Sea animals also need to drink water, but sea water is too salty to drink, so how do they drink water?
Since the middle and late part of the last century, human beings have gradually moved into the distant space, and can look back at the familiar earth from a distance from a more unique angle-a light blue water drop.
This is because the earth has a very rich water storage capacity. About 72% of the earth's surface is covered by water, which can add up to 1.45 billion square kilometers. However, most of the water resources are seawater, and fresh water resources are only about 0.5% , and most of the fresh water resources are frozen in the ice, and some are located underground, only a few of which are 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 fresh water resources on the earth are very scarce. Although it can meet the needs of the population of some countries at present, many countries are in the predicament of water shortage.
Seawater with a volume of up to 1.37 billion square kilometers is much more than freshwater resources, but it cannot be directly used by humans at all, and the cost of large-scale conversion of seawater is too high, often countries that are short of water cannot support it.
Why can't sea water be drunk?
Some people may think that if we are facing a critical moment of life and death, such as a shipwreck, lying on a plank, in the endless sea, and there is no sign of a continent around us, in such a situation, in order to survive, we must You can abandon some of the "dirty" concepts of the ocean and drink sea water to survive.
In fact, when we are drifting on the sea, it is best not to drink sea water directly even if we are thirsty . It is completely impossible to live by drinking seawater to quench your thirst. In addition to the necessary dry food and other necessary dry food, the crew will also bring full drinking water when they go to sea, and they will not drink sea water at all. Why is this?
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 body fluid in the human body is about 0.85% to 0.9%, which is why we get sick The concentration range of saline injected at the time.
Salt water can only be used in physiological experiments and clinically if it is kept at such a concentration to ensure that its osmotic pressure is consistent with that of the outside of the cell, so as to prevent cells from dehydrating or absorbing water due to different osmotic pressure, which will cause them to rupture.
However, the concentration of seawater is significantly higher than the concentration of human body fluids. Once we drink a lot, we may not only not quench our thirst, but also cause the water in the cells to flow out under osmotic pressure, causing the cells to shrink. This can lead to various adverse reactions, and even shock and death due to dehydration.
Another reason is that there are as many as 80 elements in seawater, and there are 3750×10t of solid matter per cubic kilometer, which greatly exceeds the normal drinking water hygiene standards . There are even countries that dump nuclear pollution into seawater. , and a large amount of industrial pollution.
Under such circumstances, seawater is not just ordinary "dirty", it has become a "garbage pool" where human beings blatantly discharge polluting garbage, which is extremely harmful to human beings . If you drink this water, even if you will not be dehydrated to death due to excessive salt content, it will be greatly affected due to water quality.
How do marine animals drink water?
We all know that no creature in the world can live without water, and the creatures that cannot live without water are probably the ones 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. On the contrary, fish living in the ocean need water frequently.
This is actually related to the osmotic pressure we mentioned above, because not only humans, but all organisms are composed of cells. The body fluid concentration of fish is about 0.5%, whether it is freshwater fish or saltwater fish. concentration.
In fresh water, the body fluid concentration of fish is higher than the salinity of the water in fresh water areas , which leads to high osmotic pressure inside fresh water fish. It will continue to penetrate into its body, and there is more water inside.
At the same time, in addition to the water infiltrated into the body, freshwater fish 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 water, but also need to keep the excess water away. The water is discharged to ensure that the osmotic pressure inside and outside the body reaches a balance.
The body fluid concentration of seawater fish is lower than that of the surrounding seawater, and the water in the seawater fish will seep into the surrounding ocean, thus facing the danger of dehydration. So how do seawater fish drink water?
Of course, not all creatures living in the ocean need to drink water. For example, cartilaginous fishes do not need to drink water, including sharks, rays, etc. As the name suggests, the skeleton of cartilaginous fishes 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 poisonous, and they will quickly excrete useless urine, but cartilaginous animals such as sharks keep urine in their blood and have evolved special mucous membranes to avoid Excretion of urea.
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. On the contrary, water molecules in seawater will continuously penetrate into the body from the gill slit on the outside of the shark , so they don't need to drink water at all, just like freshwater fish can easily get water.
Marine mammals will obtain water supplements from the body of the prey they catch, and they can also obtain part of the fresh water through occasional metabolism, and because they live in the middle, they will not be subject to the evaporation of sunlight like mammals on the mainland , so the water lost by itself is very small, and the demand for fresh water is naturally small.
However, scientists later discovered that the salt content of the urine of some marine mammals was significantly greater 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 will "double" filter in the kidney after drinking seawater.
First, the glomerulus conducts preliminary filtration to "shut out" all the large molecules in the blood plasma, and only allow smaller elements such as water molecules and salt molecules to enter the kidneys . Then the blood plasma is continuously screened by another "filter", and finally waste products such as salt and other marine mammals are discharged.
This kind of 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 a kind of animal called "dugong". They are herbivorous animals , so they cannot obtain fresh water from other marine life by hunting prey, and they do not have the function of desalinating sea water. Go to the mouth of the river to get fresh water resources.
Teleosts are very ancient vertebrates . They are more advanced than cartilaginous fishes, and their structures are more complex and successful. Teleosts have also evolved a unique "sea water desalination device" during their long-term ocean life .
For example, bony fishes have sensory "chlorine-secreting cells" that grow in their gills. These cells can excrete seawater salt by secreting chloride, thus forming a "seawater desalination workshop" in bony fishes. Constantly screen the "passing" sea water, and will not let any "suspicious elements" go.
However, because the osmotic pressure of seawater is still higher than that of bony fishes, it is easy to cause the water in fishes to seep and lose. Therefore, bony fishes 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 to penetrate the water molecules in the seawater into the body after drinking seawater, 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 "cry" silently, as if they have been wronged, and they are silently venting their emotions.
Of course, these so-called "emotions" are only added to animals by humans based on their own "feelings". Sea turtles do shed tears, but they are not because of "sadness" or "grievance". of salt.
According to the research of scientists, there is a kind of "salt gland" behind the eye socket of sea turtles, and the excess salt in its body will enter the eye socket through this unique gland, and be discharged along the "tears", becoming what humans think of as "weeping tears" .
Not only sea turtles have salt glands, but crocodiles, albatrosses, etc. also have similar glands. They all discharge unnecessary salt in the body through the above-mentioned method, which is why there is a legend of "crocodile tears" . It is because the crocodile will increase the salt content after eating the prey, so it has to shed tears to discharge the excess salt to maintain stability, and it also has the effect of lubricating the eyes.
After seeing this, we may know more about marine creatures. In nature, every creature has evolved the most suitable way of survival, and they all reproduce and develop according to their own best model . In the seawater with a lot of salt, these animals can use various methods to make themselves better.