AP Biology Unit 2 Review

[Music] hey dr h here today's video will be our review of unit 2 for the ap biology test where we will go over cell structure and function okay here in part one we'll go over some basics of cell structure and very quickly go review some of the important organelles found in the cell uh and then in part two we will get into a cell membrane structure and function and get into cell transport okay so let's go ahead and get started with part one we'll start here with some basics on cell structure of course as you know cells are very small right and the reason that they are small is to help uh with the exchange of materials with the environment right both materials coming into the cell and materials coming out and this small size uh helps with this exchange because of the very high surface area to volume ratio okay small cells uh have a volume or area to volume ratio of about six to one uh if we increase that size to a larger cell then you see that the volume these the volume surface the surface area to volume ratio there falls down to about 1.2 so that that very small ratio there with the large cells would not work well to keep cells alive and efficiently exchanging materials with the environment on the ap formula sheet you will have all of these formulas in terms of surface area of different shapes and volumes of different shapes i have seen a few example questions uh using these formulas um but again if you're given the formulas and you have all the numbers and you have the calculator uh you certainly should be able to uh plug all the numbers in to remember that they are often looking for this surface area to volume ratio right so then you just divide one by the other another way that cells uh will try to maximize this surface area to volume ratio is by greatly expanding their surface area uh with some structural features like little tiny projections like the uh cilia here or the uh microvilli these might be in in the small intestine um and these little projections uh they don't add a whole lot of volume to the cell but they greatly expand the the surface area right so any uh cells that are along a surface where exchange is going to be happening now we would certainly expect to see some sort of structural feature like this to increase that surface area and maximize that exchange with the environment uh the next uh the next general topic uh with regard to cell structure um is this idea of compartmentalization okay and this basically just means that inside of a cell there are different regions that perform specific tasks right and uh certainly when we think about complex cells like eukaryotic cells uh we see that there is a whole lot of compartmentalization here um and we'll certainly talk a little bit more about this when we get into membranes and organelles but we also see this compartmentalization in these simple bacterial cells even though there are no internal membranes no internal organelles here there are still regions uh where certain aspects of their life will occur like the nucleoid region where the dna is contained right they don't have a nucleus right with a membrane around it but they do have a region where the dna will be concentrated okay so this idea of compartmentalization kind of separating out all of these different functions of the cell is very important again to maximize the efficiency so that's our basics of cell structure really not a whole lot there um so you know we're just really just looking very basically at cells um so the next thing we want to talk about here are some of the important organelles now remember these organelles are just small uh internal structures of the cell that perform specific uh molecular biochemical roles the only organelle that is found in all domains of life right bacteria archaea and eukaryotes are the ribosomes right all the rest of these are all membrane bound right so they're surrounded by a membrane so those would only be found in eukaryotes okay and you can see around here uh the list of seven organelles uh that the that uh the ap course um lists as being important i'm not going to go into detail on all of these i'm going to run through them really quick and just say a few words about them there are a couple here though that we will see again as we go through specific cellular processes and i will certainly highlight those as we go um so first off we have the ribosome right this is the site of protein synthesis obviously we will see this again when we get to the process of translation right making proteins and remember this is the only organelle that is found in all domains of life right bacteria archaea and eukaryotes the endoplasmic reticulum uh two types here right smooth er and rough er uh the rough endoplasmic reticulum has ribosomes around the outside um and we will we'll see the rough er again again when when we get to protein production because it is involved in sending proteins out of the cell or moving proteins around the cell to the right location right so we will see this one again again when we get to that point uh the golgi complex kind of works with the rough er in sending proteins out to where they belong i'm not really going to see this one again too much lysosome as is involved in digestion in some unicellular uh eukaryotes this the lysosome may be their entire digestive system right they bring in food particles transfer those into a lysosome and the digestive enzymes inside will break those food particles down they're also used um to recycle organelles right as organelles wear down uh they are sent to the lysosome and they're broken about broken down again into their molecular components and can then be reused see the the vacuole this is just a large kind of a central storage area it's especially important especially prominent in plant cells where it will fill up with water and will actually put pressure on the cell walls of the plant and that pressure is called turgor pressure okay and that is what actually allows plants to stand up straight right against gravity they don't have um you know a skeleton to hold them up as as many animals do so they re they rely on this vacuole being full of water and pushing out on the cell wall to maintain that upright the next mitochondrion so this is this is an important one again we we will see this one this will come back in unit 3 about energy so we will certainly talk much more about it then so this is where a lot of the aerobic reactions of cellular respiration will occur okay and we'll talk about a lot of these structural features here um and some of these specific locations um in unit three with the mitochondrion and will also hit in unit three uh the other big energy uh organelle the chloroplast right this is the site of photosynthesis right right so again we'll hit all of these structural features and and some of these specific reactions that happen in each of those areas when we get to unit three okay so those are the organelles that you should be somewhat aware of um very rarely have i seen questions that are just straight up asking about one of these organelles like there's not going to be like a big matching section where they give you a function and you have to match the organelle to it um really though the ones that come up again later um are the ones that you should really be aware of and those we will definitely cover uh when we get to them when we go over you know future content right like the ribosome mitochondria chloroplast maybe the rough er in terms of moving proteins around the cell other than that i think those are the main important ones okay we'll now go over uh cell membrane structure and function okay and with the function part uh we'll mainly be talking about cellular transport okay so first uh just some general information about membranes um of course all cells are surrounded by membranes right this is true for all domains of life and there are a few cell types uh such as plants fungi bacteria probably should throw archaea in there as well um that do have cell walls uh around the outside of the membrane um but we're not really gonna talk about that too much right now okay in terms of the major roles of these cell membranes uh there are three major roles here um first just very basically they separate the inside from the outside right they form the boundary of the cell they regulate transport which is what we'll really be getting into uh in in this video and as we'll see in unit 4 um they also play a big role in communication looking at internal membranes uh those of course are only found in eukaryotic cells uh the main role of those is in compartmentalization something that i talked about back in part one but when we have all of these internal membranes here dividing the cell out into all of these organelles um that is one of the major roles right and again this is to help um increase the efficiency right each different biochemical process has its own location right bounded by a membrane okay so let's talk a little bit about membrane structure right the the current model of uh how cell membranes work is called the fluid mosaic model and this is made up of two pieces right the fluid portion of the membrane is the phospholipids right kind of shown here uh in white and orange um and then the the mosaic portion is uh all of the proteins and those are sort of uh the the purple pieces in the membrane diagram here right so we'll talk about each of these structural features uh starting with the phospholipids right as the name implies these are lipids right and remember that lipids um generally are insoluble in water right they have the the big long fatty acid tails uh which make them very hydrophobic phospholipids are a little unique in that they have a polar region right they have what are called a polar head which makes that region hydrophilic means that it can form hydrogen bonds with water because of these two different properties right the the hydrophilic polar head group and the hydrophobic nonpolar tails when phospholipids are mixed with water they will spontaneously form this bilayer structure right with the heads facing out towards the water and the tails sandwiched in the middle pushing all the water away right so this is the bilayer structure that we see in cell membranes right and this is this will spontaneously form meaning that this is very energetically stable right this is the lowest energy form a few different um structural features to talk about with uh the different phospholipids that we may find in the cell membrane first are the phos are the hydro carbon tails the the fatty acid tails are they unsaturated or saturated remember unsaturated uh means that there will be some carbon-carbon double bonds and that introduces a little bend a little kink in that fatty acid tail that plays a very important role in maintaining the fluid state of the membrane at colder temperatures remember that little kink will prevent the phospholipid molecules from packing too tightly together so as it gets cold and molecules tend to stop moving around so much tends to pack in a little bit these unsaturated fatty acids will maintain the membrane's fluidity organisms that are adapted to living in cold environments would tend to have more of these unsaturated fatty acids in their membranes cholesterol there also is found in some animal cell membranes and that sort of works as a kind of a a moderation molecule i guess um it keeps the membrane from getting too liquid and from getting too viscous right so it kind of keeps it right in the middle right kind of like the uh it's like a little goldilocks molecule i guess right it keeps the the membrane uh fluidity right where it should be um so that's the phospholipid portion um the protein portion that's that's the mosaic part of the fluid mosaic model and there the proteins are all over the membrane and one important structural aspect of these proteins to think about is if they go through if they span the membrane they're going to have they're going to have different surface characteristics on these different regions of the protein so if we look for example at a protein here that is going through the membrane right the uh the portions of the membrane that are exposed either to the outside the extra cellular side of the membrane or on the inside of the cell the the cytoplasmic side since those are going to be exposed to this aqueous solution those regions would be hydrophilic or polar the regions in the middle that are sandwiched in between that are embedded in the membrane that are associating with those fatty acid tails right those regions of the protein surface uh should be hydrophobic right or nonpolar right and they would interact well with that region okay so that's a membrane structure so let's get into a little bit about membrane function okay the main function that we're going to talk about here in with regard to the membranes is transport okay regulating what gets in and what gets out of a cell okay and this is mainly due to the phospholipid uh portion of the membrane right these uh this hydrophobic um polar region in the middle of the membrane there is going to prevent any any polar molecule any large molecule from moving into the cell easily there certainly are some molecules like for example oxygen or um that can dissolve very easily through the bilayer right any dissolved gas will should be small enough to sort of fit right through right and this is called simple diffusion um and we will talk more about this uh the different types of transport uh one um in a few minutes uh the protein portion of the membrane has many different roles as you would expect from proteins right in general proteins have lots of different jobs and we see a few of those uh those roles here again in this video for this unit the main thing we're going to be talking about with regard to proteins are the transport proteins right which i think is in the upper left-hand corner of the diagram there all right so let's talk about transport before we get into cell transport we really need to talk about a few kind of more general terms mainly diffusion right diffusion um i have the the definition written over there it's basically just the movement of substances from an area of high concentration to an area of low concentration right so we call this substance is moving down the concentration gradient and it's very important that we understand this idea of concentration gradient because it's going to come back in in a few different units we will see this idea of concentration gradients right and it is simply just a difference in concentration of some substance in two different areas and what's going to happen if things are able to freely diffuse then they will move from high to low until equilibrium is reached right and at equilibrium there will be equal concentrations of the substance on uh both areas right on throughout the throughout the whole area uh at equilibrium that does not mean that molecules stop moving right they are still moving around um just there is no net movement from one area to another one way that uh we can look at this in um in a laboratory setting is with the use of uh this piece of equipment called a youtube right and it is a piece of glass there shaped like a u and down at the bottom there will be a membrane right in this case it is a membrane a selectively permeable membrane that is going to let some molecules through and other molecules not right in this case we see that it this this membrane is letting water through but not the large uh dissolved sugar molecules so what's going to happen uh the water is going to move uh but the sugar is not and it's the water um is going to kind of try to reach equilibrium okay so in this case the water is going to be moving from left to right and that movement of water it's really just the diffusion of water is called osmosis okay and there's there's nothing really special about osmosis it is just the diffusion of water from an area of high concentration to an area of low concentration right and we usually don't think about water as having a concentration right but there there are some ways that that we can think about it that we will go over in a few slides all right so looking at uh looking at cellular transport um the first type of transport that we'll talk about here is passive transport okay and as the name implies passive this requires no energy input from the cell okay these are material these are uh molecules that are moving by diffusion right moving down the concentration gradient from an area of high concentration to an area of low concentration okay and there are a few different types of uh passive transport um there is this simple diffusion right and these are uh this is the small uh nonpolar molecules that are able to fit right through the membrane right you can see the the oxygen gas there um kind of squeezing right in between the molecules of the phospholipid bilayer hey so dissolved gases move very easily through this through this through this type of transport right simple diffusion larger molecules or polar or charged molecules are not going to be able to move through the membrane like this right either they are too big to squeeze between the phospholipids or if they're charged or polar they're not going to be able to get through that nonpolar hydrophobic region of the membrane so for those molecules there is a a process called facilitated diffusion which again this is completely passive right no energy from the cell but now there is a protein that is involved right either a channel protein which literally just has a hole through the middle for a specific solute to move through or a carrier protein that will change shape a little bit and allow this solute to move into or out of a cell right both of these diagrams show things moving in but diffusion can certainly work to move things out of a cell as well okay but again there is no energy input from the cell for any of these um any of this diffusion any of these passive transports right simple diffusion or facilitated diffusion as shown here one other um kind of thing to touch on here um this is the idea of tonicity and osmo regulation okay like i said uh when we when we think about osmosis right the the direction that that osmosis will move the direction that water is going to diffuse will go from high concentration to low concentration and we usually don't think of water as having a concentration so instead of looking at osmosis in terms of water concentration we can think of it in terms of water potential okay and the water will move will osmose from high potential to low potential okay and there are a couple formulas here to calculate the water potential of a sample okay and you see uh the formulas here where water potential is the sum of two um two half potentials right the pressure potential and the solute potential and there is a the the second formula there um is how to calculate the solute potential again with every formula that i'm giving you here these will be on the formula sheet that you get with the test so do not feel like you need to memorize these um i have seen questions in using these formulas show up on the test in the past but these are really pretty straightforward formulas right one is adding two things together um the other is multiplying what four things together right and you will be given all of that information if you need to calculate water potential or the solute potential right but remember the the usefulness of this is to determine what direction is water going to diffuse and it's going to move from high potential to low potential the other uh piece here or the the next piece that we should talk about tonicity is what happens to a cell when it is placed in different concentrations of solute and we use these three terms here um to talk about the relative concentration of solutes inside versus outside of a cell okay so hypotonic uh that means that there is a lower concentration of solute outside the cell when compared to inside right isotonic means that they are the same so they would be at equilibrium and hypertonic means that there is a higher concentration of solute outside of the cell and we see with the arrows there what would be happening to the water right in a hypotonic solution water is going to be coming into the cell right because the water potential will be higher outside in a hypertonic solution the water will be moving out and the cell will be drying up because the water potential is higher inside of the cell keep those three terms in mind and remember that they are relative right in this case um you know we're saying that the the solution the outside solution is hypotonic to the cytoplasm right you can't just have a solution a beaker of salt water and say that this is hypotonic right it has to be hypotonic to something else right and generally it's to the inside of a cell one final thing here to talk about um with this and this is this little guy here this is a freshwater paramecium they really love to talk about um this guy uh just because it's a great example of an evolutionary adaptation to a specific environment so like i said this is a freshwater paramecium so it will live in a hypotonic environment so water is constantly going to be entering in to this cell in order to survive so it doesn't swell up and burst these paramecium have the structure called a contractile vacuole so this vacuole fills up with this excess water and when it gets full it contracts and removes the water so this is a evolutionary adaptation that allows this paramecium to live in this hypotonic fresh water environment it's always important um it's always a good idea to kind of keep track of these evolutionary adaptations right the college board loves to throw in evolutionary connections whenever they can right so this is a really good evolutionary adaptation that has to do with cell transport so that wraps up i think uh passive transport so now let's take a look at active transport not surprisingly um this active transport is now going to require the input of energy from the cell right and the the main type of energy that this is we'll be using here will be atp right that is the main energy molecule right and we'll certainly go over that in you in the unit 3 video um so this is now moving substances against the concentration gradient moving up the gradient right going from an area of low concentration to an area of high concentration right and these are always going to involve uh some sort of protein now usually they are referred to as pumps to move substances against the gradient requires an active protein and they're not just going to do this on their own like we saw with passive transport so the one most widely used example of active transport is the sodium potassium pump okay and here we see the steps of the sodium potassium pump basically what is happening three sodium ions bind uh to the pump from the inside of the cell from the the cytoplasm uh atp is used and that causes the protein to change shape the sodium ions are released to the outside of the cell and now two potassium ions from the outside of the cell can bind to the other side of the protein and the protein flips back to its original state and the potassiums are released into the cell okay so the overall effect of this sodium potassium pump is to re to pump three sodium ions out of the cell and two potassium ions into the cell okay so it is a three for two exchange right and we will talk about this sodium potassium pump again briefly uh when we get into the cell communication unit because this does form the basis for our nervous system so let's talk about a few different types of active transport that are important first one here is called co-transport okay and this is when there is a concentration gradient produced through active transport and that gradient is then used to transport something else okay and this kind of introduces this uh concept of a concentration gradient having energy and energy is sometimes very tough um to con to conceptualize because it's you you can't really show a picture of energy right you can't draw a diagram of energy you can't point to energy and say there it is it's just uh you know a thing that systems have right and whenever that just remember that whenever there is a gradient set up whenever there is a concentration gradient across a membrane there is energy in that gradient and co-transport is a way for cells to use that energy gradient to move something else into the cell so here is an example of a co-transport system um there are two proteins involved right the uh the proton pump there that is the actual um active transport prot uh protein right and you see it is using atp to pump hydrogen ions out of the cell right and create this hydrogen ion gradient where there is high hydrogen concentration outside of the cell and a lower hydrogen concentration inside of the cell right so now that there is this gradient set up across the cell membrane there is energy here the cell can now use that energy in the gradient through this other protein the hydrogen sucrose co-transporter which will allow hydrogens to diffuse back into the cell right hydrogens normally don't diffuse very well through the membrane right because they're charged but this co-transporter allows the hydrogens to to diffuse in and as they diffuse in down the gradient right releasing that energy the sucrose molecule the sugar molecule is pulled along with it right and we see the sucrose there moving from low outside of the cell to high inside of the cell right so the proton pump sets up the gradient puts energy in right that energy comes from atp initially and then is found in the gradient and then the co-transporter protein uses that energy allows hydrogen to diffuse back in back down the gradient that releases the energy and pulls the sucrose along with it okay so this idea of co-transport it's very important uh used to move a lot of nutrients right in our in the small intestine right not just sucrose but a lot of the amino acids um a lot of the other sugars are pulled into our cells through this same type of mechanism um i think the final thing that we need to talk about here um with active transport is uh what we call bulk transport okay so this would be endocytosis or exocytosis right depending on which way things are moving right endocytosis will be bringing things into the cell exocytosis is moving things out right and what happens here uh i think i have some pictures yep um for uh phagocytosis or pinocytosis that is bringing in samples so the membrane just sort of moves around and forms the little vesicle and brings um brings in pieces right in phagocytosis that's bringing in a large solid uh piece right so it says they're a food particle um or it could be another cell um in pinocytosis it's really just bringing in a little sample of the extra cellular fluid um for receptor mediated and endocytosis um there are receptors on the cell surface which are specifically binding to a particular solute out in the um in the exterior of the cell and they those come in and sort of increase the the concentration of that one particular solute in the little vesicle there right so receptor mediated endocytosis is a little bit more specific than pinocytosis which just takes a random sample so that is the end there of uh transport so that wraps up the unit 2 review video um so i hope that all made sense and good luck dropping science like galileo dropped the orange

Channel: Christopher Himmelheber

Views: 16,363

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Id: EuFTCOD7gdQ

Length: 37min 31sec (2251 seconds)

Published: Thu Apr 01 2021