Marine animals also need to drink water, but the sea water is too salty to drink, so how do they drink water?
Since the middle and late last century, human beings have gradually moved to the distant space, and can look back at the earth we are familiar with from a distance from a relatively unique perspective - a light blue water droplet.
This is because the earth has a very rich water storage capacity. About 72% of the surface of the earth is covered by water, which can add up to 1.45 billion square kilometers. However, most of the water resources are seawater, and the freshwater resources are only about 0.5% , and most of the freshwater resources are frozen in the ice layer, and some are located underground, only a small amount of freshwater about 0.26% of the total water on the earth. Resources can be directly used by humans.
From the above, we can also know that the freshwater resources on the earth are very scarce. Although it can meet the needs of the population of some countries at present, many countries are caught in the dilemma of water shortage.
Although seawater with a volume of 1.37 billion square kilometers is much more than freshwater resources, it cannot be directly used by humans, and the cost of large-scale transformation of seawater is too high, often unable to support water-deficient countries.
Why can't you drink sea water?
Some people may think that if we are faced with a life-or-death juncture, such as a shipwreck, lying on a wooden board, in the endless sea, and there is no sign of the mainland around, in such a situation, in order to survive, we are You can get rid of some of the "dirty" concepts of the ocean and drink seawater to survive.
In fact, when we are floating on the sea, even if we are thirsty, it is best not to drink seawater directly . Of course, it is okay to drink a few mouthfuls of seawater. Who would not accidentally swallow seawater when swimming and playing in the sea, but It is impossible to survive by drinking sea water to quench your thirst. When the crew members go out to sea, in addition to the necessary dry food, they will also bring a full amount of drinking water, and they will not drink seawater at all. Why?
One of the reasons is that seawater is too salty, its salinity is about 35%, that is, there are 35 grams of salt per liter of seawater, and the concentration of human body fluids is about 0.85% to 0.9%, which is why we are sick range of saline concentrations to be injected.
Saline can only be used in physiological experiments and clinical applications if it is maintained at such a concentration, to ensure that its osmotic pressure is consistent with that outside the cell, and to prevent cells from dehydration or water absorption due to differences in osmotic pressure, thus causing them to rupture.
However, the concentration of seawater is significantly higher than that of human body fluids. Once we drink a lot of it, it may not only not quench our thirst, but also cause the water in the cells to continuously flow out under the osmotic pressure due to the inflow of highly osmotic seawater into the body, causing the cells to shrink. This can lead to various adverse reactions, and even death due to shock due to dehydration.
Another reason is that there are as many as 80 kinds of elements in seawater, and there are 3750×10t solid substances per cubic kilometer, which greatly exceeds the normal drinking water hygiene standards . There are even countries dumping nuclear pollution into seawater. , and a lot of industrial pollution.
Under such circumstances, seawater is not just ordinary "dirty", it has become a "garbage pond" where human beings blatantly discharge polluting garbage, which is extremely harmful to human beings . If you drink this water, even if it will not cause dehydration and death due to excessive salt content, it will be greatly affected by the water quality.
How do marine animals drink water?
We all know that no creature in the world is inseparable from water, and the most inseparable from water is probably the creatures that live in water. However, many people may not know that not all fish can drink water. Fish living in freshwater areas basically never need to drink water. Instead, fish living in the ocean need water often.
This is actually related to the osmotic pressure we mentioned above, because not only human beings, but all living things are composed of cells, and the concentration of body fluid in fish is about 0.5%, whether it is freshwater fish or saltwater fish. concentration.
In freshwater, the body fluid concentration of fish is higher than the salt content of the water in freshwater areas , which leads to high osmotic pressure inside freshwater fish. According to the principle that water will flow from low osmotic pressure to high places, the water near freshwater fish It will continuously penetrate into its body, and the water inside is more.
At the same time, in addition to the water infiltrated into the body of freshwater fish, they also inhale part of the water when they eat. In order to avoid swelling due to too much internal water, freshwater fish not only do not need to drink any more water, but also need to keep the excess water at all times. The water is excreted to ensure that the osmotic pressure inside and outside the body reaches a balance.
The body fluid concentration of marine fish is lower than that of the surrounding sea water, and the water in the marine fish will infiltrate into the surrounding ocean, thus facing the danger of dehydration. So how do marine fish drink water?
Of course, not all creatures living in the ocean need to drink water. For example, cartilaginous fish do not need to drink water, including sharks, rays, etc. As the name suggests, the skeleton of cartilaginous fish is cartilage, and most of them have streamlined bodies and opposite fins. Cartilage in the body cannot even be said to be true bone tissue.
For ordinary animals, urine is toxic and they quickly excrete useless urine, but cartilaginous animals such as sharks store urine in their blood and have evolved special mucous membranes to avoid urea excretion.
The urea content of sharks is almost 100 times that of other marine animals. According to this method, sharks can make their own body fluid concentration higher than that of seawater. Instead, water molecules in seawater will continuously penetrate into the body from the gill slits on the outside of the shark. , so they don't need to drink water at all, just like freshwater fish can get it easily.
Marine mammals are supplemented with water from captured prey, occasionally metabolized to obtain some fresh water, and because they live in the middle, they are not subject to the evaporation of sunlight like mammals on the mainland. Therefore, the loss of water itself is very small, and the demand for fresh water is naturally small.
However, scientists later found that the urine salt content of some marine mammals is significantly higher than the average salt content of the ocean, which is enough to show that they do not only obtain fresh water from their prey, but can also drink salt water and maintain body hydration. This is actually because these marine mammals have a very powerful kidney, and they "double" filter in their kidneys after drinking seawater.
First, the glomerulus performs preliminary filtration to "keep out" all macromolecules in the plasma, and only allow smaller elements such as water molecules and salt molecules to enter the kidneys . The plasma is then continuously screened by additional "filters," which finally remove unwanted waste, such as salt, from marine mammals.
Such a filtering operation seems simple, but it is actually more powerful than human kidneys, which is why they can grow and reproduce freely in the ocean.
However, among marine mammals, there is also an animal called "dugong". They are herbivorous , so they cannot obtain fresh water from other marine creatures by preying on their prey, and they also do not have the function of desalinating seawater. Go to the estuary of the river to obtain fresh water resources.
Teleosts are very ancient vertebrates , they are more advanced than cartilaginous fish, their structures are more complex and successful, and teleosts have also evolved unique "desalters" during long-term marine life .
For example, teleost fish have sensory "chlorine-secreting cells" that grow in their gills. These cells can excrete the salt of seawater by secreting chloride, thus forming a "desalination workshop" in the body of teleost fish. Constantly screening the "passing" sea water, and will not let any "suspicious elements".
However, because the osmotic pressure of seawater is still higher than that of teleost fish, it is easy to cause the water in the fish to seep out and lose. Therefore, teleost fish will continue to drink water and reduce excretion to maintain a relative balance.
At the same time, some fish will use the pressure difference during breathing and the semi-permeable membrane inside the mouth after drinking seawater, so as to penetrate the water molecules in the seawater into the body, and then discharge the unnecessary salt.
In addition to these, if we often observe the animals on the seashore, we will find that sometimes the turtles will silently "weep", as if they have been wronged, and silently vent their emotions.
Of course, these so-called "emotions" are only what humans add to animals based on their own "feelings". The tearing phenomenon of sea turtles does exist, but it is not because of "sadness" or "grievance" at all. They are actually for the purpose of expelling from the body of salt.
According to the research of scientists, there is a kind of "salt gland" behind the eye socket of sea turtle, and the excess salt in its body will enter the eye socket through this unique gland and be discharged along the "tear", which becomes what humans think of as "tears" .
Not only sea turtles have salt glands, but crocodiles, albatrosses, etc. also have similar glands. They all excrete unnecessary salt from the body through the methods mentioned above. This is why there is a legend of "crocodile tears" . It is because the crocodile will increase the salt after eating its prey, so it needs to shed tears to maintain stability and lubricate the eyes.
Seeing this, we may know a little more about marine creatures. In nature, every creature has evolved the most suitable way of living, and they all reproduce and develop according to their own best model . In the salty seawater, these animals can use a variety of methods to make themselves better.