Outline • Water Availability • Water Content of Air • Water Movement in Aquatic Environments • Water Movement Between Soils and Plants • Water Regulation on Land • Water Acquisition by Animals • Water Acquisition by Plants • Water Conservation by Plants and Animals • Water and Salt Balance in Aquatic Environments
Water Availability • Water moves from greater to lesser concentration • Relative concentrations of water • In air: relative humidity • In water: osmolarity or salinity • Balance of water gain and loss impacts survival of organisms in a particular environment.
Evaporation – Loss of Water from Organism to Atmosphere • Important for terrestrial organisms • Provides cooling • Represents major loss of water. • Greatest in dry climates – water vapor in air less – where ‘humidity’ is lower • Concentration gradient greater • Cooling from evaporation greatest in dry climates.
Dry Environment: Great water pressure deficit: High saturated vapor pressure (air could hold a lot of water) Low actual vapor pressure Greater movement of water from organism to environment
Dew • Condensation of water on surfaces cooled by radiation of heat to atmosphere • Impacted by absolute humidity – amount of water vapor in atmosphere • Fog: Forms at dew point on nucleation sites, small particles • Important source of moisture in summer along California coast – some other dry environments
Water Movement in Aquatic Environments • Water moves down concentration gradient by diffusion. • Water is more concentrated in freshwater environments than in the oceans. • Aquatic organisms can be viewed as an aqueous solution bounded by a selectively permeable membrane floating in an another aqueous solution • Osmosis – special case of diffusion - water movement across a membrane.
Water concentration in solutions • Osmolarity: a measure of concentration of dissolved substances in water • Salinity: concentration of dissolved salts - salt water solution contains relatively less water than fresh water • That means ? • Water moves from area of less dissolved salts to more dissolved salts
Concentration of solutes and cells Hyperosmotic or Hypertonic – more dissolved substances outside cell – like a pickle water leaves the cell crenation Hypoosmotic or Hypotonic – less dissolved substances outside water enters the cell cell swells and bursts Isoosmotic or Isotonic – same concentration inside and out, the cell is at dynamic equilibrium
Organisms must maintain cellular/tissue osmolarity within narrow limits • Osmoregulation • Adapted to particular osmotic environment • Generally water moves in and out of cells freely • Salt movement is restricted due to charged nature of salt ions
Water and Creatures in Terrestrial Environments • Terrestrial organisms face (2) major challenges: • Evaporative loss to environment. • Reduced access to replacement water.
Water and Plants • Earliest plant lived in moist habitats • No means to transport water within structure • Required moisture film for reproductive processes • Later plants developed vascular system • Movement by transpiration
Water moves from soil to top of plant in unbroken stream • Transpiration provides the pull • Rate of transpiration is regulated by action of guard cells • > 90% of water taken in by roots is lost to the atmosphere • Adaptations include reduced leaf area, modifications to leaf surface
Dermal Tissue • The epidermis of a plant is often covered with a thick waxy layer called the cuticle • Guard cells • Paired cells with openings between them (stomata) • Allow gas exchange
Guard cells turgid Guard cells flaccid
Plant adaptations: • Root system development • Low growth habit (reduced wind exposure) • Hirsute leaves • Leaf coloration
Water Acquisition by Plants • Extent of plant root development often reflects differences in water availability. • Deeper roots often help plants in dry environments extract water from deep within the soil profile. • Park found supportive evidence via studies conducted on common Japanese grasses, Digitaria adscendens and Eleusine indica.
Water Regulation on Land - Animals • Wia= Wd + Wf + Wa - We - Ws • Wia= Animal’s internal water • Wd = Drinking • Wf = Food • Wa = Absorbed by air • We = Evaporation • Ws = Secretion / Excretion
Physiological Regulation of Tissue-Water Balance in Animals • Kidneys evolved to produce hypertonic uring in terrestrial organisms • Other mechanisms exist as well – eg. Certain sea birds
Osmoregulation in Animals • Osmoregulation is the regulation of the body’s osmotic (water and salt) composition • Adaptation to dry terrestrial habitats: produce hypertonic urine • Insects: Malpighian tubules Active transport ofK+, water is drawn osmotically, reabsorbtion in the hindgut • Vertebrates: Kidneys • Hydrostatic filtration (blood under pressure) • Selective reabsorption • Mammals, birds produce hypertonic urine
Marine birds (Procellarids) minimize water loss by excreting salt through specialized glands • Additional water is absorbed in the cloaca
Water Summary • Number of unique properties due to chemical nature • Concentration of water drops as percent salt in solution rises • Movement of water from greater to lesser concentrations occurs by specialized diffusion: osmosis • Development of various strategies to deal with water has lead to patterns of distribution of species of plants and animals