AGRI 31 2ND LE EXAM

• Transpiration - process which water moves in liquid form and release in vapor form through aerial parts.
• ATP - an energy utilized to transform liquid into gas in transpiration
• Transpiration - a chemical process in plants that is energy-dependent
• 97-99.5% - amount of water loss in transpiration
• 540 cal g-1 - the amount of heat energy required for transforming liquid H20 in gaseous form
• Importance of Transpiration

  • Keeps the cell hydrated
  • Maintains favorable turgor pressure for nutrients to transport and be absorbed by roots
  • Cools the plants
• Wilting, Desiccation, and Death - occurs when the transpiration is extremely high
• Types of Transpiration

  • Cuticular
  • Lenticular
  • Stomatal
• Cuticular transpiration - Loss of water through cuticle; 5-10% of the water loss
• Cuticle - A layer of keratin that covers the surface of the leaf to protect it from water loss
• Cuticle - outermost layer (upper part) of the leaf surface
• Lenticular transpiration - loss of water that takes place through lenticels which are small minute pores present on the stem of many woody plants
• Stomatal transpiration - the movement of water vapour through the stomata, in which most of the water is lost from most of the plants
• Stomata - composed of two guard cells that allow gases to pass through the leaf
• Factors Affecting Diffusion of Water from Leaves to Atmosphere

  • Relative Humidity
  • Vapor Pressure Deficit
• Xylem - Vascular tissue responsible for the transportation of water and minerals throughout the plant body.
• Phloem - Vascular tissue responsible for the transportation of organic substances such as sugars and amino acids throughout the plant body.
• Relative Humidity - The amount of water vapour in the air compared to the maximum amount of water vapour that can be held at a given temperature
• If the Relative Humidity is high, Transpiration rate is low
• Vapor Pressure Deficit - a driving force for the water to diffuse from leaves to the atmosphere
• Vapor Pressure Deficit - The difference between the vapor pressure of the air and the vapor pressure of the liquid
• When Relative Humidity is at 100%, the Vapor Pressure Deficit is 0Pa. This means that there is no net movement of water
• The relationship of Relative Humidity and Vapore Pressure Deficit is inversely related.
• When the RH of the atmosphere is low given that the temperature is high, the VPD is high and the transpiration rate is faster since it increases the demand for water.
• Soil-Plant-Air Continuum of Water

  • Movement of water from root->root xylem->leaf xylem->air
• Extracellular/Apoplastic route - a pathway where water moves through non-living parts of the cell such as capillary spaces
• Symplastic Pathway - a type of intracellular route where it utilized plasmodesmata
• Plasmodesmata - a gated plant cell wall channel that allows water and mineral ions to pass between cells
• Transcellular pathway - A type of intracellular route that uses the plasma membrane and vacuolar membrane (tonoplast) to move substances from one cell to another
• Movement of water from root xylem to leaf xylem utilizes the transpiration-cohesion-adhesion theory
• Water vapor leaves the air space of the pant via stomates
• Water molecules are cohesively attracted since the molecule has the same substance
• Adhesive forces occur when water is attached to the walls of the xylem vessels, which prevents them from collapsing due to negative pressure.
• Factors that Affect Transpiration (Plant Factors)

  • Efficiency of evaporative surface
  • Efficiency of water absorption
  • Stomatal modification
  • Phytohormones
  • Canopy structure
• Factors that Affect Transpiration (Environmental Factors)

  • Edaphic (soil) factor
  • Atmospheric factor
• Atmospheric factors (L-e-RHT-WVe-OCDC)

  • Light
  • Relative Humidity
  • Temperature
  • Wind Velocity
  • Oxygen and Carbon Dioxide Concentration
• The higher the value the light, the higher the transpiration
• If Relative Humidity is high, Transpiration is low and vice versa
• If the Temperature is high, Transpiration rate is also high
• The higher the Wind Velocity, The higher the Transpiration rate since it triggers the opening of the stomates of a plant leaf