Understanding Organisms: Prokaryotes, Eukaryotes, and Endosymbiosis

we're going to be talking about organisms because well that's what biology is all about it's the study of

life so diving right into it we have so many different types of organisms

how do we different how do we categorize organisms we have an otter we have a mongoose we have a

mango tree we have grass we have bacteria we have mushrooms we have

algae so many different types of organisms so the best way to classify organisms is

to put them into two big groups of us and the two big groups are called prokaryotes and eukaryotes

prokaryotes are basically organisms where their cells do not have a nucleus and eukaryotes are

basically organisms where their cells will have a nucleus that's the easiest way to classify the

organisms first and of course under prokaryotes examples of prokaryotes will

be bacteria and under eukaryotes over here we have four different types of eukaryotes

they're divided into many different kingdoms kingdom animalia kingdom plantae kingdom

protists and kingdom fungi but our main focus for this chapter will be

bacteria animals and plants as i've highlighted over there but before we start with anything

we have to ask ourselves the question how did life come to be where did animals come from where did

plants come from how have they always existed on earth we are not exactly sure how life came to

be but there are a few ideas of how life happened and to understand that we are going to

be looking at something called the endosymbiotic theory so about 3.5 billion years ago life on

earth was extremely different from what it is right now you know

right now the world is a bit more stable you know uh we have a lot of oxygen in the air that

can support a lot of life but 3.5 billion years ago was probably a different time

a lot of volcano eruption not much of an ozone layer and not much of oxygen that was in the

atmosphere so life 3.5 billion years ago was probably just

there were no animals but what the earth was filled with was probably all these small little

organisms that were microscopic known as prokaryotes and how do we know that

these are prokaryotes as you can see these prokaryotes were all made up of

simple fundamental structures they had dna they had ribosome they had a cell

membrane and they also had the cytoplasm inside the cell i didn't i did not label cytoplasm but this is just basically an

example of a prokaryote right here and this is known as an anaerobic prokaryote

it would have carried out anaerobic respiration there would have been many other

different types of prokaryotes these prokaryotes might have been smaller but their basic structures were

still the same they would have had their dna they would have had a ribosome they would have had a cell surface

membrane and also a cytoplasm and for example just for our own situation here we have our

aerobic prokaryote the difference between aerobic and anaerobic prokaryotes

well it's in the name any aerobic prokaryotes carry out a process known as anaerobic

respiration aerobic prokaryotes carry out a process known as aerobic

respiration aerobic respiration just means that they use oxygen when they're breaking down organic

molecules now life for this prokaryote were pretty simple

it's either eat or be eaten by the other organism and as you can see in this diagram over

here which organism has the advantage yes obviously it's the anaerobic prokaryote because its size is bigger

so if it saw the aerobic prokaryote it would have been thinking is this food for me

so its main goal is it would have tried to ingest the aerobic prokaryote it would

have tried to engulf it for a process known as endocytosis so it would have tried to swallow the

aerobic prokaryote and it might have succeeded in doing so so right now the aerobic prokaryote is

inside the organism as you can see here and the enablement prokaryote

would have tried to digest the smaller organism but here's where something interesting

might have happened this might have started the beginning of a sort of beautiful friendship

because in this case over here instead of one organism eating and digesting the other

these two organisms started living together or to be more specific one organism was

living inside another organism why is this important or why did i call this a beautiful friendship

because the beautiful friendship is as such this smaller microorganism could

now be protected by the larger organism and the smaller organism can actually provide

more atp the larger organism however because it's large it can provide protection for the

smaller organism and the small organism right now does not have to focus on looking for food

the large organism can provide food and all the small organism has to do is it just has to provide atp

and thus these two organisms over here started living together and this was known as the concept

endosymbiosis symbiosis meaning working together and dominating within so an organism

living within another organism and both of them starting to work together

these two organisms had a higher chance of survival and because of the extra surplus of

energy the prokaryote could have become slightly larger

perhaps during one point in the evolution the cell wanted to become more organized now what

does it mean by becoming more organized remember the characteristic of life it needs to carry out respiration

it needs to move it needs to grow it needs to carry out it needs to get nutrition it needs to reproduce it

needs to excrete and also more importantly it needs to carry out homeostasis

how can the cell carry out all these processes in a more organized fashion and that's

where the cell did something pretty brilliant and they did something called

compartmentalization compartmentalization just basically means putting things into rooms or

compartments to make things more efficient what do i mean by that

how do you make it more efficient and how do you make it more organized basically what the cell did the cell

actually just became slightly larger they started to build smaller rooms within the cell you can

see a room which is i've put a room where it's a yellow circle over there and inside the room

with the yellow circle they start the dna of the organism they also created

another room within the cell and inside that room they stored the ribosomes to make it more efficient

they created another room to put specific enzymes inside there another room over there perhaps for

another function so each of these rooms inside these cells

were all having their own partition and the partition were all made out of membranes they were

separated by membranes if you are a little bit confused by this imagine a house

if you had a house but there were it was not organized you did not have a bedroom you do not have a toilet you do

not have a kitchen everything is so mish-mashed basically you want to create partitions in your

home so that there is one room that is designated for the bedroom

there is another room that is designated for the kitchen there is another bit there is another room that is designated

as the toilet so it makes that one entire space divided into smaller spaces in an

attempt to make it more organized same concept happened in the cell as well the cell created

divisions and rooms so that they could be more organized and as you can see here

some of the rooms or one of the room is there to modify protein one of the room is to store dna

synthesize lipid synthesize proteins and another room is to produce atp now you might be thinking okay so fine

the cell is more organized it has specific rooms do specific things again how is this

relevant and this is where it became through a longer period of time the room that stored the dna

changed over millions if not billions of years and that's when you get the nucleus what

about the room that is to synthesize the protein that is how the endoplasmic reticulum

came to be the room that is to synthesize the lipid that's how you get the smooth

endoplasmic reticulum the womb that was supposed to modify the proteins golgi apparatus

the room that is supposed to produce atp that is the mitochondrion you see by having all these cell structures did

not just accidentally came to be it was an attempt

of the cell trying its very best to be more organized in order to increase its chances of

survival and lo and behold this is how you get an animal cell

if you remember 3.5 billion years ago there were two organisms there were two prokaryotic organisms

over there and the two prokaryotic organisms carried out a process known as endosymbiosis

they started living together the combination of these two organisms became larger they became more

organized and they evolved to become what is known as the typical or ancestor animal cell over here

and it is also very important to note that if you look at this cell this animal cell where is the dna found

most of the times students will say that the dna is found in the nucleus but never forget

that the mitochondrion will also have its own dna some students will be very surprised what do you mean that the

mitochondrion has its own dna yes because look at the link from 3.5 billion years ago

look at that smaller organism on the left the one on the corner of the left over

there where i'm going to be highlighting it in a blue color the smaller prokaryote had its own dna

i'm just linking the bridge to show you how they're all connected to each other there you go so the mitochondrion

has its own dna and our nucleus also inherited the dna from the larger prokaryote

and that dna was stored in the nucleus and that's how we get a present day dna so what you have to understand

from this is the first animal cells that were formed on earth

was actually the result of two prokaryotes living together you and i we are animals we are humans

obviously but we are made up of animal cells we are so used to thinking of ourselves

as humans that we actually share a link we are just the

result of two prokaryotes working together how's that for an existential crisis

but are you a bacterium no of course not you are still a human at the end of the day

we all have such humble beginnings let's look at plant cells blood cells also have uh

we think that plant cells also have a humble beginning just like the animal cells

but in this case over here it involves three prokaryotes about billions of years ago and this

prokaryote the one in green in color right there it also had its own dna and this was

called a photosynthetic prokaryote it could carry out the process known as photosynthesis on its own it was a

living organism but what probably would have happened is it might have been swallowed by the

larger organism as well the larger organism yeah it is a little bit hungry it's following everything

that is smaller and they started working together so right now the photosynthetic

prokaryote is living inside the larger organism it has protection all it has to do is

carry out photosynthesis and it could feed all the other organisms

and they can work together so now you have three organisms living together how could it become more organized it

became a bit larger that was the photosynthetic area right there i'm just adding it in

and now because of compartmentalization you could have created another room remember because to make it more

organized and that other room over there what was its function inside this cell this function over here was

to carry out a process known as photosynthesis through billions of years of evolution

became what is known today as the chloroplast and there you go and the cell might have had its own

vacuole and because it had chloroplasts it could have created special type of carbohydrates known as cellulose and lo

and behold it could have also built its own cell wall perhaps and that is how you got the ancestor plant cells

and of course the global class it also has its own dna because it actually originated from a

prokaryote billions of years ago how is it able to have its own dna let's see the link from the one on the

left the photosynthetic prokaryote it was engulfed by the organism

it became larger they started working together and lo and behold it became what is

known as the clover plus and it also has its own dna you