Question

Saltwater fish constantly drink water but still excrete concentrated urine to compensate for the water loss. They also have gills to help excrete excess salts. Conversely, freshwater fish absorb salt from their surroundings using their gills and their bodies reabsorb salt from their urine. This describes how salt- and freshwater fish _______.

a.
use their gills to drink
b.
keep the salinity levels even in their aquatic environments
c.
have adapted to deal with osmosis
d.
have evolved behavior patterns to match their physiology

Answer 1

This describes how salt- and freshwater fish have adapted to deal with osmosis. The correct option among all the options that are given in the question is the third option or option "c". The fishes basically maintain the salinity within their body, rather than trying to maintain the salinity in the water.

Answer 2

The above paragraphs describes that how salt- and fresh-water fish regulates their osmoregulation. Hence, the correct answer would be c. have adapted to deal with osmosis.

Osmosis is the process by which solvent's molecule move from region of low concentration (hypo-tonic) to the region of high concentration (hyper-tonic) through a semi-permeable membrane.

In sea-water fishes, the body fluids are hypo-tonic to the surrounding water and thus water is kept moving out of their gills. In order to prevent the excess water loss they need to drink water constantly and excrete concentrated urine.

In contrast, fresh-water fishes body fluids are hyper-tonic to surrounding water and hence, water keeps entering in their body through gills. So, in order to prevent excess dilution they absorb salt from surrounding with the help of gills and also their bodies reabsorb salt from urine.