Final answer:
Freshwater organisms face the challenge of osmotic gain of water due to lower solute concentrations in their environment, leading to potential cell swelling. They have adapted by excreting dilute urine, and larger organisms like fish urinate frequently to maintain internal balance.
Step-by-step explanation:
Organisms that live in fresh water face a unique challenge: the osmotic gain of water into their cells. Freshwater environments have a lower concentration of solutes compared to the solutes within the cells of aquatic organisms. This difference in solute concentration sets up a gradient that causes water to rush into the cells by osmosis, potentially leading to cell swelling or even bursting if not regulated properly.
Many freshwater organisms, therefore, have developed adaptations to manage this influx of water. For example, they might excrete very dilute urine to rid excess water and maintain solute concentrations within their cells. Larger creatures, such as freshwater fish, urinate frequently to balance their internal environment.
In contrast, saltwater organisms face the opposite problem of having a high solute concentration in their environment. Again, osmoregulation is key, but through the excretion of excess salts. An example of an organism adapting to different environments is salmon, which migrate from saltwater to freshwater, triggering hormonal changes that help regulate their internal solute levels.
When studying freshwater environments, it is essential to note that issues such as salinity, sunlight, and dissolved oxygen play significant roles in the survival of aquatic life. Plants in these environments also display adaptations like leaf hairs or a waxy cuticle to reduce water loss, while solute concentration remains a critical factor in determining the diversity of life within these ecosystems.