Question

1. A batch of cells are found to contain 300 mM glucose and 150 mM CaCl₂ inside the cell. The cell membrane has pores which are permeable to glucose but not to ions. These cells are then placed in a NaCl solution which has an osmolarity of 450 milliosmoles. What happens to the cells after the solution comes to equilibrium?  

       a. The cells remain the same size as they were originally
       b. The cells swell
       c. The cells shrink
       d. There is not enough information given in the problem to determine what happens

2. You now find new cells which contains 200 mM CaCl₂ and 15 mM glucose.   The cell membrane is permeable to Ca++ ions, impermeable to Cl- ions, impermeable to Na ions and impermeable to glucose. You transfer these cells into a solution which has 140 mM (NaCl) and 150 mM glucose. What happens to the cells after the solution and cell have come to equilibrium?

       a. They cells are the same size as they were originally
       b. The cells have swelled
       c. The cells shrank
       d. There is not enough information given in the problem to determine what happens

3. An new group of cells is found to contains 300 mM glucose and 150 mM CaCl₂ inside the cell. The cell membrane of the cells is not permeable to glucose or to ions. These cells are then placed in a CaCl₂ solution which has an osmolarity of 450 milliosmoles. What happens to the cells after the solution and cells have come to equilibrium?  

       a. The cells remain the same size as they were originally
       b. The cells swell
       c. The cells shrink
       d. There is not enough information given in the problem to determine what happens

4. You now find a new group of cells where the interior contains 150 mM CaCl₂.   The cell membrane of the cells is not permeable to ions but is now permeable to glucose. You place these cells into a solution which has 200 mM (NaCl) solution with 100 mM glucose. What happens to the cells?

       a. They remain the same size as they were originally
       b. The cells swell
       c. The cells shrink
       d. There is not enough information given in the problem to determine what happens

Answer 1

1. c) the cell will shrink as glucose will get out of the cells.

Explaination: please note in these types of questions furst calculate the Osmolarity of both inside and outside. Osmolarity is no of osmoles of solute per kg of solvent. Calculated osmolarity = 2 Na + Glucose + Urea (all in mmol/L).

That means for ionic compounds Osmolarity= Molarity × no of dissociated ions

For non dissociated compounds like Glu, Urea Osmolarity is just thw concentration in mmoles per Litre.

So calculations are

Inside the cell: 300 mmoles/L (mM) + 150×3 mmoles/L = 750 millimoles/L or millimoles/kg of solvent i.e 750 milliosmolar.

Outside cell: 450 milliosmoles NaCl i.e 450 millimoles/kg of solvent.

So inside the cell, concentration is high and hence since cell is permeable to Glu, Glu will do exoosmosis in order to attain an equilibrium concentration and cell content will decrease so it will shrink.

Incase cell was impermeable to Glu then water will do endoosmosis which will make the cells to swell.

Try to do the remaining questions like this. Tell in comments if you find any problems.