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Imbibition

Transport In Plants of Class 11

Imbibition and Characteristics of Imbibition

Water is most important part of protoplasm. It makes 80-90% of the fresh weight in herbaceous plants and 50% of fresh weight in woody plants. In plants osmoregulation is a function of absorption, transport and retention of water in their bodies. Water is lost by transpiration.

IMBIBITION

A dry wooden piece when soaked in water shows considerable swelling and sometimes leads to considerable increase in volume, which is due to imbibition. e.g., wooden doors in rainy season swell due to imbibition phenomenon.

Due to imbibition, sometimes a considerable pressure is developed which is known as imbibitional pressure, e.g., a wooden piece driven into a hole in the rock on imbibition swells so much that the pressure developed by it breaks the rock.

First step in imbibition is adsorption, i.e., attachment of liquid on the surface.

Adsorption is the property of colloids and hence the materials which have high proportion of colloids, are good  imbibants. 

It is for this reason, the wood (plant material) is good imbibant, because it contains proteins, cellulose and starch as colloidal substances.

Characteristics of Imbibition

  • Volume is increased, in the imbibant (solid).
  • Heat is produced and is known as heat of wetting.
  • Pressure is developed called imbibition pressure (matric potential)

Significance of Imbibition

  • It is the first step of water absorption.
  • Imbibition is also the first phenomenon in germination of seeds.

Factors influencing the rate of imbibition

  •  Nature of imbibant: Imbibition capacity is maximum in phycocolloids followed by protein, starch & cellulose.
  • Surface area of imbibant: If more surface area of the imbibant is exposed and is in contact with liquid, the imbibition will be more.
  • Temperature: Increase in temperature causes an increase in the rate of imbibition.
  • Concentration of Solutes: Increase in the concentration of solutes in the medium decreases imbibition.

Diffusion

Diffusion may be defined as, “movement of particles of a matter due to their own kinetic energy”.

Diffusion is always from region of higher concentration of particles of a matter to region of lower concentration.

Diffusion of particles of one substance is independent of diffusion of particles of another substance.

i.e., diffusion of each substance is according to its own concentration gradient.

Factors Affecting Diffusion

  • Temperature : Directly proportional factor, because temperature increases kinetic energy of particles.
  • Density : Hydrogen diffuses 4 times faster than O2, according to Graham’s law of diffusion, i.e., rate of diffusion of a substance is inversely proportional to square root of their densities.
  • Concentration gradient : More is the concentration gradient (difference in concentration on two sides), more will be the rate of diffusion i.e. Rate of diffusion is directly proportional to the difference of diffusion pressure at the two ends of system and inversely proportional to the distance between two.
  • Concentration of medium through which diffusion occurs : More dense is the medium, lesser will be the rate of diffusion.

Types Of Membranes

  • Permeable membrane,
  • Impermeable membrane,
  • Semipermeable membrane and
  • Selectively or differentially permeable membrane.
  •  Permeable : Which allow all solutes and solvents to pass through them are called permeable membranes, e.g., cellulosic cell walls and lignified cell walls.
  • Impermeable : Which do not allow any solute or solvent through them are called impermeable membranes, e.g., cutinized cell wall and suberized cell walls.
  • Semipermeable : Which allow all solvents but no solute to pass through them are called semipermeable membranes, e.g., Colloidal membrane, parchment membrane, egg membrane cellophane, copper ferrocyanide membranes.
  •  Selectively permeable : Which allow all solvents and few selected solutes to pass through them are called selectively or differentially permeable membranes, e.g., all biological membranes, plasma membrane, tonoplast, and all membranes surrounding different cell organelles.
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