can likely burst.

In a hypotonic solution, an animal cell will swell as the water moves into the cell from the environment and since animal cells do not have cell walls like plants, they can burst. This is why animals must go through osmoregulation, where the amount of salt and water in the body is controlled despite the external environment. Humans go through osmoregulation using their kidneys. The kidneys filter the blood and ensure a concentration of salt and water that allows for homeostasis within our cells. This is why if a frog egg cell is placed into a hypotonic solution, it will swell via osmosis. Also, if a red blood cell is placed in a hypotonic solution, it will bloat up and may explode. This means a red blood cell in hypotonic solution would rupture due to the influx of water.

A Hypotonic solution example using the RBC as an illustration
RBC in a hypotonic solution

Furthermore, tonicity and the osmotic gradient are the reason why freshwater fishes cannot thrive in seawater and vice versa. An example of a hypotonic solution is freshwater, so, the cells of the freshwater fishes have a higher salt concentration than their surrounding water. These fishes need to flush out the excess water from their body and thus have adapted and developed a system to continuously do that. However, freshwater fishes, if exposed to seawater would have hypotonic cells in comparison to the external hypertonic environment. Therefore, the removal of water from their body will occur in such conditions and this would eventually dehydrate them and let them perish. This means that fluctuation in the salt content of water would drastically affect the population of fish in any water body.

Fungal cells in a hypotonic solution

The species of fungi live in hypotonic environments. These organisms like plant cells have strong walls that keep them from bursting after they take in water. For instance, if you put a mushroom in a cup of water, the mushroom would absorb the water around it and become mushy and swollen. That is also how it works in the soil, the fungi cells take in the water from the soil, as they ensure the environment is always hypotonic.

A picture of hypotonic solution effect on cells in comparison to an isotonic and hypertonic solution
A picture of hypotonic solution effect on cells in comparison to an isotonic and hypertonic solution

Hypotonic solution examples

  1. Distilled water
  2. Half-Normal Saline
  3. Quarter-Normal Saline
  4. 5% Dextrose in Water (D5W)

Typical examples of hypotonic solutions include anything that has more water and less solute compared to the cells. Let’s discuss each example of the hypotonic solution listed above.

Distilled water

Distilled water is an archetypal hypotonic solution example, though this can be subjective to the solution it is being compared with. Water is a solvent and purified distilled water will always be hypotonic when compared to the aqueous solution of a solute that contains any amount of the solute. Distilled water is devoid of any substance and is therefore said to be hypotonic to an aqueous solution of a solute.

Half-Normal Saline

The half-normal saline (or 0.45% sodium chloride NaCl dissolved in sterile water) is one example of hypotonic solution used in IV drips. Half-normal saline is usually used as a maintenance fluid because it has a composition that is similar to the plasma in the body. These hypotonic solution iv fluids are effective for patients that are burned, malnourished, experiencing diabetic ketoacidosis, or are mildly dehydrated. This is one of the types of hypotonic solution that provides dehydrated cells with the necessary fluid.

Quarter-Normal Saline

A 0.22% sodium chloride and 5% dextrose make up the quarter-normal saline. This hypotonic solution has half the amount of sodium chloride as half-normal saline. Hence, it is the most hypotonic form of saline available. The quarter-normal saline is usually used in pediatric cases and neonatal intensive care units.

5% Dextrose in Water (D5W)

The 5% dextrose in water also known as D5W or D5 is an example of a hypotonic solution that is used by medical professionals. This D5W dilutes extracellular fluid and renders free water for the kidneys in renal patients. The remaining water remains in the extracellular fluid in order to maintain balance once the body cells have absorbed the sugar (dextrose).

Hypotonic solution uses

An isotonic solution that involves an equal concentration of solute in the cell and the solution is normally used in medicine. However, some cases require a hypotonic solution. An exemplary case of when to give hypotonic solution is when patients become severely dehydrated during diabetic ketoacidosis.

Such patients get administered a 0.45% saline solution intravenously in order to provide rehydration to the intercellular space. In essence, nurses and doctors use intravenous (IV) drips and injections to rehydrate their patients all the time. Common hypotonic solutions that are used to replenish water in cells include hypotonic saline i.e., 0.45% sodium chloride or 0.25% sodium chloride with or without dextrose, 2.5% dextrose solution, etc.

Furthermore, let’s look at the aquatic animals living in seawater or fresh water, for instance. They use the mechanism of osmoregulation to control the effect of osmosis. As a result of this osmoregulation, the salt content in the water is essential for the aquatic life in the water body. With the help of salt glands, sea turtles have adapted themselves to form a hypertonic internal environment. Due to the hypertonic internal environment, the external environment relatively becomes hypotonic to them. Hence, helping the marine animals survive even in a highly hypertonic environment.

Hypertonic vs hypotonic solution

The concept of hypertonic solution vs hypotonic solution work in opposite ways. Even though the hypertonic and hypotonic solutions may sound similar, they differ. The difference between a hypotonic solution vs hypertonic solution is that when a cell is placed in a hypotonic solution, water flows into the cell; whereas water flows from the cell into the solution when the cell is immersed in a hypertonic solution.

This is because, in a hypertonic solution, there are more solutes in the solution as compared to the cell. Therefore, in order to achieve homeostasis, water flows from the cell into the solution. In a hypotonic solution, on the other hand, there are more solutes in the cell than in the solution. Whereas, isotonic solutions have the same amount of solutes as the cells inside of them. If you put a cell into a hypotonic solution, it would bloat, swell, and/or burst, but a cell placed in a hypertonic solution would shrivel and dehydrate. Whereas, in an isotonic solution, the cell would remain the same.

Below is a video showing the animal cell before and after hypotonic solution, isotonic and hypertonic solution

A microscopic examination of red blood cells in hypotonic solution, isotonic and hypertonic solution

FAQs

Whats a hypotonic solution?

In order to explain the hypotonic solution meaning, let’s look at the meaning of the word. The prefix to the word- tonicity (which means push or thrust) is ‘hypo’, which means “low”. This means a hypotonic solution is a solution that contains a lower amount of solute as compared with the solute concentration in the other solution across a semipermeable membrane.

Is d5w a hypotonic solution?

Yes, the 5% dextrose in water also known as D5W or D5 is an example of a hypotonic solution that is used by medical professionals. This D5W dilutes extracellular fluid and renders free water for the kidneys in renal patients.

What is a hypotonic solution in biology?

A hypotonic solution in biology definition can be defined as a solution with a low amount or concentration of the non-penetrating solutes as compared to the other solution across a semipermeable membrane.

What happens to red blood cells when placed in a hypotonic solution?

In a hypotonic solution, an animal cell will swell and lyse. This is why red blood cells placed in a hypotonic solution will bloat up and may rupture due to the influx of water. Therefore, RBC in hypotonic solution will swell and eventually burst.

What happens when a cell is placed in a hypotonic solution?

In a hypotonic solution, the amount of non-penetrating solutes in the solution is less and the water concentration is higher than that present in the cytosol of a cell. As a result, if a cell is placed in a hypotonic solution, an osmotic gradient is generated resulting in the movement of the solvent or water into the cell which causes the cell to swell up and eventually lyse.

Why does water enter a cell that is placed in a hypotonic solution?

Water enters a cell that is placed in a hypotonic solution because hypotonic solutions have a lower solute concentration (such as salt and electrolytes) than the cells inside of them. Due to this, the water from the solution will cross the cell membrane and enter the cell.

What does a hypotonic solution look like?

A solution is hypotonic if the solute concentration outside the cell is lower than inside the cell, and the solutes cannot cross the membrane.

Is lr a hypotonic solution?

LR which means Lactated Ringer’s solution, or Lactated Ringer’s is one of the intravenous (IV) fluids that doctors usually use. This solution is used to restore hydration and fluid balance in the body. LR is not a hypotonic solution but an isotonic fluid because it has the same osmotic pressure or weight as blood.

Osmosis occurs from a hypertonic to a hypotonic solution. True or false?

False. Osmosis occurs from a hypotonic to hypertonic solution because it occurs from a region of low concentration to a high concentration.

What does hypotonic solution mean?

The definition of hypotonic solution is defined as a solution that has a lower solute concentration compared to another solution.

What happens in a hypotonic solution?

When a cell is placed in a hypotonic solution, endosmosis takes place. This means, that water enters the cell and causes the cell to be turgid, creating a cell turgor pressure. An animal cell in a hypotonic solution may eventually burst as a result of this turgor pressure because they lack a cell wall. Whereas, in plant cells, the turgor pressure is countered due to the presence of a cell wall that keeps the plant cells from bursting.

When is hypotonic solution used?

Some cases require a hypotonic solution, such as when patients become severely dehydrated during diabetic ketoacidosis. Nurses and doctors use hypotonic intravenous (IV) drips and injections to rehydrate their patients all the time.

What is an example of a hypotonic solution?

Examples of hypotonic solutions include distilled water, half-normal Saline, quarter-normal saline, and 5% dextrose in water (D5W).

A red blood cell is placed in a hypotonic solution what is the fate of the cell?

Red blood cells in a hypotonic solution would bloat and rupture.

What keeps plant cells from bursting in a hypotonic solution?

A plant cell in a hypotonic solution will become turgid (swell up) but not burst because the cell wall prevents the cell from bursting by maintaining the integrity of the plant cell.

What was the appearance of the elodea cells in hypotonic solution?

Elodea cells would appear to swell in a hypotonic solution with a lower concentration of solute, due to water osmosis, diffusing from the outside to the inside of the cell.

A plant cell is placed in a hypotonic solution. what will happen to the plant cell?

When a plant cell is placed in a hypotonic solution e.g distilled water, water rushes into the cell and fills the central vacuole. The plant cell will expand but wouldn’t burst because of the cell wall that maintains the integrity of the cell.

What is hypotonic solution used for?

In medicine, the issue of when to use hypotonic solution arises when a patient is dehydrated. Medical personnel usually use hypotonic solutions to give fluids intravenously to hospitalized patients in order to treat or avoid dehydration.

If a cell is placed in a hypotonic solution what will occur?

A cell in a hypotonic solution will have an influx of water and due to this, the cell swells and bloats. This occurs because hypotonic solutions have a lower solute concentration (such as salt and electrolytes) than the cells inside of them. Due to this, the water from the solution will cross the cell membrane and enter the cell. An animal cell placed in hypotonic solution will swell and lyse whereas plant cells will swell and not lyse.

How does the cell wall protect prokaryotic cells in a hypotonic solution?

As prokaryotic cells swell in a hypotonic environment, the cell wall counteracts the outward osmotic pressure and prevents the cell from bursting.

Why does blood become transparent in the hypotonic solution?

Red blood cells in hypotonic solution will enlarge or become haemolysed. When hemolyzed, the red blood cells break down or become destroyed so that the contained oxygen-carrying pigment hemoglobin is freed into the surrounding medium. Blood becomes transparent in the hypotonic solution because of the enlargement and hemolysis of the red blood cells.

What happens to a red blood cell in a hypotonic solution?

Placing a red blood cell in a hypotonic solution will cause it to swell up or become haemolysed.

What will be the effect of placing a plant cell in a hypotonic solution?

In a hypotonic solution, a plant cell will swell but will not lyse due to the presence of a cell wall.

What happens if a cell is placed in a hypotonic solution?

A cell placed in a hypotonic solution will swell and bloat. An animal cell may lyse eventually but plant cells do not because of the presence of a cell wall. Also, fungal cells like plant cells have strong walls that keep them from bursting when placed in a hypotonic solution.

Moreso, single-celled organisms like the protist (such as paramecia and amoebae) do not have a cytoskeleton or cell wall, but due to tonicity regulation, they can retain a rigid structure. In order to prevent lysis, these cells possess a specialized organ known as a contractile vacuole that helps to accumulate and expel excess water in the cell.

Is salt water a hypotonic solution?

A solution that contains 0.5% salt is said to be hypotonic with respect to the cell.

Scroll to Top