Questions and Answers
The movement of water in the xylem vessels is facilitated by adhesion and ______ forces.
cohesion
Transpirational pull creates a ______ pressure that pulls water up the xylem vessels.
negative
Water moves through the ______ pathway by passing through the cytoplasm and plasmodesmata.
simplast
Water diffusion from neighbouring cells occurs via ______.
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Due to the presence of Casparian strips, water cannot move through the ______ pathway.
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The spongy mesophyll cells lose water and have low water ______ towards adjacent cells.
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When water evaporates from the leaves, it creates a ______ pull that helps in water movement.
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Adhesion forces facilitate the attraction between water molecules and the wall of the ______ vessel.
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Water molecules are pulled upwards by the adhesion force and held together by the ______ force.
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The movement of water in the xylem is also assisted by the capillary action produced by adhesion and cohesion ______.
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Study Notes
Movement of Water in Xylem Vessels
- Water movement in xylem vessels relies on adhesion and cohesion forces.
- Adhesion force: Attraction between water molecules and xylem vessel walls.
- Cohesion force: Attraction between water molecules themselves.
- Together, these forces create a continuous column of water in the xylem.
- Tall plants cannot rely solely on root pressure to transport water to leaves.
- Capillary action from adhesion and cohesion, along with transpirational pull, aids in water transport.
Transpirational Pull
- Transpirational pull is a key mechanism in water movement, especially in tall plants.
- Occurs when water evaporates from leaves, creating a negative pressure in xylem vessels.
- Water vapor diffuses out of leaf cells through open stomata.
- Spongy mesophyll cells lose water, leading to low water potential and facilitating osmosis.
- This results in a force that pulls water molecules in xylem vessels upward.
Simplast and Apoplast Pathways
- Water travels from root cells to xylem through two main pathways:
- Simplast Pathway: Involves movement through cytoplasm and plasmodesmata.
- Apoplast Pathway: Involves movement through spaces between cellulose fibers in cell walls.
- Endodermis cell walls contain Casparian strips, which are water impermeable.
- Casparian strips direct water into the cytoplasm of endodermal cells, ensuring efficient transport.
- This mechanism prevents water loss through the apoplast pathway, channeling it directly to the xylem for upward movement.
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Description
Explore the factors that facilitate water movement in xylem vessels, including adhesion and cohesion forces. Learn how these forces create a continuous column of water.
