hello everybody my name is Iman welcome back to my YouTube channel today we're gonna do practice problems relating to chapter seven which was about biological membranes so in the first video of course we did some review today we're gonna go ahead and jump into some practice problems this first problem says a student is trying to determine the type of membrane transport occurring in a Cell she finds that the molecule to be transported is very large and polar and when transported across the membrane no energy is required which of the following is most likely the mechanism of transport so we're here we're being asked to identify the type of transport that would allow this large polar molecule to cross the membrane with no energy required that's a very important point this scenario pretty much describes passive transport a type of passive transport all right so it requires no energy so we know it's passive transport what that means is we can cancel out active transport now it's going it's being transported across the membrane um it's not being consumed into a vesicle and out of the membrane so we can also cancel out exocytosis now the scenario it describes facilitated diffusion which requires a transport protein or Channel and I say this because what's being transported is a very large polar molecule so it's not happening through simple diffusion across the membrane right because usually things that occur through simple diffusion across the membrane with no help of a transmembrane protein are things that are nonpolar and small this is a very large and polar molecule and yes of course no energy is required but that usually means that there that it's going through some sort of transmembrane protein that has a hydrophilic interior that allows that to happen all right and this is a description exactly of facilitated diffusion right which uses a transport protein or a channel to facilitate the movement of a large polar molecule across this nonpolar hydrophobic membrane all right and it requires no energy so the answer here to this question is C so one is C two says a researcher treats a solution containing animal cells with obeying a poisonous substance that interferes with the sodium potassium atpase embedded in the cell membrane and the cell lyses as a result which of the following statements best describes oben's effect so let's read the answer choices and then let's work through the logic a says treatment with Open results in high levels of extracellular calcium B says treatment with Open results in high levels of extracellular potassium and sodium C says treatment with oven increases intracellular concentrations of sodium and D says treatment with open decreases intracellular concentrations of sodium okay cool now this question it requires an understanding of osmosis and our the sodium potassium pump when a cell is placed in a hypertonic solution all right in a solution that has more solutes on the outside than it does on the inside all right fluid what will happen with water is that water there's a greater water concentration inside than there is outside all right and that means water will diffuse outside of the cell all right that's hypertonic right because there's more solutes on the outside which means there's less water on the outside and water is going to diffuse out of the cell into the environment all right that's hypertonic now when a cell that means fluid will diffuse out of the cell and it could result in the cell shrinking now when a cell is placed in a hypotonic solution all right there is more let me change this there's going to be more solutes inside the cell than there is on the outside and what that means is water is going to move into the cell right so that's a hypotonic solution that's going to cause the cell to swell all right so here in hypertonic cell shrinks in hypotonic cell swells all right because fluid is going to diffuse from the solution into the cell now the sodium potassium pump what does that do it's gonna sodium potassium pump it's going to move three sodiums out three sodium ions out two potassium ions in all right therefore inhibition of this sodium potassium pump bioibit is going to cause a net increase in the sodium concentration inside the cell all right and so if we're increasing sodium concentration in the cell then what is going to happen water is going to move into the cell and it's going to cause the cell to swell and then lyse all right and so treatment with open is going to increase intracellular concentration of sodiums it's going to cause water to come in and that's going to cause the cell to swell until it lyses as a result all right and so that's going to be answer Choice C treatment of open is going to increase that concentration of sodium inside the cell water going to come in cell is going to potentially lice fantastic three says the resting membrane potential depends on blank one says the differential distribution of ions across the membrane two says active transport processes and three says selective permeability of the phospholipid bilayer now the polarization of the membrane at rest is the result of an uneven distribution of ions between the inside and the outside of a cell the difference is actually achieved through active pumping of ions predominantly sodium and potassium into and out of the cell and the selective permeability of the membrane which allows only certain ions to cross and that means all three of these are correct statements are all things that the resting membrane potential depends on it depends on the differential distribution of ions across the membrane on active transport processes that will move in and out ions and the selective permeability of the phospholipid bilayer which is going to let some things in and not other things that all affects the resting membrane potential and so the correct answer here is going to be G one two and three are all true statements about what the resting membrane potential depends on Fantastic 4 .4 says which of the following is not a function of the cell membrane which of the following is not a function of the cell membrane cytoskeletal attachment protein synthesis transport regulation second messenger Reservoir all right ribosomes are the site of protein synthesis within a cell all right and they are not coupled to the cell membrane all right the answer here is B protein synthesis is not a function of the cell membrane the cell membrane does function as a site for cytoskeleton cytoskeletal attachments through proteins and lipid refs all right transport regulation is accomplished through channels Transporters and selective membrane all right and phospholipids do act as reagents for second membrane formation so everything else here is true but protein synthesis so four is B five says the dynamic properties of molecules in the cell membrane are most rapid in blank all right are they most rapid in phospholipids moving within the plane of the membrane that's a or phospholipids moving between the layer of membranes that's b or proteins moving within the plane of the membrane that's C or proteins exist exiting the cell through exocytosis now the movement of individual molecules in the cell membrane they are going to be affected by size and polarity just as with diffusion so lipids are much smaller than proteins in the plasma membrane they will move more quickly lipids will move fastest within the plane of the cell membrane because the polar head group does not need to pass through the hydrophobic tail region in the same way that it would if it were moving between the membrane layers and so that's going to make answer Choice a correct all right the dynamic properties of molecules in the cell membrane are most rapid in phospholipids moving within the plane of the membrane so 5 is a 6 says which lipid type is least likely to contribute to membrane fluidity all right which lipid type is least likely to contribute to membrane fluidity now compounds that will contribute to membrane fluidity are going to lower the melting point or disrupt the crystal structure and so cholesterol and unsaturated lipids and um yeah so cholesterol which is C and unsaturated lipids which is a these are known for those functions all right trans glycer uh glycerophosphate lipids tend to increase the melting point of the membrane and so they decrease membrane fluidity and so the correct answer here is B transglycer that glycerol phospholipids um they're going to be the least likely to contribute to to membrane fluidity all the other answer choices unsaturated glycerophospholipids cholesterol unsaturated sphingolipids they're all going to contribute to membrane fluidity not transglycerol phospholipids so 6 is B seven says a membrane receptor is more likely is most likely to be a blank embedded a says embedded protein with catalytic activity B says transmembrane protein was sequestration activity C says membrane-associated protein um with with sequestering activity and decis transmembrane protein with catalytic activity all right which one of these is a membrane receptor most likely to be well membrane receptors they're they have they must have both an extracellular and intracellular domain so therefore they are considered transmembrane proteins in order to initiate a second messenger Cascade they typically display enzymatic activity although some may act strictly as channels and so considering all that transmembrane proteins a membrane receptor is most likely to be a transmembrane protein with catalytic activity all right so the answer to this here is the eight says which of the following is not a cell cell Junction in animals all right we talked about three we said it was Gap Junctions tight junctions and desmosums all right C is not one of those three that we talked about so eight is C plasma desmada this plasmodesmata are um they are cell to cell Junctions but they're not found in animals they're found in plants the other three are all found in animals nine says which of the following is true of diffusion and osmosis diffusion and osmosis rely on the electrochemical gradient of only the compound of Interest this is a true statement diffusion and osmosis rely on the extra on the electrochemical gradient of all compounds in the cell that is not true just the compound of Interest diffusion and osmosis will proceed in the same direction if there's only one solute not necessarily true either diffusion and osmosis cannot occur simultaneously also not true the movement of any soluble or water by diffusion or osmosis is dependent only on the concentration gradient of that molecule and on membrane permeability so the answer here for nine is a 10 says the bulk movement of liquid into a cell through vesicle in foldings is known as bullet link this is the definition of pinocytosis by the way pinocytosis is a type like we've mentioned in the review is a type of endo cytosis all right so the endocytosis of fluid is known as pinocytosis fantastic phagocytosis by the way as a reminder is the endocytosis intake of solutes solids I'm sorry solids all right so this is dealing with solids Pinot deals with liquids both of these are types of endocytosis all right exocytosis is um the the movement of things to the outside of the cell so it has nothing to do with this all right drinking is what humans do all right um 11. so so 10 is B 11 says which of the following is least likely to be the resting membrane potential of a cell now cell membranes are most likely to have a resting membrane potential that is non-zero because the resting membrane potential it actually creates a state that is capable of responding to stimuli the signaling molecules and channels would not be as useful with a membrane potential of zero so that's definitely not um that is definitely the least likely um resting member membrane potential of a cell um and so that's going to be answer Choice C all right signaling molecules and channels they wouldn't be useful at a membrane potential of zero and the values given in the answer choices minus 70 minus 55 plus 35 they correspond to different stages of the action potential all right but the key information is that a resting potential of zero is not going to maintain greater gradients for later activity so it's going to be the least likely to be the resting potential of a of a membrane of a cell awesome so 11 is C and 12 says how does the inner mitochondrial membrane differ from the outer mitochondrial membrane the outer mitochondrial membrane is very permeable while the inner membrane is highly impermeable I know we didn't talk about this in the review but let me state it now right the outer mitochondrial membrane very permeable inner membrane not very permeable and so the inner mitochondrial membrane is really unique within the cell because um it's going to actually lack cholesterol and so if we go through these in answer choices we want an inner we want a choice that says that the inner mitochondrial membrane is less permeable and lacks cholesterol so 12 is going to be answer Choice B looks like that's all I have for you I hope this was helpful if you have any questions comments concerns leave them down below other than that good luck happy studying and have a beautiful beautiful day