Salt, Water and Nitrogen

Question 0

Why is the regulation of the ionic and osmotic composition of body fluids linked to nitrogenous excretion?

Answer 0

Because the excretion of nitrogenous waste requires water.

Question 1

How do most marine organisms eliminate nitrogenous waste?

Answer 1

Mostly in the form of highly toxic ammonia.

Question 2

Why did most animal life begin in the sea?

Answer 2

Because of the relative constancy of the environment, including the salt concentration of the medium.

Question 3

Why is it important that the body fluids of most marine animals have a similar composition to that of the seawater around them?

Answer 3

It means that they have an osmotic concentraion close to that of their medium and do not experience significant water losses or gains.

Question 4

What is one osmole?

Answer 4

A mole’s worth of osmotically functional particles.

Question 5

What is the colligative property of osmotic potential?

Answer 5

The osmotic effect is purely dependent on the number of particles NOT chemical nature: the number of particles determines osmotic effect.

Question 6

How is an osmole measured?

Answer 6

Usually by depression of freezing point, e.g. seawater with a salinity of 35 freezes at -1.86 degrees, so a solution whose depression of freezing point is -1.86 degrees is considered to have an osmotic concentration of 1 osmole.

Question 7

What is the definition of osmotic concentration?

Answer 7

It measures the concentration of osmotically active particles in a solution.

Question 8

How is osmotic concentration usually measured?

Answer 8

In milliosmoles as few organisms have body fluids concentrations exceeding one osmole.

Question 9

What is an osmoconformer?

Answer 9

An organism which may regulate the ionic composition of their body fluids but the overall osmotic concentration is always approximately isosmotic with seawater. Most marine invertebrates are osmoconformers.

Question 10

What is an osmoregulator?

Answer 10

An organism which regulates the ionic and osmotic composition of their body fluids to maintain a stable (within limits) internal fluid composition. Migratory fish and some estuarine invertebrates do this.

Question 11

What is a Euryhaline animal?

Answer 11

An animal which can tolerate a wide range of salinities, usually by a combination of osmoconforming and osmoregulatory processes. Most estuarine forms are euryhaline.

Question 12

What is a Stenohaline animal?

Answer 12

An animal that is restricted to a narrow salinity range. (NB, many species may be stenohaline but are still active ionic and osmotic regulators, such as most marine teleosts which maintain their body fluids around 330-350 mOsmoles.

Question 13

Do osmoconformers regulate ions at all?

Answer 13

Yes, sometimes to a high degree.

Question 14

How do osmoconformers show changes as water enters or leaves by osmosis?

Answer 14

They will change volume in the short term. In the long term volume may adjust towards original level as both ions and water move.

Question 15

How do estuarine polychaetes avoid rapid changes in salinity?

Answer 15

By burrowing into the sediment where changes in external salinity are much less extreme.

Question 16

What is an example of an invertebrate that changes its volume due to changes in external salinity?

Answer 16

The sipunculid worm Themiste lageniformis swells in 50% seawater and shrinks in 140% seawater, and partially regulates its volume at 80% seawater.

Question 17

How do animals regulate intracellular volume?

Answer 17

Cells are isosmotic to body fluids, but have a different ion composition (higher K+ and lower Na+).

Question 18

If the osmotic concentration of an animals body fluid changes?

Answer 18

This is matched by changes of organic molecules in cells.

Question 19

How are concentrations of free amino acids affected by salinity stress?

Answer 19

They increase, and are regulated by changing the level of protein degradation or synthesis.

Question 20

Which organic molecules are used inside cells as ionic regulators?

Answer 20

Amino acids and amines, as enzymes and other proteins are sensitive to change in the ionic composition of the intracellular fluids.

Question 21

What do many marine invertebrates use in osmotic regulation?

Answer 21

Glycine, as it can be accumulated to high levels with no adverse effects. 70% of the osmotic concentration in barnacle muscle cells is produced by amino acids, of which >50% is glycine.

Question 22

What other methylamines are used to maintain OC? Which are not?

Answer 22

Betaine - cephalopods
Arginine - used in metabolic function.
Lysine and Arginine can’t be accumulated like glycine as they interact w/ proteins and change their conformation.

Question 23

What does hypotonic mean?

Answer 23

Having a lower osmotic concentration than a particular fluid, in this situation, seawater.

Question 24

Are all marine vertebrates hypotonic?

Answer 24

No, hagfish are not. However, osmotically there are three groups.

Question 25

What are the characteristics of vertebrates that are iso-osmotic with seawater?

Answer 25

These are elasmobranchs. They have an osmotic concentration similar to that of seawater, e.g. hagfish, dogfish and coelacanths. Dogfish have salts only 1/3 of SW, but have 100x more urea in their blood.

Question 26

How do animals that are iso-osmotic with seawater regulate their body fluids?

Answer 26

Similar to marine inverts but urea and TMAO are accumulated to avoid damaging high intracellular salt concentrations.

Question 27

What does urea do to enzymes and proteins?

Answer 27

Destabilises proteins and lowers denaturation temperature of enzymes.

Question 28

What does production of TMAO do to enzymes and proteins?

Answer 28

It is osmotically useful and the production of it minimises the effect on enzymes.

Question 29

Are elasmobranchs active ionic regulators?

Answer 29

Yes, they remove salts that diffuse in by the gills by secreting them in fluid from the cloacal gland.

Question 30

What are hypo-osmotic marine vertebrates? What are their characteristics?

Answer 30

Marine teleosts. Body fluids of these are only 1/4 to 1/3 of SW OC, in both SW and FW spp.

Question 31

How do hypo-osmotic marine vertebrates maintain their OC?

Answer 31

They lose water by osmosis from gills but compensate by drinking SW. They eliminate the excess salts by excreting Mg2+ and SO42-, excess NaCl secreted at gills: active transport of Cl- in gill epithelium, Na+ follows passively.

Question 32

How do air-breathing marine vertebrates (birds and reptiles) maintain their OC?

Answer 32

Still terrestrial for osmoregulation - isolated from SW as no gills. No FW to drink & high salt in food. Birds & reptiles have salt glands in head that secrete hyperosmotic NaCl solution.

Question 33

What is different about the Chinese swap turtle Pelodiscus sinensis?

Answer 33

It secretes urea from specialised tissues in its mouth, reducing the amount of water needed for the kidneys.

Question 34

How do mammals regulate their OC?

Answer 34

Marine mammals are able to form hyperosmotic urine, more concentrated than SW. Whale urine can have up to 820MM of Cl- (sw=530mM), so they can remove excess salts from food or ingested SW. Humans can’t so we can’t drink SW.

Question 35

What is osmoregulation and excretion like in marine inverts?

Answer 35

The Porifera and Coelenterates rely on diffusion to remove nitrogenous waste, however most inverts have some variation on a tubular filtration system.

Question 36

What is the marine invertebrates tubular system like?

Answer 36

It consists of three basic processes in a tubular system that penetrates into the tissues and opens to the outside environment. It FILTERS, SELECTIVELY REABSORBS AND SECRETES and EXCRETES.

Question 37

What are protonephridia?

Answer 37

They are found in platyhelminthes and rotifers. The system of tubules is diffusely spread through the body. Beating cilia at the closed end of the tube draw interstitial fluid into the tubule. Solutes reabsorbed before dilute urine excreted.

Question 38

What are metanephridia?

Answer 38

Found in polychaetes. They have internal openings or nephrostomes that collect coelomic fluid when the cilia present on the funnel shaped opening beat. They have both excretory and osmoregylatory functions.

Question 39

What is the crustacean antennal gland?

Answer 39

Found in crustaceans like crayfish. They are situated at the base of the second antennae. It consists of a bulb-like sac called a ‘coelomosac’ connected to the ‘labyrinth’. A tubular nephridial canal joins the labyrinth and the bladder. They are osmotically active. Urine formed in lumen of c/sac and send out through bladder.

Question 40

What are the physiological characteristics of an osmoconformer?

Answer 40

The osmotic concentration of the body fluids follows approximately that of the surrounding medium, within limits.

Question 41

How do osmoconforming invertebrates regulate intracellular composition?

Answer 41

They use certain amino acids e.g. glycine and also TMAO.

Question 42

How do osmoconforming vertebrates regulate their intracellular composition?

Answer 42

They use urea and TMAO, e.g. sharks.

Question 43

What is the approximate osmotic concentration of the body fluids od an osmoregulating fish?

Answer 43

300-350 milliOsmoles.

Question 44

What are the three basic processes seen in the tubular excretory systems of higher invertebrates and all vertebrates?

Answer 44

Filtration, Selective reabsorption and secretion and Excretion.