[Music] hi everyone this is andy from med school eu and we're going to begin our second lecture of the biology section from the imath specifications and the second unit will include the cell as the basis of life and the first two topics that we're going to discuss in this video will be cell theory and cell size so let's talk about cell theory first and laid the foundation for biological science so cell theory was proposed by robert hook and he was an engineer he was a scientist who was using the original microscope as we've got here in the image to come up with these three laws and these three generalizations of of living organisms so here they are number one all organisms are composed of one or more cells number two the cell is the basic structural and functional unit of all living organisms and number three cells arise only from the division of pre-existing cells so this is true about all life in general and uh let's uh discuss each one a little bit further so number one organisms are composed of one or more cells so on earth there's um there's plenty of organisms multicellular unicellular like prokaryotes eukaryotes plant cells animal cells fungal cells protists bacteria these are all composed of one or more cells there's no organic there's no living organism that is composed of inorganic substances and that could live on its own right so this this uh generalization is uh holds true to this day now number two the cell is the basic structural and functional unit of all living organisms and here i i attempted to draw a a cell and it's it's bursting so it's an open cell so if you are to split a cell right so if you were to slice a cell and to see if a cell would survive on its own and usually if cells are broken up the property of life is lost they're unable to grow reproduce or respond to outside stimuli in in a coordinated potentially independent fashion so this confirms the second tenet of the cell theory because life as we know it does not exist in units simpler than just individual cells like here so this confirms the second tenet now if you're looking at the third cells arise only from the division of pre-existing cells meaning that cells can only arise from asexual and sexual reproduction asexual and sexual reproduction and you cannot just get a cell coming up on its own without uh without cells going through sexual reproduction mitosis and meiosis and or or asexual reproduction like bacteria you cannot get a cell just coming up out of nowhere from from matter it needs to come from pre-existing cells and so all these three generalizations hold true to this day so next let's discuss cell size and we're going to go over just a a couple of examples just to give you an idea of of of how big and how small parts of a cell are so before we do that we need to know our units of measurement so some of the basic units and conversions that you should know for the imath exam are are here so we've got one meter that and we got centimeters we got millimeters micrometers and nanometers so uh you should know the conversions of if you are given a a number of uh millimeters how to convert them to nanometers or meters and and so forth so you're going to need to know the units of measurement in case a question comes up in terms of the cell sizes and evaluating exactly how big or how small they are now with that said let's look at an example so we're going to begin with the smallest and go up to the largest some of the largest units of a cell so first here we have two oxygen atoms double bonded so this is an o two so this oxygen gas the diameter of an oxygen atom is 0.07 nanometers so it's it's in nanometers that means it's it's a billion right this is 0.07 of a billionth of a meter just imagine how you know a meter isn't very big but imagine how tiny a 0.07 billionth of a meter is now if we look at another example going a little bit bigger we're looking at a dna double helix structure here and this the width of the base pairs the the dna double helix the width of it is two nanometers so this is a a couple units higher than the uh atom uh however it's still quite tiny right it's it's it's very small and we're going to look at how how small this is in comparison to the entire cell or just the nucleus the next example here is shown [Music] the cell membrane now the width of the cell the thickness of the of the cell membrane the phospholipid bilayer is nine nanometers so it's it's several times bigger than the width of the dna double helix so it's uh in comparison if we take a look at the next bigger structure and this is a virus so this virus is it's one of the larger viruses 100 nanometers viruses are usually typically smaller but this is an hiv virus taken under the light microscope and this hiv virus is is one of the larger ones influenza is another large virus that's also around 100 nanometers and you can see in comparison to the thickness of the cell membrane that it's uh it's it's more than 10 times bigger than the thickness of the membrane now looking at the next example next bigger example we're moving from nanometers to micrometers and in micrometers we actually have this is e coli bacteria so these each of these uh grains here these are all each e coli bacteria the width of e coli bacteria labeled here is one micrometer now one micrometer that's going to be 10 times the size of a virus one of the larger viruses right the next example we're going to start looking into the cell size and and the some of the structures and the organelles associated with cells because they are in the range of micrometers so as you can see here this is again taken under the light microscope and what we see here is a mitochondrion and the mitochondrion is typically around one to five micrometers and if you can see here it's it's comparable to the e coli bacteria in terms of size and this is one of the reasons why mitochondrion is uh there's a theory that a mitochondrion was has evolved and had used to be a bacteria that lived on its own and eventually it migrated and in some ways it evolved to coexist with other cells and becoming the powerhouse producing lots of atp for the cell however the size of it and the structure it even has its own genetic material this uh could could have been a bacteria at the start of evolution on earth so now we're going to move on right into the the entire cell structure so as you can see here this is a an animal cell it has that round shape without the cell wall and that would be the nucleus here and the the size of it is typically around 5 to 30 micrometers and and here we're just talking about a typical animal cell so because there are animal cells that are much bigger than this for example the human egg is is about 100 micrometers which is a couple times bigger than just a typical just a typical cell and the final example here we're going to discuss uh the plant cell so if you can see the arrangement here it's got a unique shape because plant cells are tightly packed together like this one after the other and in the middle here so we've got the nucleus and we have a central vacuole where a lot of the storage of nutrients takes place and this is again taken under a light microscope where you can see just the the little structures associated with with the cell now you need to know that a plant cell is on average averages to be a little bit bigger than [Music] the animal cells as they are 10 to 100 micrometers big and how does this compare to what we can see with with an unaided human eye is that we can typically see one millimeter right this is something we can see on the ruler and we can kind of look into and we can really picture that however this is still a couple of times smaller than that one micrometer so again that is not detectable by by the unaided eye now in terms of the imat exam and the things that might come up uh with cell size and cell theory is that you might get a question that asks how uh in terms of ranking so if you were given a couple of structures for example given a mitochondrion a ribosome a chloroplast and a dna and a plant cell in an animal cell and you have to rank those from smallest to biggest so you're going to need to know just some of the basic structures just to evaluate really how just the range at which at which these structures exist in terms of their size so you're really going to need to know how to rank them in order of largest to smallest or smallest to largest and typically those are the kinds of questions that will come up however the most important thing that you would need to know is that a plant cell is generally a little bit bigger than the animal cell and the units that are associated with them which would be the micrometers they're typically measured in micrometers then you are going to need to know that viruses are a little bit smaller than bacteria in bacteria cells you should know that they are much smaller than animal or plant cells and then moving on to the smaller structures like these you would know that the atom is the smallest measurable structure that we have and that we could we could potentially detect under the electron microscope so that'll be all for today's lecture and in the next one we're going to take a look at the prokaryotic and eukaryotic cells as well as animal and plant cells [Music] you