44 Osmoregulation and Excretion Flashcards
What is the process by which organisms maintain their solute concentration?
Osmoregulation
As an organism takes in solutes, what odes osmosis dictate will happen to its water intake?
It will increase.
What would happen if animals did not properly osmoregulate?
Their cells would become swollen or shrivelled form too much or too little water.
How is the solute concentration with regard to osmosis quantified?
With the property “osmolarity” which relates to the total solute concentration expressed as moles per litre.
What is the unit of osmolarity most often used?
milliOsmoles per litre (mOsm/L)
What is the osmolarity of sea water?
1,000 mOsm/L
What is the osmolarity of human blood?
300 mOsm/L
In what direction does water flow through from osmosis?
A hypoosmotic solution to a hyperosomotic solution
How does hyperosmotic differ from hypertonic and so on?
Hypertonic etc. refers to the what happens i.e. water moves to it, as opposed to hyper osmotic which refers simply to the relative concentration of solutes with no implication of water movement.
What are the basic strategies to respond to chaining osmotic conditions?
Be a osmoregulator or an osmoconformer
What type of animals are osmoconformers?
All osmoconformers are marine animals (but not all marine animals are osmoconformers, nor are any freshwater fish)
Where do osmoconforming marine animals typically live?
Areas with constant osmolarity, such as the sea.
Could they be freshwater osmoconformers? Why?
No, to be an osmoconformer the animal must be isoosmotic with the water. In freshwater the osmolarity is essential 0 whereas the fish would have a higher osmolarity from all the cells and products they produce.
Based on their ability to tolerate osmotic change, what can animals be grouped into and what do these groups denote?
“Stenohaline” organisms can only tolerate a narrow range of osmolarity whereas “euryhaline” organism can tolerate a wide range of osmotic conditions.
Are osmoconformers typically stenohaline or euryhaline?
Stenohaline (narrow range of osmotic condition) as the sea has a relatively constant osmolarity.
What is an example of a euryhaline osmoconforming organism?
Barnacles that tolerate begin covered and uncovered as the tide goes in and out.
What is an example of a euryhaline osmoregulator?
Salmon etc. that spend part of their life in freshwater and part of their life in the ocean
How is osmoregulation achieved in marine invertebrates?
Most marine invertebrates are osmoconformers so face no significant osmoregulatory difficulties.
Since the ion concentration of specific solutes does differ between their cells and the ocean they do have to actively transport some out i.e. chloride ions.
How is osmoregulation achieved in marine vertebrates?
Most marine invertebrates, and a few marine vertebrates, are osmoregulators.
Since they have a lower solute concentration in their body than the ocean there is a strong tendency for water to be lost from them, possibly causing dehydration.
To rectify this marine fish such as cod drink large volumes of water to replace the water that is lost. In the gills cells called “chloride cells” actively transport sodium out of the body, while allowing sodium ions to follow passively.
In the kidneys, excess calcium, magnesium, and sulfate ions are ex- creted with the loss of only small amounts of water.
What marine animals have a distinct osmoregulation strategy and what is is?
Chondrichthyans (Cartilaginous animals like sharks)
While they have a lower salt concentration they have a higher osmolarity than the sea water. This is achieved because the shark has a high concentration of urea in its cells. This osmolarity is also increased by the presence of TMAO (trimethylamine oxide), an organic molecule that protects against the urea
How does the situation of freshwater fish differ form marine fish and how does this affect their osmoregulatory strategies?
They must be hyperosomotic to the water, as they could not tolerate the slow solute concentration of fresh water.
They are therefore adapted to drink very little water and excrete any water that enters through diffusion with their very dilute urine. They maintain their salts by eating food and from uptake across the gills.
In freshwater fish “chloride cells” of the gills actively transport Cl- ions into the body, with Na+ following passively.
How do salmon adapt to moving between fresh and salt water environments?
When living in rivers and streams, salmon osmoregulate like other freshwater fishes,
producing large amounts of dilute urine and taking up salt from through their gills.
When they migrate to the ocean, salmon produce more of the steroid hormone cortisol, which increases the number and size of salt-secreting chloride cells. Salmon in salt water excrete excess salt from their gills and produce only small amounts of urine.
What is extreme dehydration called in animals?
Desiccation
What is it called when animals that can survive without water called?
Anhydrobiosis
What type of animals typically undergo anhydrobiosis?
Small invertebrates that live in ponds that often dry up or that live in the film of water between soil particles.
What is an example of an animal that can undergo anhydrobiois?
Tardigades (‘water bears’), some roundworms (nematodes)
What is a typically adaptation that allows animals to undergo anhydrobiosis?
They produce a disaccharide called trehlose that replaces the water in their cells during dormancy
How do insects prevent freezing during winter?
The can produce trehalose, a disaccharide that replaces water in their cells and thus prevents the formation of ice crystals.
What are some typical adaptions that prevent animals from losing water?
Insect exoskeletons have a waxy layer like the waxy cuticle.
Land snails have shells
Humans and many animals have layers of dead keratinised skin cells on their surface.
In desert animals, with what mechanism is the majority of water gained?
Metabolism i.e. eespiration
How are solutes and waste products move throughout the body?
In transport epithelia.
How can many sea birds drink salt water?
They have “nasal glands” that consist of capillaries that wrap around “secretory tubules” so that the NaCl diffuses out of the blood. These secretory tubules carry the NaCl to a central duct which secretes it out of the bird’s nostrils.
Note that this process uses countercurrent exchange.
What leads nitrogenous waste?
The break down of proteins and nucleic acids for energy or conversion to carbohydrate or fats etc.
When these breakdowns occur an enzyme removes the nitrogen in the form of NH2 amino groups, which become ammonia.
What is the issue with ammonia nitrogenous waste?
It is highly toxic and for example disrupts oxidative phosphorylation.
What animals release nitrogenous waste in the form of ammonia?
Pretty much only fish and marine invertebrates (not sharks) as they can release the ammonia in a very dilute form as they are surrounded by plentiful water to dilute it.
How do fish/marine invertebrate lose nitrogenous wastes?
In many inverte-brates, ammonia release occurs across the whole body surface. In fishes, most of the ammonia is lost as NH4 across the epithelium of the gills. The kidneys excrete only minor amounts of nitrogenous waste.
In what form do many land animals release nitrogenous waste?
Urea.
What animals specifically use urea excretion?
Mammals, most amphibians, sharks and some bony fish
Why is urea excretion beneficial over ammonia?
Ammonia can only be tolerated at very low concentrations and thus would have to be very dilute. Therefore a large, bulky, heavy bladder would be needed.
This need to dilute the ammonia would also lead to significant water loss during urination.
How and where is ammonia converted to urea?
In the liver, where is is combined with CO2
What disadvantage does urea formation have?
It takes energy
What form of excretion do frogs use?
In their tadpole stages they use ammonia excretion as it does not require energy and since they live in water it can be easily diluted.
As adults frogs use urea excretion of nitrogenous waste.
What alternative to urea production is used by some animals?
Uric acid production
What animals specifically excrete waste in the form of uric acid?
Many reptiles, birds, insects and land snails
What are the advantages of uric acid production?
Uric acid is even less toxic than urea and does not readily dissolve in water. This means the organism that produces it does not need to dilute it as much.
In animals that live in the desert this is beneficial as it means less water loss through excretion.
In other animals like birds this is beneficial as it means that they don’t need large bladders to dilute the nitrogenous waste.
What mammals produce uric acid and under what circumstances?
All mammals including humans produce some uric acid form the metabolism of the amino acid purine.
What can an inability to break down the amino acid purine cause?
Uric stones in the bladder (why?)
Also gout, a form of joint inflammation caused by purine crystals forming in the joints.
What form of nitrogen waste do embryos secrete?
In amphibians the embryos of the egg release urea as their eggs have no shells.
Reptile and bird eggs have shells that are permeable to gases but not liquids so uric acid is produced due to its low toxicity.
What is the general purpose of excretory systems
To filter usable products out and thus package the waste appropriately i.e. into urea.
