Water Balance in Plants

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  1. Plants take in water through their...?
  2. The continuous passage of water (and ions) through a plant from root to leaf is called the...?
    Transpiration stream
  3. Briefly describe the route water takes through a plant
    • Water in soil enters root hairs by osmosis from a HWC to a LWC down a concentration gradient
    • Water moves across the root cortex through cells, cell walls and intercellular spaces by osmosis from a HWC to a LWC down a concentration gradient
    • Water enters the xylem by osmosis
    • Transpiration pull causes continuous, thin, tense columns of water to be drawn up xylem in stem and into leaves. Water pulled up in very thin columns without breaking is due to cohesion and adhesion
    • Root pressure helps move water up the plant
    • Water moves into leaf cells by osmosis froma HWC to a LWC down a concentration gradient
    • Water evaporates into air spaces of leaf
    • Water evaporates out of leaf through stomata
  4. What is a root hair?
    It is an extension of an epidermal cell which has a large surface area to absorb more water from the surrounding soil
  5. What other function can a root hair have?
    It can provide anchorage for the plant
  6. How does water move through a plant?
    • Water moves:
    • between cells
    • across cell walls
    • across cell membranes through the root cortex by osmosis
  7. The force by which water is pushed up the stem by the roots is called...?
    root pressure
  8. What is transpiration?
    The process by which water is lost by evaporation from the aerial parts of a plant
  9. Where does most transpiration occur in a plant?
    Through stomata
  10. What ions are needed for the formation of chlorophyll?
    Mg and Fe
  11. How do ions enter the plant?
    By active transport only
  12. What is the importance of the transpiration stream?
    • Provides water for photosynthesis (photolysis)
    • Water keeps cells turgid which gives a plant structure and support
    • Cooling effect for the plant
    • Involved in uptake and transport of mineral ions to cells
  13. How can the rate of transpiration from a leaf be measured?
    Using a potometer
  14. As temperature rises the rate of transpiration...?
  15. As humidity increases the rate of transpiration...?
  16. As wind increases the rate of transpiration...?
  17. As light intensity increases the rate of transpiration...?
  18. What effect does air pollution have on transpiration?
    Soot blocks the stomata thus reducing transpiration
  19. What are stomata?
    Tiny pores on the surfaces of leaves
  20. What do guard cells do?
    They change shape to open and close the stomata
  21. Describe briefly how stomata open
    • Water enters the flaccid guard cells and so they become turgid
    • The thin outer parts of the guard cells stretch more than the thick inner parts
    • The two guard cells bulge out and the thick inner walls become pulled apart, opening the stomata
Card Set
Water Balance in Plants
Higher Biology - Unit Two - Water Balance in Plants
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