Organisation in plants

• What is a leaf organ?


  A leaf organ is a structure that performs photosynthesis.
• How is the palisade mesophyll adapted for its function?


  It has tightly packed cells with many chloroplasts to absorb light for photosynthesis.
• How is the spongy mesophyll adapted for its function?


  It contains air spaces that increase surface area and allow gases to diffuse quickly.
• What is the function of the guard cells?


  Guard cells control the opening and closing of the stomata.
• What is the function of the xylem?


  The xylem transports water and mineral ions from the roots to the rest of the plant.
• Give three adaptations of the xylem.


  • Made of dead cells
  • No end wall between cells
  • Walls strengthened by lignin to withstand water pressure
• What is the function of the phloem?


  The phloem transports dissolved sugars from the leaves to the rest of the plant.
• What is the purpose of translocation?


  To transport dissolved sugars from the leaves to other parts of the plant for respiration, growth, and storage.
• Define the term transpiration.


  Transpiration is the movement of water from the roots to the leaves through the xylem.
• What is the purpose of transpiration?


  To provide water to keep cells turgid, for photosynthesis, and to transport mineral ions to leaves.
• Name four factors that affect the rate of transpiration.


  Temperature, light intensity, humidity, and wind speed.
• What effect does temperature have on the rate of transpiration?

  Higher temperatures increase the rate of transpiration.
• What effect does humidity have on the rate of transpiration?

  Higher levels of humidity decrease the rate of transpiration.
• Why does increased light intensity increase the rate of transpiration?


  Increased light intensity causes stomata to open wider to let more carbon dioxide into the leaf for photosynthesis.
• What is the function of the stomata?


  Stomata allow diffusion of gases into and out of the plant.
• Where are most stomata found?


  Most stomata are found on the underside of leaves.
• What is the advantage to the plant of having a high number of stomata at this location?


  A high number of stomata reduces the amount of water loss through evaporation.
• How is the upper epidermis adapted for its function?

  • Single layer of transparent cells allow light to pass through
  • Cell secrete a waxy substance that makes leaves waterproof