Osmosis and reverse osmosis are processes involving the movement of solvent molecules across a semi-permeable membrane. Osmosis occurs naturally from an area of lower solute concentration to higher concentration. Reverse osmosis applies pressure to overcome this, forcing solvent from the higher concentration side to the lower side. It is used in water purification to remove salts and other contaminants, making the water potable. The document provides detailed explanations, examples, and diagrams of both processes.

1. Osmosis
“Osmosis is a process by which the molecules of a solvent pass from a solution
of low concentration to a solution of high concentration through a semi-
permeable membrane.”
Table of Contents
 Explanation
 Solutions
 Types
 Effects
 Osmotic Pressure
 Significance
 Examples
What is Osmosis?
Osmosis is a passive process and happens without any expenditure of energy. It
involves the movement of molecules from a region of higher concentration to lower
concentration until the concentrations become equal on either side of the membrane.
Any solvent can undergo the process of osmosis including gases and supercritical
liquids.
Let us have a detailed look at the different types and effects of osmosis in detail.
Osmotic Solutions
 Isotonic Solution
 There are three different types of solutions:
 Hypertonic Solution
 Hypotonic Solution

2. An isotonic solution is one that has the same concentration of solutes both inside and
outside the cell.
A hypertonic solution is one that has a higher solute concentration outside the cell
than inside.
A hypotonic solution is one that has a higher solute concentration inside the cell than
outside.
Types of Osmosis
Osmosis is of two types:
 Endosmosis– When a substance is placed in a hypotonic solution, the solvent
molecules move inside the cell and the cell becomes turgid or undergoes
deplasmolysis. This is known as endosmosis.
 Exosmosis– When a substance is placed in a hypertonic solution, the solvent
molecules move outside the cell and the cell becomes flaccid or undergoes
plasmolysis. This is known as exosmosis.
Also Read: Difference between endosmosis and exosmosis
Effect of Osmosis on Cells
Osmosis affects the cells differently. An animal cell will lyse when placed in a hypotonic
solution compared to a plant cell. The plant cell has thick walls and requires more water.
The cells will not burst when placed in a hypotonic solution. In fact, a hypotonic solution
is ideal for a plant cell.
An animal cell survives only in an isotonic solution. In an isotonic solution, the plant cells
are no longer turgid and the leaves of the plant droop.
The osmotic flow can be stopped or reversed, also called reverse osmosis, by exerting
an external pressure to the sides of the solute. The minimum pressure required to stop
the solvent transfer is called the osmotic pressure.
Osmotic Pressure

3. Osmotic pressure is the pressure required to stop water from diffusing through a
membrane by osmosis. It is determined by the concentration of the solute. Water
diffuses into the area of higher concentration from the area of lower concentration.
When the concentration of the substances in the two areas in contact is different, the
substances will diffuse until the concentration is uniform throughout.
Osmotic pressure can be calculated using the equation:
Π=MRT
where Π denotes the osmotic pressure,
M is the molar concentration of the solute,
R is the gas constant,
T is the temperature
Significance of Osmosis
 Osmosis influences the transport of nutrients and the release of metabolic waste products.

4.  It is responsible for the absorption of water from the soil and conducting it to the
upper parts of the plant through the xylem.
 It stabilizes the internal environment of a living organism by maintaining the
balance between water and intercellular fluid levels.
 It maintains the turgidity of cells.
 It is a process by which plants maintain their water content despite the constant
water loss due to transpiration.
 This process controls the cell to cell diffusion of water.
 Osmosis induces cell turgor which regulates the movement of plants and plant
parts.
 Osmosis also controls the dehiscence of fruits and sporangia.
 Higher osmotic pressure protects the plants against drought injury.
Also Refer: Passive Transport
Examples of Osmosis
Osmosis has a significant role to play in plants, animals and also in humans. In
an animal cell, osmosis helps in absorbing water from the intestines to the blood.
Listed below are more examples of Osmosis.
 The absorption of water from the soil is due to osmosis. The plant roots have a
higher concentration than the soil. Therefore, the water flows into the roots.
 The guard cells of the plants are also affected by osmosis. When the plant cells
are filled with water, the guard cells swell up, and the stomata open.
 If a freshwater or saltwater fish is placed in the water with different salt
concentrations, the fish dies due to the entry or exit of water in the cells of the
fish.
 Humans suffering from cholera are also affected by osmosis. The bacteria that
overpopulate the intestines reverse the flow of absorption and do not allow water
to be absorbed by the intestines, which results in dehydration.

5.  When the fingers are placed in water for a longer period of time, they become
pruney due to the flow of water inside the cells.
Also Read: Reverse Osmosis
For more information on osmosis, its definition, types, effects and osmotic pressure,
keep visiting BYJU’S Biology website or download the BYJU’S app for further reference.
Frequently Asked Questions
Q1
How do you define osmosis?
Osmosis is the movement of solvent from a region of lower solute concentration to a
region of higher solute concentration through a semi-permeable membrane.
Q2
What are the three types of osmotic conditions that affect living cells?
The three types of osmotic conditions include- hypertonic, isotonic, and hypotonic.
Q3
What are the different types of osmosis?
The different types of osmosis include:
1. Endosmosis- when a substance is placed in a hypotonic solution, the solvent molecules
move inside the cell and the cell becomes rigid.
2. Exosmosis-when a substance is placed in a hypertonic solution, the solvent molecules move
out of the cell and the cell becomes flaccid.
Q4
Why is osmosis important for the cells?
Osmosis is important for the cells for many reasons. It helps in the movement of
important materials inside and out of the cell. The nutrients, water and other solutes
move in and out of the cell by the process of osmosis.
Q5

6. How is osmosis different from diffusion?
Osmosis is a process of movement of solvents through a semi-permeable membrane
from a region of lower solute concentration to higher solute concentration. On the
contrary, diffusion does not require a semi-permeable membrane to occur and the
molecules move from a region of higher concentration to lower concentration.
Q6
Do dead cells exhibit osmosis?
Yes, dead cells also exhibit osmosis. If a dead cell is placed under a hypotonic solution, water
moves inside the cell and it bulges.
Q7
What is the main function of osmosis?
Osmosis helps in stabilizing the internal environment of the organism by balancing the
levels of water and intracellular fluids. Also, the nutrients and minerals enter the cell by
osmosis which is necessary for the survival of cells.
Q8
What is forward osmosis?
Forward osmosis is a natural phenomenon that occurs around us on a daily basis. It is
the type of osmosis that uses a semi-permeable membrane in the separation of water
from dissolved solutes. This type of osmosis is widely used in wastewater treatment,
osmotic power generation, etc.
Q9
List of some examples of osmosis.
The real-life examples of osmosis are:
1. Feeling thirsty after having salty food.
2. Dialysis of kidney in the excretory system.
3. Swelling of resins and other seeds when they are soaked in water.
4. Movement of salt-water in the animal cell across our cell membrane.
5. Movement of water and minerals from root nodules to various parts of plants.

7. Q10
What are the factors affecting the rate of Osmosis?
The factors affecting the rate of osmosis include:
1. Pressure.
2. Temperature.
3. Surface Area.
4. Water Potential.
5. Concentration gradient.
Q11
What is Osmotic pressure?
Osmotic pressure is defined as the minimum pressure applied to a solution to stop the
flow of solvent molecules through a semipermeable membrane. The osmotic pressure
of a solution is proportional to the molar concentration of the solute particles in the
solution.
π = iCRT is the formula used for finding the osmotic pressure of a given solution.
Q12
What is a semipermeable membrane?
The semipermeable membrane is a biological membrane, which functions by permitting
the movements of certain molecules or ions to pass through it.
Q13
What is reverse osmosis?
Reverse osmosis is a natural phenomenon that occurs in the opposite direction of the
natural osmosis. This type of osmosis is used for removing the majority of contaminants
from water by pushing the water under pressure through a semi-permeable membrane.
Q14
What is the significance of osmosis?
The biological importance of osmosis includes:

8. 1. It is essential for the survival of a cell.
2. Osmosis plays a key role during the germination of seeds.
3. Involved in the movement of water molecules between the cell and cell organelles.
4. In plants, it is involved in the movement of water molecules from the soil into the root
nodules.
5. The mechanism of stomata is mainly because of the response to the osmotic pressure of the
guard cells in relation to the epidermal cell
Newdata
What is Reverse Osmosis?
The process of movement of solvent through a semipermeable membrane from the
solution to the pure solvent by applying excess pressure on the solution side is
called reverse osmosis.
Reverse osmosis is a membrane treatment process primarily used to separate
dissolved solutes from water. Reverse osmosis is most commonly known for its use in
drinking water purification, particularly with regard to removing salt and other effluent
materials from water molecules.
Table of Contents
 Introduction to Reverse Osmosis
 Reverse Osmosis Principle
 Reverse Osmosis Process
 Experiment of reverse osmosis
 Advantages of Reverse Osmosis
 Disadvantages of Reverse Osmosis
 Frequently Asked Questions – FAQs
Introduction to Reverse Osmosis

9. Reverse osmosis is one of the oldest and most popular separation techniques used
mainly for the purification of water. The process was mainly adopted for the
desalination of seawater in the year 1950 when the whole process was relatively slow
and limited to certain laboratories. However, after a lot of research and advancements
in technology, there were significant developments, especially in the field
of polymers and the production of efficient membranes.
Today, this technique is extensively used by many around the world to purify water for
industrial, residential, commercial and scientific purposes. While reverse osmosis
technology is one of humanity’s important scientific innovations we will develop a basic
understanding of the whole process here on this page.
Reverse Osmosis Principle
To break down the process further, due to the presence of a membrane, large
molecules of the solute are not able to cross through it and they remain on the
pressurised side. The pure solvent, on the other hand, is allowed to pass through the
membrane. When this happens the molecules of the solute start becoming concentrated
on one side while the other side of the membrane becomes dilute. Furthermore, the
levels of solutions also change to some degree.
In essence, reverse osmosis takes place when the solvent passes through the
membrane against the concentration gradient. It basically moves from a higher
concentration to a lower concentration.
Reverse Osmosis Process
Osmotic pressure is the minimum pressure required to stop solvent flow through the
semipermeable membrane. Therefore, when the solution side (the side where the solute
concentration is high) is subjected to a pressure greater than the osmotic pressure, the
solvent particles on the solution side move through the semipermeable membrane to
the region where the solute concentration is low. Such inverse solvent movement
through the semipermeable membrane is called reverse osmosis.
It is important to note that the pressure applied to the solution side must be higher than
the osmotic pressure for the reverse osmosis process to proceed. Osmotic pressure is a
colligative property, which depends on the concentration of the solution. In water

10. purification, the reverse osmosis process is very important. Many water purifiers used
today use reverse osmosis in the purification process as one of the steps.
Experiment of Reverse Osmosis
The reverse osmosis process is explained below with the help of an experiment.
How does Reverse Osmosis work?
An easy experiment can be conducted by taking some freshwater and a concentrated
aqueous solution. The solutions should be kept on opposite sides with a semipermeable
membrane placed in between to separate the two solutions. Pressure should be applied
on the side with the concentrated solution. Now this will result in water molecules
moving through the membrane to the freshwater side. This basically sums up the
process of reverse osmosis.
Benefits of Reverse Osmosis
Some of the benefits of reverse osmosis are discussed below.
 This process can be used to effectively remove many types of dissolved and suspended
chemical particles as well as biological entities (like bacteria) from the water.
 This technique has a wide application in treating liquid wastes or discharges.
 It is used in purifying water to prevent diseases.
 It helps in desalinating seawater.
 It is beneficial in the medical field.
Advantages of Reverse Osmosis
Reverse Osmosis has several advantages, including the following:
 Bacteria, viruses and pyrogen materials are rejected by the intact membrane. In this respect,
RO water approaches distilled water in quality.
 Available units are relatively compact and require little space. They are well suited to home
dialysis.
 In average use, the membrane has a life of a little more than one to two years before
replacement is necessary.
 Periodic complete sterilization of the RO system with formalin or other sterilant is practical.

11. Disadvantages of Reverse Osmosis
The disadvantages of RO systems include the following;
 Cellulose acetate membranes have limited pH tolerance. They degrade at temperatures
greater than 35o
C. They are vulnerable to bacteria. They eventually hydrolyze.
 Polyamide membranes are intolerant of temperatures greater than 35oC. They have poor
tolerance for free chlorine.
 Thin-film composites are intolerant of chlorine. High flux polysulfones require softening or
deionization of feed water to function properly.
Frequently Asked Questions – FAQs
Q1
How does reverse osmosis work?
Reverse Osmosis works by using a high-pressure pump to increase the pressure on the
salt side of the RO and force the water across the semipermeable RO membrane,
leaving almost all (around 95 to 99 %) dissolved salts in the reject stream behind.
Q2
What is an example of the use of reverse osmosis?
Reverse osmosis is a means of pulling clean water out of polluted water or salt water by
pushing water through a membrane under pressure. An example of reverse osmosis is
the process by which contaminated water is filtered under pressure.
Q3
What are the disadvantages of reverse osmosis?
The drawback of RO water is that it can significantly reduce the good minerals which
can help in the overall health of the heart and muscles. Those who use reverse osmosis
as their primary source of water may suffer from side effects such as tiredness, muscle
cramps, general weakness and cardiovascular disorders in severe cases.
Q4
What are osmosis and reverse osmosis?

12. Osmosis is a process in which liquid water flows through a semipermeable membrane
from a diluted solution into a more concentrated solution. The process of movement of
solvent through a semipermeable membrane from the solution to the pure solvent by
applying excess pressure on the solution side is called reverse osmosis.
Q5
What is the principle of reverse osmosis?
Reverse osmosis ( RO) is a water purification process that removes ions, unwanted
molecules and larger particles from drinking water using a partially permeable
membrane. As a result, the solute is kept on the membrane’s pressurised side and the
pure solvent is allowed to pass to the other sid