Osmosis and diffusion are the two distinct forms of passive transport that play an essential role in transporting molecules through and out of the cell. Students are mostly asked to clarify the similarities and disparities between osmosis and diffusion or to compare the two modes of transport and contrast them.
You need to learn the meanings of osmosis and diffusion to address the issue, and fully appreciate what they mean.
Osmosis vs Diffusion
The main difference between Osmosis and Diffusion is their dependency and requirements. Osmosis relies on the number of dissolved solute shreds in the solution. Nonetheless, the diffusion relies upon the existence of additional components. The former needs water for the activity of particles. Whereas the latter move without the requirement of water.
Comparison Table Between Osmosis and Diffusion (in Tabular Form)
| Parameter of Comparison | Diffusion | Osmosis |
|---|---|---|
| Semi-permeable membrane | The availability of a partly-permeable membrane is essential | For this process to occur, the availability of a partly-permeable membrane is essential |
| Hydrostatic and Turgor pressure | Normally hydrostatic pressure and turgor pressure are not important in diffusion. | Osmosis is opposed by hydrostatic pressure and turgor pressure. |
| Pressure, water, and solute potentials | Pressure potential, water potential, and solute potential do not affect diffusion. | The solute potential is necessary for osmosis to take place. |
| Reliability on other molecules | Diffusion relies mainly upon the existence of other molecules. | Osmosis relies primarily on the number of dissolved solute particles in the solvent. |
| Medium | This is a versatile process and it can take place in any type of medium regardless of whether it is a liquid, gaseous or solid medium. | A liquid medium is necessary for this process to take place |
What is Osmosis?
Osmosis, a form of diffusion that involves water flow through a membrane that is partially-permeable, from a zone that has a high concentration of water to a low concentration zone.
Osmosis is a process that occurs in all the cells. For example, in the case of red blood cells when put in water, they must let the water flow through its membrane.
The red blood cell simply shrinks when putting in a concentrated solution of sugar, as the water travels through osmosis into the region with lower concentration. For this reason, when seen through a microscope, the cells look shrank.
Luckily, this rarely occurs inside the bloodstream, as the kidneys ensure that the blood content is the same as the water content within the red blood cell.
Like the red blood cells, the cells in plants on the exterior of the cell membrane have a somewhat thicker and more stable cell structure. It helps the plant cells to consume a lot of water without bursting through osmosis.
Plants would not be able to remove water from the soil without osmosis. When osmosis allows plant cells to expel so much water, they become less compact and gradually the membrane shrinks.
What is Diffusion?
This process refers to the passive transfer of substances from a zone that consists of highly molecular concentration to a zone of low concentration. When it occurs between cells is the mode of transfer of small substances via the cell membrane.
Molecules are always continuously moving. Temperature, a popular measure for people in their everyday lives, is closely linked to this motion. This is a measurement of the molecules ‘average kinetic energy (average) in a substance.
The molecular energy induces spontaneous motion that in effect stimulates diffusion. Collisions between molecules are common.
Diffusion renders air quality standardized by redistributing chemical compounds, such as atmospheric oxygen, till equilibrium is reached. The factors affecting this process are temperature, distance particles must travel and concentration gradient
Here are some instances of diffusion. Spraying a scent in a space will make things feel good for a moment, but the odor molecules will be dispersed overtime before their frequency becomes imperceptible to the human nose.
Another excellent illustration of diffusion is dipping a color in a container of water, which can alter the appearance of the entire solution (water).
As there are various conditions for diffusion, scientists have identified several forms of this process.
- Simple diffusion: This is where materials are transferred without protein assistance.
- Facilitated diffusion: Needs transport proteins to move materials via the membrane of a cell.
- Dialysis: is the diffusion of solutes through a membrane that is partially permeable.
- Osmosis: This is referred to as water diffusion which is generally characterized as a solvent of choice over a selectively permeable membrane in all living systems.
Main Differences Between Osmosis and Diffusion
- Osmosis involves solvent movements from lower to higher concentration regions while diffusion is characterized by solvent movement from higher to lower concentration regions.
- Diffusion can be observed in any combination of a mixture, even a partially-permeable membrane, whereas osmosis is only observed across a partially permeable membrane.
- Solvent and solute materials can travel during diffusion while only the solvent materials are allowed to pass through the membrane in osmosis and in this situation they are water molecules.
- During osmosis, particle movement happens only in one direction while the movement of particles happens in all directions during diffusion.
- Once the osmosis process is in effect, extra pressure on the solution side may either halt or reverse the process while the diffusion process can neither be halted nor reversed.
Conclusion
For both non-living and living organisms, diffusion is a common and essential mechanism. Substances such as water and minerals have to move across the partially permeable membrane to reach and leave a cell.
One of the mechanisms enabling this is diffusion. A semi-permeable membrane is one that enables other substances to move quickly through it while other substances move through it so slowly.
These two forms of transport mechanisms occur to facilitate the shifting of molecules in and out of the cell, namely osmosis and diffusion. They are both passive transport systems since they do not need any extra energy to run.
The key distinguishing factor between the two processes is the environment they occur in. Osmosis can occur in a liquid environment only, however, diffusion can take place in all three media (solid, liquid, and gas).
Moreover, osmosis requires a partially permeable membrane, which does not apply for diffusion. An instance of osmosis is the uptake of water into plants.
Diffusion can be seen when a drop a certain color is applied to a bottle of water and the entire water content gradually becomes colored.
References
- https://trid.trb.org/view/354006
- https://www.lifescied.org/doi/pdf/10.1187/cbe.11-04-0038
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC541081/