Problem 9 - Campbell Biology

Question

SCIENTIFIC INQUIRY You are exploring kidney function in kangaroo rats. You measure urine volume and osmolarity, as well as the amount of chloride (Cl-) and urea in the urine. If the water source provided to the animals were switched from tap water to a 2\(\%\) NaCl solution, indicate what change in urine osmolarity you would expect. How would you determine if this change wasmore likely due to a change in the excretion of \(C\) - or urea?

Step-by-Step Solution

Answer

Switch to 2% NaCl solution increases urine osmolarity. Measure Cl- and urea concentrations to determine the cause.

Step 1: Identify the Problem

Determine the impact on urine osmolarity when the water source is switched from tap water to a 2% NaCl solution.

Step 2: Understand Osmolarity Concept

Osmolarity refers to the concentration of a solution expressed as the total number of solute particles per liter. A higher concentration of solutes results in higher osmolarity.

Step 3: Predict the Change

Switching from tap water to a 2% NaCl solution will increase the sodium intake of the kangaroo rats. This increased sodium will likely cause the body to excrete more sodium through urine, increasing urine osmolarity.

Step 4: Measure Osmolarity

Measure the osmolarity of urine before and after the switch to a 2% NaCl solution to confirm that the urine osmolarity has increased.

Step 5: Assess Cl- and Urea Levels

Measure the concentrations of Cl- and urea in the urine before and after the change in water source.

Step 6: Determine Primary Factor

Compare the changes in Cl- and urea concentrations. If Cl- levels increase significantly while urea levels remain relatively constant, the change in osmolarity is primarily due to increased excretion of Cl-. If urea levels increase significantly, the osmolarity change is more influenced by urea excretion.

Key Concepts

Urine Osmolarity

Urine osmolarity is a measure of the concentration of solutes in the urine. This concept is crucial for understanding how the kidneys balance water and salt in the body. Osmolarity is expressed as the number of solute particles per liter. If there are more solutes, the osmolarity is higher.

When kangaroo rats switch from drinking tap water to a 2% sodium chloride (NaCl) solution, their bodies need to handle the increased intake of sodium. Sodium is a major solute that contributes to urine osmolarity.

The kidneys will excrete extra sodium to maintain balance, leading to increased urine osmolarity. By measuring urine osmolarity before and after the switch, you can observe this change.

Sodium Chloride Solution

A 2% sodium chloride solution contains sodium and chloride ions. Sodium (Na+) and chloride (Cl-) have significant roles in maintaining fluid balance in the body.

In kangaroo rats provided with this solution, the extra sodium is absorbed into their bloodstream. The kidneys then work hard to excrete this excess to prevent harmful buildup. This process increases the concentration of sodium in the urine, affecting its osmolarity.

Measuring the urine osmolarity after the switch to 2% NaCl helps ascertain how the body is managing the increased sodium intake. Observing whether there is a significant rise in urine osmolarity supports the idea that the increased sodium is being excreted through urine.

Excretion of Chloride and Urea

To pinpoint the primary factor influencing the change in urine osmolarity, we compare the levels of chloride (Cl-) and urea in the urine. These are key solutes found in urine.

Urea is a waste product formed from protein metabolism, whereas chloride is an essential electrolyte usually found together with sodium.

If you observe a notable increase in chloride concentration and the urea levels remain steady, it indicates that the change in osmolarity is majorly due to increased chloride excretion.

Conversely, if urea levels spike with little change in chloride, urea excretion is driving the osmolarity change. By measuring both before and after switching the water source, you can determine which solute is primarily responsible.