Botanik (Fach) / Gewebe (Lektion)

Tissue

Diese Lektion wurde von lina2407 erstellt.

Lektion lernen

zurück  |  weiter 1 / 1

• Tissue =combination of many cells of similar forms and / or function, formed through cell division -more cells can have more diverse functions (they differentiate) and become specialized for different tasks -number of plant cell types is more limited and clearer to distinguish than in animals
• Multicellularity Pros: -competition: bigger organisms are able to access more nutrients  -distribution of risk: one dead cell in an unicellular organism = the end of that organism; in a multicellular organism it is more or less irrelevant Cons: -longer period of growth until reproduction -therefore more vulnerable in juvenile stages -better living conditions and more resources necessary Specialization: formation of multiple functional cell types allows the fulfilment of multiple tasks Establishment: after a longer period of growth more energy can be invested in reproduction
• Multicellular plants: Thallus -simple forms -cells little differentiated -simple tissues -no true roots, leaves and stems "thallophytes" are mosses, algae and others that are not closely related (seaweed, common liverwort)
• Multicellular plants: Cormophytes -have shoots, roots and leaves -include ferns and spermotophytes (sea plants) -complex tissues -also calles vascular plants (for their water-transport tissue) e.g. basket fern, turkey oak, dittany
• Seed plants -gymnosperms like conifers, ginkgo, cycads "fern palm" -angiosperms like magnoliidae (primitive dicotyledons) ->seeds are the product of fertilization via pollen, which can be transported through air -seeds are dispersed (zerstreut) and feed to early embryo e.g. eudicots - advanced dicots (Zweikeimblättrige) and monocots (Einkeimblättrige)
• Cell cycle from one cell division to the next -before cell division, the DNA has replicated in the synthesis (S) phase of the cell cycle DNA + proteins = chromatin -Nucleosomes (DNA wrapped around proteins)
• Mitosis -durng mitosis the nucleus divides -chromosomes are seperated and two daughter nuclei are formed Prophase: DNA forms chromosomes, nucleus dissolves Metaphase: spindle apparatus is formed and chromosomes arrange in the middle Anaphase: chromatids (daughter chromosomes) are separated Telophase: chromosomes disappear, new nucleus forms, new cell wall starts
• Control of the cell cycle Mostly, cells do not divide; the control of the cell cycle is essential and various checkpoints have to be passed before a cell continues to divide
• Cytokinesis -after mitosis, the actual cell division (formation of a new cell membrane and cell wall) -new nuclei and the start of a new cell wall are built
• Cell communication -important for complex organisms -the protoplasts of all living cells are connected via plasmodesma (plasma strands) that pass through the cell wall via pits -the combination of all protoplasts connected is the symplast
• Tissues Tissue = group of cells that are connected and originate from cell division 
• Embryonic tissues Meristem (Bildungsgewebe) -primary meristem -secondary meristem -apical, lateral, intercalary and wound meristem
• Permanent tissue -Dermal tissue (Abschluss-, Hauptgewebe):   ->primary - epidermis and rhizodermis    ->secondary - periderm -Vascular tissue (Leit-, Gefäßgewebe)   ->phloem and xylem for long distance transport -Ground tissue: between dermal and vascular tissue (or everything else)
• Meristems Apical (Scheitel, an der Spitze liegend) meristems: the tips of shoots and roots   ->all tissues are directly or indirectly derived from apical meristems   ->serve for growth in length   ->apical shoot meristems are protected in buds (Knospe)   ->apical root meristems are protected by root caps Meristems are tissues that divide and have retained their embryonic character   ->their cells continue to pass the cell cycle Cells of the apical meristems -are isodiametric (approximately round) -have a thin primary wall and undeveloped plastids (proplastids) -vacuole is small -nucleus is comparatively large and active
• Lateral meristems (Sekundärmeristeme) -arranged in a cylinder in shoots and roots -the cambium emerges from the apical meristem and forms the vascular tissue and subsequently leads to thickness growth -the cork cambium forms as a secondary meristem in more long-lived plants and forms cork, a dermal tissue
• Permanent tissue -cells of the permanent tissue stem (Stamm, Stängel) from meristem cells that stop dividing, grow and differentiate -depending on the position of a cell in the plant body, chemical signals lead to the expression of different genes and cells develop different forms and functions
• Parenchyma (ground tissue) -living, thin-walled, isodiametric and mostly have intercellular spaces -do not divide but retain the ability to convert back to meristem cells Intercellular spaces: small or large spaces between cells that are mostly filled with gas / sometimes filled with plant products   can be formed when:   ->the middle lamella (pectine) is enzymatically dissolved   ->the entire cell wall is dissolved   ->cells are torn apart by growth Parenchyma occurs in a variety of uses in plants   ->occurs as a storage tissue - especially in storage organs (often belowground), fruits and      seeds like potatoes Photosynthetic parenchyma: typically in leaves but also other parenchyma cells can photosynthesize, when in light
• Aerenchyma = air supply tissue with very big intercellular spaces for fast gas diffusion ->important for O2 supply under water / in water-logged soils (e.g. soft rush - Flatter-Binse) -as a water storage tissue in shoots and leaves, especially in succulent plants (they have thick, leshy organs for water storage, which is an important adaptation in dry regions, e.g. aloe)
• Idioblasts = cells / cell groups that differ in form and function from the surrounding tissue -often include crystals, sich as calcium oxalate (Calciumsalz der Oxalatsäure)   ->serve as a protection from herbivores (Pflanzenfresser) - they irritate when eaten and can         lead to kidney damage in vertebrates (Wirbeltiere)      e.g. oxalate druse in the sprout parenchyma of a waxflower
• Supporting tissue with increasing size, land plants require special mechanical or supporting tissue for their weight ->provided by thickened cell walls in two different types in the ground tissue: collenchyma and sclerenchyma ->additionally, the xylem (wood) part of the vascular tissue contributes to stabilisation  Kollenchym: besteht aus lebenden Zellen mit nicht verholzten, dehnungsfähigen Zellwänden Sklerenchym: besteht aus meist toten Zellen mit sekundär verdickten, meist verholzten (lignifizierten) Zellwänden
• Sclerenchyma -has thickened cell walls on all sides -these are additionally strengthened with lignin -in a functional state the cells are dead -sclerenchyma cells that are approximately isodiametric are called stone cells (sclereids)             e.g. in pears -stone cells make seed and fruit shells hard and highly resistant against compression                   e.g. waltnut, sweet cherry, hazel -sclerenchyma fibres are elongated (gestreckt) (prosenchymatic) cells   ->they are long, slender cells with pointed ends   ->they usually occur in strands or bundles and result in high bending and tensile (dehnbar)         strength    ->mostly in stems, but also in leaves -in vascular plants (Gefäßpflanzen), sclerenchyma fibres are the longest cells   ->depending on the degree of lignification, they are softer or harder   ->depending on the degree of cellulose fibre, they are more or less elastic   ->fibres of some plants are important technical resources for textiles or ropes                           e.g. ramie, hemp, flax, sisal   ->these fibres need to be removed from the tissue   ->cotton fibres on the contrary are seed hairs, that are free and almost pure cellulose
• Collenchyma -the high strength of sclerenchyma is a problem during plant growth when the tissues still need to expand and be flexible -collenchyma has cell walls that are only locally thickened -they remain alive and cell walls are not lignified -they mainly support plant parts that are still in development but can be retained
• Vascular tissue (Leitgewebe) -thallophytes such as mosses and algae cover their water supply through diffusion and capillary absorption of water   ->they have no true vascular tissue   ->their water content is poorly regulated   ->they quickly dry out when not in humid enviroment, however they survive extreme water            loss -higher plants (vascular plants) do not tolerate their cells drying out   ->they need a continuous water supply to their top leaves   ->the vascular tissue supplies all organs with water   ->it also mechanically supports larger plants, so vascular plants can grow much taller than         thallophytes and dominate earth   ->oriented axially (along the axes) they are used for mass transport and stabilisation
• Xylem primarily transport of water and mineral nutrients from root (soil) to leaves
• Xylem primarily transport of water and mineral nutrients from root (soil) to leaves ->arranged in vascular bundles Cell types: sieve tubes (Siebzellen), companion cells (Geleitzellen), phloem fibres, phloem parenchyma 
• Phloem mainly transport of organic substances (especially products of photosynthesis) from the place of production or storage to the place of storage or consumption ->Xylem is arranged in vascular bundles Cell type: tracheids, vessels (Gefäße) - angiosperms or few ferns, xylem fibres (wood fibre) - angiosperms, xylem parenchyma
• Cell types: Tracheids -elongated single cells -connected via pits -dead -lignified -thick-walled -water transport and stabilisation -water hats to go from cell to cell through pits in the cell wall (high resistance) -cell type is responsible for water transportation and stabilisation in conifers
• Cell types: Vessels -long tubes made up of barrel shaped individual cells, lead, lignified -more efficient form of water transportation -pits between vessels, for water transportation -found in angiosperms (Bedecktsamer) and some ferns -water is transported by negative pressure (from the water loss by the leaves) -therefore vessels and tracheids need to have reinforced (verstärkte) walls to avoid collapsing under tension -lignified and thickened cell wals, stiffened with special structures
• Cell types: Xylemparenchyma -living cells -can be lignified or not -no role in stabilisation -used for storage and transport over short distances
• Cell types: xylem fibre -single cells and narrow, long, pointed ends -is dead with thick, lignified cell walls and small pits -only meant for stabilisation and not for transport
• Cell types:Sieve tubes and companion cells -physiological unit consisting of two cell types -sieve tube elements lose the nucleus, ribosomes and vacuole   ->they are therefore no longer capable of protein synthesis and are controlled and supplied            by their companion cells via numerous plasmodesmata -both have thin walls, stay alive and are not lignified
• Cell types: Phloem parenchyme, Phloem fibre Phloem parenchyma: living cell, thin-walled, not lignified, for storage Phloem fibre: elongated, often highly thick-walled cells, sometimes lignified, for stabilisation
• Dermal tissue: epidermis -epidermis covers the above-ground parts of plants (shoots, leaves, fruits) in their primary stage functions: -protection: mechanical (thick cell wall), radiation (UV light), water loss, biological (defense) -gas interchange: CO2 for photosynthesis, O2 for respiration, H2O for transpiration -excretion (Absonderung) -absorption: of water, nutrients, especially in roots ->rhizodermis Epidermal cells have no intercellular spaces (except stomata) ->form a single layer of cells ->these cell walls are often wavy and have no chloroplasts ->the outer walls are often thickened ->the surface of the outer walls is covered by the cuticle (Oberhaut), a coatin of cutin and wax ->this waterproof layer protects the plant from dehydration ->sometimes an extra crystalline wax film is deposited on top of the actual cuticle  ->this gives plant surfaces a blueish colour and makes them water-repellent ->cuticle can be flat but is often not ->the microscopic surface structure additionally affects its function: for instance, cuticular wrinkles reduce wettability. Water droplets roll off the leaves and carry particles such as dust or fungal spores with them. This effect was first described in lotus leaves and is therefore called the lotus effect
• Guard cells -present in pairs and from the stomata or pores -cell walls are unevenly thickened   ->enables changes in shape, which lead to opening and closing of the stoma when the          turgor changes -in contrast to other epidermal cells, guard cells contain chloroplasts -stomata regulate gas interchange, especially CO2 and H2O -open when the trugor increases -for this K+ joins are actively transported into the guard cells -this increases the concentration, water is osmotically absorbed, the turgor increases and the shape changes
• Epidermis, special cells -special cells in the epidermis form trichomes -they are mostly hair-shaped but can be of very diverse form and function -living hairs can increase the water release of plants but often serve for the excretion of substances by glandular hair -dead hair can reduce water loss, reflect light or help in seed dispersal (Verbreitung)
• Trichomes =hairs on seeds -can function als flight hairs -used for seed dispersal by wind (anemochory); e.g. willow, cotton -a dense cover of dead hairs protects against excessive water loss by reducing wind speed on the surface of the leaf + excessive heating by solar radiation is avoided; e.g. Königskerze
• Stinging hairs -efficient defence against larger animals, e.g. stinging nettle -cell content is under high turgor pressure: when it breaks, the content will be injected causing pain and swelling
• Dermal tissue: rhizodermis -primary dermal tissue of the root -different functions compared to the epidermis -absorbs water, nutrients -many root hairs are formed to enlarge the surface -in contrast to the epidermis, the rhizodermis is thin walled, has no cuticle (which would prevent water uptake) and no stomata
• Secondary dermal tissue: periderm -epidermis and rhizodermis are permanent tissue that no longer divide and thus cannot keep pace when stems or roots grow thicker -periderm = secondary dermal tissue, replaces epidermis and rhizodermis -formed by a lateral meristem, the cork cambium, which forms from parenchyma under the epidermis -cells released to the outside are densely packed (without intercellulars) -cell wall include suberin, cells die and form cork -the water repellent and insoluble suberin makes the cork water-and-gas-tight -mostly they have abundant antimicrobial substances (tannis)
• Cork -a thick cork layer is an excellent waterproof seal and thermal insulator -cork is generalyy much softer than wood -it is harvested from cork oak from the West-Mediterranean basin
• Bark -many trees form new cork cambium to build new peridem layer in deeper tissues -this causes all tissues external to the innermost cork to die  -all periderm layers together with tissue that was cut off forms the dead bark -Borke is the dead bark -the living tissue inside is the living bark: bast

zurück  |  weiter 1 / 1