Major plant hormones (& how to remember) | Control & Coordination | Biology | Khan Academy

let's study the five major plant hormones see what their functions are and more importantly see how to remember them for our exams so let's start with the first one it's called auxin now i've written that in green because that's a growth hormone things which are in green are growth hormone okay so what does auxin do well auxin's main job is to cause cell elongation so when oxygen accumulates inside a cell it just makes that cell elongate longer more oxygen means more elongation so what happens because of this well if you look at a plant we

usually see that auxin since it's a growth hormone is found in the growing regions of the plant the growing regions of the plant would usually be like the tip of the leaves the tip of the shoot the birds these are the growing regions and that's where oxygen is found in abundance a lot of very concentrated over there and so if it causes the cells to elongate at that point let's say it causes the cells to elongate over here what do you expect to happen well the tip of the shoot will start growing taller but that's

not all auxin is also important for phototropism remember what phototropism is it's where when you shine light on a plant the plant automatically turns towards that light and of course if you need more info we've talked about tropism in great detail in previous videos okay anyways how does that happen this also is due to auxin but how does oxygen make this happen so you know what let's go back and let's zoom into a small section of the plant over here if we could see all the cells over here let's see what happens once you know

auxin comes over there so let's imagine these purple dots are auxin their job is to elongate cells now if light starts falling then auxins have a habit of moving away from the light that's important all right so this is the shaded region right this is the region where there's a lot of light so auxins will usually move away from the light and that means the oxygen concentration increases on the shady side of the plant and so what happens because of that and as a result we'll now find that this side will elongate more these cells

will start elongating more compared to this side and as a result we now find that the left side the shady side will start elongating more will start becoming longer more compared to the right side of the plant now just think about it what happens if this side elongates more and kind of see that this side starts pushing more the left side starts pushing more over here compared to the right side and if you push more from here what happens automatically this will start bending towards the right and that's how the shoot starts bending towards the

light all right how do i remember this now the technique that i'm going to use to remember all the hormones is i'm going to come up with weird stories the idea is if you have weird stories it's always easier to remember our brains tend to remember weird things so in the spirit of that how do you remember this well oxen has the word ox in it so i remember this weird picture of an ox with an elongated head so this picture helps me remember so every time i hear the word auxin this picture comes to

my hair mind and so this elongated head helps me remember ah it causes cell elongation and the fact that it's the head that is elongated the tip that gets elongated reminds me that augustine is more concentrated usually at the tip of the shoot and this elongation is what causes the turning of the plants towards the light so to remember this you have to visualize it's not enough if you just tell yourself this story but you have to visualize this okay try this and it works okay that brings us to our next hormone to talk about

next hormone here's the question we know that oxygen will cause the shoot to grow taller but what will make the stem taller right what what does what makes the stem taller that brings us to the next hormone so let me zoom out over here and click on the next hormone which is called gibberellin now gibberellin also causes the cells to elongate it's also a growth hormone as you can see it's written in green but its major role is seen in stem elongation so if here is our plant then we saw that oxide makes this part

grow but gibberellins are usually concentrated over here where new leaves are formed we call that as nodes all right and so javelin causes these cells to elongate cells over here so if these cells elongate what you expect to happen you'll find that the distance between this will start increasing and the stem starts elongating and so that's why we usually say giberlin is responsible for stem elongation if a plant has less gibberellin in it it'll tend to be dwarf if it has more gibberel in it it tends to be tall so today we can extract gibberellin

and store it in our labs and so if there are dwarf plants we can artificially spray gibberellin on it and just make it grow taller now before we move on let me tell you some other functions as well since this is a growth hormone not only does it cause stem elongation but it's also responsible for causing elongation in the fruits that we find the fruits also grow tall or basically grow long because of gibberin itself and this means that if you have let's say these seedless grapes which are great right we love it at least

i like it a lot but these are usually tiny so to make them bigger what we can now do is we can artificially spray gibberellin on it and as a result the grapes will become big and so you get more money for that so that's great another important function of gibberin is seen even during germination of a seed if you want a seed to germinate you need a lot of gi berlin without it the seed will not germinate at all so once enough gibberellin accumulates over there only then the seed will start growing so this

hormone is useful in various stages of growth in the plants anyways as far as our syllabus is concerned we can just remember the stem elongation part that's what it's famous for and so now comes the question how do we remember this for this i like to go back to the story of how jay berlin was even discovered turns out that in japan a few farmers found that their rice plants were growing taller for no reason they would grow so tall and then they would just die before giving out any seeds and on further investigation they

found that that was because of excess gibberellin that was added to this plant due to some fungus that could attach to it anyways now how i like to remember this gi berlin's connection to stem elongation is i like to remember this story and what i do is i imagine that people talk gibberish to a rice plant gibberellin has the word gibberish in it so i imagine people talking gibberish to a rice plant and the plant starts growing tall so again a weird story but i want you to visualize that every time you hear the word

gibberellin visualize gibberish talking to a plant growing tall and that helps me remember that its major function is in stem elongation okay so we saw both auxin and gibberellin cause elongations of the stem by elongating the cell itself that's great but if you want to grow and if you want to grow new leaves and new fruits and everything then you need to be able to make new cells not just make the cells elongate so how do we make new cells out of it that brings us to the next hormone and so let me zoom out

over here the next carbon we're going to talk about is cytokinin so the major job of cytokinin is to do cell division so it takes one cell if cytokinin is present over there it divides it into two so cytokinin is mostly responsible for creating new cells in a plant and so without that you cannot have new leaves you cannot have fruits basically you can't have new cells a plant will not grow okay and the word cytokinin itself comes from cell division the word cyto kind of means cell and the word kinin means division and it's

also cytokinin that causes branching to happen in plants we see plants have lots of branches right to do that also you require new cells without cytokinin this would be impossible of course the plant will not survive without cytokinin itself okay so cytokinin's main job is cell division how do we remember this well one way is just to remember it this way but if we forget then again i have a trick for you a weird story so when you hear the word saito the word sight comes to my mind and that reminds me of eyes and

kinin well there is a word key and so that reminds me of a key so here's my story okay it's it's it's gonna be weird so i imagine a key entering my eyes it hurts my eyes like anything and but magically what happens afterward is my eyes just split into two now i know how this sounds you might be wondering what does this really work can you really remember things like this but yes it does work okay so weird things we can remember so give this a shot right cytokinin site key cell division i division

that helps me so these were the three growth hormones that we discussed now let's talk about a hormone that actually inhibits the growth that actually prevents growth so zooming out that brings us to the next hormone called the abscisic acid this is shown in red indicating that it's not a growth promoter it's a growth inhibitor its job is to try and prevent growth from happening and its major function it again has many functions but one of its major functions what it's associated with is the wilting of leaves so people found that the leaves that fall

on the ground they have a high concentration of acetic acid so maybe that's the reason why leaves get cut down it's this particular hormone that is responsible for that now it turns out that the recent studies show that this is not the real reason why the leaves fall down it shows that abscisic acid is not really the cause for the cutting down of the leaves okay so let me just give you a couple of major actual functions of abscisic acid one of its functions is to make sure that in the drought condition meaning when there

is not much water present its main job is to ensure the stomata of the leaves stay closed remember what stomata is stomata is a small opening in the leave that causes water loss transpiration we call that evaporation of water well during drought condition it's a stomata abscisic acid gets built up over here and it makes sure it stays shut so that it doesn't lose water so that's one of the jobs of abscisic acid another job as a growth inhibitor now can be seen in seed germination if there's a lot of acidic acid found in the

seeds then it will not allow it to germinate it will not allow it to grow and you might be wondering why is this important this is important because we need to make sure when the seed germinates it's in the right condition so for example when the seeds are in the desert right a lot of appstick as it gets built up over there it doesn't allow it to grow and when it starts raining then the conditions are right the rain washes the acetic acid away and once it gets washed away then the gibberellin can start acting

on it and can start making it grow so absolutely as it is super useful as a growth innovator even in the earlier stages of the plant growth anyways fortunately or unfortunately our ncrt or syllabus has not picked up and so in exams you are still expected to write that the wilting of the leaves is caused by abscisic acid and so that's what we need to remember so again the question now is how do we remember this well one is you can look at the word abscess abscess actually means cutting down that's where the name comes

from even though it's not really true but if we don't remember that then what i like to do is split this word as abs see sick okay and now i imagine a person which has great abs who has great abs but he's feeling super sick seasick on a boat and starts throwing up but instead of puke it you know it starts throwing up leaves and that's how i can remember abscisic cutting down of leaves so again visualize this and you will see you can remember in fact i dare you to forget this now this is

impossible for you to forget ab sea sick welting of leaves you cannot forget it now this now brings us to the last hormone which is called ethylene it's put in yellow because it's hard to categorize that as a growth inhibitor or a growth promoter so we'll not categorize this at all ethylene is a chemical that you'll learn a lot about in chemistry and its major job is in fruit ripening ethylene is a gas that gets released and it causes the cell wall to get broken down and that's what makes it softer and it also releases

the stored sugar making the fruit sweet so it's a fruit ripening hormone okay now this picture might make you feel very uncomfortable because you don't usually see just one banana being ripened and that's because when a banana when fruit ripens it causes more ethylene to be formed and ethylene is a gas and that's why that gas gets released and it accelerates the ripening of other fruits and then they start releasing more ethylenes and such a chain reaction happens and that's how when you keep a fruit next to a ripe fruit it becomes it ripens faster

so how do i remember this again playing with the words the word ethylene reminds me of eat thai eat thailand and so the story over here is i eat very spicy thai food which actually hurts my stomach and as a result i start releasing gas and that gas starts ripening the banana i'm really sorry about this dirty example but i just couldn't come up with a better one to remember that ethylene is a gas and it's a fruit ripening hormone so there we have it we have listed the major functions of the major hormones which

we see in plants great idea now to pause the video and see if you can remember our technique and remember the functions and in the future if you like this please keep using the same visualization you have to keep visualizing it over and over again to make that memory solid