•
•
•
Chapter 5 Concepts
The movement of water and solutes is linked to concentration gradients and
water potential
Terrestrial plants and animals must balance water gain and loss
Aquatic organisms jointly regulate water and solutes
Desert Temperature Profiles
•
•
•
•
•
•
•
•
•
•
•
Water and Concentration Gradients in the Terrestrial World
Water loss from a surface linked to evaporation rate
Evaporation rate controlled by concentration of water in atmosphere
Atmospheric water content linked to temperature
Concentration Gradients in Aquatic Environments
“Quantity” of water determined by concentration of solutes
Movement of water goes from areas of low solute concentration to areas of
high solute concentration
Movement across a semipermeable membrane can alter this
Given this, what terms can we use to describe these circumstance? (Fig. 5.4)
– Isosmotic = internal and external concentrations equal
– Hyperosmotic = internal solute higher than external
– Hypoosmotic = internal solute lower than external
Water Potential and Plant Water Transport (Fig. 5.5)
Energy = ability to work
Potential energy = ability to do work based on position or condition
One indication that work has been done is movement
Water moves from areas of low solute concentration to areas of high solute
concentration
• Water in soil and plant tissues has potential energy due to:
– Osmotic forces
– Matric forces
– Evaporative forces
• Water moves from areas of high potential to areas of low potential
Forces
• Osmotic forces
– Pure water has highest water potential
– Increasing solutes decreases water potential
• Matric forces
– Greater surface area increases matric forces
– Increased matric forces increase water potential
– Soil composition alters matric forces
• Evaporative forces
– Loss of water at the top of a column reduces water potential at the surface
Soil Composition
• Particle sizes
– Sand = 0.05 to 2 mm
– Silt = 0.002 – 0.05 mm
– Clay = < 0.002 mm
• Given these particle sizes, which soil combination has the potential to extert
the highest matric force?
Water potential gradients in terrestrial vascular plants (Fig. 5.5)
•
Given these forces, water tends to move from areas of high water potential to
areas of low water potential
Terrestrial Water Budgets
•
•
Animals
– Water content =
• Water intake through drinking, plus
• Water intake through food, plus
• Water absorbed from the air, minus
• Water lost through evaporation
• Water lost through secretions and excretions
Plants
– Water content =
• Water intake through roots, plus
• Water intake through the atmosphere, minus
• Water lost through transpiration, minus
• Water lost through excretions and structures
Balancing Water Budgets
•
Water intake
– Animals
• Drinking – duh….
• Metabolic water
• Atmospheric water
– Plants
• Root development
Metabolic water
•
Basic respiration
– C6H12O6 + O2 = 6CO2 + 6H2O
– For the chemically challenged:
• Sugar plus Oxygen = Carbon Dioxide plus water
Namib Desert Beetles (Fig. 5.8, 5.9)
Kangaroo Rats (Fig. 5.10)
Root Development (Fig. 5.11)
Aquatic Organisms
• Balance between solute concentrations and water movement
– Isosmotic
– Hyperosmotic
– Hypoosmotic
 Which of these three types of organisms faces stresses similar to those faced
by organisms in dry environments?