Water Regulati

on on Land

6.2

Allocation of

Organisms

???

Major Environmental

Challenges1.Massive losses of water due to evaporation.

2.Reduced access to water replacement.

In order to meet such Environmental Challenges…

Terrestrial Organisms regulate their internal water intake.

Howd

oorganisms theirintern

alwaterintak

e ?regulate

Internal WaterRegulation of Animals ()𝐖 𝐢𝐚=𝐖𝐝+𝐖 𝐟+𝐖𝐚−𝐖𝐞−𝐖𝐬

WATER SOURCES:Wd = DrinkingWf = FoodWa = Absorbed from the air

AVENUES OF WATER LOSS:We = water lost by EvaporationWs = Secretion / Excretion

𝐖𝐞𝐖𝐚

𝐖𝐝𝐖𝐟𝐖𝐬

(water acquisition through absorption)

(water acquisition through drinking &

food)

(water loss through evaporation)

(water loss through secretions)

Internal WaterRegulation of Plants ()𝐖 𝐢𝐩=𝐖 𝐫+𝐖𝐚−𝐖 𝐭−𝐖 𝐬WATER SOURCES:

Wr = Water taken by the rootsWa = Water absorbed from the

airAVENUES OF WATER LOSS:

Wt = Water lost by transpirationWs = Water lost by secretions

𝐖𝐬

𝐖𝐚

𝐖𝐭

𝐖𝐫

(water acquisition from moist air)

(water loss through transpiration) (water loss through

secretions such as nectar)

(water acquisition by roots)

Water Acquisiti

on by

Animals

Their need of acquiring water depends upon their environment.

Moist Environment

(forest)

Arid Environment

(desert)

Acquisition of Water in moist climates through…

Drinking

Food

Air

Acquisition of Water in dry climates through…

Metabolic Water

Air Moisture

Some desert animals acquire water in unusual ways.

(Lepidochora)

(Onymacris Unguicularis

)

Lepidochora

Collects moisture by

digging trenches on the face of sand dunes to condense and

concentrate fog.

Onymacris Unguicularis

Collects moisture by orienting its

abdomen upward.

Other MechanismWATER can also be gained via metabolism through oxidation of glucose:

C6H12O6 + 6O2 6CO2 + 6H2O

METABOLIC WATER refers to the water released during cellular respiration.

Kangaroo Rat

In every 100 g of barley that it eats, it gains 60 ml of water. 6 mL of it is the absorbed water that can be driven off by drying while the remaining 54 mL of water is released as the rat metabolizes the carbohydrates, fats, and proteins in the grain.

Water Acquisiti

on by

Plants

Plants acquire water through…

ROOTS

Plants in dry climates grow more roots than do plants in moist climates.

Moist Sites Dry Sites

In dry climates, plant roots tend to grow deeper in the soil and to constitute a greater proportion of biomass.

In deserts and semiarid grasslands, roots may account for up to 90% of total plant biomass while in coniferous forests, roots only constitute 25%.

Root Development

R. Coupland and R. Johnson (1965) compared the rooting characteristics of Artemesia frigida in the temperate grasslands of western Canada.

Soil moisture influences the extent of root development by Artemesia frigida.

OBSERVATION:Microclimate affects

root development.Deeper roots often

help plants from dry environment extract water from deep w/in soil.

Y.M. PARK studied two common grasses that grow in Japan

Digitaria adscendens Eleusine indica

Grows on coastal sand dunes

Does not grow on coastal sand dunes

Park’s Investigation on Root Growth

Park planted both grasses into tubes filled with sand from coastal dunes and kept them unwatered for 19 days.

He noticed that the root mass of Digitaria increased almost sevenfold over the 19 days of no watering, while the roots of Eleusine increased about threefold.

Leaf Water Potential

If a plant has lower root mass, its leaf water potential decreases.

If a plant has higher root mass, it maintains a higher leaf water potential.

Water Conservati

on by Plants & Animals

WaterproofingMany terrestrial

plants and animals cover themselves with a fairly waterproof “hide” impregnated with a variety of waterproofing waxes.

Neil Hadely & Thomas Shultz studied the waterproofing of 2 tiger beetles in different microclimates.

Cicendela oregona Cicendela obsoleta

(active in spring & fall)

(active in summer)

Waterproofing Cuticlesof Tiger Beetles

• The waterproofing cuticles of terrestrial insects are provided by hydrocarbons : Lipids & Waxes

“The lesser the hydrocarbon content, it is less waterproofed. The greater the hydrocarbon content, it is more waterproofed.”

Other Water-Conserving Mechanisms of Animals

Producing concentrated urine or feces with low water content

Condensing and reclaiming the water vapor in breath

Restricting activities to times and places that decrease water loss.

Plant Water Conservation

“How much water a plant can conserve depends in part on its leaf relative to its root area or length.”

Plants with more leaf surface per length of root lose more water.

Plants reduce leaf area by dropping of leaves.

Ocotillo

(produces leaves in times of rain)

(reduces leaf area to zero in times of

drought)

Temporary Wilting

It is a water-conserving mechanism that reduces leaf area exposed to solar radiation by 55% and leaf temperature up to 4⁰ to 5⁰C.

It decreases the rate of transpiration by 30% to 50%, which is a substantial water savings.

After 8 minutes, wilting reduces the surface area.

Other Plant Adaptations that Conserve Water

• Plants with thick leaves• Few stomata on leaves• Structures on the stomata that blocks

the movement of water• Dormancy during times when moisture

unavailable• Alternative water-conserving for

photosynthesis.