we are going to be looking at red blood cells in this video so uh just as an introduction to red blood cells where do they come from they are formed in the part of our body known as the bone marrow for example if you were to eat a piece of chicken let's say the drumstick and you were to crack the bone you would see that the inside of the bone has this reddish material and that is known as the bone marrow and we also have that in our body that is the bone marrow and it is located within the bone structure we as humans also have these as well so the bone marrow itself is full of blood stem cells now before we go into red blood cells let's do a bit of revision for stem cells in chapter five stem cells are just these types of cells that can continuously divide without any limits because if you remember they have an enzyme called telomerase which allows them to top up their telomeres which gives them the capability to divide an unlimited amount of time then the blood stem cell also has another capability where it can give rise to specialized cells and one example is the blood stem cell can specialize to become the red blood cell so that is how red blood cells are formed red blood cells are formed in the bone marrow and they come from this particular cells known as blood stem cells so if they won't usually ask questions as to where the red blood cell comes from but this is just an extra bit of knowledge that we should know okay like our bones actually produce blood cells they are not just there to protect our body or to support our body uh or keep things in place the bones also have capabilities of producing red blood cells now when we talk about red blood cells the first thing that we want to look at we want to see the structure of the red blood cells now the red blood cell itself in terms of diameter is seven micrometers in diameter we know this because if you remember it is almost the same diameter as the Lumen of the capillaries which will allow the blood cells to move in the capillaries in a single line so why is it important that the red blood cells are seven micrometers and it moves in the capillary in a single line it's so that it brings the oxygen to the cells as near as possible to allow easy diffusion to happen now if we were to take the red blood cell and if we were to cut it okay obviously we could cut a bit blood cell but imagine if the red blood cell were a slice of cake and I just cut it to look at its cross section the closed section of the wet blood cell will have a rather weird shape and that shape of the red blood cell is referred to as a biconcave disk now immediately students will ask me or students May wonder what is the word by concave mean the word concave means curved inwards and the word by means two okay so what that actually means is on two sides of the red blood cell the surface curves inwards as we can see over that now why is the surface of the wet blood cell curved inwards how does this help you see to answer this question we will have to compare three types of cells now I have a cell on the left which is just a normal cell that is not curved in any way uh another cell in the middle the cloth section where it's curved inwards and another cell where it's curved outwards so there is a normal cell biconcave cell and it by convex cell all right where it's curved outwards the first thing we want to cover is its total surface area the normal cell will have a normal total surface area but the biconcave cell will have an increased surface area because certain parts of its surface is curved inwards that creates an extra surface area for the biconcave cell the biconvex cell also has a larger surface area because the area is curved outwards creating extra surface so in terms of cells we would like the cell to have a larger surface area so we can eliminate out the normal cell now between the biconcave cell and the by convex cell we when we compare their volume you will notice that the volume within the biconcave cell is lower and the volume within the biconvex cell is higher as I have shaded in Black just to show you that how the space within the cells are different between the two of them okay all right so in terms of total surface area both of them have larger total surface areas but in terms of volume the cell on the left has a lower volume and the cell on the right has a higher volume why do I care the next thing we have to compare is the total surface area to volume ratio we always want a higher total surface area to volume ratio for easier diffusion of substances and in mathematics if you want a high total surface area to volume ratio the total surface area has to be high but the volume has to be low as an example if we both assume that the surface area of both cells are 100 units and if we also assume that the volume of the biconcave cell is 20 units and the volume of the biconvex cell is 60 units again these are all just assumptions if we were to compare the ratio for the cell on the left the ratio is five to one but the cell on the right the ratio is five to three okay so what that means is buy concave cells have a larger total surface area to volume ratio in general and this is important because it allows easier diffusion of oxygen in and out of the cell okay if the cell had too large of a volume diffusion would have been extremely difficult because the total surface area to volume ratio would have been much smaller and we don't want that to happen so the red blood cell solves this problem by having its shape become a by concave disc now the next one we want to also look at about the red blood cell is the fact that it is flexible the red blood cell can actually Bend okay and when it when it's bent it can change its shape but then it will always go back and bounce back to its normal shape so why is this good that the red blood cell is able to change its shape depending on the situation because sometimes capillaries can be narrower than usual imagine if a capillary is too narrow especially when you bend your legs if the blood cells were not flexible what will happen is they will get stuck within the naval space and that's not good because it may lead to blood clots and we don't want that to happen because it's quite dangerous so the red blood cell having a flexible shape allows itself to squeeze through the narrow capillaries by being flexible and after that it will return back to its normal body shape so flexible with blood cells allow it to change its shape squeeze through navel or tight junctions and then just go back to its normal shape when necessary that's what that means now the last thing that we have to understand about the red blood cell is is what goes on within the red blood cell so inside a typical cell we will have a nucleus rough ER Golgi apparatus we'll have mitochondria and all these other organelles however inside the red blood cell nope it doesn't have any of those organelles at all the reason it doesn't have a nucleus it doesn't have endoplasmic reticular ribosomes mitochondria Golgi body none of that at all the reason is because it wants to have more space to contain hemoglobin and the more hemoglobin it has the more oxygen it can transport these are the four things that you will have to know about the red blood cells the fact that it's that the fact that it is 7 micrometers in diameter it has a biconcave disk shape it is flexible and the fact that it has no nucleus ER ribosomes or mitochondria if a question asks you to describe the adaptation of red blood cells then you just have to say it's oh it has a biconcave disk shape but if the question says explain the structure of the white blood cell then you have to say it has a biconcave disk shape to allow a higher total surface area to volume ratio so that oxygen can diffuse in and out of the cell okay the one on the left where I've highlighted are just their description the one on the right for each of the description are they are corresponding explanations