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Transport in Plants (TRANSPIRATION LITE (Factors affecting rate of…

- - - - excessive transpiration
        
        plant cells becomes flaccid
        
        Leaves often wilt first
        
        Guards cells are flaccid, thus stomata close and the rate of transpiration is reduced
        
        REDUCING WATER LOSS obv
    - - Advantages
        
        Reduces rate of transpiration and thus prevents excessive water loss
        
        Disadvantages
        
        Stomata close, decreasing intake of CO2
        
        Leaves droop and decrease the absorption of sunlight
        
        decreasing the rate of photosynthesis
  - - - Water vapour that diffuses our of the stomata tend to accumulate in a layer around the leaf
        
        Wind blows away at this layer of water capour maintaining the water vapour concentration gradient the air spaces in the leaf and the atmospheric air
        
        Rate of transpiration increases as wind speed increases
    - - Intercellular air spaces are very saturated with water vapour
        
        Thus air humidity plays a part in regulating the concentration gradient
        
        In dry air, the humidity is low, and thus there is a steeper gradient in the concentration gradient between the air spaces in the leaf and the surrounding air, thus the rate of transpiration is high
    - - As temperature increases, water molecules gain kinetic energy and move faster
        
        Thus rate of evaporation of water from mesophyll cells and the rate of diffusion of water vapour out through the stomata increases --> Rate of transpiration increases
    - - In the day, the stomata open, thus rate of transpiration increases
        
        At night, the stomata close, thus rate of transpiration decreases
  - - - Impermeable to water which reduces rate of transpiration from cuticle surface (i.e. cuticular respiration)
    - - Traps water vapour closer to the leaf, increasing the humidity around the stomata, thus reducing the transpiration rate
- - - - made if living tube-like elements joined end-to-end
      - sieve plates (end walls of sieve tube elements) is perforated with many tiny pores
      - degenerate protoplasm
    - - provides nutrients to the sieve tube element
      - numerous mitochondria --> provide energy for active transport
  - - - Adaptation
        
        numerous mitochondria
        
        provide energy for active transport
        
        provide sieve tube with nutrients and energy to aid sieve tube element to carry out metabolic processes
        
        Pores in sieve plate
        
        Sucrose and animo acids can flow through sieve tubes
- - - - xylem -- star shaped structure at the centre of the root
      - phloem found between xylem arms
      - xylem and phloem alternate with each other
    - - Storage Tissue for starch granules
    - - Outermost layer of cells
      - Root hairs (thin walled-tube like protrusion) develop from this layer
        
        ⬆️SA:V Ratio --> ⬆️rate of water & mineral salt uptake
    - - Contain a strip of suberin
  - - - xylem and phloem
        
        grouped together to form vascular bundles
      - cambium
        
        lies between the xylem and phloem
        
        actively divides and differentiates into new xylem and phloem (giving rise to the thickening of the stem)
    - - cortex is the region between the vascular bundles and the epidermis
      - vascular bundles arranged around the pith
      - Stores starch granules
    - - cells are protected with waxy, waterproof cuticle
        --> reduces the evaporation of water from the stem
- - - - capillary action is the tendency of water to move up narrow tubes due to:
        
        cohesion: attraction of water molecules to one another
        
        adhesion: attraction of water molecules to the walls of the narrow tube (xylem vessel)
        
        the narrower the tube, the higher the water rises
    - - Definition
        
        Transpiration pull is the pulling force caused by transpiration as illustrated below
        
        water movement through the plant begins with the loss from the leaves and is completed with water absorption from the soil through the roots
        
        water is pulled up the xylem in a continuous unbroken column called a transpiration stream
        
        how is it possible for water to be pulled up in an unbroken column?
        
        cohesion prevents water column from breaking apart and adhesion prevents water from slipping back down
      - Process
        
        Movement of water out of the cells to replace the thin film of moisture that has evaporated decreases the mesophyll cell's sap's water potential
        
        The mesophyll cells absorb water via osmosis from the cells deeper in the leaf
        
        These cells absorb water from the xylem vessels
        
        resulting in a production of a suction force or tension that pulls the column of water in the xylem vessels up, in a process known as transpiration pull.
        
        [continued below at 1]
    - - Root pressure is pressure resulting from the constant entry of water into the roots
        
        cells that surround the xylem vessels in the root actively pump mineral salts into it
        
        water potential in the xylem vessel decreases, creating a water potential gradient
        
        causing water to enter it by osmosis, and this pressure pushes the water column up the xylem
        
        however it is minor as it could not bring water all the way to the tops of tall trees
        
        however in small plants it can causes guttation, forcing after through special openings in the leaves of some plants, in the night and early morning when transpiration is low and the moisture is high
  - - - loss of water vapour through the aerial parts of the plant, mainly through the stomata of the leaves
      - waxy cuticle reduces water loss from other aerial surfaces
      - transpiration is a consequence of gaseous exchange in plants. how so?
      - stomata need to open for gaseous exchange, allowing for water to evaporate from the surfaces of the spongy mesophyll cells.
      - water vapour is lost to the atmosphere due to the lower concentration of water vapour in the atmosphere
    - - Water in xylem vessel enters a mesophyll cell and moves from cell to cell via osmosis
        
        Water exits mesophyll cells to form a thin film of moisture over the cell surfaces
        
        Water exits mesophyll cells to form water vapour to form water vapour in the intercellular air spaces
        
        Water vapour accumulates in the intercellular air spaves
        
        Water vapour from air spaces diffuses through the stomata into the drier air outside the leaf, in a process known as transpiration
        
        [continued above]
- - - - elements that are:
        
        dead at maturity
        
        joined end-to-end with no protoplasm
    - - types of lignification
        
        annular and spiral
        
        accommodate growth of plants as it allows xylem vesssels to stretch with region while growing
        
        pitted
        
        ⬆️lignin -->⬆️mechanical support for plant
        
        lignification found in older xylem tissues
        
        pits allow transport of water into neighbouring tissues
  - - - adaptation:
        
        empty lumen without protoplasm and end-walls reduces resistance to water flow
    - - adaptation
        
        walls of xylem vessels strengthened with lignin (lignified) which prevents the collapse of xylem vessels when it transports water and mineral salts