8. Water Constraints Flashcards
Water budget
How organisms regulate their internal water concentration, balancing water inputs and water outputs
-Differs between plants and animals, terrestrial vs aquatic
What are the components of a water budget for marine organisms?
•Drinking (gain)
•Secretion (loss)
•Osmosis (gain/loss)
Osmolarity
The amount of solute/water in solution
Hyperosmotic: high solute, low water
Hypoosmotic: low solute, high water
What are the 3 types of osmolarity an aquatic animal can have?
•Hyperosmotic: Lower water concentration/ higher solute concentration than environment
•Hypoosmotic: higher water concentration/ lower solute concentration than environment
•Isosmotic: Same water/solute concentration as environment
What osmolarity do freshwater organisms have?
Hyperosmotic
-Risks surplus water inflow and loss of salts
-Do not drink
-Excrete large amounts of dilute urine
-Absorb sodium/chloride in gills and from food
What osmolarity do most marine fish and invertebrates have?
Isosmotic
-no need to regulate
How do hypoosmotic marine fish regulate?
-risk water loss and surplus salt intake through gills
-drinking to counteract dehydration
-specialized chloride cells in gills to excrete excess salt
What osmolarity do sharks/skates have?
Slightly hyperosmotic
-retain urea inblood to avoid osmosis water loss
-surplus water intake from gills counteracting by urea
Anadromous
Born in freshwater, move to the ocean to live, return to freshwater to spawn
Cope with changes in salivanity by adapting their secretion cells
Taking in salt - freshwater
Excretion salt - marine
Catadromous
Lives in freshwater, goes to saltwater to spawn and be born
What are salmon? (Anadromous or catadromous)
Anadromous
What are eels? (Anadromous or catadromous)
Catadromous
What factors are involved in terrestrial animals internal water?
• Drinking (gain)
•Food (gain)
•Air (gain)
•Evaporation (loss)
•Secretion (loss)
What factors are involved in terrestrial plants internal water?
•Roots (gain)
•Air (gain)
•Transpiration (loss)
•Secretion (loss)
What is water vapour density?
The quantity of water vapour the air actually holds
What is saturation water vapour density?
The amount of water vapour the air can potentially hold
What is water vapour pressure?
Humidity, pressure exerted by water in the air
What is saturation water vapour pressure?
Total pressure exerted by water vapour in water-saturated air (100% humidity)
Can cold or warm air hold more water?
Warm
What are the components of water potential?
ψ = ψ⁰ (water potential of pure water at 1 atm) + ψgravity + ψsolute (osmotic pressure) + ψhumidity + ψmatric (pull through adhesion) + ψpressure
Where is water potential highest in a tree?
•Soil (highest)
•Roots (medium-high)
•Trunk (low-moderate)
•Canopy (low)
ψ becomes more negative as height increases, can pull water up and resist gravity
What are the main methods of water acquisition for terrestrial animals?
Food and drinking
What are the main methods of water conservation for terrestrial animals?
•Thick, waxy exoskeleton (evaporation)
•Storing water in the body
•Conserving urine, sweat, feces (secretion)
•Behavioural adaptations (e.g. burrows with cooler climate, lower transpiration)
What are the main methods of water conservation for terrestrial plants?
•Wilting (reduce surface area, reduce transpiration)
•Drop in turgor pressure
