Question

Organisms that live in fresh water are almost hypertonic to their environment. In what way is this a serious problem? How could some organisms cope with this problem?

Answer 1

Hypertonic means when the concentration of solutes are higher outside than the inside of the organism. Although the ions concenration is higher inside feshwater organism body like fish, but as they are staying constatntly in water, there is a tendency water will come inside the fish body and fish will swell . The skin of some of the organism living in fresh water is very thin and water can easily pass through this by the process of osmosis or diffusion. In fish water can also invade through gills. Excess water in body can also lead to dilution of ion concentration.This will result is a loss balace of internal water and essential ions required for body activity for these organisms.

To avoid or to adapt to these situation some of the organism of freshwater have developed a process called osmoregulation. Osmoregulation can help to maintain the balance of ions and water inside the body irrespective of their environment. They also use mechanism though which ions can be pumped back into body. For eg in freshwater fish, they produce a large amount of urine though kidney. As this process also combine with ion lose, thes also have some special structure in gills capable of absorbing ions from environment and later transported into blood.