PLANT WATER RELATION

PLANT WATER RELATION:

 

Introduction:

·         Water is the most abundant constituent of all physiologically active plant cells. For example, leaves have water content which lie mostly within a range of 55% -85% of their fresh weight.

·         Succulents’ parts of plants contain approx. same proportion of water and even largely non-living tissue as wood which may be 30-60% water on a fresh weight basis.

·         Smallest water contents in living parts of the plant occur mostly in dormant structure such as mature seeds and spores.

·         The great bulk of the water in any plant constitutes a unit system. This water is not in static condition; rather it is part of a hydrodynamic system, which in terrestrial plants involves absorption of water from the soil, its translocation throughout the plant and its less to the environment; principally in the process known as transpiration.

IMBIBITION:

·         Imbibition traces back to latin “imbibere”, a verb whose meaning “to drink in” including absorption of liquids, consuming drink and appropriating ideas.

·         It is the phenomenon of adsorption of water or any other liquid by the solid particles of a substance without forming a solution.

·         It is the action or process of assimilating, taking into solution or taking in liquid especially the taking up of fluid by colloidal system.

·         Imbibition is a diffusion process in which water is absorbed by solids, causing them to enormously increase in volume.

·         Imbibition is along the concentration gradient and depends upon affinity between adsorbent and liquid being absorbed.

·         Examples: Imbibition of water by seeds that causes seedling to emerge out of soil, swelling of wooden door during rainy season , swelling of raisin when soaked in water.

·         Imbibition is a type of diffusion where water is absorbed by solid particles called colloids, without forming a solution causing an enormous increase in volume. To define, the absorption of water by hydrophillic colloids, imbibitions is known.

·         Various factors of imbibitions including pressure, pH of medium, pressure, texture of imbibant and the affinity of the imbibant for the imbibate.

·         The solid substance or absorbent which take part in imbibition are called imbibants and the liquid is imbibed is known as imbibate. Example is absorption of water by seed or drywood.

·         Capacity of imbibing will differ in different imbibants. For instance consider protein, since it is a hydrophilic colloids it will have maximum imbibing capacity.

 

Features of Imbibition :

·         Adsorption

·         Water potential

·         Water potential gradient

·         Heat of wetting

·         Increase in volume

Condition necessary for imbibitions:

There are three conditions which are necessary for imbibitions process:

·         A water potential gradient should occur between imbibant and the liquid imbibe.

·         There should be some force of attraction between imbibant and imbibed liquid.

·         Increase in temperature brings about an increase imbibition.

Importance of imbibitions to plants:

·         It is the initial step in seed germination.

·         Imbibition causes swelling of seeds and results in breaking of testa.

·         It is dominant in the initial stage of water absorption by roots.

·         The water move into ovules which are ripened into seeds by imbibitions.

OSMOSIS:

·         Word is originated from the Latinized form of now absolute“osmose”

·         The movement of water molecule through a semipermeable membrane from the region of higher water concentration to the region of lesser water concentration is called osmosis.

·         When two solution of different concentration are separated by a semi-permeable membrane, the diffusion of solvent will take place from less concentration solution into the more concentrated solution, till both the solution attain equal concentration. The semi-permeable membrane allows only solvent and not the solute to pass through it. The phenomenon of osmosis can be demonstrated by thistle funnel experiment.

·         Osmosis is naturally occurring phenomenon and one of the most important processes in nature. It is a process in nature. It is a process where weaker saline solution will tend to migrate to a strong saline solution. Example, plant roots absorb water from the soil, kidney absorb water from our blood.

·         Osmosis is specialized use of diffusion that involves thee passive transport of water. In osmosis water moves through selectively permeable membrane from a region of higher concentration to a region of its lower concentration. The membrane selectively allows passage of certain types of molecule while restricting others.

·         If two solution of different concentration are separated by semi-permeable membrane which is permeable to the smaller solvent molecule but not to the larger solute molecule then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is known as osmosis.

·         Osmosis is of great importance in biological processes where the solvent is water. The transport of water and other molecule across biological membrane is essential to many processes in living organisms. The energy which derives the process is usually known as osmotic pressure.

·         Osmosis is selective diffusion process derived by the internal energy of the solvent molecule. It is convenient to express the available energy per unit volume in terms of osmotic pressure.

·         If there is pure water on both the sides of membrane then the osmotic pressure would be zero. But if the normal human blood were on right side of the membrane, the osmotic pressure would be about 7atm.

·         The net direction and rate of osmosis depends upon pressure gradient and concentration gradient. Net movement of water molecule through semi-permeable membrane from an area of higher water potential to an area of lower water potential.

·         Water moves from higher concentration to lower concentration until equilibrium is achieved.

·         The two chambers across semi-permeable membrane have the same water potential at equilibrium.

·         When an animal cell is placed in hypotonic solution surrounding the water molecule will move into the cell causing the cell to swell. If osmosis continues and become excessive the cell will eventually burst. In a plant cell, excessive osmosis is prevented by the cell wall, stabilizing the cell. Osmotic pressure is main cause of support in plants. However, if a plant cell is placed in hypertonic solution surrounding the cell wall cannot prevent the cell from losing water. It results in shrinking or cell becoming flaccid.

REVERSE OSMOSIS:

·         It is a technology that is used to remove a large majority of contaminants from water by pushing the water under pressure through semi-permeable membrane.

How does reverse osmosis works?

RO works by using a high pressure pump to increase the pressure on the salt side of the RO and force the water across semi-permeable membrane. RO membrane leaving almost 95%-99% of dissolved salts behind in the reject stream. The amount of pressure required depends on the salt concentration of the feed water. The more concentrated the feed water, the more pressure is required to overcome the osmotic pressure. The desalinated water I.e. demineralized or deionized, is called permeate (or product) water. The outer stream that carries the concentrated contaminants that didn’t pass through the RO membrane is called the reject (or concentrated) stream.

                                     As the feed water enters the RO membrane under pressure(enough pressure to overcome osmotic pressure) the water molecule pass through the semi-permeable membrane of the salts and other contaminants are not allowed to pass and are discharged through the reject stream (also known as concentrate or brine stream) which goes to the drain or can be fed back into the feed water supply in some circumstances to be recycled through the RO system to save water. The water that makes it through the RO membrane is called permeate or product water and usually around 95-99% of the dissolved salts removed from it.

PLASMOLYSIS:

·         Plasmolysis is defined as the process of contraction or shrinkage of the protoplasm of a plant cell, occurred due to loss of water in the plant cell. It is one of the outcome of osmosis and rarely occur in nature.

·         Scientific definition of plasmolysis is stated as the contraction of the protoplasm of cells within plants due to the loss of water through osmosis. It is when the cell membrane peels off of the  cell wall and the vacuole collapses when placed in a hypotonic solution.

·         When a plant cell is placed in concentrated salt solution water concentration inside the cell is greater than that which is outside the cell. Therefore, water moves through the cell membrane into the surrounding medium. Ultimately, the protoplasm separate from the cell wall and assumes spherical shape. It is called plasmolysis.

·         Deplasmolysis is the process, where a plasmolysed cell is placed in hypotonic solution (i.e. solution having solute concentration lower than the cell sap), the water moves into the cell because of the higher concentration of water outside the cell than in the cell. The cell then swells to become turgid.

·         If we placed living cell in isotonic solution (i.e. both solution have same amount of solute concentration), there is no net flow of water towards the inside or outside. Here, the water moves in and out of the cell and is in equilibrium, so the cells are said to be flaccid.

·         When a plant cell is placed in hypertonic solution, the plant cell loses water and hence it loses the turgor pressure. This makes the cell flaccid. The plant cell wilts in this condition. Further water loss results in plasmolysis.

·         At this point, the pressure decreases to an extent where the protoplasm of the cell peels away from the cell wall. This lowers gap between the cell wall and the membrane.

·         This can led to cytorrhysis or complete collapse of the cell wall.

·         Plasmolysis can be reversed by putting the cell in hypotonic solution.

·         Plant cells full of water are known as turgid cells, they exert turgor pressure on each other. The cell’s rigid cell wall keeps them from bursting. Unlike plant cell, animal cells do not have a cell wall in addition to their cell membrane. When animals are placed in a hypotonic solution and too much water rushes in, they will lyse or burst.

Types of Plasmolysis:

Plasmolysis is basically of two types:

        I.            Concave plasmolysis: It is a process that can usually be reversed, if the cells placed in hypotonic solution, which will cause water to rush back into the cell. During concave plasmolysis the protoplasm and the plasma membrane shrink away from the cell wall is placed due to the loss of water, the protoplasm is then called protoplast once it has started to detach from the cell wall.

      II.            Convex plasmolysis: Convex plasmolysis is more severe than concave palsmolysis. When a cell undergoes complex plasmolysis, the plasma membrane and protoplast loose so much water that they completely detach from the cell wall. The cell wall collapses in a process called cytorrhysis. Convex plasmolysis cannot be reversed and results in the destruction of the cell.

·         Plasmolysis can be conveniently demonstrated in plant cells under microscope containing colored cell sap since the contracting protoplasm can now be readily distinguished in the cell matrix.

·         When the turgor pressure becomes equal to the osmotic pressure, the suction pressure of such a cell is zero and the cell has taken up maximum amount of water from the surrounding medium. Such a cells is known as turgid and the phenomenon associated with it, turgidity.

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