Podcast
Questions and Answers
What is the main driving force behind the movement of soil water to the atmosphere?
What is the main driving force behind the movement of soil water to the atmosphere?
How do water molecules move up the plant stem molecule by molecule?
How do water molecules move up the plant stem molecule by molecule?
Which structure in plant foliage allows water vapor to exit into the atmosphere?
Which structure in plant foliage allows water vapor to exit into the atmosphere?
Why does transpiration pose a tremendous risk for a plant when water availability is low?
Why does transpiration pose a tremendous risk for a plant when water availability is low?
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What role does diffusion play in the movement of water from plant foliage into the atmosphere?
What role does diffusion play in the movement of water from plant foliage into the atmosphere?
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How is the movement of water from roots to stems facilitated during transpiration?
How is the movement of water from roots to stems facilitated during transpiration?
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What happens when the pull of water from the foliage exceeds the supply of water from the roots?
What happens when the pull of water from the foliage exceeds the supply of water from the roots?
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Why does cavitation in xylem tubes lead to the death of tissues downstream?
Why does cavitation in xylem tubes lead to the death of tissues downstream?
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What happens to stomata when a plant senses a decrease in water uptake due to soil drying?
What happens to stomata when a plant senses a decrease in water uptake due to soil drying?
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Why do plants regulate their water uptake as soil dries?
Why do plants regulate their water uptake as soil dries?
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What is the consequence of a plant's stomata being completely closed at the permanent wilting point?
What is the consequence of a plant's stomata being completely closed at the permanent wilting point?
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How do plants respond when soil water drops to the permanent wilting point?
How do plants respond when soil water drops to the permanent wilting point?
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Study Notes
Transpiration and the Soil-Plant-Atmosphere Continuum
- Water in soil moves from a state of higher potential energy to a state of lower potential energy via transpiration, similar to water flowing from higher to lower elevation.
The Process of Transpiration
- Water vapor exits plant foliage via microscopic stomata, which are pores open to the atmosphere.
- As water molecules exit the stomata, other water molecules are drawn toward the stomata due to cohesion.
- An entire chain of water molecules is dragged molecule by molecule up the plant stem, extending to the roots in contact with the soil.
The Role of Cohesion and Adhesion
- Water molecules are attracted to each other via cohesion, allowing for the continuous column of water to form.
- The advancing column of water extends from the roots to the stem, with water being drawn into the root from the film of water clinging to soil particles.
Risks of Transpiration
- When water availability is low, transpiration poses a tremendous risk for a plant, as the continuous column of water can break, or cavitate, introducing air bubbles.
- Cavitation can cause the death of all tissues downstream from the site of cavitation.
Plant Adaptations to Regulate Water Uptake
- Roots can sense when water uptake slows and send hormones to the foliage, causing the stomata to partially close and slow the rate of water loss.
- This helps minimize the risk of cavitation, but reduces carbon dioxide entry and photosynthesis.
- When soil water drops to the permanent wilting point, a plant's stomata will completely close to prevent cavitation, but this can only be sustained for a limited time before the lack of photosynthesis starves the plant.
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Description
Learn about the movement of water in plants from higher potential energy (soil water) to lower potential energy (atmosphere) through transpiration. Explore how water vapor exits plant foliage via stomata. Discover the relationship between water flow, elevation, and potential energy.
