Water Balance in Aquatic Organisms Flashcards
(30 cards)
Passive diffusion
- Passive movement of material from an area of high concentration to an area of low concentration of the same substance (along a concentration gradient)
Osmoregulation/Osmotic cocentration/Osmolarity
- Quantity of solute particles per litre of solution
- Measured in osmoles of solute per litre (osmol/L ir mosmol/L)
- Seawater: 1000 mosm/L
- Freshwater: ~0.5-10mOsmol/L
- Sharks: 1000-1050 mosm/L
- Human blood: 300 mosm/L
Osmosis
- Passive diffusion of water across a semi-permeable membrane
Isotonic
- environment has same water concentration as cell
Hypotonic
- too much water - cells gain too much water -explode
Hypertonic
- too little water - cells lose water ad shrivel up
Isosmotic
- internal concentrations of water and salt equal concentrations in the environment
- Salt and water diffuse at approximately equal rates in and out
Hyperosmotic
- Lower internal concentration of water and higher internal concentration of salt compared to environment
- Salts diffuse out at higher rate
- Water diffuses in at higher rate
- Higher osmolarity inside because more solutes than outside
Hypoosmotic
- Higher internal concentration of water, lower internal concentration of salt compared to environment
- salts diffuse in at higher rate
- water diffuses out at a higher rate
- Lower osmolarity inside because there are less solutes inside
Osmoregulation
- Regulation of water and solute concentrations
Challenges for marine, freshwater and terrestrial species in osmoregulation
- Marine: how to not become dehydrated (limit water loss)
- Freshwater: how to not become overhydrated (limit water gain)
- Terrestrial: how to not become dehydrated
Why is water necessary?
Transport
Metabolism
Excretion
Excretion
- Eliminating waste
- Must be considered when discussing osmoregulation because water and solutes are eliminated
- Some occurs through gills in aquatic organisms
- most occurs through the excretory system
Three different nitrogenous bi-products
- Ammonia; very toxic, freshwater and some marine organisms which excrete is across gills and urine
- Urea; produced in liver and kidneys from ammonia, less toxic, terrestrial vertebrates except birds and reptiles, cartilaginous fish
- Uric Acid; excreted as paste (guano in birds), insects, birds and diapsids (crocodiles, snakes, turtles, lizards)
Kidneys
- Made up of nephrons
- Filtrates water and solutes (nitrogenous waste), pushed by blood pressure through a filter called glomerulus
- Reabsorbs water and solutes needed passively or actively
- Whatever left is excreted
Why is salt necessary?
- Sodium-Potassium pump
- Active transport by Na/K ATPase pump, an enzyme in the plasma membrane that pumps Na out and K into the cell, moving ions across a steep concentration gradient
- Powers cellular activities like signaling in neurons
Stenohaline vs. Euryhaline
o Stenohaline; function in a small range of osmolarity
o Euryhaline; survive much larger fluctuations in external osmolarity (they can adjust themselves)
- Ex: barnacles, muscles, bass and some salmon
Time frame of adaptations to different salt concentrations
o Genetic adaptation: conditions change over evolutionary time
- Ex: freshwater fish evolve from marine fish
o Phenotypic plasticity: conditions change from one generation to the next
- Ex: freshwater stickleback fish grown in salt water have longer jaws and tend to be thinner
o Acclimatization/acclimation: conditions change at least once in lifetimes
- Ex: salmon and other diadromous fish
o Regulation: conditions fluctuate regularly
- Ex: intertidal zones
Osmoconformer
- Isoosmotic with environment; same internal conditions as it’s environment
- Generally marine animals (intertidal)
- Constant exchange, but no net gain or lost
- Tend to live in environment where osmolarity is fairly constant
- Excretion of salt ions and water is done in a minimal way; small amount of urine form kidney
Osmoregulators
- Controls independent osmolarity to it’s environment
- Freshwater, marine or terrestrial usually
- Survive changes in external osmolarity
- In freshwater, deal with an inflow of water from environment and in salt water resists loss of water from tissue
- Excretion of salt ions and large amounts of water in dilute urine from kidneys (freshwater)
Marine: Algae and invertebrates
o Isosmotic
o Conformers
o Environment: constant, with reasonable osmotic concentration (OC)
o Ex: hagfish, slime eel (skull but not vertebral column or jaw)
Marine: Cartilaginous fish, Crab, eating frog, Coelacanth
o Slightly hyperosmotic (internal environment has a higher concentration of solutes BUT less salty – i.e salt isn’t the solute that is higher)
o Conformers (generally)
o Fish: environment constant with reasonable OC
o Crab-eating frog: the only frog that can tolerate salt water: lives in freshwater but hunts in brackish or salt water
o How do these animals maintain such high solute concentrations?
- Counteracting solute strategy
• Retain urea in blood to increase Osmotic Concentration (urea is a waste product of metabolism; most animals excrete urea through urine and across gills)
• Urea is toxic, it degrades proteins
• To counteract urea, increase TMAO, a protein stabilizer that counteracts the effects of urea
o Shark: slightly higher osmolarity than seawater so water diffuses into the shark; BUT high osmolarity due to urea, sodium concentration is slightly lower in the shark than in the seawater, so sodium diffuses into the shark
o Excretion of nitrogen waste
- Cartilaginous fish
• Tend to gain water
• Absorbs water through osmosis
• Large amounts of dilute urine
• Excrete some urea
• Urea is produced in liver and mostly reabsorbed in kidneys
Marine bony fishes (teleost)
o Hypoosmotic to seawater (lower solute concentration to environment)
- Body OC ~1/3 that of seawater
- Tendency to lose water, mostly across the gills
o Osmoregulators; they maintain their osmolarity at 1/3 that of seawater
o How?
- Impermeable skin
- Drink seawater
- Active transport of salt out through gills (chloride cells)
- Urine scant, but isosmotic
• Highly concentrated especially relative to cartilaginous fish
o Excretion of nitrogenous waste
- Bony marine fish:
• Tend to lose water
• Drinks water
• Little urine, less concentrated than body fluid
• Some ammonia or urea
o Marine bony fish kidneys
- Reduced or no glomerulus to minimize water loss
- Rely on tubular secretion
• Active transport of waste into tubules for excretion
Marine and intertidal plants
o Seagrasses, generally near-shore o Osmoregulators o Special glands to excrete salts in the leaves o Accumulation of salts in roots - Lower osmotic pressure draws water in o Large vacuoles store Na+
