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Tissues and the primary growth of stems (Internal Organization of stems…

- - - - inexpensive to build, requires little glucose; cell walls are only 80-100 nm thick with just 5-10 layers of microfibrils
    - - chlorenchyma cells: parenchyma cells involved in photosynthesis
        
        have multiple chloroplast, has thin walls to allow light and carbon dioxide to pass
        
        pigmented cells (flower petals and fruits) must be parenchyma cells with thin walls because of pigments that are visible.
      - glandular cells: secrete nectar, fragrances, musilage, resins and oils are parenchyma cells
        
        contain few chloroplasts, have elevated amounts of dictyosomes and endoplasmic reticulum
        
        transport sugar and minerals, use them metabolically, transport product out
      - transfer cells: mediate short-distance transport of materials are parenchyma cells
        
        have large extensive membranes which hold numerous molecular pumps
        
        increase their surface area with extensive knobs, ridges
    - - some die at maturity so pollen, seeds, and gas may be released
  - - - wind, animals or snow are detrimental
    - - sclereids have strong walls on all three sides, both brittle and strong at same time
      - conducting sclerenchyma transports water
- - - - nodes: where the leaves are attached
      - internodes: region between nodes
      - leaf axil: stem area just above where a leaf attaches
      - axillary bud: within leaf axil, miniature shoot with a dormant apical meristem and several young leaves
        
        if its a vegetable bud it'll grow in a branch, if its flower bud it will grow in to flowers or group of flowers
      - bud scales: small corky wax that protects the delicate organs inside
      - terminal bud: at the very tip
    - - alternate phyllotaxy: leaves alternate up the stem, one leaf at each node
      - opposite phyllotaxy: two leaves per node
      - three or more leaves per node is whorled
      - distichous phyllotaxy: leaves are arranged in only two rows, like corn
      - decussate phyllotaxy: leaves are arranged in four rows, only in species with opposite leaves
      - spiral phyllotaxy: each leaf is located slightly to the side of the on immediately above or below it, most common arrangement
- - - - shields delicate internal cell from abrasion by dust particles, passing animals, leaves and stems that might rub together
      - reflectivity protects the plant from overheating in the sunlight
    - - builds up as a layer called cuticle
      - when cuticle isn't enough it will have a layer of wax, which together resist digestive enzymes and provide defense against pathogens
    - - guard cells have a radial arrangement of cellulose microfibrils which makes the opening of the stomatal pore possible
      - guard cells swell when absorbing water and the walls on the back are weak and form an arc which creates the opening
      - after photosynthesis is done and the stomatal pores close, somethings a trichomes forms
        
        "hairs" elongate outward making it hard for plants to land on or animals to chew on
  - - - open tissue with large intercellular air spaces
    - - these have large cortical air chambers which gives buoyancy
    - - water and minerals enter through the roots and the xylem sap travels through dead, hollow cells
      - when its in the shoots, most water evaporates the rest and the minerals is used by surrounding cells
    - - cells are living, they pick up sugar where there is plenty and it transports the sugar where its needed
  - - - young cell matures into a treachery element it must enter cell cycle arrest and stop duplicating first
      - initially a small parenchyma cell with a thin wall but becomes long , narrow and then deposits a secondary wall #
        
        once secondary wall is reinforced the cell dies leaving a hollow tubular wall
        
        primary wall must remain uncovered for water to enter and leave the cell because secondary is impermeable to water
        
        annular thickenings set of rings that are the secondary wall, what allows water in and out of cell, not very strong
        
        helical thickening: gives support to the primary wall, secondary wall exists as three helices
        
        scalariform thickening provides more strength
      - treachery elements with annual thickening are weak but a large percentage of there primary wall is free on the secondary wall
      - pitted element s are the oposite , they are very strong but water leaves and enter slowly because of the secondary wall lining
      - tracheids obtain water from other tracheids below them and pass it onto ones above
        
        must be near each other with overlapping
        
        Pitts are aligned so that water can pass through
        
        aligned set of pits is a pit pair and the set of primary walls and middle lamella between them makes a pit membrane
        
        very permeable to water, but does offer resistance
      - vessel elements provide a way to move water with less friction then tracheids
        
        are individual cells that produce both primary and secondary walls
        
        however an entire region of primary and secondary wall is missing
        
        during the final stage of differentiation a large hole called perforation is digested through a particular site of the primary wall
        
        an entire stack of vessel elements is a vessel, on each end of a vessel is only one perforation
        
        vessels must absorb water from parenchyma cells, tracheids, or other vessels and they must pass it on
  - - - they are parenchyma cells, primary walls only and must remain alive to conduct
      - immature sieve elements begin to differentiate and enlarge to a diameter of more then 1 mcm that is when there called sieve pores
      - plasmodesmata occurs in groups and create sieve areas
      - sieve elements stay alive during differentiation and the plasma membrane continues to line the sieve pore
      - cytoplasm within the pore also increases and rapid, bulk movement from cell to cell happens
      - sieve pores must be aligned for phloem sap to pass through
      - sieve elements that have cells that are elongate and spiel shaped and sieve areas all over it is a sieve cell
        
        evolved first, found in fossils and in non-angiosperm vascular plants
- - - - visible differentiation begins, certain cells stop dividing and start elongating
      - and differentiating into first tracheids or vessel elements of the vascular bundles
      - constitute the first xylem to appear, called protoxylem
      - have had the longest time for growth before differentiation, they develop into metaxylem
    - - cells closet to the metaxylem become metapholem
        
        cells are smaller then metaxylem
      - these sieve elements don't have a secondary wall so they are identical