chapter 5.5 - Osmosis Flashcards
What is Osmosis?
The diffusion of water across a partially permeable membrane, along a concentration gradient.
What is water potential, and what is it measured in?
Water potential is the pressure exerted by water molecules as they collide with a membrane or a container - measured in kPa (kilopascals) and represented by the letter ψ
What is the water potential of pure water?
0 kPa
What is the highest possible value for water potential?
0 kPa in pure water - any presence of a solute lowers the ψ below 0.
True or false: water molecules and solutes can move through partially permeable membranes
false - only water can move through the membrane.
How do two bodies of water seperated by a membrane interact?
The water from the solution with the higher water potential will move to the side where there is a lower water potential - this is due to the fact that the lower water potential has more solute, and is therefore less concentrated, meaning that the water follows the ordinary rules of osmosis.
What is Hydrostatic pressure?
the increase of pressure in a closed system after the diffusion of water into the closed system - measured in kPa - dangerous for the cell
What is Cytolysis?
When the hydrostatic pressure within a cell becomes too large for the cell membrane to sustain and the cell will burst.
What is Crenation?
When a cell loses too much water, and the cell-surface membrane “puckers”.
How do animal bodies prevent crenation and cytolysis?
Constantly surrounding cells with aqueos solutions with an equal water potential (isotonic) - in blood this aqueous solution is blood plasma.
How do plant cells prevent bursting?
They have a strong outer wall made of cellulose - when too much water enters the cell the hydrostatic pressure pushes against the cell wall, causing the cell to become turgid - when the cell is in this state, water can no longer enter the cell.
What is plasmolysis?
When so much water is lost from the cell that the membrane seperates from the cell wall.
