Biology 205Ecology and Adaptation

Lecture 6:Water relations

Dr. Erik D. Davenport

Learning Outcomes

Water Availability – what determines it? Water Content In the

– Water content in air – humidity– Water content in water -- osmosis

Water Regulation on Land– Water Acquisition and conservation by Plants and

Animals on the Land Water and Salt Balance in Aquatic

Environments

Water availability

Water Concentration

Water is not pure in the environments.

There are many substrates that dissolve into water

and dilute water (less water concentration).

Water availability

What determine whether an organism tends to lose water or gain water from the environment?

The tendency of water to move down water concentrations, Water will move from high water concentration place to low water concentration

place.

Water content of Air

The water in the air (water content of air) is mostly from evaporation

Evaporation accounts for much of water lost by terrestrial organisms.

How is the water content of air measured?

The quantity of water vapor in the air is expressed conveniently in relative terms:

Relative humidity = (x 100)

Water vapor density is measured as the amount of water vapor per unit volume of air (how much water in the air).

Saturation water vapor density is measured as the quantity of water vapor air can potentially hold (how much water the air can hold).

Temperature strongly influence the relative humidity -- Warm air hold more water vapor than cold air!!!!

density or water vapSaturationdensityr water vapo

Relative Humidity

Which color represents water vapor density?

Which color represents saturation water vapor density?

True or False?

If the water content (water vapor density) in the air is constant. Increasing of the air temperature will cause the increase of relative humidity.

This statement is True or False?

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Relative humidity and evaporative water lossFigure 5.3

5-3    

Low relative humidityStronger evaporation

High relative humidityweak evaporation

Water movement in the aquatic environments

Sounds silly…. However, in aquatic environment, water also moves

down a concentration gradients. The salt in the water dilutes the water. From this perspective, water is more concentrated in

freshwater than sea water. The relative concentration of water strongly influence

the biology of the organisms live in them.

Water osmosis

The fluids in the body of organisms contain water and solutes (salt, inorganic ions and amino acids.)

They are separated from the external environment by a permeable membrane.

If there is a water concentration gradients: The water will move down the concentration

gradient, this water movement is called diffusion, also called osmosis.

Three kinds of aquatic organisms

Isosmotic organisms: the organisms with body fluids containing the same concentration of water as the external environments.

Hypoosmotic organisms: organisms with body fluids containing high concentration of water than external environment. Water move out from the body.

Hyperosmotic organisms: organisms with body fluids containing a lower water concentration than the external medium. And water move into the body.

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Isosmotic, hyperosmotic, and hypoosmotic aquatic organismsFigure 5.4

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Water movement between plant and soils

Water moving from the soil through aplant and into atmosphere flows down a gradient of water potential

(still water concentration)

Water regulation on the land

Terrestrial plants and animals regulate their internal water by balancing water acquisition

against water loss

Potential water lose:– Evaporation– Reduce access to replacement of water

Water regulation by terrestrial animals

Water within the body is a function of: Water gain:

– Water taken by drinking– Water taken in with food– Water absorb from the air

Water loss:– Water lost by evaporation– Water lost with various secretions and excretions in

including urine, mucus, and feces.

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Water gains/losses by terrestrial plants and animalsFigure 5.8

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Water acquisition by animals

most terrestrial animals satisfy their need for water by drinking or taking water in with food. However, under water limiting environments, they have evolved adaptation for living in arid environments.– Behavioral activities– Metabolic water (metabolize the carbohydrates,

proteins to produce the water)

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Fog harvesting by desert beetleFigure 5.9

5-9    

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Water balance in kangaroo ratFigure 5.11

5-11     Source: Schmidt-Nielsen 1964

Water acquisition by plants

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

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Desert living approaches in dissimilar organismsFigure 5.21

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Dissimilar Organisms with Similar Approaches to Desert Life

Camels– Can withstand water loss up to 20%.

Face into sun to reduce exposure. Thick hair: Increased body temperature lowers heat

gradient. Saguaro Cactus

– Trunk / arms act as water storage organs.– Dense network of shallow roots.– Reduces evaporative loss.

Water and salt balance in aquatic environments

Marine and freshwater organisms use complementary mechanisms for water and salt regulation.

Most marine invertebrates maintain an internal concentration of solute equivalent to that in the seawater around them. (isosmotic organisms)

Sharks, skates generally elevate the concentration of solutes in their blood to levels slight hyperosmotic to seawater. So they slowly gain water through osmosis, and had to excrete excess water through urine.

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Osmoregulation by sharksFigure 5.27

5-24    

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Osmoregulation by marine fish and mosquitoesFigure 5.28

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In contrast to most marine invertebrates and sharks, marine bony fish have body fluids that are strongly hypoosmotic (less salts) to the surrounding medium.

They will lose the water to the environments. Marine bony fish make up this by drinking. However, they have the specialized cell at the

gill to excrete the excess salts to the surrounding seawater.

Other Marine fishes -- Marine bony fish

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Osmoregulation by freshwater fish and mosquitoesFigure 5.29

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Freshwater fish and invertebrates

Freshwater fish and invertebrates are hyperosmotic They have body fluids that contains more salts and

less water than the surrounding medium. Water diffuse inwards and salt diffuse outward

across their gills. Excrete excess internal water as large quantities of

dilute urine. They use the specialized cells at gills to absorb the

salt.