BSC 385 - EcologyLecture 8

Water Relations - Chapter 5

Water movement in aquatic organisms

Water movement in plants

Water acquisition and utilization in terrestrial plants and animals

Water balance in aquatic animals

Water Movement in Aquatic Environment - definition of terms with respect to

organisms

• Isosmotic: Body fluids and external fluid are at the same concentration.

• Hypoosmotic: Body fluids have a higher concentration of water and a lower concentration of solute than the external environment.

• Hyperosmotic: Body fluids have a lower concentration of water and a higher concentration of solute than the external environment.

• Note that an inverse relationship exists between water and solutes

Effects of solute concentration on cells - note that only the water moves

Isosmotic Hyperosmotic Hypoosmotic

Shading depicts solute concentration - what is the relationshipwith respect to water concentration?

Effects of solute concentration on multicellular organisms - note that water and solute can move - the solute can leak around the junctions of the cells that make up tissues (but not cell membranes!)

Figure 5.4

Osmotic condition can be related to environment or organisms

environmentorganism

Relative concentrations

[environment solute] < [organism solute][organism solute] > [environment solute]

Result

H2O flows into organism H2O flows into organism

Hypo <Hyper >

BSC 385 - EcologyLecture 8

Water Relations - Chapter 5

Water movement in aquatic organisms

Water movement in plants

Water acquisition and utilization in terrestrial plants and animals

Water balance in aquatic animals

Water Movement Between Soils and PlantsWater moving between soil and plants flows down a water concentration gradient

This gradient is described in the book as “water potential” or (PSI; sigh). This complex term is used because vpd, osmosis and the laws governing movement of water through small places all play a roleH H

O

H HO

H HO

H HO

H HOH H

O

H HO

H HO

H HO

H HO

H HO

Water potential

Addition of a solute to water causes < 0

Matric Forces: Water’s tendency to adhere to solid surfaces. In small places (soil, plant cells) these can be very strong and causes negative water potentials

Evaporation from leaves creates a negative pressure that cause negative water potentials - all water vapor pressures less than saturation water vapor pressure cause a negative water potential

of pure water is set to zero, any change causes become negative. For example:

Cartoon of the microenvironments of a soil crumb

Water potential of a plant-soil system

soil = matric + solute while

plant = matric + solute + pressure

Figure 5.5

EvaporationThe soil matrix is as depicted in the previous slide and the plant matrix is the xylem (plus some effects from the phloem)

Summary of forces moving water from soil through plant

Figure 5.6solute

BSC 385 - EcologyLecture 8

Water Relations - Chapter 5

Water movement in aquatic organisms

Water movement in plants

Water acquisition and utilization in terrestrial plants and animals

Water balance in aquatic animals

Water Regulation on Land - Animals

• Wia= Wd + Wf + Wa - We - Ws

• Wia= Animal’s internal water

• Wd = Water gained from drinking

• Wf = Water gained from food (includes metabolic water)

• Wa = Absorbed from air

• We = Evaporation

• Ws = Secretion / Excretion

Water Regulation on Land - Plants

• Wip= Wr + Wa - Wt - Ws

• Wip= Plant’s internal water

• Wr = Absorbed by roots

• Wa = Absorbed from air

• Wt = Transpiration

• Ws = Secretions

Comparison of the main routes of water gain and loss for terrestrial plants and animals

Figure 5.7

Animals in dry climates must either acquire significant water …

Figure 5.8

The desert beetle Onymacris

Water budget for Onymacris(total water usage 49.9 g H2O g-1 body weight)

Figure 5.9

… or conserve(Kangaroo rat - 60 g H2O per day (total); average weight 40-50 g)

Figure 5.10

It is the same for plant, either acquire significant water or conserve

observation Laboratory experiment

Figures 5.11 & 5.12

The effect of having dense, deep penetrating roots is having sufficient water to maintain

leaf water potential

Figure 5.13

Figure 5.14 + 5.15

Water conservation is most often seen in organisms from dry environments

Figure 5.16

Mechanisms involve reduction of water loss(one example is evolving a waterproof cuticle)

Changes in conservation measures can occur among populations within a species

Figure 5.17

Reducing leaf area is one mechanism involved with the reduction of water

loss

Figures 5.18 & 5.19

Other are behavior, storing water, insulation and physiological adaptations to

high body heat

Figure 5.20

Figure 5.21

Scorpions show behaviors that conserve water, waterproofing and a low metabolism (reduces

need for respiration, thus reducing evaporation) while …

… cicada shows behaviors that conserve water and evaporative cooling!

Figure 5.22, 5.23 & 5.24

How can a desert insect afford evaporative cooling?

Figure 5.25

Using its food source’s ability to tap into water deep underground

BSC 385 - EcologyLecture 8

Water Relations - Chapter 5

Water movement in aquatic organisms

Water movement in plants

Water acquisition and utilization in terrestrial plants and animals

Water balance in aquatic animals

Water regulation in aquatic organisms

Marine environments - many invertebrates are isosmotic

Sharks (and relatives) slightly hyperosmotic relative to environment (although salt is ~1/3 total solute)

Figure 5.26

Wi = Wd - Ws ± Wo

Saltwater bony fishes and saltwater mosquitoes are hypoosmotic relative to the

environment

Figure 5.27

Freshwater bony fishes and freshwater mosquitoes are hyperosmotic relative to the

environment

Figure 5.28

Investigating the evidence - Sample size or the number of samples needed to accurately

characterize a population