8. Water Constraints

Question 1

Water budget

Answer 1

How organisms regulate their internal water concentration, balancing water inputs and water outputs
-Differs between plants and animals, terrestrial vs aquatic

Question 2

What are the components of a water budget for marine organisms?

Answer 2

•Drinking (gain)
•Secretion (loss)
•Osmosis (gain/loss)

Question 3

Osmolarity

Answer 3

The amount of solute/water in solution

Hyperosmotic: high solute, low water
Hypoosmotic: low solute, high water

Question 4

What are the 3 types of osmolarity an aquatic animal can have?

Answer 4

•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

Question 5

What osmolarity do freshwater organisms have?

Answer 5

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

Question 6

What osmolarity do most marine fish and invertebrates have?

Answer 6

Isosmotic
-no need to regulate

Question 7

How do hypoosmotic marine fish regulate?

Answer 7

-risk water loss and surplus salt intake through gills
-drinking to counteract dehydration
-specialized chloride cells in gills to excrete excess salt

Question 8

What osmolarity do sharks/skates have?

Answer 8

Slightly hyperosmotic
-retain urea inblood to avoid osmosis water loss
-surplus water intake from gills counteracting by urea

Question 9

Anadromous

Answer 9

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

Question 10

Catadromous

Answer 10

Lives in freshwater, goes to saltwater to spawn and be born

Question 11

What are salmon? (Anadromous or catadromous)

Answer 11

Anadromous

Question 12

What are eels? (Anadromous or catadromous)

Answer 12

Catadromous

Question 13

What factors are involved in terrestrial animals internal water?

Answer 13

• Drinking (gain)
•Food (gain)
•Air (gain)

•Evaporation (loss)
•Secretion (loss)

Question 14

What factors are involved in terrestrial plants internal water?

Answer 14

•Roots (gain)
•Air (gain)

•Transpiration (loss)
•Secretion (loss)

Question 15

What is water vapour density?

Answer 15

The quantity of water vapour the air actually holds

Question 16

What is saturation water vapour density?

Answer 16

The amount of water vapour the air can potentially hold

Question 17

What is water vapour pressure?

Answer 17

Humidity, pressure exerted by water in the air

Question 18

What is saturation water vapour pressure?

Answer 18

Total pressure exerted by water vapour in water-saturated air (100% humidity)

Question 19

Can cold or warm air hold more water?

Answer 19

Warm

Question 20

What are the components of water potential?

Answer 20

ψ = ψ⁰ (water potential of pure water at 1 atm) + ψgravity + ψsolute (osmotic pressure) + ψhumidity + ψmatric (pull through adhesion) + ψpressure

Question 21

Where is water potential highest in a tree?

Answer 21

•Soil (highest)
•Roots (medium-high)
•Trunk (low-moderate)
•Canopy (low)

ψ becomes more negative as height increases, can pull water up and resist gravity

Question 22

What are the main methods of water acquisition for terrestrial animals?

Answer 22

Food and drinking

Question 23

What are the main methods of water conservation for terrestrial animals?

Answer 23

•Thick, waxy exoskeleton (evaporation)
•Storing water in the body
•Conserving urine, sweat, feces (secretion)
•Behavioural adaptations (e.g. burrows with cooler climate, lower transpiration)

Question 24

What are the main methods of water conservation for terrestrial plants?

Answer 24

•Wilting (reduce surface area, reduce transpiration)
•Drop in turgor pressure