Imbibition by Raisins

Objective

The objective of doing this experiment is to determine the percentage of water imbibed by raisins.

The Theory

Raisins when soaked in water swell up due to imbibition. As a result of absorption or imbibition of water, the size of the raisins increases. The difference in mass between the swollen and dry raisins gives the amount of water imbibed by the raisins.

Transportation of water in plants

Water is the most important constituent of plants and is essential for the maintenance of life, growth and development. Transportation of water into and through a plant takes place by different processes like osmosis, diffusion and imbibition.

What is Imbibition?

Imbibition is the process of adsorption of water by substances without forming a solution. Swelling of seeds when immersed in water is an example of imbibition. Imbibition is the temporary increase in the volume of the cell. Imbibition is a passive transport of materials that does not require energy during the process.

The substance that imbibes water is called imbibant and the liquid which is imbibed is called adsorbent. The process of imbibition occurs mainly due to the presence of hydrophilic or lyophilic colloids. Water is imbibed through the sub microscopic capillaries present on the surface of the body. Substances such as cellulose and starch are hydrophilic and are imbibants. (Hydrophilic means ' water loving, or readily absorbing moisture' .)

The movement of water into the plant parts continues until a dynamic equilibrium is attained. Imbibition of water increases the volume of the imbibant, which results in imbibitional pressure. This pressure can be of tremendous magnitude. This fact can be demonstrated by a method used to split rocks.  Here, dry wooden stalks are inserted into the crevices of the rocks and soaked in water, a technique used by early Egyptians to cleave stone blocks.

Imbibing does not necessarily mean the ability to imbibe all kinds of liquids. For example, dry plant parts immersed in ether do not swell appreciably, however, a rubber plant imbibes ether and swells if submerged in it. On the other hand, the product rubber does not imbibe water.

Factors affecting the rate of Imbibition

  • Nature of imbibant:Different types of organic substances have different imbibing capacities. Proteins have a very high imbibing capacity, starch has less capacity and cellulose is the weakest imbiber. That is why proteinaceous pea seeds swell more on imbibition than starchy wheat seeds
  • Temperature:The rate of imbibition increases with the increase in temperature.
  • Concentration of the solute: Increase in concentration of the solute decreases imbibition due to a decrease in the diffusion pressure gradient between the imbibant and the liquid being imbibed.
  • Surface area of imbibant:The imbibition will be greater when the surface area of imbibant is larger.

Biological importance of Imbibition

  • Imbibition is dominant in the initial stage of water absorption by roots.
  • Seed germination is initiated by imbibition.
  • Imbibition force is useful in adhering water to the walls of xylem elements.
  • Fruits retain water by imbibition.
  • The movement of water into ovules that are ripening into seeds is made possible by the process of imbibition.

Learning outcomes

  1. Students understand the terms imbibition and imbibant.
  2. Students understand factors affecting the rate of imbibition and the biological importance of imbibition.
  3. Students will acquire skills to detect the process of imbibition through the animated demonstrations and simulations.

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