bio 3.2 plants

• Specialisation and organisation of plant cells


  Cells organised into tissues for specific functions in vascular plants, including intake, movement and loss of water
• Plant systems


  • Shoot system
  • Root system
• Vascular plants


  • Plants with xylem and phloem tissue, majority being flowering plants and conifers
• The multicellular land plants with which people are familiar are the vascular plants. Their cells are organised at the system, organ and tissue levels.

  
• Plant organs


  • Shoot system organs: stem, leaves, reproductive organs (flowers, fruit)
  • Root system organs: root, lateral roots, root hairs
• Plant tissues


  • Meristematic tissue
  • Permanent tissue: dermal, ground, vascular

  
• Meristematic tissue


  Plant tissue made of unspecialised cells that can reproduce by mitosis, found in tips of roots and shoots
• Permanent tissue


  Plant cells that can no longer divide
• Types of permanent tissue

  • Dermal tissue
  • Ground tissue: parenchyma, collenchyma, sclerenchyma
  • Vascular tissue: xylem, phloem
• Dermal tissue


  Protects plants and minimises water loss, e.g. epidermal tissue
• Ground tissue


  All plant tissues that are not dermal or vascular
• Parenchyma


  Thin-walled living plant cells, site of photosynthesis in leaves and storage of starch/oils in roots, tubers, seeds
• Collenchyma


  Thick, flexible walled cells, main supporting tissue of stems
• Sclerenchyma


  Dead cells with thickened walls for strength and rigidity
• Vascular tissue


  Plant tissue composed of xylem and phloem
• Xylem


  Transports water and minerals, provides plant support
• Phloem


  Transports sugars and other organic compounds
• Each plant organ (root, stem and leaf) contains all three tissue types (dermal, ground, vascular)
• Root hairs


  Extensions of epidermal cells responsible for absorption and uptake of liquid water
• Uptake of water by plants occurs through osmosis by the root hairs
• Tracheids


  Major water conducting cells in xylem of all vascular plants
• Vessels


  Major water conducting cells in xylem of angiosperms
• Xylem tissue is responsible for the movement of water and nutrients in a plant
• Xylem tissue is composed of tracheids, fibres, parenchyma cells, and in flowering plants, vessels
• Plants use less than 5 per cent of the water absorbed by roots for cell functions. The remainder simply passes out of plants directly into the atmosphere in a process called transpiration.
• Transpiration


  Loss of water from the surfaces of a plant
• Water loss by transpiration occurs in the leaves of plants, through the stomata located mainly in the lower epidermis
• A loss of water vapour will occur if there is a concentration gradient between the water content in the leaf spaces (high) and in the air outside the leaf (low), and the leaf stomata are open.
• Transpiration


  The process of water loss from plants, influenced by temperature, relative humidity, wind movements, and water availability in the soil
• Higher temperature


  Higher transpiration rate
• Higher wind movements


  Higher transpiration rate
• Lower relative humidity


  Higher transpiration rate
• Higher water availability in soil

  Higher transpiration rate
• Tissues involved in transpiration


  • Stomata pores surrounded by guard cells
  • Air spaces in spongy mesophyll tissue of leaves saturated with water vapour
  • Stomata located mainly in lower epidermis of leaves are exit points for water vapour