Osmosis is the movement of solvent from higher water potential to lower water potential through a semi-permeable membrane until equilibrium state is maintained. Whereas, diffusion is the movement of solute/ions/solvent particles from region of higher concentration to the region of lower concentration until evenly distributed throughout the available spaces.
In osmosis higher water potential refers to solutions having high concentration of water and are dilute while lower water potential refers to solutions having low concentration of water or concentrate solutions. Water is universal solvent so, water is major solvent in many solutions and during the process of osmosis in plants. Osmosis can also be defined as the movement of solvent molecules from higher chemical potential to lower chemical potential through a semi-permeable membrane. Semi-permeable membrane is special type of membrane which allows only solvent molecules and selective solute to pass through it. It is also called as differentially permeable membrane.
Some examples of semi-permeable membrane are egg membrane, plasma membrane, fish bladder, parchment paper, animals bladder etc. Under normal conditions, diffusion occurs faster than osmosis. At normal temperature and pressure density is greater in solids and least in gases. so, rate of diffusion in gases is fastest and slowest in solids.
|It occurs by movement of solvent molecules from higher water potential(i.e dilute solution) to lower water potential solution(i.e concentrate solution) until equilibrium is maintained.||It occurs by movement of solute/ions/solvent from higher concentrated region to lower concentrated region until evenly distributed throughout the available space.|
|It occurs only in liquid medium by the movement of solvent molecules between their liquid solutions.||
It occurs in all 3-types of medium i.e solid, liquid & gases by movement of solute/ion as well as solvent molecules.
|It require biological membrane (e.g semi-permeable membrane).||It does not requires any biological or physical membrane. The rate of diffusion is highest in vacuum.|
|It is unidirectional and occurs only in one direction.||It is multidirectional and may occurs in all available directions.|
|The solvent molecules move toward higher concentrated solution resulting increase in quantity.||There is no such markable increase in quantity to solution or to diffusing region as it is distributed in the available space. But, it may increase density to certain extent.|
What is so special about osmosis compared with diffusion?
Osmosis is a special type of diffusion. It is the scattering of only solvent molecules while there is scattering of both solute and solvent in diffusion to maintain concentration difference. Osmosis requires semi-permeable membrane but diffusion does not requires any membrane or medium to happen. In osmosis, water or solvent moves from high water potential to low water potential while movement of solute and solvent occurs from high concentrate region to low concentrate region in diffusion.
Similarities between osmosis and diffusion
Both are passive transport processes which does not require ATPs or energy during the process.
They both tends to maintain concentration difference between the two solutions or regions.
Examples of osmosis
opening and closing of guard cells of stomata, absorption of water from soil by roots, germination of seeds by absorbing water, maintenance of water equilibrium inside cells and tissues, brusting and dying of bacterias inside prickles, vomiting blood by leeches on sprinkling salt on its body surface, swelling of legs and fingers during rainy season due to frequent touch with water etc.
Examples of diffusion
spreading of perfumes odour in whole room while spraying on body, spreading a drop of ink throughout the water of the beaker, dissolving copper sulphate in water, dissolving and shaking salt into water, diffusion of coal and cigarette smoke in air, sweetening of water after putting sugar in it, delicious food aroma from kitchen, diffusion of oxygen and carbondioxide in lungs etc.
Application and significance of osmosis
- Plant absorbs water from soil by the process of osmosis.
- The regulation of water between cells of plant is due to osmosis which maintains water equilibrium.
- Germination of seed is due to osmosis. Seed absorbs water molecules from soil surrounding resulting into swelling up. When it gets required amount of water it germinates into embryo.
- Cells and fruits have definite shape due to the turgor pressure resulting from osmosis.
- During drought conditions, osmotic pressure generated inside cells of plant protect it from being dried up.
- There are different types of osmosis. Out of which, forward and reverse osmosis have great applications in our daily life.
Application and significance of diffusion
- The exchange of CO2 and O2 during photosynthesis and respiration occurred by the process of diffusion.
- During transpiration, excess water in vapour form is lost from exposed aerial parts of plant by process of diffusion.
- It is an effective means of transportation of substances in very short distance like between cells and within cells.
- During uptake of salts by roots, the ions are absorbed by this process.
- It is used for carburisation to increase hardness of steel, doping of semiconductor, diffusion imaging in detecting stroke etc.
Factors affecting rate of osmosis
The factors affecting rate of osmosis are:
Temperature: When pure water at different temperature is separated by semipermeable membrane, the molecules and solvents moves from higher temperature region to lower temperature region. From here, it's clear that temperature induce osmosis from higher temperature solution to lower temperature solution.
Pressure: When water at different pressure is separated by semipermeable membrane, water molecules moves from higher pressure region to lower pressure region.
Concentration of solutions: Rate of osmosis is directly proportional to the difference of concentration of two solutions. When concentration of one solution increases, solvent (or water molecules) from lower concentration solution diffuses faster into higher concentration solution and maintain equilibrium to each solution.
Hydrostatic and turgor pressure decreases rate of osmosis.
Factors affecting rate of diffusion
Temperature: When temperature is increased, the molecules gains energy in the form of kinetic energy. As K.E of ions increases solute particles moves faster thus, rate of diffusion increases by increasing temperature.
Density of medium: Low density medium increases rate of diffusion while high density medium decrease rate of diffusion speed. High density medium acts as barrier during diffusion of solute/ions.
Density of diffusing particles: According to Grahams law of diffusion, rate of diffusion is inversely proportional to the square root of the diffusing particles. So, gases having high density diffuses slower than gases with low density. And as we know that mass is directly proportional to density(Mass=volume x density) massive gases diffuses slower than lighter gases.
Concentration: The rate of diffusion depends on the concentration of molecules. Higher the concentration of diffusing molecules, rapid is the rate of diffusion.