B2.3 HL Cell Specialisation [IB Biology HL]

this video covers the higher level content from B 2.3 on sale specialization now we know that surface area to volume affects how quickly cells can get materials into and out of their cells in tissues where there needs to be a rapid exchange of materials cells must have a large surface area to volume ratio and so what we'll find is that cells have unique shapes and adaptations in places where this is really important two examples to highlight here one which is a red blood cell so red blood cells are small and that means that they automatically

have a relatively high surface area to volume ratio but they also have kind of this like flattened concave shape I'm drawing this from the side that again allows for a lot more surface area the proximal convoluted tubule cells these are found in the nefron of the kidney so so if you haven't already studied that this may sound a little intimidating but what we need to know there from now is that they have to be very good at absorbing things okay and absorbing things means a you need like room to do that membrane space but also

they're going to need membrane proteins like channel proteins and protein pumps and those are embedded in the membrane so they're going to have little um kind of like protrusions like this these are called microvilli and what microvilli do is they increase the surface area for absorption and that surface area that membrane is what contains all of the proteins you know necessary for transport of things like ions and glucose so great adaptations there to help increase that surface area to volume ratio another great example of this concept of surface area to volume ratio can be found

in our lung tissue so our lung tissue and well there's like a lot of different types of tissues in lungs but we have a couple of cell types down here in these sacs called Alvi so if I think about where's the air going if you haven't already studied gas exchange yet so air comes in through the mouth or the nose down through the trachea and then it branches into bronchi which branch into bronchioles and ends in these little air sacks called Alvi I've zoomed in on one of them here these Alvi are made up of

two cells and these cells are called pneumocytes site means cell pumo refers to the lungs like kind of like thinking about pneumonia and there are two cells so all outline um type one pneumocytes here in blue look at these cells they are flat okay this flat buted shape and this very thin shape increases the surface area to volume ratio so these guys have an incredibly high surface area to volume ratio and that's because that's where gas exchange is taking place it's where the diffusion of gases happens and we know that's more efficient when the surface

area to volume ratio um is very high we're going to see relatively few mitochondria in there because we don't need a lot of ATP for active transport remember diffusion is a passive process we're also going to find a different type of pumy these type 2 pneumocytes they look like this they're more cuboidal in shape so they have a relatively low surface area to volume ratio but that's okay because they're not used for transport they're not used for getting gases to diffuse into or out of the Alvi or the bloodstream they're there to produce what's called

a surfactant and a surfactant keeps these Alvi from collapsing in on each other but also provides moisture for more efficient diffusion there are lots of organel in there and again this is covered in more detail in a different topic but since we're in this um bit here on Cell specialization and Form and Function it's important to recognize that these two types of cells have entirely different types of shape because they have different functions within the Alvi of our lungs now let's take a look at another example this comes from a different system from our skeletal

muscle system and we'll start with talking about these striated muscle fibers striated means striped and they look striped on micrograph um pictures and the reason is because they are separated into these units called circom again that's from a different topic this is about Form and Function so what's the form what's the function well they are very long they so one muscle Viber will span the entire length of a muscle and when they're um contracted they can shorten um quite a bit to create a very strong pulling Force they are multinucleated um so they have a

lot of nuclei again it helps with like efficient transmission of um messaging more on that another topic and again that striation comes from the stripes those repeating units of contractile um units all right and then we have cardiac muscle cells so these have some similarities to the striad muscle cells that we find in our skeletal muscles except they're not multinucleated they're only one nucleus and that's really okay because they're much shorter so they don't need those multiple nuclei they are however branched and those branch BR Es are um connected through features called intercalated discs this

is because it's very important for cardiac muscle cells to contract in unison to be coordinated and so that structure very much helps their function the egg and the sperm are also great examples of cells that have very specific adaptations um or structures for their unique functions so we'll start out by drawing the sperm first and I'm going to start by just drawing this head area okay and the head is going to narrow into this like mid piece type area which is then going to narrow even further into this tail or flagella okay not a great

drawing I'm hoping yours looks a little bit better here now this sperm has several features which are very important so it does have this flood gel and that is for movement inside of the mid piece it's going to have several helical mitochondria okay so these are helical mitochondria all right and then let's see inside of this head region it's going to have um two very important things so it is going to have a haid nucleus and and in this like almost like nose type area is how I think of it um this is a structure

called the acrosome and this is all surrounded by the plasma membrane of the sperm okay so the plasma membrane would go all the way around the outside not just up here on the front but all the way around there are lots of other features and you may see them in like a textbook about like microtubules and proteins and those are important too but here we'll focus on the main bits so this flagella um or tail if you want to call it that um is there for movement okay so for like a swimming action that as

you can imagine is going to require lots of energy so these helical mitochondria become very helpful in that regard the hloy nucleus doesn't necessarily have a huge function in terms of like I don't know a specialized shape but it does contain the chromosomes which will fuse with the chromosomes of the egg upon fertilization now this acrosome contains tons of enzymes that's the key word here enzymes and those enzymes are going to help like eat through the outer layer of the egg more on that in just a moment to help that sperm reach the cell membrane

or the plasma membrane of the egg and then this plas membrane I'm going to leave that in black um has binding proteins and these binding proteins are going to match up with proteins on the eggs cell membrane to help them fuse together so great example here of Form and Function now let's talk about some features of the egg and how it helps perform its function so the egg is comprised of several layers so I'm going to start out with the main part of the egg which is surrounded by the plasma membrane inside the egg we're

going to have a haid nucleus just like the sperm that contains the chromosomes and a uh it's going to be filled with cytoplasm and that cytoplasm is going to have all the normal things like organel but it will also have yolk which is what um the fertilized egg or the zygo would use for energy it will also have these things that look like dots um they're actually quite large they're visible on a microscope these are called cortical granules okay and then I'm going to find two kind of things surrounding the egg there's this layer of

follicle cells called the corona radiata so leftover follicle cells after ovulation Corona kind of meaning Crown radiata going out like this and then I have that space in between the follicle cells and the egg and that is called the Zona palua all right so I've colorcoded a few of them I left the plasma membrane black um same with the cortical membrane or cortical granules and the cytoplasm so let's have a quick chat about what these different features help the egg to do so we'll start with some that might be a little bit more obvious right

so the haid nucleus contains the chromosomes that will fuse with the chromosomes of the sperm upon fertilization okay the cytoplasm or Yol contains energy energy and this Corona radiata is just serving as this outer layer here it's one of the things that the sperm will have to pass through in order to fertilize the egg now this plasma membrane much like the sperm has binding proteins again those are going to help match up with the binding proteins on the sperm ensuring that Fusion takes place and so once that Fusion takes place once one sperm fuses with

the plasma membrane of the egg the egg is going to release these cortical granules so they'll move from the um cell into this Zona palua and that is going to cause the Zona palua I say hardens it's because we haven't really it's not really a topic for B 2.3 but it makes it impenetrable so that no more sperm can get to the egg and fertilize the egg so again if you haven't studied the ins and outs of production yet that is okay the important part here is understanding that the egg and the sperm are both

examples of specialized cells that have different features because they have different functions