⚡ Quick summary
The words hypotonic, hypertonic, and isotonic are most often used when comparing chemical solutions while discussing osmosis. A hypertonic solution has a higher concentration of solute than another solution, meaning water will flow into it. A hypotonic solution has a lower concentration of solute than another solution, meaning water will flow out of it. An isotonic solution has the same or very similar concentration of solute as another solution, meaning the water flow will reach equilibrium.
Hypertonic, hypotonic, and isotonic are three words that are commonly used in science. Specifically, they are used to explain how water will flow between two different chemical solutions. Solutions with a lot of stuff in them, such as saltwater, are often referred to as hypertonic while plain ol’ water is said to be hypotonic. But what does this really mean?
In this article, we will define all three of these words, explain the differences between them, and give examples of things that are typically described as being hypotonic, hypertonic, or isotonic.
What is the difference between hypotonic and hypertonic?
The words hypertonic and hypotonic are most often used in science when comparing chemical solutions in relation to osmosis. In simple terms, osmosis is the movement of water from low solute concentration to high solute concentration through a semipermeable membrane (a barrier that only lets water molecules through). Solute is the stuff that’s mixed into a solution. If a solution is low solute, it has a low amount of stuff in it. If it is high solute, the solution has a high amount of stuff in it. Water basically wants to move from a place with a low solute to a place with a high solute.
A hypertonic solution has a higher concentration of solute than the solution it’s being compared to. This means that water will move into the hypertonic solution. Let’s say we placed a plant cell in saline (saltwater). Compared to the plant cell, the saline solution has a much higher concentration of solute (in this case, salt). So water will leave the plant cell and move into our saline through osmosis. In this situation, saline is a hypertonic solution.
A hypotonic solution has a lower concentration of solute than the solution it’s being compared to. This means that water will move out of the hypotonic solution. Let’s say we put another plant cell into a glass of pure water. Compared to the plant cell, the water has a much lower concentration of solute (in this case, none). So the water will enter into the plant cell via osmosis. In this situation, pure water is a hypotonic solution.
To help keep these two terms straight, look at the prefixes. The prefix hypo- means “low” or “under” while hyper- means “high” or “over.” A hypotonic solution has a lower concentration of solute, while a hypertonic solution has a higher concentration of solute.
Usually we compare hypertonic and hypotonic solutions to a baseline solution. In medicine and nutrition, the most commonly used baseline solution is one of the human body fluids, such as blood or cellular fluid. For example, if you drink a glass of distilled water, you’re drinking a hypotonic solution. Because the water has nothing in it all, it’s going to be hypotonic compared to body fluids. If you drink an alcoholic beer, you’re drinking a hypertonic solution compared to body fluids.
hypertonic vs. hypotonic vs. isotonic
In discussions of osmosis and solutions, you might also hear the term isotonic. An isotonic solution has the same or nearly the same solute concentration as the solution it is being compared to. As a result, water will flow equally between both solutions, and it will appear as though nothing is happening. If we place a plant cell in an isotonic solution, we won’t see any net change in the amount of water in the plant cell or the solution it is immersed in.
Examples of hypotonic solutions
Using bodily fluids as a baseline, here are some examples of hypotonic solutions:
- Pure water
- Plain, unsweetened tea
- Sports drinks that are low in sugar and salt
Examples of hypertonic solutions
Using bodily fluids as a baseline, here are some examples of solutions that would be considered hypertonic:
- Lemonade
- Orange juice
- Alcoholic beverages
- Ocean water
Examples of isotonic solutions
In order for a solution to be isotonic compared to bodily fluids, it must have the same or a very similar solute concentration. Because this would rarely happen naturally, most solutions we would consider to be isotonic are designed to be that way. Some examples of this include:
- Isotonic energy drinks
- Normal saline (0.9% NaCl solution)
- Lactated Ringer’s solution
