Questions and Answers
What is the cohesion-tension hypothesis?
Cohesion-tension is when water is transported in plants to great heights against the force of gravity.
What happens in the first step of the cohesion-tension hypothesis?
Water evaporates into the air spaces out of the stomata by transpiration, pulling the next water molecule with it due to high cohesion.
What occurs during the second step of the cohesion-tension hypothesis?
The entire column of water in the xylem is stretched and the water is under surface tension.
What is the main action described in the third step of the cohesion-tension hypothesis?
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What happens in the fourth step of the cohesion-tension hypothesis?
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What occurs during the fifth step of the cohesion-tension hypothesis?
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Study Notes
Cohesion-Tension Hypothesis Overview
- Water transport in plants occurs against gravity due to the cohesion-tension mechanism.
- This hypothesis explains how trees can draw water from roots to leaves, even at significant heights.
Step 1: Transpiration
- Water evaporates from stomata, creating air pockets in leaf spaces.
- High cohesion among water molecules pulls the next molecule along, initiating a chain reaction.
Step 2: Xylem Stretching
- Water's evaporation leads to the stretching of the entire column within the xylem vessels.
- The water is under surface tension, which helps maintain the integrity of the water column.
Step 3: Tension Generation
- The tension created by continuous water loss through transpiration is sufficient to pull water upward through the xylem.
Step 4: Stomatal Function
- Stomata open in sunlight, enhancing transpiration and causing the stem to slightly narrow due to reduced pressure.
Step 5: Restoration of Xylem Shape
- When transpiration ceases, the tension in the xylem reduces, allowing it to revert to its original, wider shape.
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Description
Explore the principles of the cohesion-tension hypothesis that explains water transport in plants. Learn how transpiration, xylem stretching, and tension generation allow trees to feed from roots to leaves efficiently. This quiz covers key concepts essential for understanding plant water dynamics.
