Water Regulation on Land Plants

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Water Regulation on Land - Plants

• Wip Wr Wa - Wt Ws
• Wip internal water
• Gains
• Wr via roots
• Wa via water vapor in air
• Losses
• Wt via transpiration
• Ws via secretions

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Water movement between soil and plants

• Water follows a water potential gradient.
• Water potential (?) is a capacity to perform
  work.
• Pure Water ? 0.
• therefore, ? in nature is negative.

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• ?plant ?solute ?matric ?pressure
• ?solute reduction in water potential due to
  dissolved substances.
• ?matric reduction in water potential due to
  tendency of water to adhere to surfaces in small
  channels (matric forces) e.g., xylem vessels,
  pores in soil.
• ?pressure reduction in water potential due to
  negative pressure created by evapotranspiration
  from leaves.
• As long as ?plant lt ?soil, water flows from the
  soil to the plant.

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05_07.jpg
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Water Regulation on Land

• Two major challenges
• 1. Evaporative water loss.
• Decreases as water vapor in the air increases.
• Good for water conservation not good for
  evaporative cooling.
• 2. Reduced access to replacement water.

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Water Regulation on Land - Animals

• Wia Wd Wf Wa - We Ws
• Gains
• Wia internal water
• Wd via drinking
• Wf via food (2 sources)
• Wa absorbed from air (e.g., terrestrial
  amphibians)
• Losses
• We via evaporation
• Ws Secretion / Excretion

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05_19.jpg
Adaptations for conserving water
A common adaptation for conserving water --
Ocotillo
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Water Acquisition by Animals

• Most terrestrial animals get their water from
  drinking and eating.
• Can also be gained via metabolism through
  oxidation of glucose
• C6H12O6 6O2 ? 6CO2 6H2O
• Metabolic water water released during cellular
  respiration.

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example of metabolic water use