okay everybody hope you're doing well today in this lesson we're going to go over passive transport which is a form of diffusion it's important that we understand how diffusion works because you have a lot of different substances that are capable of moving into and out of the cell and these are generally substances uh substances that the cell very much needs so this is going to be types of transport this is going to be a two-part lesson and the first part here is going to be passive transport that's what this video in this lesson is going to be all about all right well quick little uh prelude is one of my hobbies is i like to go on paddleboard i have a big paddleboard i go out into the garrison channel i go by davis island harbor island um the hillsborough river sometimes out into old tampa bay off bay shore and sometimes i'll just go out there and unwind from the day relax and i'll just sit on the paddleboard and really not do anything i'll just let the tide take me wherever it goes hopefully not into the wall but sometimes i'll be in the garrison channel over by let's say jackson's an american social and tampa general hospital and before i know it i'm all the way down by sparckman wharf and i didn't do a thing because the current is just taking me from one place to another no energy no uh no motor no paddles no kicking no nothing just going with the flow and that's what passive transport is really like passive transport is the movement of molecules and those molecules can be of any type that does not require energy and that energy is typically going to be in the form of adenosine triphosphate atp the stuff that the mitochondria and the chloroplasts produce now in order for this to actually proceed and go forward the particle the molecule whatever we're talking about must move down a concentration gradient from an area of high concentration to an area of low concentration all right now what the heck does that mean okay well let me uh describe a few things let me give an example if we if i was actually in class with you guys during this particular lesson we would actually do this example in class and check this out let's say that this is our classroom and what i would do is i would ask one of the guys one of the girls if they have some sort of body spray or perfume that's aerosolized you can spray it and we've always got at least someone that has some sort of perfume so let's say that you have this little sort of perfume or body spray whatever and what i would do is i would walk over here in front of the projector screen like right here and i would just spray it all over the place i mean back and forth back and forth back and forth back and forth and what i would do is i would ask you guys to raise your hand when you smell it and so you know how my my room is set up we got all these students i should probably use different color um we have all these students each pink circle represents a student okay so right now this area is a high concentration of this um this perfume or whatever i whatever it is i spray we'll just call it a perfume there's a high concentration everywhere else in the room here and here and here and anywhere that there isn't the perfume is going to be low concentration and according to the loss of just passive transport these particles are going to spread across the room without any energy you don't need a fan you don't need to like blow it around it's just going to do it all on its own to try to reach a state of equilibrium so i would say within two minutes tops two minutes tops this particle would be all over the room and it would basically be equalized and what would happen is as we start to progress this way more students will start to raise their hand and then the students in the back row finally raise their hand and we know it's gotten throughout the whole room so generally molecules are going to diffuse from a high concentration to a low concentration under the laws and the rules of passive transport that is simple diffusion at its finest to give you another example imagine that we have a permeable membrane this black line represents a permeable membrane permeable means that molecules and particles can pass through it and imagine that i just have a lot of particles over here and we're going to call this so let's say we're going to say this is 5 molar if you are if you haven't taken chemistry yet or if you're taking it out you likely have not gotten to malaria molarity is a measurement of concentration how much of something there is within a given space to give you a really crude example of this um this or if we were to talk about like say the hallways of playing high school during class change we would say the molarity of students is very high there's a lot of people in a very small space um as opposed to when the hallways during class change there's hardly any people um in there okay so this is on the left side we're going to call this a very high concentration but high is subjective you know high compared to what you can say that's high but what if i double the amount on the right so over here i'm just going to draw a few this is definitely low in comparison so according to the loss of passive transport these molecules are going to diffuse across the membrane from left to right which is from high concentration to low concentration until you've reached a state of equilibrium and almost forgot let's say that this side is 0.5 molar so just half half moles per liter so that's generally passive transport you see this if you put food coloring in like a bathtub eventually you put several drops or of food coloring or you put the food coloring tablet into a big body not a big body water but something like a bathtub or a toilet and eventually the entire area is going to be that food color because it's going from high concentration to low concentration okay so there are three types of passive transport that you'll need to know number one simple diffusion now warning warning warning this is the form of passive transport that students forget the most i think by now you guys are starting to know that i don't just make up these warnings i don't make up these ahas and you might be saying oh you keep saying this it's not gonna happen to me why not i hope it doesn't happen to you but so did the same so do the students that said that so trust me simple diffusion seems to be the one that students forget the most and i have a hypothesis as to why it doesn't have some fancy scientific name it doesn't say osmosis it doesn't say endoplasmic it doesn't say photosynthesis it's just simple diffusion not very not a very tough word i think it's so easy just seem to overlook it so what happens during simple diffusion well molecules move from an area of high concentration to low concentration through a permeable membrane now i'm going to put something parenthetically that means in parentheses no pumps no channels all right just straight through the membrane now we need to be very clear about something here this is going to stop when equilibrium is reached which generally means it's even on both sides okay now generally guys in biology most of more often than not but not all the time the membrane that is in question here is going to be a phospholipid bilayer like the ones we learned a week or so ago the same stuff that makes up the endomembrane system organelles the mitochondria the chloroplast the nucleus and the plasma membrane of cells okay now a few things that you need to remember about this plasma membrane it is nonpolar the interior is made up of lipids lipids are non-polar molecules so only nonpolar molecules can pass through and if you're still having trouble determining if something is nonpolar or not if it is polar it has a charge in chemistry polarity means positivity and negativity if something is positively charged negatively charged or has um areas of the molecule that has both it is considered to be polar it possesses poles um nonpolar doesn't have that now not only do non-polar molecules pass through but also small molecules i'm going to make sure i mention that you can't have something really big in nonpolar it's got to be small so with this in mind let me ask you this could h2o pass through this just diffuse to the other side over here the answer is no because h2o is polar it cannot pass through the interior of the membrane because the interior of the membrane is non-polar so let's get rid of that so what kinds of things can pass through only non-polar substances and generally substances are very small okay and i'll illustrate this all out for you in a little bit but only non-polar substances and small substances all right number two we have facilitated diffusion remember this is all passive transport the word facilitate means to aid or to assist or to help like i am facilitating your education when it comes to college-level biology i'm not doing it for you i'm just helping you well in facilitated diffusion this is a means of passive transport and when you hear passive transport molecules are moving from an area of high concentration to low concentrations so that's something we need to make sure that is a staple of passive transport molecules move from an area of high concentration to low concentration okay now this is going to be within or or let me rephrase it but with the aid of a channel protein now why do you need a channel protein here's why the molecules that are diffusing are either too large or they are polar and we know that they cannot just simply slip through the plasma membrane so let's draw out one of these examples so okay this is obviously a phosphate bilayer and i'm gonna keep beating this to death until everybody knows the interior is nonpolar because of those lipids so only non-polar substances can pass through however you have this protein pump so let's say i have these big old molecules it doesn't matter what they are but here's what you need to know they're polar polar polar polar and polar well there's a bunch of them over here i'm going to draw a few more just draw them all over the place and over on this this side there's hardly any i'll just go ahead and write all this out just for the sake of it so no one gets confused polar polar polar and polar so if we were in class i'd ask you which side is a higher concentration the top and the bottom it's definitely the top and so these molecules want to diffuse through and that is exactly what they're going to do they're going to travel through this channel protein to get to the other side that's their opening this is facilitated diffusion that channel protein is facilitating their diffusion from an area of high concentration to an area of low concentration high low got it okay now for the third and final type of transport that is a passive that you'll need to know it is called osmosis remember osmosis is passive transport no energy required osmosis is the movement of water molecules from excuse me um across a membrane from an area of low solute concentration to high solute concentration now you might be thinking i just made a typo wait what do you mean why are you going from low to high that's that's not it there's a lot here this is the most confusing one so i'm going to take my time to slow it down a little bit in order to understand what's going on here we need to first remember what a solute is a solute is a substance that is dissolved in a solvent a solvent is a substance that the way i like to phrase it it does the dissolving so if you were to think of the gulf of mexico the gulf of mexico has salt water the solute is salt the solvent is the water when i was in school like in a junior in high school or of sophomore in high school and i took bio um i never got that right i could never figure out the two of them so a little way to help you remember this is remember that water is nicknamed the universal solvent and that might help you remember which one is which now why am i why does solvent have to do with this water is attracted to a solvent um if you want to do something really cruel and really mean pour salt on a slug and all the moisture that's in that slug is going to leave his tissues and go towards the salt basically drying out the slug another example would be if you were to actually drink salt water from the gulf of mexico or from tampa bay or anywhere in the world what happens is you drink the salt water and the salt water has more salt in it than the salt that is in your own body in your cells and so the common rule here is this is very important water is attracted to the region with the most solute so if you are drinking salt water i can assure you that the salt water has more solute in it more salt in this case than the salt that is in your body and so the liquid the the water that is in your cells and in your tissues is going to diffuse out of your cells and in your tissues and towards your digestive system because you just drink all that water and that actually really dehydrates you if you didn't know this drinking salt water dehydrates you uh kind of a gross story a few weeks ago i took my dog to a beach park over in pinellas county and it was he's he's still kind of a puppy so he hasn't been to the beach very much and when he was in the water swimming around he was drinking all that salt water he was pooping straight up water for half the day just salt water no poop no diarrhea just salt water because all the salt that is in his cells and in his tissues was drawn towards the salt that he just drank and so he had a lot of water in his digestive system way more than he should have and so he was just flushing out his whole system and when we finally got him some fresh water he drank a couple buckets hole because he was so parched because all that salt basically dehydrated him it's it it attracted all the salt out of this um or all the water out of his cells so let's make a drawing here to hopefully really make this give you that um aha moment and then i hope that you will understand it and if it's challenging don't be surprised this is typically the hardest one to understand so this purple line you see here is going to be a um it's a membrane but it's not going to be a phospholipid bilayer this is a membrane in which only water may pass through okay so let's put our water up in here and we're going to put sodium ions all throughout this sodium ions are an atom of sodium that has one more proton than electron so has a positive one charge so i'm just going to draw a whole bunch of these guys okay a lot of them lots of sodium and over here i'm just going to draw a few now listen carefully here we go according to this as far as solute is concerned the left is a high concentration the right is a low concentration but this is the diffusion of water osmosis is not the diffusion of ions it is not the diffusion of sodium ions it is the diffusion of water so here is how you're able to determine which way water is going you need to ask yourself which side has more solute it is clearly the left side all this water is attracted to any area or any region that has more solute in it so water is going to want to go in the left direction okay that is one way to look at this and when that happens here's what you guys are going to find out this area of water is going to rise and this is going to lower until both sides are roughly equal but if you look at it like this you still see that there's more sodium on the left so this way might not be the best to understand how this works so here's a different way and this is the one i would actually prefer for you let's get the water level back up being equal uh you can come up with some arbitrary number it doesn't matter what you are what it is but what you have here is salt water so there's salt water here and there's salt water here what i want to know is uh what percent is solute and what percent is solvent and we all know that percent said to equal 100. so you can make up some arbitrary number but just make sure that it makes sense okay so let's just say that on the left the amount of solute is 15 and the amount of solvent which is water is 85 percent okay now over here solute let's say it's about five percent solute 95 solvent i want you to ask yourself which side has more water the left or the right we have 85 percent we have 95 percent i'm not the mathematician i don't claim to be didn't really study a whole lot of math in school but i do know that 95 is higher than 85 so when it comes to actual water this is the high concentration this is the low concentration and according to the laws of passive diffusion and passive transport which way do you do particles diffuse towards across the concentration gradient is it low to high or is it high to low it is high to low so the the water is going to diffuse across until the difference between them is equalized so as you add more water to the left this side is going to become more diluted and this side is going to become more concentrated and so what's happening is the water level is actually going to change so you can have water rising all the way up to here and then the water on the other side is going to still be very lower so you have less water the amount of salt you didn't change this is going to be saltier water because it is a smaller volume but this is going to be less salt to your water because you added more of it so if i were to try to give you another analogy here imagine you have a bathtub filled with food coloring okay and it's like a bright green what would happen to the color of that green if you turned on the faucet to the bathtub and allowed more water to fill the bathtub with the green get more brighter which would mean it's it's more concentrated or would it start to get uh would it start to fade away which means it's starting to dilute the correct answer is it would start to dilute and so you are decreasing the concentration of the solutes in that bathtub so by adding water to the left side here we are decreasing the concentration of solute in the water and by decreasing the water on the right side we are increasing the solid the concentration of the solutes on the right side i hope that makes sense so now let's actually do some examples just begin to conclude okay so i'm going to make some some regions here okay so let's say in both of the in oops there we go let me make sure you guys are still seeing what i'm seeing i just have a little glitch there okay good we're all fine uh let's imagine that there's a semi-permeable membrane here here and here okay now stipulation this this and this is a phospholipid bilayer so you tell me is that polar or is that nonpolar it is nonpolar so only nonpolar substances can pass through it let's get our water okay so in this first example i'm going to have oxygen molecules we're going to put five of them on the left we will put one on the right we're going to say that this is .5 molar and we're going to say this is 0.1 molar okay just stay tuned next i'm going to have this box have hydrogen ions on the left side probably i drew one too many i just want to keep it at five and i have one on the left so again 0.5 molar 0.1 molar and then finally over on this side we're going to say i have sodium ions one two three four five and then on the right we have one and again 0.5 molar 0.1 molar we're going to do i'm going to actually give you some visual examples of simple diffusion facilitated transport and osmosis all right so let's uh draw some of these boxes again and this is going to become like a before and after okay this box is going to be simple diffusion according to simple diffusion do you need a like a channel protein to move across no you do not also because i already stipulated this green line is a plasma membrane or a phospholipid bilayer roughly the same thing um polar and nonpolar substances can pass through the answer is polar and so what we have here is just three oxygens on the left and three on the right because two of them diffuse through so we have 0.3 molar and 0.3 molar it's equal now some people say that diffusion stops it does not stop what happens is diffusion continues but it it continues at an equal ratio if one oxygen is going to diffuse from right to left that means that the one oxygen is going to diffuse from left to right and this is going to be static it's going to be this is what we mean by it has reached an equilibrium okay the next one is going to be facilitated diffusion we have our phospholipid bilayer we have the water and we have these hydrogen ions but actually before i start drawing them um if you already drew it they'll be back if you look up hydrogen ions have a charge like and if i were a student in ap bio and i wasn't in a cameo i'd be like how am i supposed to know if it's polar or not i didn't take ap bio or i didn't take him you see that thing right there you see this symbol that means it's positively charged does that mean that it has a charge yes in chemistry what does it mean to be polar you have either a positive charge or you have the polar opposite which means you have a negative charge this is going to be polar so can polar can a polar substance like this molecule diffuse through this plasma membrane the answer is no negative it cannot so because i told you this is going to be facilitated transport what you need are a couple channels there's one there's the other so the hydrogen ions can pass through so we have three hydrogens on the left we have three hydrogens on the right it has now reached in equilibrium 0.3 molar 0.3 molar they pass through those channels these gaps here are going to be channels protein channels okay now for the last one the one that's the trickiest let's go ahead and get it all set up there's a membrane here's our water and i originally had sodium ions um on one side the other or i had five on the left and i had one on the right so remember what i did over there which side and think before you speak which side has a higher concentration of water compared to the other side well again if you just make up some arbitrary numbers you can do the same numbers i did for the example let's say that this side is 15 solute 85 solvent which means 85 water let's say this side is 5 solute 95 solvent that means that water is going to diffuse from left to right sodium ions cannot pass through that membrane because it is um polar but if you really know your biology some of you might just your ears might approach i'd be saying wait water is polar too water can't pass that plasma membrane and you're absolutely right so what we have to do is we have to draw some pumps are going to be called if you remember from lecture these are called aquaporins aquaporins are a type of protein pump which allows water to diffuse across them so it doesn't have to worry about the membrane so with that being said the water level is going to change water is going to diffuse from left to right all right i totally said that wrong i apologize right to left it's going to diffuse from right to left and that's going to cause the water level to actually change because we're diffusing from right to left this side is going to be really high this side is going to be really low and so we have one two three four five and over here we have one now it's going to still be equal remember we're talking about concentrations and dilution or dilutions and all that so this is still good this could be 0.3 molar and this could be 0.3 molar you're like well i don't get it it's the this side is going to be the diluted side so there's more water added and this side is going to be the concentrated side which means there's less water water was taken away all right there's one last thing i want to go over and then we'll call it a day and that's going to be the concept of hypertonic hypotonic and isotonic so let's do this hypertonic hypotonic and isotonic hypotonic is a lower solute concentration that's what hypo means i messed that up darn it hyper means a higher solute concentration hypo means a lower solute concentration and an isotonic means the same solute concentration okie dokie so hyper means higher hypo means lower and iso means the same so let's actually put this to an actual test i'm going to draw a beaker here we're going to do a before and after so here's our beaker inside the beaker we're gonna have some sort of solution [Music] and we're gonna have a cell like a red blood cell okay now let's say that inside the red blood cell is .4 molar uh sodium chloride just some some solute there and you also have sodium chloride in the water but the water is going to be 0.1 molar sodium chloride which region has more solute inside the cell or in the solution the solution is what the cell is floating inside of all this is the solution what has more solute if you said the cell has more you are correct and so which way is water going to diffuse towards water is going to diffuse from the solution into the cell and this is going to possibly cause the swell to swell up and maybe even burst this phenomenon is known as a hypertonic solution and i am tripping it must be late because you know i think it is late it's like 1202 when i'm recording this it is hypotonic i had a student a long time ago came up with a little rhyme um hypo like a hippo so hypotonic you need to really pay attention to the actual prefix here guys because you need to make it make sense when we say that the solution is hypotonic you have to understand that we're talking about the solution you can look at this in two different ways you can say the following i could say that the solution is hypotonic to the cell or i can say the cell is hypertonic to the solution so you can say it's a hypertonic cell or it's a hypotonic solution but the cell is going to swell up and possibly burst example number two let's get back to having our cell let's say this is 0.4 molar sodium chloride and out here it is 0.9 molar sodium chloride which side has more solute obviously the solution does and so water is going to diffuse out of the cell towards the solution what effect does this have well water is going to cause the the water level to rise and that is also going to cause the cell to shrivel up this is known as being a hypertonic solution and as i said this is subjective you have to know which one you're looking at if i'm looking at the solution i would say the solution is hypertonic to the cell or we could say the cell is hypotonic to the solution there's two different ways to look at it you just are you looking at this from the perspective of the solution or are you looking at looking at this from the perspective of the cell okay and then the last example we have our cell wrong color we have our cell and inside the cell is 0.4 molar sodium chloride and in the solution is 0.4 molar sodium chloride this would be equal now diffusion doesn't necessarily stop but what does happen is for any water that diffuses out you have the same ratio of water diffusing in same ratio diffusing in same ratio water diffusing out and so the cell really doesn't change it's still going to be the same this is known as being isotonic and it's going to be the same either way but for just the sake of writing it i'll write it out the solution is isotonic to the cell or you could say the cell is isotonic to the solution okay that is pretty much it that is the conclusion of passive transport we will do another lesson which will cover active transport which is the use of energy to go against the concentration gradient from low to high and that requires the use of atp which is cellular energy i'll see you then