| Talk in general about meristematic tissues. | Meristem cells are in state of rapid division, form undifferentiated tissues (embryonic), which will turn into differentiated ones, some remain meristematic and divide repeatedly, initials that serve to perpetuate (infinite continuation) the meristems Two main types primary and secondary
(differ by location, cytology, role in formation of tissues.) |
| Talk about primary meristems. | AKA apical meristems, found at or near the growing tips of plant organs, such as roots or shoots, insure growth in length (primary growth) small isodiametric and contiguous (without intercellular space) cells.
Stained section shows thin primary cellulosic wall a large nucleus cytoplasm containing small spherical or arranged in a fine network vacuoles and many mitochondria and proplatids (no differentiated ones) Tissues produced are called primary tissues. |
| Talk about secondary meristems. | AKA lateral, cambia, localized in older parts of some roots and stems insuring growth in width, secondary growth, thin primary cell wall, large vacuoles pushing nucleus to the cell periphery and proplastids, cells have rectangular shape and regularly disposed, tissues produced by it are called secondary tissues |
| What are the types of cambia? | Vascular Cambium: referred to as cambium, produces secondary tissues that play a role in support and conduction (Xylem and phloem)
Cork Cambium :outside of the vascular cambium between cork and phelloderm and it produces them. |
| Talk about protective tissue. | form protective outer layer covering plant body, these tissues protect plant organs from external factors such as climatic variations, mechanical injury and pathogens attack, they are resistant and impermeable to water, two types: epidermis and periderm |
| Talk about origin of epidermis and their fate | primary tissues originating from apical meristem and found in all plants, is some they are replaced by cork and phelloderm in older plants. |
| talk about epidermal cells | epidermis is usually one layer thick but may be thicker in plants living in dry habitats, epidermal cells are variable and irregular in shape. interlock tightly like puzzle pieces with no intercellular space (to be a good barrier) They are living cells and generally have a large vacuole and only a thin layer of cytoplasm, lack chloroplast except aquatic plants often their upper and side walls are thicker than inner ones. |
| Talk about cuticle | those in aerial part of the plant secrete a waxy, water resistant layer, cuticle on their surface, composed of fatty material (cutin) and waxes. Cuticle thickness varies depending on age and species of plant. very thin and absent in plants living in humid environments but very thick in plants in dry environments , the cuticle with the outer wall helps in protection against water loss, mechanical injury and invasion by fungi and bacteria |
| Talk about root epidermal cells. | In piliferous layer at a short distance from the root tip epdiermal cells have no cuticle and function in water absorption, these cells produce tubular hairlike extensions called root hairs, which greatly increase absorptive surface area. |
| Talk about stomata. | Among epidermal cells of leaves and young green stems may be found numerous pores called stomata, surrounded by pairs of crescent shaped ecells called guard cells, below each stoma is a space called sub-stomatal space which is an air chamber |
| What is the role of stomata? | Allowing gas exchange between interior of the leaf and atmosphere and in regulation of evaporation (transpiration) of most water entering the plant from the roots. |
| Talk about guard cells. | Have thicker walls towards the pores and contain chloroplast and capable of undergoing changes in size and shape dependent upon changes in their turgor pressure, increased turgor pressure causes them to open and vice versa. |
| Talk about Hydathodes | AKA water pores, In some plants especially those living in humid environments, excess water is expelled through special pores called hydathodes, these are located at leaf border are always open are not associated with chlorophyllian guard cells and sub-stomatal chamber, loss of water in liquid form is called guttation. |
| Talk about epidermal hairs | AKA trichomes, elongated outgrowths of one or more epidermal cells, may be unicellular or multicellular (simple or branched) glandular or non-glandualr these may protect the plant against biotic and abiotic factors (insects, high sunlight...) |
| Talk about the periderm. | As stem and roots of woody plants with active lateral meristems increase in diameter, the epidermis is slowly replaced by the periderm, which is mostly composed of cork cells produced by cork cambium and some parenchyma cells forming the phelloderm. |
| What is cork? | protective tissues composed of many layers of dead flat cells with suberified waterproof primary wall, gas exchange takes place through the lenticles (pockets of loosely arranged parenchyma cells that are not impergnated with suberins and appear as dots and stripes on the back surface. |
| Talk about parenchyma. | Is a simple tissue found in all plants, can be primary or secondary, consisting of parenchyma cells with various functions and shapes containing well-developed vacuoles, various types of parenchyma have in common usually a thin primary cell wall with intercellular space, parenchyma cells are living cells, at maturity and are capable of mitotic division which is important for plant repair, according to the function we have many types.
Also found as a part of conductive tissues |
| Talk about the chlorophyll parenchyma. | Abundant in aerial parts of the plants (leaves, stems) for which it gives green colour, their presence has a photosynthetic role, cells are detached from each other at their corners forming intercellular spaces and sometimes cavities of air ensuring gas flow, In leaves, it is called mesophyll, surrounded by the epidermis and crossed by veins |
| Talk about chlorophyll parenchyma in monocots and dicots. | In monocots, mesophyll is homogenous, whereas in dicots it is heterogenous made of two parts, upper called palisade parenchyma of one or more layers of elongated chloroplastic cells, clamped against each other.
and a lower spongy parenchyma formed by rounded cells separated by air cavities communicating with stomata |
| Talk about chlorophyll parenchyma in monocots and dicots. | In monocots, mesophyll is homogenous, whereas in dicots it is heterogenous made of two parts, upper called palisade parenchyma of one or more layers of elongated chloroplastic cells, clamped against each other.
and a lower spongy parenchyma formed by rounded cells separated by air cavities communicating with stomata |
| Talk about reserve parenchyma. | located in plant roots, stems and seeds, devoid of chloroplast, cells different reserve substances such as starch grains, sucrose oils proteins cellulose and can also store water where it is called aquifer parenchyma, in leaves and stems of succulent plants (juicy like aloevera) |
| Talk about aerenchyma. | In aquatic plants, intercellular spaces are quite extensive and full of air and form a network throughout the whole plant, this type of parenchyma is called aerenchyma, responsible for air circulation between roots and shoots. |
| Talk about collenchyma. | Primary supportive tissues located on the periphery, underneath the epidermis, of aerial organs only, composed of several layers of living cells with no air spaces, although more elongated, they ar structurally similar to parenchyma (have a large vacuole, surrounded by peripheral layer of cytoplasm absence of secondary cell wall) except their cellulosic primary cell wall is thicker than that of parenchyma |
| What are the main forms of collenchyma? | Based on the type of cellulosic thickenings:
-annular: uniformly thickened
-Lamellar: thickenings are on tangential wall
-Angular collenchyma: thickening are at intercelluar contact points. |
| What is the role of collenchyma? | supprot and strengthening in young plants, stems of non woody older plants and leaves, plastic and stretches irreversibly with the growth of the organ in which it occurs, provides flexible support for both growing organs and mature organs such as leaves and floral parts. |
| Talk about Seclerenchyma. | Dead supportive simple tissue that can have a primary or secondary origin, usually found in old organs throughout the whole plant bod, uniformly heavily thick lignified secondary cell wall gives strength to the seclerenchymal body, devoid of air spaces and stiffer and harder than collenchyma |
| What are the types of Sclerenchyma? | Fibers: elongated fusiform (spindle shaped) flexible cells, occur in roots, seeds, leaves and fruits as supportive elements, used in textile industry
Stone cells: (sclereids) short cells of different shapes with very thick lignified wall, common in the shells of nuts and in the hard part of seeds and flesh of hard fruits, form cores of apples and produce gritty texture of pears |
| Talk about the xylem. | Ensures the circulation of the crude sap, a very dilute aqueous solution of mineral salts, from the roots to the aerial parts of the plant. This tissue can be primary or secondary tissue (wood). The wood insures a mechanical support to the whole plant. The xylem is a complex tissue consisting of conducting elements (vessels and tracheid), parenchyma cells and fibers. |
| Talk about the tracheid. | Primitive conducting elements found in all vascular plants, elongated cells with tapered ends (thickening is reduced to one end). Their heavily lignified secondary cell wall gives them a supporting role in addition to their sap conduction role. Pits may occur anywhere on the cell wall, but they are often particularly numerous on the tapered end of the cell. The sap circulation occurs within the pits. |
| How do tracheid degenerate? | The tracheid of the first matured primary xylem are stretched during development of the plant and become non functional. |
| Talk about the secondary walls of tracheid. | In primary xylem, their secondary walls are usually in the form of rings (annular tracheid) or spiral (spiral tracheid) it will be replaced by a secondary tracheid.
Secondary xylem tracheid arise after all lengthwise growth has ceased, they are not stretched, they are thicker and more continuous, being interrupted by only a numerous pits (pitted tracheid) in Gymnosperms, In pteridophytes they are ladder like (Scalariform) |
| Talk about the vessels of xylem. | Highly specialized conducting element of the most evolved vascular plants (angiosperm) made up of dead cells called vessel elements or vessel cells. These dead cells form a large diameter cavities bounded by a lignified cell wall. During the differentiation process vessels are formed by the breaking down of the transverse wall forming the perforation plate. If the transverse walls are extensively perforated they form compound perforation plates, whereas if they are completely dissolved they form a simple perforation plate. As in tracheid vessels may be annular , spiral, reticulate or pitted. |
| Talk about the fibers of xylem | Have a supporting role along with the tracheid |
| Talk about the parenchyma of xylem and phloem | Living cells play a role in lateral conduction of sap (ray parenchyma) or storage |
| Talk about the phloem. | Conductive tissue of the elaborated sap (organic matter) produced by photosynthesis throughout the plant. It can be primary or secondary complex tissue. It comprises the conducing sieve elements, companion or albuminous cells, fibers and parenchymal cells. |
| Talk about the conductive elements of the phloem. | The most important structural and functional element of the phloem. It consists of the sieve tubes associated with companion cells in angiosperms, and of sieve cells associated with albuminous cells in gymnosperms and pteridophytes. |
| Talk about sieve cells | Superposed elongated living cells with cellulosic cell wall. They are found in gymnosperms and pteridophytes, having their longitudinal and transverse walls perforated with pores interrupting the cell walls and the middle lamella allowing the flow between adjacent cells.
Unlike the vessels and tracheid, their nuclei disintegrate at maturity but their cytoplasm remains and is very active in conducting food material in solution throughout the plant. |
| Talk about sieve tubes. | They are formed of superposed elongated living sieve tube elements with cellulosic cell wall.
These elements have in their longitudinal walls perforated with pits but their transverse walls are thickened with larger pores, forming the sieve plate, which allows the flow of larger molecules such as proteins from one sieve element to another. |
| Talk about the companion cells of phloem | Specialized elongated parenchymatous cells, retain both their nuclei and their cytoplasm at maturity. They are closely associated with sieve tubes communicating through numerous plasmodesmata. Their nucleus controls both their own and the cytoplasm of the adjoining sieve elements after the latter nucleus is disintegrated. The function of a sieve cell lasts for a short time, when they die companion cells divide longitudinally to give two cells one of which replaces the dead sieve cell and the other gives the companion cell. |
| Talk about the fibers of phloem | Less abundant than those of xylem. |
| Talk about secretory tissues. | Plant specific and localized in specific locations of the plant body. It consists of epidermal or parenchymal cells that synthesize substances representing the secondary metabolic products of the plant (essential oils, tannins, latex...) They can accumulate the products synthesized in the cells or secrete them in cavities. |
| Talk about secretion cells isolated in parenchymal cells. | Secretion sacs accumulate in their vacuoles the product they secrete like the tannin in the secretory cells of rose stems and the essential oils in the secretory cells of camphore leaves. |
| Talk about the secretory epridermis. | Epidermal cells can develop and accumulate in their cytoplasm essential oils (rose petals), multicellular trichomes can also be secretory (glandular hairs) They accumulate in their terminal cells essential oils like in thyme, oregano, lavender.. |
| Talk about glands and canals. | Glands are globular cavities situated in the parenchyma of leaves, stems and fruits (oranges, tangerines, lemons). They are surrounded by cells which excrete the products they elaborate in the glands . When these cavities are not restricted in location, but extend all the length of an organ; they are tube-like spaces, elongated in the longitudinal plane of the organ (leaf, petal, and stem), they are called secretion canals or ducts. In cross section, they appear as circular cavities surrounded by one or two layers of small secretory cells (Example: pine leaves secreting resin). |
| Talk about laticiferous tissue | Laticiferous tissue is a living tissue containing secretory tubes (laticifers) elaborating the latex; a milky white (e.g. in lettuce, fig) or colored (e.g. brown yellow in cannabis, yellow in celandine and red in bloodroot) viscous liquid (very complex mixture containing water, sugar, mineral salts, organic acids, enzymes, etc.). Some forms of latex are commercially very important: rubber, chewing gums, medicinal drugs… The laticifers are limited by a cellulosic primary wall. Their cytoplasm forms a thin layer surrounding a large central vacuole containing latex. |
| Talk about the types of laticifers. | -Non-articulated laticifers: each laticifer is formed by a single large cell, very elongated and containing many nuclei (coenocyte) which may reach several meters or even ten meters long. These laticifers remain independent and will not anastomose.
-Articulated laticifers: Unlike non-articulated laticifers that are derived from a single cell, each articulated laticifer is a structure made of individual laticiferous cells arranged in rows. Transverse walls that separate the various individual cells may persist or be perforated or be dissolved . These laticifers can remain independent or anastomose at certain points. |
