what is Osmosis, hypertonic solution, Hypotonic solution and isotonic solution. class 9th biology

Osmosis is the movement of water across a semi-permeable membrane from a solution of lesser solute concentration to a solution of higher solute concentration. The rules of osmosis can be best understood through the concept of tonicity of solutions. The term tonicity refers to the relative concentration of solutes in the solutions being compared. • A Hypertonic solution has relatively more solute. • A Hypotonic solution has relatively less solute. • Isotonic solutions have equal concentrations of solutes. When an animal cell, such as red blood cell, is placed in an isotonic solution, the cell volume remains constant because the rate at which water is entering cell is equal to the rate at which it is moving out. When a cell is placed in a hypotonic solution, water enters and cell swells and may rupture like an over-filled balloon. Similarly, an animal cell placed in a hypertonic solution will lose water and will shrink in size. So in hypotonic environments (e.g. freshwater) animal cells must have ways to prevent excessive entry of water and in hypertonic environments (e.g. seawater) they must have ways to prevent excessive loss of water. Water balance problems are somewhat different for plant cells because of their rigid cell walls. Most plant cells live in hypotonic environment i.e. there is low concentration of solutes in extracellular fluids than in cells. As a result, water tends to move first inside cell and then inside vacuole. When vacuole increases in size, cytoplasm presses firmly against the interior of cell wall, which expands a little. Due to strong cell wall, plant cell does not rupture but instead becomes rigid. In this condition, the outward pressure on cell wall exerted by internal water is known as turgor pressure and the phenomenon is turgor. In isotonic environment, the net uptake of water is not enough to make the cell turgid and it is flaccid (loose / not firm). In a hypertonic environment a plant cell loses water and cytoplasm shrinks. The shrinking of cytoplasm is called plasmolysis. #osmosis #hypertonicsolution