Osmosis is the movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. It is a crucial biological process that helps maintain cell turgidity and regulates fluid balance in living organisms. Osmosis is an important topic in Biology.
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Osmosis is the flow of water molecules across a semipermeable membrane from an area of low solute concentration to an area of high solute concentration. Such processes and similar ones in biological systems support the maintenance of cellular turgor pressure, nutrient uptake, waste removal, and generally cellular activity and homeostasis.
Osmosis is closely related to but distinct from diffusion since it deals with the movement of water across a semipermeable membrane.
The difference between diffusion and osmosis are:
Feature | Diffusion | Osmosis |
Definition | Movement of particles from high to low concentration | Movement of water molecules through a semipermeable membrane. |
Type of molecules | Solute/gases | Water only |
Membrane required | Not necessary | Semi-permeable membrane |
Biological example | CO₂ exchange in lungs | Water uptake in plant cells |
Energy Use | No (passive process) | No (passive process) |
A membrane that some molecules, mainly water, pass through while others are blocked.
Examples: The cell membrane, the membranes of mitochondria and chloroplasts.
The mechanism of osmosis is of great importance to the maintenance of cellular balance and function. It is a type of passive transport i.e., the movement of water molecules occurs down the concentration gradient and does not require any energy.
Concentration Gradient: Water moves from low to high concentration.
Direction of Water Movement: Water moves into areas with high concentrations of solutes.
This process tends to equilibrate the solute concentration inside and outside the cell.
The pressure needed to prevent water from osmotically diffusing over a membrane is known as osmotic pressure. It is based on the concentration of solute. From the area of lower concentration, water diffuses into the area of higher concentration. The compounds will disperse until the concentration is consistent throughout when the concentrations of the substances in the two places in contact are different.
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
Osmosis can occur in different kinds of solutions. These have different effects on cells.
A solution with a low solute concentration compared to that of the cell's interior.
Causes cells to swell and potentially burst due to the entrance of water.
A solution with a higher solute concentration than that of the cell's interior.
Cause cells to shrink as water exits.
A solution with the same solute concentration as that of the cell's interior.
No net movement of water, the cell stays the same size and shape.
The difference between the different types of solutions is given in the table below:
Feature | Hypotonic Solution | Hypertonic Solution | Isotonic Solution |
Definition | It has low solute concentration than the cell | It has high solute concentration than the cell | It has the same solute concentration than the cell |
Movement of water | Into the cell | Out of the cell | No net movement |
Effect on cells | Swell and may burst | Shrinks | Remain normal |
Higher water potential than the cell | Lower water potential than the cell | Same water potential as the cell | |
Example | Pure water relative to cell sap solution | Salt or sugar solution | 0.9% NaCl solution for animal cells |
Diffusion is affected by the following factors:
Concentration gradient is the difference in concentration of two different regions. The greater the difference in concentration, the faster the molecules will move.
The temperature increases the kinetic energy of molecules. Hence, raising the temperature increases the speed of the molecules and ultimately the rate of diffusion.
Smaller molecules diffuse faster than larger ones since the smaller size faces less resistance while diffusing across the medium. The larger the molecule, the less is the ability to easily pass through the medium.
Osmosis occurs from a region of higher water potential (less solute) to lower water potential (more solute) until equilibrium is reached.
Osmosis is involved in many biological processes, mainly in plant and animal cells.
Turgor Pressure: The pressure exerted by the cell's content against the cell wall, maintaining rigidity and the form of plants.
Plasmolysis and Its Effects: Due to the hypertonic solution, the plant cells lose water, detaching the cell membrane from the cell wall, which may even cause the death of the cell.
Osmoregulation: The process by which animals maintain the proper balance of water and salts within their bodies.
Effects of Osmosis: The effects of osmosis on red blood cells can be such that they may burst in a hypotonic solution and shrink in a hypertonic solution.
Osmosis is involved in various medical and industrial applications.
Dialysis: A medical procedure in which waste products and excess water are removed from blood through the principle of osmosis when the kidneys are no longer functioning.
Intravenous Fluids: Solutions given to patients to maintain osmotic balance and hydration.
Food Preservation: Osmotic pressure to prevent growth/spoiling by microorganisms.
Water Purification: Reverse osmosis, for instance, to purify water from impurities and contaminants.
The key concepts to be covered under this topic for different exams are:
Types of Solution
Osmosis vs Diffusion
Factors affecting the Water potential
Q1. Solution A with 10% concentration is separated via a semipermeable membrane from solution B with 20% concentration. What will be the direction of the movement of water molecules?
From Solution B to Solution A
From Solution A to Solution B
No net flow of water
None of the above
Correct answer: 2) From Solution A to Solution B
Explanation:
This process is known as osmosis. When two solutions of different concentrations are separated by a semipermeable membrane, the solvent (typically water) will move from the region of lower solute concentration (Solution A) to the region of higher solute concentration (Solution B). This movement occurs to equalize the concentration of solutes on both sides of the membrane. The semipermeable membrane allows only the solvent molecules to pass through, not the solute molecules, leading to the flow of water from Solution A to Solution B, thus balancing the concentrations.
Hence, the correct answer is option 2) From Solution A to Solution B.
Q2. Osmosis occurs across
Differentially permeable membrane
Impermeable membrane
Selectively permeable membrane
Semipermeable membrane
Correct answer: 4) Semipermeable membrane
Explanation:
Osmosis is the spontaneous movement of solvent molecules, typically water, through a semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration. This process occurs in an attempt to equalize the concentration of solutes on both sides of the membrane.
Hence, the correct answer is option 4) Semipermeable membrane.
Q3. All of the following involves osmosis except
Water absorption by root
Stomatal movement
Swelling of wooden door during raining season
Turgor pressure in Mimosa
Correct answer: 3) Swelling of wooden door during raining season
Explanation:
Importance of Osmosis -
1. Water absorption by roots
2. Stomatal movement
3.Turgor pressure in Mimosa and Desmodium
4 .Drought and frost resistance
Movement of water in the xylem occurs due to physical forces, like suction pull and surface tension as in the case of capillary rise of liquid.
Hence, the correct answer is option 3) Swelling of wooden door during raining season.
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Frequently Asked Questions (FAQs)
Osmosis refers to the movement of water across a semipermeable membrane. On another hand, diffusion is the phenomenon of the movement of any particles from high to low concentration.
A hypertonic solution contains a higher external concentration of solutes, which causes the cell to lose water and shrink in volume.
Osmosis is utilised in filtering waste, along with surplus fluids, from the blood during dialysis to mimetically replicate the kidneys' function in patients who have completely lost renal function.
Some real-life applications of osmosis are in medical treatments like dialysis, food preservation methods, and techniques of water purification that include reverse osmosis.
Osmosis is the flow of water through a semipermeable membrane from an area of lower to higher solute concentration. This process is vital in maintaining cellular activities or homeostasis.