Question

Differentiate between excretion and osmoregulation. Which hormonal factor is responsible for drinking of water in human beings?

Answer 1

OriginalAlphabeticalOsmoregulationprocess by which animals control solute concentrations and balance water gain and lossExcretionprocess that rids the body of nitrogenous metabolites and other metabolic waste productsRegulating the chemical composition of body fluids depends on:balancing the uptake and loss of water and solutesOsmoregulation is based on thecontrolled movement of solutes between internal fluids and external environment. Solute movement, in turn, influences water movement (osmosis)All animals face a common need:balance water uptake and lossremember turgid and flaccid cells:too much intake of water--cells burst
substantial loss--flaccid, cell shrivelsWater enters and leaves cells by:osmosisOsmosismovement of water across a selectively permeable membraneOsmolaritysolute concentration; expressed as molarityIsoosmotictwo solutions (separated by selectively permeable membrane) with same osmolarity (solute concentration)movement of water in isoosmotic solutions:no net movement because they diffuse at equal ratesHyperosmoticsolution with greater osmolarity (free water flows into)Hypoosmoticsolution with lower osmolarity (free water flows out)An animal can maintain water balance in two ways:osmoconformer or osmoregulatorOsmoconformerto be isoosmotic with its surroundings (environmentally dependent)Osmoregulatorto control internal osmolarity independent of its surroundings (environmentally independent)All osmoconformers are:marine animalsNo energy cost for osmoconformers because:their internal osmolarity is the same as their environment. there is no tendency to gain or lose waterOsmoregulation enables animals:to live in environments (like freshwater and terrestrial) that are uninhabitable for osmoconformersFor an osmoregulator to survive in a hypoosomotic environment:they must discharge excess waterFor an osmoregulator to survive in a hyperosmotic environment:they must take in waterStenohaline:Animals that cannot tolerate changes in external osmolarityEuryhaline:Animals that can endure large fluctuations in external osmolarity (Ex. barnicles--constantly covered and uncovered by ocean tides)Marine osmoconformers:face challenge of transport of SPECIFIC solutes, this is facilitated by active transportMarine invertebrates/vertebrates that are osmoregulators:ocean can dehydrate. 
solution: water loss balance by drinking LARGE AMOUNTS of water