Free Biology NEET Video Lectures for Anatomy Of Flowering Plants

00:00:44 Hello friends, I'm Shubhangi Rhodi PGT Biology KV1 AFS Hinden and I welcome you all to the first session of chapter 6 of class 11th biology that is anatomy of flanning plants. Anatomy. We all know that anatomy is the study of internal structure of an organism. So when we study anatomy, we study about the tissues, cells and various structural organizations of the body. Well, we know that the structure relates with the function. So knowledge of anatomy is used for understanding various life processes.

00:01:24 Also the anatomical studies of plants throw light on their evolutionary relations as well as their environmental adaptations. Now what happens is that uh generally uh students pupils they love to uh read and learn about the analytical biology versus biochemistry and uh biotechnology and all. But when it comes to the study of morphology and anatomy, they seem to be afraid of them because uh there the content is more uh like descriptive and people think that it needs to be crammed up. So well in today's class we will try to assign a

00:02:10 reason to all the descriptions so that the need for the cramming up can be done away with. Let us begin. So talking about the tissues we all know that the tissues are group of cells having common origin and they usually perform common function. Plant tissues can be divided into two groups meismatic tissues and permanent tissues. Let us take mematic tissues first. The word has been derived from meistos that is a Greek word and it stands for divided. Growth in plants includes two stages. First the production of new cells and

00:02:54 secondly the expansion of these cells via uptake of water by the u vacules. Now what happens is that the cell division occurs only in the meristmatic regions while expansion may occur anywhere else. Let us see here in this diagram. We had referred to this diagram in earlier chapter also. Uh so here in this diagram you can clearly see there is a reason of meristematic activity. It is the reason where new cells are being continuously produced by motic division. The cells of this region are continuously dividing and chopping off

00:03:33 new cells. These new cells are all alike all very similar to each other because none of them are specialized. So the uh they just cut off chop off a lot of new cells all through the time and when these new cells enter the system they first get elongated and later they get mature that is they are assigned their specific function and structure accordingly. So this is the region where they differentiate. we are talking about the meristematic tissue which is placed here or in other portions of the plant also as we'll see

00:04:13 earlier as we see later. So uh coming back the meismatic tissues are responsible for the division of new cells by mitosis and thus they are responsible for the growth of the plant. So we all know that plants have indeterminate growth. That is the plants have the ability to keep on growing throughout their life while the animals do not have this property. They have determinate growth. Can you think why the nature has given the property of indeterminate growth to plants only and not to the animals?

00:04:56 Do you think that this property is to compensate loss of some other things that animals have but plants don't? Yes, we are talking about the mobility. Most of the times animals are in position to escape the dangers. They can simply move away and avoid the dangers where be it be predation or natural disasters. On the other hands, plants are not mobile. They have to stand at one place. So they cannot save themsel from her worry or fire or any other natural disaster that is taking place. So just imagine what would have

00:05:39 happened if the plants had only determinate growth. Once a cow graces by and eats up the shoots or the stems, the plant would have been dead. But it is not the case. Thanks to the presence of the mematic tissue, it is present there and it keeps on chopping off new cells for the growth of the plant so that the plant body can continue to grow throughout its life. Moving on, let us now see the characteristics of messmatic tissues. The cells and the tissues we are talking about are formed exclusively by

00:06:19 undifferiated or embriionic cells. And the properties of the cells are as follows. They are relatively smaller in size. They are either rectangular or isometric that is maybe polygonal or oval in shape. They are always compactly arranged and without any intercellular spaces. In fact, whenever you are asked to draw the portion of the plant or the cellular structure of the plant showing the meismatic tissue, you can draw them like these because most of the time they are rectangular and they do not have any

00:07:02 intercellular spaces. But what is to be kept in mind is this that they have very large and conspicuous nuclei and dense cytoplasm. So this is how we draw mematic tissue. Wherever you are required to draw, draw them like these. Yes. Talking about the cell wall, their cell wall is thin and is made up of only cellulose. They have large amount of dense cytoplasm also. So while you draw, please show some cytoplasm also in your diagrams this way. Moving on, as I told you earlier also that they have a single conspicuous

00:07:57 nucleus situated in the center of the cell. The vacules are either absent or if they are present they are very small in size because the cytoplasm is dense. So the vacules are either absent or if present they are very very very small and no argic substances are also present. that is ariasic substances are non protoplasmic substances um like reserved food materials or secrettory products or excrety products they are absent from these meismatic cells. Finally uh most of the organalies are also absent except for the mitochondria.

00:08:39 Mitochondria is of course there because it is there to provide the energy for rapidly dividing cell. But other organies are either absent or present in nonfunctional state. For example, plastids. Plastid are present in non-functional state called problastids. This was about the characteristics of meismatic tissues. Let us now study the different types of merist stems that are present. Actually the meristematic tissue is present all through the plant body at different uh regions. So there are many uh ways in

00:09:14 which we can group or classify the meismatic tissue. The meismatic tissue can be classified on the basis of their origin, location in the plant body and differentiation also. So let us discuss the first type of classification that is based on the origin. When we talk about origin, the meismatic tissues can be divided into proary stems, primary merist stems and secondary merist stems. Proary stems are the ones which are present in germinating embryos or germinating seedlings when they are very young and these the derivatives of these

00:09:54 merist stems they provide new cells for the plant bodies. Some of these cells give rise to the primary merist stem also. The primary merist stem in turn divides to form the primary plant body. The young uh plant body and some of the cells of the primary merist stem give rise to secondary merist stem uh during later periods of growth. The secondary merist stem is also very important but because it causes the secondary growth the wood formation. Uh have you ever noticed this thing that uh whatever be

00:10:31 the age of the tree, whatever may be the girth of the tree, however woody it may be, but when it is a young plant growing out of the soil, when it is just a young sapling or even uh a few uh weeks older, it is herbaceious. All the plants, all the trees, they are herbaceious when they are young. There is no wood formation. The wood formation takes place only after a certain period of growth has been attained. So the period before the wood formation, it can be called as the period of primary growth.

00:11:12 Here the primary body is forming, the organs are forming, the elongation is taking place. On the other hand, wood formation is secondary growth. Here the increase in uh girth of the plant takes place. Here the wood formation takes place. So the secondary growth is associated with the secondary merist stems. Okay. So primary growth is associated with primary merist stems and secondary growth is associated with the secondary merist stems. So this was what I was talking about earlier primary versus secondary growth.

00:11:48 As I have just said that primary growth is because of activity of primary meismatic tissue while this includes the activity of only secondary meismatic tissue or by joint activity of both primary and secondary as well. It inreases the height of the plant where by secondary growth increases the girths of the plant. So it results in radial growth. It is the first growth of the plant and its parts while it is a later period of growth. The primary growth stops after complete tissue differentiation has

00:12:25 taken place. On the other hand, secondary growth occurs only after the part of the organ has completely developed. Primary growth occurs in all plants and in all parts. But secondary growth is not seen in monog. This is the diagram of epical meristans that is given in your NCRT. We'll come to it later when we will discuss the types of merist stem on the basis of position. On the basis of position the merist stems can be divided into epical, intercalary and lateral. Let us see in the diagram here. This

00:13:08 diagram is in the class 9th textbook of NCERTT. Here you can see the epical merist stem which is present at the ais. It can be present at the shootute aex or the root aex also. Then the intercalary merist stem. The intergalary meristem is present at the nodes and the lateral merist stem it is runs parallel to the plant body and it is somewhere in the lower regions of the plant. Moving back. So the epical merist stem as I said occurs at the apex of root stems and leaves. It constitutes the actively

00:13:48 growing regions of the plants and results in growth of height of the plant. It includes the bromeary stem and the primary merist stem. The intergalary stem this is special because this is placed between two permanent tissues. Actually what happens is that it must have been the part of initial merist stem but because of growth of the other tissues and cells it has been separated and now it is known as the intergalary merist stem. When we draw the meistance, we draw them like these. So here I have shown the apex. I

00:14:47 can draw the epical merist stem here. This can be the shootute epical merist stem. S A M. Then there are the nodes and from nodes arise the leaves or branches and intercalerime stem is present at the bases of these nodes or even in the leaf sheets but only in monocots. So this will be intergalary merist stem. These two types of merist stems they divide to produce increase in height of the plant body. While there is another merist stem that develops later in the life of the plant and it is in parallel to the long axis of the plant

00:15:51 body. When it will divide it will produce cells this way and this way. What will happen? The girth of the plant will increase. This merist stem which develops later and causes increase in the girth is known as lateral merist stem. So these are the three types of merist stems based on the position in the plant body. Let us move on to the permanent tissues. Now what are permanent tissues? Here the cells are structurally and functionally stabilized and specialized also that is uh the cells which were

00:16:33 chopped off from merist stems have grown and matured and have acquired their particular function and structure accordingly that is they have been differentiated. So permanent tissues are those tissues whose cells are differentiated and they also have lost the ability to divide. The permanent tissues in the plant can be simple or complex depending upon the types of cells they are made up of. If the tissue is made up of only one types of cells, then it is known as simple permanent tissue. On the other hand, if

00:17:11 it is made up of more than one type of cells, then it is known as complex permanent tissues. You have uh studied about some permanent tissues in your lower classes also. So the simple permanent tissues can be parenya, colenya or sarenima. Slenyatus tissues can also be in form of fibers or slarines. We will take them up one by one. Beginning with the parenma. This image is there in your class textbook. The parent cells. Look at the shape of the cells and note the presence of intercellular spaces. So the cells are

00:17:56 isometric and the cell walls are quite thin and they are made up of cellulose and they may have some intercellular spaces present amongst themselves. This is an uh m this is a microscopic image of parenyatus cells and look here you can clearly see the intercellular spaces and the cell walls. Please note them how thin they are. Let us talk a little bit more about the parena. Par means beside and ka means filling. So this is the cell which actually makes up the whole plant body in form of fillers. It fills up the

00:18:45 plant body. So it is present everywhere be it the cortex and pith of the stem, cortex of the root, misophil of the leaves, pulp of the root and even the endosperm of the seeds. The cells here are living and they are capable of division if stimulated. In normal conditions they won't divide. They have grown and acquired their function. They are differentiated. But if stimulated properly, they can divide. For example, if there is any wound, so they will divide to repair the wound. They have thin but flexible cellulose cell walls

00:19:23 and they are generally polyhedral when closely pegged but can be roughly sperical when isolated from their neighbors. And also the vacules are very large. And these vacules are used to store and regulate ions, waste products and water. Let us now study the functions of the parena. Since they are present everywhere, they perform a large variety of functions. For example, when they are present in the leaves and they bear uh chloroplast, then they are known as chlorena and then they take part in various activities of

00:20:08 photosynthesis. Then most of the pareny cells are specialized for storage of food. They can store starch, proteins, fats, oils and even water in roots, seeds or in cautillins also. Some of the paranky cells are specialized for secretion as in pareny cells lining the insides of raisin ducks. As I said just now that some of them are also involved in wound repairing and some others have specialized functions like arration. These arenal cells they are present in the aquatic plants and there they provide the

00:20:52 buoyancy. Here is a picture showing the arena and the arenkya not only serves the purpose of gases exchange but as I just said that in aquatic plants it also serves to maintain the buoyancy. These are the finger-like cells of paliset parenya. These dots represent the chloroplast. So they take part in photosynthesis and known as chlorena. These are spongy uh parenya cells. Here you can say see large air chambers. So they help in gases exchange and since the chloroplast is also present so they take part in photosynthesis

00:21:38 also. Moving on as I had said that this forms the filler tissue. So here is a TS of the stem and you can see the central part of the um stem that is known as the pith. It is largely made up of parenytus cells. Then some pareny cells are also specialized for storage. Here you can see the starch grains being stored in the parena. Moving on let us see the colenya. The colon karma is present below epidermis in dios and there are thickenings at the corner. These thickenings are made up of cellulose,

00:22:21 hemiselulose and pectin. They may have sometimes chloroplast also. Intercellular spaces however are absent and they provide mechanical support. Here in this microscopic image you can see the hypodermis and here in the cells of hypodermis at the corners can you see the thickenings? See here these are the thickenings that are present in the colen kima. So the cells here are elongated and the cell walls are irregularly thick. Their main function is to provide structural support especially to the growing shoots because the when the

00:23:10 plant organ is growing up it needs mechanical support but it needs elasticity as well because it has to extend. The cell walls cannot be very stiff in these regions. Why? Because otherwise the growth will be hampered. So cola is present in the regions where the uh growth is taking place. young um parts are being formed and the colon ka is there to provide mechanical support as well as the elasticity. So the cells here are usually leaving because the cell walls are not very stiff and the cell wall

00:23:49 thickness is strongly affected by mechanical stress. If the plants are under stress the mechanical stress suppose the wind is blowing very hard at a place then at those places or under such conditions the colonyus walls will be 40 to 100% thicker than those plants where there is no such stress. Also chenya cells can be very conspicuous under microscope because they have high refractive index because of their thickened cell walls. The next permanent tissue is scaren and these tissues have dead cells

00:24:32 and they do not have protolast. The cell walls are thick and they are highly liignified. Even they have they may have pits also. What is their main function? They provide mechanical support. This image is there in NCRT. You can see uh scaring cells are of two types. Fiber or sclerids. So this is a fiber and this is a sclerid. And here in the TS of a stem you can see the scaren. Please note the thick walls. Actually what happens is suppose this is a cell and now the thickenings are taking place. So the cell wall has become

00:25:20 lignified and a lot of lignen has accumulated in the walls. What will happen? The cell walls will become thick while the lumen will become narrow. This is the lumen. This is how a slided looks. Same is the case with the fibers also with thick balls and a very narrow new. To differentiate between sclerids and fibers, sclerids are broad, have blunt end walls. They may be branched and they are formed by secondary thickenings of parenta. Just what I drew here that parentus cells they develop thickenings

00:26:10 and because of these thickenings the lumen became very narrow and now the cell is known as a sclerid. On the other hand fibers are elongated and they have tapering ends. If I have to draw a fiber, I'll draw it like this. So these are the tapering ends and they are unbranched and they originate from the mismatic tissue. This was all about the simple permanent tissues. Moving on to the complex permanent tissues. Complex permanent tissues as shall recall are those which have more than one type of

00:26:51 cells. And here we will study about xyllem and phium. The xyllem elements as I just said that complex tissues have more than one type of cells and the cells here in xyllem are known as xyllem elements. The word xyllem has been derived from a Greek word xyos which stands for wood. As we know that xyllem is mainly responsible for conduction of water and mineral salts from roots to other parts of the plants and xyllem which is formed earlier from the proambium is known as primary xyllem while the one which is derived later

00:27:29 from the vascular cambium is known as secondary xylem. The four elements of xyllem are trache vessels xyllem paranya and xyllem fibers. We'll study about them one by one. This is a figure of trache given in your NCERTT book also. What are trachets? Trachits are imperforated cells with border widths on their end walls and they are arranged one above the other. Look here when we draw traches, trache are just like fibers also but uh their lumen is much broader. So we can draw a trait like this.

00:28:21 This is one trick and how is it arranged in the plant? It will be arranged with the other trick. This is how traches are arranged inside the plants with their tapering ends and their bordered beds. These beds help inflow of water from one traced to another. So conduction of water and mineral salts takes place through the bordered bits. The please note here that their end walls are closed. So the water or the salts have to move from one tricky to another and so on and so forth. As I said that they are just like

00:29:32 fibers but their lumin is broader than that of fibers. The secondary wall is lignified. So they also offer mechanical support. Wherever there is lignen remember there will be support because lignenine forms quite a hard covering on the cell walls. The cell thickenings can be of different types. Um they can be annular or scarifiform and trachets are the chief uh water conducting elements in gymnosperms and teridophites. They are also present in the uh angioperms but in gymnosperms and teridophes they are the

00:30:10 chief conducting elements. The vessels are not present there in gymnosperms and teridophyides. Moving on to the next element that is the xyllem vessels. This is a diagram of xyllem vessel. And here also you can see there are so many pits and the pits are present on the uh cell wall end also. So the lumen is much wider than that of traches. Vessels are chief conducting elements in angioperms. Traches are also there in endosperms. But vessels are the chief conducting elements there and they are absent in terophides and

00:30:48 gymnosperms. They offer mechanical support also and they occur parall to the long axis of the plant body forming up a tube. You can say that we draw a vessel like this. Suppose this is a vessel. The vessels are arranged end to end one above the other making long parallel tubes inside the plant body. The perforated plates at the end wall separate the vessels and these perforated plates may be simple or multiple with many pores. This is the perforation plate. The other two elements of the xyllem are

00:31:43 xyllem fibers and xyllem parenma. This is a picture of xylen parenma and a xyllem fiber. Xylm parendima stores food and tannins and it also allows radial conduction of water. The fibers of scaren associated with xyllem are known as xyllem fibers. They give additional mechanical support to the plant body. They are present both in primary and secondary xyllem. And xyllem fibers are dead cells and have dignified walls with narrow lumen. So here if I ask you to differentiate between a fiber and a track what will be the points of

00:32:32 difference that you will mention. We have discussed just now that both have tapering ends both have ligignification on their cell walls and both may have bits also. So what is the difference between the two and yes both of them of course provide mechanical strength also to the plant. What is the difference? Difference is that the trache wider lumen as compared to the fibers. Fibers are quite narrower when we compare them to the trache. And trachets perform the function of conduction of water in xyllem while

00:33:10 fibers they only provide mechanical support or mechanical strength. What about the xyllem parenta? XYM parenma are normal parenchymatus cells and they are present between the xyllem elements. They form uh medularary rays also and they help in radial conduction of water. Radial conduction means look suppose this is a plant the water needs to go up. This we all know from roots to other plants of the parts of the plant. But since the xyllem is here somewhere in the middle, the water also needs to be taken in

00:33:57 other directions towards the periphery and this is the radial conduction of water and this is done by xyllem parenma. Xylm the primary xyllem. It can be of two types protozyylm and metazzylm. The protozylm is the one which is formed by primary xyllem and it develops before the plant organ has completed its growth. Suppose we are talking about xyllem of the stem or xyllem of the leaf. So protozylm will be uh formed when the growth is not complete. This growth is still going on. the stem is still growing or the leaf is

00:34:40 still growing at that period of time it will have protozylm elements. So the protozylm is comparatively less prominent it is made up of smaller and narrower elements. What does that mean? that when we see this protoylm elements in a transverse section we see that the cavities made by protozylm elements are comparatively smaller. That is what I mean when I say that the protoylm elements are inconspicuous or comparatively less prominent. They are made up of smaller and narrower elements. So this is

00:35:27 protozylm elements. The wall thickenings of the conducting elements are of simple and primitive type that is annular or spiral. Annular thickenings or spiral thickenings suppose this is the element and if some thickenings like that are present then we say that these are the spiral thickenings. So protozylm elements have spiral thickenings on them and they are capable of being stretched. Obviously they are present in the growing organs. The organs are growing they are expanding. So the protosylm also needs

00:36:21 to expand with them. That is why the protozylm elements are capable of being stretched. That is they can undergo growth. Here in protoylm the fibers are absent or rare. So can you tell me in this microscopic image where are the protosylm elements? Yes, the arrows show them. These smaller elements are the protozylm elements while the xyllem which develops later and has larger elements is the metazym. So if we draw comparison we can say that it is the later formed xyllem. It differentiates when the plant organ

00:37:03 has completed its growth. Now once the growth has been completed, the size which was to be attained has been achieved. Now the protozylm will stop developing but metazylm will start to differentiate in that fully grown mature plant organ. Metazy is quite prominent. It is formed of broader and larger elements. Here you can see see notice the difference between the size of the elements in metazylm and protozylm which are too small while the metazylm elements they are so big. The wall thinking things also are

00:37:43 very complex and they are of advanced type. They are reticulate scarifiform or pitted. Metazel elements cannot be stretched. Obviously they have been formed after the growth has been completed. So they cannot be stretched much. Fibers often occur in metazylm because this is fully formed xyllem and it provides mechanical strength also. So fibers are also there. Now talking about the exact or endark condition. Have you heard these terms before? And dark xyllem is one where the protozylm elements are towards the pith.

00:38:29 Here in this stem section you can see that the metazym is towards the periphery. the larger elements please uh to an unknowing eye these will seem just like holes in a diagram but I want you to remember how xyllem actually looks like under the microscope that's why instead of taking uh the diagrams or photographs I'm using the microscopic images so you whenever you look under a microscope while cutting the sections of stems and roots in your laboratory classes you should be able to identify

00:39:10 which cell is that of xyllem and which one is that of phm. So here please notice that the ones which larger cavities these are the metazym elements while these towards the inside are the protozylm elements and such an arrangement where metazylm is towards the periphery and protozylm is towards the pith is known as endark condition. it is present in the stems. While on the other hand the exact condition is opposite of it. Here the protozylm is towards the periphery while the metazylm is towards the center. Such condition is

00:39:53 known as exact condition and it is present in the roots. So you will differentiate and remember the difference between endark and exark condition on the basis of protozylm only. When the protozylm is towards the center it is endark end means inside. So proto xyllem is towards inside while eggs for outside. Remember it like that. So protozylm is towards outside. It is present in the roots. This was all about the xylem elements. Let us take now the phm elements in trees. The phm is the innermost layer of the bark. Hence the

00:40:37 name it is derived from the Greek word floss meaning the bark. What does the phium do by the way? Yes, you are right. The phium carries the photosynthates to different parts of the body of the plant. The elements of phm originate from the proambium of epical merist stem or even from vascular cambium and as was the case with xyllem. Same is with phm also when it originates with the epical merist stem it will be primary phm. When it originates from the vascular gambium it will be secondary phm. Phm is also a hetrogenous tissue

00:41:21 that is a complex tissue that is what we are discussing. It is made up of four different types of cellular elements namely se tubes, companion cells, phen parenta and phm fibers. Let us take these one by one. CF tubes and companion cells are directly involved in transllocation of organic substances while these provide uh stability, structural maintenance and uh conduction of other things. SE elements. Now se elements are of two types se tube cells and se cells. SE elements are the conducting elements of phium. They have thick

00:42:08 primary walls and they are living cells with an intact osmotically active plasma some mitochondria and endopplasmic reticulum. So remember in xyllem the trachets and vessels they were dead cells and tissues they had just an empty lumin. On the other hand we when we compare phium with that the phenim cells they are living the conducting cells they are living and they have plasma mitochondria and endopplasmic reticulum also. However when they are in conducting state they lack cytosole ribosomes gi apparatus nucleus even the

00:42:51 central vacule. So the lumen is mostly free for the flu sap movement. A special protein named P protein is also present in the phium and it is formed in the se elements of many plants. It contains lining layer of cytoplasm and it is very important feature of se elements because conduction of food materials takes place through these cytoplasmic strands. So just I had said that se elements of are of two types se tubes. Let us talk about seieve cells. They occur in terodophyites and gymnosperms only. They have seieve areas on their

00:43:34 lateral walls only and are not arranged one above the other in linear rows. Sie cells which may be compared to trachets are narrow elongated cells without conspicuous se areas and they are more primitive than the seie cells. As I had shown you the arrangement of tracketss, this is how even the seaf cells are arranged. They are not arranged in a stacking order one over the other but they are arranged sideways in the plants and they are they are more primitive. Albuminous cells they are associated with the se cells and they

00:44:15 have a similar role to companion cells. They develop from the marginal cells of flow rays and are structurally and functionally associated to the sea cells. How structurally? Through plasmoa and how functionally because they help the seaf cells to conduct the flow seep. Now coming over to the se tubes. Sie tubes occur in angioperms. They are arranged one above the other in linear rows just like the vessels stack stacked over one over the other and they have se plates on their cell wall. Please refer to the diagram here you can

00:44:58 see this is one tube shell and this is another tube cell and there is a se plate in between on the end wall and se plate is named so because of presence of numerous pores. So it gives them an appearance of that of a seieve and they are associated with the companion cell. What is happening here? Actually uh they have to conduct the flu sap and we know that fluent sap conduction requires energy that is the ATP is required for loading and unloading of flu. So that means the conduction can not take place on its own

00:45:39 in the dead cells. That's why the C tubes are living cells. But they need new lumen for conduction. So their functions of the nucleus or cytoplasm of the seed tube cell has been taken over by the companion cell. The companion cell works to keep the seed tube cells alive. So talking about the companion cells each tube element is accompaneted by one or more usually dense cytoplasmic cells called companion cells. So if this is the seaf tube cell you can show see the se plate here. So this will be the

00:46:21 companion cell. It has dense cytolast and a conspicuous nucleus. The companion cells lie along the seieve element and in fact are product of longitudinal division from a common mother cell that is the seaf tube cell and the companion cell both originate from a common mother cell. They play important role in loading and unloading of flu and also they provide ris ribosomeless seive elements with essential proteins and ATP. They possess specific intercellular communications in their common walls and

00:47:00 have several plasmas deset. So they are in continuous communication with the se uh tube cells with the help of several plasma desk meta that are present between the companion cell and the seaf tube cell. In gymnosperms typical companion cells are lacking in the phium. But then there are no se tube cells also in the gymnosperms. Instead the seaf cells are present and the function of companion cell there is performed by the aluminous cells. So se cells and albiminous cells are present in the gymnosperms while se

00:47:37 tube cells and companion cells are present in the angioperms. These uh ones the se tube cells and companion cells they are more evolved as compared to the albinous cell and se cell. Moving on the floren parankya. The parenya cells associated with the phen are called floren paranya. They are living cells and the cell wall is primary composed of cellulose just like the normal parenimetus cells that we studied about in the earlier part of the chapter. They store starch and fats and they also contain raisins and tannins in some

00:48:16 plants. They are present in all terodopites, gymnosperms and dicords but they are absendent monocotss. There are two types of parenma in secondary phium. Exel parenma and ray parenma. Exel parenma will be somewhat parallel to the periphery of the uh plant while ray parenma will be moving from periphery to the center. Last element of the phm is the phm fiber. The fibers of scaren associated with phm are called as phm fibers or bast fibers. Again I repeat that these fibers are made up of scaren. That is

00:49:04 these are the same scarenatus fibers that you studied about under simple permanent tissues. But when they are associated with phm then they are known as phm fibers or bast fibers. They are narrow vertically elongated cells with very thick walls and a small lumen that is the cell cavity. Among the four kinds of phem elements phm fibers are only dead tissue. So the four elements of phm are the se ele elements then the companion cell the phm paranka and the phm fiber. These four out of these four three are

00:49:44 living. The seaf tube elements the companion cell and the flu paranka. These three are living. Please remember this. Even though uh seaf tube elements and companion cells are associated with conduction of the sap yet they are living. only phium fibers are dead. This is in stark comparison with the xyllem where uh most of the elements are dead. Traches are dead, vessels are dead, even fibers are dead. Their only living uh element is the xyllem paranka. And these floren fibers are very important also uh for the plant.

00:50:21 They are for strengthening and supporting and for us they hold a commercial importance because these fibers are abundantly used for manufacturer of ropes and cords. Can you give me some examples? You have studied in lower classes also about joot hemp flax all these are phm fibers protoflu and metaflowim. Protoflu is the one which is formed first and thus it has smaller se tubes. Metaflium on the other hand is formed later and thus has larger se tubes. It is just like that of xyllem and uh protozylm and metazym. So proto

00:51:11 formed first and will have smaller cavities be it xyllem or phium. Meta formed later will have larger cavities both in metaflowim and metazylm also. This was all about today's class. So today we studied about the different types of tissues that are present in the plant uh body. We began with the meismatic tissue and we continued with the permanent tissue. There are a few questions I would like you to find answers for. First, does the classification of merist stems on the basis of origin and

00:51:55 position seem to overlap? How? The meaning of this question is that you have studied two types of classification. One on the basis of origin, other on the basis of position. Do you think that there are points there are terms which are overlapping in these classifications? Please explain. The second question is have you heard that many stem cultures are done in order to obtain virus free plants? What characteristics of meismatic cells do you think help them to stay virus free? It is general knowledge uh that

00:52:34 viruses fail to uh grow and replicate in meismatic tissues. Can you think of the reasons why why viruses fail to grow in the meismatic cells? Third, what is totipety? Find about it. Which type of cells should be most suitable for tissue culture and why? Lastly, I would like you to differentiate between xyllem and phm. We have discussed a lot of points differentiating between xyllem and phium. And next colon clenma both types of cells have thickenings on the cell wall somewhere or the other. So they

00:53:18 seem to be similar but I know you will be able to find out differences between colenya and scaren. In the next class we will study about the various tissue systems the systems of tissues. So up till now we were just studying about xyllem and phium and parenas colenya and scaren. But now in the next session we will study about the tissue systems the epidermal tissue system the vascular tissue system and also the anatomy of dicot and monocod stem root and leaf. how the cells and tissues are organized in these parts of

00:53:57 the plants. This was all about today's session. Thank you.