hello everyone welcome to chapter 35 of Cambo biology um vascular plant structure growth and development so to begin what's a vascular plant a vascular plant is a plant that contains um a circulatory system I think that a system that circulates nutrients and water to different areas of the plant and in this case the most vascular plants have a xylm and flum which we'll be talking about and what you may have heard about in your earlier studies so now let's begin the basic morphology or how the shape and structure of vascular plants reflects their evolutionary history as landbased organisms that inhabit and draw resources from two very different environments below and above the ground you can see here the shoot system and the root system are both well the shoot system is above the ground and the root system is below they must absorb water and minerals from below and carbon dioxide and Light from above the ability to acquire these resources efficiently is traceable to the evolution of the three main plant organs the leaf the stem and the root which is this whole system here and these organs form a root system and a chot system so the stem and the stem and the leaves form the Chute and The Roots form well the roots roots are almost never photosynthetic for this reason how are you going to photosynthesize if you're not Expos Clos to the sunlight right both systems codependents from and sugar from the plant from the leaves in order to not starve so let's first discuss the roots a root is an organ that anchors a vascular plant in the soil and absorbs minerals in water and often stores carbohydrates and other reserves so let's begin the first primary root originating in the seed embryo is the first first route to emerge from a germinating sea so although it's not featured here the primary route is the first thing that you see break out of the germination so I don't know if you're familiar with those growing plant growing videos but the first thing that emerges apart from the shoot is going to be that main primary route and that primary route soon branches to form lateral roots that can also Branch so you see here that after their primary route is grown the it starts branching off into these big branches right oh sorry it starts branching off into those big branches and then those big branches Branch off into even smaller branches and so forth and it greatly enhances the ability not really to actually for both it it enhances the ability to Anchor the plant and to acquire resources like water and nutrients as we discussed earlier now what is this long big shoot in the middle shoot like route in the middle that's what you call the tap route the tap route which usually develops from the prim primary route um usually only serves the main purpose of it is for anchoring the lateral Roots usually take most um sorry the tips of the lateral Roots often take most of the role of absorption so the tap route is mostly there to increase enhance anchoring a tap route although energetically expensive to make again um facilitates the Anchorage of the plant in the soil and it prevents toppling which actually allows the plant to grow taller so if the topples then it will likely grow to the side like this so if a plant topples then it will just start drooping and going down right so notably tap Roots can also be specialized for food storage and there's going to be many different types of roots that we're going to see later so to summarize Roots per um are perform the duties of Anchorage and um nutrient uptake and notably there are two different parts the tap rout and the lateral roots with the main starter of this being the primary roote now let's discuss the H which one let's discuss discuss the stems first a stem is the plant organ Bears leaves and buds so you can see here these are the buds and these are the leaves right and the leaves are their own separate organ which we'll get to later but before that each stem consists of an alternating system of nodes and Inter noodes so a node is the part is the point where leaves emerge from so you see um the here the diagram has a node here but then there's also a node down here and here and then um the inter node is the space between them it's a segment of stem excuse me it's the segment of stem that encompasses them now most of the growth of a young shoe is concentrated either growing shoot tip or apical Bud which is right here apical buds are not the only types of buds found in shoots you see these little side ones those are called the axillary buds as we see right here and these can potentially form another lateral Branch a thorn or a flower and some plants have stems with alternative functions like food storage or asexual reproduction and many of these are labeled as romes stolin and tubers notably most of some of these are often mistaken for roots because they're under the soil but they are still part of the stem so as you can see the ryome here is a horizontal shoe that grows just below the surface and and vertical shoots emerge from this axillary butt onto the ribosome so uh I don't know if you can see it but you can quickly see the ryome at least here this long segment and these spindly parts are actually the root and then the stolin this is a strawberry plant the stolin are pretty much the same thing as the ryms they horizontal shoots but they grow rest above the surface and these stolin actually they allowed the plant the strawberry plant to reproduce asexually as the plantlets which will'll get to later with leaves form a nose at the along each Runner so at different points here it's going to be here's going to be a plantlet there's going to be a plantlet and those will help let them reproduce asexually and then finally we have tubers tubers we've all seen the potato right tubers such as these potatoes are enlarged ends of romes or stolen specialized for storing food so remember that we said that Roots can also be modified to um sorry stems can be modified to store food Tu bir are the best example of this and in fact the eyes of this potato are the axillary budes that emerge from the stem and that they Mark the nodes as such so now let's discuss leaves leaves consists of well first of all leaves are the main photosynthetic organ in addition to intercepting light leaves exchange gases with the atmosphere dissipate heat and defend themselves from herb herbivores and pathogens these functions may have conflicting physical physiological and anatomical or morphological requirements therefore in general a leaf often consists of a flattened blade so if we go back to here Leaf typically consists of a flat blade here so mark this down and a p or the point the segment between the point of attachment and then the big blade and this part what we discussing this part is a node actually that is and remember nodes often come from axillary Buds and furthermore when we get to the um more of during this unit we will see that monocots and uots defer in their arrangement of veins in the leaves so many most monocots have parallel major veins and Utica generally have a branch network of veins arising from a major vein so usually for this um type of leaf this type of leaf has a branch network of veins arising from a major vein this is the major vein the mid rib and thus you can clearly see that it's going to be a Utica now notably there's a big difference between simple leaves and compound leaves which we'll discuss right now so if we go back here we see that these leaves are an example of what these These are going to be an example of simple leaves right but why are they simple leaves let's go back to the diagram a simple leaf has only one leaf and not multiple leaflets it has a single undivided blade so let's write that down furthermore usually some simple leaves are deeply loed so you can see the loes here now compound leaves and contrast have many different separate leaflets these leaflets allow for potentially more sunlight more sunlight gain more carbon dioxide gain but really the difference is just that compound leaves have multiple leaflets at the end of each P and a leaflet has no ax butt this is important so why that these are how you can tell compound leaves from simple leaves is that when you see here there's an axillary butt here there's no such thing here where's our axillary butt that's how we know each Leaf is leaflet versus like a true leaf and notably each leaflet although it's relatively simple here it could be divided to even more leaflets so the really the main difference is that symbol is one blade and compound has multiple leaflets and that those leaflets are different from True leaves in the fact that they don't have Axel butts and when we see some evolutionary adaptations of Leaves we can see that leaves have been modified to be thin like tendrils so we'll write that down so the pea plant if you've seen a pee grow before yeah lasso is on a support and it forms a coil and and helps the plant support itself upright and tendrils are typically modified leaves but some tendrils like in grape Vines are modified stems so while here the PE plant there modified leaves sometimes they might be stems other times um the leaves might not conduct photosynthesis at all these are the spines of the cactus which a lot of you may have seen before the spines the spines are actually the leaves of the cactus plant but however the stems the green part is what actually carries out photosynthesis leaves can also be modified for storage so when you eat when you um have if you have ever peeled an onion each of those layers is a modified leaf and finally um they may also engage in U reproduction you can you see these uh in this succulent you can see these plantlets when when we discussed plantlets before we mentioned that um the stolin remember in the stolen strawberry plant the stolin would a allow um plant list to fall off and grow back in the soil and reproduce asexually so this is an example of reproductive leaves now what are these three vascular plants made out of I mean we know that well we know that they can be modified we know that they can be we know that they can adapt we know that they form the shoot and root system but what are they made out of well remember in the structural hierarchy we go from cell to tissue to organ so since we're discussing plant organs to the next step back must be plant tissues so we have three basic vascular plant uh tissues dermal vascular and ground so let's see first of all cons look at the blue part of this uh diagram the blue part is the dmal tissue which serves as the outer protective coverings much like your own skin so let's write that down and in non-woody plants so plants that aren't like trees that don't have bark in non-woody Plants it is usually a single tissue called the epidermis and the epidermis in particular is a layer of tightly packed cells much like again our own human skin in leaves and most stems the cuticle um helps prevent water loss so in leaves and in Woody plants um protective tissue called periderm it replace the epidermis in in older regions of stems and Roots so in a tree a tree's outer glay would probably be would probably be tougher so it would be replacing the epidermis there probably with parader so let's write that down now in shoots specialized epidermal cells called guard cells are involved in gaseous Exchange and another class of Highly specialized epidermal cells found in CHS consists of outgrowths called tricomes and tricomes are these types of outgrowths like small hairs that grow out and some triom may even defend against insects through shapes that hinder movement or glands that secret sticky fluid fluids or toxic compounds again life is very life has a lot of variations now the chief function of the vascular system tissue is to facilitate the transport of materials to the plant and it's and to provide mechanical support and the two types of vascular tissues like we mentioned ear in the beginning of the video xylm and flum so xylm and flum conduct xlum conducts water and dissolve minerals upward from Roots and flum transports sugars which made in the leaves as from photosynthesis to where they are needed like in The Roots but before we get to that we have to discuss the types of plant cells which we have here in a plant as in any multicellular organism cells undergo cell differentiation so our brain cells at first are all the same stem cells as before but as they oh well when we're like embryos all the cells that we have are pretty much the same right but after we're born or even before we're born actually they rapidly start differentiating into brain cells nerve cells and things like that plants have a similar thing too they have parenchima cells sorry they have parenchima cells they have coima cells and finally it's not listed here but they have saring saring Kima cells and then you might be wondering well what's the difference between all of them let's see first let's tackle parenchima cells parenchima cells have primary walls that are relatively thin and flexible so you can see here in comparison to the ones you'll see later these are very thin and notably that they don't have a secondary wall either so when mature parent Kima cells well sorry when mature or paring Chima cells generally have a large Central vacu so remember that a central vacle is a common organal in plant cells and that the central vacu uh helps comes as a helps act as a storage tank of sorts so it stores things like it could store toxins it could store uh food it could store water um it can really just do it can just really act as a storage tank for whatever the plant needs and paronimos cells perform most of the metabolic functions this is very important they perform most metabolic processes and for example photosynthesis occurs within the chloroplast of parenchima cells in the leaves some parenchima cells have colorless plastids those in stem and Roots called aop plast that store starch so let's make a little table leaves conduct photosynthesis which I'll abbreviate is PS via P Kima cells and naturally stems and stem and Roots as they don't really conduct photosynthesis they most likely have amop plasts and those amop plasts uh end up as something remember we said the central vacu can store food as well well amoc classs um act as those they act as starch storages the fleshy tissue of many fruits is composed mainly of parenchima most most parent comma cells retain the ability to divide and differentiate even under particular conditions so in some instances it is even possible to grow an entire plant from a single parent Kima cell so let's write that down retains differentiability now let's discuss colon Kima first of all you can see remember when we said the paren walls are really thin you can see here that's clearly not the case now what's difference apart from that well colon Kima helps support young parts of the plant shoe so remember the shoe system is the stem and the leaves colon Kima cells are generally elongated so you can't really see this you can kind of see it when you look at the paring com versus the Goen K you can see that there's kind of like lines here and the primary walls are thicker than parena but they're unevenly so so you see here they're not that they're very they're kind of thin but here they're very thick there are pretty much a solid gap between them right use a better color and young stems and pedol often have strands of colon Kima cells just below their epidermis remember we said epidermis is the dermal tissue and the three vascular tissues colon Kyo cells provide flexible support without growth restraint so let's write that and finally at maturity these cells are living and flexible unlike certain cha cells which we discuss next Now sing Kima I'll right to name again since it's not here San Chim cells also function as supporting elements in the plant but they're much more rigid so that's the first thing and inan Kima cells the secondary cell wall is thicken is thick and contains large amounts of ligant now what is ligant Lian is a relatively indigestible strengthening polymer and basically what it does it accounts for more than a quarter of the dry mass of wood it's present in all vas and it's present in all vascular plants most likely most of the time in Shan Kaa and um as you can see since it's in a lot of it's over accounts for over a quarter of wood's dry Mass lignan um lignin's rigidity has lot important impact on wood mature squaring clima cells cannot elongate so that's one thing they cannot elongate du to their um rigid Lig ligning content but they and but they occur in regions of the plant that have stopped growing in L um sharing clim cells are so specialized to support that many are dead at functional maturity so let's write that but they produce secondary Wells before the protoplast so the living part of the cell new word that when the protoplast dies um they can still support secondary walls that act as a skeleton that support the plant and two there are two types of saring clima cells there are scarids and fibers and scarids which are boxier and thicker or sorry irregular often often impart the hardness to nutshells and Seed coats and the gritty texture of pears and you can see here they're very in a pair of fruit that they're very boxy regular and but you can see here in fiber cells that they're much more slender long and they're much more or organized or uniform in shape and fibers are usually used for well you heard about them fibers can be used in clothing um and fibers can be also just used in rope making um that's pretty much it now we finally get back to our reference before the at the beginning of the video so and flow the two types of water conducting cells for the xylm trachead in vessel elements so we can see here that these are vessel elements the ones with these types of Divisions in the middle and these are the trach so what's the difference well first of all both are dead and functional maturity so let's write that here there's so much to write that we have to have an extra slide right become dead at function maturity and then I'll make the full green now trachead occur in the zum of all vascular plants in addition to trachead most angiosperms and a few seedless vascular plants and gymnosperms have vessel elements as well while the living cellular contents of a tracheid disintegrate the cells thicken walls remain behind forming a non-living conduit so the reason why they look so dried out is because well all the parts are living Parts the protoplast are dead the cells thicken walls remain behind the secondary walls are often interrupted by pits thinner regions where only primary walls are present so you can see here these pits are kind of like almost like gaps they're places where they're places where only the primary wall is present now water can migrate laterally between neighboring cells through pits that's why they're there trates are trates on the the other hand in contrast to vessel elements are relatively longer and thinner and water moves from cell to cell mainly through the pits so you can see here and vessel elements are generally wider shorter and thinner walled and they are lined end to end forming long pipes known as vessels are some cases are visible to the naked eye the end walls of vessel elements are perforation placees that allow enable water to flow freely and the secondary walls are hardened with ligant remember when we said the slen Kima and ligant this hardening provides support and prevents collapse now let's discuss the FL the FL first of all is a immaturity and before we go into the FL let's just write down Tri and mes elements and so the flam is again Alive by maturity the flam has C2 elements and unlike the water conducting cells of the zum um C2 vum um ah sorry in seedless vascular plants sugars and other organic nutrients are transported through these long neuro cells of SE cells and though alive see they lack pretty much everything about a cell that we know about they lack no nucleus no nucleus ribosomes um no no vacu or skyt skeletal elements now this reduction in cell content allows nutrients to pass more easily through the cell the end walls become sea plates and they have pores so we go back to this diagram the sea plate here you can see the many [Music] pores that allow the sugar to pass through alongside each tube element is a non-conducting cell called a companion cell companion cell is right here and what is this for this is connected to the C2 element and the nucleus and ribosomes of the companion cell serve not only the that cell but also the adjacent C tube element so now we've solv the mystery of why C tube elements can stay alive without with such a large reduction in organal content in some plants the companion cells and leaves also help load sugar into the se2 elements which then transport the sugar to other parts of the plant so now let's look at primary growth and secondary growth primary growth first of all is growth in length so always remember that primary growth is length secondary growth is width and primary growth is made possible by apical mer stems at the tops tips of shoots and roots so uh if any of you um if you do AP biology in the future you may um do a thing something with an onion with an onion root tip cell that's the apical marem so we can see here that the root apical marison is composed of once again dermal ground and vascular tissue you can see that the bottom has more mature more mature tissues and um the primary marim continues to remain primary and that they are also Leaf primordia present apical marome cells are undifferentiated when they divide some daughter cells remain there and ensure a continuing population of undifferentiated cells again like we said the AP they have to keep growing um since this the plant has to keep growing in length they have to keep some there to remain undifferentiated and other daughter cells became become partially differentiated as primary marm cells so we can see here the first cell division igal marem um is the very tip and then it goes to daughter cell and then it keeps dividing until it reaches differentiation but some of them continue to remain back here at the apical Mar now different um as time goes the young um the addition of uh sorry as time goes their growth will go up and they will the cycle will continue the apical mer stem will continue to have some um some cells remain there to undifferentiated to keep the cycle going keep growing as you can see here um a thol like root cap protects each root apical Mar draw label a simple outline so you can see here we have the root cap as the very top with the root apical marem the primary marem and the mature tissues which we can see in this section as well now secondary growth is growth in thickness so let's um make sure to label that down growth in thickness it's made possible by two lateral meristems now what are these These are the vascular cambium and the cork cambium now each how each of them grows is very different but first and foremost the vascular cambium is more close to the core of the tree and the core cium is more outer more outer and when a cium divid sometimes both daughter cells remain the cambium and grow increasing the C cambium circumference and notably when a vascular cambium cell divides sometimes one daughter cell becomes a secondary xylm or a secondary foam and usually many more zyl cells are produced and um similarly when a cork cambium divid sometimes one can be one daughter cell can become a cork cell and you can see here that after primary growth is completed the vascular cambium and the core camb start dividing out and increasing the circumference so the stem thickens as secondary syum and flum are added to the plant now the primary growth of a uard growth is a little bit it's pretty much the same but there's a little bit of difference so the entire bi mass of a primary root is derived from the root apical marem the root apical marem also makes a tho like root cap right here which protects the delicate apical merem as the root pushes through the abrasive soil the root cap secretes a polysaccharide slime that lubricates the soil around the tip of the root allowing for easier penetration growth occurs just behind the tip in three overlapping zones of cells and there the cell zones of cell division elongation and differentiation now the zone of cell division includes the stem cells of the root root apical marem and their immediate products new root cells are produced in this region including cells of the root cap typically only a few millimeters behind the tip of the root is the zone of elongation right here where most of the growth occurs as root cells elongate and even before the root cells finish lengthening many many cells already begin specializing in structure and function as this occurs the three primary Mar stems the protoderm ground Mar stem and procambium become evident in the zone of differentiation cells complete their differentiation and become distinct cell types the protoderm the outermost primary Mar stem so the blue section is a single layer of cuticle free cells covering the root root hairs are the most prominent feature of the root epidermis and sandwich between the protoderm and the procambium is the ground marem and which they give rise to the mature ground tissue the ground tissue of roots consists mostly of parenchima cells and in addition to storing carbohydrates cells in the cortex which is right here and it refers to all this ground Maran the C cells in the cortex allow for extra cellular diffusion of water and the innermost layer of the cortex is called the endodermis so around here I would say would be the endodermis and it's a cylinder one Cel thic that forms the boundary Bel the vascular cylinder now the procambium gives rise to the vascular cylinder which cons consists of a solid core of xylm and fum tissues surrounded by a cell layer called the paracycle in most ticot Roots the xylm has a star-like appearance in cross-section and the flow occupies the indentations between the arms of the xylm star so when we see here we see that this is the xylm star that we were talking about this sort of four pointed figure here and that what surrounds it is the foam and by increasing the The Roots primary growth facilitates their penetration and exploration of the soil if a resource Rich pocket is located in the soil the branching of roots may be stimulated and when you see here lateral Roots arise from Mar statically active regions of the paracycle and they actually push through the paracycle when you see here in this diagram that the lateral roote the formation of it it originates in the paracycle and destructively pushes through the outer tissues and if we look at a real life example here we um we can see that in in the Buttercup species we can see that um all the all the parts are there we can see the star of the zylon we can see the surrounding flam as well now the entire biomass of a primary shoot so if we move on the entire biomass of a primary shoot deres from a Sho epical Mar so if we go back all the way up here to the first diagram the Sho apical marem is a do shaped mass of dividing cells at the shoot tip so somewhere around here would be the thing that we discussed earlier so let's go back to the plant's primary growth you can see that um the tips of shoots have something that's pretty much this you have the leaf primordia you have um if you have young leaf at the sides when we focus on the sh shoots instead we have sh sho apical Mar stem the protoderm procambium everything same as we discussed with the zone of elongation differentiation and everything like that now the branching of shoots arises from the activation of axillary butts because of chemical communication by plant hormones which is in the future the closer an axillary but is to an active apical Bud the more inhibited it is so let's go back to this diagram remember we said that what we call the appical and axillary well this is an apical bud and this is an axillary bud and the co closer in proximity it is to the axillary is to an active apical but the more inhibited it is and that's a phenomenon known as apical dominance so let's go ahead and Define this term so as the axillary apical distance decreases goes down the inhibition decreases no sorry the in inhibition increases and again this is called apical dominance and in fact this is why most people prune their trees and things if they want to grow um more buds because when you when you uh snip off the apical Bud there a but will be free to keep going more to give rise to more lateral shoots and if an animal eats the end of a shoot the chemical communication is disrupted and or if a gardener removes it as a result the axillary buds break dorcy and start to grow now let's discuss Leaf Anatomy or rather before that stem Anatomy the stem is covered by an dermis that is usually one cell thick and covered with anaxi cuticle that prevents water loss some examples remember we discussed include guard cells and tricomes vascular tissue runs the like of a stem and Vascular bundles which consist of mostly parena but also may contain sing kimat who have some sort of rigid support unlike gal Roots which arise from vascular tissue gal shoots develop from Ax blood Mar stems on the stem surface and do not disrupt other other tissues near the soil surface in the transition zone between zo choot and root the bundled vascular arrangement of the stem converges with the solid vascular cylinder of the root the vascular tissue of stems is most Utica species consists of vascular bundles arranged in a ring the xylm in each vascular bundle is adjacent to the pith and the flow in each bundle is adjacent to the cortex in most Mona stems the vascular bundles are scattered throughout the growth tissue ground tissue rather than forming a ring as you can see here there don't really form a ring or anything like that most most in monocot they just um partition themselves randomly now for leaf growth and Anatomy remember we discussed Leaf primordia those are projections that shaped like a cow's horns that emerge along the sides of the Sho apical Mar stem so if we go back to the figure above we will see that these are the Le from Mor unlike roots and Stems secondary growth in leaves is minor or non-existent while you don't really grow thicker leaves because that does that minimizes the surface area to volume ratio the leaf at re is covered by Wax cuticle except where it is interrupted by stamata which allow for exchange of carbon dioxide and oxygen between the surrounding air the Leaf's ground tissue called the mesophile the middle Greek for Middle Leaf um consists of mainly of parim specialized for photosynthesis and has two distinct layers Palisade and spongy right here and here palis consists of one or more layers of elongated parena cells sponges below the palis the vascular tissue of each Leaf is continuous with the vascular tissue of the stem veins subdivide repeatedly and Branch throughout the mesop this network brings syum and FL into close contact with the photosynthetic tissue which obtains water and minerals from the xylem and loaded sugars for transport to other parts of the plant and each vein is enclosed by a protective bundle sheath a lay and that's a layer of cells that regulate the movement of and substances between the vascular tissue and the mesophile so in Woody plants it's a little bit different secondary growth consists of the tissues produced by vascular cambium and cork cambium the vascular camb add secondary xylem wood and secondary FL thereby increasing vascular flow and support for the shoots and in Woody plants notably in Woody plants primary and secondary occur at the same time now let's go to tree trunk Anatomy um there's not really much to discuss here it's just describing the or um layers of rings around the tree so in temporate regions um wood that develops ear in the spring has secondary on themselves with large diameters and thin cell walls and the because there's a marked contrast between the large cells of the new early wood and the smaller cells of the late wood a Year's growth appears at as a distinct growth ring and that is how researchers can estimate a tree's age by counting growth rings so as you can see here there are many layers to it in order they are growth in order of inner to Outer they are the bark layers of periderm secondary flow vascular cambium sapwood um Heartwood vascular Rin grow ring and and as a tree ages older layers of secondary xyum that we discussed earlier no longer transport water and minerals a solution called syum sou these Gs are called Heartwood and the newer outer layers are referred to as sapwood because they're able to trans transport sap now one of the most important parts of this section is really the ABC hypothesis and the ABC hypothesis specifically refers to the four the three groups of genes that control that control the parts of the plant or organ like they identifi the organ the organ that should be there so there are four worlds in typical in typical flower angiosperm flowers They're the carpal petal stamman and SE and the three genes that compose them are a b and c if we draw this um pretty if we draw this pretty simple diagram a a c c c b b we can see that there are four distinct groups here right we have a a which refers to the the SLE the SES we have AB which have which end up signaling for petals we have BC for stamans and we have c a cc where only carpal where carpal are expressed and as you can see here in this diagram you can see here that well they did a different diagam diagram but the answer is the same the a controls these two parts the B has these two and the C is only contained is C is contained in these two and when you can see here the side view of wild type flowers with organ Iden mutations when the AG Gene is when one gene is knocked out everyone is knocked out that relat to the gene so example if a gene is not if a gene is knocked out then there will be no more then there will be no more SEL or petals and I believe that comes the end of our review of chapter 35 there may be other things that we may not have discussed but if we do we will be sure to overcover them in a separate