Plant Vascular Tissues

• Vascular tissues


  Tissues in plants that transport dissolved nutrients, minerals, and water
• 2 basic kinds of vascular tissues

  • Xylem
  • Phloem
• Xylem


  • Vascular tissue that carries water and nutrients from root to leaf
  • Lignified, meaning it is fortified with lignids.
  • Dead tissue, made up of cells (dead, hollowed cells)
• Phloem


  • Vascular tissue that carries sugars from the source cells to sink cells
  • Living cells
  • Has 2 different types - Sieve tube members and Companion cells
• Vascular cylinder in dicot roots

  1. Vascular bundle in the centre

  2. Cells surrounding the bundle are parenchyma

  3. Vascular bundle has a 3 pointed star shape

  4. The 3-pointed star cells are xylem

  5. The cells within the circle but not the star are phloem
• Vascular cylinder in dicot stems

  1. Multiple vascular bundles on the outside of the plant, situated in a circle around the cambium layer

  2. Inside the vascular bundle is the xylem, on top is the phloem, on top of that is sclerenchyma
• Vascular cylinder in dicot leaves

  1. In the centre of the leaf (and in the centre of the vein), there is a bundle of xylem, underneath is the phloem

  2. Xylem vessels transporting nutrients and water branch off from the central vascular bundle
• Transpiration stream


  The movement of water through the xylem of a plant
• Forces driving the transpiration stream

  1. Osmosis

  2. Adhesion

  3. Cohesion

  4. Transpiration
• Osmosis


  The movement of water molecules from a solution with a high concentration of water molecules to a solution with a lower concentration of water molecules
• Adhesion


  The force of attraction between water and some other surfaces
• Cohesion


  The attraction of water molecules to other water molecules
• Stomata


  • Little pores in the epidermis that allow carbon dioxide into the leaves and oxygen outside
  • Can open and close to regulate water loss
• Regulation of water loss

  1. Guard cells can become turgid and open the stomata

  2. Guard cells can become flaccid and close the stomata
• Transpiration


  The evaporation of water in the form of water vapour. Causes the negative pressure caused by the loss of water from the leaves
• Translocation


  The movement of sugars through the plant from source cells to sink cells through the phloem
• Phloem cells


  • Sieve tube members
  • Companion cells
• Sieve tube members


  • Main phloem cells that carry the sap (sugary fluid) around the plant
  • Hollow cells with no nucleus, ribosomes and few organelles because they will take up too much room
  • Has endoplasmic reticulum on the outside
  • Cannot direct its own actions
  • The connection between one sieve tube member to the next is connected by sieve plates with holes for sugar to pass through
• Companion cells


  • Have organelles
  • Manages cell metabolism and regulation for themselves and the sieve tube member they sit beside
  • Sugar first goes through the Companion cell from source cells
• Sugar loading from source cell to Companion cells


  1. Active process called apoplastic phloem loading

  2. Passive process of diffusion through plasmodesmata
• Phloem transport


  Osmotic pressure causes water to diffuse from xylem into phloem, increasing turgor pressure and forcing sap through phloem
• Environmental factors that affect the rate of transpiration in plants

  • Water availability
  • Light availability
  • Temperature
  • Humidity
  • Wind
• Low sunlight vs high humidity - humidity is a stronger factor for transpiration than light availability
• Active process of how Sugar gets loaded into Companion cells

  • A carrier protein forces sugar from the source cell into the companion cell
• Vascular Plants

  • any land plant that transports water and nutrients through a specialised system of tissue
  • contains two connected systems
  • the root system - the parts of the plant that lie below the surface of the soil and are responsible for providing a constant supply of water and minerals to the stems and leaves. also anchors plant.
  • the shoot system - the part of the plant that are above the ground and are responsible for exchanging oxygen and carbon dioxide with the atmosphere and for carrying out photosynthesis.
• Non-vascular plants

  • lack vacular (transport) tissue. do not have nay internal structures capable of transporting water and nutrients.
  • simply use osmosis to transfer substances from cell to cell, and diffusion for the movement of minerals between cells.
  • small in size (restricted in ability to transport minerals internally), lacks a root system (restricts them to moist environments)
  • e.g. mosses, liverworts
• Types of Vascular Plants

  • Hydrophytes
  • Mesophytes
  • Xerophytes
  • Halophytes
• Hydrophytes

  • The plant grows either partly or totally submerged in water
  • structure not well-developed
  • lacks cuticle
  • lacks stomata
  • eg. hydrilla
• Mesophytes

  • The plant grows in an environment with a moderate supply of water.
  • Structure well-developed (roots and shoots)
  • thin cuticle
  • has stomata on leaves
  • eg. rose
• Xerophytes

  • The plant is adapted to arid environments (desert plants)
  • structure is well-developed (shallow but extensive root system)
  • thick cuticle
  • small, fleshy leaves or leaves are reduced to spines (stems act as water storage)
  • few stomata
  • adapted for water conservation
  • eg. cacti
• Halophytes

  • The plant is adapted to salty environments
  • structure is complex and well-developed
  • eg. mangroves
• Adaptions of Xerophytes (water conservation

  • thick, waxy cuticle (covering) to stems and leaves
  • reduces water loss through cuticles
  • reduced number of stomata
  • reduces number of pores for water loss
  • leaves curled, rolled or folded when flaccid
  • reduces surface area for transpiration
• Adaptions of Halophytes

  • ability to secrete salt or accumulate it in older leaves
  • specialised tissue that allows water, but not salt, to enter the roots
  • tissue tolerance for high salt levels
  • extensive root systems give support in soft substrates. oxygen diffuses through pneumatophore (like breathing roots basically)