water potential subject guide notes
D2.3.1—Solvation with water as the solvent
hydrogen bonds form between water molecules due to weak electrostatic attraction between partially negative oxygen atom of one water molecule & partially positive hydrogen atom of another water molecule
if force of attraction between ions & water molecules is greater than force of attraction between oppositely charged ions, water will dissolve the substance
when ionic compound introduced into water, partially positive hydrogen atoms are attracted to negatively charged ions & partially negative oxygen atoms attracted to positively charged ions
water molecules surround the ions, forming hydration shells
presence of hydration shells leads to separation of solute particles & their uniform distribution throughout solution - called dissolution
covalent compounds (glucose & oxygen) form intermolecular interactions with the water molecules, allowing them to dissolve in water
D2.3.2—Water movement from less concentrated to more concentrated solutions
water moves through selectively permeable membrane until both sides achieve equilibrium (are isotonic)
hypertonic - solutions with high solute concentration (high osmotic concentration)
hypotonic - solutions with low solute concentration (low osmolarity)
D2.3.3—Water movement by osmosis into or out of cells
osmosis is special type of diffusion (which is the general process of particle movement from area of high concentration to area of low concentration)
cell placed in hypertonic solution - there’s a high solute concentration & there will be net movement of water out of cell, into surrounding solution
if animal cell - cell shrinks & becomes crenated
if plant cell - cell undergoes plasmolysis
cell placed in hypotonic solution - there’s a low solute concentration & there will be net movement of water from solution into cell
causes cell to swell
if animal cell, it could burst if too much water enters the cell = lysis
in plant cell, the cell can become turgid
cell placed in isotonic solution - equal movement of water into & out of cell
no change in shape or size of cell
D2.3.4—Changes due to water movement in plant tissue bathed in hypotonic and those bathed in hypertonic solutions
measuring percentage change in tissue mass & length of plant placed in different concentrations of solution - allows us to determine the isotonic solute concentration of plant tissue
bathed in hypertonic solutions = plant loses water due to osmosis = loss in length & mass
bathed in hypotonic solutions = plant gains water due to osmosis = increase in length & mass
high standard deviation = high variability in data set
D2.3.5—Effects of water movement on cells that lack a cell wall
remember: in hypotonic solutions, water enters cell through osmosis, causing cell to swell
if cell doesnt hv cell wall, it can reach a bursting point/undergo lysis due to increased internal pressure
in hypertonic solutions, water leaves cell by osmosis
leads to cell crenating due to water loss
to prevent excessive water intake, some unicellular organisms (like Amoeba & Paramecium) hv contractile vacuoles
the vacuoles expel water from cell, maintaining correct intracellular solute concentration, preventing cell from bursting
multicellular organisms - important to maintain isotonic tissue fluid to prevent harmful changes
each cell in organism needs to be in environment with equal concentration of solutes, in order to maintain proper functioning
if cells aren’t in environments that’re isotonic, it can harmful effects on cell processes
ex: kidney
D2.3.6—Effects of water movement on cells with a cell wall
in hypotonic solution - in plant cells, as water enters the cell by osmosis, the turgor pressure increases
is exerted by the cytoplasm against the cell wall
cell is referred to as turgid (swollen & rigid due to influx of water)
cell wall prevents cell from bursting & maintains shape
in hypertonic solution - in plant cells, the cell membrane shrinks away from cell wall (plasmolysis)
loss of water = loss in turgor pressure
D2.3.7—Medical applications of isotonic solutions
organs & tissues intended for transplantation are typically bathed in a solution thats been designed to provide optimal conditions to protect organ or tissue against damage, providing organ with necessary nutrients & oxygen
isotonic fluids can be given through an IV
allows for rapid & direct absorption of medications, fluids or nutrients into circulatory system
D2.3.8—Water potential as the potential energy of water per unit volume
is usually measured in kilopascals (kPA)
low solute concentration = high water potential cuz there’s more free water molecules
high solute concentration = low water potential cuz less free water molecules
D2.3.9—Movement of water from higher to lower water potential
water moves by osmosis from areas of high water potential to areas of low water potential
D2.3.10—Contributions of solute potential and pressure potential to the water potential of cells with walls
is influenced by solute potential & pressure potential
solute potential - the attraction of water molecules to solute particles
when present, it reduces the number of free water molecules, limiting water movement
pressure potential - physical pressure thats exerted
positive pressure potential = pressure is exerted outwards from the cell
increases water potential
negative pressure potential can be seen in the suction exerted on water in xylem
decreases water potential
can be calculated:
D2.3.11—Water potential and water movements in plant tissue
when plant tissue bathed in hypotonic solution, solute potential of tissue is more negative than solute potential of solution
water moves into tissue
water moves from less negative solute potential to more negative solute potential
additional water in cell causes them to apply an outward pressure called turgor pressure
this means the pressure potential is positive (pressure inside cell is higher than pressure outside cell)
animal cells dont hv cell walls = dont generate positive pressure potentials
when plant tissue bathed in hypertonic solution, solute potential of solution is more negative than solute potential of tissue
water moves out of tissues
moves from area of less negative solute potential to area of more negative solute potential
volume of cell decreases, causing decrease in pressure in cell relative to solution, causing cell membrane to detach from cell wall
negative pressure potential