Question

A freshwater fish gains most of its water by_____. a. drinking c. osmosis b. eating food d. transport across the gills

Short answer

Freshwater fish gain most of their water by osmosis.

Step-by-step solution

Understanding the Choices

To solve the exercise, we first need to understand each option provided. - **Drinking**: This means actively taking in water through the mouth as a deliberate act. - **Osmosis**: This involves the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. - **Eating food**: This would involve gaining water through the consumption of food. - **Transport across the gills**: This involves water entering the fish through the gills or by associated mechanisms.

Analyzing Fish's Behavior

A freshwater fish lives in a hypotonic environment, meaning the external water has a lower concentration of dissolved substances than the fish's internal fluids. Due to osmosis, water naturally moves into the fish's body across the gill membranes.

Elimination of Incorrect Options

- **Drinking**: Freshwater fish do not need to drink water since water naturally enters their bodies by osmosis. - **Eating food**: While some water might be gained this way, it's not the primary method. - **Transport across the gills**: Water enters by osmosis through gills, but this isn't active transport; hence, it's not considered the primary method if osmosis is an option.

Determining the Main Method

Considering the environmental conditions and the physiological process, osmosis is the process by which freshwater fish primarily gain water, as water naturally diffuses through the gill membranes due to the hypotonic environment.

Key concepts

Hypotonic Environment

In a hypotonic environment, the concentration of solutes, such as salts and minerals, outside of an organism is lower than that inside its body. For freshwater fish, this means that the water in their environment contains fewer dissolved substances compared to the fluids inside their bodies. As a result, water naturally moves into their bodies through a process called osmosis.
This movement occurs because water tends to flow from areas of low solute concentration (the surrounding water) to areas of high solute concentration (inside the fish's body) to equalize the concentration on either side of the fish's biological membranes. This gradient-driven movement doesn't require the fish to expend energy since it happens naturally.
Being in a hypotonic environment can be a continuous challenge for freshwater fish because they must deal with the constant influx of water. The balance of solutes and water is critical for maintaining proper physiological functions, so these fish have developed various adaptations to manage this continuous water intake.

Water Transport in Fish

For freshwater fish, the primary method of water acquisition is through osmosis. Osmosis is a fascinating process in which water molecules passively move across cell membranes from the surrounding environment into the fish's body. This mainly occurs across the gill membranes, which are thin and semi-permeable, allowing water to flow easily while regulating essential ions and gases.
Fish do not need to drink water like terrestrial animals because water freely enters their bodies through osmosis. The gills are not just for breathing oxygen but are also central to maintaining water balance. Although some water is also obtained from food, this is not the main method of water intake.
The constant water influx poses a challenge, as the fish can swell up without mechanisms to expel the excess. Freshwater fish have efficient kidneys that process and excrete large amounts of diluted urine, enabling them to maintain a stable internal environment. These adaptations illustrate how crucial water transport is for their survival.

Fish Physiology

Fish physiology is uniquely adapted to deal with challenges posed by their environments. Freshwater fish, in particular, have specialized adaptations to manage the constant movement of water into their bodies due to osmosis.
One key aspect of fish physiology is the presence of highly efficient kidneys. These organs play a pivotal role in excreting excess water, thereby preventing the fish from swelling due to the hypotonic environment. Freshwater fish produce a large volume of dilute urine, which involves expelling plenty of water while conserving vital salts.
Additionally, fish gills are central to their physiological function. They not only enable fish to breathe by taking in dissolved oxygen but are also crucial for maintaining osmotic balance. The gills help fish regulate the flow of ions and gases, ensuring they don't lose essential ions while taking in necessary water. These physiological processes ensure the fish can thrive in a seemingly challenging environment.