the diffusion of water molecules across a selectively permeable membrane.
The hydrostatic pressure that develops when water enters the cells of the plants and microorganisms.
Hydrostatic pressure (Osmotic pressure)
When water moves into a body by osmosis, pressure builds up inside the body.
The tendency of water to move across a selectivelly permeablme membrane. This is used to account for differences in both concentration and pressure. It is the sum of the pressure potential and the solute potential.
- Measured in bars (1 bar is approximately equal to 1 atmosphere pressure) or megapascals (1MPa = 10 bars).
- In a living cell, water potential is always zero or negative.
- Water potential can be positive or negative.
- Negative water potentiatl = TENSION
The pressure from any externally apllied force.
- Is zero unless some force is applied, such as that applied by a cell wall.
The osmotic potential.
- Results from the presence of solutes.
- Always negative
- A higher concentration of solutes generates a smaller (or negative) solute potential
Solute type/ Solute concentration
smaller molecules (water, NaCl, glucose) can diffuse across the membrane/ tubing while larger molecules cannot.
The relative concentration of solutes inside and outside the bag determines the net flow of solutes across the membrane.
- The GREATER the solute concentration, the FASTER the initial flow of solutes.
Diffusion vs. Osmosis
The net movement of substances from an area of higher concentratipn to an area of lower concentration.
- Results from random movement of molecules.
- Osmosis is the diffusion of water molecules across a selectively permeable memrane.
The Rate of Diffusion
As water enters the cell, the vacuole expands until it exerts a force on the cell wall.
- In a healthy cells- the wall presses back with a pressure equal to and opposite of turgor pressure.
The solution surrounding the cell is ______ (higher solute concentration) relative to the contents of the cell.
The process in which the plasma membrane collapses in a hypertonic solution because the net movement of water is out of the cell, and the TURGOR decreases.
The solution surrounding the cell is ________ (lower solute concentration) relative to the contents of the cell.
- The NET movement of water is INTO the cell.
The solution surrounding the cell is ______ (equal solute concentration) relative to the contents of the cell.
- There is NO NET MOVEMENT of water in or out of the cell.
When a cell "exploads"
- Animal cells do NOT have CELL WALLS and immersing an animal cell into a hypOtonic solution wil cause the cell to expand.
- Unless the cell has a mechanism for removing EXCESS WATER, the cell will continue to expand until it breaks apart.