12 - diffusion, water and osmosis Flashcards
what does the plasma membrane do?
protects and isolates inside of cell from the outside.
what must the cell membrane allow for the cell to function?
membranes must allow exchange of ions, nutrients and waste for cell to function.
what are the two important chemical bonds?
ionic bonds and covalent bonds
how is an ionic bond created?
created by attraction between ions of opposite charge
electrons are “donated” or “accepted”.
how are covalent bonds created?
created by electron sharing between atoms.
how much of the body is water?
water is two thirds of total body weight
what is water made of and how are they bonded?
two hydrogen atoms and one oxygen atom, covalently bonded.
unequal sharing of electrons within covalent bonds; oxygen has greater electronegativity than hydrogen. water is a polar molecule.
where can hydrogen bonds form, that give water a set of unique properties?
hydrogen bonds can form between positive and negative dipoles of water molecules.
these bonds give water a set of unique properties.
what happens when a proton moves from one water molecule to another?
this results in a hydroxide ion (lost proton) and hydronium ion (gained proton)
this is a reversible reaction and these molecules exist in tiny quantities in pure H2O.
when acids dissolve, what ion do they donate to the solution?
H+ (hydrogen ion)
e.g. HCI disassociates to hydrogen ions and chloride ions
HCI –> H+ + CI-
what is a substrate that reduces the concentration of H+ ions in solution called?
a Base
e.g. ammonia reduces H+ ion concentration by attracting a H+ from solution.
do acids or bases have a high pH?
acids have a LOW pH
bases have a HIGH pH
what do ionic bonds do in H2O?
ionic bonds break up in H2O; polar molecules readily solvated.
individual ions/molecules (solutes) become distributed in the H2O (solvent)
…
in biology, chemical reactions occur in H2O and often require it/produce it (hydrolysis/condensation reactions)
why does H2O absorb and remain heat?
because of hydrogen bonding.
temperature must be high before hydrogen bonding is disrupted.
a large amount of heat is required to change the temperature of H2O.
temperature changes occur slowly in H2O, what does that make it?
a good thermal insulator.
what are examples of water being used as lubricant in the body?
aqueous solutions in knee joints, interstitial fluid in pericardium, saliva during digestion.
how are aqueous solutions formed?
by ionisation
ions dissociate in H2O
polar H2O form hydration spheres around smaller polar molecules.
interact with H2O enabling hydration spheres to form/surface spreading.
ions and polar molecules.
what happens in aqueous solutions if hydration spheres don’t form?
molecules don’t dissolve/no surface spreading
non-polar compounds (no positive and negative regions)
what is diffusion?
diffusion is the net movement from a region of higher concentration to a region of lower concentration.
what is random movement?
all molecules are constant in motion and move in random patterns.
constant motion and random movement result in mixing.
what is a concentration gradient?
concentration is the amount of solute in a solvent.
concentration gradient is the difference in concentration between two points.
what five things influence diffusion?
- distance the molecule has to move
- concentration gradient, region between high and low concentration, called chemical gradient
- molecular size, smaller molecules move faster
- temperature, more heat, faster movement
- electrical forces, opposites attract, like charges repel. where electrical forces affect diffusion, we call it a electrochemical gradient.
what are the three types of permiability?
- impermeable, nothing in or out
- freely permeable, anything in or out
- selectively permeable, restricts movement to specific molecules.
why might the cell membrane be selectively permeable?
cells need nutrients but also has to remove waste products.
what are the three methods to achieve a selectively permeable membrane?
- diffusion
- carried mediated transport
- vesicular
what is material restricted based upon in a selectively permeable membrane?
- size
- electrical charge
- molecule shape
- lipid solubility
what is simple diffusion?
lipid-soluble molecules can diffuse across the plasma membrane.
what is channel mediated diffusion?
small water-soluble molecules and ions can diffuse through membrane channels
what are transported by a carrier mechanism across the plasma membrane?
large molecules that cannot diffuse through lipids cannot cross the plasma membrane unless they are transported by a carrier mechanism.
what diffuses by simple diffusion?
small lipid soluble molecules:
- alcohols
- fatty acids
- steroids
dissolved gasses:
- O2
- CO2
does diffusion have an impact on cell size?
for each unit area of plasma membrane, there is a limit to the total amount of a substance that can cross per second.
as the radius increases, the volume increases proportionally more than the surface area.
beyond a certain size, the surface area of the plasma membrane is insufficient to support the rate of provision of required substances across the cell membrane.
what is osmosis?
net diffusion of H2O across a selectively permeable membrane is called osmosis.
how does the solute concentration effect osmosis?
the total solute concentration affects the diffusion of water.
water molecules move towards the area with the highest total concentration of solutes.
what is osmotic pressure?
The minimum pressure that would have to be applied to an aqueous solution to prevent water from moving by osmosis.
what is osmolarity?
describes the total solute concentration (measured in osmoles/L)
what does osmotic concentration depend on?
the total number of solute particles in a solution but not the identity of them.
what are the three terms used to describe relative osmolarites between solutions e.g. when comparing A to B?
- hyperosmotic = A has a higher osmolarity to B
- hypoosmotic = A has a lower osmolarity to B
- isoosmotic = A and B have the same osmolarity
what is tonicity?
ability of an extracellular solution to cause water to move into or out of a cell by osmosis.
how does tonicity differ from osmolarity?
it accounts for both the relative solution concentrations and the cell membrane’s permeability to those solutes.
what are the three stages of Hypothetical cells?
1 - equal osmolarity BUT different species of solute exist either side of selectively permeable cell membrane
2 - purple species can diffuse into the cell through channels
3 - osmotic pressure drives H2O molecules into the cell. intracellular pressure increases; cell “swells” up
what happens in a hypotonic cell?
H2O flows into the cell
cell swells
what happens in a hypertonic cell?
H2O flows out of the cell
cell shrinks
what happens in a isotonic cell?
tonicity the same inside and outside the cell
no flow of H2O
what happens to RBC in an isotonic saline solution?
no osmotic flow occurs, and these red blood cells appear normal.
what happens to RBC in a hypotonic solution?
immersion in a hypotonic saline solution results in the osmotic flow of water into the cells. the swelling may continue until the plasma membrane ruptures, or lyses.
what happens to RBC in hypertonic solution?
exposure to a hypertonic solution results in the movement of water out of the cell. the red blood cells shrivel and become crenated.
