Question

QUESTION 6 A cell containing only pure water is placed into a solution containing 1M sucrose. The cell's membrane is impermeable to water, sucrose, sodium ions and chloride ions. How could you make the cell isosmotic to the outside solution? Choose all of the correct answers.

A) Add NaCl to the inside of the cell until it contains 1M NaCl.

B) Add NaCl to the inside of the cell until it contains 0.5M NaCl.

C) Increase the number of sodium channels on the cell membrane.

D) Increase the active transport of water out of the cell.

E) Add sucrose to the cell until it contains 1M sucrose.

Answer 1

Isoosmotic means two solutions seperated by a membrane have the same osmotic pressure or same osmolarity. As both the solutions have the same osmotic pressure no solute or solvent diffusion will occur between them.

Now Osmolarity is number of osmoles of solute per litre solution.

For non-ionic compound Osmolarity = Molarity ( As it does not dissociate into ions and remain as a sigle molecule)

For ionic compounds, Osmolarity= Molarity X No of ions formed per molecule (As it can dissociate into ions and the total number of ions will exert osmotic pressure)

In the question,

Osmolarity of 1M Sucrose = 1 Osmole/L

To make the cell isoosmotic to the outer solution we need to make the osmotic concentration of the cell 1 Osmole/L.

This can be acheived by the following two ways-

Option B- Osmolarity of 0.5 M NaCl= 0.5X2 Osmole/L = 1 Osmole/L [ NaCl dissociates into Na⁺ and Cl^- ions]

Option E- Osmolarity of 1M Sucrose = 1 Osmole/L [Sucrose is a non ionic molecule]

So the correct answer is B and E.