hi everyone welcome to chapter four in this chapter we're going to be looking at cells including prokaryotic and eukaryotic cells and their major components so as we learned before cells are the smallest unit of life and everything that is considered alive is made up of at least one or more cells here we have cells from three different types of organisms on the left we have cells from the human nasal cavity in the middle we have some plant cells these are onion onion cells and then on the right we have these Rod shaped bacteria known as vibrio some organisms are single-celled they're just made up of one cell and we call those unicellular organisms but many others like humans are multicellular organisms and when you're a large organism like a human cells have to work together to perform larger or more complex functions so when we put together cells that have common functions we get tissues like muscle tissue many different tissue types usually combine to form an organ for example for our heart we have nervous tissue muscle tissue and then organs working together make up an organ system such as the cardiovascular system we talked about during one of our previous labs those multiple systems that work together like the cardiovascular system the respiratory system all of those work together to help the organism survive most cells are too small for us to see with a naked eye so we have microscopes to make them easier to see microscopes magnify the appearance of our specimen and the magnification really depends on which types of lenses you have available resolving power also known as resolution is the ability of a microscope to distinguish two adjacent structures as separate for example if I have a cell and then I have two structures inside the cell that are pretty close to each other if you have low resolving power or low resolution it might look like a Big Blob you wouldn't be able to tell that they're actually two distinct dots but the greater the resolving power of a microscope the more you are able to see them as separate structures this is similar to when I don't wear my contacts or glasses for example if I don't wear my glasses or contact lenses I can't see these as two separate dots it looks like a Big Blob to me the image on the bottom right or the two images I should say show a difference between the resolution or resolving power of two types of microscopes a light microscope shown here on the left is what we usually have in our lab and it uses visible light and bends it to magnify the specimen on the right we have a much more powerful microscope that uses electrons scatters them to allow us to see or magnify the organism and this is an example of what an electron microscope looks like on the right bottom left right side image you can see the resolution or resolving power is much higher most of the microscopes you've encountered are probably compound light microscopes that bend visible light to magnify your specimen the greater or the stronger the objective lens you use the more bending of light is happening most cells are transparent they don't have natural color that's not always true but many times it is true so in order to see it under the microscope we have to stain them using different types of dyes or stains what this usually does to the cell though is kill the cells but then we can examine them using the default setting for most of these compound light microscopes known as the bright field setting or bright field microscopy and this is an example of what we would see under bright field microscopy we have here epithelial cells and what that means it's the outermost layer of our human tissues this looks like what I would see if I were to take a toothpick and scrape the inside of my cheek rub it on a glass slide and add some blue stain I would see cells that look like this that are dead and attached to the slide and have a blue color because of the stain that I've used and our on our lab we are lucky because we have microscopes that also have an additional setting known as phase contrast and this is much more rare to have in a biology lab phase contrast allows us to see live specimens that are transparent so even if we don't stain them we are able to use phase contrast to see these organisms they look a little bit bluish here but this is really kind of a black and white image as I mentioned earlier electron microscopes are much more powerful in terms of generating a stronger magnification and resolution of our specimen specimen of interest because we're using smaller structures these electrons this was our electron microscope shown earlier and on the right I see two types of electron microscopy images the first one is often known as a tem image created with a transmission electron microscope and that allows us to see detail within cells so this is an organelle that I would see inside of the cell scanning electron microscopes you'll usually see something like sem next to these images provide three-dimensional exterior views and I can see nice images of the red blood cell here and there are three-dimensional shape here's another example of the difference you would see in your specimen using a regular light microscope on the left versus an electron microscope this looks like a scanning electron microscope image oops where did my S go there it is and then here what we're looking at are Salmonella bacteria so you've probably heard about this before we can find these on raw chicken eggs sometimes and you can't really see them here there are these tiny purple dots all over the place the tiny tiny purple dots are our Salmonella bacteria on the right using that much more powerful scanning electron microscope we can see the Salmonella bacteria in much more detail the colors in both though are artificial this is due to staining or computerized a later addition of the color one of the most important principles of biology is the cell theory and there are three tenets to this Theory the first two are kind of similar cells are the basic units of life and what that really means is everything that's alive is made of one or made up of one or more cells and all cells have to come from pre-existing cells they can't just magically appear the picture down here is really interesting as our book describes and they talk about what cytotechnologists do cell technologists and this is actually an image of cervical cells that were collected from a pap smear so these are cervical cells from the uterus and they're looking at it through it looks like a light microscope these are normal cells on the left what cells should look like and it looks like the cells on the right have been infected by a virus sometimes abbreviated HPV this is human papilloma virus these cells are abnormally large in size and some of them even have more than one nucleus inside the cell which is abnormal regardless of the type of organism you have all cells have four basic components in common the first one is all cells have to have some kind of cell or plasma membrane that protects the interior of the cell from the environment so here in this very generic picture we have the cell membrane here the outer line inside of the cell so the entire portion of the inside of the cell everything in Here is known as the cytoplasm and this includes all of the structures inside of the cell and the liquid portion inside of the cell which is known as the cytosol we always have some kind of genetic material in the cell or DNA and in this case it's shown as a singular circular DNA molecule but it doesn't have to be single or circular they could be linear DNA and there could be many different types of DNA molecules that are linear inside the cell and then finally all cells have ribosomes which are a type of organelle that makes proteins the first cell type we're going to be talking about are prokaryotes Pro refers to before and Cario refers to the nucleus so these do not have a nucleus nor do they have any membrane enclosed organelles so again they don't have a nucleus they don't have membrane-bound organelles whereas eukaryotes u meaning true nucleus those do have these structures most prokaryotes are bacteria and bacteria have cell walls that contain something known as peptidoglycan their cell walls are are made of peptidoglycan which is really a fancy way of saying a protein sugar complex prokaryotes are older than eukaryotic cells so they're much like the first cells if not identical to and then organisms in these two domains bacteria and Archaea are both prokaryotes let's look at some of the structures that we would find in a prokaryotic cell so since they don't have a nucleus a membrane-bound structure in which DNA is found their DNA is just floating around inside the cell in the cytoplasm the specific region in which we find DNA is called the nucleoid nucleoid ribosomes are also found in the cytoplasm and remember ribosomes function to make proteins they have a cell membrane because all cells have cell membranes but they also have a cell wall outside of that cell membrane some of the other structures shown here might be found in some but not all bacteria or prokaryotes so prokaryotes might have a flagellum which allows them to move around some of them have pilly which are attachment structures allowing them to attach to other bacteria for instance and then some of them not all may also have a sticky layer outside of a wall known as a capsule and capsules really help give an extra layer of protection to the cell and prevent dehydration of the cell looking at this figure showing relative sizes of different microbes and structures I can see that prokaryotes like bacteria are about 10 to 100 times smaller than eukaryotic cells or organisms so bacteria their diameter really range from around 0.1 0.125 micrometers in diameter and that is 10 to 10 to 100 times smaller than our most of our eukaryotic cells so we know that prokaryotic cells are a lot smaller than eukaryotic cells and also most cells are very very small we can't see them with the naked eye so let's take humans for example why are we made up of millions of tiny cells instead of like four really big cells wouldn't it be easier to manage our bodies if we were just made of a few cells the reason for this limitation is really because of something called the surface area to volume ratio let's say this is a cell for example I know it's a cube but just pretend it's uh it's a sphere so what happens is when we have cells their demand for nutrients really depends on the volume of the cell let's say have another big cell over here so the volume determines the amount of nutrients it needs to be taken into the cell and also how much waste is generated and needs to be transported out of the cell so the demand for nutrients and the generation of wastes is really determined by the volume of the cell but how quickly you can transport things into the cell and out of the cell really depends on the surface area the space it has to move in or out and I can see for small cells do you guys remember from other classes surface area versus volume if I want to calculate this the surface area for a cube that has a side with length x would be x squared that's the area and then of course there are six sides here so there would be six times there and then for volume U would be cubed so if I just look at the cubed versus the squared I can see as the cells get bigger the surface area increases slowly compared to the volume so the ratio decreases for bigger cells compared to smaller cells smaller cells are more favorable in terms of their surface area to volume ratio they can transport things into the cell and out of the cell in terms of wastes quickly whereas big cells cannot they're limited by their surface area although they have greater need for nutrients and a greater generation of wastes prokaryotic cells are even they have an even more difficult time because they don't have the structures the more complex structures that eukaryotic cells do that enhance transport of nutrients in and wastes out here's another example of the same thing when cells get too big their efficiency decreases they can't transport things into and wastes out of the cell quickly enough there's not enough surface area of the plasma membrane for diffusion to occur so it becomes less efficient and one way to overcome this inefficiency is really to divide so the cells can divide into smaller cells many smaller cells and increase that surface area to volume ratio other ways that cells sometimes get around this limitation is that they increase the surface area like this could be a type of cell that we see in our bodies where the cell membrane invaginates upon itself to increase surface area or sometimes cells get really flat and really thin instead of having such a great volume and we'll see that most of these adaptations occur in the more sophisticated cells or eukaryotic cells small cells have an advantage because they don't need those sophisticated structures or adaptations and we see that prokaryotic cells don't have additional specialized structures to allow for this additional diffusion or transportation of nutrients and wastes larger cells have many more organelles and structures inside the cell that kind of allow them to get past this inefficiency and that takes us to the end of part one of chapter four in the second video part two we're going to be going over eukaryotic cells in much more detail