Water and Mineral Absorption: Diffusion

• Absorption of water and minerals and transport to roots, leaves, and evaporation occurs through diffusion, osmosis, absorption, transportation, and transpiration.

Diffusion

• Diffusion is the tendency of solids, liquids, and gases to spread spontaneously and uniformly from areas of higher concentration to areas of lower concentration through any medium.

Diffusion Pressure

• Diffusion pressure is the potential pressure exerted due to the kinetic energy of molecules, causing movement from regions of higher concentration to lower concentration.

Importance of Diffusion

• Diffusion occurs in every physiological process of organisms.
• Plants absorb carbon dioxide and release oxygen during photosynthesis through diffusion.
• Oxygen enters cells and carbon dioxide is released through diffusion.
• Water loss in the form of vapor through transpiration is a result of diffusion.
• Animal respiration, exchange of oxygen and carbon dioxide, plus the movement of food and oxygen from blood to lymph, and from lymph to cells, all occur through diffusion.
• Kinetic energy is required for matter to spread out.
• Pressure, known as diffusion pressure, is needed to gain kinetic energy.

Osmosis

• Osmosis depends on the characteristics of the membrane separating two solutions with different concentrations.

Types of Membranes

• Impermeable membrane: Solute and solvent molecules cannot pass through (e.g., polythene, cell wall with cutin).
• Permeable membrane: Solute and solvent molecules can pass through easily (e.g., cell wall without cutin).
• Semi-permeable membrane: Only solvent molecules (water in plants) can pass, not solute molecules (e.g., cell membrane, eggshell membrane, fish bladder membrane, animal gallbladder membrane).
• A raisin swells in water because it absorbs water through osmosis.
• Osmosis is a type of diffusion.
• Osmosis occurs in liquids separated by a semi-permeable membrane.
• Diffusion naturally occurs when two solutions of different concentrations are together.
• Osmosis, is the process where only solvent molecules can pass through a semi-permeable, but not solute molecules.

Importance of Osmosis

• Cell membrane acts as a semi-permeable membrane, allowing mineral salts dissolved in water to enter and exit cells.
• Intracellular water and mineral salt solution together make up cell sap.
• Osmosis maintains different physio-chemical processes of the cell.
• Plants absorb water and minerals dissolved in water from the soil through root hairs via osmosis.
• Osmosis increases cell turgidity, keeping stems and leaves fresh.
• Plants can open and close petals due to osmosis.
• Digested food may be absorbed in the intestines of animals via osmosis.
• Mineral salt absorption is possible due to osmosis.

Absorption

• Absorption is the process by which living cells of plants take in water and minerals dissolved in water.
• Terrestrial plants absorb water from soil through root hairs.
• Submerged plants absorb water through their whole body.
• Plants intake capillary water of soil particles through osmosis
• Wall of root hair is permeable.
• Waters go through imbibition and absorbed waters come in contact with semi-permeable plasma membrane below the cell wall.
• The concentration of the central solution of root hair is higher than the environment.
• Water (solvent) enters the cell through endosmosis (inner osmosis).
• Cell sap concentration is not equal from the outer membrane to the center of the root cells.
• Water flows through xylem vessels from one cell to another and finally reaches the leaves due to intercellular osmosis.

Imbibition

• Imbibition is the process by which colloidal substances (cell waters in plants) absorb liquids (water in plants).
• Absorbing substances are called hydrophilic substances.
• Most colloidal substances are hydrophilic.
• Plant bodies contain starch, cellulose, and gelatine that can absorb water due to their colloidal nature.

Absorption of Mineral Salts

• Plants absorb mineral salts from the soil for development and physiological needs.
• Mineral salts remain in solution form in the soil.
• Mineral salts remain as solutes with capillary water, but the absorption process of water and mineral salts are different.
• Plants absorb salt in the form of ions.
• Salt absorption is divided into inactive and active absorption.

Transpiration

• Transpiration is a special physiological process of plants.
• Plants absorb a bulk amount of water from soil through root hairs.
• Plants use a portion of water in metabolic activities and the rest goes out as vapor.
• Water loss in the form of vapors from the moist surface of internal tissues of aerial parts of plants, especially leaves, is transpiration.

Types of Transpiration

• Stomata transpiration: Major form of transpiration.
• Cuticular transpiration: Transpiration through cuticles of leaves and stems.
• Lenticular transpiration: Water vapor loss through lenticels of the stem.

Significance of Transpiration

• Transpiration is essential for plants.
• High transpiration rates are harmful, making it a "necessary evil."
• Excess water is released, decreasing water pressure and increasing cell sap concentration, creating the right conditions for endosmosis.
• Transpiration prevents overheating and maintains humidity in leaves.
• Transpiration ensures a continuous water supply to the leaves, generating a pull in the cellular tube that helps lift water through xylem vessels from roots to leaves through the stem.
• Terrestrial plants convert land water into water vapor that enters the environment through transpiration in the water cycle.

Transportation

• Transportation is process by which absorbed water from root hairs reaches leaves and food from leaves reaches different part of plant body is known as transportation.
• Transportation takes place through vascular tissue - xylem and pholem.
• Water absorbed through the root is carried to the leaves through xylem tissue.
• Liquid food materials from leaves reach different parts of the body plant body through pholem tissue.
• Vascular tissues xylem and pholem are transporting channels of plant body.
• Water enters through root hair by osmosis and the mineral salt dissolved in water is absorbed by active and inactive absorb absorption and reach xylem tissue.
• Xylem is responsible for upward transport of sap.
• Liquid food materials manufactured in the leaves go down through the pholem tissue.
• Upward and downward transportation is known as transportation in plants.