Understanding Imbibition

Imbibition

• A type of diffusion where water is absorbed by solid particles called colloids
• Results in an enormous increase in volume
• Does not form a solution
• Is water absorption by colloids
• Colloids are hydrophilic
• Solid substances are referred to as imbibants
• Imbibed liquid is referred to as imbibate
• Examples include absorption of water by seed or dry wood
• Imbibing capacity varies among imbibants
• Proteins have the maximum imbibing capacity
• Starch has less capacity compared to proteins
• Cellulose has the least imbibing capacity

Features of Imbibition

• Volume of an imbibant increases
• Examples include swelling of soaked seeds and wooden frames during rains
• A steep water potential gradient is created when a dry imbibant contacts water
• Water diffuses from the higher potential into the imbibant
• Heat released is known as the heat of wetting
• The imbibant holds the imbibate by adsorption with an attractive force between the two substances

Factors Affecting Imbibition

• Pressure
• Texture of the imbibant
• pH of the medium
• Affinity of the imbibant for the imbibate

Imbibition in Plants

• Causes swelling of seeds, resulting in the breaking of testa
• Is the initial step in seed germination
• Water moves into ovules ripening into seeds by imbibition
• Dominant in the initial stage of water absorption by roots

Transport Across the Plasma Membrane (PM)

• Passive transport includes simple diffusion, facilitated diffusion, and osmosis
• Active transport
• Bulk flow includes endocytosis and exocytosis

Passive Transport

• Substances cross the membrane by diffusion
• Diffusion is the net movement of substances from an area of high concentration to low concentration
• Requires no energy

Simple Diffusion

• Is the tendency for molecules of any substance to spread out evenly into the available space
• Moves from high to low concentration down the concentration gradient
• Nonpolar, hydrophobic molecules diffuse directly through the lipid bilayer
• Does not require transport proteins
• Examples include O2, CO2, and steroids
• Polar, hydrophilic substances cannot pass directly through the lipid bilayer
• Examples include water, ions, and carbohydrates

Factors Affecting Diffusion Rate

• Steepness of concentration gradient
• Steeper gradient corresponds to faster diffusion
• Molecular size
• Smaller molecule corresponds to faster diffusion
• Temperature
• Higher temperature corresponds to faster diffusion

Osmosis

• Is the movement of water across a semipermeable membrane
• Affected by the concentration gradient of dissolved substances called the solution's tonicity

Tonicity

• Is the ability of a solution to cause a cell to gain or lose water
• Has a great impact on cells without walls
• Isotonic solution means the concentration of solutes is the same as inside the cell, resulting in no net movement of water
• Hypertonic environment leads to the cell losing water, called plasmolysis
• Hypotonic environment leads to the cell gaining water

Cell Walls

• Help maintain water balance

Turgor Pressure

• Is the pressure of water inside a plant cell pushing outward against the cell membrane
• A turgid plant cell in a hypotonic environment is very firm, a healthy state
• A flaccid plant cell is in an isotonic or hypertonic environment

Facilitated Diffusion

• A type of passive transport aided by proteins
• Transport proteins speed the movement of molecules across the plasma membrane

Channel Proteins

• Provide corridors that allow a specific molecule or ion to cross the membrane

Carrier Proteins

• Undergo a subtle change in shape to translocate the solute-binding site across the membrane
• Alternate between two confirmations and move a solute across the membrane as its shape changes
• Transports the solute in either direction with the net movement being down the concentration gradient of the solute

Active transport

• Uses energy to move solutes against their concentration gradients
• Requires energy, usually in the form of ATP

Imbibition vs. Osmosis

• Imbibition is water absorption through a solid substance
• Osmosis is the movement of water from high to low concentration through a semi-permeable membrane

Imbibition Importance

• The first step of water absorption
• Facilitates water absorption by roots and helps in seed germination

Imbibition vs Diffusion

• Imbibition is a reversible process; diffusion is an irreversible process
• Imbibition is the absorption of water by general surface
• Diffusion is the movement of solid, liquid, or gaseous molecules from high to low concentration

Examples of Imbibition

• Germination and swelling of soaked seeds
• Wooden doors swelling during rains
• Water absorption by roots

Imbibition vs Diffusion Differences

• Refers to the absorption of water by a general surface in imbibition
• Refers to the movement of molecules, ions of solids, liquids or gasses from the region of higher concentration to lower concentration in diffusion
• Takes place both in living and dead cells during imbibition
• Takes place in solids, liquids and gasses during diffusion
• Is a reversible process in imbibition
• Is not a reversible process during diffusion

Explore imbibition, a type of diffusion where water is absorbed by solid particles leading to a considerable increase in volume. Learn about its features, including the water potential gradient, heat of wetting, and the attractive forces between imbibants and imbibates. Discover how proteins, starch, and cellulose affect imbibition capacity.