Osmosis is the result of diffusion across a semi-permeable membrane. If two solutions of different concentration are separated by a semi-permeable 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.
Semi-permeable 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.
|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.|
Contents: Diffusion and Osmosis
Process of Osmosis vs Process of Diffusion
Diffusion is the spontaneous net movement of particles or molecules from an area of their high concentration to an area of their low concentration through a semi-permeable membrane. For example, diffusing molecules will move randomly between areas of high and low concentration but because there are more molecules in the high concentration region, more molecules will leave the high concentration region than the low concentration one. Therefore, there will be a net movement of molecules from high to low concentration. Initially, a concentration gradient leaves a smooth decrease in concentration from high to low which will form between the two regions. As time progresses, the gradient will grow increasingly shallow until the concentrations are equalized.
Diffusion is a spontaneous process. It is simply the statistical outcome of random motion. Diffusion increases entropy, decreasing Gibbs free energy, and therefore is thermodynamically favorable. Diffusion operates within the boundaries of the Second Law of Thermodynamics because it demonstrates nature's tendency to wind down, as evidenced by increasing entropy.
Osmosis is the result of diffusion of water across a semi-permeable membrane. For example, if the medium surrounding the cell has a higher water concentration than the cell, then the cell will gain water by osmosis. Water molecules are free to pass across the cell membrane in both directions. The overall result is that water enters the cell and the cell is likely to swell up. If the water concentration in the medium is exactly the same, then there will be no net movement of water across the cell membrane because, water crosses the cell membrane in both directions, but the amount coming in is the same as the amount going out, so there won’t be any overall movement of water. The cell will stay the same size.
If the medium has lower concentration of water than the cell, it will lose water by osmosis. Again, water crosses the cell membrane in both directions, but this time more water leaves the cell than enters it. Therefore the cell will shrink. The movement of solvent is from the less-concentrated (hypotonic) to the more-concentrated (hypertonic) solution, which tends to reduce the difference in concentration.
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
The two types of Osmosis are:
- Reverse Osmosis: it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
- Forward Osmosis: Forward Osmosis is an osmotic process that, like reverse osmosis, uses a semi-permeable membrane to effect separation of water from dissolved solutes.
The types of diffusion are:
- Brownian motion, for example of a single particle in a solvent
- Collective diffusion, the diffusion of a large number of (possibly interacting) particles
- Effusion of a gas through small holes.
- Electron diffusion, resulting in electric current
- Facilitated diffusion, present in some organisms
- Gaseous diffusion, used for isotope separation
- Heat flow
- Knudsen diffusion
- Momentum diffusion, ex. the diffusion of the hydrodynamic velocity field
- Osmosis is the diffusion of water through a cell membrane
- Photon Diffusion
- Reverse Diffusion
- Surface diffusion