Transpiration and Plants

• Epidermal cells


  Very thin cells that form the upper and lower epidermis of a leaf
• Upper epidermis


  • Transparent to allow light to pass through
  • Covered in a waxy cuticle to reduce water evaporation
• Lower epidermis


  • Contains tiny pores called stomata
  • Stomata allow carbon dioxide to enter and oxygen to leave
• Guard cells


  Found on either side of stomata, help control water vapor passing out of the leaf
• Palisade mesophyll


  • Packed full of chloroplasts that contain chlorophyll to absorb light for photosynthesis
• Spongy mesophyll


  • Full of air spaces to allow carbon dioxide and oxygen to diffuse
• Xylem


  Transports water and dissolved mineral ions from roots to stem and leaves
• Phloem


  Transports dissolved sugars produced by photosynthesis from leaves to rest of plant
• Translocation


  Movement of sugars through phloem tissue
• Meristem tissue


  Contains stem cells that can differentiate into different plant tissues
• Meristem tissue is found in growing tips of shoots and roots
• Transpiration


  The process of water constantly evaporating from the surfaces of leaves
• Transpiration process


  1. Water evaporates from cells inside the leaf

  2. Water vapor diffuses through air spaces in the spongy mesophyll

  3. Water vapor exits the leaf through the stomata

  4. Water passes from the xylem into the leaf to replace lost water

  5. Water is drawn into the root hair cells and up the xylem vessels to the leaf
• Importance of transpiration


  • Brings water to the leaf for photosynthesis
  • Transports dissolved mineral ions
  • Cools the leaf down in warm weather
• Factors affecting rate of transpiration

  • Higher temperatures
  • Dry conditions (low humidity)
  • Windy conditions
  • Higher light intensity
• High light intensity


  Stomata open to allow carbon dioxide to enter for photosynthesis, allowing water vapor to pass out
• Stomata


  Pores on the leaf surface surrounded by guard cells
• Stomata opening and closing

  1. Guard cells swell and change shape in high light, causing stomata to open

  2. Plant closes stomata under hot conditions to reduce water loss
• Stomata and guard cells play roles in gas exchange and water loss in plants