PLANT PHYSIOLOGY-2 BY NIKHIL PURANIK
ABOUT MIE MY NAME IS NIKHIL PURANIK PURSUING B.E IN MECHANICAL ENGINEERING FROM RNSIT LIVE IN BENGALURU PROFILE :https://unacademy.com/user/nikhilrpuranik
TOPICS COVERED PLANT WATER RELATIONS WATER POTENTIAL OSMOSIS PLASMOLYSIS IMBIBITION LONG DISTANCE TRANSPORT OF WATER HOW DO PLANTS ABSORB WATER
PLANT-WATER RELATIONS Water is essential for all physiological activities of the plant and plays a very important role in all living organisms. It provides the medium in which most substances are dissolved. The protoplasm of the cells is nothing but water in which different molecules are dissolved and (several particles) suspended. Terrestrial plants take up huge amount water daily but most of it is lost to the air through evaporation from the leaves, i.e., transpiration.
WATER POTENTIAL The greater the concentration of water in a system, the greater is its kinetic energy or 'water potential. Hence pure water will have the greatest water potential. solute potential (Ws) and pressure potential ( ) are the two main components that determine water potential. If two systems containing water are in contact, random movement of water molecules will result in net movement of water molecules from the system with higher energy/water potential to the one with lower energy water potential. This is diffusion.
If some solute is dissolved in pure water, the solution has fewer free water and the concentration of water decreases, reducing its water potential. Hence, all solutions have a lower water potential than pure water; the magnitude of this lowering due to dissolution of a solute is called solute potential or For a solution potential) at atmospheric pressure (water potential)Uw= (solute a pressure greater than atmospheric pressure is applied to pure water or a solution, its water potential increases. Pressure can build up in a plant system when water enters a plant cell due to diffusion causing a pressure built up against the cell wall, it makes the cel this increases the pressure potential Wp. Y,=Y,+Y,
OSMOSIS Osmosis is the term used to refer specifically to the diffusion of water across a differentially-or semi-permeable membrane. Osmosis occurs spontaneously in response to a driving force. The net direction and rate of osmosis depends on both the pressure gradient and concentration gradient.
SoluteO molecule Water Semi-permeable membrane Water will move from its region of higher chemical potential (or concentration) to its region of lower chemical potential until equilibrium is reached. At equilibrium the two chambers should have the same water potential.
PLASMOLYSIS The behaviour of the plant cells (or tissues) with regard to water movement depends on the surrounding solution If the external solution balances the osmotic pressure of the cytoplasm, it is said to be isotonic If the external solution is more dilute than the cytoplasm, it is hypotonic If the external solution is more concentrated, it is hypertonic. Cells swell in hypotonic solutions and shrink in hypertonic ones.
Plasmolysis occurs when water moves out of the cell and the cell membrane of a plant cell shrinks away from its cell wall H,o When the cell (or tissue) is placed in an isotonic solution, there is no net flow of water towards the inside or outside If the external solution balances the osmotic pressure of the cytoplasm it is said to be isotonic. When water flows into the cell and out of the cell and are in equilibrium, the cells are said to be flaccid.