On page 168, while Shubin discusses the effect of alcohol, he mentions the idea of diffusion across a membrane. Refering to our past studies, explain the factors behind the movement of water such as water potentional and concentration gradients. Also, relate how these movement of water effects organisms in environments in which they live as they maintain homeostasis. (i.e. fresh water fish vs salt water fish)
Kevin Jeon
Bboybyung@gamil.com
Shubin states that the diffusion of ethanol across cells in our ears is responsible for the feelings of "spins" as ethanol is lighter than water and the creates imbalances in the inner ear. When someone consumes a large amount of alcohol, ethanol (an ingredient in alcohol) builds up a large concentration gradient in our bloodstream. (Shubin 168) Since ethanol is a smaller molecule, it is easily able to diffuse across the cell membranes. Also, the solution outside of the ear cells has a high ethanol and low water gradient while the cells inside the ear have a low ethanol and high water gradient. This causes a high water potential out of the ear causing water to move out as ethanol moves in to maintain equilibrium (the high water potential out of the cells aids alcohol as a diuretic.) http://www.chemistry.wustl.edu/~courses/genchem/Tutorials/Kidney/dynamic.htm
ReplyDeleteThis same idea of high concentration gradients and water potential is seen in fresh and saltwater fish. Saltwater fish constantly lose water through osmosis due to the high salt concentration (hypertonic environment) outside versus inside the cells. Since the salt can't immediately diffuse into the cells, the water potential to leave the fish is high. To reverse this process, fish have to constantly drink to replace the lost water and then excrete the salt ions through their gills and release very concentrated urine. On the other hand, freshwater fish live in a hypotonic environment meaning their is a high water potential flowing into their cells due to the buildup of salt and ions which unless resolved, would cause their cells to lyse. Therefore, the fish only takes in salt and ions and then excretes the large amounts of water absorbed through dilute urine. (Cambell 956)
Water moves in and out of our body through the process of osmoregulation, which is the general process by which animals control solute concentrations and balance water gain and loss. All animals, regardless of their phylogeny, habitat, or type of waste excreted, need to undergo osmoregulation in order to maintain the balance between water taken in and water lost. If there is too much water taken in, animal cells will swell and lyse; at the same time, if too much water is lost, the cells will shrivel. Water is able to enter and leave the cell through osmosis, which is a special type of diffusion of water across a selectively permeable membrane. Osmosis occurs when two different solutions differ in osmotic pressure (osmolarity). If two solutions that are separated by a selectively permeable membrane have approximately the same osmolarity, then they are known to be isoosmotic.
ReplyDeleteAnimals have the ability to maintain water balance in two different ways: either be an osmoconformer (become isoosmotic with the environment it is in) or an osmoregulator (control the internal osmolarity independent of that of its surroundings. All osmoconformers are marine animals because the osmolarity of marine animals is the same as that of its surrounding environment, therefore no water is gained or lost. These osmoconforming marine animals live in water that has a stable composition and have constant internal osmolarity. Osmoregulators live in freshwater or terrestrial habitats and are usually able to maintain an internal osmolarity that is different from seawater; to survive in a hypoosmotic environment, osmoregulators discharge excess water. To survive in hyperosmotic environments, osmoregulators must take in water and off set osmotic loss.
Marine animals balance water loss that usually comes from living in waters with high concentrations of salt by drinking lots of seawater and making use of their gills and kidneys to get rid of the salts. In the gills of salt-water fish, there are specialized that actively transport chloride ions out, in which sodium ions follow through passively. In the kidneys, any excess calcium, magnesium, or sulfate ions that remain are excreted with loss of only a small amount of water. In freshwater animals, the internal fluids have an osmolarity that is higher than the osmolarity of its surroundings, and face the problem of gaining too much water through osmosis and losing salts via diffusion. In order to avoid this problem, freshwater fish and other animals drink almost no water and excrete very large amounts of very dilute urine. Any salts that are lost by diffusion are replenished through eating.
In general, water moves from places of low solute concentration to high water solute concentration; from places of high water potential to low water potential.
(Sujin Ko, sujinko93@gmail.com)
Sources: Campbell
http://en.wikipedia.org/wiki/Water_potential
The movement of water through a semi-permeable membrane is diffusion, and it happens with the difference of solute concentration in water. If there is less concentration of solute, then the water potential is high, whereas more concentration of solute leads to lower water potential. However, in case of solute with smaller molecules, such as ethanol, they diffuse according to their own concentration gradient. So, when a person drinks alcohol excessively, the liver is not able to remove the alcohol completely when it passes by it, and when alcohol passes by the inner fluid in our ear tubes, it diffuses into the fluid, since it contains very little alcohol initially, and causes to “[wreak] havoc on the intemperate among [people]” (Shubin 168). And, after the hangover, the alcohol diffuses back to the blood stream since there is very little alcohol remaining in the blood (Shubin 168).
ReplyDeleteAs for the organisms affected by the movement of water, the aquatic animals are adapted to maintain homeostasis in their respective habitat. For example, marine animals live in a very salty environment, and since the surroundings have low water potential, the water rushes out of the fish’s body. To counter it, seawater fish uptakes lots of seawater, but their gills can excrete large amounts of salt that it uptakes. Also, the seawater fish’s urine contains little water because it tries to take in as much water as possible (Campbell 956). As for sharks, they convert the ammonia to urea and spread it all around their body, so that the concentration gradient remains similar to the seawater, thus not having to worry about maintaining homeostasis. Also, since they need to constantly swim in order for the gills to function, excretion of salt via gills is not a great idea (http://users.tamuk.edu/kfjab02/Biology/Vertebrate%20Zoology/b3405_ch04.htm). However, freshwater fish, since they are surrounded in an environment with high water potential, they constantly need to excrete as many water as they can. Because of this, their uptake of water is low, their gills function oppositely as the seawater fish as they uptake salt ions, and their urine contains high concentration of water (Campbell 956).
Although not mentioned by Kevin, Aparna and Sujin, even terrestrial animals have to deal with the movement of water, though it’s not diffusion. Terrestrial animals are not surrounded by water, and so does not have constant access of water. Also, water is dried off the skin as they emerge, another source of losing water. So, they convert ammonia to urea and uric acid by using ATP so that they can carry the toxins with them longer and not have to urinate very often, as to save the water. For especially birds and reptiles, their urine contains little to no water, since they usually live in a dry habitat (Campbell 959).
All animals, in some way or another, are challenged by the movement of water, and they survive by using their own methods to maintain homeostasis and not shrivel up or explode due to too little or much water in their systems.
John Park (wisejsm@yahoo.com)
In addition to the above posts, osmosis and diffusion plays a key role in the excretion. To start off, there is a waste product from the hydrolysis from proteins called ammonia. This is a very toxic chemical and it needs to be removed from the body immediately. It is converted to urea by adding CO2 and ATP in the liver. From there, it is chanced into three different types: urea, uric acid, and ammonium. Ammonium is very toxic and it requires a lot of water to flush it out, therefore you need a constant water supply to limit yourself to only ammonium (ie fish). Uric acid is when you have limited water, or very limited amounts of water, so its used by most birds and most terrestrial animals. Urea is the middle ground for these different types of excretion. This is not very toxic, but it requires a good amount of water to flush it out and is used by amphibians and mammals. Another example of an animal using urea are sharks and snails. "Some organisms, such as sharks and snails, allow urea to accumulate in their blood to help with overall osmotic balance. Sharks, for instance, use urea in the blood to make them hyperosmotic in relation to seawater, thus they tend to gain water from the ocean and do not have to worry about dehydration." http://www.marietta.edu/~mcshaffd/aquatic/sextant/excrete.htm
ReplyDeleteAfter the urea (for example) is done being produced, it travels in the bloodstream and then diffuses into the kidney through the bowman's cap with pressure from blood rushing in. From there, many particles flow in and out (including water) but the urea stays inside the nephron the entire time. And from there, it is stored in the bladder and later excreted through the urethra.
Sources:
http://www.marietta.edu/~mcshaffd/aquatic/sextant/excrete.htm
Campbell
Nikhil Pereira (nikhil.pereira3@gmail.com)