5.5 Osmosis Flashcards
What is osmosis?
Diffusion of water across a partially permeable membrane, from a dilute solution to a concentrated solution.
What is a solute?
A substance dissolved in a solvent, forming a solution
What is water potential?
The pressure exerted by water molecules as they collide with a membrane or container.
What is water potential measured in, and what is the symbol?
Measured in Pascals, and the symbol is Psi Ψ
What is the water potential of pure water?
0 Pa
What is the highest water potential?
0 Pa, only found in pure water.
What lowers the water potential?
The presence of a solute in water.
What leads to an increase in hydrostatic pressure?
An increase in volume of solution in a closed system.
What is hydrostatic pressure measured in?
Pascals (Pa)
What happens if the water potential outside of a cell is higher than the internal cell solution’s water potential?
The water will enter the cell by osmosis, increasing the hydrostatic pressure within the cell
What happens when water enters an ANIMAL CELL by osmosis?
The cell will swell, and if it cannot withstand the pressure, the cell-surface membrane will break, and the cell will burst (cytolysis)
What is cytolysis?
When a cell bursts due to excess water diffusing into the cell.
What happens if the water potential outside of a cell is equal to the internal cell solution’s water potential?
The water will exit and leave the cell at an equal rate, and there will be no change to the state of the cell.
What happens if the water potential outside of a cell is lower than the internal cell solution’s water potential?
The water will exit the cell.
What happens when water exits an ANIMAL cell by osmosis?
The cell’s volume is reduced, and the cell-surface membrane will “pucker”
What makes plants different to animal cells in terms of osmosis?
They are unable to control the water potential of the fluid around them.
What happens when water enters a PLANT cell by osmosis?
The increased hydrostatic pressure pushes the membrane against the rigid cell walls
-This pressure is called turgor
-As turgor increases, it resists the entry of further water, and the cell is turgid
What happens when water exits a PLANT cell by osmosis?
-Water is lost from the cell
-This leads to a reduction in the volume of the cytoplasm, which pulls the cell-surface membrane away from the cell wall
-The cell is PLASMOLYSED
What is plasmolysis?
When a plant cell contracts, and shrinks its cytoplasm and plasma membrane away from the inside of its cell wall
What does hypertonic mean?
High levels of solutes in water
What does hypotonic mean?
Low levels of solutes in water
In a plasmolysed plant cell, what is the substance inbetween the plasma membrane and the cell wall?
Sucrose solution
