controlling the internal environment ii salt and water balance
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Controlling the Internal Environment II: Salt and water balance. Ammonia toxicity Urea Uric acid Osmoconformer Osmoregulator Passive transport Facilitated diffusion Active transport Uniport Antiport symport. Osmoregulation by an aquatic invertebrate Osmoregulation in marine fish

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keywords reading p 879 884
Ammonia toxicity

Urea

Uric acid

Osmoconformer

Osmoregulator

Passive transport

Facilitated diffusion

Active transport

Uniport

Antiport

symport

Osmoregulation by an aquatic invertebrate

Osmoregulation in marine fish

Osmoregulation in freshwater fish

Water loss on land

Permeable and impermeable body surfaces

Kangaroo rate water balance

anhydrobiosis

Keywords (reading p. 879-884)
the internal environment
The internal environment
  • In most animals, the majority of cells are bathed by internal fluids rather than the environment
  • This is advantageous since there can be control of substrates needed for metabolism
slide8
Good because reactions will work better and you don’t lose the products
  • Good because you can keep out molecules that you don’t want
  • Bad because there can be osmotic problems
  • Bad because hazardous by products can stay in the cell

Hazardous products

therefore the internal chemical environment is controlled
Therefore the internal chemical environment is controlled
  • A. Avoiding buildup of toxic chemicals
    • Dealing with ammonia
  • B. Osmoregulation - controlling internal solutes
hazardous products
Hazardous products
  • A major source of hazardous products is the production of nitrogenous wastes
  • Ammonia (NH3) is a small and very toxic molecule that is normal product of protein and amino acid breakdown
  • If you are an aquatic organism, ammonia can readily diffuse out of the body and this is not a problem
ammonia toxicity is a problem for terrestrial animals
Ammonia toxicity is a problem for terrestrial animals
  • Ammonia does not readily diffuse away into the air.
  • The strategy of terrestrial animals is to detoxify it then get rid of (excrete) it.
ammonia can be converted to urea which is 100 000 times less toxic
Ammonia can be converted to urea which is 100,000 times less toxic
  • Mammals, most amphibians, sharks, some body fishes
the drawback of using urea
The drawback of using urea
  • Takes energy to synthesize
  • Still need to use water to “flush it out”
some animals cannot afford to use water to excrete urea
Some animals cannot afford to use water to excrete urea
  • These animals use excrete uric acid instead
uric acid
Uric acid
  • Since uric acid is not very soluble in water, it can be excreted as a paste.
  • Less water is lost
  • Disadvantages:
    • Even more costly to synthesize.
    • Loss of carbon
who uses uric acid
Who uses uric acid?
  • Birds, insects, many reptiles, land snails
  • Related to water use, but also reproduction
  • Eggs - N wastes from embryo would accumulate around it if ammonia or urea are used. Uric acid precipitates out.
osmolarity
Osmolarity
  • Osmolarity = # of solutes per volume solution
  • Often expressed in moles (6.02 x 1023 atoms/molecules) per liter.
  • 1 mole of glucose = 1 mole of solute
  • 1 mole of NaCl = 2 moles of solute
osmotic problems
Osmotic problems
  • Humans have internal solute concentration (osmolarity) of 300 milliosmoles per liter (mosm/L)
  • The ocean is 1000 mosm/L
what would happen if your body surface is water permeable and you fall into the sea
Keep your internal concentrations the same as the environment (osmoconformer)

Regulate your internal concentrations (osmoregulator)

What would happen if your body surface is water permeable and you fall into the sea

1000 mosm/L

300 mosm/L

jellyfish in the ocean
Jellyfish in the ocean
  • Keep solutes at 1000 mosm/L no water loss or gain.
  • A relatively simple solution

1000 mosm/L

1000 mosm/L

jellyfish

life in freshwater hydra living in a pond
Life in freshwater - hydra living in a pond
  • Can the same strategy of matching the environmental osmolarity be used?

0 mosm/L

0 mosm/L

Green hydra

hydra living in a pond
Hydra living in a pond
  • If external osmolarity is very low like 0 mosm/L, hydra cannot maintain an internal osmolarity of 0 mosm/L
  • Why is this?
  • Consequently freshwater animals will most likely have a higher osmolarity than the environment.
what happens to freshwater organisms
What happens to freshwater organisms?
  • Water from the environment is continually entering tissues.
  • The diffusion gradient favors loss of solutes
  • Therefore there is a need to regulate solutes and water
two ways to deal with osmotic problems
Two ways to deal with osmotic problems
  • Keep your internal concentrations the same as the environment (osmoconformer)
  • Regulate your internal concentrations (osmoregulator)
solute regulation
Solute regulation
  • Transport solutes across the body surface
    • Note: even in the jellyfish example, there is ion regulation. Although the internal fluids have the same osmolarity as seawater, they do not have the same composition
passive transport diffusion
Passive transport: Diffusion
  • Works for lipid soluble molecules and gases
  • No good for most water soluble molecules and ions
passive transport facilitated diffusion
Passive transport: Facilitated diffusion
  • Generally used for ions, larger molecules, non-lipid soluble molecules.
  • Must be a gradient favoring diffusion
active transport
Active transport
  • Works for ions and molecules like glucose or amino acids
  • Can transport against a gradient.
  • Costs energy, usually ATP
in this diagram how might sodium get across the membrane
In this diagram, how might sodium get across the membrane?
  • A) diffusion
  • B) active transport
  • C) facilitated diffusion or active transport

Na+

Na+

Na+

Na+

in this diagram how might sodium get across the membrane34
In this diagram, how might sodium get across the membrane?
  • A) diffusion
  • B) active transport
  • C) facilitated diffusion or active transport

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

in this diagram how might sodium get across the membrane35
In this diagram, how might sodium get across the membrane?
  • A) diffusion
  • B) active transport
  • C) facilitated diffusion or active transport

Na+

Na+

Na+

Na+

- - - - - - - - - - - - -

+ + + + + + + + + +

Na+

Na+

in this diagram how might steroids get across the membrane
In this diagram, how might steroids get across the membrane?
  • A) diffusion
  • B) active transport
  • C) facilitated diffusion
  • D) all of the above

steroid

steroid

steroid

steroid

steroid

in this diagram how might steroids get across the membrane37
In this diagram, how might steroids get across the membrane?
  • A) diffusion
  • B) active transport
  • C) facilitated diffusion
  • D) all of the above

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

steroid

what type of active transport is this
What type of active transport is this?
  • A) uniport
  • B) symport
  • C) antiport

K+

what type of active transport is this40
What type of active transport is this?
  • A) uniport
  • B) symport
  • C) antiport

K+

Sodium potassium ATPase

Na+

what type of active transport is this41
What type of active transport is this?

Cl-

  • A) uniport
  • B) symport
  • C) antiport

K+

responses of soft bodied invertebrates to changes in salinity
Responses of soft-bodied invertebrates to changes in salinity
  • Marine invertebrates can often be exposed to salinity changes (e.g., tidepool drying out, estuaries)
  • If salts enter the body, pump them out using transporters
  • If salts are leaving body, take them up from the environment using transporters
  • Or just let your internal concentrations follow changes in the environment
dumping pumping amino acids
Dumping/pumping amino acids
  • One way to respond while keeping internal ion concentrations the same is to pump amino acids out.
  • Often used by bivalves living in estuaries
    • Clams, oysters, mussels
estuary high tide
Estuary - high tide

1000 mosm/L

1000 mosm/L

aa

aa

aa

aa

aa

aa

aa

aa

estuary low tide
Estuary - low tide

500 mosm/L

1000 mosm/L

aa

aa

aa

aa

aa

aa

aa

aa

estuary low tide46
Estuary - low tide

500 mosm/L

500 mosm/L

aa

aa

aa

aa

aa

aa

aa

aa

advantages of amino acid osmoregulation
Advantages of amino acid osmoregulation
  • Changing amino acid concentrations is less disruptive on internal processes (enzyme function).
  • Costs: pumping amino acids (can involve ATP), loss of amino acids (carbon and nitrogen)
osmoregulation in other aquatic organisms
Osmoregulation in other aquatic organisms
  • Example: fishes maintain internal concentration of solutes
  • Body volume does not change
  • Involves energetic cost of active transport
  • In bony fishes this can be 5% of metabolic rate
marine fishes50
Marine fishes
  • Problem: lower internal osmolarity than seawater
  • Water will leave body, sea salts will go in
  • Solution: Fish drink large amounts of seawater, then transport out ions (Na+, Cl-) at their gill surface or in urine (Ca++, Mg++, SO4--).
freshwater fishes52
Freshwater fishes
  • The opposite situation: tendency to lose solutes and gain water
  • Solutions: take up salts in food and by active transport across gills
  • Eliminate water via copious dilute urine production
water balance on land
Water balance on land
  • Unlike aquatic animals, terrestrial animals don’t lose or gain water by osmosis
  • However, water loss or solute gain can be a major problem
  • Cells are maintained at around 300 mosm/L
  • Humans die if they lose 12% of their body water
why not just prohibit water loss
Why not just prohibit water loss?
  • Impermeable surfaces: waxy exoskeleton (insects), shells of land snails, thick skin (vertebrates).
  • Not all surfaces can be impermeable because gas exchange must also occur.
  • Evaporation across respiratory surfaces is only one of the two main causes of water loss
    • The other is urine production
drinking
Drinking
  • Replenishes water that is lost
  • Water can also be gained by moist foods
  • What if there is no water to drink?
desert kangaroo rat does not drink
Desert kangaroo rat does not drink
  • Don’t lose much water
    • Special nasal passages
    • Urine doesn’t contain much water
  • Recovers almost all of the water that results from cellular respiration
slide58
Note comparison is relative not absolute
  • Greater proportion of water intake of K rat is from metabolism
anhydrobiosis tardigrades water bears
Anhydrobiosis: Tardigrades (water bears)
  • Can lose 95% of their body water
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