What is Osmosis?
The movement of water molecules across semi permeable membrane to produce a homeostatic system in cell and its environment is the process of osmosis.
Characteristic of Osmosis
Osmosis was derived from Latin which means impulse or urge; of the solvent to move uphill from lower concentration to higher concentration. The main difference between osmosis in living and non – living cells are the properties of the particular system. Osmosis in non – living cells can be demonstrated by separating the solution and water by a semipermeable membrane.
Osmosis is a type of diffusion between a solution and water when separated by a biological membrane which is permeable for solvents and restrict the entry of solutes.
Fick’s law can be theoretically applied to the diffusion where the rate of diffusion is directly proportional to the concentration gradient and area over the diffusion occurs. Experiments are done to depict the mechanism of osmosis in a living tissue where a solution and pure solvent present in two chambers A and B separated by a semi permeable membrane and observed from the initial time T. After a particular time say T’ to maintain a system equilibrium and restrain by the membrane the pure solvent enters the chamber A of solution to maintain the equilibrium. As the pure solvent enters Chamber A increasing volume of the chamber indicating the movement of the solvent from lower to higher concentration.
Water is transported by vascular tissues xylem where the nonliving tracheid are also taking up the water. In leaves mesophyll cells; the tracheid’s opens to the cells and water enters cell via Osmosis. Semipermeable part of the cells is the plasma membrane. Plasma membrane along with cellular components are protoplast. The liquid part is called as the protoplasm and other cellular components (i.e.) organelles are also separated from each other by membranes. Plant cells are specialized by carrying a vacuole and cell wall both has its specific role in plants structure.
Additionally; plasma membrane is protective and regulative in nature by the mechanism of osmosis and presence of channels and transmembrane which transports particulate compounds for cellular metabolism. Further the plant is surrounded by Rigid Cell Wall which provides a particular shape for the cell.
Vacuoles – storage part of the cells stores nutrients and water in turn maintaining the internal volume of the cell. Externally the cells are connected by rigid cellulose made cell wall mediating communication between each other cells. Inside the cell wall they are separated from other cells by intercellular spaces.
Principle of Osmosis
Osmosis works on a basic principle of chemical potential difference between 2 components separated by a semi permeable membrane. Chemical potential is the free energy available per mole of the substance in a solution. In the osmosis demonstration the pure solvent had high energy compared to the solution which had lower energy (i.e.) lower chemical potential which created a gradient to pure solvent enter the Chamber A. The potential difference arises because of the solute in the cytoplasm which are part of energy metabolic activities constantly replenishes the chemical molecules and are dynamic in nature.
Semi permeable membrane does not allow solute molecules and solute or ion uptake is mediated by ATP utilizing carrier proteins knows as active transport breaking down ATP to produce energy for ion uptake. Active transport of ions constitutes a potential difference between an internal and external environment develops a chemical potential gradient taking up water molecules from xylem. This indicates for every active uptake of ion generates a potential difference involves a passive entry of water into the cell and thereby osmosis is indirectly coupled with energy utilization.
Osmosis is Pressure Dependent
Similar experiments can be quoted to prove the pressure during osmosis. Osmotic pressure is the maximal amount of pressure developed in a system separated by a semipermeable membrane by pure water. Pressure due to osmosis is demonstrated using an osmometer; where a thistle funnel is inverted and covered with a semipermeable membrane is separated by solution A and B; where A is pure solvent and B is solution. At time T’ osmosis happens and the volume of Solution B increases.
On attaching a piston and maintaining the same volume in osmometer by producing a pressure through a piston maintains volume constant for a particular time and when the pressure in piston is increased the water flow reverses from Solution A to Solution B. The pressure of the osmosis is directly dependent on the solute concentration. Dependent on solute concentration makes the process a colligative property of a solution along with 3 other properties.
Osmosis and Turgor Pressure
Turgor pressure or the phenomenon of turgidity is maintained by the process of osmosis; involves vacuoles, protoplast wherein the water uptake in vacuole produces a basic crispness in cell structure and additionally the protoplasm as a whole requires water to maintain rigidity of plant cell thereby making the whole plant stand erect. When a cell loses its water content the leaves and stem wilts and the state is flaccid and prolonged flaccid nature of plants leads to death. To retain the structure water uptake becomes essential which is mediated by osmosis.
Importance of Osmosis
• Partially; the water uptake from soils controlled by osmosis in roots.
• Facilitate water movement from non – living part to the living part of the plant.
• Mechanical support of rigidity is provided by osmosis.
• A special ability of osmosis allows a plant to be turgid and helps in movement of ions in plants.
• Osmotic pressure produces a growth in plants.
• Opening and closing of stomata, flower is done with the help of osmosis.
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- Measuring osmosis and hemolysis of red blood cells. Adv Physiol Educ . 2017 Jun 1;41(2):298-305.