what will happen when a animal cell is placed in a hypotonic solution and hypertonic solution?
Open in App
Suggest Corrections
3
In biology, osmosis refers to the movement of water. It is a passive process, meaning it requires no energy and happens automatically. The water moves from an area of greater concentration to an area of lesser concentration until equilibrium is reached. For cells, this movement is from one compartment to another through a semipermeable membrane. The solution is the area outside the cellular compartment, also called the extracellular environment.
Solute is the number of dissolved solids in a solution regardless of what they are. It can consist of proteins, carbohydrates, ions, hormones, etc. When discussing osmosis, comparison is made between the intracellular and extracellular (solution) solute concentrations. The concentration is also called the osmolarity of the solution. The difference between the number of dissolved solids creates an osmotic pressure gradient that forces water to move to achieve equilibrium between the inside and outside environments.
In a hypotonic solution, the solute concentration is lower than inside the cell. The prefix hypo means under or below in Latin. Under these conditions, the osmotic pressure gradient forces water into the cell. Depending on the amount of water that enters, the cell may look enlarged or bloated. If the water continues to move into the cell, it can stretch the cell membrane to the point the cell bursts (lyses) and dies.
Cells don’t have the ability to regulate their water content (remember that osmosis is a passive process), so they rely on the body to provide an environment where intracellular and extracellular solute concentrations are equal or isotonic. The body regulates the composition of extracellular fluid using the kidneys, adrenal glands, and the hypothalamus in the brain which triggers thirst and drives organisms to drink water. Slight fluctuations in the solute concentration of the extracellular fluid throughout the day cause small amounts of water to be exchanged between the intracellular and extracellular compartments to maintain homeostasis.
In contrast to hypotonic and isotonic solutions, a hypertonic solution has a higher solute concentration than inside the cell. When this happens, the osmotic gradient causes water to rush out of the cell and it becomes wrinkled or shriveled. If this happens to red blood cells, it is called crenation
Plant cells respond the same way as animal cells in a hypotonic solution, but the affects may not be as severe. Plants have rigid cell walls made of cellulose covering the plasma membrane. This makes it difficult for the cell to lyse, but the increased pressure causes the sides of the cell to bulge out.
The image above shows the effects of osmotic pressure gradients on red blood cells.
References
- OpenStax College. (2018). Anatomy & Physiology. Houston, TX. OpenStax CNX. Retrieved from //cnx.org/contents/
- Tonicity. (n.d.). In Wikipedia. Retrieved April 25, 2018 from //en.wikipedia.org/wiki/Tonicity
If you're seeing this message, it means we're having trouble loading external resources on our website.
If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.
Saltwater Fish vs. Freshwater Fish?
Fish cells, like all cells, have semi-permeable membranes. Eventually, the concentration of "stuff" on either side of them will even out. A fish that lives in salt water will have somewhat salty water inside itself. Put it in the freshwater, and the freshwater will, through osmosis, enter the fish, causing its cells to swell, and the fish will die. What will happen to a freshwater fish in the ocean?
Imagine you have a cup that has 100ml water, and you add 15g of table sugar to the water. The sugar dissolves and the mixture that is now in the cup is made up of a solute (the sugar) that is dissolved in the solvent (the water). The mixture of a solute in a solvent is called asolution.
Imagine now that you have a second cup with 100ml of water, and you add 45 grams of table sugar to the water. Just like the first cup, the sugar is the solute, and the water is the solvent. But now you have two mixtures of different solute concentrations. In comparing two solutions of unequal solute concentration, the solution with the higher solute concentration is hypertonic, and the solution with the lower solute concentration is hypotonic. Solutions of equal solute concentration are isotonic. The first sugar solution is hypotonic to the second solution. The second sugar solution is hypertonic to the first.
You now add the two solutions to a beaker that has been divided by a selectively permeable membrane, with pores that are too small for the sugar molecules to pass through, but are big enough for the water molecules to pass through. The hypertonic solution is on one side of the membrane and the hypotonic solution on the other. The hypertonic solution has a lower water concentration than the hypotonic solution, so a concentration gradient of water now exists across the membrane. Water molecules will move from the side of higher water concentration to the side of lower concentration until both solutions are isotonic. At this point, equilibrium is reached.
Osmosis is the diffusion of water molecules across a selectively permeable membrane from an area of higher concentration to an area of lower concentration. Water moves into and out of cells by osmosis. If a cell is in a hypertonic solution, the solution has a lower water concentration than the cell cytosol, and water moves out of the cell until both solutions are isotonic. Cells placed in a hypotonic solution will take in water across their membrane until both the external solution and the cytosol are isotonic.
A cell that does not have a rigid cell wall, such as a red blood cell, will swell and lyse (burst) when placed in a hypotonic solution. Cells with a cell wall will swell when placed in a hypotonic solution, but once the cell is turgid (firm), the tough cell wall prevents any more water from entering the cell. When placed in a hypertonic solution, a cell without a cell wall will lose water to the environment, shrivel, and probably die. In a hypertonic solution, a cell with a cell wall will lose water too. The plasma membrane pulls away from the cell wall as it shrivels, a process called plasmolysis. Animal cells tend to do best in an isotonic environment, plant cells tend to do best in a hypotonic environment. This is demonstrated inFigure below.
Unless an animal cell (such as the red blood cell in the top panel) has an adaptation that allows it to alter the osmotic uptake of water, it will lose too much water and shrivel up in a hypertonic environment. If placed in a hypotonic solution, water molecules will enter the cell, causing it to swell and burst. Plant cells (bottom panel) become plasmolyzed in a hypertonic solution, but tend to do best in a hypotonic environment. Water is stored in the central vacuole of the plant cell.
When water moves into a cell by osmosis, osmotic pressure may build up inside the cell. If a cell has a cell wall, the wall helps maintain the cell’s water balance. Osmotic pressure is the main cause of support in many plants. When a plant cell is in a hypotonic environment, the osmotic entry of water raises the turgor pressure exerted against the cell wall until the pressure prevents more water from coming into the cell. At this point the plant cell is turgid (Figure below). The effects of osmotic pressures on plant cells are shown in Figure below.
The central vacuoles of the plant cells in this image are full of water, so the cells are turgid.
The action of osmosis can be very harmful to organisms, especially ones without cell walls. For example, if a saltwater fish (whose cells are isotonic with seawater), is placed in fresh water, its cells will take on excess water, lyse, and the fish will die. Another example of a harmful osmotic effect is the use of table salt to kill slugs and snails.
Diffusion and osmosis are discussed at //www.youtube.com/watch?v=aubZU0iWtgI(18:59).
Organisms that live in a hypotonic environment such as freshwater, need a way to prevent their cells from taking in too much water by osmosis. A contractile vacuole is a type of vacuole that removes excess water from a cell. Freshwater protists, such as the paramecium shown in Figure below, have a contractile vacuole. The vacuole is surrounded by several canals, which absorb water by osmosis from the cytoplasm. After the canals fill with water, the water is pumped into the vacuole. When the vacuole is full, it pushes the water out of the cell through a pore.
The contractile vacuole is the star-like structure within the paramecia.
- Osmosis is the diffusion of water.
- In comparing two solutions of unequal solute concentration, the solution with the higher solute concentration is hypertonic, and the solution with the lower concentration is hypotonic. Solutions of equal solute concentration are isotonic.
- A contractile vacuole is a type of vacuole that removes excess water from a cell.
Use this resource to answer the questions that follow.
- What is osmosis?
- What does salt do to water?
- What is a hypotonic solution? What happens to water in a hypotonic solution?
- What is a hypertonic solution? What happens to water in a hypertonic solution?
- What happens to water in an isotonic solution?
- What is osmosis? What type of transport is it?
- How does osmosis differ from diffusion?
- What happens to red blood cells when placed in a hypotonic solution?
- What will happen to a salt water fish if placed in fresh water?
This page titled 2.1: Osmosis is shared under a CK-12 license and was authored, remixed, and/or curated by CK-12 Foundation via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.
LICENSED UNDER