B4 Plant Organisation

• Epidermal tissue adaptations

  Waxy cuticle to reduce water loss from the leaf surface
• Palisade mesophyll adaptations

  Contains lots of chloroplasts to allow photosynthesis to progress at a rapid rate
• Spongy mesophyll adaptations

  Lots of air spaces to allow gases (carbon dioxide and oxygen) to diffuse in and out
• Xylem adaptations

  1. Made of dead cells which form a continuous hollow tube to allow movement of water and mineral ions from the roots to the leaves. 2. Strengthened by lignin to make the vessel strong and waterproof
• Phloem adaptations

  1. Made of elongated living cells 2. Have sieve plates that connect them together so cell sap can move through into other cells
• What is special about meristem cells?

  Can differentiate into many different cell types
• Guard cells function?

  Control opening and closing of stomata depending on water content of the plant
• Stomata adaptations?

  Control gas exchange and water loss. More on the base of the leaf to minimise water loss as the underside is cooler and shadier. Have guard cells to control opening and closing
• Plant root hair cells adaptations?

  Allow uptake of water and mineral ions from the soil. Large surface area to maximise rate of absorption. Contain lots of mitochondria to release energy for active transport of mineral ions
• Translocation?

  Movement of sugars from leaves (where they are made by photosynthesis) to other parts of plant
• Transpiration?

  Evaporation of water vapour from the surface of plant
• How does transpiration work?

  1. Water vapour evaporates from leaf surface via stomata 2. Water is pulled up the xylem (like a drinking straw) 3. More water is taken up from the soil (by the plant roots)
• How does temperature affect the rate of transpiration? (think washing on the line)

  Increased temperature increases rate of transpiration
• How does humidity affect the rate of transpiration? (think washing on the line)

  Increased humidity decreases rate of transpiration
• How does wind speed affect the rate of transpiration? (think washing on the line)

  Increased wind speed increases rate of transpiration. Increased air movement lowers water concentration outside leaf. Increases water vapour concentration gradient. Evaporation increases.
• How does light intensity affect the rate of transpiration? (think washing on the line)

  Increased light intensity increases rate of transpiration. Rate of photosynthesis increases