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Transport Processes (Water Potential (osmotic potential is the effect that…

- - - - one MPa is equal to 10 bars
  - - - If the water potentials of two regions are equal they are in equilibrium and there is no net movement of water :recycle:
        
        water is in constant motion unless frozen :snowflake:
      - water potentials must always be considered in pairs or groups
        
        water moves to multiple sites so knowing just one is not very useful
      - Water moves whenever there is a difference in water potential within mass of water
        
        do to protoplasts being interconnected and cell walls fully hydrated
      - temperature is not a factor as the solutions are usually the same temperature :thermometer:
  - - - adding water will expand cell creating great pressure on cell wall. will also decrease osmotic pressure
      - no way to predict value, will go till osmotic and pressure potential equal 0 and be at equilibrium with H2O
    - - even thin parenchyma in mature cells can exert force on protoplast to raise pressure potential high enough to counter osmotic pressure :fire:
      - immature, growing cells are weak and can burst do to lack of pressure to stop water absorption :red_cross:
        
        will reach hydraulic equilibrium with surrounding cells and stop growing
        
        in tips of roots and stems, cells keep very negative osmotic and water potential and will add solutes when there is influx of H2O : :explode:
        
        cell will grow rather than burst
        
        once size is reached, growth stops, walls strengthen, raise pressure potential
        
        will raise both potentials till equilibrium is reached with surrounding cells :check:, stopping influx of H2O
      - walls, secondary or primary will always resist breaking by water absorption :check:
      - though plant cells cannot burst, water loss is serious problem :non-potable_water:
        
        can cause protoplast to shrink in volume and even cause protoplast to shrivel
        
        incipient plasmoysis is the point where protoplast has lost just enough water to pull slightly away from wall :green_cross:
        
        water can move out of cell lowering osmotic pressure slightly and pressure potential greatly
        
        Plasmolyzed is when the cell continues to lose water and completely pulls away from wall and shrinks :forbidden:
        
        water continues to become more negative as osmotic potential makes solutes more concentrated
    - - very dramatic changes so osmotic pressure only changes MPa :black_flag: in reality
    - - makes the osmotic potential more negative :red_flag:
      - potential pressure also decreases as protoplasm shrinks and less pressure is agaisnt wall :red_flag:
      - both of these decreases also cause the water potential to decrease :star:
- - - - potassium cannot leave because plasma membrane is impermeable to it
      - potassium pumping is possible but diffusion is not
        
        loss of potassium cause water potential to be negative
        
        adjacent cells and guard cells thrown out of hydraulic equilibrium by potassium pumping :check:
        
        water diffuses out of surrounding cells across plasma membrane, primary walls and middle lamina and into guard cells :world_map:
        
        extra water causes guard cells to swell and push apart, opening stomata. K+ pumping then ceases :open_mouth:
        
        reverse process is needed for closing guard cells :rewind:
    - - when open, very negative osmotic potential that is countered by turgor pressure, giving large pressure potential, small negative water potential :unlock:: high K+
      - when closed, small negative osmotic potential. countered by less turgor and less pressure potential. caused by low K+ : :lock:
      - can have same water potential and be in hydraulic equilibrium despite varying internal conditions :left_right_arrow:
    - - are in hydraulic equilibrium with surrounding cells
      - H2O entering and leaving cell at same rate
  - - - creates more room for more molecular pumps :check:
      - high-volume transport can now occur across these transfer walls
      - plasma membrane pressed against all convolutions and has larger surface area than if wall was flat :<3:
      - found in areas of rapid short-distance transport is expected:
        
        glands that secrete salt
        
        areas that pass nutrients to embryos
        
        regions where sugar is loaded into or out of phloem :truck:
  - - - secreted molecule absorbed by cell neighboring the one that secreted it
      - primary wall (parenchyma cells) is thin and contact faces between 2 cells is extensive increasing chances of absorption
        
        could either diffuse into next cell or same cell is was secreted from :shrug:
      - if secreted by active transport, cell membrane is impermeable so return to original cell unlikely
  - - - to close, cell shrinks causing pressure in midrib which cause two halves to close
      - to open, K+ is added, bringing in water and causing cell to be more turgid and open
      - closing not caused by K+ pumping, membrane becomes permeable to K+ causing change in water balance a rushes out :star:
- - - - water molecules pass through rapidly through membranes with protein called aquaporins :potable_water:
    - - Use of ATP in transport is called active transport :<3:
      - without, molecule could not pass to essential areas against chemical gradient
  - - - intracellular transport in where vesicles migrate through cytoplasm and fuse with another organelle :star:
        
        in fusion, membrane merge and vesicles contents transferred to organelle
        
        common means of movement from ER to dictysome or other organelles
        
        in cell division, new cell plate formed by coalescence of ER and dictyosome :recycle:
- - - - P-protein plug is formed from this
    - - remains a solution under pressure and is brought forward when there is a drop in pressure caused by pressure drop in plant
      - contribute to the P-plug and leaking is prevented
      - when sieve elements are worn out and stop transporting, callose closes them :checkered_flag:
  - - - causes hydraulic disequilibrium between sieve elements and surrounding cells
      - since sieve elements contain holes, protoplasm is squeezed out into the surrounding cells
        
        vacuolar membrane disintegrates and watery mix is created phloem sap with mixing of vacuole water and cytoplasm :red_flag:
        
        Sinks are sites that receive transported phloem sap and are extremely diverse
        
        not all sinks are actively simultaneously :!:
        
        within sinks, sugars are actively unloaded from sieve elements into surrounding cells :star:
        
        thousands of sinks can be present on a small tree
        
        loss of sugar can lead phloem sap to be more dilute causing water and osmotic pressure to be negative
        
        end cells of phloem will not swell because of this
        
        as soon as sugars loaded from sites, they are unloaded at sinks
        
        Plants control the direction are rate of flow of the phloem sap :star:
        
        phloem transport increases greatly when activated
        
        not all buds are affected, flow could be low until time to produce fruit the phloem transport increases
        
        dormant in winter when sap is not need in large quantities
        
        Direction of transport can also change :check:
        
        when leaf is mature enough to produce nutrients on its own, plant will reverse direction and load phloem instead of unload :truck:
        
        young leaves need lots of the nutrients supplied by the phloem transport :construction:
        
        majority of protoplasm held firmly to walls and not carried away by phloem sap
      - causes osmotic and water potential to become negative :red_cross:
  - - - before new leaves are formed, sources are at storage sites such as tubers, corms, and wood
      - within sources, sugars are actively transported into sieve elements, sieve tube members (angiosperms) sieve cells (other angiosperms) :truck:
      - leaves are dominant sources in summer and spring :sunny:
      - In sources, phloem loading occurs along numerous vascular bundles causing massive loading
        
        large volume of material lows from source
        
        pressure can be high as 2.4MPa
        
        pressure builds up quickly
        
        actual amount of sugars and other nutrients (except water) transported by phloem per hour is called the mass transfer :check:
        
        mass transfer can be divided into cross sectional area of phloem called specific mass transfer :star:
        
        vascular bundles vary in speed and in amount of phloem present
- - - - as water leaves xylem, xylem drags water molecules along instead of leaving a hole :black_flag:
      - water is pure here as they are not bound by proteins and pushed upward through xylem from the roots
      - xylem's osmotic pressure not affected by loss of water from tracheary elements
    - - for every 10 meters of height, leaf water potential must be at least .1MPa more negative that root water potential
        
        this happens automatically in plants as water potentials become more negative and drying causes leaf H2O potential to be negative
      - long distance transportation is horizontal and gravity is not a factor as no lifting is involved
      - there is tension and pressure potential is a negative number. becomes negative because of increasing negative pressure potential
    - - results in layer of relatively immobile water that does not move easily :star:
        
        significant fraction of water column in narrow tracheids and vessel elements :<3:
        
        the friction hinders water movement and contributes to tendency of water to remain stationary when leaves have negative water potential
        
        leaf water potential must be at least .1MPa more negative than root water potential to overcome friction. :explode:
        
        pressure increases with more factors like multiple wide vessels or narrow tracheary elements
        
        in trachieds water molecules must be pulled from pit membranes when entering and leaving creating more friction :explode:
      - water remains fixed to walls and tend to prevent neighboring H2O molecules from being drawn upward
    - - gravity and evaporation can also move water out of soil to roots
      - in dry soil, water pressure is less and is practically immobile
        
        no root can pull water from clay that is even slightly dry
      - long distance transportation occurs in this fashion :star:
      - diversity of pore sizes allow root hairs to absorb water but prevents gravity from pulling water so deep water is not reached
      - roots remain healthy with negative water potentials and can absorb water from soils that are quite dry :check:
        
        larger plants require a more negative water potential to overcome gravity and friction :red_flag:
      - when soil and air is dry, plants are greatly stresses
        
        hydrogen bonding broken over a large region and water column braking is known as cavitation :red_flag:
        
        molecules above cavitation point are drawn rapidly upward and are free of weight of water below them
        
        molecules below cavitation rush downward because nothing supports their weight
        
        between these two portions is a space called an embolism :star:
        
        expands until surface encounters solid barrier such as pit membrane :check:
        
        can pass through perforations because they are open holes
        
        often called air pocket
        
        when in tracheid, only tracheid loses water
        
        when in vessel element, may expand until entire vessel is emptied :forbidden:
        
        cavitation often means that tracheid or vessel element can never conduct water again :warning:
        
        cohesive bonding that draws water upward is disrupted
        
        in unusual conditions, embolisms are healed when water is able to seep back in and fill embolism
        
        large amounts of energy are used to make trachaery elements and cavitation minimizing features are selectively advantageous :star:
        
        narrow elements reinforce all water molecules
        
        in wide elements, central molecules are freely mobile and cavitiate as easily as pure water. however does not damage cell wall
        
        this wall induced reinforcement of water columns is believed to allow plants to reach the heights they do :check:
        
        adhesion between water and cell wall in one advantage
        
        in places like the rain forest, reinforcement in to necessary and tree is full of vessels due to abundance of water :<3:
        
        in dry climates it is advantageous to have narrow vessels or wood filled with tracheids only :tada:
        
        in temperate climates, early wood and late wood are formed with varying sizes of vessels. wide vessels of early wood cavitate and conduction occurs in late wood only
        
        eventually all vessels and tracheids will cavitate due to various conditions such as weather. :tornado:
        
        when multiple tracheary elements in wood cavitate, parenchyma cells synthesis antimicrobial compounds and die. Region becomes heartwood :<3:
        
        leaf water potentials become more negative but water cannot move up, tension in water column increases and cohesion is overcome :star:
  - - - almost all substances except lipids interact with water :potable_water:
      - adhesion makes water molecules less free to move around than other molecules :no_entry:
    - - when soil is moist, free water can be absorbed by roots between soil particles
        
        is the same some seawater as well
      - when dry, water binds to soil and not absorbed easily :red_cross:
  - - - low night temperatures essential for stomatal openings with CAM plants in the dry desert region :cactus:
      - mild temperatures and abundant moisture cause CAM plants to open stomata in the mornings, picking up CO2 with RuBP carboxylase directly :black_flag:
        
        will return to normal cycle once soil dries
      - night temps to high, stomatal pores can close for several days
    - - open stomata represent trade-off between CO2 and water loss
      - when water abundant in soil, water loss is advantageous :star:
        
        when dry however, this represents an immediate and leathsal threat :skull_and_crossbones:
        
        numerous mechanisms evolved to help control the stomatal openings
        
        light is most important, mainly blue light, that triggers action spectrum leading to K+ pumping
        
        CO2 content important as low content will open stomatal openings
        
        if leaf is healthy, light and carbon dioxide are the normal controlling factors :check:
        
        water potential is the mechanism that takes over in healthy plants :star:
        
        low water potential causes plant to release hormone called abcisic acid
        
        causes guard cells to closes immediately no matter light or CO2 content
        
        often occurs in early afternoon on warm, dry days