Transcript for:
Understanding Plant Growth and Development

hello my dear lovely students so once again welcome back on this amazing platform of physics vala where i ayushi agarwal your botany teacher is going to teach you finally the last chapter of class 11th which is plant growth and development are you all excited for this chapter yes very good very good so as usual we are first going to start with the introduction part of this chapter that is what is growth if somebody asks you what is growth then how will you define this context we have already done while teaching the chapter first chapter that is living world growth is basically an irreversible increase in the size mass volume or number of cells in the body i say irreversible because i am talking with respect to intrinsic growth the growth which is taking place in living organisms so in living organisms the growth is intrinsic type internal type and irreversible once the body has grown it cannot shrink back to its original state right so how we do define growth growth is simply increase in the size mass irreversible increase in the size mass volume and number of cells yes or no if i'm talking about intrinsic growth which is a defining feature of all living organism be it plants animals etc in this chapter we are going to focus about plant growth the name of the chapter itself suggests plant growth so we are going to talk about plant growth we are going to see some of the features peculiar features related to plant growth number one is plant growth is indeterminate indeterminate means open type indeterminate means open type of growth the growth which is not fixed the growth which can occur throughout the lifespan so you know in some plants majority of the dicots due to the presence of lateral meristematic tissue on the lateral sides of the root and shoot the girth the thickness the diameter of the plant keeps on increasing year after year so because of this reason plant growth is indeterminate but remember plant growth with respect to thickness is only indeterminate height even in plant body is fixed is determinate correct so let's write this what do you mean by plant growth being indeterminate or open type so due to the presence of lateral meristematic tissue on the edges on the lateral walls of the root and shoot in dicot plants and some gymnosperms plant growth due to the presence of lateral meristem plant thickness increases throughout the ear throughout the lifespan not here basically throughout their lifespan yes or no but remember one thing it is only restricted to roots and shoots in leaves flowers fruits there is no secondary growth there is no indeterminate growth plus plant height is determinate plant height is restricted it will it is closed type it occurs only for certain duration but the thickness in some of the plants like dicots and some gymnosperms it is indeterminate type or open type i hope the first point is clear now moving ahead with the second peculiar feature of plant growth is that growth is measurable you can measure the growth you can measure the rate of the growth which which the plant body is growing however growth is indirect why why it is indirect because students growth if i talk about then growth why the body is growing because the number of cells are increasing because the volume of the cell is increasing yes or no that is where that is why your body is growing now that increase in the cell size that increase in the volume that increase in the number of cells is happening because due to the change in the protoplasmic amount of the cell the cell size is increasing the volume of the cell is increasing because the content inside the cell that is protoplasm that is increasing right so if you can directly measure that how much amount of protoplasm has increased then that is called as direct measure but we cannot measure the amount of increase in the protoplasm of the cell however we can measure the result of it that is increase in cell size increase in cell volume increase in the number of cell so this type of growth where you are measuring the result the outcome is known as indirect measure correct so at cellular level the growth is due to the increase in the protoplasmic content of the cell which cannot be measured as a result we measure the growth indirectly by studying the change occurring due to the increase in the protoplasm of the cell like due to the increase in the amount of protoplasm cell size will increase volume of the cell will increase because of which the cell will divide resulting in the increase in the number of cells and thus the body grows correct chalo let's read it so growth is therefore measured by different parameters right like for example i told you increase in freshwater dry weight volume number size length etc for example one maze one single maize root apical meristem can give rise to more than 17 500 new cells per hour this is the rate of division of one single cell of maize apical meristem so that means you have counted the number of cells you have seen that how the rho topical meristem is dividing how much number of cells are increasing does increasing the length of the plant body okay similarly if i talk with respect to cell size then the example coated in ncrt is a watermelon cell size which increases to about 3 lakh 50 000 times of its original size similarly if you want to increase the length of the pollen tube that how much pollen tube is growing you can measure the change in their length similarly increase in surface area is also one of the parameter to measure the growth suppose original size of the leaf is this much and now the leaf has grown to this size so you can calculate the difference in their surface area and that will be the increase in the leaf size so this is how you can measure the growth and growth which you measure is indirect method moving ahead with the next that is phases of growth if i talk about the phases of growth then there are three typical phase of growth first that is zone of meristem then zone of elongation and then zone of maturation the first stage of growth the first phase of growth is phase of meristem in this phase when the cells are in meristematic stage they are actively dividing they are quite young their cell wall is very thin and cellulosic living in nature the amount of cytoplasm is dense as a result vacuoles are very small or absent correct so the cells which are in meristematic phase are actively dividing thin cellulosic cell wall living cell wall very lesser number of vacuoles more amount of cytoplasm now as soon as the cell loses their capacity of division and they try to increase or they try to become mature then they escape the phase of meristem and enter into second phase of growth which is known as phase of elongation phase of elongation students it is characterized by two events first increased evacuation and second increase in cell wall thickness you know when the cell is young it is only having primary cell wall which is very thin and flexible but as the cell mature the primary cell wall expands gives space for more deposition of secondary cell wall and a time comes when primary cell wall vanishes and it is replaced by multi-layered secondary cell wall so that stage of formation of new cell wall is actually phase of elongation apart from cell thickening one more event takes place during phase of elongation which is increase in the size of the vacuole so increased evacuation and increased cell wall thickening these are the two characteristic feature in the phase of elongation now once the cell completes phase of elongation then it escapes and enter into the final phase of growth which is phase of maturation phase of maturation students it is characterized by complete maturation cell wall thickening is done vacuoles are completely formed cytoplasm and nucleus has shifted towards the periphery and now cell wall plant cell is completely mature and now it is ready to divide and produce ah sorry it is not ready to perform specific function correct so there are how many phases of growth three number one that is zone of meristem second phase of elongation and third phase of maturation now let's read it first let's talk about meristematic phase which is characterized by cells which are rich in protoplasm their cell wall are primary in nature thin cellulosic with abundant plasmodesmetal connections second is phase of elongation that is characterized by increased evacuation cell size increases and new cell wall deposition third is phase of maturation where you see that vacuolation and cell wall thickening is complete it is done so vacuolation and cell wall thickening is done cell is completely ready to perform a specific function so these are the three phases of growth now letting leading ahead and now let's try to study different types of growth rate so there are two ways to measure the growth rate one type of growth rate is arithmetic and second is geometric first i'll tell you what is arithmetic growth rate and then we'll talk about geometric growth rate what is arithmetic growth rate arithmetic means plus one suppose right now i'm having one toffee somebody else give me one more toffee then how many toffees now i have two third person gives me adds one more toffee three four five so like this if the number of trophies are increasing then this increase is known as arithmetic in plants also growth can be arithmetic type now what happens in arithmetic growth see if there is one cell right this is the cell which is actively dividing which wants to divide so if this cell undergoes division to produce two new daughter cell by mitosis then if one of the cell gets differentiated loses the capacity of division and if only one cell remains actively dividing that means this cell is differentiated it has lost its capacity of division only one cell is remaining so this cell will be copied as it is but this cell will undergo division producing two new daughter cells again one of the cell will undergo differentiation and only one will remain actively dividing so now what will happen these cells will remain as it is they are not dividing but this cell will undergo division to add on two new cells this method where initially there was one cell two three and then four and then keeps on going this method of increase in the number of cell is known as arithmetic growth what is arithmetic growth when out of the two cells produced one of the cell loses their capacity of division and another remains active so this method is known as arithmetic growth right so what is arithmetic one cell active another lost the capacity of division now this arithmetic growth can be studied with the help of an equation which is written in terms of length lt is equal to l naught plus rt so this is the equation of arithmetic growth which is written usually in terms of length there's no specific reason that why but it is written so we can also write it where lt stands for final length l naught stands for initial length r stands for growth rate and t stands for the time taken to reach from l naught to l t right now try to write this equation in form of y is equal to mx plus c so that we can plot the graph as well now if i want to plot the graph of arithmetic growth then this equation if i write in the form of y is equal to mx plus c then this is how i can write where y is lt that means on y axis you will plot length in time t in x axis you will plot the time taken then y intercept is also there which is equivalent to l naught and the slope of the line is r which is the growth rate so the graph of arithmetic growth is a linear straight line but not passing through the center as it is having a intercept a y-intercept whose value is equivalent to l naught clear so this much you have to remember for arithmetic growth i hope you will remember the second type of growth is geometric also known as exponential growth now what do you mean by exponential or geometric growth students geometric exponential means increasing x in general if i say increasing exponentially in multiples of something so if there is once toffee with me now somebody gives me two more then somebody gives me four more eight more 16 more so like this the number of toffees with me is increasing in multiples of what i am having originally so this type of growth is known as exponential or geometric growth right okay so what happens in plant if i talk in with respect to plant suppose this is one cell this parent cell undergoes division to produce new daughter cells now these daughter cells none of the daughter cell will differentiate rather both the daughter cells will remain actively dividing so this cell will also divide this cell will also divide so initially there was one cell then you are having two and now four again all the four daughter cells are actively dividing they will divide to make the number eight again 16 32 so like this if the number of cells are increasing within then this type of growth is known as geometric growth clear where none of the cells are differentiating all the cells are remaining active okay so this is geometric growth rate moving ahead with the equation of geometric growth which will be written in exponential form is wt is equal to w naught e k power r t the equation is written in weight terms in terms of weight and you can see this equation is written in exponential form where w t is the final weight w naught is the initial weight e key power means we are talking in terms of exponents r is again the growth rate and t is the time taken for weight change right okay and if i want to plot the graph for geometric growth it is going to be of sigmoid shape s shape graph is going to come for geometric growth in general like for example if i'm talking about a bacterial culture i'm trying to grow bacteria initially i have provided all the nutrients and favorable condition so bacteria number is going to grow exponentially right they are going to enjoy the nutrients given they will enjoy all the favorable condition and their number is going to increase exponentially however a time will come when the nutrients will drain out and because of which then the growth will become stagnant creating a s-shape sigmoid growth curve which is characterized by three phases initial phase where the growth rate is slow is known as lag phase then comes log phase where the growth is exponential and then comes the stationary phase where the growth becomes stagnant maybe due to consumption of complete nutrients or maybe due to now bacteria are saturating if i'm explaining the geometric growth of bacterias correct so i hope what is geometric growth is also clear when none of the cells are differentiating rather all are remaining actively dividing then such type of growth rate you see such type of growth curve you obtain moving ahead with the next important topic that is conditions for growth now you know conditions of growth are very important that how and when you can increase the rate of growth for that if i talk about conditions of growth your requirement of growth then my dear students conditions of growth you should provide proper light right second ample amount of water should be given right second nutrients should be provided properly to the plant next temperature optimum temperature should be maintained next oxygen should be given to the roots of the plant so that they can respire they can grow properly they can absorb more water and mineral yes and light should also be there abundantly so that proper photosynthesis takes place extreme nothing extreme don't say that extreme light should be given extreme water should be given no extreme of everything is bad if i talk about human life if i talk about plant life then extreme for every object is a wrong thing right so if light is given in optimum quantity water optimum nutrients optimum temperature optimum oxygen optimum then growth is going to be at its maximum correct okay so this is about plant growth but the chapter is also about plant development so first thing you should know what is development right cello let's try to read the definition for development development is a term that include all the changes that an organism goes through during its life cycle right if i'm talking about with respect to plant then development is all the changes which a plant sees from its seed stage till its senescence like there's a seed it will undergo germination growth of plenum radical is development then further growth of plymouth and radical to form root system and shoot system is development then flowering is a development then senescence is a development and then after senescence the plant is going to die so all the changes which you see in the plant from its seed stage till its senescence is a collectively called as development or simply you can define development also as sum total of growth and differentiation so development can also be written as sum total of growth and differentiation correct yes or no growth plus differentiation is development when the body cells are going to increase then the size number volume of the cell is going to increase they will lose their capacity of division to perform specific function then only development is going to take place okay now usually development is straight straight i mean to say if suppose when i was a child or when i was infant so in my hand i only had five fingers four finger one thumb however the size of my palm the size of my fingers thumb was very very small as i started growing up the number of fingers and thumb on my palm remained same but the size kept on increasing right i have you seen any human being who is born with five fingers and as it is growing or as he or she is growing the number has increased from five to six or six to seven or it has decreased from five to four no this does not happen because our development is straight in animals development do not show any deviation it is straight suppose when i was born i was born with two legs initially my legs were small right but number was two now as i grew up number will still remain two however the length of my legs is going to increase it is not that during my developmental stage the number of leg will become three or it will reduce to one no because our development is straight however in some plants they may show deviation from the path of development and that deviation from the path of development is known as plasticity very very important our next topic is to understand the concept of plasticity plasticity simply means deviation slight deviation from the path of development correct now this plasticity can be in in plants only in plants you observe plasticity not in animals now plasticity deviation can be in any organ of the plant maybe in leaves maybe in flowers maybe in other part of the plant body specifically if deviation occurs in leaves if plasticity occurs in leaves then that type of plasticity is known as heterophylli hetero means different philly means leaf correct now reason for plasticity why this deviation occurs so there can be two reasons one may be environmental may be genetical so my dear students plasticity reason can be two either developmental or genetical environmental or genetical if i talk about genetical plasticity in terms of leaves then best example are cotton larkspur and coriander you must have seen the juvenile leaves of cotton sorry coriander these are the juvenile leaf of coriander now once they become adult see three incisions can you see one two three so when the coriander leaf was young it is having three incisions if it would have shown the same development pathway then the size of the leaf should have increased but the number of incisions should remain three but it is not the case what actually happens the number of incisions becomes more than three that means they are showing change in the path of development so this is the young leaf with three incisions and this is the adult leaf with so many incisions so this shows what genetical this is developmental genetical plasticity which you see in case of leaf of maybe cotton maybe coriander or maybe lux per this is genetical however in some plants the plasticity reason may be environmental like for example i talk about butter cup in butter cup aquatic plant it's not completely submerged aquatic plant rather it is free floating so you see there's a change in the size of the leaf of butter cup the part of the buttercup which is underwater is having some different size of leaf and the part which is above water is having leaves of different size so size of the leaf on the same plant is variable depending upon whether they're in contact with air or whether they are contact with water so this is also plasticity why because there is change in the developmental pathway on the same plant due to change in their environmental condition so this is heterophilia type of plasticity correct cello read it like for example difference in the shape and size of the leaf produced in air and water in butter cup also represents heterophyllus type of plasticity and this is also the example of heterophilia one is environmental and second is genetical hope you have understood what is plastic plasticity that is deviation in terms of development simple as that only observed in plants not in animals now students we are going to move ahead with the next and very important segment of this chapter which is plant growth regulators now plant growth is regulated by hormones secreted by the plant body now what are hormones what are plant growth regulators what are plant growth hormones as you study the definition of hormone in zoology same is the definition is in botany what is that definition hormones are chemical messengers secreted or produced in trace amount produced produced by one part of the body utilized distantly right so same things you study the same definition you study in zoology the same replica is there in botany now read it plant growth regulators are small simple molecules of diverse chemical composition some may be uh carrot some may be carotenoids some may be terpenes some may be acids etc so we can say that chemical messengers in short hormones are chemical messengers which are produced in small quantity required in small quantity and produced on one side of the plant body but utilized somewhere else these are also known as phyto hormones now there are five hormones discovered in plant body all hormones have been discovered accidentally and out of the five hormones we can divide them on the basis of their functions they performed as positive hormones and negative hormones now what do you mean by positive what do you mean by negative positive hormones are those plant growth regulators which have some positive effect on plant body like promoting growth promoting flowering promoting fruiting etc and negative hormones are those which inhibit the growth and metabolism of plant body so under positive growth hormones we have three auxin auxins are better tryptophan derivatives some very hard they're indole compounds the most common auxin is indole acetic acid indole butyric acid they're indole compounds and they're derived from tryptophan amino acid correct second is gibberellin it is a terpene derivative positive plant growth hormone it is terpene derivative somewhere if i've written it yeah terpene derivative gibberick acid the most common used is ga3 third is cytokinin now beta cytokinin is a hormone which is found in both plant as well as animal if i specifically talk about plant cytokinin it's a positive growth hormone which is isolated these are adenine derivative isolated from zeatin or chemically they are zeatin if i talk about plant cytokinin these are adenine derivative coming to negative growth hormones there are two abscisic acid also known as stress hormone which is keratinoid derivative specifically viola xanthan derivative and then last is a gaseous hormone ethylene also known as ripening hormone so this is ethylene which is a negative plant growth hormone correct ethylene is somewhere mixed it has some good properties means growth promoting activities and it also has some growth inhibiting properties like for example it ripens the fruit so it is causing aging and senescence in the plant body hence it is characterized under negative i hope the five names and the derivatives is clear now moving ahead with the next hormone which is augsin so auxin is one of the plant growth promoting hormone which was discovered by charles darwin and his son francis darwin while working on the colluptile of canary grass now what they do what they did and how did they discover this hormone auxin let's try to understand so basically this auxin hormone was discovered by darwin and his son while working on the collective cannery grass now what they did these two people darwin and the sun they took a collectible collioptile is that leafy structure which protects the plymouth in case of monocots so they took a collyoctyle and then to this collectile they provided a unilateral light in one direction keeping the second half of the column tile in dark after some time what they observed when they were giving the light to this collioptile this collioptile started bending in the direction of light okay so now if this column tile is starting bending in the direction of light what could be the possible reason see bending always occurs when the body then like for example if i talk about my own body if my back is going to become heavy as compared to my front so my body is going to bend forward whenever you carry heavy school bags if you remember your old days you used to carry heavy school bags on your back so what used to happen your back used to just bend forward in order to bear that extra weight so similarly bending only occurs when there is some extra weight put on so if this column tile is bending in the direction of light then surely this side of the collectile is showing some extra growth which is not able to get balanced with the opposite side as a result bending is occurring in the direction of light so darwin thought that maybe in the presence of the light the tip of the collectile is capable of synthesizing some growth stimulating hormone which is causing unequal growth on the tip of the column tile because of which the darker side of the collectile is showing rapid growth and because of that rapid growth the tip is bending towards it right now to conclude his experiment or to make more clear understanding in his experiment this fellow darwin what he did he took another collectile with decapitated nature decapitated means whose tip has been removed so once the tip is removed now again light was given for the same duration in the same manner but no bending was observed why then he concluded that even after giving light the decapitated seedling is not showing bending because the tip is absent this means the hormone is synthesized on the tip the light as a stimulus is perceived by the tip if tip is not present then no matter what amount of light you give that growth promoting hormone is not synthesized because of which undifferential or sorry differential growth is not taking place on the column tile and hence no bending to further confirm this darwin also took another column tile of canary grass but this time covered with an opaque body opaque body means the body which is not able to trap light and now again gave the light but same thing happened no bending for the same reason as when opaque body is there on the tip it is covering the tip as a result tip is not able to receive the stimulus of light no hormone is synthesized and no bending is occurring that means the hormone is only synthesized when light is being given to the tip of the colliop tile because of the presence of the tip and the light this growth promoting substance is being synthesized which then travels to the opposite side of its synthesis that is towards the darker region causing some extra cell division causing some extra growth because of which the darker region becomes heavy and it starts bending towards the direction of light so this was whole experiment conducted by these two people that is darwin and his son however he could not isolate this hormone so therefore the further experiment was done by another scientist called fw vent so fw went simply repeated the experiment by darwin now working on the colleague tile of oat seedling the experiment by fw vent is known as avina curvature test avena curvature test so fw went then isolated this growth promoting hormone and the experiment performed fw went is known as avena curvature test and this experiment gives the quantitative estimation of auxin that means how much amount of this hormone is required to induce bending so therefore his experiment fw went experiment is also known as bioassay so quantitative estimation of any biological compound is known as bioassay so fw wendt proposed the bio assay of auxin while working on colleague tile of oat seedling bioassay means that promoting or telling about the biological estimation that quantitative estimation how much amount of hormone is required to induce growth to induce bending correct i hope you will remember this thing that what is the experiment by darwin while working on the uh colliop tile of canary grass so with this experiment darwin concluded that surely some growth promoting hormone is being synthesized on the tip of the colliop tile in presence of the light as a stimulus that is causing bending however it was isolated by later on by fw vent and his experiment is thus considered as bio assay right okay now moving ahead the term auxin is derived from the greek word called auxin which means to grow so basically this auxin word is derived from term auxin which means to grow it was first isolated from human urine these two things you have to remember from where the term auxin came from and what does it actually means and from where was it isolated for the first time so it was isolated from human uri that means it is synthesized in human body as well however it is of no use in our body so it is passed out through urine as a waste so it was isolated first from human urine chemically auxin is tryptophan derivative it is an endol compound now naturally in plants the type of oxide present are the natural organ found in plants isolated from plant is iaa and iba ia stands for indole acetic acid and iba stands for indole butyric acid auxin used in field of horticulture and agriculture has been extensive this hormone has been extensively used in horticultural and agricultural practices as a result scientists thought that why not to create some artificial auxin also by checking the composition of natural organ therefore some synthetic auxins the auxins which are synthesized by humans list as 2-4-d dichlorophenoxy acetic acid 2-4-5-t trichlorophenoxy acetic acid naa naphthalene acetic acid so these are the three synthetic auxins which have been prepared artificially by checking the composition of natural auxin and what is the need of preparing these synthetic oxin because auxin has been observed to be extensively used in agricultural and horticultural practices okay so this you have seen about what is auxin der it from where auxin is derived natural synthetic etc now let's try to see the roles of auxin that what are the roles physiological actions of auxin effects of auxin in the plant body okay now you read this auxin was derived auxiliaries derived from a greek word called oxine which means grow isolated from human urine already told you chemically it is iaa some other naturally existing auxin are also iba then on the basis of that synthetic auxins are also synthesized i told you the names as well now they are used extensively in agricultural and horticultural practices moving ahead with the roles number one and most common role of auxin is to induce cell division in the callus and start forming roots so auxin role of auxin one of the most common role of auxin is in callus culture you know what is callus calistudence is a mass of undifferentiated cell which can be used in tissue culture for propagating new plants artificially okay so in that callus if you pour right amount of auxin then auxin is going to initiate cell division and that cell division will further differentiate to form the root system in the callus so first and foremost important role of auxin is to induce rooting so in callous during tissue culture auxin use of auxin induces cell division and differentiation cell division and differentiation to form roots apart from rooting my dear students auxin is also used to promote ethical dominance now what is what do you mean by apical dominance you know that in a plant body there are two types of buds apical bud which are present at the tip of the shoot whose role is to induce the elongation of the plant body vertically whereas some are lateral birds which are present on the exile angle of the leaf and the stem and their role is to promote growth of the plant body horizontally correct spray of auxin is going to inhibit the activity of lateral bud and will promote the activity of apical bud because of which plant will grow vertically more as compared to literally so apical dominance is what spray of auxin or use of auxin [Music] will promote vertical growth of plant body so yes it is going to promote vertical growth as it supports apical bird over lateral bird and this is known as apical dominance correct now moving ahead with the third important role next important function of auxin is to promote abscission abscission simply means fall off what fall of fall of older parts of the plant body so oxen promotes abscession of older parts like older leaves mature fruit etc however it does not allow absolution of younger fruits younger leaves so auxin promotes abscission you can say auxin promotes fall-off older parts of plant body but inhibits the fall of younger parts clear so these are the three main role of auxin number one you have seen as promoting rooting in callous culture second is promoting apical dominance and third is promoting abscission that too of older part not of younger part apart from this auxin are also used one of the synthetic oxen that is 240 is used to prepare weed free lawns how farmers they use they spray their lawns and gardens with 240 that inhibits the growth of monocot weeds without influencing without touching the dicot wheat so this is also one of the important role of oxen that is it is used to prepare weed free lawns correct yes or no okay so i hope you have understood this much for auxin remaining you can read it from your ncrt now let's move ahead with the next topic that is gibberellin if i talk about gibberish students then gibberillin as that of auxin it is also one of the positive growth hormone it is also positive growth regulator jibrillin was first discovered by scientist a japanese scientist ikurosawa now what e kurosova did and how he actually found this gibberellin hormone which is one of the positive growth hormone positive plant growth regulator so listen to me very careful it is a very interesting story ikarosova a japanese farmer he saw certain farmers he saw certain japanese rice farmers growing rice every year but once what happened that those farmers normally planted their rice seedlings and they waited them to blossom they waited the farmers waited for their rice seedlings to grow and give some fruits however this time what happened the rice seedlings they went on growing and growing and growing they break they came they became very tall they only showed vegetative growth and does not showed any reproductive growth there was no flower there were no fruiting and because the plants became excessive tall their body became weak the stem became weak and all the plants bent down in the water and they got rotten off without flower flowering without fruiting without giving any benefits to the farmers now farmers became very upset that what happened to their rice seedlings why they only went on elongating their stem why they did not stop and why didn't they not fruit and flowered that means due to excessive growth in the rice seedlings rice seedlings became sterile weak because of which they bent down so ekoroswa came to help them how he took the samples of those rice seedling in his lab and observed that those rice seedlings are actually infected with the fungus called gibbrella fusicroi this fungus gibberella fusic roy what it causes it causes tremendous production of a growth promoting hormone gibrillin which is responsible for stem elongation now in these rice seedlings due to excessive production of gibberellin hormone the stem keep on elongating it kept on elongating and it did not get time to flower because of which there were no fruits stem became too weak to stand erect hence it bent down and got rottened up now this gibberella fusic roi a fungus infected rice seedling is responsible for production of a growth promoting hormone called gibberellin such rice seedlings which were infected with these gibberella fusicoroi and show tremendous elongation in their stem the name the disease that means that if they're infected with the fungus that means they are diseased so the name of the disease given to such rice seedlings was bakan or foolish seedling of rice correct yes or no so like this ikuroswa a japanese scientist observed that how japanese farmers got upset with their rice seedling which failed to flower and only showed stem elongation so with the simple observation and isolation e kurosawa discovered the second growth promoting hormone gibberellin chemically gibberellins are acidic and they are terpene derivatives so far hundreds of gibberellins hundreds different varieties of gibberellin has been discovered which has been named as ga1 ga2 ga3 and so on the most extensively used gibberellin out of the hundreds of jibrillin discovered so far is ga3 correct will you remember all the informations which i have given you okay very good now you have to see the roles of jibrillin that what are the functions of jibrillin number one role i have already told you promoting stem elongation so number one and very important role because of which they are actually discovered is stem elongation yes or no these gibberellins presence of gibberellin induces stem elongation suppose if a plant is not producing right amount of gibberellin then the plant body will remain small such a plant will be called as do of plant and this concept was actually used by norman berlog ms swaminathan to introduce or to produce hybrid seeds they produce semi do of varieties of rice and wheat semi dwarf means do of varieties the varieties which are going to show restricted vegetative growth but tremendous reproductive growth so this concept that how gibbelin affects the growth of the plant body was used by scientists to bring green revolution okay now coming back to stem elongation so one and the first and the foremost role of hormone gibberillin is to promote stem elongation it breaks the dwarfism in the plant body so you can simply write it breaks the dwarfism in plant body yes or no correct apart from this this hormone gibberellin also induces seed germination it breaks seed dormancy a seed which is not able to germinate maybe due to inactive embryo if you spray gibberellin if you provide that seed embryo with gibberellin then it is going to break its dormancy and will let the growth of plymouth and radical okay now let's see how what gibberellin does so i'll just give you a small hint about that how gibberellin induce seed germination how does it promote seed germination what happens beta this gibberellin hormone is going to allow the endosperm you know in seed if this endospermic seed then in endospermic seed the main source of nourishment to the embryo is the endosperm now suppose if the endosperm is starchy then it is rich in starch but that starch is present initially in complex form so that complex sugar cannot be transported to the embryo so what this gibberellin does this gibberellin is going to induce the formation of an enzyme called amylase amylase enzyme will convert complex sugar into simpler form and that simpler form sugar will then travel from endosperm to embryo embryo will start getting the nourishment and the seed seed will start germinating so how it helps in seed germination jibrillin promotes the production of amylase enzyme right so it promotes the production of amylase enzyme that converts complex sugar of endosperm into simple form that is then that is then received by the embryo for development hence this gibberellin promotes seed germination or it breaks seed dormancy now students as i was telling you about stem elongation let me quote one very good example that where stem elongation of gibberin is helping so one common example is sugarcane stem elongation with the spray of gibberellin on sugarcane stem it is said that about 20 tons per acre production of sugar from sugarcane can be increased because spray of gibberellin on sugar cane is going to make them long thick and better so if you spray gibberellin then you can increase the production of sugar 20 tons per acre so you can coat this example very important spray of gibberellin will promote the growth of sugar cane will promote the growth of sugar cane that will increase the production by 20 tons per acre correct so please remember this thing now moving ahead to the next important role of gibberellin is bolting now what do you mean by bolting bolting is the phenomena which you observe in case of rosette habit plants like cabbage or beet have you seen cabbage cabbage is simply a plant whose leaves are arranged in cyclical manner so you can say that arrangement of the plant body in case of cabbage is rosette like cyclical manner arrangement in those plants beta gibran help in inducing bolting now what is bolting bolting simply means internodal elongation just prior to flowering so that stem can rise above the soil to induce flowering ma'am you have just said some bookish lying we are not able to understand this okay so let me explain you in a better way see students what do you eat in a cabbage you know what is cabbage and cauliflower so what do you eat in cabbage do you eat their leaves or do you eat their flowers so in case of cabbage we prefer to eat leaves that means for farmers the economic importance is for the vegetative body in case of cabbage plant the economic importance lies in its leaves leaves should be healthy then only i am going to buy the cabbage from the market i want better as a farmer if i am growing cabbage then i only want that my plant should produce very pretty healthy leaves i want very good vegetative growth for my cabbage but not reproductive because we don't want flowers nobody eats flowers of cabbage right the economic importance of cabbage lies in its leaves which is a which is a part of vegetative body so normally what farmers does they try to reduce the amount of gibberellin hormone from thus these cabbage plants because of which there is no proper stem elongation in the cabbage plant as a result cabbage remains in the soil near the soil correct now when stem elongation is not taking place so there is no flowering also because in such rosette habit plants flowering occurs only when their stem comes above the soil let me show you with the help of a diagram suppose this is my soil correct now here is the seed of cabbage now this seed of the cabbage is going to get the favorable condition and it will try to grow in it will give rise to premule and radical radical will form the root system ple mule will come upward but i have inhibited the production of gibberellin because of which stem is going to remain very short near to the soil and all the leaves will then be arranged cyclically around it forming your cabbage you must have seen all the cabbages near the ground you must have never seen a cabbage which is growing which is growing on branches on tall trees no you always find cabbage growing near the soil correct so this is normal cabbage where no flowering is taking place only vegetative growth only leaf formation but beta for seeds okay you're letting this plant only perform vegetative growth you are not letting this plant to perform reproductive growth you're not letting this plant to produce flower or seeds now if you're not letting all the cabbage plants to produce seed then how will you plant the next generation because for the next generation you need seeds so in that case we need even flowering i understand economic importance lies in vegetative phase but for next generation we also want reproductive phase and for that flowering is important and for flowering stem elongation is important so use of gibberellin comes over here now what gibberellin hormone does it induces internal elongation suppose this is a seed root system shoot system now gibberellin what will does it will allow the stem to elongate stem is going to elongate it is going to come above the ground and now it will induce flowering with some poor leaves not proper leaf so this is also a cabbage plant but not forming cabbage rather giving flowers so that seeds can be produced and this stem elongation just prior to flowering in rosette habit plants like cabbage is known as bolting so this is also one of the important role of jibrillin i hope you have understood this now moving ahead with the next important role of jibrillin is inducing malting in growing industries jibrillin is used to speed up the malting process malt is like a partially germinated barley seed barley seeds they are used to prepare wine and beer so in order to initiate quick germination of barley seeds gibberellin is used and that is known as malting so malting malt is prepared so that on those malt yeast can be sprayed to produce beer or wine so what is malting melting is formation of malt formation of partially germinated barley seeds so that they can be used further to prepare the vine or beer and to enhance that rate of germination of barley seeds use of gibberellin is done so malting is basically used in brewing industry the concept of malting is used in brewing industry to prepare what to prepare wine and beer and how this is how gibberellin is used i hope gibral is clear to each and every student okay now moving ahead with the next plant growth promoting hormone which is cytokinin my dear students cytokinin is also a positive growth hormone now this hormone is exclusively used both in plant body as well as in animal body in us also the cytokinin is used to promote cell division same as it functions in plants in plants also the cytokinin is used to promote cell division so in our body as well however the chemical composition of plants or cytokinin and animal cytokinin is different plant cytokinin is adenine derivative type of z actin whereas animal based cytokinin is chemically kinetic now they were isolated by also two different scientists if i talk about plant-based cytokinin then it was isolated by scientists f skoog and score workers these people they were trying to study about callous differentiation and they observed that when in the callous right amount of auxin along with coconut milk or yeast extract was given then callus was properly growing and differentiating to produce root system and shoot system so skoog isolated this chemical from the coconut milk which is zeatin which is adenine derivative and found that this ziatin is actually inducing shooting in callus similarly there was another scientist called miller who was working on the sperm of herring fish herring is a fish is the name of a fish so he was working on the sperm of herring fish and isolated animal based cytokinin a cell division promoting hormone which is chemically kinetic correct will you remember all these points so there are two types of cytokinin one is animal based another is plant-based so the entire discovery which i have said right now is written on your screen you can directly read it we are going to now start with the roles of cytokinin first and foremost role of cytokinin i have already told you is promoting cell division what it does it promotes cell division for example in callus to induce shooting so you can say one thing that both auxin and cytokinin are responsible for promoting cell division in callus however one initiates rooting so the another initiates shooting therefore if the right amount of auxin and cytokinin sorry if the right amount of auxin and cytokinin is given to the catalyst then callus will properly flourish and develop into a new plant body correct so first and foremost important role of cytokinin is to promote cell division second beta it promotes lateral growth of plant body it inhibits apical dominance which is an antagonistic role to augsen it inhibits apical dominance now what do you mean by this apical dominance means growth of apical bud at the cost of lateral bud inhibiting apical dominance is just the vice versa that means growth of lateral bud at the cost of apical bud suppose in a plant body there is high amount of cytokinin as compared to augsin then that body is going to grow horizontally but not vertically why because role of cytokinin is to promote lateral growth is to promote lateral bud auxiliary bud at the cost of apical bud this role of cytokinin is antagonist means opposite the cell division is synergistic means same two auxin however the second function is antagonist to auxin very important from point of view of neet you should remember this thing moving towards the next important function of cytokinin is to promote nutrient mobilization the cytokinin delays senescence by promoting proper nutrient mobilization and protein synthesis so it promotes nutrient mobilization that means if there is a leaf older leaf which is about to fall off so cytokinin will promote that before that older leaf falls off all mobile elements are taken from that part and provided to the younger regions so that loss of nutrient can be protected and thus delaying the senescence so it promotes nutrient mobilization thus delaying aging apart from this cytokinin also help in chloroplast synthesis right it promotes chloroplast synthesis it also promotes promotes adventitious root formation so i hope you have unders understood this role of cytokinin as one of the growth promoting hormone remaining you can just read it from ncrt and learn it from there directly so these are the three growth promoting hormone now we are going to study about the next two hormones which are basically negative pgr the hormones which basically inhibits the growth of plant body how let's see so first we are going to talk about i'll first i'll start with aba abscesic acid which is also known as stress hormone why stress hormone because aba abscisic acid is produced in plant body when it is undergoing some stressful condition before starting with why and how aba is known as stress hormone let's discuss about its discovery so beta during mid-1960s there were three independent researchers working in three different countries but on the same topic the all the three independent researchers they were working on the same topic and when they submitted to their work to the publisher to the publishing organization then those organization thought that these three different people brought the same work with three different name then that publishing organization joined those three works joined those three names and proposed one individual independent name as acid so read it three independent researchers reportedly reported the purification and chemical characterization of three different kinds of inhibitors named as inhibitor beta abscission and dorman later on it was found that all the three chemicals were of all the three names all the three works of independent researchers was found to be one so it was joined and named as apsisic acid now the thing is that why is it known as stress hormone what does it does what does it do to inhibit the growth of plant body number one beta this abscisic acid delays or it inhibits protein synthesis it inhibits proper nutrient mobilization as a result it promotes senescence it promotes aging more amount of abscisic acid will either break down the proteins or will inhibit the formation of proteins will inhibit proper nutrient mobilization because of which plant start moving towards aging so this hormone it promotes senescence and because of this major reason aba is considered as a negative plant growth hormone so first reason is it promotes senescence that is aging by doing what by inhibiting protein synthesis by inhibiting protein synthesis and nutrient mobilization apart from this aba beta also induces closure of stomata you know levite theory when there is high co2 concentration that induces the production of aba which inhibits the uptake of potassium iron from the adjacent cell in the guard cell that induces the closure of stomata even during day time it can happen and but however it is normally during happening during night time but same thing can happen also during day time and imagine if during day time stomatas get closed then all the mechanisms will get stopped no photosynthesis no transpiration no respiration so yes surely closure of stomata by aba is one of the negative aspect for the plant body if it is occurring during daytime correct now moving ahead this aba also promotes dormancy of seed by inhibiting the seed germination so because of so many reasons this aba is considered as a negative hormone i hope you have understood what is aba now we are going to see the next negative plant growth hormone that is ethylene okay now we are going to start with the next plant negative plant growth hormone which is ethylene ethylene was actually discovered by scientist cousin but this cousin is the name of the scientist but not any kind of a relation so cousin and his coworkers release of a volatile hormone a volatile substance beta ethylene is gaseous in nature so this cousin and his co-worker they confirmed the release of volatile substance called ethylene that induces ripening in the fruit if suppose for example there are two types of fruit x and y x is ripened and y is unripened so in the presence of x y will also start ripening due to the release of this volatile substance from the ripening fruit that means what this cousin underscore worker observed that substance from ripened oranges already ripened oranges were secreting were releasing this volatile substance that caused induced ripening in unriped bananas you must have seen that if we have four bananas kept together if one is already getting ripened other three starts ripening even faster why because that ripened banana is secreting is releasing this volatile ripening hormone called now this ethylene is inducing ripening which is a type of a senescence that means we can in simple say that ethylene also promotes senescence it also promotes aging and due to this major reason ethylene is kept under negative plant growth hormone because it is considered to promote that is aging it is basically a ripening hormone which is very readily used by farmers there is one aqua solution of ethylene prepared called ethephone which is then sprayed on the field to enhance the rate of ripening so scientists farmers use equisolution of ethylene called ethefon [Music] to enhance ripening beta what ethylene does it increases the rate of respiration that promotes ripening that promotes senescence now there are two types of fruit the fruits which are ripening in the presence of ethylene such fruits are known as climatic fruits however there are some fruits maybe like some citrus fruits like maybe lemon they do not ripen in the presence of ethylene they are known as non-climatic fruits correct so there are two types of fruits climatic and non-climatic climatic means like banana is a climatic fruit why because in the presence of ethylene it gets ripened up but some citrus food not orange orange is a climactic fruit but some citrus fruits they are non-climactic they do not ripen in the presence of ethylene yes or no okay so this is all about ripening property of ethylene moving ahead with some important roles of ethylene like it also breaks seed dormancy this ethylene can also induce seed germination it can also break seed dormancy apart from this it also promote growth stem elongation in rice seedling what it does suppose is deep water rice seedling plant so spray of ethylene can also induce stem elongation and can protect those right seedling from getting dipped in water and getting rottened up so it also promotes stem elongation in deep water rice seedling it also shows apsi it also shows uh thinning in fruits like apple thinning means not very good quality of fruits are sometimes produced maybe some small sized uh fruits are produced which is called as thinning so due to ethylene thinning of fruits is the thinning is observed in case of cherry in case of walnut in case of apples so ethylene also causes thinning of fruit deteriorating the quality of fruit sometimes in case of cherry walnut and apple so these are certain list of rolls performed by ethylene rest you can read it from your ncrt with this all the roles and of all the roles of positive as well as negative plant growth hormone is done now we are going to ahead we are going to move with the next topic that is photoperiodism now what is photoperiodism we are now going to start with the concept of photoperiodism hope you have all understood the different five types of plant growth promoting hormone now we are going to move towards the next important topic which is photoperiodism hope all you can see the heading photo means light periodism means duration of exposure so like you know that plants need light for photosynthesis purpose the the green pigments that is chlorophyll which is found in the leaves of the plant body they trap the light to induce photosynthesis similarly light is also required by the plant for inducing flowering and that mechanism of flowering in plant is understood by the concept of photoperiodism so in plants light is not only required for inducing photosynthesis but it is also required for inducing flowering the concept of flowering in plant you will understand under this heading of photoperiodism photo means what i already told you light and periodism means duration of exposure right now beta it has been observed in plants that change in the relative length of day and night changes the pattern of flowering in plant right now what is this there were two people before i like before i explain you the definition part of photoperiodism first let's try to understand the experiment which led to the arising of this concept of photoperiodism so there were two people there were two scientists garner and ellard these two people they were working on a tobacco plant species called maryland mammoth right so there were two scientists garnered ellard they were working on maryland mammoth which is one of the tobacco species one thing which they observed in this tobacco plant was that it was flowering normally during winters when there were winters when they when there was low period of light and heavy exposure of darkness then this plant was flowering normally but this plant maryland mammoth could not flower under summers during summers this plant could not flower naturally however if it was artificially exposed to long night and short day condition short day of about eight hours and long night of about 16 hours when long night of about 16 hours and short day of about eight hours was artificially given to this plant then even during summers it started flowering that means for flowering maryland mammoth needs long exposure to night and short exposure to day so their response to relative change in the period of dark and light in order to induce flowering by garner and ellard is known as photoperiodism what is photoperiodism photoperiodism is the relative length the exposure of day and night given to a specific plant in order to induce flowering in them is known as photoperiodism and this concept was explained by garner and ellard correct while working on maryland mammoth so concept of photoperiodism was given by garner and ellard it has been observed that some plants require a periodic exposure to light in order to induce flowering so this it is also seen that such plants are able to measure the duration of exposure to light for example maryland memorial when it was exposed only to 8 hours of light and 16 hours of continuous darkness then only it induced flowering now if you weather give it naturally or you get give it artificially it depends upon the person if it is given naturally it happens during winters but now if i want that this tobacco plant should also flower during summers then i have to fulfill its condition artificially so this is known as photoperiodism now photoperiodism beta the site of perception of light now like where are the photoperiodism site of perception they are the leaves so the organ that is leaves are the site of perception for photoperiodism why because leaves they contain a special bluish green color pigment called phytochrome so leaves they contain a pigment called phytochrome this pigment phytochrome beta traps the light of required of required length and once this phytochrome gets the light of required length depending upon species to species this pigment gets activated in return now this pigment is going to produce a flowering hormone called fluorescein in the leaves once flourishing is produced now this flourishing from the leaf will travel to shoot apical meristem now shoe topical meristem on receiving flourishing will start converting itself into floral apical meristem once shoe topical meristem is transformed into floral apical meristem now you know instead of leaf or branch flowers will be produced so this is how flowers are born on plant every species has the specific requirement of day and night length like for example this tobacco plant it requires long night and short day so now we can call this plant as a short day plant when you fulfill this condition then in their leaves the phytochrome pigment will get activated which in return will produce the hormone flourishing hormone flourishing will then travel from the leaf to sm will convert sam into fam and the plant will start producing flowers right now this pigment if i talk about this pigment phytochrome students then this pigment phytochrome exists in two forms that is pr and pfr p stands for phytochrome est air r stands for red light and fr stands for far red light so this pigment responsible for trapping light in order to induce flowering exists in two forms the inactive form is pr which is found in cytosol and pr is the pfr is the active form now these two forms of phytochrome they are interconverted depending upon the conditions like for example during day time when red light is abundant so in that case pr will start converting into pfr so in the presence of red light this pr will convert into pfr not 100 conversion and during darkness or in the presence of diffused light that is far red light pfr will convert into pr so how many forms of phytochrome are there two forms pr and pfr both the forms are interconvertible pr is the inactive form which converts into pfr under red light conditions and same thing happens or vice versa happens during far red light or during darkness i hope you have understood that how flowers are produced and what is this phytochrome so phytochrome is a bluish green pigment right which is found in leaves thus leaves becomes the site of stimulus the site of perception of light in order to induce flowering in plants okay now garner a lot simply explained that for flowering every species require their own specific duration of exposure to light and dark on this basis we have three types of plants how many types of plants are there on the basis of duration of exposure to light and dark three types that is long day plant shot day plant and day neutral plant before i start with the three categories of plant i will tell you one more terminology that is critical period what is critical period critical period is simply a threshold value like in chemistry also you study about threshold which is the minimum so critical period is also like a threshold value above which or below which a plant starts flowering so critical period is like a standard condition right so critical period means standard exposure of light and dark to the plant above which or below which plant starts flowering so critical period is same for all the plant species now depending upon the requirement they will flower either above critical period exposure to light or below critical period exposure to light on the basis of that we have three types of plant long day short day and day neutral first let's see about long day plant the name itself suggests those plants which require more exposure of light as compared to day sorry as compared to night so those plants which require more amount of light as compared to dark are known as long day plant like for example wheat correct now let's talk about long day plant so if i want to draw the long day plant scenario the condition then see how will i draw this so long day plant critical period this line is depicting critical period this is a standard value above which or below which plant will start flowering so now long day plant means the plant which require more amount of light more than critical period so when you give the plant more light more than critical period so this much is the duration of exposure to light and darkness is of shorter duration then this plant will start flowering if you fulfill this condition in a long day plant then long day plant will start flowering talking about short day plant like for example soya bean like for example tobacco what happens in short they plant now just see this when duration of exposure of light is below critical period suppose this is critical period now in short they plant light amount required is less but dark amount required is more so when light is given below critical period and darkness is of longer duration if this condition is fulfilled then the short day plant will start flowering like for example soya bean like for example tobacco the one which you have seen the the one which was taken by garner and ellard one of the species of tobacco maryland memorial is actually a short day plant third is day neutral the name itself suggests the plant which will flower under all conditions may be long day conditions or maybe short day conditions so those plants which flower under all durations of exposure of light and dark are known as day neutral like for example tomatoes cucumber they are day neutral plant so day neutral means what suppose this is how i am going to depict the flowering pattern in day neutral critical period now under all conditions maybe you give them more light maybe you give them less light whatever may be the condition they are going to flower example tomato cucumber so these are some examples of day neutral plant now i hope you have understood the three types of plant on the basis of the duration of exposure to light and dark now what is the benefit you know that okay tomato is a day neutral plant so it is going to flower under all conditions now you know that soya bean is a short day plant it requires shorter conditions to flower so what what is the benefit what is the benefit and importance what is the application of this photo periodism how garner and ellard has helped you to or how garner and ellard has helped mankind with their experiment on photoperiodism so beta they have decoded the flowering pattern in plants and you know that flowering is very important for us to understand because when the flower when the plant will flower then only seeds will be produced and those fruits will be produced and fruits have great economic importance as well as seeds so our major concern with the plant is their flower right and now if you know the flowering pattern in the plants then even under artificial conditions you can or provide the plant with all those conditions which they require for flowering and you can even make them flower other than their normal conditions like for example tobacco tobacco naturally flowers during winter it does not flower during summer but suppose if i need tobacco flowers even during summers then shall i wait no now i know that flowering pattern in tobacco is short short day long night so that if i will provide them artificially even during summers i can obtain flowers i can obtain their seeds so concept of photoperiodism by garner and ellard has helped to decode the flowering pattern and does now we can exploit the plant more for our economic welfare we can make them flower even when they don't want by just providing them all those conditions artificially you know that is the reason only that now why we can even enjoy mangoes during winters mango is a summer plant but nowadays there is no such time duration even in winters also you get the summer fruits and in summers also you get the winter fruits why because we know their flowering patterns we artificially make the plants flower we obtain their fruits even under artificial condition so this is how we are exploiting plants for our own benefit by understanding the concept of photoperiodism given by garner and ellard now moving ahead with the next important topic vernalization students vernalization is also one of the method of flowering what is vernalization it is also one of the method of flowering but in a different manner how in a different manner vernalization simply means inducing flowering in plants by either giving them quantitatively or qualitatively low temperature so flowering under exposure of low temperature is known as vernalization so let's read the definition first vernalization plants there are some plants for which flowering is either quantitatively or qualitatively dependent on the exposure to low temperature right some plants are such which need the exposure to low temperature in order to induce flowering so that type of flowering is known as vernalization correct now let me explain you the mechanism or the concept behind vernalization okay now before we enter into the concept you should know one more thing that the site of perception of low temperature is either the embryo of the seed or mature shoot apex as you studied in photoperiodism the site of perception are the leaves so similarly in vernalization the site of perception are either the embryo of the seed or mature shoot apex so this you have to remember let me write it somewhere over here site of perception invernalization is either mature shoot apex or embryo of the seed right now there are two varieties now basically vernalization is seen in winter annuals and some biennials like cabbage carrot etc so concept of vernalization we can study in some winter annuals see every plant does not require vernalization there are only some groups of plant species which require exposure to low temperature in order to induce flowering like for example winter annuals and few biennials thick like carrot now if i talk about some winter animals like for example rye okay now in case of winter animals better there are two varieties some spring varieties and some winter varieties okay spring varieties are those varieties which you sow in the season of maybe feb and you reap in the month of april so just spring varieties are those which just require three to four months of production however winter varieties are those which you sow in the month of either october and reap in the month of march so winter varieties they require six months now farmers thought that why not to plant even winter variety in the month of in the month of uh feb like we do for spring variety so that the development time of winter variety will also be reduced and in three months they are going to flower i am repeating it once again please please listen to me carefully there are two varieties of winter annuals like spring variety and second is either autumn variety you can call them or you can call them as winter variety if i talk about spring variety then we sow them in the soil in the month of feb and reap them by the month of april by the end of april or may right if i talk about winter variety then we sow them in the month of october and reap them in the month of march okay october november december january february march so they are almost taking six months and these are taking near about four months february march april three to four months maybe we are sowing in the month of jan so spring varieties are taking only three to four months to flower but winter varieties are taking six months so tell me farmers are going to prefer which variety obviously they will think that winter that spring varieties are better than winter varieties why because in less time they are flowering okay but what happened actually spring variety they were taking less time but they were not giving tremendous production however winter variety they were taking longer time but they were giving tremendous production so farmers thought that why not to plant winter variety in the month of feb and within three to four months why not to obtain tremendous flowering so they tried and they did the same what farmers did they took the seeds of winter variety they sow it in the soil in the month of february and waited in the month of april that this variety is going to flower tremendously as it used to do when we used to sow them in the month of october but to surprise nothing happened those winter variety when they were sown in the soil in the month of february by the end of april they did not flower farmers got confused that what happened by these winter varieties when they were sown in the month of october and when reaped in the month of march then they were giving flowers tremendously everything fine but when same we are doing but in different months then why this variety is not giving the flour then scientists came to rescue farmers they came to help farmers and told them that guys these winter variety they need exposure to low temperature their embryo when they are germinating they need exposure to low temperature which is naturally fulfilled when you saw them in the month of october because october is then followed by november and december and january which are phases of extreme low temperature temperature in our northern part of country so when you saw them in the month of october their requirement of exposure to low temperature is naturally fulfilled the embryo of the seed it perceived that low temperature germinate properly flowered tremendously by the month of march however when you were planting the same variety in the month of february then april was not giving any fruit because from feb to april there is only one month that is march which is not condition which is not fulfilling their conditions of requirement of low temperature naturally so when seed they are not getting the low temperature in the month of feb hence they are not flowering that means winter variety will only flower if you give them low temperature otherwise they are not going to flower this is known as natural vernalization what is natural vernalization natural vernalization is due exposing the seeds to right amount of low temperature either quantitatively or qualitatively in order to produce tremendous flour in a required span of time so six months is also taken low temperature is also received so they will flower tremendously this is viralization now farmer says that okay we understood what scientists are saying but still we want that these winter varieties which are of good quality they are flowering highly we still want them to sow them in the soil during the month of feb now scientist says that okay farmer sorry said that okay we understood what scientists are saying but still we want that winter varieties which are responsible for giving high amounts of production should be planted in the month of feb and should reap in the month of april but with tremendous flowering so scientists said okay no issues what farmers will want we will give them how so scientists told farmers that if you want to plant your winter varieties in the month of feb then before planting your seeds in the soil first expose them to low temperature artificially first keep your seeds in low temperature and then plant them in the soil and then you see in three months only your winter variety will flower and will give you tremendous production so same thing farmers did and they found that yes they were tremendous flowering there was tremendous production even from winter varieties when they were sown in the month of feb by just giving them artificial vernalization so what artificial vernalization does artificial vernalization helps you to increase the production in lesser duration of time in three months you will do the same thing which naturally is required by six months so this one is natural vernalization and this is artificial vernalization artificial viralization increases the production in lesser time and natural vernalization prevents early development prevents precautious development and still gives you tremendous production i hope you have understood the concept of vernalization as well with this we come to the end of the chapter plant growth and development along with this class 11th syllabus is also over now we have few questions to discuss the number one question says plant growth is your options are intrinsic intrinsic means internal growth so you know that plant growth is intrinsic all living organisms without any exception shows internal type of growth plan shows open type of growth absolutely true they show open type of growth which is indefinite and indeterminate plant growth can also be measured but indirectly either by measuring the size the number the volumes leaf area length etc so all the three options are true with respect to plant growth hence the answer of the question will become four that is all of the above moving ahead with the next question that is stimulus of vernalization is perceived by right now i explained you that stimulus of vernalization is perceived either by mature shooter picks or the embryo of the seed hence first and third both the options are correct leaf is wrong so the answer of the question will become d that is more than one option is correct hope you have understood this question moving ahead with the next that is plasticity in leaves is known as now what is plasticity then we will talk about plasticity specifically in leaf plasticity simply means deviation from the path of development which is only observed in case of plants in plants that different organs like leaf root shoot etc may show deviation from the path of development which is known as plasticity if plasticity is specifically observed in leaves then this is known as heterophili hetero means different philly term is used for leaves so plasticity in leaf is known as heterophili so the correct answer of the question will become a homophily is wrong heterophylloid innovator phylloid is the term used for untrue leaves the leaves which are made up of haploid cells so this is also wrong hence the answer of the question will become a hope you have understood this question with this moving ahead and time to say goodbye take care keep working hard the 11th syllabus is finally done we are soon launching or it has been rather i should say the yakin badge the dropper neat batch is already launched on the uh pw app as well as on the channel of pw so please if you have still not enrolled go get yourself enrolled there you will not only get detailed explanation of every chapter in every subject but along with that you will also get the questions to solve on the uh with the help of the daily practice sheets and tests will also be conducted and it is of minimal cost so still if still you have not enrolled yourself for that batch then go and grab the opportunity till then bye bye to everyone thank you