Lecture 17: Water Balance II (Multicellular Organisms) (Water Balance of…
Lecture 17: Water Balance II (Multicellular Organisms)
Osmoregulator: must discharge excess water in hypoosmotic environment or take up water to offset loss in hyperosmotic environment.
Marine bony fishes, hypoosmic to seawater, drink saltwater and transport Cl- actively & Na+ passively out of their body- produce very little urine.
Land animals lose water through evaporation and waste removal
Osmoconformers have the salinity of their environment
Hemolymph in open circulatory systems & interstitial fluid in closed circulatory systems
Animals control salinity of cells by maintaining salinity of these fluids.
Transport epithelia transport solutes in controlled amounts in specific directions
Cells of epithelium are joined by tight junctions
Examples: Salt-secreting glands of some marine birds; in gills of freshwater fish, salts pumped into blood
Water Balance of Plants
Shoot system consists of stems & leaves; photosynthesis occurs here
Root system anchors plant, provides water & nutrients
Dermal Tissue System: Outer covering of plant
Ground Tissue System: Carries out photosynthesis, stores products of this, helps support plant.
Vascular Tissue System: Conducts water & solutes throughout the plant
Xylem: distributes water taken up by roots
Tracheary elements &, in flowering plants, vessel elements
Uses negative pressure
Cohesion-Tension Theory: Relies on polarity of water molecule - Water lost by transpiration "pulls" water up through plant against gravity
Gas bubbles can break continuous column of water- can from in very hot or very cold conditions (Cavitation)
Plants can deal with this by rerouting water
Phloem: Transports carbohydrates in solution away from leaves (site of production)
Sieve tube elements
Water absorption from soil
As soil particles dry, water moves first from center of largest spaces between particles
Root hairs make contact with soil particles & amplify surface area for absorption by plant.
Stomata perform gas exchange, but water is lost through them as well- because of this, guard cells close at night
Cutin is waxy covering on leaves that prevents water diffusion
When swollen, guard cells are open due to ions still inside cells