Question

Which statement is false? a. Sweat has a lower solute concentration than internal body fluids such as blood. b. Some animals can survive without drinking water. c. A solution with an osmolarity of \(1,000 \mathrm{mOsm} / \mathrm{L}\) is hyperosmotic relative to the body fluids of most fishes. d. Marine fishes, but not freshwater fishes, drink the water they swim in. e. \(\mathrm{A} 300 \mathrm{mOsm} / \mathrm{L}\) solution of \(\mathrm{NaCl}\) contains \(300 \mathrm{mOsm} / \mathrm{L} \mathrm{Na}^{+}\) and \(300 \mathrm{mOsm} / \mathrm{L} \mathrm{Cl}^{-}\) .

Short answer

The false statement is statement e.

Step-by-step solution

Analyze Statement a

Sweat has a lower solute concentration than internal body fluids such as blood. This statement is expected to be true because sweat is mainly water with small amounts of salt, proteins, and urea. Therefore, it has a lower solute concentration than blood, which contains a wide variety of solutes including various electrolytes, proteins, and glucose among others.

Analyze Statement b

Some animals can survive without drinking water. Yes, this is true. Some creatures like kangaroo rats, for example, have metabolic adaptations that allow them to survive without ever drinking any water.

Analyze Statement c

A solution with an osmolarity of \(1,000 \, \text{mOsm} / \text{L}\) is hyperosmotic relative to the body fluids of most fishes. This statement is also correct. Most marine fishes maintain their body fluids at an osmolarity slightly less than that of their environment, which would typically be much less than \(1,000 \, \text{mOsm} / \text{L}\). The fluids of freshwater fishes, living in a hyposmotic environment, would have even lower osmolarity.

Analyze Statement d

Marine fishes, but not freshwater fishes, drink the water they swim in. This line is true. To counteract dehydration from the salty sea water environment, marine fishes need to drink the water. Freshwater fishes on the other hand, do not drink water.

Analyze Statement e

A \(300 \, \text{mOsm} / \text{L}\) solution of NaCl contains \(300 \, \text{mOsm} / \text{L} \, \text{Na}^{+}\) and \(300 \, \text{mOsm} / \text{L} \, \text{Cl}^{-}\). This statement is false. When NaCl is dissolved in water, it disassociates into Na+ and Cl- ions. Therefore, a solution that is \(300 \, \text{mOsm} / \text{L} \, \text{NaCl}\) would contain \(300 \, \text{mOsm} / \text{L}\) of solute particles, but only \(150 \, \text{mOsm} / \text{L}\) each of Na+ and Cl- ions.

Key concepts

Solute Concentration

In biological systems, the solute concentration of a solution refers to the amount of dissolved substances present in a given volume of solvent. This is key to various physiological processes, such as maintaining cell structure and function. The solute concentration is typically measured in osmoles per liter (Osm/L), which indicates the number of particles capable of exerting osmotic pressure in a solution.

Consider your sweat, for example. When analyzed, it's realized that sweat is primarily made up of water with some dissolved salts, mainly sodium chloride (NaCl), and to a lesser extent, small quantities of other compounds such as proteins and urea. Despite its salt content, the solute concentration in sweat is notably lower than that of your blood, which comprises a complex mix of electrolytes, proteins, glucose, and other solutes. For this reason, our bodies can use sweating as a mechanism not only to cool down but also to regulate solute concentrations within our blood and tissues.

Understanding these principles is crucial. For example, it's vital to be aware of the solute concentration of intravenous solutions in medical settings, as they must closely match the osmolarity of blood to prevent adverse effects on cells.

Hyperosmotic

Hyperosmotic is a term used to describe a solution that contains a higher concentration of solutes, and therefore a higher osmolarity, than another solution to which it is compared. In terms of osmolarity, a solution is said to be hyperosmotic if it has a greater number of osmoles of solute per liter of solution compared to another.

For example, marine environments can have an osmolarity much higher than the bodily fluids of marine organisms. A solution with an osmolarity of 1,000 mOsm/L would be considered hyperosmotic to the body fluids of most fishes since their bodies typically maintain a lower solute concentration. This discrepancy in osmolarity requires marine organisms to have specialized adaptations, such as drinking seawater, to balance the intake and excretion of solutes and water, and to maintain overall osmotic balance.

Osmoregulation in Fishes

The process of maintaining an optimal balance of solutes and water in the body is known as osmoregulation, which is incredibly important in fishes due to their aquatic environments. This regulation ensures their bodily fluids maintain a concentration of solutes that is conducive to proper cellular function.

In marine fishes, their body fluids are less concentrated with solutes compared to the salty sea water they inhabit. To prevent dehydration, marine fishes must actively consume seawater and utilize specialized cells to excrete excess salts. On the flip side, freshwater fishes live in an environment where their body fluids possess a higher solute concentration than the surrounding water. Thus, they face the challenge of absorbing too much water and must expel excess water while retaining solutes.

Marine fishes practice a process called 'drinking' for water intake, followed by salt excretion through their gills and kidneys. Freshwater fishes, however, do not drink their environment water; instead, they constantly absorb water through their skin and gills, while their kidneys work to produce diluted urine to remove excess water. Both groups possess intricate osmoregulatory mechanisms which highlight the evolutionary strategies that organisms develop to survive in different types of aquatic environments.