- MUSOWE EDSON .A
Write an essay on the topic “patterns of Osmoregulation in aquatic and terrestrial environments”.
Osmoregulation refers to the process by which living organisms maintain the constant osmotic conditions in the body. It involves the regulation of water and solute concentration of the body fluids such as potassium, sodium and chlorides so that their body fluids are maintained within homeostatic limits. In order for the cells in the body of an organism to function effectively the body fluids such as the cell contents as well as fluids outside cells such as tissue fluids, lymph and blood plasma must remain constant. Freshwater, marine and terrestrial organisms consists of varying modes adaptations for Osmoregulation that meet the challenges of these diverse environments. Therefore, this essay will disclose the patterns of Osmoregulation in aquatic and terrestrial environments.
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The environment of an organism influences the process of Osmoregulation and the nature of excretion because Osmoregulation involves the same body structures with nitrogenous wastes. This is attributed to the fact that the elimination of nitrogen wastes is usually associated the problem of losing and gaining water. Different organisms live in different environments such as aquatic which includes fresh water and marine environment, and terrestrial environment. In all these environments, organisms employ specific patterns of controlling the concentration of water and salt so that their body fluids do not become too dilute or too concentrated through their environment as a media, (Solomon, P.E et-al 1069).
As earlier alluded to, aquatic organisms include those which live in fresh water and also those which live in marine water.
Osmoregulation in freshwater organisms
Organisms which live in fresh water are able to regulate the concentration of water and salts in their bodies through the pattern of gaining water and losing salts. This is because fresh water organisms in hypotonic medium. This is attributed to the fact that these organisms have a lower water potential than the surrounding environment, (Taylor D.J et-al 2011). As a result, there a constant tendency for water to enter the cells by osmosis through the cell surface membrane which poses a constant threat of organisms becoming water logged. To overcome this challenge, different organisms employ particular mechanisms; for example, species protozoans such Amoeba uses the organelles known as contractile vacuoles which eliminates the water entering the cell by osmosis, thereby osmoregulating the internal environment of an organism.
Certain species such as Paramecium have vesicles in the cytoplasm which fills with fluid from the cytoplasm and then most of the ions are pumped out of the fluid by active transport with energy from the surrounding mitochondria. Then the vesicles loads the remaining watery fluid into the contractile vacuole whose membrane cannot allow water to escape back into the cytoplasm by osmosis and suddenly the water is reduced hence osmoregulating its content.
Furthermore, in fresh water organisms such as fishes undertake Osmoregulation through the release of excess water through the gills and through the excreting of large amounts of dilute urine. Solomon, P.E et-al (2011: 1072) adds that “these organisms tend to lose salts by diffusion through the gills into the water”. In this way such organisms control the concentration of body water and salts. In addition to this, some amphibians such as frogs have their pattern of osmoregulating the body environment which is through producing large amounts of dilute urine and also active transport of salts into the body by specialised cells in the skin compensates for the loss of salt through the skin and urine.
Osmoregulation in marine environments
Another pattern of Osmoregulation in aquatic organisms occurs in marine species which involves the losing of water and gaining of salts to maintain a favourable and constant internal environment. To this, aquatic organisms adapt successfully. These organisms live in a hypertonic environment meaning that their inner water content is higher than the surrounding environment, hence they lose water by osmosis and then they gain salts from the seawater they drink by diffusion. Solomon, P.E et-al (2011:1073) adds that, “to compensate for fluid loss marine fishes drink a lot of sea water, excrete the salts through the gills and also produce a small volume of urine thereby osmoregulating their body fluids.
Then also, other marine species such as those of marine cartilaginous fishes i.e. sharks and rays have their own pattern of carrying out Osmoregulation. They have different osmoregulatory adaptations that allow them to tolerate the salt concentration of their environment. These organisms are able to accumulate and tolerate urea because their kidneys undertake the reabsorption of urea in high concentration such that their body tissues become hypertonic to their surrounding medium resulting in a net inflow of water by osmosis. Then also they excrete quantities of dilute urine and excess salt is excreted also by the kidneys and in most species by a rectal gland, hence osmoregulating the body fluids.
And for marine snakes they carry out Osmoregulation by using salivary sublingual gland to get rid of excess leaving a normal blood concentration. Additionally, some reptiles, snakes and marine birds ingest sea water and take in a lot of salt in their food. To control the concentration of salts and water they posses glands in their heads which undertake the excretion of excess salts from their blood plasma.
Osmoregulation in terrestrial environments
Organisms which live on land have a common challenge of regulating water in the body due to their contact with the atmosphere. However, each species has a particular pattern and adaptation to life on land for example insects. These, they contain an almost impermeable waxy layer which covers their exoskeletons to reduce loss of water from the body surface. Then also insects have wave-like structures in their spiracles which reduce the loss of water from tubes which connect spiracles to cells, (Taylor D.J et-al 2011).
In addition to this, water loss through excretion is prevented through the help of the malpighian tubules whose lower segment absorbs water and various salts and then the nitrogenous wastes precipitates out of the solution as solid crystals of uric acid. Thereafter, concentrated fluids of the tubules enter the rectum in which they mix with digestive wastes. From there the rectal gland absorb water again from uric acid and faeces suspension and then the dry waste is eliminated from the body as pellets. All the above adaptations form a suitable pattern for controlling and maintaining a constant osmotic condition of the insect’s body.
Other terrestrial organisms i.e. invertebrates such as flateworms consists of nephridial organs with branching tubes called nephridiopores excess fluid leaves the body thereby osmoregulating the internal fluid content, and also protonephridia composed of tubes with flame cells. They also have complex nephridial organs known as metanephridia whose end opens into a coelom and the fluid from the coelom passes into the tubule bringing with it whatever it contains i.e. glucose, salts or even wastes. As the fluid moves through the tubule, needed substances like water and glucose are removed from the fluid by tubules are reabsorbed back in blood capillaries, hence carrying out Osmoregulation.
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Organisms such as a Kangaroo rat carry out Osmoregulation by using its fur to prevent the loss of water to the air and also during the day it remains in a cool burrow. Mader, S.M (2010) adds that a Kangaroo rat carries out Osmoregulation by using its nasal passage which has a highly convoluted mucous membrane surface capture condensed water from exhaled air and also conserves water by producing very concentrated urine and almost dry fecal matter.
Solomon, P.E (2010:1070) states that “to animals moved on the land, natural selection favoured the evolution of structures and processes that conserve water”. Thus this, facilitates Osmoregulation. The excretory system in terrestrial organisms such as birds, reptiles and mammals gives them a pattern by which they maintain fluid and electrolyte homeostasis by selectively adjusting the concentrations of salts and other blood substances and body fluids. Because this system is adapted to collect fluids from the interstitial fluids and blood it is able to control the fluid’s composition by selectively returning those required by the body into the body fluids. For example; birds undertake the process of Osmoregulation by excreting nitrogen as uric acid which only releases a little water and also by efficiently reabsorbing water through their cloaca and interstine. In addition to this, birds osmoregulate by excreting salt solution from the salt-excreting glands through their nostrils thereby maintaining a normal body fluid content. Then also, large terrestrial organisms are able to control their body fluid content because their skins are adapted to minimze the loss of water through evaporation and also by drinking water to compensate the water lost through the skin, respiratory passages and through urination, hence Osmoregulation their body fluid content. .
Furthermore, terrestrial organisms consists of a very effective and efficient kidneys enables them osmoregulate the body fluids and conserve water though a series of processes i.e. filtration, reabsorption of the needed substances by the body in the body fluids and the tubular secretion in the nephron. For example; Water passes out of the descending limb of the loop of Henle, leaving a more concentrated filtrate inside. The heavy outline along the ascending limb indicates that this region is relatively impermeable to water. NaCl diffuses out from the lower and thin part of the ascending limb. In the upper and thick part of the ascending limb, NaCl is actively transported into the interstitial fluid. The saltier the interstitial fluid becomes, the more water moves out of the descending limb. This process leaves a concentrated filtrate inside, so more salt passes out. Water from the collecting ducts moves out osmotically into this hypertonic interstitial fluid and is carried away by capillaries, hence osmoregulation is carried out,( Eckert, R et-al 2005).
As indicated above Osmoregulation is the process by which organisms control the concentration of water and salts in the body so that their body fluids are maintained within homeostatic limits. This process occurs in organisms depending on the environment in which an organism live i.e. aquatic which include fresh water and marine water, and also terrestrial environment.
Eckert Roger and Ranall David (2005), Animal Phsysiology; mechanisms and adaptations, New York, CBS Publishers & Distributors Pvt. Ltd.
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Solomon, P.E, Berg, R.L. and Martin, W.D. (2011), Biology 9th edition, Canada, Life Sciences.
Taylor, D.J, Green, N.P.O, and Stout, G.W, (2011), Biological Science 3rd edition, London; Cambridge University Press.
Verma, P.S and Agarwal, V.K (2007), Cell Biology, Genetics, Molecular Biology, Evolution and Ecology, New Deihi; S.Chand & Companies.
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