Osmosis is the result of diffusion across a semipermeable membrane. If two solutions of different concentration are separated by a semipermeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is called osmosis. At the cellular level, both processes are types of passive transport.

Semipermeable membranes are very thin layers of material that allow small molecules, like oxygen, water, carbon dioxide, ammonia, glucose, amino-acids, etc., to pass through. However, they do not allow larger molecules, like sucrose, protein, etc., to pass through.

Comparison chart

Diffusion

Osmosis

What is it? Diffusion is a spontaneous movement of particles from an area of high concentration to an area of low concentration. (ex. tea flavoring moving from an area of high to low concentration in hot water.) Osmosis is the spontaneous net movement of water across a semipermeable membrane from a region of low solute concentration to a solution with a high solute concentration, down a solute concentration gradient.
Process Diffusion mainly occurs in gaseous state or within gas molecules and liquid molecules.(e.g. The molecules of 2 gases are in constant motion and if the membrane separating them is removed the gases will mix because of random velocities.) It occurs when the medium surrounding the cell has a higher water concentration than the cell. The cell gains water along with important molecules and particles for growth. It also occurs when water and particles move from one cell to another.
Importance To create energy; Helps in exchange of gases during respiration, photosynthesis, and transpiration. In animals, osmosis influences the distribution of nutrients and the release of metabolic waste products. In plants, osmosis is partially responsible for the absorption of soil water and for the elevation of the liquid to the leaves of the plant.
Concentration Gradient Goes from a high concentration gradient to a low concentration gradient Moves down concentration gradient
Water Doesn’t need water for movement Needs water for movement
Examples Perfume or Air Freshener where the gas molecules diffuse into the air spreading the aroma. Movement of water into root hair cells.

Process of Osmosis vs. Diffusion

The process of diffusion. Some particles (red) are dissolved in a glass of water. Initially, the particles are all near one corner of the glass. When the particles all randomly move around ("diffuse") in the water, they eventually become distributed randomly and uniformly.
The process of diffusion. Some particles (red) are dissolved in a glass of water. Initially, the particles are all near one corner of the glass. When the particles all randomly move around ("diffuse") in the water, they eventually become distributed randomly and uniformly.

Diffusion occurs when the spontaneous net movement of particles or molecules spreads them from an area of high concentration to an area of low concentration through a semipermeable membrane. It is simply the statistical outcome of random motion. As time progresses, the differential gradient of concentrations between high and low will drop (become increasingly shallow) until the concentrations are equalized.

Diffusion increases entropy (randomness), decreasing Gibbs free energy, and therefore is a clear example of thermodynamics. Diffusion operates within the boundaries of the Second Law of Thermodynamics because it demonstrates nature's tendency to "wind down", to seek a state of less concentrated energy, as evidenced by increasing entropy.

Osmosis is the process of diffusion of water across a semipermeable membrane. Water molecules are free to pass across the cell membrane in both directions, either in or out, and thus osmosis regulates hydration, the influx of nutrients and the outflow of wastes, among other processes.

Osmosis in a plant cell
Osmosis in a plant cell

For example, if the medium surrounding the plant or animal cell has a higher water concentration than the cell, then the cell will gain water by osmosis. The overall result is that water enters the cell and the cell is likely to hydrate and swell. If the medium has lower concentration of water than the cell, it will lose water by osmosis as this time more water leaves the cell than enters it. Therefore the cell will shrink. If the water concentration in the medium is exactly the same then the cell will stay the same size while that concentration balance remains. In every situation, the movement of solvent is from the less-concentrated (hypotonic) to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentration (equalization).

Differences in Function

While osmosis influences the distribution of nutrients and the release of metabolic waste products in animals; in plants, osmosis is partially responsible for the absorption of soil water and for the elevation of the liquid to the leaves of the plant.

Diffusion can occur through a cell membrane, and the membrane allows small molecules like water (H2O), oxygen (O2), carbon dioxide (CO2), and others to pass through easily. Hence while osmosis helps the plants in absorbing water and other liquids, diffusion helps other molecules to pass through and hence both facilitate the photosynthesis process. Both processes help plants to create energy and other important nutrients.

Different Types of Osmosis and Diffusion

Osmotic effect of different solutions on blood cells
Osmotic effect of different solutions on blood cells

The two types of Osmosis are:

The types of diffusion are:

References

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