PHY2011 Lecture Notes - Lecture 5: Biological Membrane, Osmotic Pressure, Semipermeable Membrane
20 Jun 2018
School
Department
Course
Professor
Week 2 L2 (T1L4) -Osmosis and tonicity
Osmosis -Passive diffusion of water
Osmolarity -Pressure or force driving that diffusion (number of solute particles in the solution)
high osmolarity = high [solutes] therefore more water will move towards that end (hyperosmotic)
Osmotic pressure -tendency for water to move down its concentration gradient
Tonicity -says what is the consequence to cells when water moves in and out of cells
Permeability -measure of the ease of which a substance can penetrate a membrane
Ideal Semi-permeable membrane -permeable only to solvent, usually water
Selectively permeable membrane: permeable to some substances, not all. This is a biological
membrane.
Osmosis
The movement of water and the force driving this is the Osmolarity of the solutions
Osmolarity = concentration (M) of solvent x n(particles the molecule dissociates into)
Expressed in Osmolar units
Tonicity
What happens to cells in a solution due to water movement (do they swell, shirk, or remain
unaffected)
Tonicity depends on the effective concentration of non-penetrating particles (NNP)
If particles can’t move, or if they are at unequal concentrations in the cell vs outside, then water has
to move
Calculation:
Add up conc. of each NNP to get total osmolarity
If this is equal in extracellular and intracellular environments, then no net water change will
occur
If there is a difference, net water movement will occur
oIf conc outside is LESS than conc inside- hypotonicity -water will move into cell
oIf conc outside is MORE than conc inside -hypertonicity -water will move out of cell
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Osmolarity -pressure or force driving that diffusion (number of solute particles in the solution) high osmolarity = high [solutes] therefore more water will move towards that end (hyperosmotic) Osmotic pressure -tendency for water to move down its concentration gradient. Tonicity -says what is the consequence to cells when water moves in and out of cells. Permeability -measure of the ease of which a substance can penetrate a membrane. Ideal semi-permeable membrane -permeable only to solvent, usually water. Selectively permeable membrane: permeable to some substances, not all. The movement of water and the force driving this is the osmolarity of the solutions. Osmolarity = concentration (m) of solvent x n(particles the molecule dissociates into) What happens to cells in a solution due to water movement (do they swell, shirk, or remain unaffected) Tonicity depends on the effective concentration of non-penetrating particles (nnp)
