Osmosis and tonicity

Awais_Nasir · December 28, 2021, 4:22pm

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.” while tonicity is the ability of an extracellular solution to make water move into or out of a cell by osmosis.

Osmosis and tonicity

Have you ever gone a few days without watering a plant, only to return to discover your once-vibrant arugula wilted? If that’s the case, you’re well aware that water balance is critical for plants. When a plant wilts, water escapes from its cells, causing them to lose the internal pressure (called turgor pressure) that keeps the plant alive.

What causes water to escape the cells? As the plant loses water, the amount of water outside the cells decreases, but the amount of ions and other particles in the space outside the cells remains constant. In a process known as osmosis, a rise in solute, or dissolved particle, concentration draws water out of the cells and into the extracellular spaces.

Osmosis is defined as the net transport of water over a semipermeable membrane from a low-solute-concentration area to a higher-solute-concentration area. This may seem strange at first because we generally discuss the diffusion of dissolved solutes in water rather than the movement of the water itself.

Osmosis, on the other hand, is vital in many biological processes, and it frequently occurs at the same time as solute diffusion or transport. We’ll take a closer look at how osmosis works and how it affects cell water balance in this section.

How it works

Why does water travel from locations with lower concentrations of solutes to areas with higher concentrations? This is a difficult question to answer. Let’s take a step back and review why dispersion occurs in the first place.

Diffusion occurs when molecules move from a location of higher concentration to one of lower concentration due to probability, not because they are aware of their environment. When a substance is in the form of a gas or a liquid, its molecules are in a constant state of random motion, bouncing or sliding around one another.

If there are a lot of molecules of a substance in compartment A but none in compartment B, a molecule moving from B to A at random is extremely unlikely—possibly impossible. A molecule, on the other hand, is quite likely to migrate from point A to point B.

You may imagine all of those molecules bouncing around in compartment A, with some crossing over to compartment B. As a result, the net migration of molecules will be from point A to point B, and this will continue until the concentrations equalize.

You can imagine molecules—this time, water molecules—in two compartments separated by a membrane in the case of osmosis. Water molecules will be equally likely to travel in either direction between the compartments if none contains any solute.

However, if we add a solute to one compartment, it will affect the possibility of water molecules migrating from that compartment to the other—specifically, it will decrease this likelihood.

Why is it the case? A few different theories are floating around. The theory that appears to have the most scientific support involves solute molecules physically knocking water molecules backward and away from the membrane, making them less likely to cross1,21,2start superscript, , comma, , end superscript.

The crucial fact is that the more solute water contains, the less likely it is to pass over a membrane into an adjacent compartment, regardless of the particular mechanisms involved. This causes a net flow of water from low-solute-concentration areas to higher-solute-concentration areas.

In the beaker example above, there will be a net flow of water from the compartment on the left to the compartment on the right until the solute concentrations are nearly balanced, as shown. The hydrostatic pressure exerted by the increasing water column on the right will counteract the osmotic driving force, resulting in an equilibrium that stops short of equal concentrations.

Osmolarity

The overall concentration of solutes in a solution is referred to as osmolarity. A low osmolarity solution has fewer solute particles per liter of solution, whereas a high osmolarity solution contains more solute particles per liter of solution.

Water will migrate from the side with lower osmolarity to the side with higher osmolarity when solutions of differing osmolarities are divided by a membrane permeable to water but not to the solute.

To define relative osmolarities between solutions, three names are used: hyperosmotic, hypoosmotic, and isoosmotic. When two solutions with differing osmolarities are compared, the solution with the higher osmolarity is said to be hyperosmotic, whereas the solution with the lower osmolarity is said to be hypoosmotic. Isoosmotic refers to when two solutions have the same osmolarity.

Summary:

When you eat or drink something, it passes via your mouth, esophagus, and into your stomach. Chyme is a mixture of food and stomach fluids; this is where osmosis occurs. Your blood then flows to your kidneys, where it is processed. Osmosis is a process that draws water out of cells and into extracellular spaces. Our fingers’ skin wrinkles as a result of nerves, rather than osmosis. In dialysis machines, fluid from the blood passes through a semipermeable membrane. Osmosis is the net transport of water over a membrane from a low-solute-concentration area to a higher concentration.

Tonicity

It’s often useful to consider how solutions will affect water movement into and out of cells in healthcare settings and biology labs. Tonicity refers to an extracellular solution’s ability to cause water to migrate into or out of a cell via osmosis.

Tonicity differs from osmolarity in that it considers both relative solute concentrations and the permeability of the cell membrane to those solutes. To explain whether a solution will cause water to move into or out of a cell, three terminologies are used: hypertonic, hypotonic, and isotonic.

When a cell is placed in a hypertonic solution, it will lose volume due to a net flow of water out of the cell. If the concentration of solutes in a solution is higher than that inside the cell, and the solutes cannot cross the membrane, the solution is hypertonic to the cell.

When a cell is placed in a hypotonic solution, it will grow volume due to a net flow of water entering the cell. The solution is hypotonic to the cell if the solute concentration outside the cell is lower than inside the cell and the solutes cannot cross the membrane.

When a cell is submerged in an isotonic solution, there is no net movement of water into or out of it, and the volume of the cell remains constant. The solution is isotonic to the cell if the solute concentration outside the cell is the same as inside the cell and the solutes cannot cross the membrane.

Tonicity in living systems

When a cell is submerged in a hypertonic solution, water escapes, and the cell shrinks. There is no net water flow in an isotonic environment, hence the cell size does not vary. Water will enter a cell when it is placed in a hypotonic environment, causing it to swell.

Isotonic conditions are excellent for red blood cells, and your body’s homeostatic (stability-maintaining) processes keep these conditions constant. A red blood cell may balloon up and possibly explode if placed in a hypotonic solution, while it will shrivel—making the cytoplasm compact and its contents concentrated—and may die if placed in a hypertonic solution.

A hypotonic extracellular solution, on the other hand, is appropriate for a plant cell. The plasma membrane can only expand to the rigid cell wall’s limit, preventing the cell from bursting or lysing. Water will enter a cell until its internal pressure—turgor pressure—prevents further influx.

It is critical for the plant’s health to maintain this balance of water and solutes. If a plant isn’t watered, the extracellular fluid becomes isotonic or hypertonic, forcing water to escape from the cells.

This causes a drop in turgor pressure, which you’ve probably noticed as wilting.
Plasmolysis occurs when the cell membrane detaches from the cell wall and constricts the cytoplasm under hypertonic conditions. Tonicity is a concern for all living things, but especially for those without rigid cell walls who live in hypertonic or hypotonic environments.

Paramecia (shown below) and amoebas (shown below), which are protists without cell walls, may have specialized structures termed contractile vacuoles. A contractile vacuole collects and pumps out surplus water from the cell, preventing the cell from lysing as it absorbs water from its hypotonic environment.

Frequently Asked Questions:

1: What is osmosis in biology?

The transfer of a solvent via a semipermeable membrane that separates two solutions with different solute concentrations is known as osmosis. The solvent transfers from a solution with a lower solute concentration to a solution with a greater solute concentration during osmosis.

2: How osmosis works in the human body?

Chyme is absorbed into the small intestine. This is where osmosis occurs. The concentration of chyme is higher than that of the epithelial cells that line your intestines. To achieve homeostasis, water enters these cells through semipermeable membranes, bringing with it tiny nutrients.

3: What is the importance of osmosis in our daily life?

For starters, it aids the movement of essential materials into and out of cells. Through osmosis, important nutrients and waste dissolved in the water move into and out of the cell. Plants absorb water through their roots and use osmosis to transfer it throughout their bodies. Plants’ stomata are open and close with the help of osmosis.

4: What is osmosis in the cell membrane?

Osmosis is a process in which water diffuses across cell membranes. Osmosis is the process of transferring water through a semipermeable membrane, with the solvent (for example, water) going from a low solute (dissolved substance) concentration to a high solute concentration.

5: How does osmosis occur in the body?

Chyme is absorbed into the small intestine. This is where osmosis occurs. The concentration of chyme is higher than that of the epithelial cells that line your intestines. To achieve homeostasis, water enters these cells through semipermeable membranes, bringing with it tiny nutrients.

6: How do cells get rid of co2?

The lungs and respiratory system allow oxygen from the air to enter the body while also allowing carbon dioxide from the air to leave the body. Carbon dioxide is produced by cells as they perform their functions, and it flows out of the cells into the capillaries, where it dissolves in the blood plasma.

7: What is osmosis Class 9 biology?

Osmosis is the passage of water molecules or a solvent through a semi-permeable membrane from an area of low water concentration to a region of high water concentration of a solute. Osmosis is a fundamental biological process that takes place in liquids, supercritical liquids, and gases.

8: What is osmosis in animals?

Osmosis is the net transport of water molecules through a partially permeable membrane from an area of higher water potential (dilute solution) to a region of lower water potential (concentrated solution). Animal cells, like plant cells, can lose and acquire water through osmosis.

9: What is osmosis Class 11?

Osmosis is the process of water molecules diffusing through a semi-permeable barrier from an area of higher chemical potential (or concentration) to a region of lower chemical potential until equilibrium is attained. Both the pressure and concentration gradients influence the net direction and rate of osmosis.

10: What is water ultrafiltration?

Ultrafiltration (UF) is a method of water purification that involves forcing water through a semipermeable membrane. Water and low-molecular-weight solutes filter through the membrane to retentate the side.

Conclusion:

Tonicity refers to an extracellular solution’s ability to cause water to migrate into or out of a cell via osmosis. It considers relative solute concentrations and the permeability of the cell membrane to those solutes. Tonicity differs from osmolarity in that it considers both solute concentration and membrane permeability. Isotonic conditions are excellent for red blood cells, and your body’s homeostatic processes keep these conditions constant.

Osmosis and tonicity