Abiotic factors: water

Image that the salt flats of Utah pictured were once sitting below an inland sea. With changes in rising mountains and subsequent climate changes, the aquatic organisms were rapidly replaced by those that could survive life without practically any water. Reptiles replaced fish, dry shrubs, beds of algae.

Before we go into adaptations of organisms that live either in or alternatively with little water. let's review the incredible properties of H2O
I. Properties of water:
Water is the solvent, the medium and the participant in most of the chemical reactions occurring in our environment.

Although a water molecule in itself is quite simple, made up of two hydrogen and one oxygen it is its' architecture of these units taken together which produces a matrix with incredible properties

A. Water can store tremendous quantities of heat. One must add or remove a large amount of heat energy to change the temperature of water. Energy applied to water goes into breaking hydrogen bonds and not into raising the kinetic energy (T) of the molecules

Specific heat of water : the energy required to raise the temperature of water 1C is 1 calorie. Water has a high specific heat
Biological implications?

  • Contrast the environment of aquatic vs. terrestrial organisms: which is a more stable environment?
  • Contrast the environmental stress of living in small vs. large water bodies------are there seasons in large bodies of water?
  • Differences in temperature between lakes and rivers and the surrounding air may have a variety of effects. For example, local fog or mist is likely to occur if a lake cools the surrounding air enough to cause saturation; consequently small water droplets are suspended in the air
    • Large bodies of water, such as the oceans or the Great Lakes, have a profound influence on climate. They are the world's great heat reservoirs and heat exchangers and the source of much of the moisture that falls as rain and snow over adjacent land masses.
    • When water is colder than the air, precipitation is curbed, winds are reduced, and fog banks are formed.

    Heat of melting: the energy required to melt ice is even higher; to create 1 gm of water from ice requires 80 calories of energy. This is the same amount of energy it takes to raise water from 0 to 80C. Why?
    Biological implications? how does this protect aquatic organisms?

    Heat of vaporization: to evaporate 1 gram of water requires 597 calories of energy at 0 C and 536 calories at 100C
    Biological implications? the lizard...your body. If this value were substantially less, you would need to loss much more water to cool down. If so, what would be the limits on organisms who live in drier climates?

    B. Thermal conductivity: flux of heat through 1 cm2

    • is .006 at 40C
    • is .02 at 0C

    Biological relevancy- water conducts heat 20x faster than air.
    Why? water is denser than air by a factor 800 Given this, what is the best way to facilitate heat gain or loss in a body? how would this impact the ambient temperature of the environment of aquatic vs terrestrial creatures?

    C. Water expands upon freezing - this is critical in lakes and ponds. Could fish survive if ice sunk?
    D. Water has an immense capacity to dissolve organic compounds

    A drop of rain water falling through the air dissolves atmospheric gases, often cleansing the skies. When rain reaches the earth, it affects the quality of the land, lakes and rivers through its additions - we know of acid rain and its impacts...

    E. Due to water's cohesiveness ( attraction of water molecules to each other) bodies of water have surface tension. This may act as a barrier or support for individuals sitting on or moving through water-air surfaces. This cohesiveness is critical for water movement in plants.

    Surface tension is a measure of the strength of the water's surface film. The attraction between the water molecules creates a strong film, which among other common liquids is only surpassed by that of mercury.

    • This surface tension permits water to hold up substances heavier and denser than itself. A steel needle carefully placed on the surface of a glass of water will float. Some aquatic insects such as the water strider rely on surface tension to walk on water.

    Surface tension is essential for the transfer of energy from wind to water to create waves which permit rapid oxygen diffusion in lakes and seas.

    G. Viscosity, a property of hydrogen bonding, is high in water. Not only does it cause problems in terms of eddy and laminar viscosity ( see text) but also as it is so high, forms a frictional resistance to objects that must move through water. This has a major impact on the way aquatic organisms are shaped and whether they are passive or active movers in water.

    Movement of organisms through water ( or air):

    Aquatic organisms can decide to be:

    • sessile ( nonmotile- no energy strategy)
    • passive or floaters, a low energy strategy or
    • active swimmers, a high energy strategy.

    What are the constraints?

    For a floater: Stokes Law states

    Velocity of free fall ( sinking rate) = [ K * r2 * (p1 - p2)] / v
    where

    K is the constant determined by shape where it may be tight or expansive; some organisms go through cyclomorphosis where they will change shape expanding in warmer times with translucent projections

    r is the radius or size: as r increases the organism will begin to sink so it must remain small in order to float - however must consider the consequences of being small in terms of temperature, metabolism etc.

    p1 or density of the falling object: as p1 increases it will sink, so to float its value must approach 1, the density of water. It can drop p1 by including fats or oil droplets or by including air bladders ( as in shells which trap air or specific bladders which can hold gases).

    p2 refers to the density of the medium itself:

    • air: 1.3 x10-3
    • water = 1
    • glycerin = 1.26

    v refers to the viscosity of the medium i.e.. resistance of a liquid to flowing over itself.

    • air = 1.8 x 10-4
    • water = 0.01
    • glycerin = 15

    Since water is so viscous relative to air, small organisms can stay afloat by modifying their shape and density.

 

TO be a swimmer, that is to move forward in a fluid, you must be able to overcome drag ( which acts against the front of the object)

Here another predicitve equation is involved, the Reynolds number where:

Reynolds # = [p2 * s * length of object] / v

where p2 is the density of water = 1, and s = speed of the fluid relative to the object and v is the viscosity as above ( water = .01).

If R = 1 or less you have a situation where the fluid feels viscous and you have high drag -> felt by small objects like diatoms, zooplankton with low speeds and short lengths so it may be better to be a floater or passive

If R is high, 1000+ you feel primarily a pressure drag due to the area of the organism contacting the fluid. You must be either big & fast or slender and stream lined to compensate for the the drag.

 

Next page 2 general biological considerations

Next page 3 on animal adaptations

Next page 4 on plant adaptations