MB 44.1

What is an osmoregulator?

A osmoregulator is an animal that controls its internal osmolarity independent of the external environment.

Why does the urea not damage the shark's tissue?

A shark's body fluids also contain trimethylamine oxide (TMAO), an organic molecule that protects proteins from damage by urea.

What will all animals face?

All animals - regardless of habitat or type of waste produced- face the same need to balance water uptake and loss.

How does the cod, an osmoregulator survive in the strongly dehydrating environment of the ocean?

Cod are constantly losing water by osmosis. Such fishes balance the water loss by drinking large amounts of sea water.

What seems to be the mechanism behind anhydrobiosis?

Desiccated individuals contain large amounts of sugar. In particular, a disaccharide called trehalose seems to protect the cells by replacing the water that is normally associated with proteins and membrane lipids. Many insects that survive freezing in the winter also use trehalose as a membrane protectant, as do some plants resistant to desiccation.

What does it mean for an animal to be euryhaline?

Euryhaline animals can survive large fluctuations in external osmolarity. Euryhaline osmoconformers include barnacles and mussels. Examples of euryhaline osmoregulators are striped bass and the various species of salmon.

Define dessication.

Extreme dehydration.

What does it mean for two solutions to be isoosmotic?

If two solutions separated by a selectively permeable membrane have the same osmolarity, they are said to be isoosmotic. Water molecules continually cross the membrane, but under these conditions they do so at equal rates in both directions. Thus is there no net movement of water by osmosis between isoosmotic solutions.

What happens to an animal if water uptake is excessive? or if water is loss?

If water uptake is excessive, animal cells swell and burst; if water loss is susbstantial, they shrivel and die.

How does an osmoregulator survive in a hyperosmotic environment?

In a hyperosmotic environment, an osmoregulator must instead take in water to offset osmotic loss. Osmoregulation also allows many marine animals to maintain an internal osmolarity different from that of seawater.

How does a cod rid itself of salts?

In ridding itself of salts, the cod makes use of both its gills and kidneys. In the gills, specialized chloride cells actively transport chloride ions out and allow sodium ions to follow passively. In kidneys, excess calcium, magnesium, and sulfate ions are excreted with the loss of only small amounts of water.

What does osmoregulation enable animals to do?

It enables animals to live in environments that are uninhabitable for osmoconformers, such as freshwater and terrestrial habitats.

Define anhydrobiosis.

It is a dormant state involving loss of almost all body water.

What is osmosis?

It is a special case of diffusion and is the movement of water across a selectively permeable membrane.

What is an osmoconformer?

It is an animal that is isoosmotic with its environment. All osmoconformers are marine animals. Because an osmoconformer's internal osmolarity is the same as that of its environment, there is no tendency to gain or lose water.

What is osmolarity?

It is solute concentration expressed as molarity.

What is excretion?

It is the disposal of nitrogen-containing metabolites and other waste products.

What is osmoregulation?

It is the regulation of solute concentrations and water balance by a cell or organism.

What are tardigrades?

Less than 1 mm long, these tiny invertebrates are found in marine, freshwater, and moist terrestrial environments. In their active state, hydrated state, they contain about 85% water by weight, but they can dehydrate to less than 2% water and survive in an inactive state, dry as dust, for a decade or more. Just add water, and within hours the rehydrated tardigrades are moving about and feeding.

What is the unit of measurement for osmolarity in this chapter?

MilliOsmoles per liter (mOsm/L).

What does it mean for an animal to be stenohaline?

Most animals, whether osmoconformers or osmoregulators, cannot tolerate substantial changes in exernal osmolarity and are said to be stenohaline (from the Greek stenos, narrow, and halos, salt).

Is it possible to take the genes that code for trehalose and possibly insert into other plants and crops that grow across the United States in order to make them resistant to desiccation in the cold?

Need to research this and look at some the papers that Monsanto has manufactured, and possibly other food companies. Reread the book the Wind Up girl by Paoli Baccigulpi.

How do salmons acclimatize when in the ocean?

They produce more of the steroid hormone cortisol, which increases the number and size of salt-secreting chloride cells. As a result of these and other physiological changes, salmon in salt water excrete excess salt from their gills and produce only small amounts of urine - just like bony fishes that spend their entire lives in salt water.

Why are marine sharks not hypoosmotic to water?

This is because the shark tissue contains high concentrations of urea, a nitrogenous waste product of protein and nucleic acid metabolism.

Why are sharks considered osmoregulators?

This is because the solute concentration is actually higher than ocean water. Water slowly enters the shark's body by osmosis and in food (sharks do not drink). This small influx of water is disposed of in urine produced by the shark's kidneys. The urine also removes some of the salt that diffuses into the shark's body; the rest is lost in feces or is secreted from a specialized gland.

How does an osmoregulator survive in a hypoosmotic environment?

To survive in a hypoosmotic environment, an osmoregulator must discharge excess water.

How does the shark have internal osmolarity that is so close to that of seawater?

Together, the salts, urea, TMAO, and other compounds maintained in the body fluids of sharks result in an osmolarity very close to that of seawater. For this reason, sharks are often considered osmoconformers.

When two solutions differ in osmolarity, which of the solutes is said to be hyperosmotic? Hypoosmotic?

When two solutions differ in osmolarity, the one with the greater concentration of solutes is said to be hyperosmotic, and the more dilute solution is said to be hypoosmotic. The water flows by osmosis from a hypoosmotic solution to a hyperosmotic one.