how do aquatic mammals breathe underwater?
921701
They hold their breath. They can hold their breath for a very long time because they have a very efficient metabolic rate that allows them to control the amount of oxygen required by their bodies. Their heart rate drops and blood supply to external parts that do not require so much oxygen are reduced.
760601
Dolphins have to be conscious to breath. This means that they cannot go into a full deep sleep, because then they would suffocate. Dolphins have "solved" that by letting one half of their brain sleep at a time. This has been determined by doing EEG studies on dolphins. Dolphins sleep about 8 hours day in this fashion. \n\nA dolphin's behavior when sleeping/resting depends on the circumstances and possibly on individual preferences. They can either:\n1. swim slowly and surface every now and then for a breath\n2. rest at the surface with their blowhole exposed \n3. rest on the bottom (in shallow water) and rise to the surface every now and then to breath.
612472
Observations of bottlenose dolphins in aquariums and zoos, and of whales and dolphins in the wild, show two basic methods of sleeping: they either rest quietly in the water, vertically or horizontally, or sleep while swimming slowly next to another animal. Individual dolphins also enter a deeper form of sleep, mostly at night. It is called logging because in this state, a dolphin resembles a log floating at the water's surface.\nWhen marine mammals sleep and swim at once, they are in a state similar to napping\n\nAdult male dolphins, which generally travel in pairs, often swim slowly side by side as they sleep. Females and young travel in larger pods. They may rest in the same general area, or companionable animals may pair for sleeping while swimming.\n\nWhile sleeping, the bottlenose dolphin shuts down only half of its brain, along with the opposite eye. The other half of the brain stays awake at a low level of alertness. This attentive side is used to watch for predators, obstacles and other animals. It also signals when to rise to the surface for a fresh breath of air. After approximately two hours, the animal will reverse this process, resting the active side of the brain and awaking the rested half. This pattern is often called cat-napping.
878508
Guppies don't really hear... And if they did, it wouldn't be by their gills. They use their gills to breathe. Instead, they follow vibrations. I'm not quite sure how, but I think they have a sense organ that detects vibrations in the water.
271806
dolphins sleep by "turning off" half their brain at a time. They can't sleep as we do because for them breathing is not an autonomic impulse. In other words, they breathe like we move our arms, they need to decide to breathe, then get their muscles to carry out the orders. So a dolphin will shut off half their brain at a time. While one half gets some r & r, the other half makes sure the dolphin keeps surfacing at regular intervals to breathe.
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Mainly because they're filled with water, and don't have to breathe air.  We have difficulty at depths that don't bother fish because we have open cavities in our bodies (such as the periteneal sac around our abdomenal organs), and our lungs need to expand for us to take in air.\n\nHowever, there are still limits to the depths to which many fish can dive.  Buoyancy regulation in bony fishes is controlled through the swim bladder.  By contracting or relaxing the bladder, it essentially changes the density of the fish and they can rise or sink in the water column.  Below certain depths though, the swim bladder becomes too contracted, and can even be crushed, and the fish can die or be unable to return to safer depths.\n\nDeep sea fish (like those weird angler fish and gulper eels and others) have a variety of adaptations that allow them to survive under such intense pressures.  Other critters, like octopus and crabs and tube worms have other adaptations, but most of them involve making sure there's no sealed body cavities that can be compressed by deep ocean pressures.
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In order to withstand pressure, their cells must counterbalance the extreme pressure outside. Also, animals at such depths are generally colourless and are blind. They navigate by sound.
111141
A frog can respire in two ways- pulmonary respiration(through lungs) and cutaneous respiration(through skin).Thus under water it can respire through skin and on land, with the help of lungs.The sklin of a frog is thin and richly supplied with blood vessels to facilitate exchange of gases.It is moist and slimy for protective purposes.
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Simple... fish can breathe in water, as Oxygen is dissolved in the water already. Otherwise, its dangerous for the fish to breathe above water.\n\nn order to live, fish must extract oxygen from the water and transfer it to their bloodstream. This is done by gills, lungs, specialized chambers, or skin, any of which must be richly supplied with blood vessels in order to act as a respiratory organ. Extracting oxygen from water is more difficult and requires a greater expenditure of energy than does extracting oxygen from air. Water is a thousand times more dense (heavier per unit volume) than air, and at 20 deg C (68 deg F) it has 50 times more viscosity (resistance to flow) than air and contains only 3% as much oxygen as an equal volume of air. Fishes, therefore, have necessarily evolved very efficient systems for extracting oxygen from water; some fishes are able to extract as much as 80% of the oxygen contained in the water passing over the gills, whereas humans can extract only about 25% of the oxygen from the air taken into the lungs.\n\nGills are made efficient in a number of ways. (1) A large surface area for gaseous exchange means that more oxygen can enter the bloodstream over a given period of time. A single gill of a bony fish consists of a curved gill arch bearing a V-shaped double row of gill filaments. Each filament has many minute folds in its surface, giving it a sort of fuzzy appearance and increasing the amount of surface area along a given length of filament. Consequently, the surface area of the gills is commonly 10 to 60 times more than that of the whole body surface. (2) A short diffusion, or travel, distance for the oxygen increases the rate of oxygen entry into the blood. The blood traveling in the folds of the filaments is very close to the oxygen-containing water, being separated from it by a very thin membrane usually 1 to 3 microns (4/100,000 to 1/10,000 in) thick, and possibly less. (3) By using countercurrent circulation in the gill, the blood in the filament folds travels forward, in the opposite direction to the water flow, so that a constant imbalance is maintained between the lower amount of oxygen in the blood and the higher amount in the water, ensuring passage of oxygen to the blood. If the blood were to flow in the same direction as the water, oxygenated blood at the rear of the gills would be traveling with deoxygenated water and not only could not extract oxygen from the water but would even lose oxygen to it. (4) Gills have little physiological dead space. The folds of the filament are close enough together so that most of the water passing between them is involved in the gas-exchange process. (5) Water flows continuously in only one direction over the gills, as contrasted with the interrupted, two-way flow of air in and out of lungs of mammals.
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The tissues and cells of creatures that inhabit the deep oceans are filled with fluid and thus air space is significantly minimized . Air is subject to compression, whereby a fluid such as water cannot be compressed.\n\nWithout internal compression, the creatures have negated the potential external pressure of the depths.
628752
Unlike marine mammals such as whales and dolphins with lungs that store oxygen from the surface air, fishes have gills. Gills are a series of membranes located on each side of the fish that function as respiratory organs. As water passes over this system of extremely fine gill membranes, the fishes absorb the oxygen from the water. The gills contain a network of fine blood vessels (capillaries) that take up the oxygen and diffuse it through the membranes. When fishes are taken out of water, they suffocate, because their gills collapse and they are unable to absorb oxygen.In many ways, the interior of the fish resembles that of many other animals. The digestive, circulatory, and nervous systems are very similar to those of other vertebrates. However, what really makes a fish different from other animals is its respiratory system. \n\n\n\nA fish’s respiratory system is determined primarily by the fact that it spends its entire life in water. Unlike the marine mammals such as whales, a fish has evolved in such a way as to not require frequent trips to the surface to breathe air. Fish have developed gills, on which they rely for the oxygen necessary for a fish’s limited metabolism. \n\nMany animals have gills at some stage of their life (even humans have them at an early stage of their development in the womb), but fish retained these gills and they are still a functional part of their anatomy. Fish use their gills to extract oxygen from their watery environment. The process starts with the fish’s mouth, which is how the fish takes in water. When a fish opens and closes its mouth, it is actually pumping water back through the gills and is thus breathing. Most fish have an effective pumping system that involves the mouth and the outer cover of the gills, called the operculum. When the fish’s mouth opens, the operculum closes, drawing water into the fish’s mouth. When the fish closes its mouth, the operculum opens, allowing fresh water to cross the gills. Other fish have a less effective pumping system, requiring them to swim constantly to keep fresh, oxygenated water flowing over the gills. These types of fish, such as tuna, generally swim with their mouths partly open. Incidentally, while many fish have nostrils, the nostrils are used only for a sense of smell, and play no part in respiration. \n\nOnce through the mouth, the water continues past structures called gill rakers. The gill rakers are essentially a filter system for the gills, straining the water to sift out floating food particles or foreign material. After passing through the gill rakers, the water continues through the gill arches and actually passes over the gills, which are suspended between the mouth cavity and the operculum. Each gill is made of two rows of gill filaments, which are extremely thin membranes sticking out into the water flow. Each of the gill filaments is composed of rows upon rows of lamellae, which are thin, disc-like membranes loaded with a capillary network. The water flows across the lamellae, and oxygen and carbon dioxide are exchanged directly across the capillary membrane. The capillaries are situated to take best advantage of the water flow; fish can actually extract up to 85% of available oxygen out of the water. Since water contains only 2-5% of the available oxygen that air at sea level does, such a high efficiency is extremely important. \n\nFrom the gills, the deoxygenated water passes out the operculum, and the oxygenated blood joins the circulatory system. Despite the efficiency, some fish require more oxygen than others. This helps to explain why some fish thrive in specific habitats. For example, trout prefer northern streams because the cool water of the streams tends to retain dissolved oxygen, and the active trout need the extra oxygen. Carp, on the other hand, are sluggish and do not need as much oxygen, which is why carp can thrive in warm, relatively stagnant ponds, such as ornamental ponds. Goldfish, unlike most f
448554
they use gills. the gills are filled with lots of blood vessels.  the fish draws in water from the mouth, which passes by and out the gills. as the water moves by, the blood cells take in oxygen and the waste gases are released.
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Living cells cannot absorb oxygen directly.  It has to be disolved in water.  Fish do not have any mechanism for disolving the oxygen in the air (they don't need it, since they live in the water), and so cannot survive on air.\n\nOur lungs have a lining of special mucous which is produced specifically to disolve oxygen and put it into a liquid so it can be used by our bodies.  It is remarkably similar to sea water... evolution has basically preserved the underlying transfer mechanism, and given us a way to carry our own little bit of ocean around with us!\n\nThe hylan membranes make this special fluid.  These membranes are not needed in the womb and so grow late in fetal deveolpment; hylan membrane disease results when a child is born before these membranes are fully developed, and they are at risk of suffocating in the air, just as a fish would.
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Harbor Seals have the ability to modify their hunting strategies and diet in such cases. A diversified diet is key to their survival. In some cases it can go down to the sea floor and dig up eels and octopi, or if necessary just dine on the smaller available fish locked in the low tide.\n\nAlso it's an air breather and can hold its breath a very long time. It can haul itself out onto the beach without any harm which is a feature other aquatic denizens don't have. This advantage limits any negative repercussion to low oxygen levels in the water.
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Hollow-bodied animals are the second simplest invertabrates. Some examples are jellyfish, hydra, coral, and sea anemones. Hallow-bodied animals are invertabrates with one opening and a hollow center.Hollow-bodied animals are like sponges in some ways. Hollow-bodied animals live in water, and some of them look like plants.Some hydra, sea anemones, and most coral attach themselves to rocks or the ocean floor.Some, like jellyfish swim or float in the water. Hollow-bodied animals can regenerate or regrow missing body parts.Hollow-bodied animals are more complex than sponges because they have a mouth and tentacles that help get their food into their mouth. Tentacles also can protect from predetors because they sting. Coral unlike hydra and sea anemones lives in colonies or large groups. Coral may look like tree branches and can be used in many different ways like for decorating.
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Oxygen is carried in the blood.  The oxygen transfers from the atmosphere to your blood through an exchange in your lungs...\n\nA fish's gills accomplish the same thing, but they get the oxygen from the water.
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Breathing, the process whereby an organism (living thing) obtains oxygen from its surroundings, to take part in internal chemical reactions which break down food to release energy. Breathing also usually gives out waste carbon dioxide as an unwanted by-product of these reactions. Breathing is one aspect of respiration, which is a term that includes both physically obtaining oxygen, and also using it in chemical pathways inside cells to release energy—the process of cellular respiration\n\nMany aquatic animals obtain oxygen dissolved in the water by muscle-powered movements, such as when the forward motion of a fish or the pumping actions of its mouth and throat force a flow of water over its gills ( See also Fish). This is underwater breathing. Tiny organisms “breathe” by the process of passive seepage or diffusion of oxygen through their body surfaces. Plants also obtain oxygen by diffusion from the air or water around them, usually into the leaves.