Final answer:
Transport problems for freshwater organisms involve preventing too much water from entering their cells due to a hypotonic environment, whereas saltwater organisms must eliminate excess salt and conserve water in a hypertonic environment. Freshwater species excrete dilute urine and absorb salts through gills, while saltwater species excrete concentrated urine and dispose of extra salt through gills.
Step-by-step explanation:
The transport problems of a freshwater organism differ from those of a saltwater organism due to differences in water salinity, which in turn affects osmotic pressure. Freshwater organisms live in a hypotonic environment, meaning their internal salt concentration is higher than that of their surrounding water. To prevent water from rushing into their cells and causing them to swell, they have adaptations such as excreting dilute urine and actively taking in salts through their gills.
In contrast, saltwater organisms live in a hypertonic environment, where the water's salinity is higher than their internal salt concentration. These organisms cope with the osmotic pressure by excreting excess salt through their gills and producing highly concentrated urine to conserve water.
Species like salmon that move between freshwater and saltwater environments must osmoregulate extensively to survive in these contrasting conditions. These organisms rely on hormonal changes to trigger adaptations for osmoregulation, ensuring they can handle the water salinity wherever they are.