osmosis Flashcards
what is osmosis
the net diffusion of water molecules from a region of where are more water molecules to an area where there are fewer water molecules across a partially permeable membrane
what is a solute
a substance dissolved in a solvent to form a solution
what does the amount of solute in a certain volume of aqueous solution determine
the concentration
what is the solvent
the liquid in which solute molecules are dissolved in a solution
in aqueous solutions what is the solvent
water
what can easily pass through the phospholipid bilayer
water molecules
what are protein channels for water called
aquaporins
what do aquaporins allow water molecules to do
diffuse more rapidly through the bilayer
where is water present in cells
in the cytoplasm and the medium of cells as cells are surrounded by extracellular tissue fluid
what happens when solute molecules are added to water
the relative number of water molecules in the resulting solution is changed. if the solute molecules dissociate into charged ions (for e.g NaCl dissociating into Na+ and Cl- ions), they exert more effect on the number of water molecules than larger non ionic molecules.
what happens when solute molecules dissociate into charged ions
if the solute molecules dissociate into charged ions (for e.g NaCl dissociating into Na+ and Cl- ions), they exert more effect on the number of water molecules than larger non ionic molecules (glucose for e.g) this is because as NaCl molecules dissociate into Na+ and Cl- the number of particles in the solution doubles
how does osmosis occur in prokaryotic cells
water molecules can enter or leave them across the partially permeable plasma membrane. if they lose enough water, then their metabolism can’t proceed and they can’t reproduce.
what can adding salt or sugar to food do
preserve food and prevents spoilage as any bacteria can’t respire, grow or multiply as water is lost by the bacterial cells by osmosis.
what does penicillin prevent
some types of growing bacteria from synthesising their peptidoglycan wall. this makes them vulnerable to the effects of osmosis. if they swell up whilst water enters, they will burst
what is the net diffusion of water by osmosis determined by
the differences in water potential between two solutions connected by a partially permeable membrane
what is water potential
a measure of the tendency of water molecules to diffuse from one region to another
what is the unit for water potential
kilopascals
what is the water potential of pure water
0kPa - pure water has the highest water potential
what is the water potential of solutions
they have a lower water potential than pure water with a negative water potential
what is the water potential of a solution affected by
the amount of solute it contains
the greater the amount of solute, the lower the water potential
why does greater amount of solute lower the water potential
water molecules bind to the solute molecules reducing the number of water molecules that are free to diffuse
what is the solute potential
the contribution that solutes make to the water potential of a solution is the solute potential
is the solute potential negative or positive
negative
how do water molecules move if they are separated by a partially permeable membrane
they will move from the solution with a higher water potential to a solution with a lower water potential
what happens when the water potential on both sides becomes equal
there will be no net osmosis, the water molecules still move randomly
what happens to the solute potential as more solute molecules are added
water potential is lowered so the value becomes negative
how else is the water potential of a solution affected
by the pressure applied to it
how does pressure affect the water potential
greater pressure = higher water potential
why is pressure potential always positive
due to the constant flow of water into the cell causing a force or pressure against the cell membrane or cell wall.
why is solute potential always negative
When solute is dissolved in water, the amount of free water molecules reduces causing the kinetic energy of the molecules to reduce.
what is the equation for water potential
solute potential + pressure potential
what is osmotic concentration
refers to the amount of dissolved solutes in a solution
what is another name for a concentration solution
a solution with a high osmotic concentration and a low water potential
what is another name for dilute solution
a solution with a low osmotic concentration and a high water potential
how do insoluble molecules affect osmotic concentration
they dont
how does water move along the concentration gradient
it moves DOWN it
which protein channel does water move through
aquaporins
what does a partially permeable membrane result in
an uneven distribution across the membrane - it only lets small water molecules through
what is an isotonic solution
any external solution that has the same solute concentration and water concentration compared to a cell. in an isotonic solution, no net movement of water will take place
what is a hypertonic solution
any external solution that has a high solute concentration and low water concentration compared to a cell. in a hypertonic solution, the net movement of water will be out of the body and into the solution
what is a hypotonic solution
any external solution that has a lower solute concentration compared to the intracellular solute concentration. when a red blood cell is placed in a hypotonic colution, there will be a net movement of water into the cell.
in an animal cell, describe the movement of water in a isotonic solution
the water potential outside the cell is the same as the water potential of the cell cytoplasm. there is no net movement of water
in an animal cell, describe the movement of water in a hypertonic solution
the water potential outside the cell is lower than the cell cytoplasm. water has therefore moved out of the cell.
what happens if water moves out of an animal cell
the cell becomes crenated as the cytoplasm pulls away from the cell membrane
in an animal cell, describe the movement of water in a hypotonic solution
the water potential outside the cell is higher than inside of the cell. water has therefore entered the cell.
what happens if water moves into a animal cell
because the cell has no protective cell wall, it eventually bursts (lysis)
which solutions have the same osmotic concentration as the cytoplasm
isotonic solutions
which solutions have a lower osmotic concentration as the cytoplasm
hypotonic solutions
which solutions have a higher osmotic concentration as the cytoplasm
hypertonic solutions
in a plant cell, describe the movement of water in a hypertonic solution
the water potential outside the cell is lower than inside the cell. water has therefore moved out the cell
what happens when water moves out of a plant cell
the cytoplasm has pulled away from the cell wall and the cell is plasmolysed
in a plant cell, describe the movement of water in a hypotonic solution
the water potential outside the cell is higher than inside the cell. water has entered the cell.
what happens when water moves into a plant cell
the cytoplasm is pushing against the cell wall and the cell is turgid
